Method and device of optimizing plug flow in aerobic biological wastewater treatment reactor

Abstract

To provide a method of treating wastewater in a biological treatment reactor.SOLUTION: The method of treating wastewater in a biological treatment reactor comprises (a) a step of introducing wastewater influent to the bottom of the reactor while concurrently decanting treated wastewater effluent at the uppermost operation water level of the reactor, (b) an aeration step and (c) a settling step of settling biomass. The step (a) is carried out in a vertical plug flow condition, and during the step (a), the uniform distribution of influent wastewater flowing across the distribution pipe and / or the degree of the plug flow in the reactor are monitored, and when suboptimal uniform distribution and / or a suboptimal degree of plug flow are detected, an influent distribution system and / or an effluent decanter system are cleaned by removing fouling and / or blockages. The invention also relates to a liquid inflow system and a facility to be used in such a method of treating wastewater.SELECTED DRAWING: Figure 3

Description

[Background technology]

[0001] [Field of the Invention]

[0002] The present invention relates to a method for the treatment of wastewater in a biological treatment reactor, in which vertical plug flow conditions are optimized during part of the method. The present invention also relates to a liquid inflow system and an installation for use in such a method for the treatment of wastewater.

[0003] [Background of the invention]

[0004] Wastewater treatment typically involves several steps. During primary treatment, heavy solids settle to the bottom of a basin while light oily materials accumulate on the surface of the water. The heavy solids and light oils are removed and the primary treated wastewater is further treated. Such further treatment typically involves biological treatment using microorganisms (MOs) to convert organic pollutants in the wastewater into MO-sludge and remove inorganic pollutants such as phosphates and nitrates. This biological process can occur either anaerobic or aerobically.

[0005] A widely applied method for the aerobic treatment of wastewater is called the "conventional activated sludge" (CAS) method. It involves air or oxygen being introduced into a biological treatment reactor containing purified biomass, also called "activated sludge", and wastewater. The wastewater is, for example, sewage and / or industrial wastewater that has been screened and optionally primary treated. Mixed liquor suspended solids (MLSS) grow into biomass-containing flocs, which typically grow into suspended floccules, also called "flocs". In the next settling tank (usually called the "final clarifier"), the biological flocs are allowed to settle, whereby clarified sludge is separated from the treated water. The settled sludge is recycled to the biological process as "return activated sludge" (RAS). To maintain the biomass in the treatment reactor at a desired level during biomass growth, a portion of the RAS is periodically discarded as "waste activated sludge" (WAS). The CAS method is applied in various configurations with one or more tanks in parallel or sequential treatment trains. Such a tank may be operated, for example, as a continuous stirred tank reactor (CSTR), a sequencing batch reactor (SBR) or a plug flow reactor, in particular a plug flow reactor under vertical plug flow (VPF) conditions.

[0006] Although the CAS method is widely used, a significant drawback is the relatively poor settling characteristics of activated sludge due to its floc-like structure.

[0007] Modern methods and processes for extensive biological treatment of wastewater utilize aerobic granular sludge (AGS). Compared to conventional aerobic activated sludge systems such as Carrousel®, in oxidation ditch and sequencing batch reactors (SBR), the aerobic biomass exists as a flocculent dispersed material called activated sludge, containing mostly particles smaller than 0.2 mm, in AGS, the same type of biomass forms larger aggregates called granules. These granules have a typical size of 0.2-5 mm and have excellent settling properties. These settling properties are important so that after aerobic biological treatment, the biomass sludge is separated from the pure water by settling. Because AGS settles multiple factors faster than activated sludge, the treatment reactor required is much more compact, often requiring only 25% of the footprint that a conventional solution uses. In addition, the energy consumption for wastewater treatment is less than half.

[0008] The most applied AGS technology at present is Nereda®, developed by Royal HaskoningDHV. This technology utilizes an aerobic granular sludge vertical plug flow reactor (AGS-VPF), in which wastewater is fed to the bottom of the reactor and purified wastewater is simultaneously decanted from the top. In these reactors, it is important that good plug flow conditions are achieved while the wastewater flows upwards to prevent the raw wastewater from contaminating the decanted purified wastewater. The level of plug flow also determines the amount of wastewater that can replace each batch with respect to the total reactor volume without raw wastewater being discharged, the so-called exchange ratio (ER), and therefore the level of plug flow is an important parameter that determines the compactness of the AGS-VPF reactor.

[0009] Biological wastewater treatment using aerobic granular sludge is described in WO 2004 / 024638. WO 2004 / 024638 discloses a method for treating wastewater containing organic pollutants, in which in a first step the wastewater is contacted with sludge granules containing microorganisms, and in a second step an oxygen-containing gas is fed to the sludge particles. The method further comprises a third step including settling of the sludge granules and discharging wastewater reduced in organic pollutants. During the second step, the granules are in a fluidized state. The method effectively removes organic pollutants, nitrogen compounds and phosphates. Preferably, at least a portion of the nutrient-depleted wastewater is discharged during the wastewater feed in the first step.

[0010] In both the CAS-VPF process using flocculated sludge and the AGS-VPF process using granular sludge, the biological wastewater treatment process using aerobic sludge under vertical plug flow conditions includes the following steps: The wastewater influent is introduced at the bottom of the reactor, and the treated wastewater effluent is simultaneously decanted at the top of the reactor. Under vertical plug flow conditions, the introduction of the influent and the recovery of the effluent are carried out simultaneously. This step is followed by an aeration step and a sedimentation step to settle the biomass. Typically, the process is carried out in cycles, where the sedimentation step is followed by a simultaneous introduction of the wastewater influent and decantation of the wastewater effluent, the aeration step and the sedimentation step are repeated. The aeration step can include periods of extensive aeration, periods of low level aeration, periods of mixing and periods of intermittent aeration or no aeration, depending on the desired removal target of nitrogen and phosphate compounds.

[0011] To obtain suitable vertical plug flow conditions, it is essential to have an even and sufficient distribution of the wastewater influent across the bottom of the reactor, as well as to have the treated wastewater effluent collected through an even and sufficient distribution decanter at the top of the reactor. Among these, distribution at the bottom of the reactor is particularly important, requiring a fine mesh and even distribution of the wastewater influent across the reactor bottom surface. This distribution can be achieved using different types of distribution systems (also called distributors), but it is important that the cost of such distributors is not high.

[0012] However, such distributors become fouled over time due to debris, particles, grease, fibers, wipes, etc. in the wastewater, and through biological fouling. Such fouling leads to unequal distribution and therefore reduced plug flow levels, and therefore reduced throughput of the AGS-VPF or CAS-VPF reactor.

[0013] Another aspect that leads to reduced plug flow in the AGS-VPF and CAS-VPF PF reactors is that because these reactors are aerated during part of the reactor cycle operation, air can become entrained or accumulate in the distributor, resulting in maldistribution.

