Granular sludge reactor system including external separator

Abstract

The present invention relates to a method for treating an aqueous fluid containing biodegradable organic matter in an apparatus comprising an upflow bioreactor containing a sludge bed, the sludge bed comprising biomass; an external separator; and a regulating tank, the method comprising: - treating the fluid in the regulating tank; - feeding the treated fluid to the lower part of the bioreactor and forming biogas; - discharging the fluid from the upper part of the bioreactor, the discharged fluid containing biomass; - feeding the aqueous fluid discharged from the upper part of the bioreactor to the external separator, wherein the aqueous fluid containing biomass is separated into a liquid phase and a biomass-rich fluid phase; - returning the biomass-rich fluid phase from the external separator to the bioreactor; and - returning part of the liquid phase to the regulating tank.

Description

Technical Field

[0001] The present invention relates to a method for treating an aqueous fluid, thereby producing biogas in an installation comprising a bioreactor. The invention also relates to an installation suitable for carrying out the method. Background Art

[0002] Biological treatment of aqueous fluids such as wastewater uses active biomass (microorganisms such as bacteria and / or archaea) to convert pollutants (organic matter) into harmless components.

[0003] There are two main methods. In the so-called anaerobic treatment (without oxygen), anaerobic microorganisms convert the pollutants into biogas in large quantities.

[0004] In aerobic treatment, the pollutants are largely reduced under aerobic (oxygen) conditions to new microorganisms (excess sludge), which then need to be separated from the treated wastewater and treated separately.

[0005] Anaerobic sludge blanket reactor systems utilize anaerobic microorganisms to convert pollutants in aqueous liquids into biogas. These anaerobes grow primarily in aggregates, often referred to as granular biomass. Due to the low net production of the anaerobic microorganisms involved, this system is often characterized by a low net biomass yield (typically 2-4% of converted COD).

[0006] This is on one hand a great advantage since the excess biomass produced in wastewater treatment systems has to be disposed of as solid waste at significant cost, but it on the other hand constitutes a sensitive aspect to retain / maintain sufficient active biological sludge in the treatment system (reactor).

[0007] The method of retaining biomass in an anaerobic treatment reactor can be carried out in various ways. Fixing the biomass on a fixed or mobile carrier is a method of separating the liquid retention time from the biomass retention time. However, a better and preferred method is to mainly use granular biomass, such as applied in an upflow anaerobic sludge blanket (UASB) reactor, a granular sludge blanket reactor and an IC reactor, for example, see WO 2007 / 078195, Frankin RJ (2001). Full scale experiences with anaerobic treatment of industrial wastewater. Wat Sci. Tech., 44 (8), 1-6).

[0008] Granular sludge blanket (GSB) reactors such as expanded granular sludge blanket (EGSB) reactors are common reactors used to treat wastewater from, for example, the food processing and beverage industry, breweries, the pharmaceutical industry, and pulp and paper mills. Such wastewater often contains large amounts of organic pollutants that need to be removed before the water can be reused or discarded.

[0009] In a typical (E)GSB reactor, wastewater is introduced into the lower part of an upflow bioreactor. The water then flows upward through a granular sludge bed containing microorganisms that decompose the organic waste present in the wastewater, thereby forming biogas, especially methane and carbon dioxide, which can be used as a green energy source, such as providing energy. The efficiency of high-speed anaerobic reactors (expanded granular sludge beds) depends largely on good sludge bed expansion, liquid turbulence and high flow rates, as these promote good material transfer, less blockage and less short circuiting (Van Lier, JB, van der Zee, FP, Frijters, ME Ersahin, Rev Environ Sci. Biotechnol. 2015, 14 (4), 681-702).

[0010] The key to an efficient process is the effective separation of biomass (particles), water (effluent) and biogas, in other words, the ability to remove effluent and biogas while retaining biomass in the system to achieve a net increase in particle biomass. There are multiple parameters that affect good separation of liquid, solid and gas phases in a GSB reactor such as an EGSB reactor.

[0011] As known to those skilled in the art, an important parameter for achieving this effective separation is the settling behavior of biomass. Good settling behavior of particles is necessary for achieving effective phase separation. The settling of particles is affected by multiple factors, such as the presence and design (turbulent and laminar flow, turbulent and upflow velocity) of the hydraulics or fluid dynamics (liquid and gas) in the reactor and / or the three-phase separator device in the reactor. In addition, the settling behavior can depend on the composition of the sludge particles, such as biomass content and / or mineral (inorganic, mineral) part. For example, sludge particles with high inertia parts (any non-biodegradable material) can settle faster, but their degradation activity may be lower or even do not exist any degradation activity. Therefore, inert sludge particles have the risk of not being able to expand and / or recirculate due to biogas production and / or flow recirculation. Therefore, in conventional systems, they will tend to stay at the bottom of the reactor, thereby blocking the sludge extraction port and causing major operational problems.

[0012] In addition, the settling behavior of the particles is affected by the presence of gases within the particles. Since GSB systems, especially EGSB systems, can have a very large height (usually 15 to 25 meters) and the pressure caused by the water column, the biomass at the bottom of the reactor is subject to a higher pressure than the biomass at the top of the reactor, usually 1.5-2.5 bar. Therefore, the gas in the particles at the bottom of the reactor is compressed, resulting in a higher density of the particles and therefore faster settling of the particles.

[0013] Secondly, separation devices such as settlers are valuable devices for achieving improved separation of different phases, thereby increasing the overall efficiency of the wastewater treatment process.

[0014] The effective separation of the phases can be further enhanced by creating specific flows inside the reactor that promote, for example, the settling properties of the biomass (by pushing the solids downwards). Such flows can be introduced by the separation system (e.g. inclined plates in an internal settler), can be caused by turbulence generated by the dissolution of carbon dioxide in the water, or can be caused by the simple movement of the phases due to density differences, e.g. sludge tends to move downwards by gravity while biogas flows upwards.

[0015] An example of an EGSB reactor is described in WO 2007 / 078195. More widely known is the BIOTHANEBiobed Advanced EGSB. This reactor has a three-phase separator in the bioreactor and also includes a regulating tank. In the upper part of the bioreactor, there is a tilted plate settler (TPS), which helps to separate biogas from effluent and biomass. Due to the pressure difference below the tilted plate relative to the top of the plate (top part), a giant flow effect will be generated in the lower part (lower part) of the tilted plate settler, making it possible to better separate biogas and guide the settled biomass downward.

[0016] EP 0 493 727 relates to a reactor for continuous mechanical and anaerobic biological purification, optionally with external separation means, preferably a cyclone separator. The lower part of the reactor comprises a settling zone separated from the reactor, the bottom of which has channels allowing the passage of fluids while preventing the passage of solids.

[0017] The disadvantage of this system is that the sludge settles below the inlet line, making the interaction between wastewater and sludge suboptimal, reducing the efficiency of the system.

[0018] WO2012 / 005592 aims to overcome this problem by designing a reactor having a second settler placed at the bottom of the bioreactor, wherein the biomass is separated from the liquid effluent with higher efficiency because the separation occurs at a higher pressure. The fluid that has been separated from the biogas in the inclined plate settler located in the upper part of the reactor is conveyed to the second settler via an external separator feed conduit. The disadvantages of this system found by the inventors include:

[0019] Lack of adequate control of recirculation in the reactor, especially when biogas production is low or absent, such as during start-up

[0020] The second settler placed at the bottom of the bioreactor has a high probability of clogging

[0021] The separation chamber cannot be maintained and maintenance requires complete draining of the reactor

[0022] · Operation is difficult when there is no biogas production (start-up). Summary of the invention

[0023] The inventors have now surprisingly found an efficient method for treating aqueous fluids which overcomes these disadvantages by not using a second settler located in the reactor. Instead, an external separation chamber located outside the bioreactor is provided, usually before the return line connected to a conditioning tank which is configured to treat the aqueous fluid containing biodegradable substances upstream of the bioreactor. However, in a specific embodiment, the device according to the invention or the device used in the method according to the invention does not have such a conditioning tank.

[0024] The present invention therefore relates to a method for treating an aqueous fluid containing biodegradable organic matter in an apparatus comprising an upflow bioreactor (1) containing a sludge bed comprising biomass and an external separator (2), wherein the method comprises:

[0025] - feeding an aqueous fluid into the lower portion of the bioreactor so that the feed fluid contacts the biomass, thereby forming biogas from the biodegradable organic matter;

[0026] - discharging the fluid that has been in contact with the biomass from the upper part of the bioreactor, wherein the discharged liquid contains the biomass;

[0027] - Feeding the biomass-containing fluid discharged from the upper part of the bioreactor to an external separator (2), the external separator comprising a separation chamber, preferably provided with inclined internal members, wherein the biomass-containing fluid is separated into a liquid phase and a biomass-rich fluid phase, the liquid phase having a reduced biomass content or being substantially free of biomass. The biomass-rich fluid phase from the external separator (2) is subjected to a density reduction downstream of the external separator. The density reduction provides a lifting effect of the fluid phase, providing at least part of the driving force to generate fluid flow. The biomass-rich fluid phase is subsequently returned to the bioreactor while the fluid phase still has a reduced density or after a process in which the density has been increased again has been carried out. Alternatively or in addition, the biomass-rich fluid phase from the external separator is returned to the bioreactor using a venturi ejector.

