Flow control apparatus and rotational sewage distribution apparatus

Abstract

A sewage distribution system 200 comprises a rotational sewage distribution apparatus 100 and an inlet pipe (202, Fig. 1) for supplying sewage from a reservoir (302, Fig. 1) to an inlet of the rotatio

Description

FIELD The present disclosure relates to a flow control apparatus and a sewage distribution system. Aspects of the disclosure relate to a flow control apparatus, to a rotational sewage distribution apparatus, to a sewage distribution system, and to a filter system. BACKGROUND It is known to treat sewage liquid by passing said sewage liquid through a filter bed formed of filter media. Such treatment systems are commonly termed trickling filter beds. One system which has been used for distributing sewage liquid to such a filter bed includes a sewage liquid reservoir which is connected via an inlet pipe to a rotational sewage distribution apparatus. The rotational sewage distribution apparatus includes longitudinally extending distribution channels which are situated over the filter bed. Sewage liquid flows from the sewage liquid reservoir along the inlet pipe, into the rotational sewage distribution apparatus, along the longitudinally extending distribution channels and onto the filter bed. When a flow of sewage liquid is passed through the rotational sewage distribution apparatus, the rotational sewage distribution apparatus causes rotation of the longitudinally extending distribution channels about a vertical axis. In this way, the longitudinally extending distribution channels rotate over the filter bed and thereby distribute the sewage liquid over the entire surface of the filter bed overtime. Such a system is described in UK patent number GB2181187B. For optimal filtering performance, it is desirable for sewage liquid to be distributed at a particular flushing intensity factor (otherwise known as “SK” value). If the SK value is too high (e.g., at high flow rates through the rotational sewage distribution apparatus), excessive hydraulicshearing of biofilm in the filter bed may occur. Conversely, if the SK value is too low (e.g., at low flow rates through the rotational sewage distribution apparatus), there may be an excessive buildup of biofilm or other organic matter in the filter bed. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY The present teachings provide a flow control apparatus, a rotational sewage distribution apparatus, a sewage distribution system, and a filter system according to the appended claims. A first aspect of the disclosure provides a flow control apparatus for directing a flow of sewage liquid onto a paddle wheel of a rotational sewage distribution apparatus. The flow control apparatus comprises: a housing defining an internal volume for sewage liquid; a housing inlet for receiving a flow of sewage liquid from an inlet pipe into the internal volume; and a housing outlet configured to direct the flow of sewage liquid from the internal volume onto a paddle wheel. The housing outlet may comprise a first position (e.g., with respect to a front of the housing) and a second position (e.g., with respect to a front of the housing), wherein the second position is different to the first position. The housing outlet may be configured so that sewage liquid flowing through the internal volume at a first flow rate is free to exit the housing outlet at the first position and is inhibited (e.g., prevented) from exiting the housing outlet at the second position, and so that sewage liquid flowing through the internal volume at a second flow rate greater than the first flow rate is free to exit the housing outlet at the second position. It will be understood that variations in flow rate of the sewage liquid will result in variations in the horizontal distance travelled by the sewage liquid between leaving the housing outlet and hitting the paddle wheel. Therefore, by having the housing outlet configured so that sewage liquid flowing through the internal volume at a first flow rate exits the housing outlet at a first position and sewage liquid flowing through the internal volume at a second flow rate exits the housing outlet at a second (i.e., different) position, it is possible to control where fluid flows of different flow rates hit the paddle wheel. This may be beneficial for achieving a desired relationship between sewage liquid flow rate and paddle wheel rotation rate (e.g., so that when the flow rate increases, rotation rate of the paddle wheel increases proportionally). The first and second positions may be different positions with respect to a front of the housing. The housing outlet may be proximal to a front surface of the housing. For example, the housing outlet may be provided in a surface which faces in a substantially forward direction. The front surface may define a front portion of the housing (i.e., may define a frontmost surface of the housing). Alternatively, the front surface may be set back from the front portion of the housing, but facing the generally forward direction. In some embodiments, the housing may have a substantially cylindrical side wall, and the front surface may be a portion of the cylindrical side wall which faces in the generally forward direction. The housing may have a front portion, a rear portion and a horizontal axis extending between the front portion and the rear portion. The first and second positions may be different axial positions with respect to the horizontal axis. The housing outlet may be configured to direct the flow of sewage liquid from the internal volume onto a paddle wheel in an outlet direction (i.e., a general downstream direction in relation to a flow of sewage liquid through the flow control apparatus). The housing outlet may be intended to be positioned such that the first and second positions are at different distances to the paddle wheel, when in use. For example, the first position may be closer to the paddle wheel than the second position, when in use. An axis may be defined extending between the first and second positions, wherein said axis is intended to be transverse to a rotational axis of the paddle wheel when in use, such that the first position is closer to the paddle wheel axis when in use. Optionally, the second position is further from the front of the housing than the first position. For example, the first position may be at the front of the housing and the second position may be set back from the front of the housing. Alternatively, the first and second positions may both be set back from the front of the housing, but with the second position set back further from the front of the housing than the first position. In other words, the first position is proximal the front of the housing and the second position is distal the front of the housing. Having the second position further from the front of the housing than the first position may facilitate a more consistent position at which the flow of sewage liquid hits the paddle wheel at different flow rates. For example, where the flow rate is lower, the sewage liquid exits the housing outlet at a more forward position, but travels a smaller horizontal distance between the housing outlet and the paddle wheel. On the contrary, where the flow rate is higher, the sewage liquid exits the housing outlet at a less forward position, but travels a greater horizontal distance between the housing outlet and the paddle wheel. In this way, flows of sewage liquid exiting the housing outlet at the first and second positions may both hit the paddle wheel at approximately the same horizontal position. Directing the flow of sewage liquid in this way may facilitate an approximately linear relationship between flow rate of sewage liquid and rotation rate of the paddle wheel. Where the paddle wheel is used to drive rotation of a rotating sewage distribution apparatus for distributing sewage liquid to a filter bed, such a linear relationship may improve performance of the filter bed. In particular, having such a linear relationship may allow a greater flow rate of sewage liquid to be passed through the sewage distribution apparatus whilst reducing increase in flushing intensity factor of the associated filter bed. This reduces the risk of excessive hydraulic shearing of biofilm in the filter bed at higher sewage liquid flow rates. Optionally, the housing outlet is configured to direct the flow of sewage liquid in an outlet direction which is transverse (e.g., perpendicular) to the front of the housing. This may allow the flow control apparatus to be retrofitted to existing rotating sewage distribution apparatuses which have a housing outlet configured to direct sewage liquid from the front portion of the housing. Optionally, sewage liquid flowing through the internal volume at the second flow rate is free to exit the housing outlet at either of the first and second positions. In other words, there is no barrier or mechanism which limits sewage liquid flowing at the second flow rate from exiting the housing outlet at the first position. This may allow the housing outlet to be constructed more simply (e.g., as a static mechanical structure). Alternatively, sewage liquid flowing through the internal volume at the second flow rate may only be free to exit the housing outlet at the second position (i.e., not at the first position as well). For example, the housing outlet may be defined by an adjustable structure which is movable between the first and second positions, and there may be a control system configured to move the adjustable structure based on a flow rate of sewage liquid through the internal volume. Optionally, the first position and / or second position is adjustable. For example, the housing may include an adjustable first member which defines the first position and an adjustable second member which defines the second position. Alternatively, the housing may include an adjustable member which defines both the first and second positions. The adjustable member(s) may be pivotal and / or slidable relative to the rest of the housing. The first and / or second positions being adjustable may allow tuning of the housing outlet geometry to optimise the position at which sewage liquid impacts the paddle wheel. For example, to tune a relationship between sewage liquid flow rate and paddle wheel rotation rate to affect the sewage system rotation speed and thereby reduce variations in flushing intensity factor (SK value) of the associated filter bed at different sewage liquid flow rates. As another example, if the height of flow control apparatus varies relative to a height of the paddle wheel in different applications, this may result in a variable average horizontal distance travelled by sewage liquid between the housing outlet and the paddle wheel. Therefore, it may be desirable to adjust the first and / or second positions to account for height changes in the flow control apparatus, so that the sewage liquid impacts the paddle wheel at a desired position of the paddle wheel (e.g., a position which optimises rotation of the paddle wheel). The first and / or second positions may be manually adjustable (e.g., by pivoting the adjustable member(s) and then bolting into place). Alternatively, the first and / or second positions may be adjustable by an actuator (e.g., a linear actuator to move the adjustable member(s)). Where adjustable by an actuator, the actuator may be part of a control system for automatically adjusting the first and / or second positions based on a flow rate through the flow control apparatus. Optionally, a base of the housing comprises a first base portion proximal the first position and a second base portion proximal the second position, wherein the second base portion is further from the front of the housing than the first base portion. Such a configuration provides a simple means of expelling fluid from the housing outlet at different positions relative to the front of the housing. Optionally, the base of the housing of the flow control apparatus steps rearwards, with respect to the front of the housing, from the first base portion to the second base portion. Such a stepped configuration provides a simple construction and allows sewage liquid to exit the housing outlet at two discrete locations. Optionally, the base of the flow control apparatus tapers gradually away from the front of the housing between the first position and the second position. Such a gradual tapering contrasts with configurations in which there is a step change between the first and second positions. Optionally, the first base portion and / or second base portion is adjustable. For example, the first base portion and / or second base portion may be coupled to a hinge and / or slide mechanism to change the extent to which the second position is inboard of the first position. The first and / or second base portion being adjustable allows tuning of the housing outlet geometry to optimise the position at which sewage liquid impacts the paddle wheel. For example, to tune a relationship between sewage liquid flow rate and paddle wheel rotation rate to affect the sewage system rotation speed and thereby reduce variations in flushing intensity factor (SK value) of the associated filter bed at different sewage liquid flow rates. As another example, if the height of flow control apparatus varies relative to a height of the paddle wheel in different applications, this may result in a variable average horizontal distance travelled by sewage liquid between the housing outlet and the paddle wheel. Therefore, it may be desirable to adjust the first and / or second base portions to change the first and / or second positions and thereby account for height changes in the flow control apparatus, so that the sewage liquid impacts the paddle wheel at a desired position of the paddle wheel (e.g., a position which optimises rotation of the paddle wheel). The first and / or second base portion may be manually adjustable (e.g., by pivoting the first and / or second base portion and then bolting into place). Alternatively, the first and / or second base portion may be adjustable by an actuator (e.g., a linear actuator). Where the first and / or second base portion is adjustable by an actuator, the actuator may be part of a control system for automatically adjusting the position of the first and / or second base portion based on a flow rate through the flow control apparatus. Optionally, the housing outlet comprises a weir which extends upwards from a base of the housing so, when a level of sewage liquid in the internal volume is below a height of the weir, sewage liquid is inhibited (e.g., prevented) from exiting the housing outlet at the second position. It will be understood that the level of sewage liquid in the internal volume will be higher when the flow rate of sewage liquid through the flow control apparatus is higher. Therefore, such a weir provides a simple means of ensuring that sewage liquid flowing at lower flow rates (i.e., sewage liquid flowing when the level in the internal volume is lower) is not expelled from the housing outlet at the second position, where it may not travel sufficient horizontal distance to reach the paddle wheel due to insufficient flow rate. Optionally, the weir defines a substantially flat surface. Optionally, the substantially flat surface is parallel to the front of the housing. A flat surface parallel to the front of the housing provides a simple means of constructing the weir. Optionally, the substantially flat surface is angled relative to the front of the housing. An angled flat surface provides a simple means of constructing the weir. Optionally, the height of the weir is constant along a length of the weir. Optionally, the weir has a first weir end proximal to the first position and a second weir end distal the first position, and wherein the height of the weir increases from the first weir end to the second weir end. In this way, the innermost position at which sewage liquid tops the weir moves inboard as the level of