[0014] Wastewater distributors are also used in other types of biological treatment reactors, for example, the anaerobic sludge blanket reactor described in KR1019950008046. These reactors are used especially in industrial applications where the size of the reactor is limited. More importantly, the requirements for distributing the wastewater are less stringent than in aerobic sludge reactors with vertical plug flow feed (AGS-VPF and CAS-VPF reactors). In such anaerobic reactors, the important objective is to inject and somewhat distribute the wastewater across the bottom of the reactor so that it is in sufficient contact with the anaerobic granules. In these systems, establishing a vertical plug flow is not the goal, nor is it possible, since by introducing the wastewater through the anaerobic biological conversion gases (mainly methane), a result is produced that results in mixing (thus preventing plug flow), and a three-phase separator at the top of the reactor is used to separate the biomass, treated wastewater and gas. As a result, wastewater distributors used in these different types of biological reactors are not suitable for use in AGS-VPF or CAS-VPF. Also, since anaerobic reactors do not utilize aeration at the bottom of the reactor, there is no risk of air accumulating in the distributors and reducing the level of wastewater distribution across the bottom of the reactor. Compared to AGS-VPF or CAS-VPF reactors, the number of distribution pipes is often only 2-5, due to the less significant distribution and the limited size of these anaerobic reactors. To ensure that cleaning of these pipes is possible without draining the anaerobic reactor when blockages occur, the pipes often extend across the reactor wall and have isolation valves and blind flanges, allowing pumps and cleaning equipment to be connected to backflush the distributors during manual maintenance. In larger reactors, such as those used in AGS-VPF or CAS-VPF, which typically utilize 10-75 distribution pipes, such designs with many wall ducts, isolation valves and flanges are excessively expensive and not conducive to economical application of AGS-VPF or CAS-VPF.Also, in anaerobic reactors with only 2-5 distribution pipes, each distribution pipe can be equipped with a flow meter to measure the even distribution of wastewater across the various distribution pipes, which is not economically feasible in AGS-VPF or CAS-VPF reactors. Furthermore, distributors used in anaerobic reactors do not prevent the reduction in even distribution due to gas entrainment / accumulation in the distributor.

[0015] CN109231436A describes a wastewater distribution system that can be used with AGS-VPF or CAS-VPF. It consists of a water inlet device placed at the top of the reactor. These include a water inlet inner channel, a water inlet weir and a water inlet outer channel. A vertical water inlet branch pipe is connected to this channel and transports the wastewater towards the bottom of the reactor where a horizontal pipe with a vertical bellmouth at the end injects the wastewater into the AGS-VPF or CAS-VPF.

[0016] The CN109231436A equipment has the advantages of reasonable structural design, convenient operation and use, low running energy consumption, low later maintenance cost, high automation and intelligence, and can realize a good contact effect between organic matter and sludge. However, this equipment has some very important disadvantages, such as: Although the equipment may realize a good contact between organic matter in the wastewater and AGS or CAS, it does not provide a sufficient level of vertical plug flow conditions to enable high quality treated wastewater. To do so, a large number of bellmouths are required, resulting in many inlet weirs, water inlet channels and vertical water inlet branches, which makes the structure very complicated as well as expensive. For example, to establish a suitable level of plug flow in a reactor with a width / length of only 25×25 m, the number of vertical branches required is already more than 50 pieces. In addition, many access platforms are required at the top of the reactor to be able to maintain all these water inlets. In addition, a large amount of vertical and horizontal branches has a strong negative effect on the vertical water plug flow due to wall effect and flow pattern interference. Additionally, air from the aeration stage of the reactor operation accumulates in the bellmouth and in the horizontal pipes connected to the vertical branch, resulting in a reduced level of even wastewater distribution and therefore a reduced level of vertical plug flow. It is further noted that CN109231436A does not teach the level of plug flow that may be achieved, nor does it teach how fouling, if it occurs, may be monitored or corrected.

[0017] Also, CN207811359 discloses an apparatus for distributing wastewater to the bottom of the reactor through a splitter box at the top of the reactor connected to a vertical branch. This apparatus has the same drawbacks as CN109231436A mentioned above. There is a need to solve the aforementioned drawbacks of the existing VPF-AGS and VPF-CAS methods. In particular, there is a need in the art to obtain optimal vertical plug flow conditions and maintain these optimal conditions during the process. Summary of the Invention

[0018] The present invention relates to a method for treating wastewater in a biological treatment reactor, comprising the steps of: (a) introducing inflowing wastewater into the bottom of the reactor while simultaneously decanting treated wastewater at an operating level at the top of the reactor; (b) an aeration step, and (c) A settling step in which the aerobic sludge is allowed to settle. Step (a) is carried out under vertical plug flow conditions achieved by introducing influent wastewater into the reactor through an inflow distribution system comprising one or more distribution pipes, said one or more pipes preferably having downwardly directed nozzle outlets and arranged to provide an even distribution of the influent wastewater across the bottom surface of the reactor, and discharging treated wastewater through an effluent decanter system configured to evenly discharge the treated wastewater across the top operating level of the reactor. During step (a), the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow within the reactor is monitored, and when suboptimal distribution or a suboptimal degree of plug flow is detected, the inflow distribution system and / or the effluent decanter system are cleaned by removing fouling and / or blockages.

[0019] In particular, if a suboptimal distribution of the influent wastewater across the distribution pipe is detected during step (a), the influent distribution system is cleaned, and if a nonoptimal degree of plug flow is detected during step (a), the influent distribution system and / or the outflow decanter system are cleaned.

[0020] The present invention also relates to a liquid distribution system comprising one or more distribution pipes, the one or more pipes having one or more nozzle outlets arranged to provide an even distribution of influent wastewater across a bottom surface of the reactor, and a vertical vent pipe connected to each distribution pipe, wherein during operation, the vertical bends extend above the operating water level of the reactor comprising the liquid distribution system to release air or oxygen entrained in the corresponding distribution pipe.

[0021] Furthermore, the present invention relates to the use of the liquid distribution system according to the invention in a process for the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor, in particular in a process for the treatment of wastewater according to the invention.

[0022] The invention further relates to an installation for carrying out the method for treating wastewater according to the invention, said installation comprising a reactor with a liquid inlet system at the bottom of the reactor, a liquid outlet system at the top of the reactor and a gas inlet at the bottom of the reactor, the liquid inlet system comprising one or more distribution pipes, each of said one or more pipes comprising one or more nozzle outlets arranged to provide an even distribution of the liquid across the bottom surface of the reactor, connected to each distribution pipe is a vertical vent pipe, which ends above the operating water level of the reactor for releasing air entrained in the distribution pipes.The invention particularly relates to an installation for carrying out the method for treating wastewater according to the invention, said installation comprising a liquid inlet system according to the invention.

[0023] The present invention also relates to the use of a device as defined above in a process for the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor, in particular in a process for the treatment of wastewater according to the invention.

[0024] The present invention addresses the aforementioned shortcomings of existing aerobic VPF processes and the liquid distribution systems (also referred to as influent distribution systems) used in such processes. As discussed above, such distribution systems become fouled over time due to debris, particles, grease, fibers, wipes, etc. in the wastewater, and through biological fouling. Such fouling reduces the even distribution of the wastewater influent, and therefore reduces the degree of plug flow and discharge of insufficiently treated wastewater. The present invention allows such fouling to be removed, preferably without emptying the reactor contents. In addition, and equally important, the occurrence and level of such maldistribution is determined using cost-effective means and corrected before treatment performance is affected. The present invention not only ensures that wastewater can be distributed to a CAS-VPF or AGS-VPF reactor using a cost-effective structure, but importantly, safeguards optimal distribution of wastewater influent and optimal plug flow conditions during operation of the AGS-VPF or CAS-VPF reactor. This is ensured by monitoring the distribution through the individual distribution pipes and / or the plug flow conditions achieved, and if suboptimal distribution and / or suboptimal plug flow conditions are detected, the distributor is cleaned and / or air that has accumulated in the distribution pipes during normal operation is removed without interrupting or interfering with the performance of the wastewater treatment process.