[0028] The invention also relates to a device for the microbial treatment of an aqueous fluid containing biodegradable organic matter, wherein the device comprises

[0029] - a bioreactor (1) comprising a biogas outlet;

[0030] an external separator (2) comprising a separation chamber provided with inclined internals, arranged to separate a liquid phase from a fluid phase containing biomass, the external separator comprising an inlet (4) for an aqueous fluid connected to an inlet (5) of a conduit (6) for discharging the aqueous fluid from the bioreactor (1); an outlet (7a) for the aqueous fluid; an outlet (8) for a biomass-rich fluid connected to an inlet (9) for a biomass-rich fluid which flows into the bioreactor (1) via a conduit (10);

[0031] - at least one of: (a) an ejector configured to eject a fluid medium, in particular an expandable fluid medium such as a gas or a (pressurized) liquid containing a soluble gas or a (pressurized) liquefied gas, into the biomass-rich fluid downstream of the external separator, (b) a venturi ejector configured to return the biomass-rich fluid from the external separator to the bioreactor, the venturi ejector having an internal structure suitable for producing a venturi effect.

[0032] The device according to the invention or the device used in the method according to the invention is thus configured to generate at least part of the driving force for returning the biomass-rich fluid phase from the external separator to the bioreactor; in an advantageous embodiment, this is achieved by utilizing the density reduction of the fluid phase, which is returned to the bioreactor by a lifting effect due to the density reduction (usually a gas lift effect) in the conduit for returning the fluid phase and / or in the bioreactor (see, for example, Figure 1-5The reduction in density causes the upward movement, usually by providing a gas phase in the biomass-rich fluid, which is drawn into the bioreactor from an external separator. The fluid phase may be returned to the bioreactor while it still has a reduced density, or a step of increasing the density of the fluid phase may first be performed, preferably to about the same density as before the density reduction treatment. If the mobile phase has previously been subjected to a reduction in density by the introduction of a gas (to produce a gas lift effect), the step of increasing the density of the fluid phase typically involves removing at least part of the gas that has been introduced from the fluid phase.

[0033] In another advantageous embodiment, which can be used as an alternative or in combination with the density reduction, the Venturi effect is used (see, for example, Figure 6 ).

[0034] For the favorable lifting effect, density reduction is usually achieved by introducing the gas phase into the biomass-rich fluid that returns to the bioreactor from the external separator. The gas phase can be introduced by spraying the gas phase in the channel (10) of the described fluid between the external separator (2) and the bioreactor (1). However, it is also possible to introduce liquefied gas or gas dissolved in liquid into the channel of the described fluid between the external separator and the bioreactor, wherein when introduced into the biomass-rich fluid, the liquefied gas or dissolved gas expands or evaporates. This is usually by introducing the described liquefied gas or liquid containing dissolved gas at a pressure higher than the pressure in the described channel.

[0035] It is advantageous to apply density reduction (e.g., by producing a gas lift effect) and / or a Venturi effect to a biomass-rich fluid phase (particularly the granular biomass from an external separator to a bioreactor), particularly because fluid circulation can be achieved without the need for a mechanical pump through which the biomass-rich fluid must pass or simultaneously using a reduced mechanical pumping power. This is a major advantage, because the mechanical pump for pumping a fluid with a relatively high solid content is omitted, reducing the risk of failure, such as clogging due to blockage of the moving parts of the pump. Another advantage of omitting a mechanical pump is that the net growth of biomass in the bioreactor can be increased. Without wishing to be bound by theory, it is believed that the long-term use of a mechanical pump is disadvantageous for the structure of biomass, particularly the granular biomass in the bioreactor, because the pump can cause shear stress on the biomass. Therefore, by omitting the use of a mechanical pump at least most of the time, the structure of biomass, particularly granular biomass, in the reactor can be strengthened, thereby improving the efficiency of biodegradable substances being converted into biogas. In addition, it can save energy.

[0036] Similarly, the Venturi effect can be used to generate a fluid pressure difference in the fluid flow, so that another fluid (i.e., the biomass-rich fluid phase from the external separator) is sucked into the fluid flow flowing through the Venturi ejector from the high-pressure inlet side to the low-pressure outlet side of the Venturi ejector. Omitting (extending the use of) a mechanical pump for returning the biomass-rich fluid or reducing the required power of the mechanical pump simplifies the device / method and can increase the structure of biomass, especially granular biomass. It can also provide energy saving and / or reduce maintenance requirements. In particular, when the Venturi effect is utilized, the biomass-rich fluid phase from the external separator is returned to the bioreactor through a Venturi ejector (42) having a high-pressure inlet, a low-pressure outlet and a suction port, wherein the aqueous fluid containing biodegradable substances to be treated in the bioreactor enters the Venturi ejector via the high-pressure inlet, the biomass-rich fluid phase from the external separator enters the Venturi ejector via the suction port, and the biomass-rich fluid phase and the aqueous fluid to be treated in the bioreactor together leave the Venturi ejector through the low-pressure outlet and are fed to the bioreactor. A mechanical pump (11) can still be used, but is usually present in the pipeline of the aqueous fluid (16) to be treated upstream of the Venturi ejector.

[0037] It has been found that device according to the present invention is particularly suitable for gas-liquid-solid mixture to be effectively separated into gas phase, liquid phase substantially free of particulate biomass and fluid phase rich in solids, especially rich in particulate solids, especially rich in particulate biomass. Although device is efficient, its design is quite simple, especially reactor interior only needs a limited number of technical devices to strengthen separation, thereby reducing the risk of failure and simplifying maintenance and cleaning. For good separation, it is important to have an external separator. The means of configuring this device helps the fluid rich in biomass to return to the bioreactor via a lifting effect or via a venturi effect, thereby further promoting a favourable design.

[0038] Having an external separator can improve maintenance, improve start-up of the process and further allow installation of a partial reactor, ie allow upgrading an existing system with an external separator, thereby improving the efficiency of the reactor.

[0039] It has been found that an external separator (usually a settler with inclined internals) is particularly suitable for obtaining a liquid phase with a reduced content of particulate biomass compared to the fluid fed to the external separator. This is advantageously achieved by allowing the particulate biomass to settle. The settled particulate biomass is then at least largely returned to the bioreactor (as part of the particulate biomass-rich fluid phase).

[0040] Figure 1The general arrangement of the device according to the invention (for use in the method) is schematically shown. It schematically shows how an aqueous fluid can be introduced into a preferably present conditioning tank (12) via an inlet (13), in which the aqueous fluid (e.g. wastewater) is subjected to a conditioning step. The conditioning tank (12) also includes a biogas outlet (17), the outlet of the pre-conditioned fluid being connected to an inflow distribution system (IDS) (15) at or near the bottom of the bioreactor (1) via a pipeline (16). Advantageously, the pipeline (16) also includes a recirculation pump (11) for continuous and controlled recirculation of the fluid. The aqueous fluid passes through a sludge bed containing microorganisms capable of converting biodegradable organic matter into biogas.

[0041] The presence of a recirculation pump (11) from the adjustment tank (12) to the bioreactor (1) enables:

[0042] -Controlled dilution of inhibitory compounds

[0043] - Constant flow rate to EGSB

[0044] -Constant rising flow rate (independent of COD loading rate)

[0045] -Better pH control in CT due to returned anaerobic effluent alkalinity"

[0046] exist Figure 1 In the embodiment of the invention, the bioreactor (1) further comprises an internal baffle or guide plate / separator (3) located in the upper part of the bioreactor (1) for removing biogas from the gas-aqueous fluid mixture; and a biogas outlet (18). The bioreactor (1) further comprises an internal feed pipe (6) having an inlet (5) for the solid-containing aqueous fluid from which the biogas has been separated, the internal feed pipe being connected to an inlet (4) of an external separator (2) for separating the solids from the liquid phase. The inlet (5) of the pipe (6) is located below the baffle or guide plate (3). The pipe (6) further comprises a valve (27) for isolating the external separator (2) from the device in the event of maintenance, repair or replacement of the external separator (2). A pipeline (10) connects the outlet (8) of the external separator (2) with the inlet (9) of the solids-rich fluid from the bioreactor (1), wherein a pipeline biogas injector (23) is provided, which is configured to introduce biogas into the solids-rich fluid in the pipeline (10); and a biogas pipeline (21) is provided between the biogas injector (23) and a biogas collection hood in the bioreactor (22). The pipeline (10) also includes a valve (28) for isolating the external separator (2) from the device in the event of maintenance, repair or replacement of the external separator (2).

[0047] Figure 1The biogas pipeline (21) further comprises a T-joint (24) for connecting the biogas pipeline (21) to a biogas pipeline (26) for introducing the biogas into the regulating tank (12) via the inlet (25) for mixing the aqueous fluid in the regulating tank.

[0048] Figure 1 Also shown is a device (7) for discharging and recycling the liquid phase from the external separator. It comprises an outlet (7a) for discharging the liquid phase with reduced biomass content (which may be substantially free of biomass) from the separator. From this outlet (7a) a discharge conduit (7b) can be provided, through which the treated phase can leave the device, and a circulation line (37) for returning the liquid phase to the adjustment tank (12).

[0049] like Figure 1 The external separator (2) shown also includes an inlet / outlet (29) connected to the inlet / outlet (31) of the adjustment tank (12) and connected to the inlet (32) of the bioreactor (1) via a pipe (33). The pipe (33) includes a pump (30) for returning sludge from the external separator to the bioreactor if necessary. In addition, this pipe (together with isolation valves (27) and (28)) allows the recirculation of aqueous fluids (usually acidic chemicals) for cleaning at the external separator (by completely isolating the reactor and the adjustment tank using valve (2)).

[0050] In addition, if Figure 1 As shown, the device comprises a biogas pipe (20) for connecting the biogas outlet (18) to the biogas inlet (19) of the regulating tank. Such a device may be provided to ensure that the pressure in the regulating tank is substantially the same as in the bioreactor.