sewage liquid in the internal volume increases. In other words, the housing outlet comprises an outlet width between the weir and an opposing side of the housing outlet, wherein the outlet width increases from a base of the housing upwards. In this way, as the sewage liquid level rises in the internal volume, the flow of the sewage liquid through the housing outlet widens, thereby impacting a larger proportion of the length of the paddle wheel, leading to greater rotation rate of the paddle wheel. Optionally, the height of the weir gradually tapers upwards from the first weir end to the second weir end. Optionally, the height and / or position of the weir is adjustable. For example, the weir may be coupled to a hinge and / or slide mechanism to change the orientation, position and / or or height of the weir. The weir being adjustable allows tuning of the housing outlet geometry to optimise the position at which sewage liquid impacts the paddle wheel. For example, to tune a relationship between sewage liquid flow rate and paddle wheel rotation rate to affect the sewage system rotation speed and thereby reduce variations in flushing intensity factor (SK value) of the associated filter bed at different sewage liquid flow rates. As another example, if the height of flow control apparatus varies relative to a height of the paddle wheel in different applications, this may result in a variable average horizontal distance travelled by sewage liquid between the housing outlet and the paddle wheel. Therefore, it may be desirable to adjust the weir to change the second position and thereby account for height changes in the flow control apparatus, so that the sewage liquid impacts the paddle wheel at a desired position of the paddle wheel (e.g., a position which optimises rotation of the paddle wheel). The weir may be manually adjustable (e.g., by pivoting the weir and then bolting into place). Alternatively, the weir may be adjustable by an actuator (e.g., a linear actuator). Where the weir is adjustable by an actuator, the actuator may be part of a control system for automatically adjusting the position of the weir based on a flow rate through the flow control apparatus. Optionally, the housing outlet comprises a third position with respect to a front of the housing, wherein the third position is different to the first and second positions, wherein the housing outlet is configured so that sewage liquid flowing through the internal volume at a third flow rate, greater than the second flow rate, is free to exit the housing outlet at the third position. Optionally, the third position is further from the front of the housing than the second position. Optionally, the housing outlet comprises first and second weirs which extend upwards from a base of the housing so that, when a level of sewage liquid in the internal volume is below a height of the first weir, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet at the second position, and so that, when a level of sewage liquid in the internal volume is below a height of the second weir, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet at the third position, wherein the height of second weir is greater than the height of the first weir. Optionally, the flow control apparatus comprises a plurality of housing outlets for directing the flow of sewage liquid from the internal volume onto a plurality of paddle wheels. Such a configuration may facilitate greater throughput of sewage liquid and / or increase a rotation rate of a transmission driven by rotation of the one or more paddle wheels. Optionally, the plurality of housing outlets comprises a first housing outlet proximal a first side of the flow control apparatus and a second housing outlet proximal a second side of the flow control apparatus. Optionally, the flow control apparatus comprises a bypass weir arrangement (e.g., an adjustable bypass weir arrangement) for releasing (e.g., selectively releasing) at least some of the flow of sewage liquid from the internal volume to bypass the housing outlet and the paddle wheel. Such a weir arrangement allows a proportion of sewage liquid flowing through the flow control apparatus which impacts the paddle wheel to be reduced, which may be beneficial in certain operating conditions (e.g., high flow conditions). An adjustable bypass weir arrangement allows a proportion of sewage liquid flowing through the flow control apparatus which impacts the paddle wheel to be adjusted. As such, it allows the rotation rate for a given flow rate of sewage liquid into the flow control apparatus to be adjusted. This allows the flow control apparatus to be tuned to meet different flow requirements of different applications and / or to compensate for the effects of changes in temperature, wind speed, and other environmental factors. Optionally, the adjustable weir arrangement comprises a bypass opening and a bypass weir which is movable in order to adjust a width of the bypass opening. This contrasts with a weir which moves vertically upwards and downwards to adjust a height of the weir (and thus a height of the bypass opening). It will be understood that, by adjusting a width of the bypass opening rather than a height of the weir, better control of the proportion of sewage liquid which bypasses the paddle wheel can be achieved. For example, sewage liquid can flow through the bypass opening even at low flow rates allowing a bypass of the paddle wheel even at such low flow rates. Optionally, the bypass weir is movable (e.g., slidable or pivotable) in a direction approximately parallel to a base of the housing (e.g., in an approximately lateral or horizontal direction). Optionally, the bypass weir is movable between a closed state in which the bypass weir fully covers the bypass opening to inhibit (e.g., prevent) flow of sewage liquid through the bypass opening, an open state in which the bypass opening is uncovered to permit flow of sewage liquid through the bypass opening, and optionally, one or more partially open states between the closed state and the open state in which the bypass weir partially covers the bypass opening. This provides a range of different options fortuning the proportion of sewage liquid which exits the housing through the bypass opening. Optionally, the adjustable weir arrangement is configured so that the bypass weir is manually adjustable. Optionally, wherein the adjustable weir arrangement comprises a securing arrangement for releasably securing the bypass weir at a desired position. Optionally, the adjustable weir arrangement comprises an actuator configured to move the bypass weir. A second aspect of the disclosure provides a flow control system comprising a flow control apparatus in accordance with the first aspect of the disclosure and a deflector spaced apart from the flow control apparatus and positioned downstream of the housing outlet, such that sewage liquid flowing from the housing outlet impacts the deflector when a flow rate of said sewage liquid is greater than a threshold value. The deflector is configured to change a direction of said sewage liquid to direct said sewage liquid in a desired direction (e.g., towards a paddle wheel). Optionally, the deflector comprises at least one of an angled, a curved and / or a concave surface arranged to be impacted by said sewage liquid to direct said sewage liquid in a desired direction. Optionally, the deflector comprises an elongate blade. Optionally, a longitudinal axis of the elongate blade is approximately parallel to the paddle wheel axis, or a longitudinal axis of the elongate blade is provided at an angle to the paddle wheel axis. Optionally, the elongate blade comprises at least one of: a linear cross-section; an angled cross-section; a curved cross-section; a concave cross-section (e.g., an approximately C-shaped cross-section); and a cross-section comprising at least two straight portions coupled together at an angle (e.g., an approximately C-shaped cross-section). Optionally, the deflector overlaps a full width of the housing outlet or the deflector partially overlaps a width of the housing outlet. Optionally, the deflector overlaps the first position of the housing outlet. Optionally, the deflector does not overlap the second position of the housing outlet. Optionally, the deflector is positioned such that sewage liquid flowing from the housing outlet does not impact the deflector when the flow rate of said sewage liquid is less than the threshold value. A third aspect of the disclosure provides a rotational sewage distribution apparatus. The rotational sewage distribution apparatus comprises: a paddle wheel which is rotatable about a paddle wheel axis; and a flow control apparatus. The flow control apparatus may comprise: a housing defining an internal volume for flow of sewage liquid, a housing inlet for receiving a flow of sewage liquid from an inlet pipe into the internal volume, and a housing outlet through which a flow of sewage liquid exits the internal volume. The housing outlet may be configured to direct the flow of sewage liquid from the internal volume onto the paddle wheel to cause rotation of the paddle wheel about the paddle wheel axis. The housing outlet may be configured so that sewage liquid flowing through the internal volume at a first flow rate is free to exit the housing outlet at a first distance from the paddle wheel axis, and so that sewage liquid flowing through the internal volume at a second flow rate greater than the first flow rate is free to exit the housing outlet at a second distance from the paddle wheel axis, different to the first distance. Such a rotational sewage distribution apparatus benefits from the advantages of the flow control apparatus outlined above. In particular, the configuration of the housing outlet allows the point at which different flow rates of sewage liquid hit the paddle wheel to be controlled more easily. This facilitates achieving a desired relationship between sewage liquid flow rate and paddle wheel rotation rate (e.g., so that when the flow rate increases, rotation rate of the paddle wheel increases proportionally). Optionally, the flow control apparatus is in accordance with the first aspect of the disclosure. Optionally, sewage liquid flowing through the internal volume at the second flow rate is free to exit the housing outlet at both the first and second distances from the paddle wheel axis. In other words, there is no barrier or mechanism which limits sewage liquid flowing at the second flow rate from exiting the housing outlet at the first distance from the paddle wheel axis. This may allow the housing outlet to be constructed more simply (e.g., as a static mechanical structure). Alternatively, sewage liquid flowing through the internal volume at the second flow rate may only exit the housing outlet at the second distance from the paddle wheel axis (i.e., not at the first distance as well). For example, the housing outlet may be defined by an adjustable structure which is movable to positions between the first and second distances. There may be a control system configured to move the adjustable structure based on a flow rate of sewage liquid through the internal volume. Optionally, sewage liquid flowing through the internal volume at the first flow rate is free to exit the housing outlet at the first distance from the paddle wheel and is inhibited (e.g. prevented) from exiting the housing outlet at the second distance from the paddle wheel. Optionally, the second distance is greater than the first distance. In other words, sewage liquid flowing at the second flow rate exits the housing at a second position which is inboard of a first position at which sewage liquid flowing at the first flow rate exits the housing. In this context, “inboard” will be understood to mean further upstream in a general flow direction of the sewage liquid through the housing outlet. Having the second distance greater than the first distance may facilitate a more consistent position at which the flow of sewage liquid hits the paddle wheel at different flow rates. For example, where the flow rate is lower, the sewage liquid is expelled from the housing outlet at a shorter distance to the paddle wheel axis, but travels a smaller horizontal distance between the housing outlet and the paddle wheel. On the contrary, where the flow rate is higher, the sewage liquid is expelled from the housing outlet at a further distance from the paddle wheel axis, but travels a greater horizontal distance between the housing outlet and the paddle wheel. In this way, flows of sewage liquid being expelled from the housing outlet at the first and second distances from the paddle wheel axis may both hit the paddle wheel at approximately the same horizontal position. Directing the flow of sewage liquid in this way may facilitate an approximately linear relationship between flow rate of sewage liquid and rotation rate of the paddle wheel. Such a linear relationship may improve performance of the filter bed by spreading sewage liquid flowing at higher flow rates over a wider area than sewage liquid flowing at lower flow rates. In addition, having such a linear relationship may allow a greater flow rate of sewage liquid to be passed through the sewage distribution apparatus whilst reducing increase in flushing intensity factor of the associated filter bed. This reduces the risk of excessive hydraulic shearing of biofilm in the filter bed at higher sewage liquid flow rates. Optionally, the housing outlet is configured to direct the flow of sewage liquid from the internal volume onto the paddle wheel in an outlet direction which is transverse (e.g., perpendicular) to the paddle wheel axis. This may provide a more efficient rotation of the paddle wheel than alternative configurations in which the outlet direction is parallel to the paddle wheel axis. Optionally, the paddle wheel axis is a horizontal axis. Optionally, the rotational sewage distribution apparatus is configured so that sewage liquid flowing through the internal volume at the first flow rate and at the second flow rate impacts the paddle wheel on the same side of the paddle wheel axis; optionally, at a position between the paddle wheel axis and the housing outlet. Impacting the paddle wheel on the same side of the paddle wheel axis allows fluid flowing at the first and second flow rates to effect rotation of the paddle wheel in the same angular direction. Impacting the paddle wheel at a position between the paddle wheel axis and the housing outlet may facilitate an improved rotation rate of the paddle wheel in comparison to alternative configurations (e.g., those where the sewage liquid impacts the paddle wheel on an opposite side of the paddle wheel axis to the housing outlet). Optionally, the first distance and / or second distance is adjustable. Optionally, the rotational sewage distribution apparatus comprises a plurality of paddle wheels and the flow control apparatus comprises a plurality of housing outlets which are configured to direct the flow of sewage liquid from the internal volume onto the plurality of paddle wheels to cause rotation of the plurality of paddle wheels. Such a configuration may facilitate greaterthroughput of sewage liquid and / or increase a rotation rate of a transmission driven by rotation of the plurality of paddle wheels. Optionally, the rotational sewage distribution apparatus further comprises a deflector spaced apart from the flow control apparatus and positioned downstream of the housing outlet, such that sewage liquid flowing from the housing outlet impacts the deflector when a flow rate of said sewage liquid is at or greater than a threshold value. Optionally, the deflector is configured to change a direction of said sewage liquid to direct said sewage liquid onto the paddle wheel. It will be understood that sewage liquid which leaves the housing outlet at a greater flow rate will travel further horizontally before impacting the paddle wheel than sewage liquid which leaves the housing outlet at a lower flow rate. It