[0025] The present invention will be described in detail below. [Brief description of the drawings]

[0026] [Figure 1A] FIG. 1A shows the concentration profiles at times t1, t2 and t3 when plug flow conditions are favorable and plug flow conditions are favorable. [Figure 1B]FIG. 1B shows the concentration profiles at times t1, t2 and t3 when plug flow conditions are poor. In FIG. 1A and FIG. 1B, a side view of a VPF reactor (1) is shown, which is equipped with a distribution pipe (3) with a nozzle outlet (4) and connected to a vertical vent pipe (8) and an (optional) end cap (9). The reactor further comprises an effluent decanter system (5) with an opening (6) for decanting the treated wastewater effluent. FIG. 1A shows the concentration profiles at times t1, t2 and t3 when plug flow conditions are good. FIG. 1A shows diagrammatically how the interface profile between the introduced untreated wastewater and the treated wastewater in the reactor develops over time during step (a) in the method and reactor according to the invention. As time progresses from t1 to t2 and t3, the interface profile is regular and moves upwards as a result of the vertical plug flow characteristics. This is shown for t1 in the left part of the figure, t2 in the middle part of the figure, and t3 in the right part of the figure. At time t3, this profile reaches one or more openings (6) of the effluent decanter system (5) (also called overflow weir) and breakthrough begins, through which part of the untreated wastewater leaves the reactor together with the treated water. Figure 1B shows the concentration profiles at times t1, t2 and t3 when plug flow conditions are insufficient. Figure 1B shows diagrammatically how the concentration profile develops when vertical plug-flow characteristics are insufficient, for example because the wastewater is being treated through a method, apparatus or reactor not according to the invention, or because of blockage of some of the distribution pipes (3), including one or more nozzle outlets, or because of blockage of one or more of the openings (6) of the effluent decanter system (5). The resulting interfacial profile is irregular and breakthrough begins at t2. [Diagram 2] FIG. 2 shows a reactor equipped with an inflow distribution system according to the invention. [Diagram 3] FIG. 3 shows a reactor equipped with an inflow distribution system according to the invention. [Figure 4] FIG. 4 shows a reactor equipped with an inflow distribution system according to the invention. [Diagram 5] Figure 5 shows examples of locations across a reactor from bottom to top for measuring suitable parameters during step (a) of the method according to the invention. For example, samples may be taken manually at these locations to determine said parameters during step (a). Alternatively, said parameters may be determined automatically at these locations. [Figure 6] 6 shows how the profile of a suitable parameter is determined by using an analyzer or probe at a certain distance h1, for example 1 m, from the bottom of the reactor. As an example, the ammonium concentration can be determined, for example, by an ion-selective probe. [Figure 7] FIG. 7 shows how the profile of the appropriate parameters is determined at a certain distance h2, say 0-3 m, from the reactor overflow weir opening at the top of the reactor by using a probe or analyzer. [Figure 8] Figure 8 shows a VPF reactor (1) with an inlet distribution pipe (3) fed through a header (10). The header (10) is at least partially located above the water level in the reactor. Wastewater influent is fed to the distribution pipe (3) through pipe (2) and the header (10). Cleaning of the distribution pipe (3) can be performed from the top side through the header (10). Figure 8 further shows an effluent decanter system (5) including an opening (6). [Figure 9A] FIG. 9A shows an example of the connection between the vent pipe (8) and the distribution pipe (3). [Figure 9B] FIG. 9B shows an example of the connection between the vent pipe (8) and the distribution pipe (3). [Figure 9C] FIG. 9C shows an example of the connection between the vent pipe (8) and the distribution pipe (3). [Figure 9D] FIG. 9D shows an example of the connection between the vent pipe (8) and the distribution pipe (3). Detailed Description of the Invention

[0027] The method, apparatus and reactor according to the present invention and preferred embodiments thereof are described in more detail below. Those skilled in the art will recognize that, according to the same principles, many alternative embodiments can be designed with modified details that achieve the same results, and are also considered to be covered by the scope of the claims.

[0028] definition

[0029] As used in this specification and claims, the verb "comprise" and its conjugations are used in their open sense, meaning that the items following the word are included but not excluding items not specifically mentioned.

[0030] Furthermore, the reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that only one of the element is present. Thus, the indefinite article "a" or "an" normally means "at least one."

[0031] [Wastewater treatment method]

[0032] In a first aspect, the present invention relates to a method for the aerobic biological treatment of wastewater, the aerobic biological treatment being carried out using aerobic granular sludge containing microorganisms.

[0033] Thus, the present invention relates to a method for treating wastewater in a biological treatment reactor, comprising the steps of: (a) introducing inflowing wastewater into the bottom of the reactor while simultaneously decanting treated wastewater at an operating level at the top of the reactor; (b) an aeration step, and (c) A settling step in which the aerobic sludge is allowed to settle. Step (a) is carried out under vertical plug flow conditions achieved by introducing the inflowing wastewater into the reactor through an inflow distribution system comprising one or more distribution pipes, preferably having downwardly oriented nozzle outlets and positioned to provide an even distribution of the inflowing wastewater across the bottom surface of the reactor, and discharging the treated wastewater through an effluent decanter system configured to discharge the treated wastewater evenly across the top operating water level of the reactor. During step (a), the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow within the reactor are monitored, and when suboptimal distribution or a suboptimal degree of plug flow is detected, the influent distribution system and / or the effluent decanter system are cleaned by removing fouling and / or blockages.

[0034] The present invention relates in particular to a method for treating wastewater in a biological treatment reactor, comprising the steps of: (a) introducing inflowing wastewater into the bottom of the reactor while simultaneously decanting treated wastewater at an operating level at the top of the reactor; (b) an aeration step, and (c) A settling step in which the aerobic sludge is allowed to settle. Step (a) is carried out under vertical plug flow conditions achieved by introducing inflowing wastewater into the reactor through an inflow distribution system comprising one or more distribution pipes, preferably having downwardly oriented nozzle outlets and positioned to provide an even distribution of the inflowing wastewater across the bottom surface of the reactor, and discharging the treated wastewater effluent through an effluent decanter system configured to discharge the effluent evenly across the top operating water level of the reactor. During step (a), the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow within the reactor are monitored, and when suboptimal distribution or a suboptimal degree of plug flow is detected, the influent distribution system and / or the effluent decanter system are cleaned by removing fouling and / or blockages. When a suboptimal distribution of the influent wastewater across the distribution pipe is detected during step (a), the influent distribution system is cleaned. If a suboptimal degree of plug flow is detected during step (a), the influent distribution system and / or the outflow decanter system are cleaned.

[0035] The biological treatment reactor contains biomass in the form of aerobic sludge containing microorganisms. The aerobic sludge may be in granular form, also called aerobic granular sludge (AGS), or in flocculated form, also called activated sludge or conventional activated sludge (CAS). The method was carried out in a vertical plug flow (VPF) reactor. When AGS is used, the biological treatment reactor is also called an AGS-VPF reactor. When CAS is used, the biological treatment reactor is also called a CAS-VPF reactor.

[0036] In a preferred embodiment of the method of the present invention, more than 70% of the biomass particles in the reactor have a particle size of more than 0.2 mm, preferably in the range of 0.2-50 mm. In this embodiment, the aerobic sludge is in the form of AGS. As mentioned above, in this embodiment, the biological treatment reactor is also called an AGS-VPF reactor.