[0051] Figure 2 A second arrangement of the device according to the invention (for use in a method) is schematically shown. Figure 1 Description of the invention. The bioreactor is provided with a feed conduit (34) for feeding an aqueous fluid to an external separator (2). A guide plate / baffle (36) is located below the inlet (35) of the conduit (34) in the bioreactor for directing the aqueous fluid containing solids into the external feed conduit (34). This is a particularly preferred way of feeding the aqueous fluid from the bioreactor to the external separator, especially from a low maintenance point of view.

[0052] Figure 3 A further embodiment is shown, with Figure 1 and Figure 2In contrast, it shows an additional arrangement for injecting the exhaust biogas into the pipe (10) to return the biomass-rich fluid to the bioreactor. The additional arrangement is a gas pipe (38) from the head space (39) of the bioreactor (1) to the gas injector (23). It is configured to feed biogas from the head space into the pipe (10). There is usually a mechanical pump or compressor or the like to cause sufficient flow of biogas from the head space (39) to the injector (23). This design is particularly suitable for the method according to the present invention, wherein biogas is taken from the head space of the bioreactor and introduced into the biomass-rich fluid phase downstream of the external separator (2), thereby reducing the density of the biomass-rich fluid downstream of the external separator. Therefore, the biogas promotes or causes a gas lift effect of the fluid circulating from the separator (2) to the bioreactor (1). If present, the biogas from the head space of the regulating tank can also be used as an alternative or additional source of biogas introduced into the biomass-rich fluid downstream of the external separator (2) to produce or promote the gas lift effect ( Figure 3 not shown).

[0053] Figure 4 Schematically shows Figure 3 An alternative to the schematically shown embodiment; both embodiments can be combined. Here, the ejector (23) is connected via a conduit (41) to an external source (40) of a fluid medium which can be used to produce a gas lift effect in the conduit (10). This fluid medium is preferably a gas, in particular an inert gas such as nitrogen. Other particularly suitable gases include methane and carbon dioxide. The gas can be a mixture containing any of these gases. The fluid medium does not necessarily have to be injected as a gas phase. It can also be injected in a substantially liquid form, such as a (pressurized) liquefied gas or a (pressurized) liquid containing a dissolved gas, whereby at least a large portion of the liquefied gas or dissolved gas expands / evaporates to produce a decrease in density within the passage of the biomass-rich fluid between the separator (2) and the bioreactor (1), thereby producing a gas lift effect.

[0054] exist Figure 3 and 4In the embodiment, a characteristic construction involving the injection of a fluid medium (e.g., gas) into a conduit (10) is shown in combination with an internal biogas collector (22) and a conduit (21) for feeding the collected biogas to a fluid medium injector (23). In this embodiment, biogas from the head space and / or an external source for producing a gas lift effect can be used to balance air flow fluctuations from the biogas collector. Biogas from the head space or an external gas source can, for example, be used as the only fluid medium to produce a little effect. It can also be used to supplement the gas from the biogas collector (22) inside the bioreactor when the air flow from the biogas collector (22) to the injector (23) is insufficient. This may occur in particular during the start-up of the device. In addition, this may occur if the collector becomes (partially) blocked or if the biogas flow from below the collector to the collector in the bioreactor is relatively low. However, in a method / device in which biogas from the head space or an external source is used to produce or promote a gas lift effect, the biogas collector (22) can also be omitted. The internal design of the bioreactor is thereby simplified, which is advantageous because maintenance requirements are reduced. This design is also advantageous for retrofitting existing bioreactors, as it can be incorporated without changing the interior of the reactor. Figure 3 ) or external gas source ( Figure 4 ) The method / device for gas lift effect can also be used in an apparatus having a bioreactor in which a guide plate / baffle (36) is located below the inlet (35) of the conduit (34) for introducing an aqueous fluid containing solids into the external feed conduit (34) ( Figure 2 ).

[0055] Figure 5 A device according to the invention without a regulating tank is schematically shown. It shows an ejector (23) connected to each of an internal biogas collector (22), a headspace (39) of the bioreactor for producing or promoting a gas lift effect, and an external source of a fluid medium. The presence of only one of them is sufficient; preferably, the device is at least configured to provide biogas from the headspace (39) of the bioreactor (1) to the ejector (23) and / or to provide an external source of a fluid medium for producing or promoting a gas lift effect. In this embodiment, a biogas outlet (48) is typically provided in the headspace of the bioreactor and is configured to allow biogas to leave the device; in embodiments with a regulating tank, such a biogas outlet may also be present, and additionally or alternatively (if there is a biogas passage between the headspace of the bioreactor and the regulating tank), it may be provided in the headspace of the regulating tank (12).

[0056] exist Figure 8, features involving separation of gas from a biomass-rich fluid that has been subjected to a density reduction treatment before the biomass-rich fluid is returned to the bioreactor are shown. Figure 4 Or 5 combinations. It shows that a fluid-gas separator (50) is provided with an inlet (51), wherein the inlet is connected to a pipeline (10) of a biomass-rich fluid that has been subjected to density reduction, through an outlet (52). The fluid-gas separator (50) is configured to separate the fluid into a gas phase and a fluid phase containing biomass and is arranged relative to the bioreactor (1) so that during use, the liquid level in the fluid-gas separator (50) is higher than the liquid level in the bioreactor (1). The fluid-gas separator also includes an outlet (53) for discharging gas and an outlet (54) for the fluid containing biomass. The outlet (54) of the fluid containing biomass is connected to an inlet (56) for returning the fluid containing biomass to the bioreactor via a pipeline (10'). Here, the outlet (54) configured to discharge the returned mixture into the bioreactor is located at a higher position than the ejector configured to eject the fluid medium, and the outlet (54) configured to discharge the returned mixture into the bioreactor is preferably located in the middle or lower part of the bioreactor.

[0057] exist Figure 8 An example of a preferred fluid-gas separator (50) that is particularly useful in the apparatus shown is Fig. 9 As shown. Here, the pipeline (10) is connected to the inlet of the fluid-gas separator at an angle τ relative to the y-axis or vertical axis of the fluid-gas separator. The pipeline (10) is also provided with an outlet (55) for discharging gas. The outlet (52) is generally located at a height h2, higher than the liquid level in the bioreactor. In addition, the fluid-gas separator (50) is provided with an inlet (51) connected to the outlet of the pipeline (10), and is configured so that during use, a fluid rich in biomass and containing gas enters the fluid-gas separator (50) at a height h1, wherein h1 is higher than the liquid level in the bioreactor (1). The fluid-gas separator is also provided with an outlet (53) configured to discharge gas from the fluid-gas separator and an outlet (54) configured to discharge a fluid containing biomass to the bioreactor through the pipeline (10').

[0058] Figure 6 The design of the device according to the invention is schematically shown, in which the Venturi effect is used. The high pressure inlet side (44) of the Venturi ejector (42) is connected to the pipeline 16 for the aqueous fluid to be treated in the bioreactor (e.g. Figure 6As shown, the feed fluid is the fluid from the adjustment tank 12), usually downstream of the pump 11 (so that the biomass-rich fluid from the external separator (2) does not have to pass through the pump). The suction port (45) of the contraction part of the venturi ejector is configured to allow the biomass-rich fluid from the external separator 2 to be sucked into the flow path of the aqueous fluid that has entered the venturi ejector through the high-pressure inlet side 44 via the conduit 43, so that during use, the aqueous fluid to be treated and the biomass-rich fluid from the external separator leave the venturi ejector (42) together via the low-pressure outlet side 47 of the venturi ejector and are sent to the bioreactor (1) via the inlet 15.

[0059] The advantages of the embodiment using the Venturi effect include a simple design. It does not require an ejector and a biogas collector (23) of a gas or a pressurized liquefied medium or a liquid containing dissolved gas (expanded to produce a reduction in density), which helps to transform existing devices of bioreactors that do not contain a biogas collector (23) because the interior of the bioreactor does not have to be changed. The embodiment using the Venturi principle can also be used in combination with an embodiment using a reduction in density (e.g., gas lift). It can be used, for example, when there is insufficient airflow from a biogas collector (22) in a bioreactor or from a bioreactor to the head space (39) of the ejector (23), for example during the start-up of the device, or when the collector becomes (partially) blocked, or when the biogas flow entering the collector from below the collector in the bioreactor is relatively low. The aqueous fluid treated in the method according to the invention can in principle be any aqueous fluid comprising biodegradable, particularly biodegradable organic matter under anaerobic conditions. Preferably, the aqueous fluid is selected from the group of municipal wastewater, industrial wastewater, sewage, aqueous fluid waste (such as residual fermentation liquid) from fermentation process, aqueous slurry and aqueous sludge. With regard to the water content of the waste stream processed in the method according to the present invention, this can change in a wide range. Usually, the water content of aqueous fluid to be treated is that the gross weight of fluid is greater than 80wt.%, particularly at least 80wt.%, more particularly 90wt.% or more. Usually, water content is 99.9wt.% or less, preferably 99.5wt.% or less, more preferably 99wt.% or less, particularly 98wt.% or less, or more particularly 96wt.% or less. The total organic matter content of the aqueous fluid to be fed to the bioreactor is generally 0.1g COD / l or more, preferably in the range of 0.3-100g COD / l, particularly in the range of 5-50g COD / l.

[0060] Examples of aqueous fluids that are particularly suitable for treatment according to the present invention are aqueous wastes from dairy production or processing (e.g. processing / production of milk, cheese, butter), beverage production or processing (e.g. wine, beer, distilled beverages, juice, milk), biofuel or petrochemical production or processing, chemical plants, agricultural facilities, pulp and paper production or processing, sugar processing or yeast production.