will also be understood that there may be an optimum position at which sewage liquid impacts the paddle wheel to rotate the paddle wheel about the paddle wheel axis. If the housing outlet is positioned so that sewage liquid flowing at a nominal flow rate impacts the paddle wheel at this optimum position, this may lead to sewage liquid flowing at higher flow rates (e.g., in high flow conditions following heavy rainfall) overshooting the optimum position or even missing the paddle wheel altogether. Therefore, by having a deflector which is impacted by higher velocity sewage liquid and which directs sewage liquid onto the paddle wheel, sewage liquid travelling at both low and high flow rates may be directed effectively to impact a suitable position on the paddle wheel. Optionally, the deflector is positioned above the paddle wheel to direct sewage liquid downwards onto the paddle wheel. This provides a simple construction for directing sewage liquid onto the paddle wheel. Further, such a configuration may be assisted by gravity to urge the sewage liquid downwards after impacting the deflector. Optionally, the deflector comprises at least one of an angled, a curved and / or a concave surface arranged to be impacted by said sewage liquid to direct said sewage liquid in a desired direction with respect to the paddle wheel axis (e.g., diagonally downwards and away from the paddle wheel axis). This may facilitate direction sewage liquid onto the paddle wheel in an approximately tangential direction, which may increase the rotation rate of the paddle wheel for a given output of sewage liquid. In this context, “diagonally downwards and away from the paddle wheel axis” will be understood to mean that the sewage liquid is directed in a direction which has both a downwards vertical component and an horizontal component in a direction away from the paddle wheel axis. For example, the horizontal component may be towards the flow control apparatus. In this way, sewage liquid may be directed through a turn of greater than 90 degrees between exiting the housing outlet and impacting the paddle wheel. Optionally, the deflector comprises an elongate blade. This offers a simple means of constructing the deflector. Optionally, a longitudinal axis of the elongate blade is approximately parallel to the paddle wheel axis. This facilitates directing sewage liquid onto the paddle wheel at an approximately constant radial distance from the paddle wheel axis, which may improve performance of the paddle wheel in comparison to other arrangements. Optionally, a longitudinal axis of the elongate blade is provided at an angle to the paddle wheel axis. Optionally, the elongate blade comprises a linear cross-section. This offers a simple construction. For example, a piece of plate material (e.g., plate metal) could be used to form the elongate blade. Optionally, the elongate blade comprises an angled cross-section. This may facilitate direction sewage liquid onto the paddle wheel in an approximately tangential direction, which may increase the rotation rate of the paddle wheel for a given output of sewage liquid. Optionally, the elongate blade comprises a curved cross-section. This may facilitate direction sewage liquid onto the paddle wheel in an approximately tangential direction, which may increase the rotation rate of the paddle wheel for a given output of sewage liquid. Optionally, the elongate blade comprises a concave cross-section (e.g., an approximately C-shaped cross-section). This may facilitate direction sewage liquid onto the paddle wheel in an approximately tangential direction, which may increase the rotation rate of the paddle wheel for a given output of sewage liquid. Optionally, the elongate blade comprises a cross-section comprising at least two straight portions coupled together at an angle (e.g., an approximately C-shaped cross-section). This may facilitate direction sewage liquid onto the paddle wheel in an approximately tangential direction, which may increase the rotation rate of the paddle wheel for a given output of sewage liquid. Optionally, the deflector overlaps a full width of the housing outlet. This facilitates directing sewage liquid onto the paddle wheel with the deflector across an entire width of the housing outlet, which may improve performance of the paddle wheel. Optionally, the deflector partially overlaps a width of the housing outlet. This may provide additional space and a reduction of materials in comparison to a full overlap. Optionally, the deflector overlaps a portion of the housing outlet at which sewage liquid exits the housing outlet at the first distance from the paddle wheel axis. Optionally, the deflector does not overlap a portion of the housing outlet at which sewage liquid exits the housing outlet at the second distance from the paddle wheel axis. It will be understood that sewage liquid exiting the housing outlet at the second distance from the paddle wheel axis may impact the paddle wheel at a suitable position with respect to the paddle wheel axis, even at higher velocities. In other words, sewage liquid exiting the housing outlet at the second distance from the paddle wheel axis may have dropped lower than the deflector before it reaches the horizontal position of the deflector, and thus the deflector may be omitted in such a region. Optionally, the deflector is positioned such that sewage liquid flowing from the housing outlet does not impact the deflector when the flow rate of said sewage liquid is less than the threshold value. Optionally, the rotational sewage distribution apparatus further comprises a transmission coupled to the paddle wheel, wherein the transmission is configured to translate rotation of the paddle wheel to rotation of the sewage distribution apparatus about a vertical axis. Such a transmission allows work done by sewage liquid rotating the paddle wheel to be harnessed to rotate the sewage distribution apparatus. In other words, this removes the need for an external energy supply (e.g., electricity for powering an electric motor). Optionally, the rotational sewage distribution apparatus further comprises an outlet tray extending beneath the paddle wheel to receive sewage liquid therefrom and direct said sewage liquid to one or more longitudinally extending distribution channels. Such an outlet tray allows the sewage liquid to be directed to a distribution channel for distribution on a filter bed, after it has been used to drive rotation of the paddle wheel. Optionally, the rotational sewage distribution apparatus further comprises one or more longitudinally extending distribution channels coupled to the outlet tray to receive sewage liquid therefrom and distribute the sewage liquid to a filter bed. It will be understood that because the one or more longitudinally extending distribution channels are coupled to the outlet tray, the distribution channel(s) will rotate with the outlet tray. In this way, sewage liquid in the distributions channel(s) will be distributed about the surface area of the filter bed overtime. Optionally, the rotational sewage distribution apparatus comprises a plurality of longitudinally extending distribution channels, optionally 2, 3 or 4 longitudinally extending distribution channels. A fourth aspect of the disclosure provides a sewage distribution system. The sewage distribution system comprises a rotational sewage distribution apparatus. The rotational sewage distribution apparatus comprises an apparatus inlet for input of sewage liquid, an apparatus outlet for directing the sewage liquid to a longitudinally extending distribution channel, and a rotation mechanism for rotating the rotational sewage distribution apparatus about a vertical axis. The sewage distribution system also comprises an inlet pipe for supplying sewage liquid from a sewage liquid reservoir to the apparatus inlet. Optionally, the rotational sewage distribution apparatus is in accordance with the third aspect of the disclosure. Optionally, the inlet pipe comprises a non-circular cross-sectional shape. Typically, circular inlet pipes are used in such sewage distribution systems because these are the most commonly-available type of pipe. However, for a given desired level of sewage liquid in the sewage liquid reservoir, a relatively small amount of the cross-sectional area of the pipe is below the desired level of sewage liquid. This inlet pipe volume may be inadequate for the flow rates desired, which leads to a higher sewage liquid level in the reservoir than desired, which can in turn cause flooding of the reservoir. Where greater flow is required, a larger diameter pipe can be used to increase the cross-sectional area below the sewage liquid level, but this decreases the proportion of the total cross-sectional area which is positioned below the sewage liquid level Alternatively, it may be possible to lower the height at which the pipe is positioned, however this is restricted by the height at which the sewage distribution system is located. By having an inlet pipe with a non-circular cross-sectional shape, the proportion of the total cross-sectional area of the pipe which is positioned below the desired sewage liquid level can be increased in comparison to circular pipes of similar total cross-sectional area. This results in a greater flow rate of sewage liquid along the inlet pipe for a given sewage liquid level. This may allow retrofitting of the rotational sewage distribution apparatus and inlet pipe to existing sewage distribution systems where the relative heights of the sewage liquid reservoir and filter bed are constrained, whilst maintaining and / or increasing flow rates through the rotational sewage distribution apparatus. Optionally, the housing inlet is provided at a cover portion of the flow control apparatus and the inlet pipe is arranged above the flow control apparatus. In this way, the flow control apparatus can be fed from the inlet pipe under gravity (i.e., without the need for a pump). Optionally, the inlet pipe comprises one of a substantially rectangular cross-sectional shape, a substantially square cross-sectional shape, a substantially oblong cross-sectional shape, a substantially oval cross-sectional shape, a substantially triangular cross-sectional shape or a partially circular (e.g., semi-circular) shape. A rectangular cross-sectional shape may be particularly beneficial for increasing flow rate along the inlet pipe. In addition, rectangular pipes may be more readily available and / or easily constructed than alternatives shapes. A square cross-sectional shape may also be beneficial for increasing flow rate along the inlet pipe, and may be more readily available and / or easily constructed than alternative shapes. Oblong, oval, triangular or partially circular cross-sectional shapes provide alternatives that can also increase flow rate along the inlet pipe in comparison to circular cross-sectional shapes. Optionally, a cross section of the inlet pipe comprises a substantially vertical dimension and a substantially horizontal dimension, wherein the horizontal dimension is larger than the vertical dimension. Having a larger horizontal dimension increases flow rate at lower sewage liquid levels for a given cross-sectional area of the pipe, in comparison to alternative configurations in which the vertical dimension is greater than or equal to the horizontal dimension. Optionally, the horizontal dimension is at least 20% greater than the vertical dimension, optionally at least 40% greater than the vertical dimension, optionally at least 60% greater than the vertical dimension, optionally at least 80% greater than the vertical dimension, optionally at least 100% greater than the vertical dimension. Optionally, a cross-section of the inlet pipe comprises a lower end, an upper end, a first side and a second side, wherein the inlet pipe comprises a pipe height extending from the lower end to the upper end and a pipe width extending from the first side to the second side, wherein the pipe width is greater than the pipe length. Having a greater pipe width increases flow rate at lower sewage liquid levels for a given cross-sectional area of the pipe in comparison to alternative configurations in which the pipe height is greater than the pipe width. Optionally, the pipe width is at least 20% greater than the pipe height, optionally at least 40% greater than the pipe height, optionally at least 60% greater than the pipe height, optionally at least 80% greater than the pipe height, optionally at least 100% greater than the pipe height. Optionally, the cross section of the inlet pipe comprises a lower end and wherein an area of the cross-sectional shape defined between the lower end and a height of 50 mm above the lower end is at least 8,000 mm2, optionally at least 9,000 mm2, optionally at least 10,000 mm2, optionally at least, 11,000 mm2, optionally at least 12,000 mm2. Such a configuration has been found to provide good sewage liquid flow rates through the inlet pipe and rotational sewage distribution apparatus for typical sewage liquid levels in existing sewage liquid reservoir infrastructure. Optionally, the area of the cross-sectional shape defined between the lower end and a height of 50 mm above the lower end is at least 20% of a total area of the cross-sectional shape, optionally at least 25% of a total area of the cross-sectional shape, optionally at least 30% of a total area of the cross-sectional shape. Such a configuration increases flow rate at lower sewage liquid levels for a given cross-sectional area of the pipe in comparison to alternative configurations in which the area of the cross-sectional shape defined between the lower end and the height of 50 mm above the lower end is less than 20% of the total area of the cross-sectional shape. Optionally, the cross section of the inlet pipe comprises a lower end, an upper end and a cross section pipe height extending from the lower end to the upper end, wherein a lower area of the cross-sectional shape defined below 25% of the pipe height is at least 20% of a total area of the cross-sectional shape; optionally at least 25% of the total area of the cross-sectional shape; optionally at least 30% of the total area of the cross-sectional shape. Such a configuration increases flow rate at lower sewage liquid levels for a given cross-sectional area of the pipe in comparison to alternative configurations in which the lower area of the cross-sectional shape defined below 25% of the pipe height is less than 20% of the total area of the cross-sectional shape. Optionally, the apparatus inlet is provided at an upper end of the rotational sewage distribution apparatus and the inlet pipe is arranged above the rotational sewage distribution apparatus. In this way, the rotational sewage distribution apparatus can be fed from the inlet pipe under gravity (i.e., without the need for a pump). A fifth aspect of the disclosure provides a filter system. The filter system comprises: a sewage liquid source; a filter media tank; a filter bed provided within the filter media tank; and a sewage distribution system as disclosed herein. Such a filter system benefits from the advantages of the sewage distribution apparatus outlined above. Optionally, the rotational sewage distribution apparatus comprises a vertical shaft which defines the vertical axis. Optionally, the vertical shaft is coupled to the filter media tank in a centre of the filter bed. It will be appreciated that any feature of any of the aspects of the disclosure outlined above may be combined with any compatible features of any of the other aspects of the disclosure above. For the sake of brevity, not all combinations are explicitly recited above. BRIEF DESCRIPTION OF DRAWINGS Embodiments will now be described by way of example only with reference to the accompanying figures, in which: Figure 1 is a plan view of a filter system including a sewage distribution system according to an embodiment; Figure 2 is side cross-sectional view of the filter system of Figure 1, taken along