[0037] In another preferred embodiment of the method of the present invention, at least 70% of the biomass particles in the reactor have a diameter of less than 0.2 mm. In this embodiment, the aerobic sludge is in the form of CAS. As mentioned above, in this embodiment, the biological treatment reactor is also called a CAS-VPF reactor.

[0038] As mentioned above, the method according to the present invention comprises a step (a) of introducing a wastewater influent whilst simultaneously decanting a treated wastewater effluent, an aeration step (b) and a settling step (c) of settling an aerobic sludge.

[0039] During step (b) of the process, the aeration step, an oxygen-containing gas is introduced into the reactor. Any oxygen-containing gas can be used, but typical examples include oxygen, air, and mixtures thereof. Most preferably, air is used. The introduction of the oxygen-containing gas is via means known in the art, such as an aeration device or blower.

[0040] The method according to the invention further comprises a sedimentation step (c), in which the biomass is allowed to settle.

[0041] Typically, the process is carried out in cycles, with one or more cycles of settling step (c), simultaneous introduction of wastewater influent and decanting of treated wastewater effluent step (a), aeration step (b) and settling step (c). The process according to the invention typically comprises two or more cycles of steps (a), (b) and (c). In a preferred embodiment, the process comprises a plurality of these cycles.

[0042] The method according to the invention may include additional steps. For example, in another preferred embodiment, the simultaneous decanting of the treated wastewater effluent at the operating level at the top of the reactor in step (a) is stopped when the plug flow profile interface is near the opening of the effluent decanter system, while the introduction of the influent at the bottom of the reactor continues. Thus, the operating level in the reactor increases above the effluent decanter system. After carrying out steps (b) and (c) and before carrying out step (a) of the next cycle, the water level above the effluent decanter system is lowered to the level of the opening of the effluent decanter system by removing the treated wastewater effluent through the effluent decanter system. The effluent decanter system is shown in the figure. For example, FIG. 3 shows the opening (6) of the effluent decanter system (5).

[0043] In this embodiment, the method includes the following steps: (a) introducing influent wastewater into the bottom of the reactor while simultaneously decanting treated wastewater effluent at an operating level at the top of the reactor; (i) stopping the decanting of treated wastewater effluent while continuing the introduction of influent at the bottom of the reactor when the plug flow profile interface is near the opening of the effluent decanter system, such that the water level in the reactor is higher than the effluent decanter system; (b) aeration step; (c) a settling step in which the aerobic sludge is allowed to settle; (d) decanting the treated wastewater effluent through an effluent decanter system to lower the water level in the reactor to an opening in the effluent decanter system. Step (a) is carried out under vertical plug flow conditions achieved by introducing wastewater influent into the reactor through an inlet distribution system comprising one or more distribution pipes, preferably having downwardly oriented nozzle outlets and arranged to provide an even distribution of the influent wastewater across the bottom surface of the reactor, and discharging treated wastewater effluent through an effluent decanter system configured to discharge the treated wastewater effluent evenly across the operating water level at the top of the reactor; During step (a), the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow within the reactor are monitored, and when suboptimal distribution or a suboptimal degree of plug flow is detected, the influent distribution system and / or the effluent decanter system are cleaned by removing fouling and / or blockages.

[0044] In this embodiment of the process according to the invention, the effluent decanter system is placed at a fixed height within the reactor.

[0045] In another preferred embodiment, the height of the effluent decanter system in the reactor is variable. In this embodiment, in step (i) of the method, the decantering of the treated wastewater effluent is stopped when the plug flow profile interface is near the opening of the effluent decanter system, while continuing the introduction of influent at the bottom of the reactor, the vertical position of the effluent decanter system in the reactor is raised and maintained above the operating water level in the reactor. Thus, the water level does not rise above the effluent decanter system, but the height, i.e. the vertical position, of the effluent decanter system in the reactor remains raised above the decanter level. This can be achieved, for example, by using a float on the decanter or a mechanical lever controlled by the operating water position. In step (d) of this embodiment, the vertical position of the effluent decanter system is returned to its original position during step (a), thereby lowering the water level in the reactor to the opening of the effluent decanter system by decanting the treated wastewater through the effluent decanter system.

[0046] In another embodiment, a floating decanter or a decanter with a mechanically adjustable height position is used, and the flow of the co-decanter is reduced when the development of the plug flow profile is such that the feed rate cannot decant the remaining influent without reaching the opening (6) within the remaining feed time. The operating water level of the reactor is then raised.

[0047] Also in these embodiments, when a suboptimal distribution of the influent wastewater across the distribution pipe is detected during step (a), the influent distribution system is cleaned, and when a suboptimal degree of plug flow is detected during step (a), the influent distribution system and / or the outflow decanter system are cleaned.

[0048] In another embodiment, step (d) can be combined with step (a).

[0049] In a variant of the method for the treatment of wastewater, a floating decanter, a decanter with a mechanically adjustable height position or a decanter that can be submerged below the water surface is used, and in step (a) the operating water level is raised since no decanting is applied at the same time. After carrying out steps (b) and (c), in the next cycle the height of the outflow decanter is lowered to the normal level during the start of step (a) or in the preceding step (d) where the effluent is decanted but no influent is introduced.

[0050] In step (a) of the method according to the invention, the wastewater influent is introduced into the bottom of the reactor and the treated wastewater (also called wastewater effluent, treated wastewater effluent or effluent) is simultaneously decanted at the top of the reactor at the operating level. Here, the bottom of the reactor refers to the lower part of the reactor. The wastewater influent is typically introduced at a height of 30-800 mm from the bottom of the reactor, preferably at a height of 50-750 mm from the bottom of the reactor, more preferably at a height of 60-500 mm from the bottom of the reactor, even more preferably at a height of 80-300 mm from the bottom of the reactor, and most preferably at a height of 100-300 mm from the bottom of the reactor. The optimal height for introducing the wastewater influent depends on the size of the reactor, in particular the height of the reactor during step (a) of the method and the operating level in the reactor. The treated wastewater effluent is decanted at the top of the reactor during step (a) of the method, typically at the operating level at the top of the reactor.

[0051] The wastewater influent is, for example, sewage and / or industrial wastewater. The wastewater influent is optionally pretreated, for example by primary treatment to remove heavy solids and / or light oily materials.

[0052] Step (a) of the method according to the invention is carried out under vertical plug flow conditions.

[0053] Vertical plug flow conditions are achieved by even distribution of the wastewater influent across the bottom surface of the reactor and simultaneously discharging the treated wastewater effluent evenly along the water surface at the operating water level during step (a) at the top of the reactor, resulting in a vertical plug flow of the wastewater influent replacing the treated wastewater effluent by decanting it at the top of the reactor.

[0054] An even distribution of the wastewater influent along the bottom of the reactor is achieved by introducing the influent into the reactor through an inflow distribution system comprising one or more distribution pipes, each having one or more nozzle outlets. The nozzle outlets are preferably directed downwards. The optimal number of nozzle outlets depends, inter alia, on the size of the reactor, in particular on the surface area of ​​the bottom of the reactor. Preferably, the number of nozzle outlets is less than m of the bottom surface of the reactor. 2 There are 0.5-50 nozzle outlets per m of the reactor bottom surface. These nozzles are typically evenly distributed across the reactor bottom surface to provide an even distribution of wastewater influent across said surface. In one embodiment, the nozzles are distributed over m of the reactor bottom surface. 2 In some embodiments, there are 0.25-50 nozzle outlets per nozzle, and in other embodiments, there are 0.25-25 nozzle outlets per nozzle.