[0061] Typically, a conditioning tank (12) is present in the device according to the invention. In such a tank, during use, the aqueous fluid to be treated in the bioreactor is conditioned for the bioreactor. Advantageously, the conditioning tank is not only fed with the aqueous fluid (aqueous feedstock) not yet treated in the bioreactor, but also receives part of the liquid phase (having a reduced biomass content compared to the effluent of the bioreactor) leaving the external separator. This liquid phase is very suitable for conditioning the raw aqueous fluid newly entering the device.

[0062] The advantage of using a regulating tank is that the unnecessary fluctuations of aqueous fluid entering bioreactor and the unnecessary fluctuations of aqueous fluid quality can be avoided. The circulation from separator to regulating tank allows further improvement in the relatively constant flow of various streams maintained between the different units of the device, for example from regulating tank to bioreactor and from bioreactor to external separator. It also provides further robustness (robustness), allowing the liquid level in the unit to remain relatively constant, even when there is a large fluctuation in the supply of aqueous fluid to be treated to the device. The relatively constant flow of the flow inflow / outflow unit and / or the relatively constant liquid level in the unit maintained by the circulation from separator to regulating tank is required for effective operation and for keeping the low risk of, for example, pipeline clogging or separator clogging.

[0063] Preferably, the raw material aqueous fluid to be treated, such as raw material wastewater, first enters the adjustment tank, where specific parameters, such as temperature and / or pH, can be monitored. Those skilled in the art will be able to determine favorable parameter values ​​according to the composition of the biomass. The temperature of the adjustment tank contents is usually maintained at or adjusted to a temperature within the range of 20-55°C. Particularly good results have been obtained using a method in which the aqueous fluid in the adjustment tank is maintained at or adjusted to a temperature within the range of about 30 to about 40°C, more particularly about 33 to about 37°C, such as within the range of 34 to 36°C. The pH of the adjustment tank contents is usually adjusted to or maintained within the range of about 6.0 to about 8.0, preferably within the range of 6.0-7.5, particularly about 6.5 to about 7.2, such as within the range of 6.6 to 6.8. As known to those skilled in the art, different temperatures or pH can be optimal for specific microbial cultures. For example, for alkaliphilic bacteria, a higher pH can be favorable, such as up to about pH 11.

[0064] Preferably after pretreatment in a conditioning tank, the aqueous fluid is fed to the lower part of the upflow bioreactor, preferably via an influent distribution system suitable for providing at least substantially equal distribution of the aqueous fluid over a horizontal cross-section of the bioreactor, wherein it passes upwardly through a sludge bed comprising biomass, preferably granular biomass.

[0065] The upflow bioreactor is preferably a granular sludge blanket, in particular an expanded granular sludge blanket (EGSB), wherein the (E)GSB comprises anaerobic microorganisms and wherein biodegradable organic matter is converted by the anaerobic microorganisms, thereby forming biogas.

[0066] Suitable anaerobic microorganisms are generally known in the art.Preferably the bioreactor comprises a consortium of microorganisms comprising at least one hydrolytic bacterium, at least one acidogenic bacterium, at least one acetogenic bacterium and at least one methanogenic bacterium.

[0067] Another factor relevant to good sedimentation and thus good separation of sludge, in particular biomass pellets, is the height of the bioreactor at which the biomass is present. Typically, biogas can also be present inside the pellets, which can cause flotation. At the bottom of the reactor, the pellets experience a higher pressure and thus biogas is released from the pellets and the sedimentation of the sludge increases.

[0068] Preferably, the apparatus (for use in the method) comprises a bioreactor having a height in the range of about 15 to about 25 m, more preferably in the range of 18 to 22 m. Typically, the bioreactor is filled with an aqueous fluid up to 85-98 vol%, preferably up to about 90-95 vol%.

[0069] After digestion of the biodegradable organic matter in the bioreactor, a gas-aqueous fluid mixture is obtained.

[0070] The gas phase consists of biogas produced by the microorganisms. As is known, biogas usually consists at least essentially of methane and carbon dioxide, but may also contain small amounts of other gases, such as hydrogen, ammonia, water vapor and / or hydrogen sulfide.

[0071] The aqueous fluid comprises solids, in particular biomass particles and other optionally inorganic and / or organic suspended solids.

[0072] Aqueous fluids also include liquids that typically consist essentially of water and water-soluble materials such as organic acids and soluble materials that are not digested by microorganisms or other molecules that are normally present in water, such as minerals or salts.

[0073] The gas-aqueous fluid mixture moves upward through the reactor, where the biogas separates from the mixture. This can occur spontaneously or the separation can be enhanced by an internal separator.

[0074] The biogas leaves the bioreactor via a biogas outlet located at or near the top of the reactor (above the liquid level). It may leave the bioreactor directly or may first enter the upper part of a conditioning tank and leave the device via an outlet located at or near the top of the tank. Optionally, the biogas is further processed in a manner known per se. The biogas may be used to provide energy to the process, i.e. to make the process self-sustainable, for example by means of a heating system. Alternatively, the biogas may be converted into electrical energy by means of a generator or upgraded to methane for transport elsewhere to provide energy for other purposes or as a source of methane for use in chemical processes. Figure 3 As shown, biogas from the bioreactor headspace can also be used to generate or promote the generation of gas lift in the pipeline (10) located between the external separator (2) and the bioreactor (1).

[0075] In an advantageous embodiment, part of the biogas formed is conveyed from the bioreactor to the lower part or the middle part of the conditioning tank in order to improve the mixing of the aqueous fluid in the conditioning tank.

[0076] In an embodiment, the bioreactor further comprises an internal separator, wherein the separation of biogas from the aqueous fluid containing solids is promoted. If present, the internal separator is typically located at the top of the bioreactor. Preferably, the internal separator is a fluid-gas separator, more preferably a guide plate or baffle located at the top of the bioreactor. Preferably, the baffle or guide plate is located above the feed pipe leading to the external separator and promotes the separation of biogas from the aqueous fluid due to the natural upflow of biogas or biogas-fluid mixture.

[0077] In an embodiment, the feed conduit to the external separator is an internal feed conduit. The internal feed conduit is at least mostly located inside the bioreactor. An inlet for collecting the aqueous fluid from which the biogas has been separated is located below the baffle or guide plate and collects the aqueous fluid that is then fed to the external separator.

[0078] In another embodiment, the feed conduit to the external separator is an external feed conduit. The inlet for the aqueous fluid is located on one side of the bioreactor, and the external conduit to the external separator is located outside the bioreactor. Preferably, the bioreactor includes a baffle or guide plate located near the inlet of the external feed conduit for directing the aqueous fluid into the external feed conduit, preferably directly below the external feed conduit.

[0079] An internal or external feed conduit feeds the aqueous fluid into an external separator 2 comprising a separation chamber, which is typically provided with inclined internals for separating the aqueous fluid comprising biomass and optionally other solids into a liquid phase and a biomass-rich fluid phase (compared to the aqueous fluid entering the external separator).

[0080] In another embodiment, the internal separator is a funnel, preferably a mammoth pump (gas lift pump, mammoth pump) funnel. If there is a funnel, the lower part of the funnel is connected to the inlet of the internal feed pipe. The funnel promotes an effective mammoth flow (gas lift flow, mammoth flow) effect, thereby helping to separate biogas from aqueous fluid (comprising liquid and solid) before the aqueous fluid enters the external separator. The gas-fluid separator mammoth pump funnel preferably includes an inclined wall, which is shaped as a funnel connected to the internal feed pipe towards the bottom.

[0081] In another embodiment, the internal separator is a gas-fluid separator comprising an inclined internal member, preferably an inclined plate or a tube. Preferably, the gas-fluid separator is an inclined plate settler. The inclined plate causes turbulence in the separator, which helps the separation of biogas. The inclined plate can be flat or corrugated. Such inclined internal members promote the separation of biogas from fluid and solid phases. Usually the inclined internal members are placed at an angle of about 45-65 °. Particularly good results have been obtained using an angle of about 55 to about 60 °. Adjacent internal members are usually placed at a distance of at least 2 cm, particularly 2-10 cm from each other, to enhance separation and avoid clogging of the separator. Preferably, the aqueous fluid enters the internal separator via the upper part of the separator. If there is a gas-fluid separator comprising an inclined internal member, the inlet of the internal feed conduit is connected to the lower part of the separator for collecting solid-rich fluid. Usually the aqueous fluid containing solids is collected at the bottom of the internal separator and fed to the external separator (2).

[0082] External separators are usually configured so that during use, aqueous fluids containing solids enter via an inlet located at the bottom of the separator. External separators usually include inclined internal components to enhance the sedimentation of solid particles. The inclined plate can be flat or corrugated. Such inclined internal components promote the separation of biogas from liquid and solid phases due to the "lamella effect". Usually the inclined internal components are placed at an angle of about 45-65 °. Particularly good results have been obtained by placing at an angle of about 55 to about 60 °. Adjacent internal components are usually placed at a distance of at least 2 cm, particularly 2-10 cm from each other, to enhance separation and avoid clogging of the separator. The use of inclined internal components increases the settling surface for solid sedimentation.

[0083] The aqueous fluid flows upward through the inclined internals where laminar flow promotes downward movement of solid particles while allowing liquid to move upward where the outlet for the aqueous fluid (effluent) is located.

[0084] Preferably the external separator comprises an isolation valve to allow maintenance, replacement and repair of the module without affecting the reactor.The isolation of the external separator may also be used to provide regular cleaning at the external separator by means of an isolation device.

[0085] It is further preferred to have a pipeline (33) connecting the external separator and the bioreactor and optionally the external separator and the adjustment tank. The pipeline also preferably has a pump (30), preferably a screw pump, for returning the sludge to the bioreactor and circulating the chemicals through the external separator. These chemicals can be acidic or alkaline, depending on the impurities that need to be removed. The pump can be cleaned at the external separator.