plane A-A; Figure 3 is a side cross-sectional view of a sewage distribution system and rotational sewage distribution apparatus for the filter system of Figures 1 and 2; Figure 4 is a plan view of the rotational sewage distribution apparatus of Figure 3; Figure 5 is a side cross-sectional view of a further sewage distribution system and rotational sewage distribution apparatus for the filter system of Figures 1 and 2; Figure 6 is a plan view of the rotational sewage distribution apparatus of Figure 5; Figure 7A is a plan view of a portion of a flow control apparatus of the rotational sewage distribution apparatus of Figures 5 and 6; Figure 7B is a front view of the portion of the flow control apparatus of Figure 7A; Figure 8 is an isometric view of the portion of the flow control apparatus of Figures 7A and 7B; Figure 9 is an isometric view of a paddle wheel and the flow control apparatus of the rotational sewage distribution apparatus of Figures 5 and 6; Figure 10 is a side cross-sectional view of a further sewage distribution system and rotational sewage distribution apparatus for the filter system of Figures 1 and 2; Figure 11 is a plan view of the rotational sewage distribution apparatus of Figure 10; Figure 12 is a graph of sewage liquid flow rate against rotation rate of the rotational sewage distribution apparatuses of Figures 3 to 11; Figure 13 is a side cross-sectional view of a flow control apparatus for the filter system of Figures 1 and 2; Figure 14 is a plan view of the flow control apparatus of Figure 10; Figures 15A to 15C are side cross-sectional views of a portion of a rotational sewage distribution apparatus including a flow control apparatus without a deflector, with a flat deflector, and with a convex deflector, respectively; Figure 16 is a perspective view of the rotational sewage distribution apparatus of Figures 15B; Figure 17 is a graph of sewage liquid flow rate against rotation rate of the rotational sewage distribution apparatuses of Figures 3 and 4, 15A and 15C; Figure 18 is a side cross-sectional view of different shaped inlet pipes forthe sewage distribution system of Figures 1 and 2; Figure 19 is a side cross-sectional view of further different shaped inlet pipes forthe sewage distribution system of Figures 1 and 2; Figure 20 is a side cross-sectional view of further different shaped inlet pipes forthe sewage distribution system of Figures 1 and 2. DETAILED DESCRIPTION In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments and the teachings. However, those skilled in the art will understand that: the present teachings may be practiced without these specific details or with known equivalents of these specific details; that the present teachings are not limited to the described embodiments; and, that the present teachings may be practiced in a variety of alternative embodiments. It will also be appreciated that well known methods, procedures, components, and systems may not have been described in detail. References to vertical and horizontal in the present disclosure should be understood to be in relation to the respective apparatus / system when installed and in use. Referring firstly to Figures 1 and 2, a filter system is indicated at 300. The filter system 300 includes a sewage liquid source 302, a filter media tank 304, a filter bed 306 provided within the filter media tank 304, and a sewage distribution system 200. The sewage distribution system 200 has an inlet pipe 202 for providing a flow of sewage liquid from the sewage liquid source 302 to a rotational sewage distribution apparatus 100. In this embodiment, the sewage liquid source 302 is a sewage liquid reservoir, and the inlet pipe 202 is coupled to an opening in a side of the sewage liquid reservoir 302, so that sewage liquid can flow passively along the inlet pipe 202 under the force of gravity. In alternative embodiments, a pump or other device may be used to actively drive sewage liquid along the inlet pipe 202. The inlet pipe 202 is arranged above the rotational sewage distribution apparatus 100, so that sewage liquid can enter an apparatus inlet of the rotational sewage distribution apparatus 100 from above (as will be described in more detail below). In the illustrated embodiment, the inlet pipe 202 is supported at one or more different positions along its length by a support structure 204. The illustrated support structure 204 includes a vertical support 206, and one or more support arms 208 coupled between the inlet pipe 202 and the vertical post 206. In particular, the support structure 204 includes support arms which are coupled to the inlet pipe 202 at different positions along a length of the inlet pipe 202. In the illustrated embodiment, there are three support arms 208, but other suitable numbers of support arms 208 may be provided. In other embodiments, any other suitable support structure 204 may be used. The rotational sewage distribution apparatus 100 includes one or more longitudinally extending distribution channels 114. In particular, the illustrated rotational sewage distribution apparatus 100 includes two longitudinally extending distribution channels 114, although it will be appreciated that in other embodiments there may be more or less than two longitudinally extending distribution channels 114 (e.g., one, three, four, five or more). The longitudinally extending distribution channels 114 are arranged above the filter bed 306. In this way, sewage liquid which is input from the inlet pipe 202 to the rotational sewage distribution apparatus 100 can be distributed along the longitudinally extending distribution channels 114 for distribution to the filter bed 306. As will be described in more detail below, the rotational sewage distribution apparatus 100 includes a rotation mechanism for rotating the rotational sewage distribution 100 apparatus about a vertical axis 104. In this embodiment, the vertical axis 104 is defined by a vertical shaft 102 of the rotational sewage distribution apparatus 100 which is coupled to the filter media tank 304 in a centre of the filter bed 306. In this way, as the rotational sewage distribution apparatus 100 is caused to rotate by the rotation mechanism, the longitudinally extending distribution channels 114 rotate above the filter bed 306 (e.g., as illustrated by the block arrows on Figure 1, and the dashed lines on Figure 1 illustrating a position at which the rotational sewage distribution apparatus 100 will have rotated after a period of time). This causes sewage liquid to be distributed evenly throughout the filter bed 306. The filter system 300 described above may be referred to as a “trickling filter” system. Referring now to Figures 3 and 4, the rotational sewage distribution apparatus 100 will be described in more detail. In the illustrated embodiment, the rotation mechanism which causes the rotational sewage distribution apparatus 100 to rotate includes one or more paddle wheels 106A, 106B which are rotatable about a paddle wheel axis 108. In particular, the paddle wheels 106A, 106B are rotated by a flow of sewage liquid supplied to the rotational sewage distribution apparatus 100 by the inlet pipe 202, as will be described in more detail below. In the illustrated embodiment, the paddle wheel axis 108 is a horizontal axis, but the paddle wheel axis 108 may be a vertical axis or a transverse axis arranged at an angle to both horizontal and vertical directions. In the illustrated embodiment, there is a left paddle wheel 106A and a right paddle wheel 106, although it will be understood that more or less than two paddle wheels 106A, 106B may be provided in other configurations. In the illustrated embodiment, the left and right paddle wheels 106A, 106B are coaxially aligned (i.e., they share the same paddle wheel axis 108). In other embodiments, the left and right paddle wheels 106A, 106B have different paddle wheel axes 108 (e.g., parallel but spaced-apart axes). The rotational sewage distribution apparatus 100 also includes a transmission 110 coupled to the paddle wheels 106A, 106B. The transmission 110 is configured to translate rotation of the paddle wheels 106A, 106B about the paddle wheel axis 108 to rotation of the rotational sewage distribution apparatus 100 about the vertical axis 104. For example, the transmission 110 may include one or more gears or other mechanical components for converting rotation in one direction to rotation in another direction. The transmission 110 is rotatably coupled to the vertical shaft 102 to facilitate rotation about the vertical axis 104. The transmission 110 allows work done by sewage liquid rotating the paddle wheels 106A, 106B to be harnessed to rotate the rotational sewage distribution apparatus 100. In other words, this removes the need for an external energy supply (e.g., electricity for powering an electric motor). However, it will be understood that in other embodiments the transmission 100 and paddle wheels 106A, 106B may be replaced by an electric motor or other means for actively rotating the rotational sewage distribution apparatus 100. In the illustrated embodiment, the rotational sewage distribution apparatus 100 includes an outlet tray arrangement 112 extending beneath the paddle wheels 106A, 106B to receive sewage liquid (e.g., from the paddle wheels 106A, 106B). The outlet tray arrangement 112 is configured to direct the sewage liquid to the longitudinally extending distribution channels 114. In the illustrated embodiment, the outlet tray arrangement 112 includes: a left outlet tray 112A extending beneath the left paddle wheel 106A to receive sewage liquid from the left paddle wheel 106A; and a right outlet tray 112B extending beneath the right paddle wheel 106B to receive sewage liquid from the right paddle wheel 106B. In other embodiments, the outlet tray arrangement 112 may be defined by a single outlet tray. For example, in embodiments where there is a single paddle wheel, a single outlet tray may be used. Alternatively, a single outlet tray may be provided to extend under both the left and right paddle wheels 106A, 106B with a sealing arrangement provided in the centre proximal to the vertical shaft 102, to permit rotation of the single outlet tray around the shaft. Each outlet tray 112A, 112B includes a base surface 122 and one or more sides 124. A lower surface of the longitudinally extending distribution channels 114 is provided at or below the level of the base surface 122 of the respective outlet tray 112A, 112B. In particular, the illustrated configuration has the lower surface of the longitudinally extending distribution channels 114 provided below the level of the base surface 122 of the respective outlet tray 112A, 112B. Further, in the illustrated embodiment the lower surface of the longitudinally extending distribution channels 114 tapers upwards along a length of the longitudinally extending distribution channels 114. Openings 126 are provided in the one or more sides 124 of each outlet tray 112A, 112B. In this way, sewage liquid flows from each outlet tray 112A, 112B to the longitudinally extending distribution channels 114. The longitudinally extending distribution channels 114 may be open channels (i.e., having an open upper end). In this way, once a level of sewage liquid in the longitudinally extending channels 114 reaches the open upper end, the sewage liquid passes over the open upper end and falls onto the filter bed 306 below. In some embodiments, the longitudinally extending distribution channels 114 may include sides with a series of recesses. In this way, sewage liquid is able to pass through the recesses and fall onto the filter bed 306 before the sewage liquid level reaches the open upper end. Alternatively, the longitudinally extending channels 114 may be closed channels (e.g., pipes) with a series of apertures along a length of the channel, such that sewage liquid can pass through the apertures and fall onto the filter bed 306 below. In the illustrated embodiment, a cross-sectional area of each longitudinally extending distribution channel 114 decreases along its length in a radially outboard direction (with respect to the vertical axis 104). In this way, the cross-sectional area reduces as the amount of sewage liquid in the longitudinally extending channels 114 decreases (due to falling out onto the filter bed 306). This allows a velocity of sewage liquid to be maintained along the length of the longitudinally extending channels 114. In the illustrated embodiment, the decreasing cross-sectional area is achieved by having a lower surface of the longitudinally extending distribution channels 114 taper upwards from the respective outlet tray 112A, 112B towards a tip of the longitudinally extending distribution channel 114, as illustrated in Figures 2 and 3. A further decrease in the cross-sectional area of the longitudinally extending distribution channels 114 is achieved by having a narrowing width along the length of the longitudinally extending distribution channels 114, as illustrated in Figure 1. In the illustrated embodiment, the rotational sewage distribution apparatus 100 also includes a flow control apparatus 10 for directing the flow of sewage liquid onto the paddle wheels 106A, 106B. The flow control apparatus 10 includes a housing 12 defining an internal volume 14 for flow of sewage liquid. In the illustrated embodiment, the housing 12 has a front portion 16, a rear portion 18, and a base 22 extending therebetween. The housing 12 also has a cover portion 24 and left and right sides 26A, 26B extending between the base 22 and the cover portion 24. A horizontal axis 20 is defined between the front portion 16 and the rear portion 18. The flow control apparatus 10 includes a housing inlet 28 for receiving the flow of sewage liquid from the inlet pipe 202 into the internal volume 14. In the illustrated embodiment, the housing inlet 28 is an opening in the cover portion 24. The vertical axis 104 passes through the housing inlet 28, so that sewage liquid can fall from the inlet pipe 202 through the housing inlet 28 and into the internal volume 14 of the flow control apparatus 10 regardless of the rotational orientation of the flow control apparatus 10. The flow control apparatus 10 also includes a housing outlet 30A, 30B through which a flow of sewage liquid exits the internal volume 14. In particular, there is a left housing outlet 30A proximal the left side 26A of the housing 12 and a right housing outlet 30B proximal the right side 26B of the housing 12. Each housing outlet 30A, 30B, is configured to direct the flow of sewage liquid from the internal volume 14 onto the respective paddle wheel 106A, 106B to cause rotation of the paddle wheel 106A, 106B about the paddle wheel axis 108. It will therefore be understood that the number of housing outlets 30A, 30B may differ in accordance with variations in the number of paddle wheels 106A, 106B. Alternatively, there may be multiple housing outlets 30A, 30B configured to direct sewage liquid onto the same paddle wheel 106A, 106B (i.e., at different axial positions along a length of the paddle wheel 106A, 106Bwith respect to the paddle wheel axis 108). The housing outlets 30A and 30B are provided above the paddle wheels 106A, 106B so that sewage liquid flowing through the housing outlets 30A, 30B can fall under the force of gravity onto the paddle wheels 106A, 106B. The kinetic energy of the falling sewage liquid hitting the paddle wheels 106A, 106B causes the paddle wheels 106A, 106B to rotate about the paddle wheel axis 108. As best illustrated in Figure 4, the housing outlets 30A, 30B overlap the paddle wheels 106A, 106B in plan view. However, it will be understood that the housing outlets 30A, 30B may not overlap the paddle wheels 106A, 106B. For example, in configurations where the flow control apparatus 10 is higher relative to the paddle wheels 106A, 106B, the sewage liquid will travel a greater horizontal distance after leaving the housing outlets 30A, 30B before hitting the paddle wheels 106A, 106B, and so the housing outlets 