[0055] In a preferred embodiment, the inflow distribution system comprises two or more distribution pipes. The optimal number of distribution pipes depends, inter alia, on the size of the reactor, in particular on the surface area of ​​the bottom of the reactor. Preferably, the inflow distribution system comprises two or more distribution pipes, more preferably three or more, even more preferably five or more. In a typical AGS-VPF reactor or a typical CAS-VPF reactor, the inflow distribution system comprises 5-50 distribution pipes. A plurality of distribution pipes together is also called a distribution grid.

[0056] The number of distribution pipes and nozzle outlets are described in more detail below.

[0057] In a further preferred embodiment, each distribution pipe is connected to a common manifold or header. In a further preferred embodiment, the grid with the header is liftable, in other words, the grid with the header may be raised above the operating water level in the reactor.

[0058] The treated wastewater effluent is discharged through an overflow decanter system configured to discharge the effluent evenly over the surface at the operating level during step (a). Overflow decanter systems are known in the art.

[0059] During step (a) of the method according to the invention, the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow in the reactor are monitored, and when suboptimal distribution and / or suboptimal plug flow is detected, the influent distribution system and / or the outflow decanter system are cleaned by removing fouling and / or blockages. In this regard, it is noted that for optimal plug flow conditions, even distribution of the influent wastewater across the distribution pipes and therefore even distribution across the reactor bottom surface is necessary. Uneven distribution of the influent wastewater across the distribution pipes results in suboptimal plug flow conditions. Similarly, uneven release of the treated wastewater effluent across the water surface at the operating water level can also result in suboptimal plug flow conditions.

[0060] In one embodiment of the method according to the invention, in step (a), the even distribution of the influent wastewater across the distribution pipe is monitored. In another embodiment of the method according to the invention, in step (a), the extent of plug flow in the reactor is monitored. In yet another embodiment of the method according to the invention, both the even distribution of the influent wastewater across the distribution pipe and the extent of plug flow in the reactor are monitored. Methods for monitoring the even distribution of the influent wastewater across the distribution pipe and the extent of plug flow in the reactor are described in more detail below.

[0061] In particular, when a suboptimal distribution of the influent wastewater across the distribution pipe is detected during step (a) of the method according to the invention, the influent distribution system is cleaned. If a suboptimal degree of plug flow is detected during step (a), the influent distribution system and / or the outflow decanter system are cleaned.

[0062] Methods known in the art for the aerobic biological treatment of wastewater in CAS-VPF or AGS-VPF reactors are carried out without such monitoring of the even distribution of influent wastewater across the distribution pipe and / or the degree of plug flow within the reactor, a drawback of which is that it remains unclear whether the methods are carried out under optimal plug flow conditions or not. As a result, if these methods are carried out under suboptimal plug flow conditions, resulting in a deterioration of treated water quality, it remains undetected and no action is taken to improve these conditions.

[0063] When the degree of plug flow is monitored during step (a), suboptimal plug flow conditions can be detected as follows: First, when the reactor is initially operated, or after extensive cleaning of the inlet distribution system (also called distribution grid) and the outlet decanter, the amount of wastewater inflow that can be fed to the reactor in step (a) before contaminant or temperature breakthrough occurs is determined. This amount is called the initial influent amount and represents the optimal (ideal) plug flow conditions. Second, during continued operation of the reactor, the amount of wastewater inflow that can be added to the reactor in step (a) before contaminant or temperature breakthrough occurs is measured. The amount of wastewater inflow monitored during continued operation of the reactor is compared to the initial amount of wastewater inflow. If the amount of wastewater inflow monitored during continued operation is more than 25% lower than the initial amount of wastewater, the plug flow conditions are considered suboptimal. Under optimal plug flow conditions, the wastewater inflow rate monitored during continued operation is at most 25% less than the initial wastewater rate, preferably at most 20% less, more preferably at most 15% less, even more preferably at most 10% less, even more preferably at most 5% less, and most preferably at most 2% less. The determination of the amount of wastewater inflow that can be fed to the reactor in step (a) before contaminant or temperature breakthrough occurs is described in more detail below.

[0064] If during step (a) of the method according to the invention, an even distribution of the influent wastewater across the distribution pipes is monitored, a suboptimal distribution can be detected by comparing the flows and / or pressures in two or more distribution pipes with each other. If one or more monitored distribution pipes show a value that deviates from the average value of all monitored distribution pipes by more than 25%, the even distribution is considered suboptimal, i.e. unequal distribution occurs. If the distribution of the influent wastewater across the distribution pipes is even, two or more monitored distribution pipes all show values ​​for flow and / or pressure that deviate from the average value of all monitored distribution pipes by at most 25%, preferably at most 20%, more preferably at most 15%, even more preferably at most 10%, even even more preferably at most 5% and most preferably at most 2%.

[0065] Figure 1A shows the concentration profiles at times t1, t2 and t3 when plug flow conditions are good, and Figure 1B shows the concentration profiles at times t1, t2 and t3 when plug flow conditions are bad. Figures 1A and 1B show a side view of a VPF reactor, which includes a distribution pipe (3) with a nozzle outlet (4) and is connected to a vertical vent pipe (8) and an (optional) end cap (9). The reactor further includes an effluent decanter system (5) with an opening (6) for decanting the treated wastewater effluent.

[0066] A schematic diagram of optimal plug flow characteristics is shown in FIG. 1A, showing the concentration profiles at times t1, t2 and t3 when plug flow conditions are good. FIG. 1A shows diagrammatically how the interface profile between the introduced raw wastewater and the treated wastewater in the reactor develops over time during step (a) in the method and reactor according to the invention. The wastewater influent is introduced through one or more distribution pipes (3) equipped with one or more nozzle outlets (4). As time progresses from t1 to t2 and t3, the interface profile is regular and moves upwards, as a result of good vertical plug flow characteristics. This is shown for t1 in the left part of FIG. 1A, for t2 in the middle part, and for t3 in the right part of FIG. 1A. At time t3, this profile reaches one or more openings (6) of the effluent decanter system (5), also called overflow weir, and breakthrough begins, and a small portion of the raw wastewater is discharged from the reactor together with the treated effluent.

[0067] A schematic diagram of suboptimal plug flow characteristics is shown in Figure 1B, showing the concentration profiles at times t1, t2 and t3. Figure 1B shows diagrammatically how the concentration profile develops when the plug flow characteristics are poor, because wastewater is treated by a prior art method without monitoring plug flow conditions and / or even distribution of the wastewater influent across the bottom of the reactor, due to severe blockage of one or more distribution pipes (3) with one or more nozzle outlets (4) and / or blockage of one or more openings (6) of the outflow decanter system (5). The resulting interface profile is irregular, and breakthrough begins already at t2.