[0086] The external separator preferably has an elongated design.

[0087] The liquid phase that leaves separator is usually at least substantially free of granular biomass.In an embodiment, wherein the fluid that is fed into separator contains suspended solids (in the form of granular biomass decay fragments, flocculation-non-granular-biomass and / or non-degradable suspended matter), the liquid phase that leaves separator will have the suspended solids (particularly biomass content) of minimization compared with the feed fluid, but can contain residual flocculation biomass.If necessary, this fluid can be purified in a manner known per se, for example, taking out liquid phase from device to abandon or further use, for example, as process water.For example, the liquid phase that is returned to bioreactor via adjustment tank can be returned without removing these suspended solids.

[0088] Typically, the system according to the invention comprises a regulating tank. If a regulating tank is present, part of the liquid phase obtained in the external separator can be returned to the regulating tank in order to keep the volume of fluid in the tank at approximately the same level.

[0089] The fluid phase rich in biomass reenters the bioreactor. It is necessary to have an effective process with a net increase of biomass during this process. During the start-up period of the reactor, it is important to have a net increase of biomass in the system for obtaining a sufficient amount of biomass for the effective conversion of biodegradable substances. In the later stage of the process, the net increase of biomass allows to extract sludge from the reactor and will not have a negative impact on turnover rate (turnover rate) (that is, the conversion rate of COD). In addition, having excessive biomass also increases income because biomass can be easy to store, transport and sell.

[0090] As already explained above, according to the invention, the density difference is utilized to generate or promote a gas lift effect and / or the Venturi effect is utilized, which promotes or generates a driving force for returning the biomass-rich fluid from the external separator to the bioreactor.

[0091] The use of different densities to produce or promote a gas lift effect and / or a Venturi effect advantageously allows the omission of the use of a mechanical pump to return a biomass-rich fluid from an external separator to a bioreactor for a long period of time. Thus, the biomass structural stability can be enhanced and the risk of device and energy failure of the method can be reduced. However, the device according to the present invention (used in the method), in addition to an ejector or a Venturi ejector configured to eject a fluid medium, optionally also includes a mechanical pump configured to return a biomass-rich fluid from an external separator to a bioreactor, typically disposed in a pipeline (10). The mechanical pump can be used as a backup device for returning a biomass-rich fluid to a bioreactor. Preferably, this mechanical pump is used when the gas or Venturi ejector is temporarily not in use, for example when the ejector is undergoing maintenance or other failures occur. In terms of efficiency, this configuration allows an optimal process because during use, when an ejector temporarily fails, the method according to the present invention can continue. Surprisingly it has been found that temporary use of such a mechanical pump, preferably for 1 hour to two weeks, such as 12 hours to one week, in particular 24 hours to 96 hours, has no adverse effect on the structure of the particulate biomass in the bioreactor.

[0092] Particularly good results have been obtained by using a reduction in density to produce a gas lift effect in the pipeline to return the biomass-rich fluid from the external separator 2 to the bioreactor 1 or the bioreactor itself. The density reduction is usually achieved by injecting a fluid medium, such as a gas phase, a liquefied gas or a liquid containing dissolved gas, into the biomass-rich fluid downstream of the external separator, usually in the pipeline (10). During use, the fluid medium is injected into the biomass-rich fluid, usually into the pipeline (10) of the (particulate) biomass-rich fluid, which connects the external separator (2) to the bioreactor (1), thereby promoting the flow of the (particulate) biomass-rich fluid from the external separator (2) to the bioreactor (1). The gas is usually an inert gas, preferably nitrogen or a nitrogen-rich gas, such as air or biogas. One or more components commonly found in biogas, in particular carbon dioxide, can also be used.

[0093] Therefore, in a preferred method, one or more of the following features apply:

[0094] - biogas is withdrawn from the head space of the bioreactor and introduced into the biomass-rich fluid phase downstream of the external separator, thereby reducing the density of the biomass-rich fluid downstream of the external separator (and generating or promoting gas lift);

[0095] - introducing an external gas phase into said biomass-rich fluid phase downstream of the external separator, thereby reducing the density of said biomass-rich fluid phase downstream of the external separator (and generating or promoting gas lift);

[0096] - introducing a (pressurized) liquefied gas or a (pressurized) gas dissolved in a liquid phase into said biomass-rich fluid phase downstream of the external separator, wherein the liquefied gas or dissolved gas expands or evaporates (on the return of the biomass-rich fluid phase to the bioreactor or in a conduit within the bioreactor), thereby reducing the density of said biomass-rich fluid phase downstream of the external separator;

[0097] - the density of the biomass-rich fluid phase decreases downstream of the external separator by 10-95%, preferably 20-80%, in particular 25-75%;

[0098] - The density of the biomass-rich fluid phase is reduced downstream of the external separator to 10-900 kg / m 3 Density in the range, preferably 100-850kg / m 3 Density in the range, especially 200-800kg / m 3 The density is in the range of 250-750 kg / m 3 Density within the range.

[0099] "External gas" is a gas which is not produced in the device comprising (for) the bioreactor according to the invention, but is supplied from a different source. The (pressurized) liquefied gas or the (pressurized) gas dissolved in the liquid phase can also be an external (pressurized) liquefied gas or (pressurized) gas, but it is also possible to use biogas produced in the device (usually in the bioreactor) or part thereof to provide the (pressurized) liquefied gas or the (pressurized) gas dissolved in the liquid phase.

[0100] Furthermore, once the (particulate) biomass-rich aqueous fluid, the density of which has been reduced by introducing the gas phase into it, is returned to the bioreactor (1), the gas phase promotes the upward flow of the aqueous fluid in the external separator (2) by the gas lift effect. Supplying the fluid with gas has the additional advantage that clogging of the pipes is minimized, preferably prevented.

[0101] If the biogas for the injection pipe (10) is collected from a bioreactor with a biogas collector, the biogas collector preferably has one or more biogas collector hoods which are immersed in the fluid (suspension) in the bioreactor at least during use. If present, it is particularly preferred to have an internal biogas collector (22) located at a certain height so that the biogas collector, at least during use of the device, is immersed in the sludge bed in the bioreactor.

[0102] If present, the biogas collector hood (22) is preferably located below the inlet (9) for the (particulate) biomass-rich fluid coming from the external separator (2).

[0103] If present, the biogas collector hood (22) is preferably located below the inlet (5) of the duct (6) or below the inlet (35) of the duct (34) for the aqueous fluid of the external separator (2).

[0104] However, in particular, if an external gas, an external (pressurized) liquefied gas or an external (pressurized) gas dissolved in a liquid phase is used according to the present invention, rather than methane or a methane-rich gas such as biogas, then before the biomass-rich fluid is returned to the bioreactor, preferably at least most of the external gas or (pressurized) liquefied gas is removed from the biomass-rich fluid having undergone density reduction. The removal of the external gas advantageously prevents the formation of a biogas-external gas mixture in the head space of the bioreactor, thereby diluting the biogas portion. The formation of this biogas-external gas mixture is disadvantageous. In the case where it is intended to use biogas as an energy source, the formation of a biogas-external gas mixture is disadvantageous because the energy value of the biogas-external gas mixture will be lower than the energy value of the biogas conventionally produced during the use of the bioreactor. In the case where biogas is used as a starting material source to synthesize other chemical products of interest, diluting with another gas is also undesirable because it will add additional processing to remove gas before further processing of the biogas component of interest. Furthermore, when using gases containing large amounts of oxygen, such as air, there is a risk of forming a potentially explosive mixture unless precautions are taken to maintain the oxygen content at a safe level. It should be noted that the presence of air in the fluid returning to the bioreactor is also acceptable in itself for the microorganisms, and is also acceptable for anaerobic microorganisms (under substantially anaerobic conditions).

[0105] Therefore, the present invention also relates to an apparatus according to the present invention (for use in a method), wherein the ejector configured to eject the fluid medium is connected to an external gas source (40), an external liquefied gas source or an external dissolved gas source, wherein the conduit (10) for returning the mixture of gas and biomass-rich fluid is provided with an outlet (52) connected to an inlet (51) of a fluid-gas separator (50) arranged to separate the gas phase from the biomass-containing fluid phase, wherein the fluid-gas separator (50) is provided with an outlet (53) configured to discharge gas from the gas-fluid separator and an outlet (54) configured to discharge the biomass-containing fluid to a bioreactor, wherein the outlet (54) configured to discharge the biomass-containing fluid to the bioreactor is located at a higher level than the ejector configured to eject the fluid medium, and wherein the outlet (54) configured to discharge the biomass-containing fluid to the bioreactor is preferably in the middle or lower part of the bioreactor. This is desirable because it is advantageous for keeping the solid content of the upper part of the bioreactor relatively low.

[0106] The fluid-gas separator (50) is configured to separate a fluid into a gas phase and a fluid phase comprising biomass and is typically arranged relative to the bioreactor (1) such that during use, the liquid level in the fluid-gas separator (50) is higher than the liquid level in the bioreactor (1).

[0107] Any fluid-gas separator known in the art can be used to separate from the biomass-rich fluid that has been subjected to density reduction.Preferably, the fluid-gas separator passes through a gas-liquid separator, a gas stripping column and a gas separation drum.

[0108] Preferred examples of fluid-gas separators for use in the device according to the invention are Fig. 9 As shown. The fluid-gas separator (50) is connected to the pipeline (10) at an angle τ, which is preferably 5 to 85°, more preferably 40 to 80°, and even more preferably 60 to 75° relative to the vertical axis. During use, this angle advantageously allows the biomass-rich fluid that has been subjected to density reduction to be effectively loaded into the fluid-gas separator (50), because it allows the biomass-containing fluid to be transported into the fluid-gas separator using gravity. Therefore, the risk of clogging the pipeline (10) is minimized.