30A, 30B may not overlap the paddle wheels 106A, 106B in plan view. The paddle wheels 106A, 106B include an inboard side 120 and an outboard side 121. The inboard side 120 is positioned to a side of the paddle wheel axis 108 which is distal a front side 124A of the outlet tray arrangement 112 in plan view. Conversely, the outboard side 121 is positioned to a side of the paddle wheel axis 108 which is proximal to the front side 124A of the outlet tray arrangement 112 in plan view. In other words, with respect to a forward end F and rearward end R of the rotational sewage distribution apparatus 100 (illustrated on Figure 4), the inboard side 120 is a rear side of the paddle wheels 106A, 106B, whereas the outboard side 121 is a front side of the paddle wheels 106A, 106B. In the illustrated embodiment, the housing outlets 30A, 30B are positioned above the inboard side 120 of the paddle wheels 106A, 106B in plan view. In the configuration of Figures 3 and 4, each housing outlet 30A, 30B is a generally forward-facing opening (i.e., facing generally towards the forward end F of the rotational sewage distribution apparatus 100). In other words, each housing outlet 30A, 30B is an opening in a generally front-facing surface 48 of the housing 12. In this context, the term “generally front-facing surface” will be understood to mean a surface which faces a generally forward direction (i.e., towards or from the front portion 16 of the housing 12). In some embodiments, “front-facing” will be understood to mean proximal the respective paddle wheel 106A, 106B. However, it will be understood that the front-facing surface 48 does not have to be arranged exactly perpendicular to the horizontal axis 20 extending between the front portion 16 and the rear portion 18 of the housing 12. The openings of the housing outlets 30A, 30B each have a notional central axis that is approximately parallel to the horizontal axis 20 extending between the front portion 16 and the rear portion 18 of the housing 12. In this context, the term “approximately parallel” will be understood to mean that the central axis / outlet direction is within a few degrees (e.g., 30 degrees or less) of the horizontal axis 20 extending between the front portion 16 and rear portion 18 of the housing 12. It will be understood that the structure of the illustrated housing outlets 30A, 30B causes sewage liquid flowing through the housing outlets 30A, 30B to exit the housing 12 in an outlet direction 32 which is approximately parallel to the horizontal axis 20 extending between the front portion 16 and rear portion 18 of the housing 12 (i.e., an approximately forward direction). However, because of the nature of flow of sewage liquid inside the internal volume 14 of the flow control apparatus 10, some of the sewage liquid will be directed through the housing outlets 30A, 30B in a direction which is angled relative to the horizontal axis 20. In other words, the outlet direction 32 may be a generally forwards direction encompassing a range of angles relative to the horizontal axis 20. The outlet direction 32 is transverse to the paddle wheel axis 108. In other words, sewage liquid exiting the housing 12 via the housing outlets 30A, 30B travels in a direction towards the paddle wheel axis 108. In the illustrated embodiment, the front-facing surface 48 of the housing 12 is set back from the front portion 16 of the housing 12. This allows the housing inlet 28 to be positioned forward of the housing outlets 30A, 30B (i.e., at a central location, so that the housing inlet 28 stays central as the rotational sewage distribution apparatus 100 rotates. In other embodiments, the front-facing surface 48 may define the front portion 16 of the housing 12. In the illustrated embodiment, the front-facing surface 48 is slightly angled relative to the front portion 16 of the housing 12. In other words, the front-facing surface 48 is not exactly perpendicular to the horizontal axis 20 extending between the front portion 16 and the rear portion 18 of the housing 12. In the illustrated embodiment, the flow control apparatus 10 includes one or more bypass weir arrangements 52 for releasing at least some of the flow of sewage liquid from the internal volume 14 to bypass the housing outlets 30A, 30B and the paddle wheels 106A, 106B. For example, such a bypass path is illustrated by the dot-dash-dot arrows on Figures 3 and 4. In the illustrated embodiment, there are two bypass weir arrangements 52 at the left and right sides 26A, 26B of the housing 12. In other embodiments, a single bypass weir arrangement 52 may be provided. The illustrated bypass weir arrangements 52 each include a bypass opening 52A and a bypass weir 52B. The bypass weir 52B inhibits flow of sewage liquid through the bypass opening 52A until a level of sewage liquid in the internal volume 14 of the flow control apparatus 10 is greater than a height of the weir 52B. Once the level of sewage liquid in the internal volume 14 tops the bypass weir 52B, at least some of the sewage liquid flows through the bypass opening 52A and thus does not impact the respective paddlewheel 106A, 106B. In the illustrated embodiment, the bypass weir arrangements 52 each include a channel 52C for guiding the flow of sewage liquid from the bypass opening 52A downwards into the respective outlet tray 112A, 112B. In other embodiments, the channel 52C may be omitted. Referring now to Figures 5 to 9, an alternative rotational sewage distribution apparatus 100 for the sewage distribution system 200 of Figures 1 and 2 is illustrated. Common features between the rotational sewage distribution apparatus 100 of Figures 5 to 9 and the previous rotational sewage distribution apparatus 100 of Figures 3 and 4 are given the same reference numerals, and only differences are discussed in detail. In the embodiment of Figures 5 to 9, each housing outlet 30A, 30B has a first position 34 with respect to the front portion 16 of the housing 12 and a second position 36 with respect to the front portion 16 of the housing 12. Each housing outlet 30A, 30B is configured so that sewage liquid flowing through the internal volume 14 at a first flow rate is free to exit the housing outlet 30A, 30B at the first position 34 and is inhibited (e.g., prevented) from exiting the housing outlet 30A, 30B at the second position 36, and so that sewage liquid flowing through the internal volume 14 at a second flow rate greater than the first flow rate is free to exit the housing outlet 30A, 30B at the second position 36. In the illustrated embodiment, the first and second positions 34, 36 are different positions with respect to the front portion 16 of the housing 12. In other words, the first and second positions 34, 36 are different axial positions with respect to the horizontal axis 20 extending between the front portion 16 and the rear portion 18 of the housing 12. Put another way, the first and second positions 34, 36 are at different distances 116, 118 from the paddle wheel axis 108. It will be understood that variations in flow rate of the sewage liquid will result in variations in the horizontal distance travelled by the sewage liquid between leaving the housing outlets 30A, 30B and hitting the paddle wheels 106A, 106B. Therefore, by having the housing outlets 30A, 30B configured so that sewage liquid flowing through the internal volume 14 at different flow rates exits the housing outlets 30A, 30B at different positions, it is possible to control where fluid flows of different flow rates hit the paddlewheel 106A, 106B. In the illustrated embodiment, the second position 36 is further from the front portion 16 of the housing 12 than the first position 34. In particular, the second position 36 is set back from the front portion 16 of the housing 12 to a greater extent than the first position 34 is set back from the front portion 16 of the housing 12. In other words, the second position 36 is inboard of the first position 34 with respect to the horizontal axis 20. Put another way, the first position 34 is closer to the paddle wheel axis 108 than the second position 36 (i.e., the second distance 118 is greater than the first distance 120). Having the second position 36 further from the front portion 16 of the housing 12 (i.e., further from the paddle wheel axis 108) may facilitate a more consistent position at which the flow of sewage liquid hits the paddle wheels 106A, 106B at different flow rates. For example, where the flow rate is lower, the sewage liquid exits the housing outlets 30A, 30B at a more forward first position 34, buttravels a smaller horizontal distance between the housing outlets 30A, 30B and the paddle wheels 106A, 106B. On the contrary, where the flow rate is higher, the sewage liquid exits the housing outlets 30A, 30B at a less forward second position 36, but travels a greater horizontal distance between the housing outlets 30A, 30B and the paddle wheels 106A, 106B. In this way, flows of sewage liquid exiting the housing outlets 30A, 30B at the first and second positions 34, 36 may both hit the paddle wheels 106A, 106B at approximately the same horizontal position (e.g., as indicated schematically by the block arrows extending on through the right housing outlet 30B on Figure 6). Directing the flow of sewage liquid in this way may facilitate an approximately linear relationship between flow rate of sewage liquid and rotation rate of the paddle wheel. For example, the dashed line on Figure 12 illustrates the results of experiments performed with the flow control apparatus 10 of Figures 5 to 9 at different flow rates of sewage liquid throughput. In the dashed line of Figure 12, the rotation rate of the rotational sewage distribution apparatus 100 (y-axis) increases in an approximately linear relationship with the flow rate of sewage liquid (x-axis) up to around 12 l / s. This contrasts with the non-linear relationship illustrated by the solid line of Figure 12, which shows the results of experiments performed with the flow control apparatus 10 of Figures 3 and 4 at different flow rates of sewage liquid throughput. The linear relationship between sewage liquid flow rate and rotation rate illustrated by the dashed line in Figure 12 may improve performance of the filter bed 306. In particular, having such a linear relationship may allow a greater flow rate of sewage liquid to be passed through the rotational sewage distribution apparatus 100 whilst minimising increase in flushing intensity factor (SK value) of the associated filter bed 306. This reduces the risk of excessive hydraulic shearing of biofilm in the filter bed 306 at higher sewage liquid flow rates. For example, Table 1 below outlines flushing intensity factors (SK values) for different flow rates of sewage liquid for the configuration of Figures 3 to 4, Table 2 below outlines flushing intensity factors (SK values) for different flow rates of sewage liquid for the configuration of Figures and 5 to 9. These tables illustrate a significant reduction in flushing intensity factor values at higherflow rates forthe configuration of Figures 5 to 9 in comparison to the configuration of Figures 3 and 4. Table 1 Flow Rate (l / s) 1.9 5.5 11 SK (mm / pass) 4.1 11.9 23.9 Table 2 Flow Rate (l / s) 1.9 5.5 11 SK (mm / pass) 3.8 9 14.9 Referring again to Figures 5 to 9, it will be understood that sewage liquid flowing through the internal volume 14 at the second flow rate is free to exit the housing outlets 30A, 30B at either of the first and second positions 34, 36. In other words, there is no barrier or mechanism which limits sewage liquid flowing at the second flow rate from exiting the housing outlet at the first position 34 as well as the second position 36. In alternative embodiments, sewage liquid flowing through the internal volume 14 at the second flow rate may only be free to exit the housing outlets 30A, 30B at the second position 36 (i.e., not at the first position 34 as well). For example, the housing outlets 30A, 30B may be defined by an adjustable structure which is movable between the first and second positions 34, 36, and there may be a control system configured to move the adjustable structure based on a flow rate of sewage liquid through the internal volume 14. In some embodiments, the first position 34 and / or second position 36 is adjustable. In other words, the first distance 116 and / or the second distance 118 is adjustable. For example, the housing 12 may include an adjustable first member which defines the first position 34 and / or an adjustable second member which defines the second position 36. Alternatively, the housing 12 may include an adjustable member which defines both the first and second positions 34, 36. The adjustable member(s) may be pivotal and / or slidable relative to the rest of the housing 12. The first and / or second positions 34, 36 may be manually adjustable (e.g., by pivoting the adjustable member(s) and then bolting into place). Alternatively, the first and / or second positions may be adjustable by an actuator (e.g., a linear actuator to move the adjustable member(s)). Where adjustable by an actuator, the actuator may be part of a control system for automatically adjusting the first and / or second positions 34, 36 based on a flow rate through the flow control apparatus 10. As best illustrated in Figures 6 and 7A, the base 22 of the housing 12 of the flow control apparatus 10 includes a first base portion 38 proximal the first position 34 and a second base portion 40 proximal the second position 36. For example, the first base portion 38 defines the first position 34 and the second base portion 40 defines the second position 36. The second base portion 40 is further from the front portion 16 of the housing 12 than the first base portion 38. In the illustrated embodiment, the base 22 of the housing 12 of the flow control apparatus 10 tapers gradually away from the front portion 16 of the housing 12 between the first position 34 and the second position 36. In some embodiments, the second base portion 40 and / or the first base portion 38 is adjustable. For example, the second base portion 40 and / or first base portion 38 may be coupled to a respective hinge and / or slide mechanism to change the extent to which the second position 36 is inboard of the first position 34. The second base portion 40 and / or first base portion 38 may be manually adjustable (e.g., by pivoting the second base portion 40 and / or first base portion 38 and then bolting into place). Alternatively, the second base portion 40 and / or first base portion 38 may be adjustable by an actuator (e.g., a linear actuator). Where the second base portion 40 and / or first base portion 38 are adjustable by an actuator, the actuator may be part of a control system for automatically adjusting the position of the second base portion 40 and / or first base portion 38 based on a flow rate through the flow control apparatus 10. In the illustrated embodiment, each housing outlet 30A, 30B has a weir 42 which extends upwards from the base 22 of the housing 12 so that sewage liquid only exits the housing outlets 30A, 30B at the second position 36 when a level of sewage liquid in the internal volume 14 is greater than a height of the weir 42. It will be understood that the level of sewage liquid in the internal volume 14 will be higher when the flow rate of sewage liquid through the flow control apparatus 10 is higher. Therefore, such a weir 42 provides a simple means of ensuring that sewage liquid flowing at lower flow rates (i.e., sewage liquid flowing when the level in the internal volume 14 is lower) does not exit the housing outlets 30A, 30B at the second position 36, where the sewage liquid may not travel sufficient horizontal distance to reach the paddle wheels 106A, 106B due to insufficient flow rates. In the illustrated embodiment, the weir 42 defines a substantially flat surface which is angled relative to the front portion 16 of the housing 12 (i.e., not perpendicular to the horizontal axis 20 or parallel to the paddle wheel axis 108). This