[0068] Thus, the method according to the invention comprises: The wastewater to be treated (wastewater influent) is introduced into a vertical plug flow reactor, which may be a CAS-VPF or AGS-VPF reactor, via a distributor, such that an even distribution of the wastewater across the bottom of the reactor is achieved, and treated wastewater (treated wastewater effluent) is simultaneously decanted at an operating level at the top of the reactor, resulting in a vertical plug flow, while · monitoring that even distribution of wastewater across the distributor is achieved and / or that the maximum level of plug flow practically achievable is achieved; If non-optimal distribution and / or non-optimal plug flow are detected and dirt, blockages, entrained air, etc. are removed by cleaning the distributor and / or the treated water decanter, thus Ensuring that the CAS-VPF or AGS-VPF reactor is operated at an optimum degree of plug flow and exchange ratio (ER); It is characterized by:

[0069] In a preferred embodiment of the method according to the invention, the wastewater inflow distribution system comprises two or more distribution pipes. Each distribution pipe comprises one or more nozzle outlets, preferably directed downwards. As mentioned above, more preferably, 0.5-50 nozzle outlets are provided per m 2per reactor bottom surface. In a more preferred embodiment, two or more distribution pipes are connected to a common manifold or header.

[0070] In one embodiment, the m of the reactor bottom surface 2 In some embodiments, there are 0.25-50 nozzle outlets per nozzle, and in other embodiments, there are 0.25-25 nozzle outlets per nozzle.

[0071] If suboptimal distribution or a suboptimal degree of plug flow is detected during step (a), the inlet distribution system and / or the outlet decanter system are cleaned by removing dirt and / or blockages. In particular, if suboptimal distribution of the inlet wastewater across the distribution pipe is detected, the inlet distribution system is cleaned. If a nonoptimal degree of plug flow is detected, the inlet distribution system and / or the outlet decanter system are cleaned.

[0072] In a particular embodiment of the method according to the invention, the inflow distribution system is cleaned by: (i) draining the reactor and manually cleaning one or more of the distribution pipes and their nozzles; or (ii) lifting one or more distribution tubes for manual cleaning; or (iii) inserting an internal pipe cleaning device (e.g., a pipe pig, a cleaning robot, or a hydrojet) into the header; or (iv) temporarily increasing the flow rate through the inlet distribution system.

[0073] Where the inlet distribution system comprises two or more distribution pipes connected by a manifold or header, it is preferred that said header comprises the inlet for the cleaning device.

[0074] When cleaning is performed by method (i), the CAS-AGF or AGS-VPF reactor is drained and the distribution pipes and nozzles are manually cleaned. Draining the VPF reactor is disadvantageous and therefore cleaning method (i) is not preferred.

[0075] When cleaning is performed via method (ii), the distribution pipe(s) are connected to the main pipe or channel with the incoming wastewater by a flexible connection, allowing the distribution pipe(s) to be elevated for manual cleaning. Draining of the reactor is not required, and wastewater treatment operations can continue while maintaining the elevated distribution pipe(s).

[0076] The cleaning method (iii) comprises the step of inserting an in-pipe cleaning device into said header or manifold. In-pipe cleaning devices are known in the art. Examples include pipe pigs, pipe cleaning robots, hydro jets, etc. For this purpose, the header is preferably equipped with one or more isolation valves that allow the introduction and removal of the cleaning device without the need to drain the reactor.

[0077] In a variation of this embodiment (FIG. 8), the inlet distribution pipe (3) or the feed header to which the distribution pipe header is connected is routed so that part of the header is above the water level in the reactor, allowing evaluation of the inside of the pipe without draining the reactor or requiring an isolation valve. This embodiment is shown in FIG. 8, where the inlet distribution pipe (3) is fed through a header (10). The header (10) is placed at least partially above the water level in the reactor. Wastewater (2) is fed to the distribution pipe (3) through the pipe (2) and the header (10). Cleaning of the distribution pipe (3) can be done from the top side through the header (10).

[0078] In method (iv), flushing of the distribution pipes is established by temporarily increasing the flow rate through the inlet distribution system, for example for a period of 5-30 minutes. Such a temporary increase can be achieved, for example, by temporarily increasing the overall wastewater flow or, more preferably, by closing one or more distribution pipes from the inlet distribution system such that the overall wastewater flow is distributed to the reactor through fewer distribution pipes.

[0079] In a preferred embodiment of the method according to the invention, the input distribution system is cleaned by method (ii), (iii) or (iv), more preferably by method (iii) or (iv).

[0080] Cleaning of outflow decanter systems is typically performed manually, for example by hosing, pressure hosing, raking and / or brushing.

[0081] The size of the distribution pipe or pipes and the number and size of the nozzle outlets depend on the wastewater composition, wastewater flow and reactor size. Typically, the diameter of the distribution pipes is 100-1000 mm. The number of distribution pipes depends on the wastewater characteristics and the size of the VPF reactor. Smaller reactors may only have one or two distribution pipes, whereas larger reactors can have tens or even hundreds. To ensure that good plug flow conditions are obtained, the number of distribution pipes in the reactor and the distance between them, as well as the number of nozzle outlets per distribution pipe and the distance between them, should be such that the total number of nozzle outlets does not exceed 100 m of the reactor bottom surface. 2 The optimum number depends on the wastewater characteristics and the target quality of the wastewater to be treated. In one embodiment, the number of m of the bottom surface of the reactor is in the range of 0.5-50. 2 In some embodiments, there are 0.25-50 nozzle outlets per nozzle, and in other embodiments, there are 0.25-25 nozzle outlets per nozzle.

[0082] If two or more distribution pipes are used, they may be connected to a common manifold, also called a header. This header may be located inside or outside the VPF reactor. The connection of the header to the raw wastewater channel or pump may be made by leading one or more pipes through or across the reactor wall and connecting them to the distribution pipes or manifold / header pipes at the bottom of the reactor.

[0083] In a preferred embodiment of the method according to the invention, each distribution pipe is connected to a distribution pipe manifold or header. In another embodiment, the entrainment and accumulation of air in the distribution system is prevented by routing the header to which the distribution pipes or distribution pipe headers are connected such that a portion of said header is above the water level in the reactor. A static head in the header prevents air entrainment into the header. Optionally, the inlet of a cleaning device is placed in the header.

[0084] The distribution pipes and nozzle outlets distribute the untreated wastewater evenly over the reactor surface during the filling / decanting stage of the AGS-VPF or CAS-VPF. If the nozzle outlets of one or more distribution pipes are directed downwards, i.e., toward the reactor bottom, the wastewater influent flow initially directed downwards is diverted by the reactor bottom into a vertical upward flow toward the reactor water surface, where it overflows into a treated wastewater effluent decanter containing an overflow opening and / or a weir. The treated wastewater effluent is discharged as wastewater after purification. The number of effluent decanters depends on the wastewater characteristics and the size of the CAS-VPF or AGS-VPF. Smaller reactors are equipped with only one or two effluent decanters, whereas larger reactors can be equipped with 10 or even 50 effluent decanters or more.

[0085] The combination of an even distribution of the wastewater effluent at the bottom of the reactor via one or more distribution pipes and the discharge of the treated wastewater effluent at the top of the reactor through a well-distributed effluent decanter provides excellent hydraulic plug flow conditions. This allows a large part of the reactor volume to be discharged by the fed raw wastewater influent without the breakthrough of the raw wastewater affecting the quality of the discharged treated wastewater. Depending on the number of nozzle outlets and effluent decanters, typically up to 65-70% of the reactor volume can be discharged (this is the so-called exchange ratio, also called ER), while the reactor requires only 1-10 m per reactor cross-section. 3 / h of wastewater flow.

[0086] For CAS-VPFs and AGS-VPFs targeting very stringent effluent requirements, or utilizing relatively shallow reactors with water heights of less than 5 m, this maximum volumetric displacement before breakthrough can be reduced to 40-55%, still significantly higher than the typical 20-30% obtained with prior art processes.