[0109] The pipeline (10) is also configured to include a gas outlet (55), preferably located at the upper part of the pipeline for discharging gas, preferably air. The outlet (55) allows the discharge of gas from the pipeline (10). The outlet (55) is generally located at a height h2, which is higher than the liquid level in the bioreactor (during use). The height h2 can be selected within a wide range. Those skilled in the art will be able to select a suitable h2 based on the information disclosed herein and common knowledge. For example, a suitable h2 is 0.5m or greater, particularly 1.0m or greater, more particularly about 1.5m or greater. In an embodiment, h2 is 10m or less, particularly 5m or less, more particularly about 2.5m or less.

[0110] Furthermore, the fluid-gas separator (50) is configured to include an inlet (51) connected to the outlet of the pipeline (10) for the biomass-rich and gas-containing fluid, the separator being configured such that during use, the biomass-rich and gas-containing fluid enters the gas-fluid separator (50) at a height h1, wherein h1 is higher than the liquid level in the bioreactor (1). Preferably, the inlet is configured such that h1 is 0.5 to 1.5 m higher than the liquid level in the bioreactor, more preferably 0.7 to 1.3 m higher. Good results are obtained with h1 of about 1 m or more, as it enables effective phase separation of the biomass-containing fluid phase and the gas phase.

[0111] The fluid-gas separator (50) is also provided with a gas outlet (53) and an outlet (54) for a biomass-rich fluid. The gas leaves the fluid-gas separator (50) via an outlet (55) located at the top (above the liquid level) or in the vicinity of the fluid-gas separator. It may leave the fluid-gas separator directly or it may be further processed in a manner known per se. The solids-rich fluid leaves the fluid-gas separator through a conduit (10') in the lower part of the fluid-gas separator. Preferably, the conduit 10' is substantially straight, i.e. substantially free of bends or twists with an angle of less than 160°, preferably less than 180°, to avoid blockages or clogging due to accumulation of biomass into the conduit 10'. As described above, the height of the outlet (54) configured to discharge a biomass-containing fluid into the bioreactor is higher than that of the ejector configured to eject the fluid medium. This is desired in order to optimally benefit from the gas lift effect provided by the ejection of the fluid medium. Further, the outlet (54) is configured to discharge a biomass-containing fluid into the bioreactor, preferably in the middle or lower part of the bioreactor. This is advantageous because it is desirable to keep the solids content in the upper portion of the bioreactor relatively low.

[0112] The invention also relates to a separator device (which can be used as an external separator in the method according to the invention or it can be an external separator of the device according to the invention), in particular a settler, comprising a separation chamber provided with a module tilting internal component unit and a sealable entrance to the module tilting internal component unit, such as a cover or a removable flange, which allows the tilting internal component to be replaced or temporarily removed, for example for maintenance of the separator. Such a module can be a TPS module box. Therefore, the internal component can be easily replaced by a set of spare internal components, thereby minimizing the downtime of the separator; when the internal component can be easily removed, it is also convenient to clean / maintain the remaining part of the external separator. The separator device according to the invention is usually elongated, such as essentially rectangular or essentially cylindrical. The separator device includes an inlet for the fluid to be separated, usually entering the separation chamber at one end (base side, 102a) of the separator or near it, and the separation chamber includes the internal component module (102e). The inlet preferably includes an inlet distribution chamber. At least when in use, the replaceable module (102e) comprising the inclined separation internals is present at least substantially along the separation chamber, preferably along an at least substantially horizontal axis, the outlet (107a) for the fluid with reduced solids content and the outlet (108) for the fluid with increased solids content (sludge) being generally arranged at or near the opposite extremity of the inlet side. Typically, the outlet (107a) for the fluid with reduced solids content will be arranged at least substantially above the internals, while the outlet (108) for the fluid with increased solids content (sludge) will be arranged at least substantially below the internals.

[0113] In a preferred embodiment the (external) separator device according to the invention has a substantially rectangular shape and comprises a cover, such as a roof or a side along the length of the internals module, via which the separation chamber can be opened and the internals module can be removed.

[0114] In a further preferred embodiment, Figure 7 Schematically shown, the (external) separator device according to the invention has a separation chamber having an at least substantially cylindrical shape, in which a module (102e) comprising inclined internals is present.

[0115] The inventors have realised that an at least substantially cylindrical design is particularly advantageous in which the module internals are adapted to be replaceable from the separation chamber via at least one openable and closable base side, not only because it facilitates repair / maintenance, but also because such a design facilitates that the openable / closable separator can withstand the pressures (typically up to about 2.5 bar) that are advantageously applied to the separation chamber.

[0116] Thus, in an advantageous embodiment, the separator comprises a separation chamber of at least substantially cylindrical shape, which is placed substantially horizontally during use (i.e. its radial axis is substantially horizontal), wherein at least when in use, a replaceable module (102e) of the separation chamber comprising an inclined separation internal component is present at least substantially along the radial axis of the separation chamber, and its separation chamber has at least one sealable and openable base side (102a, 102b) and an opening suitable for allowing the module comprising the inclined separation internal component to be placed into its working position and removed from its working position. For example, a flange (102c, 102d) can be provided on the sealable and openable base side. Figure 7 In the embodiment, the inlet (104) of the solid-containing fluid to be processed is schematically shown at the right arrow. In use, the fluid preferably enters the separator via the inlet distribution chamber and then flows into the separation chamber. The separator also includes an outlet (107a) for the fluid with reduced solid content (shown at the upper left arrow) and an outlet (108) for the fluid (sludge) with increased solid content (shown at the lower left arrow).

[0117] In a particularly advantageous embodiment, the (external) separator device according to the invention (an external separator of an apparatus according to the invention or an external separator of an apparatus used in a method according to the invention, respectively) comprises: an at least essentially rectangular or at least essentially cylindrical separation chamber, which is arranged essentially horizontally during use (i.e. its radial axis is essentially horizontal), in which the inclined separation internals module is present at least essentially along its radial axis; an inlet, configured to feed a fluid containing solids (e.g. biomass from a bioreactor) to the lower part of the external separator below the internals; a channel for an aqueous fluid containing solids to flow from the inlet through the internals towards a first outlet for an aqueous fluid with a reduced solids content, located at least essentially above the internals, and a second outlet for an aqueous fluid rich in solids (sludge), located at least essentially below the internals.

[0118] In the device used according to the invention, the inlet of the external separator is usually connected to the inlet (5) of the internal feed pipe (6) or the inlet (35) of the external feed pipe (34). During use, the aqueous fluid is separated into a liquid phase and a fluid phase rich in particles (granules). The external separator also includes an outlet (8) for returning the aqueous fluid rich in (granules) biomass to the bioreactor, which outlet is connected to the inlet (9) of the aqueous fluid rich in (granules) biomass of the bioreactor via a pipe (10). The pipe (10) is equipped with a biogas injector (23) for injecting biogas into the fluid rich in (granules) biomass, and the biogas injector is connected to a biogas collector (22) via a pipe (21).

[0119] Can be during reactor startup, when biogas generation is not enough to cause enough upward flow, the fluid rich in (granular) biomass is discharged from the external separator to the bioreactor without mechanical assistance or the use of an external gas source. In this case, there can be mechanical assistance such as a recirculation pump to suck the biomass-rich fluid from the external separator into the bioreactor. In addition, the presence of such a pump minimizes or prevents the pipeline from being blocked due to the precipitation of sludge in the pipeline.

[0120] Preferably, there is a conditioning tank (12) from which an aqueous fluid is supplied to the bioreactor during use. To improve mixing of the aqueous fluid present in the conditioning tank, a biogas line is preferably provided for introducing biogas from the bioreactor into the conditioning tank.

[0121] Preferably, a recirculation pump is used to create sufficient upflow to draw settled solids from the external separator into the bioreactor.

[0122] The external separator is located outside the bioreactor to improve accessibility, thereby facilitating maintenance and start-up procedures, and further enables installation of partial reactors, ie, allows upgrading existing systems with external settlers, thereby improving the efficiency of the reactor.

[0123] Preferably, the pipeline connecting the external separator to the other parts of the device comprises an isolation valve, which allows the isolation of the external separator and is therefore convenient for cleaning or maintenance in situ at the external separator. In addition, because the external separator is usually placed below the inlet of the feed pipeline of the external separator, the pressure in the external separator is higher than the pressure on the bioreactor top. Usually the pressure difference is about 1.5-3 bar. Higher pressure compresses the biomass particles, thereby removing the possible gas still present in the particle interior and therefore strengthening the sedimentation of the particle, thereby improving the removal of solids from the liquid phase.

[0124] As explained in detail above, at least part of the driving force for circulating the biomass-rich fluid phase from the external separator to the bioreactor utilizes the gas lift principle. In order to use this principle, the external separator is preferably placed low enough to allow the circulation pipe (10) to extend upwardly enough to produce gas lift and return the biomass-rich fluid phase to the middle or lower part of the bioreactor. This is desirable because it is desirable to keep the solid content in the upper part of the bioreactor relatively low. Therefore, the external separator is advantageously placed at or near the floor of the device, or at or below the approximately same height as the bottom of the bioreactor, while the inlet (9) for the biomass-rich circulating fluid entering the bioreactor (1) via the pipe (10) is placed at a position at least higher than the outlet (29) of the biomass-rich fluid of the external separator, and preferably at a position higher than the top of the external separator. A satisfactory height difference between the biomass-rich outlet (29) of the external separator, the gas injector (23) entering the circulation conduit (10) and the inlet (9) for the biomass-rich circulating fluid from the external separator can be based on the information disclosed herein, common general knowledge and optionally a limited amount of routine trial and error. In particular, a person skilled in the art will be able to select the height difference so that the pressure difference causes them to drive the fluid / solid / gas in the correct direction.