provides a simple means of constructing the weir 42, but it will be understood that the weir 42 may have any suitable configuration. As best illustrated in Figures 7A to 8, the weir 42 has a first weir end 44 proximal to the first position 34 and a second weir end 46 distal the first position 34. In the illustrated embodiment, the height of the weir 42 increases from the first weir end 44 to the second weir end 46. In particular, the height of the weir 42 gradually tapers upwards from the first weir end 44 to the second weir end 46. In this way, the innermost position at which sewage liquid tops the weir 42 moves inboard (i.e., further backwards) as the level of sewage liquid in the internal volume 14 increases. In other words, the housing outlets 30A, 30B define an outlet width between the weir 42 and an opposing side of the housing outlet 30A, 30B, and the outlet width increases from the base 22 of the housing 12 upwards. In this way, as the sewage liquid level rises in the internal volume 14, the flow of the sewage liquid through the housing outlets 30A, 30B widens, thereby impacting a larger proportion of the length of the paddle wheels 106A, 106B, leading to greater rotation rate of the paddle wheels 106A, 106B. In the illustrated embodiment, the second position 36 of each housing outlet 30A, 30B is closer to the respective side 26A, 26B of the housing 12 than the first position 34. Similarly, the second weir end 46 of each weir 42 is closer to the respective side 26A, 26B ofthe housing 12 than the first weir end 44. In alternative embodiments, the first position 34 of each housing outlet 30A, 30B and the first weir end 44 of each weir 42 may be closer to the respective side 26A, 26B. In some embodiments, the position of the weir 42 is adjustable. For example, the weir 42 may be coupled to a hinge and / or slide mechanism to change the orientation, position and / or or height ofthe weir 42. The weir 42 may be manually adjustable (e.g., by pivoting the weir 42 and then bolting into place). Alternatively, the weir 42 may be adjustable by an actuator (e.g., a linear actuator). Where the weir 42 is adjustable by an actuator, the actuator may be part of a control system for automatically adjusting the position ofthe weir42 based on a flow rate through the flow control apparatus 10. It will be understood that the weir 42 extends from the base 22 proximal the second base portion 40. Therefore, in embodiments where the weir 42 is adjustable, the second base portion 40 may also be adjustable. For example, the weir 42 and second base portion 40 may define a contiguous piece of material with a horizontal portion defined by the second base portion 40 and a vertical portion defined by the weir 42. In such embodiments, the weir 42 and second base portion 40 may be movable together (e.g., pivoted via a common hinge and / or moved via a common slide mechanism). The rotational sewage distribution apparatus 100 of Figures 5 to 9 is configured so that sewage liquid flowing through the internal volume 14 at the first flow rate and at the second flow rate impacts the paddle wheels 106A, 106B on the same side ofthe paddle wheel axis 108. In particular, on the inboard side 120 ofthe paddle wheels 106A, 106B at a position between the paddle wheel axis 108 and the housing outlets 30A, 30B. Referring now to Figures 10 and 11, an alternative rotational sewage distribution apparatus 100 for the sewage distribution system 200 of Figures 1 and 2 is illustrated. Common features between the rotational sewage distribution apparatus 100 of Figures 10 and 11, and the previous rotational sewage distribution apparatuses 100 of Figures 3 to 9 are given the same reference numerals, and only differences are discussed in detail. In the configuration of Figures 10 and 11, the bypass weir arrangements 52 are omitted. Instead, each housing outlet 30A, 30B has a third position 37 with respect to the front 16 of the housing 12, and is configured so that sewage liquid flowing through the internal volume 14 at a third flow rate, greater than the second flow rate, is free to exit the housing 12 outlet at the third position 37 (e.g., as illustrated by the dot-dash-dot arrows on Figure 10). In the illustrated embodiment, the third position is further from the front 16 of the housing 12 than the second position 36. Put another way, the third position 37 is at a further distance 119 from the paddle wheel axis 108 than the second distance 118. The housing outlets 30A, 30B each have a second weir 43 (e.g., in addition to the angled weir 42 described above with reference to Figures 5 to 9) which extends upwards from the base 22 of the housing 12. In this way, when a level of sewage liquid in the internal volume 14 is below a height of the second weir 43, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet 30A, 30B at the third position 37. It will be understood that the third position 37 of the housing outlet 30A, 30B may function similarly to the bypass weir arrangement 52 of the previous embodiments, because sewage liquid may not travel far enough from the third position 37 to impact the respective paddle wheel 106A, 106B (e.g., in medium flow conditions). However, in other conditions (e.g., high flow conditions), sewage liquid may leave the housing outlets 30A, 30B at the third position 37 with sufficient velocity to impact the respective paddle wheel 106A, 106B (as indicated by the dot-dash-dot block arrow on the right hand side of Figure 11) and thereby drive faster rotation of the paddle wheel 106A, 106B about the paddle wheel axis 108. In the illustrated embodiment, the height of second weir 43 is greater than the maximum height of the angled weir 42 (as best illustrated in Figure 10). In other embodiments, the height of the second weir 43 may be the same or less than the maximum height of the angled weir 42. In the illustrated embodiment, the second weir 43 is approximately parallel to the front 16 of the housing 12 (as best illustrated in Figure 11). Similarly, the second weir 43 is approximately parallel to the paddle wheel axis 108 (as best illustrated in Figure 11). In some embodiments, the second weir 43 may be adjustable (e.g., movable upwards and downwards in order to change a height of the second weir 43). The dot-dash-dot line on Figure 12 illustrates the results of experiments performed with the flow control apparatus 10 of Figures 10 and 11 at different flow rates of sewage liquid throughput. In the dot-dash-dot line of Figure 12, the rotation rate of the rotational sewage distribution apparatus 100 (y-axis) increases in an approximately linear relationship with the flow rate of sewage liquid (x-axis) upto around 16 l / s (e.g., greater than the dashed line, which starts to level off around 12 l / s). This may further improve performance of the filter bed 306. In particular, having such a linear relationship may allow a greater flow rate of sewage liquid to be passed through the rotational sewage distribution apparatus 100 whilst minimising increase in flushing intensity factor (SK value) of the associated filter bed 306. This reduces the risk of excessive hydraulic shearing of biofilm in the filter bed 306 at higher sewage liquid flow rates. Referring now to Figures 13 and 14, an alternative flow control apparatus 10 for the sewage distribution system 200 of Figures 1 and 2 is illustrated. Common features between the flow control apparatus 10 of Figures 13 and 14, and the previous flow control apparatuses 10 of Figures 3 to 11 are given the same reference numerals, and only differences are discussed in detail. In the configuration of Figures 13 and 14, each housing outlet 30A, 30B has a first position 34, a second position 36, and a third position 37 with respect to the front 16 of the housing 12. In the illustrated embodiment, the second position 36 is further from the front 16 of the housing 12 than the first position 34, and the third position 37 is further from the front of the housing than the second position 36. Each housing outlet 30A, 30B is configured so that sewage liquid flowing through the internal volume 14 at a first flow rate is free to exit the housing outlet 30A, 30B at the first position 34 and is inhibited (e.g. prevented) from exiting the housing outlet 30A, 30B at the second position 36 and the third position 37. Each housing outlet 30A, 30B is also configured so that sewage liquid flowing through the internal volume 14 at a second flow rate greater than the first flow rate is free to exit the housing outlet 30A, 30B at the second position 36 and is inhibited (e.g., prevented) from exiting the housing outlet 30A, 30B at the third position. Each housing outlet 30A, 30B is also configured so that sewage liquid flowing through the internal volume 14 at a third flow rate, greater than the second flow rate, is free to exit the housing outlet 30A, 30B at the third position 37. In the illustrated embodiment, the housing outlets 30A, 30B each have first and second weirs 42, 43 which extend upwards from the base 22 of the housing 12. In this way, when a level of sewage liquid in the internal volume 14 is below a height of the respective weirs 42, 43, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet 30A, 30B at the respective position 36, 37. In the illustrated embodiment, the height of the second weir 43 is greater than the height of the first weir 43. In the illustrated embodiment, the first and second weirs 42, 43 each define a substantially flat surface. In the illustrated embodiments, the substantially flat surfaces defined by the first and second weirs 42, 43 are parallel to the front 16 of the housing 12 (e.g., as opposed to the angled weir 42 of Figures 5 to 11). The height of each weir 42, 43 is constant along a length of the weir 42, 43 (e.g., as opposed to the weir 42 of Figures 5 to 11 which tapers upwards). As will be understood from the description above, the base 22 of the housing 12 of the flow control apparatus 10 steps rearwards with respect to the front 16 of the housing 12 from a first base portion 38 to a second base portion 40. The base 22 of the housing 12 also steps rearwards from the second base portion 40 to a third base portion 41. Similarly, because the first and second weirs 42, 43 are of constant height, and the second weir 43 is higher than the first weir 42, there is an upwards step from the base 22 to the top of the first weir 42, and a further upwards step from the top of the first weir 42 to the top of the second weir 43. Such a configuration may approximate the function of the angled weir 42 of Figures 5 to 11, albeit with discrete steps instead of a gradual tapering of the weir 42 backwards and in height. In some embodiments, the first and / or second weirs 42, 43 may be adjustable (e.g., using any of the adjustment means described for other embodiments above). In some embodiments, there may be a single rearwards step from the first position 34 to the second position 36. In other words, the third position 37 and second weir 43 may be omitted. In such embodiments, the weir 42 at the second position 36 may be wider than in the embodiment of Figures 13 and 14. For example, the weir 42 may have a length equal to the combined lengths of the first and second weirs 42, 43 in Figures 13 and 14. In Figure 14, a flow control system is illustrated, including the flow control apparatus 10 as described above, and one or more deflectors 54. In the illustrated embodiment, there are two deflectors 54, but more or less than two deflectors 54 may be provided (e.g., to track the number of housing outlets 30A, 30B in the flow control apparatus 10). Each deflector 54 is spaced apart from the flow control apparatus 10 and is positioned downstream of the respective housing outlet 30A, 30B such that sewage liquid flowing from the housing outlet 30A, 30B impacts the deflector 54 when a flow rate of said sewage liquid is greater than a threshold value. Each deflector 54 is configured to change a direction of said sewage liquid to direct said sewage liquid in a desired direction (e.g., as illustrated schematically by the dashed arrows on Figure 14). Referring now to Figures 15A, to 15C, the function of the deflector 54 will be described in more detail. In Figure 15A, no deflector 54 is present. As a result, when the flow rate of sewage liquid through the housing outlet 30 is high, the sewage liquid travels in the direction indicated by arrow 56 and impacts the paddle wheel 106 on a far side of the paddle wheel axis 108. This may reduce performance of the paddle wheel 106. In contrast, in Figures 15B and 15C where a deflector 54 is present, the deflector is configured to change the direction of the sewage liquid to direct the sewage liquid onto the paddle wheel 106 at a more suitable position. This may improve performance of the paddle wheel 106. In particular, the deflectors 54 of Figures 15B and 15C are positioned above the paddle wheel 106 to direct sewage liquid downwards onto the paddle wheel 106 (as indicated by arrows 58 and 60). In the illustrated embodiments, the deflectors 54 are configured to direct sewage liquid to impact the paddle wheel 106 on a side of the paddle wheel axis 108 proximal to the housing outlet 30. In other embodiments (e.g., those in which the paddle wheel 106 is flipped through 180 degrees in comparison to the illustrated configured so that the paddle wheel 106 rotates in the opposite direction), the deflector 54 may be configured to direct sewage liquid to impact the paddle wheel 106 on a fair side of the paddle wheel axis 108 distal the housing outlet 30. In Figure 15C, the deflector 54 has a concave surface 61 arranged to be impacted by the sewage liquid to direct the sewage liquid diagonally downwards and away from the paddle wheel axis 108 (i.e., in a direction having a downwards vertical component and a horizontal component towards the flow control apparatus 10). In Figures 14, 15B and 15C, the deflector 54 is an elongate blade, and a longitudinal axis 62 of the elongate blade 54 is approximately parallel to the paddle wheel axis 108. In other embodiments, the longitudinal axis 62 may be provided at an angle to the paddle wheel axis 108. In Figure 15B, the elongate blade 54 has a linear cross-section. In contrast, in Figure 15C the elongate blade 54 has a concave cross-section formed of three straight portions coupled together at angles to each other (e.g., in an approximately C-shaped cross-section). In other embodiments, the elongate blade 54 may have any other suitable profile (e.g., including at least one of: a linear cross-section; an angled cross-section; a curved cross-section; a concave cross-section; and a cross-section comprising at least two straight portions coupled together at an angle). In the embodiment of Figure 14, each deflector 54 overlaps a full width of the respective housing outlet 30A, 30B. In other embodiments, one or more deflectors 54 may only partially overlap a width of the respective housing outlet 30A, 30B (e.g., overlapping only the first position 34 of the housing outlet 30A, 30B). The deflectors 54 are each spaced apart from the respective housing outlet 30A, 30B by a spacing distance 64 (illustrated on Figure 14). Therefore, sewage liquid flowing at low flow rates (e.g., below the threshold value) may not travel sufficient horizontal distance to impact the deflector 54. The deflector 54 may be mounted to the flow control apparatus 10 and / or other portions of the rotational sewage distribution apparatus 100 by any suitable means. For example, Figure 16 illustrates a bracket 66 which couples the deflector 54 to the cover portion 24 of the housing 12 of the flow control apparatus 10. The bracket 66 has a slot 68 and a releasable fastening 70 which allows the spacing distance 66 between the deflector 54 and the respective housing outlet 30A, 30B to be adjusted. Referring again to Figures 13, 14 and 16, the flow control apparatus 10 includes two bypass weir arrangements 52 similar to the bypass weir arrangements of Figures 3 to 9. However, in this embodiment, each