[0087] In a preferred embodiment of the method according to the invention, in step (a), the even distribution of the wastewater influent across the distribution pipe results in a plug flow to the extent that at least 30% of the reactor volume is discharged towards the treated wastewater outflow decanter system without significant breakthrough of raw wastewater. More preferably, more than 50%, even more preferably more than 60%, and most preferably more than 70% of the reactor volume is discharged towards the treated wastewater outflow decanter system without significant breakthrough of raw wastewater.

[0088] In a particularly preferred embodiment of the method according to the invention, in the inflow distribution system, a vertical vent pipe is connected to each distribution pipe, which ends above the operating water level of the reactor in order to release the air and / or oxygen entrained in the distribution pipe. The air and / or oxygen (or other oxygen-containing gas) used during the aeration step (b) may be entrained in the distribution system during the aeration step. The entrained air and / or oxygen may prevent an even distribution of the wastewater influent across the bottom surface of the reactor during step (a) of the next cycle of the method according to the invention, resulting in suboptimal plug flow conditions. It is therefore preferred that the entrained air and / or oxygen is removed from the distribution system. By connecting a vertical vent pipe to each distribution pipe of the inflow distribution system, the entrained air and / or oxygen is released from the system during step (a).

[0089] Thus, in a particularly preferred embodiment, the present invention relates to a method for treating wastewater in a biological treatment reactor comprising the steps of: (a) introducing inflowing wastewater into the bottom of said reactor while simultaneously decanting outflowing treated wastewater effluent at an operating level at the top of said reactor; (b) an aeration step; (c) a settling step to allow the biomass to settle; Including, Step (a) is carried out under vertical plug flow conditions achieved by introducing wastewater influent into said reactor through an inlet distribution system comprising one or more distribution pipes, said one or more distribution pipes preferably including one or more nozzle outlets oriented downwardly and positioned to provide an even distribution of the influent wastewater across a bottom surface of said reactor, discharging treated wastewater effluent through an effluent decanter system configured to discharge evenly across an operating level at the top of said reactor, a vertical vent pipe connected to each distribution pipe of the inlet distribution system and terminating above the operating level of the reactor for releasing air and / or oxygen entrained in the distribution pipes, During step (a), the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow within the reactor are monitored, and when suboptimal distribution or suboptimal plug flow is detected, the influent distribution system and / or effluent decanter system are cleaned by removing fouling and / or blockages. When suboptimal distribution of the influent wastewater across the distribution pipes is detected, the influent distribution system is cleaned.

[0090] If a suboptimal degree of plug flow is detected, the inlet distribution system and / or the outlet decanter system are cleaned. Also in this embodiment, the method may include further steps, as described in more detail above. In particular, the method according to this embodiment may further include steps (i) and (d), as described in more detail above. The method may include one or more cycles.

[0091] In this particularly preferred embodiment, i.e. when the method according to the invention is carried out with a distribution system in which a vertical vent pipe is connected to each distribution pipe of the inflow distribution system, cleaning of the distribution pipes is preferably carried out by inserting a high pressure lance or an alternative mechanical or hydraulic mechanical device for pipe cleaning into the vent pipe, as will be explained in more detail later. Mechanical or hydraulic mechanical devices for pipe cleaning are known in the art and include, for example, pipe cleaning robots, power drives, snakes, etc.

[0092] An example of an inflow distribution system applied in this embodiment of the method according to the invention is shown in FIGS.

[0093] Figures 2, 3 and 4 show various cross-sectional views of a vertical plug flow reactor (1) in which untreated wastewater is fed to the bottom of the reactor via one or more distribution pipes (3) with outlet downstream nozzles (4). As explained in more detail above, the number and size of the distribution pipes and the number and size of the nozzle outlets depend on the wastewater composition, the wastewater stream and the size of the VPF reactor.

[0094] If more than one distribution pipe is used, they may be connected to a common manifold or header. This header may be located inside or outside the VPF reactor. Connection of the header to the raw wastewater channel or pump may be through the reactor wall as shown in Figures 2 and 4, or by passing one or more pipes through the reactor wall and connecting to a distribution pipe or manifold / header pipe (10) at the top of the reactor (Figure 8).

[0095] An important feature in this preferred embodiment of the method according to the invention is that each distribution pipe (3) of the inlet distribution system is equipped with a vertical vent pipe (8) that extends well above the operating water level of the CAS-VPF or AGS-PVF. The vent pipe ensures that the air entrained in the distribution pipe during the aeration phase of the treatment cycle is released. This is very important, since such air entrainment would otherwise cause an uneven distribution of the wastewater, resulting in a significantly reduced plug flow characteristic, a lower achievable exchange ratio and a larger required reactor volume. To prevent the released air from causing unsafe spraying into the passages or surroundings, each vent pipe is optionally equipped with a removable end cap (9) with a vertically positioned opening or a U-shaped bend (9) with an open end. The height of the vent pipe above the reactor water surface depends on the maximum pressure that occurs in the distribution pipe when feeding the maximum designed value for the water flow.

[0096] Another important feature is that the vent pipes allow for effective monitoring of the distribution pipes' condition and fouling levels or blockages. During the feeding of the VPF reactor, the pressure in the vent pipes is similar to the pressure in the distribution system, which is higher than the pressure at the bottom of the reactor. The pressure in the distribution system can be monitored by measuring the water level in the vent pipes, which should be higher than the reactor top water level. If all distribution pipes are clean and air-free, the water levels in all vent pipes will be the same. If a distribution pipe is fouled or the nozzle outlet is blocked, the water level in the corresponding vent pipe will be higher than the others. According to the method of the present invention, the water level in the vent pipes is monitored by manually registering or measuring the water level in the vent pipes. If the level / pressure of one or more vent pipes differs from the others or from the values ​​corresponding to a recently cleaned distributor receiving the same flow rate, the even distribution and thus the optimal plug flow conditions are threatened. The affected distribution pipes need to be cleaned to protect the proper plug flow and wastewater treatment capacity.

[0097] Thus, in a preferred embodiment of the method according to the invention, in step (a), the even distribution of the wastewater influent across the distribution pipe is monitored by measuring one or more of the water level, pressure, temperature and / or one or more other suitable parameters in the vent pipe, including for example pH, conductivity, turbidity and redox potential.

[0098] In a preferred embodiment, the vent pipe is equipped with a water level and / or pressure gauge. In a further preferred embodiment, these gauges are connected to the plant control system which will activate an alarm when a pressure / level difference is detected between the vent pipe itself and / or between the vent pipe and the historical value of the clean distributor.

[0099] In another preferred embodiment, as an alternative or in addition to flow, pressure or water level, the vent pipe and / or distribution pipe are equipped with a distribution temperature sensing cable (DTS) or similar sensing device to detect uneven temperature distribution throughout the pipe. As with flow, pressure or water level, such uneven temperature distribution is indicative of uneven water distribution throughout the distribution pipe.

[0100] In another (less preferred) embodiment, the distribution pipes (as opposed to vent pipes connected to the distribution pipes) are equipped with pressure or flow meters, which are used to monitor whether unequal distribution occurs. In this embodiment, in step (a), equal distribution of the wastewater influent across the distribution pipes is monitored by measuring the flow and / or pressure in two or more distribution pipes.

[0101] In accordance with the method of the present invention, when unequal distribution of wastewater influent across the reactor bottom surface is detected, the distribution tube is cleaned.