[0125] In a particular embodiment, the conduit for feeding the aqueous fluid from the bioreactor to the external separator is at least substantially straight, ie contains no sharp corners or edges, to prevent sludge from settling in the conduit and causing blockages in the system.

[0126] As used herein, the term "or" is defined as "and / or" unless stated otherwise.

[0127] The terms "a" or "an", as used herein, are defined as "at least one", unless otherwise stated.

[0128] When referring to a noun in the singular (eg, compound, additive, etc.), the plural is included.

[0129] The term "(at least) substantially" is generally used herein to indicate that it has the specified general characteristics or functions. When referring to a quantifiable characteristic, the term is particularly used to indicate that it is at least 50%, more particularly greater than 75%, and even more particularly greater than 90% of the maximum value of the characteristic. The term "substantially free" is generally used herein to indicate that the substance is not present (below the detection limit achievable by the analytical technology available on the effective filing date) or is present in such a low amount that it does not significantly affect the characteristics of the product that is substantially free of the substance. In fact, in terms of quantity, if the content of a substance is 0-1wt.%, particularly 0-0.5wt.%, more particularly 0-0.1wt.%, then the product is generally considered to be substantially free of the substance.

[0130] In the context of the present application, the term "about" generally refers to a deviation of 15% or less, particularly a deviation of 10% or less, more particularly a deviation of 5% or less from a given value.

[0131] As used herein, "biodegradable organic matter" is organic matter that can be converted by biomass in a reactor, typically under substantially anaerobic conditions, particularly to biomass or methane.

[0132] The term "fluid" refers herein to fluids and fluid mixtures and at least one other phase, such as suspensions, which flow without the application of external pressure (other than gravity).

[0133] The term "liquid" herein refers to an aqueous fluid that is substantially free of macroscopic particles (ie, <0.1 mm in size).

[0134] As used herein, "organic matter" is any organic matter that is chemically oxidizable, as measured by the Chemical Oxygen Demand (COD) test as described in ISO 6060: 1989. The amount of organic matter is usually expressed in g COD, which is the grams of oxygen consumed to oxidize the organic matter.

[0135] The skilled person is familiar with terms such as "above", "below", "in the middle", "at the bottom", "near the bottom", "at the top" and "near the top". Usually these are read relative to one another and the skilled person will be able to put them into practice based on common general knowledge, the information disclosed and citations herein and the details of the device unit (e.g. a bioreactor, a separate container or a volume of material contained in a bioreactor or part).

[0136] As a rule of thumb, unless the context otherwise requires, "close to" a reference point (e.g., "bottom" or "top") typically means "at most + / -20% relative height from the reference point," particularly "at most + / -15% relative height from the reference point," and more particularly "at most + / -10% relative height from the reference point." The relative height is the distance from the bottom divided by the total height of the unit (the height difference between the bottom and the top).

[0137] As a rule of thumb, unless otherwise specified in the context, the "upper" portion generally refers to the upper 1 / 2 of the unit and particularly the upper 1 / 3 of the unit, and the "lower" portion generally refers to the lower 1 / 2 of the unit and particularly the lower 1 / 3 of the unit. When the middle portion is mentioned, this particularly refers to the middle 1 / 3 of the unit (1 / 3 from the bottom to 1 / 3 from the top).

[0138] For purposes of clarity and concise description, features are described herein as part of the same or separate embodiments; however, it should be understood that the scope of the present invention may include embodiments having a combination of all or some of the described features.

[0139] Legend: (1) Bioreactor; (2) External separator; (3) Internal baffles or guide plates / separators; (4) Inlet for aqueous fluid in the external separator; (5) Inlet of the pipe (6) for removing aqueous fluid from the bioreactor (1); (7a) Outlet for aqueous fluid in the external separator; (8) Outlet for biomass-rich fluid; (9) Inlet for biomass-rich fluid into the bioreactor (1); (10) Pipe for biomass-rich fluid that has been subjected to density reduction; (11) Mechanical pump; (12) Adjustment tank; (13) Inlet for wastewater; (14) Outlet for aqueous fluid; (15) Inlet for bioreactor containing aqueous fluid from the adjustment tank; (16) Inlet of aqueous fluid to the bioreactor (17) Biogas outlet from the regulating tank; (18) Biogas outlet from the bioreactor; (19) Biogas inlet from the regulating tank; (20) Biogas pipeline; (21) Biogas injector; (22) Biogas collection hood; (23) Biogas injector; (24) T-joint connecting the biogas pipeline (21) to the biogas pipeline (26) for introducing biogas; (25) Inlet of the regulating tank; (26) Biogas pipeline; (27) Valve; (28) Valve; (29) Inlet / outlet connected to the regulating tank inlet / outlet (31); (30) Pump for returning sludge from the external separator to the bioreactor; (32) Inlet of the bioreactor; (33) Pipe for returning sludge to the bioreactor ; (34) a feed conduit configured to feed an aqueous fluid containing solids from the bioreactor to an external separator; (35) an outlet of the bioreactor located above (36) a guide plate or baffle; (37) a return line for the liquid phase from the external separator to the adjustment tank; (38) a gas conduit from (39) the head space of the bioreactor to the gas injector; (40) an external gas source; (41) an external gas conduit; (42) a venturi injector; (43) a conduit for drawing a biomass-rich fluid into the flow path of the aqueous fluid that has entered the venturi injector from the high pressure inlet side (44); (45) a suction port; (47) a low pressure outlet of the venturi injector; (50) a gas-fluid separator; (51) an inlet for a gas-fluid separator for a biomass-rich fluid whose density has been reduced; (52) an outlet for a conduit (10) for a biomass-rich fluid whose density has been reduced; (53) an outlet for a gas-fluid separator for discharging gas; (54) an outlet for a gas-fluid separator for discharging a biomass-rich fluid; (55) an outlet for discharging gas; (102a, 102b) a base side of the separator; (102c, 102d) a flange; (102e) a replaceable module comprising inclined separation internal components; (104) an inlet for a fluid containing solids to be treated; (107a) an outlet for a fluid with a reduced solids content; (108) an outlet for a fluid with an increased solids content (sludge). DETAILED DESCRIPTION

[0140] Example

[0141] Wastewater from the pulp and paper industry is treated in the apparatus according to the invention (see, for example, Figure 3 and 4 ). Two different methods of reducing the density of the biomass-rich fluid downstream of the external separator were used and compared in terms of velocity turnover rate (VLR) at two time intervals of 50 and 150 days respectively.

[0142] During the first fifty-day time interval, the wastewater was treated in the device according to the invention, wherein the biogas within the bioreactor was collected using a collecting hood and subsequently introduced into the biomass-rich fluid phase downstream of the external separator.

[0143] After fifty days, air is introduced into the biomass-rich fluid downstream of the external separator by using a mechanical pump or compressor to reduce the density of the biomass-rich fluid downstream of the external separator.The wastewater is treated for an additional 150 days.

[0144] The volume loading rate (VLR) and average total COD (tCOD) and soluble COD (sCOD) of the effluent stream during the entire treatment process were determined. Fig.10 And as shown in Table 1.

[0145] like Fig.10 As shown in Figure A, during the first fifty days of treatment, a VLR of 10-30 kg COD / L day was achieved, wherein the density of the biomass-rich fluid downstream of the external separator was reduced by introducing biogas collected in the bioreactor using a collection hood into the fluid. In addition, a slightly higher VLR was obtained when the density of the biomass-rich fluid downstream of the external separator was reduced using external gas. Fig.10 A further showed that the VLR showed less variation, for example, it was more stable when using external gas to reduce the density of the biomass-rich fluid downstream of the external separator compared to using biogas collected inside the bioreactor using a biogas hood. The process was stable and no operational issues were observed over a processing period of at least 200 days.

[0146] In addition, from Table 1 and Fig.10 B It can be concluded that an average sCOD removal rate of more than 92% and an average tCOD of more than 80% were achieved.

[0147] Table 1. Biomass contents in the bioreactor, external separator and effluent line. Average values ​​are shown in brackets.

[0148]

[0149] As can be seen from Table 1 and Fig.10 A shows that using the process according to the invention 16-24 kg COD / m 3 The VLR of the present invention is 1.5 to 3 times smaller than that of the conventional EGBS. This makes the device more compact.

[0150] Furthermore, as can be gathered from Table 1, the concentration of biomass in the effluent was always below 5 mL biomass per L effluent and on average below 1.5 mL biomass per L effluent. These results demonstrate that the separation efficiency of the method according to the invention is outstanding.

[0151] Excellent separation efficiency is also shown in Fig.11 It shows that the effluent has been substantially purified, with a biomass content of 2 ml / L ( Fig.11 B). This is much lower than the samples taken at the inlet of the external separator, where a biomass content of 45 ml / L ( Fig.11 A), the sample from the biomass return line showed a biomass content of about 100 ml / L ( Fig.11 C).

[0152] From the results it can be concluded that the process according to the invention allows to treat wastewater with high efficiency as reflected by high VLR and high purity and by excellent COD removal.