bypass weir arrangement 52 is adjustable for selectively releasing at least some of the flow of sewage liquid from the internal volume 14 to bypass the housing outlets 30A, 30B. Having such an adjustable bypass weir arrangement 52 allows a proportion of sewage liquid flowing through the flow control apparatus 10 which impacts the paddle wheel 106 to be adjusted. As such, it allows the rotation rate for a given flow rate of sewage liquid into the flow control apparatus 10 to be adjusted. This allows the flow control apparatus 10 to be tuned to meet different flow requirements of different applications and / or to compensate for the effects of changes in temperature, wind speed, and other environmental factors. In the illustrated embodiment, the bypass weir 52B is movable in orderto adjust a width 53 of the bypass opening 52A (for example, such a width 53 is indicated on Figure 16). In the illustrated embodiment, the bypass weir 52B is movable in a direction approximately parallel to the base 22 of the housing 12 (e.g., in an approximately lateral or horizontal direction). In particular, the bypass weir 52B is slidable in a horizontal direction (as indicated by the block arrow on Figure 16). In other embodiments, the bypass weir 52B may be pivotable (e.g., about a vertical axis) to change the width 53 of the bypass opening 52A. In the illustrated embodiment, the bypass weir 52B is movable between a closed state (illustrated in Figure 14) in which the bypass weir 52B fully covers the bypass opening 52A to inhibit (e.g., prevent) flow of sewage liquid through the bypass opening 52A, and an open state (illustrated in Figure 16) in which the bypass opening 52A is uncovered to permit flow of sewage liquid through the bypass opening 52A. The bypass weir 52B is also movable through one or more partially open states between the closed state and the open state, in which the bypass weir52B partially covers the bypass opening 52A. In the illustrated embodiment, each adjustable weir arrangement 52 is configured so that the bypass weir 52B is manually adjustable. For example, the adjustable weir arrangement 52 has a securing arrangement 52D for releasably securing the bypass weir 52B at a desired position. In the illustrated embodiment, the securing arrangement 52D is in the form of a slot in the bypass weir 52B and a releasable fastening (e.g., bolt) which engages the slot to secure the bypass weir 52B in a desired position. In other embodiments, one or more of the adjustable weir arrangements 52 may include an actuator configured to move the bypass weir 52B to a desired position. In alternative embodiments, the bypass weir52B may move vertically upwards and downwards to adjust a height of the bypass weir 52B (and thus a height of the bypass opening 52A). Figure 17 illustrates a similar graph to that of Figure 12 for the embodiments of Figures 13 and 14. In particular, the solid line indicates the configuration of Figures 3 and 4, the dashed line indicates the configuration of Figures 13 and 14 without a deflector 54 (e.g., as illustrated in Figure 15A), and the dot-dot-dash line indicates the configuration of Figures 13 and 14 with a deflector 54 of the kind illustrated in Figure 15C. As can be seen in Figure 17, the embodiments of Figures 13 and 14 provide a more linear relationship between flow rate and rotation speed than the embodiment of Figures 3 and 4. Further, the addition of the deflector 54 provides an even more linear relationship between flow rate and rotation speed than the configuration without a deflector 54. The addition of the deflector 54 also provides a higher rotation speed for a given flow rate. It will be understood that the gradient which defines of the relationship between flow rate and rotation speed may not be substantially affected by the state of the adjustable bypass weir arrangement 52. However, the lines illustrated in Figure 17 may move upwards and downwards in the y-axis depending on the state of the adjustable bypass weir arrangement 52. For example, when the bypass weir 52B is moved to close the bypass opening 52A, a greater proportion of the sewage liquid will impact the paddle wheel 106, and thus rotation speed will be higher. Similarly, when the bypass weir 52B is opened to increase the width of the bypass opening 52A, a lower proportion of the sewage liquid will impact the paddle wheel 106 and thus rotation speed will be lower. This is particularly useful, since different filter systems may have different requirements for rotation speed at given flow rates. In other words, the adjustable bypass weir arrangement 52 may allow the same rotational sewage distribution apparatus 100 to be used for a variety of different applications with different requirements. In addition, the relationships illustrated on Figure 17 may change with environmental factors such as temperature, wind speed etc., and thus the adjustable bypass weir arrangement 52 allows tuning of the system to compensate for such environmental factors. In any of the embodiments of Figures 5 to 16 described above, the second position 36 may be set back from the first position 34 by a distance in a range of around 20 mm to about 140 mm, e.g., about 40mm to about 120 mm, e.g., about 60mm to about 100 mm, e.g., about 80 mm. In otherwords, the difference between the first and second distances 116,118 may be in a range of around 20 mm to about 140 mm, e.g., about 40mm to about 120 mm, e.g., about 60mm to about 100 mm, e.g., about 80 mm. Similarly, in the embodiments of Figures 10, 11, 13 and 14, the third position 37 may be set back from the second position 36 by a distance in a range of around 20 mm to about 140 mm, e.g., about 40mm to about 120 mm, e.g., about 60mm to about 100 mm, e.g., about 80 mm. In otherwords, the difference between the second and third distances 118, 119 may be in a range of around 20 mm to about 140 mm, e.g., about 40mm to about 120 mm, e.g., about 60mm to about 100 mm, e.g., about 80 mm. In other embodiments, the first and second positions 34, 36 may be spaced apart by a distance outside of the ranges indicated above (e.g., by a distance of less than 20 mm orgreaterthan 140 mm). Similarly, in the embodiments of Figures 10,11,13 and 14, the second and third positions 36, 37 may be spaced apart by a distance outside of the ranges indicated above (e.g., by a distance of less than 20 mm or greater than 140 mm). Referring now to Figures 18 to 20, the inlet pipe 202 of the sewage distribution apparatus 200 of Figures 1 and 2 will be described in more detail. Typically, inlet pipes 202 used in sewage distribution apparatuses 200 are of circular cross-sectional shape (e.g., as illustrated on the left-hand side of Figure 18). However, for a given desired level of sewage liquid in the sewage liquid reservoir 302 (indicated by a dashed line on Figures 18 and 19), a relatively small amount of the available cross-sectional area of the pipe 202 (i.e. a relatively small volume of the inlet pipe 202) is below the desired level of sewage liquid. This inlet pipe 202 volume may be inadequate for the flow rates desired, which leads to higher sewage liquid levels in the reservoir than desired, which can in turn result in flooding of the reservoir. Where greater flow is required, a larger diameter inlet pipe 202 can be used to increase the cross-sectional area below the sewage liquid level, but this decreases the proportion of the total cross-sectional area which is positioned below the sewage liquid level and results in a higher cost pipe. Alternatively, it may be possible to lower the height at which the pipe is positioned, however this is restricted by the height at which the sewage distribution system 200 is located. In some embodiments, the inlet pipe 202 has a non-circular cross-sectional shape 210. For example, in the embodiments of Figures 1 and 2 the inlet pipe 202 has a rectangular cross-sectional shape 210 (as illustrated on the right-hand side of Figure 18). The rectangular cross-sectional shape 210 is of a similar cross-sectional area to the circular cross-sectional shape of the inlet pipe 202 on the left-hand side of Figure 18. By having an inlet pipe 202 with such a rectangular cross-sectional shape, the proportion of the total cross-sectional area of the inlet pipe 202 which is positioned below the desired sewage liquid level can be increased in comparison to circular pipes of similar total cross-sectional area. This results in a greater flow rate of sewage liquid along the inlet pipe 202 for a given sewage liquid level. This may allow retrofitting of the rotational sewage distribution apparatus 100 and inlet pipe 202 to existing sewage distribution systems 200 where the relative heights of the sewage liquid reservoir 302 and filter bed 306 are constrained, whilst maintaining and / or increasing flow rates through the rotational sewage distribution apparatus 100. Figure 19 illustrates alternative non-circular cross-sectional shapes 210 for the inlet pipe 202. For example, Figure 19 illustrates (from left to right), a substantially oval cross-sectional shape 210, a substantially oblong cross-sectional shape 210, a substantially triangular cross-sectional shape 210, a substantially square cross-sectional shape 210 and a partially circular (i.e., semicircular) cross-sectional shape 210. These non-circular cross-sectional shapes 210 are alternative shapes to the rectangular cross-sectional shape of Figure 18, which provide similar benefits of increasing cross-sectional area below a desired sewage liquid level and increased flow rate at lower sewage liquid levels. In some embodiments, the cross section 210 of the inlet pipe 202 includes a substantially vertical dimension 212 and a substantially horizontal dimension 214, and the horizontal dimension 214 is larger than the vertical dimension 212. For example, the horizontal dimension 214 may be at least 20% greater than the vertical dimension 212 (e.g., at least 40% greater than the vertical dimension 212, at least 60% greater than the vertical dimension 212, at least 80% greater than the vertical dimension 212, or at least 100% greater than the vertical dimension 212). Put another way, the cross-sectional shape 210 of the inlet pipe 202 may include a lower end 216, an upper end 218, a first side 220 and a second side 222, and the inlet pipe 202 may include a pipe height 212 extending from the lower end 216 to the upper end 218 and a pipe width 214 extending from the first side 220 to the second side 220. The pipe width 214 may be greater than the pipe length 212. For example, the pipe width 214 may be at least 20% greater than the pipe height 212 (e.g., at least 40% greater than the pipe height 212, at least 60% greaterthan the pipe height 212, at least 80% greater than the pipe height 212, or at least 100% greaterthan the pipe height 212). In some embodiments, an area of the cross-sectional shape 210 defined between the lower end 216 and a height of 50 mm above the lower end 216 is at least 8,000 mm2, e.g. at least 9,000 mm2, e.g. at least 10,000 mm2, e.g. at least, 11,000 mm2, e.g. at least 12,000 mm2. Such a configuration has been found to provide good sewage liquid flow rates through the inlet pipe 202 and rotational sewage distribution apparatus 100 for typical sewage liquid levels in existing sewage liquid reservoir infrastructure. In some embodiments, the area of the cross-sectional shape 210 defined between the lower end 216 and a height of 50 mm above the lower end 216 is at least 20% of a total area of the cross-sectional shape 210 (e.g., at least 30% of the total area of the cross-sectional shape 210, or at least 40% of the total area of the cross-sectional shape 210). Such a configuration increases flow rate at lower sewage liquid levels for a given cross-sectional area of the pipe in comparison to alternative configurations in which the area of the cross-sectional shape 210 defined between the lower end 216 and the height of 50 mm above the lower end 216 is less than 20% of the total area of the cross-sectional shape 210. In some embodiments, a lower area of the cross-sectional shape 210 defined below 25% of the pipe height 212 is at least 20% of a total area of the cross-sectional shape 210 (e.g., at least 25% of the total area of the cross-sectional shape 210, or at least 30% of the total area of the cross-sectional shape 210). Such a configuration increases flow rate at lower sewage liquid levels fora given cross-sectional area of the inlet pipe 202 in comparison to alternative configurations in which the lower area of the cross-sectional shape 210 defined below 25% of the pipe height is less than 20% of the total area of the cross-sectional shape 210. Table 3 below illustrates an example of the submerged cross-sectional area of different inlet pipes at different sewage liquid levels. In this context, “submerged cross-sectional area” is the area of the cross-sectional shape which is below the respective sewage liquid level. As can be seen from the table, the rectangular inlet pipes (pipes D and E) have a substantially greater submerged cross-sectional area than the circular inlet pipes (pipes A to C), across the whole range of sewage liquid levels. Submerged Cross-sectional Area (% of Total Cross-sectional Area) Sewage Liquid Level 25mm 50mm 75mm 100mm 125mm 150mm A) 100mm Diameter 1535 mm2 3927 mm2 6318 mm2 7853 mm2 7853 mm2 7853 mm2 Circular Pipe (20%) (50%) (80%) (100%) (100%) (100%) B) 150mm Diameter Circular Pipe 1935 mm2 5156 mm2 8835 mm2 12515 mm2 15735 mm2 17671 mm2 (100%) (11%) (29%) (50%) (71%) (89%) C) 200mm Diameter Circular Pipe 2266 mm2 6142 mm2 10760 mm2 15708 mm2 20655 mm2 25274 mm2 (7%) (20%) (34%) (50%) (66%) (80%) D) 250x150mm Rectangular Pipe 6250 mm2 (17%) 12500 mm2 (33%) 18750 mm2 (50%) 25000 mm2 (67%) 31250 mm2 (83%) 37500 mm2 (100%) E) 300x150mm Rectangular Pipe 7500 mm2 (17%) 15000 mm2 (33%) 22500 mm2 (50%) 3000 mm2 (67%) 37500 mm2 (83%) 45000 mm2 (100%) Figure 20 illustrates the information in Table 3 graphically, with the hatched areas indicating the submerged cross-sectional area. It will be understood that the rectangular inlet pipes 202 of Figures 18 and 20 and / or the other inlet pipes 202 of Figure 19 may be used with either of the rotational sewage distribution apparatuses 100 5 of Figures 3 to 11 or 13 to 16 to form the sewage distribution system 200 of Figures 1 and 2. In alternative embodiments, the sewage distribution system 200 may have a standard inlet pipe 202 of circular cross-section (e.g., one of pipes A to C illustrated in Figure 20). The one or more embodiments are described above by way of example only and it will be appreciated that the variations are possible without departing from the scope of protection afforded by the appended 10 claims. It should also be noted that whilst the appended claims set out particular combinations of features described above, the scope of the present disclosure is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. A flow control apparatus for directing a flow of sewage liquid onto a paddle wheel of a rotational sewage distribution apparatus, the flow control apparatus comprising:a housing defining an internal volume for flow of sewage liquid;a housing inlet for receiving a flow of sewage liquid from an inlet pipe into the internal volume; anda housing outlet configured to direct the flow of sewage liquid from the internal volume onto a paddle wheel;the housing outlet comprising a first position with respect to a front of the housing and a second position with respect to a front of the housing, wherein the second position is different to the first position;wherein the housing outlet is configured so that sewage liquid flowing through the internal volume at a first flow rate is free to exit the housing outlet at the first position and is inhibited (e.g. prevented) from exiting the housing outlet at the second position, and so that sewage liquid flowing through the internal volume at a second flow rate greater than the first flow rate is free to exit the housing outlet at the second position.