Claims

1. A method for treating an aqueous fluid containing biodegradable organic matter in an apparatus comprising an upflow bioreactor (1) containing a sludge bed comprising biomass and an external separator (2), wherein the method comprises: - feeding the aqueous fluid into the lower part of the bioreactor so that the feed fluid contacts the biomass, thereby forming biogas from the biodegradable organic matter; - discharging the fluid that has been in contact with the biomass from the upper part of the bioreactor, wherein the discharged fluid contains the biomass; - feeding the biomass-containing fluid discharged from the upper part of the bioreactor to the external separator (2) comprising a separation chamber, wherein the biomass-containing fluid is separated into a liquid phase and a fluid phase, the liquid phase having a reduced biomass content or containing no biomass, and the fluid phase being rich in biomass; - density reduction of the biomass-rich fluid phase downstream of the external separator; and - returning the biomass-rich fluid, which has been subjected to a density reduction, to the bioreactor, wherein the density reduction comprises removing biogas from the head space of the bioreactor and introducing the biogas into the biomass-rich fluid phase downstream of the external separator, thereby reducing the density of the biomass-rich fluid downstream of the external separator; or Wherein the density reduction comprises introducing an external gas into the biomass-rich fluid phase downstream of the external separator, thereby reducing the density of the biomass-rich fluid downstream of the external separator. The method according to claim 1 , wherein the external gas is nitrogen.

3. The method of claim 1 , wherein a pressurized liquefied gas or a pressurized gas dissolved in a liquid phase is introduced into the biomass-rich fluid phase downstream of the external separator, the liquefied gas or the dissolved gas expanding thereby reducing the density of the biomass-rich fluid phase downstream of the external separator.

4. The method according to claim 1 or 2, wherein the biomass-rich fluid which has been subjected to density reduction is fed into a fluid-gas separator (50), wherein the fluid is separated into a gas phase and a fluid phase comprising biomass, and wherein the fluid phase comprising biomass is returned to the bioreactor (1).

5. The method according to claim 4, wherein the fluid-gas separator (50) is a gas-liquid separator, a gas stripping column or a gas separation drum. The method according to claim 1 , wherein the separation chamber is provided with inclined internal components.

7. A method for treating an aqueous fluid containing biodegradable organic matter in an apparatus comprising an upflow bioreactor (1) containing a sludge bed comprising biomass and an external separator (2), wherein the method comprises: - feeding the aqueous fluid into the lower part of the bioreactor so that the feed fluid contacts the biomass, thereby forming biogas from the biodegradable organic matter; - discharging the fluid that has been in contact with the biomass from the upper part of the bioreactor, wherein the discharged fluid contains the biomass; - feeding the aqueous fluid containing biomass discharged from the upper part of the bioreactor to the external separator (2) comprising a separation chamber provided with inclined internals, wherein the aqueous fluid containing biomass is separated into a liquid phase and a fluid phase, the liquid phase having a reduced biomass content or being free of biomass, and the fluid phase being rich in biomass; as well as - returning the biomass-rich fluid phase from the external separator to the bioreactor via a venturi ejector (42), the venturi ejector (42) having a high-pressure inlet, a low-pressure outlet and a suction port, wherein an aqueous fluid containing biodegradable organic matter to be treated in the bioreactor enters the venturi ejector via the high-pressure inlet, the biomass-rich fluid phase from the external separator enters the venturi ejector via the suction port, and the biomass-rich fluid phase and the aqueous fluid to be treated in the bioreactor leave the venturi ejector together via the low-pressure outlet and are fed to the bioreactor.

8. The process according to claim 7, wherein the density of the biomass-rich fluid phase decreases by at least 10% downstream of the external separator to a value between 10 and 900 kg / m 3 Density within the range.

9. The method according to claim 7 or 8, wherein the apparatus comprises a conditioning tank (12) into which the aqueous fluid to be treated in the bioreactor (1) is fed, the aqueous fluid being fed from the conditioning tank (12) to the bioreactor (1), and wherein a portion of the fluid phase having a reduced biomass content or being free of biomass is fed from the external separator (2) to the conditioning tank (12), wherein the aqueous fluid is subjected to a treatment comprising: - maintaining or adjusting the pH of the aqueous fluid in the adjustment tank to a pH in the range of 6.0 to 7.5, and / or - maintaining or adjusting the temperature of the aqueous fluid in the regulating tank to a temperature in the range of 20 to 55°C.

10. The method of claim 1 or 7, wherein the bioreactor comprises a granular sludge bed (GSB), the GSB comprising anaerobic microorganisms and wherein the biodegradable organic matter is converted by the anaerobic microorganisms, thereby forming the biogas.

11. The method of claim 10, wherein the bioreactor is an expanded granular sludge blanket (EGSB) reactor.

12. The method according to claim 10, wherein the fluid discharged from the upper part of the bioreactor contains particulate biomass, wherein the particulate biomass settles in the external separator (2), and wherein the fluid phase returned to the bioreactor (1) is enriched in particulate biomass.

13. The method according to claim 1 or 7, wherein the external separator (2) is placed below an inlet (5) of a feed pipe (6) which discharges an aqueous fluid from the bioreactor (1) and which feeds the fluid to the external separator.

14. An apparatus for microbiological treatment of an aqueous fluid containing biodegradable organic matter, wherein the apparatus comprises: - an upflow bioreactor (1), said bioreactor comprising a biogas outlet; - an external separator (2) comprising a separation chamber, the separation chamber being arranged to separate a liquid phase from a fluid phase comprising biomass, the external separator comprising an inlet (4) for an aqueous fluid, the inlet (4) being connected to an inlet (5) of a conduit (6) for discharging the aqueous fluid from the bioreactor (1); an outlet (7a) for the aqueous fluid; an outlet (8) for a biomass-rich fluid, the outlet (8) being connected via a conduit (10) to an inlet (9) for the biomass-rich fluid to flow into the bioreactor (1), and - At least one injector selected from the group consisting of: (a) an injector configured to inject a fluid medium into the biomass-rich fluid downstream of the external separator, wherein - the bioreactor (1) has a head space, and a conduit providing a biogas flow path from the head space to the injector, the injector being configured to inject a fluid medium, and the injector being located in the conduit (10), the conduit (10) being used to return a mixture of the biomass-rich fluid phase and the biogas injected into the fluid phase, or - the injector configured to inject the fluid medium is connected to an external gas source, and (b) a venturi ejector configured to return biomass-rich fluid from the external separator to the bioreactor.

15. The apparatus of claim 14, wherein the bioreactor is a granular sludge bed reactor.

16. The apparatus according to claim 15, wherein the granular sludge blanket reactor is an expanded granular sludge blanket reactor.

17. The device according to claim 14, wherein the separation chamber of the external separator is provided with an inclined internal member.

18. The device according to claim 14, wherein the pipe (10) between the outlet (8) for the biomass-rich fluid of the external separator and the inlet (9) for returning the biomass-rich fluid to the bioreactor (1) is provided with an inlet (51) connected to a fluid-gas separator (50), the fluid-gas separator (50) being arranged to separate a gas phase from a fluid phase containing biomass, wherein the fluid-gas separator (50) is provided with an outlet (53) configured to discharge gas from the fluid-gas separator and an outlet (54) configured to discharge the biomass-containing fluid to the bioreactor, the outlet (54) configured to discharge the biomass-containing fluid to the bioreactor being located at a higher height than the ejector configured to eject the fluid medium, and the outlet (54) configured to discharge the biomass-containing fluid to the bioreactor being located in the middle or lower part of the bioreactor.

19. The apparatus according to claim 18, wherein the fluid-gas separator (50) is arranged relative to the bioreactor (1) such that during use the liquid level in the fluid-gas separator (50) is at a higher level than the liquid level in the bioreactor (1).

20. The apparatus according to claim 14, wherein the pipe (10) for returning the mixture of gas and the biomass-rich fluid is provided with an inlet (9) configured to discharge the returned mixture into the bioreactor, the inlet (9) configured to discharge the returned mixture into the bioreactor is at a higher height than the biogas ejector (23), and the inlet (9) configured to discharge the returned mixture into the bioreactor is located in the middle or lower part of the bioreactor.

21. The device according to claim 14, comprising a conditioning tank (12) for pre-treating the aqueous fluid, comprising an inlet (13) for wastewater, an outlet (14) for the aqueous fluid connected to the inlet (15) of the bioreactor via a pipe (16), a return line (37) of the fluid phase from the external separator (2) to the conditioning tank (12), and a biogas outlet.

22. The device according to claim 14, wherein - The bioreactor (1) comprises an internal biogas collector (22) located at a height such that it is immersed in the sludge bed in the bioreactor at least during use of the device, the biogas collector being connected to a biogas injector (23) configured to inject biogas into the pipe (10) for returning solids-rich fluid from the external separator (2) to the bioreactor (1).

23. The device of claim 14, wherein the external separator is located at the same height as the bottom of the bioreactor or below the bottom of the bioreactor.

24. The apparatus of claim 23, wherein the external separator is located on the floor.

25. An apparatus according to claim 14, wherein the apparatus comprises an external feed conduit (34) configured to feed an aqueous fluid containing solids from the bioreactor (1) to the external separator (2), wherein the external feed conduit (34) has an inlet (35) located above a guide plate or baffle (36) present in the bioreactor (1), the guide plate or baffle being configured to guide the aqueous fluid containing solids present in the bioreactor (1) into the external feed conduit (34).

26. The device according to claim 14, wherein the external separator (2) comprises a separation chamber provided with a modular tilting internal component unit and a sealable and openable access allowing replacement of the modular tilting internal component unit.

27. A device according to claim 26, wherein the separation chamber is a cylindrical separation chamber, which is placed with its radial axis horizontal during use, and at least in the separation chamber when in use, a replaceable module (102e) including a tilted separation internal component is present along the radial axis of the separation chamber, and the separation chamber has at least one base side (102a, 102b) that is sealable and openable to provide an opening, wherein the opening is suitable for allowing the module including the tilted separation internal component to be placed in its working position and removed from its working position.

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