2. The flow control apparatus of claim 1, wherein the second position is further from the front of the housing than the first position.

3. The flow control apparatus of any preceding claim, wherein sewage liquid flowing through the internal volume at the second flow rate is free to exit the housing outlet at either of the first and second positions.

4. The flow control apparatus of any preceding claim, wherein a base of the housing comprises a first base portion proximal the first position and a second base portion proximal the second position, wherein the second base portion is further from the front of the housing than the first base portion; optionally, wherein the base of the flow control apparatus steps rearwards, with respect to the front of the housing, from the first base portion to the second base portion, or wherein the base of the flow control apparatus tapers gradually away from the front of the housing between the first position and the second position.

5. The flow control apparatus of any preceding claim, wherein the housing outlet comprises a weir which extends upwards from a base of the housing so, when a level of sewage liquid in the internal volume is below a height of the weir, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet at the second position; optionally, wherein the weir defines a substantially flat surface; optionally, wherein the substantially flat surface is substantially parallel to the front of the housing or is angled relative to the front of the housing.

6. The flow control apparatus of claim 5, wherein the height of the weir is substantially constant along a length of the weir.

7. The flow control apparatus of claim 5 or 6, wherein the height and / or position of the weir is adjustable.

8. The flow control apparatus of any preceding claim, wherein the housing outlet comprises a third position with respect to a front of the housing, wherein the third position is different to the first and second positions, wherein the housing outlet is configured so that sewage liquid flowing through the internal volume at a third flow rate, greater than the second flow rate, is free to exit the housing outlet at the third position; optionally, wherein the third position is further from the front of the housing than the second position; and / or optionally, wherein the housing outlet comprises first and second weirs which extend upwards from a base of the housing so that, when a level of sewage liquid in the internal volume is below a height of the first weir, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet at the second position, and so that, when a level of sewage liquid in the internal volume is below a height of the second weir, sewage liquid is inhibited (e.g. prevented) from exiting the housing outlet at the third position, wherein the height of second weir is greater than the height of the first weir.

9. The flow control apparatus of any preceding claim, wherein the flow control apparatus comprises a plurality of housing outlets for directing the flow of sewage liquid from the internal volume onto a plurality of paddle wheels; optionally, wherein the plurality of housing outlets comprises a first housing outlet proximal a first side of the flow control apparatus and a second housing outlet proximal a second side of the flow control apparatus.

10. A rotational sewage distribution apparatus, comprising:a paddle wheel which is rotatable about a paddle wheel axis; anda flow control apparatus comprising: a housing defining an internal volume for flow of sewage liquid, a housing inlet for receiving a flow of sewage liquid from an inlet pipe into the internal volume, and a housing outlet through which a flow of sewage liquid exits the internal volume;wherein the housing outlet is configured to direct the flow of sewage liquid from the internal volume onto the paddle wheel to cause rotation of the paddle wheel about the paddle wheel axis; and wherein the housing outlet is configured so that sewage liquid flowing through the internal volume at a first flow rate is free to exit the housing outlet at a first distance from the paddle wheel axis, and so that sewage liquid flowing through the internal volume at a second flow rate greater than the first flow rate is free to exit the housing outlet at a second distance from the paddle wheel axis, different to the first distance.

11. The rotational sewage distribution apparatus of claim 10, wherein sewage liquid flowing through the internal volume at the second flow rate is free to exit the housing outlet at both the first and second distances from the paddle wheel axis; and / or wherein sewage liquid flowing through the internal volumeat the first flow rate is free to exit the housing outlet at the first distance from the paddle wheel and is inhibited (e.g. prevented) from exiting the housing outlet at the second distance from the paddle wheel; and / or wherein the second distance is greater than the first distance.

12. The rotational sewage distribution apparatus of claim 10 or 11, wherein the rotational sewage distribution apparatus is configured so that sewage liquid flowing through the internal volume at the first flow rate and at the second flow rate impacts the paddle wheel on the same side of the paddle wheel axis; optionally, at a position between the paddle wheel axis and the housing outlet.

13. A rotational sewage distribution apparatus, comprising:a paddle wheel which is rotatable about a paddle wheel axis; anda flow control apparatus comprising: a housing defining an internal volume for flow of sewage liquid, a housing inlet for receiving a flow of sewage liquid from an inlet pipe into the internal volume, and a housing outlet through which a flow of sewage liquid exits the internal volume towards the paddle wheel to cause rotation of the paddle wheel about the paddle wheel axis; anda deflector spaced apart from the flow control apparatus and positioned downstream of the housing outlet, such that sewage liquid flowing from the housing outlet impacts the deflector when a flow rate of said sewage liquid is greater than a threshold value,wherein the deflector is configured to change a direction of said sewage liquid to direct said sewage liquid onto the paddle wheel.

14. The rotational sewage distribution apparatus of claim 13, wherein the deflector is positioned above the paddle wheel to direct sewage liquid downwards onto the paddle wheel; optionally, wherein the deflector comprises at least one of an angled, a curved and / or a concave surface arranged to be impacted by said sewage liquid to direct said sewage liquid in a desired direction with respect to the paddle wheel axis (e.g. diagonally downwards and away from the paddle wheel axis).

15. The rotational sewage distribution apparatus of claim 13 or 14, wherein the deflector comprises an elongate blade; optionally wherein a longitudinal axis of the elongate blade is approximately parallel to the paddle wheel axis; optionally wherein a longitudinal axis of the elongate blade is provided at an angle to the paddle wheel; and / or optionally, wherein the elongate blade comprises a linear crosssection, an angled cross-section, a curved cross-section, a concave cross-section, and / or a crosssection comprising at least two straight portions coupled together at an angle, (e.g., an approximately C-shaped cross-section).

16. A rotational sewage distribution apparatus in accordance with any of claims 10 to 12 and any of claims 13 to 15.

17. A flow control apparatus for directing a flow of sewage liquid onto a paddle wheel of a rotational sewage distribution apparatus, the flow control apparatus comprising:a housing defining an internal volume for flow of sewage liquid;a housing inlet for receiving a flow of sewage liquid from an inlet pipe into the internal volume;a housing outlet configured to direct the flow of sewage liquid from the internal volume onto a paddle wheel; andan adjustable bypass weir arrangement for selectively releasing at least some of the flow of sewage liquid from the internal volume to bypass the housing outlet and the paddle wheel;wherein the adjustable bypass weir arrangement comprises a bypass opening and a bypass weir which is movable in order to adjust a width of the bypass opening; optionally, wherein the bypass weir is movable (e.g., slidable or pivotable) in a direction approximately parallel to a base of the housing (e.g., in an approximately lateral or horizontal direction); and / or optionally, wherein the bypass weir is movable between a closed state in which the bypass weir fully covers the bypass opening to inhibit (e.g. prevent) flow of sewage liquid through the bypass opening, an open state in which the bypass opening is uncovered to permit flow of sewage liquid through the bypass opening, and optionally one or more partially open states between the closed state and the open state in which the bypass weir partially covers the bypass opening.

18. A rotational sewage distribution apparatus, comprising the flow control apparatus of claim 17 and a paddle wheel which is rotatable about a paddle wheel axis; optionally, wherein the rotational sewage distribution apparatus is in accordance with any of claims 10 to 16.

19. The rotational sewage distribution apparatus of any of claims 10 to 16 or 18, further comprising a transmission coupled to the paddle wheel, wherein the transmission is configured to translate rotation of the paddle wheel to rotation of the sewage distribution apparatus about a vertical axis; optionally, further comprising an outlet tray extending beneath the paddle wheel to receive sewage liquid therefrom and direct said sewage liquid to one or more longitudinally extending distribution channels; optionally, further comprising one or more longitudinally extending distribution channels coupled to the outlet tray to receive sewage liquid therefrom and distribute the sewage liquid to a filter bed; optionally, comprising a plurality of longitudinally extending distribution channels, optionally 2, 3 or 4 longitudinally extending distribution channels.

20. A sewage distribution system comprising:the rotational sewage distribution apparatus of any of claims 10 to 16, 18 or 19; andan inlet pipe for providing the flow of sewage liquid to the housing inlet of the flow control apparatus; optionally, wherein the inlet pipe comprises a non-circular cross-sectional shape.

21. A sewage distribution system, comprising:a rotational sewage distribution apparatus comprising: an apparatus inlet for input of sewage liquid, an apparatus outlet for directing the sewage liquid to a longitudinally extending distribution channel, and a rotation mechanism for rotating the rotational sewage distribution apparatus about a vertical axis; andan inlet pipe for supplying sewage liquid from a sewage liquid reservoir to the apparatus inlet, wherein the inlet pipe comprises a non-circular cross-sectional shape.

22. The sewage distribution system of claim 20 or 21, wherein the inlet pipe comprises one of a substantially rectangular cross-sectional shape, a substantially square cross-sectional shape, a substantially oblong cross-sectional shape, a substantially oval cross-sectional shape, a substantially triangular cross-sectional shape or a partially circular (e.g., semi-circular) shape.

23. The sewage distribution system of claim 20, 21 or 22, wherein a cross section of the inlet pipe comprises a substantially vertical dimension and a substantially horizontal dimension, wherein the horizontal dimension is larger than the vertical dimension.

24. The sewage distribution system of any of claims 20 to 23, wherein the cross section of the inlet pipe comprises a lower end and wherein an area of the cross-sectional shape defined between the lower end and a height of 50 mm above the lower end is at least 8,000 mm2, optionally at least 9,000 mm2, optionally at least 10,000 mm2, optionally at least, 11,000 mm2, optionally at least 12,000 mm2; and / or wherein the area of the cross-sectional shape defined between the lower end and a height of 50 mm above the lower end is at least 20% of a total area of the cross-sectional shape, optionally at least 25% of a total area of the cross-sectional shape, optionally at least 30% of a total area of the cross-sectional shape; and / or wherein the cross section of the inlet pipe comprises a lower end, an upper end and a cross section pipe height extending from the lower end to the upper end, wherein a lower area of the cross-sectional shape defined below 25% of the pipe height is at least 20% of a total area of the cross-sectional shape; optionally at least 25% of the total area of the cross-sectional shape; optionally at least 30% of the total area of the cross-sectional shape.

25. A filter system comprising:a sewage liquid source;a filter media tank;a filter bed provided within the filter media tank; andthe sewage distribution system of any of claims 20 to 24.s

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