[0102] Another important purpose of the vent pipes (8) in this preferred embodiment is to allow easy access to each distribution pipe for cleaning, to remove dirt and / or blockages as needed. Such removal of dirt and / or blockages can be accomplished using, for example, a high pressure lance, or alternative mechanical or hydro-mechanical devices, which can enter through an opening at the top of the vent pipe and move into the corresponding distribution pipe. High pressure lances are known in the art, as are alternative mechanical or hydro-mechanical devices for pipe cleaning, including, for example, pipe cleaning robots, power drives, snakes, and the like.

[0103] The fouling removed by the high pressure lance or alternative cleaning device flows through the nozzle outlet to the AGS-VPF or CAS-VPF and is periodically removed together with the excess sludge. By doing so, fouling and clogging of the distribution pipes is effectively prevented or easily resolved and does not result in a decrease in performance or a decrease in the treatment capacity caused by suboptimal plug flow characteristics and / or suboptimal exchange ratios. Moreover, such cleaning operations are relatively simple, not time consuming and can be carried out during normal operation without the need to empty or stop the AGS-VPF or CAS-VPF. In small reactors with only one or two distribution pipes, such cleaning is carried out while the VPF reactor is in aeration or settling mode. For larger reactors with several distribution pipes, cleaning can also be carried out during the feed phase. An additional advantage is that the diameter of the vent pipe only needs to be large enough to allow access to the high pressure lance or alternative cleaning device, often 50-100 mm. The diameter of the vent pipe can therefore be much smaller than the diameter of the distribution pipe, resulting in a cost-effective construction. Additionally, the vent tube may be configured as a flexible tube or hose, further reducing costs.

[0104] In the method according to the invention, during step (a), the even distribution of the influent wastewater across the distribution pipes and / or the degree of plug flow within the reactor are monitored and when suboptimal distribution or a suboptimal degree of plug flow is detected, the influent distribution system and / or the outflow decanter system are cleaned by removing fouling and / or blockages.

[0105] By doing so, even distribution and optimum plug flow are preserved and the AGS-VPF can be operated at the maximum practically achievable exchange ratio, providing maximum hydraulic throughput.

[0106] In a preferred embodiment, as described in more detail above, the even distribution of influent wastewater across the distribution pipes is monitored.

[0107] In another preferred embodiment, the degree of plug flow within the reactor is monitored.

[0108] This will be explained in more detail later.

[0109] In another preferred embodiment, both the even distribution of influent wastewater across the distribution pipes and the degree of plug flow within the reactor are monitored.

[0110] The degree of plug flow achieved in the reactor can be monitored during step (a) of the method by measuring a profile of a suitable parameter from the bottom to the top of the reactor at different times throughout step (a). In this regard, suitable parameters are parameters that have different values ​​for the untreated wastewater influent delivered to the reactor and the treated wastewater effluent discharged from the reactor. Suitable parameters include, for example, COD (chemical oxygen demand), concentrations of contaminants such as ammonium and phosphate. In such cases, concentration profiles of such contaminants may be measured. Additional suitable parameters include, for example, turbidity, pH, redox potential, conductivity, temperature, etc.

[0111] These profiles show how the interface between the incoming wastewater and the treated water moves up during the feeding operation. This is illustrated in Figure 5, which shows how the profiles are determined by collecting grab water samples and measuring certain parameters at various times during step (a) at various sample points in the reactor and at various heights, thus monitoring the position of said interface in time and height between the incoming wastewater and the treated water. Finally, at a certain time and corresponding ER, this interface reaches the outflow decanter system, reducing the quality of the discharged water. This method is labor intensive.

[0112] In a preferred embodiment of the process according to the invention, during step (a) the degree of plug flow in the reactor is monitored by determining a profile of a suitable parameter across the reactor from the bottom to the top of the reactor. Said suitable parameter profile is preferably determined during step (a) by measuring said parameter several times across the reactor from the bottom to the top of the reactor.

[0113] This is illustrated in Figure 5. Suitable parameters are for example turbidity, pH, redox potential, conductivity or temperature, or the concentration of a pollutant, preferably chemical oxygen demand (COD), ammonium or phosphate.

[0114] Determining the parameter profile can be performed by manually sampling at various times during the reactor feed operation and using these samples to analyze one or more parameters / concentrations. In a more preferred embodiment, one or more parameters are measured online by probes connected to cables that are moved manually or automatically to different heights in the CAS-VPF or AGS-VPF reactor during step (a). In another embodiment, a DTS (Distributed Temperature Sensing) cable or similar sensor equipment is used to determine the profile across the reactor levels.

[0115] As explained in more detail above, the monitored plug flow characteristics or ER are compared to the characteristics of a non-fouled / non-blocked distribution. If suboptimal plug flow conditions are determined, corrective actions are initiated. These corrective actions include cleaning of one or more of the distribution pipes and nozzles as described above, and / or cleaning of the effluent decanter system, as poor plug flow conditions can also be caused by uneven collection of decanter water across the operating water level surface at the top of the reactor.

[0116] In another preferred embodiment, the plug flow characteristics are monitored by measuring one or more suitable parameters at one or more fixed locations and heights in the reactor. For example, FIG. 6 shows how a profile of a suitable parameter is determined at a fixed distance, e.g., 1 m, from the bottom of the reactor using an analyzer or probe. As an example, the ammonium concentration can be determined, for example, by an ion-selective probe. Since the concentration of this parameter in the inflowing wastewater is higher than that in the process water displaced by the plug flow feed, the monitoring can detect when the interface between the introduced wastewater and the process water reaches the probe and calculate the corresponding ER when this occurs. This calculation takes into account measurement delays such as delays due to probe reaction times, processing of the sample in the sample line and the on-line analyzer. According to the method of the present invention, the monitored plug flow characteristics, i.e., ER, are compared to those for an unfouled / unblocked distribution and compared to the above-mentioned corrective measures that are initiated if a reduction in plug flow is determined.

[0117] In another preferred embodiment, the parameters are measured near the bottom of the reactor, preferably 0.5-3 m or 0.5-1.5 m from the bottom, and near the effluent decanter, preferably 0-3 m or 1-3 m below the decanter. If the interface is detected by both probes, this allows to distinguish whether a reduction in plug flow is due to unequal distribution of the wastewater influent or unequal release of treated wastewater effluent.

[0118] In another preferred embodiment, the plug flow characteristics are monitored by using one or more online measurement devices placed only near the effluent decanter, such as 0-3 m or 1-3 m below the decanter, so that these devices can also be used to monitor the quality of the discharged treated water.

[0119] FIG. 7 shows how a suitable parameter profile is determined using a probe or analyzer at a certain distance h2, e.g., 0-3 m, from the reactor overflow weir opening at the top of the reactor. For example, an ammonium analyzer may be used. Since the amount of wastewater being treated can vary widely during the day and can be affected by rain for treatment plants connected to combined sewers, the location of the equipment is selected such that during maximum flow, the interface reaches or reaches beyond the equipment location. If such maximum flow occurs very infrequently, such as less than once a year or less than once a month, periodically, such as once a month, the duration of step (a) into the reactor for one cycle is increased to determine at which ER breakthrough begins or the height of the equipment sample is adjusted for one cycle.

[0120] Thus, in a preferred embodiment of the method according to the invention, the extent of plug flow in the reactor during step (a) is monitored by measuring one or more suitable parameters at one or more fixed locations in the reactor. The one or more suitable parameters are, for example, the concentration of pollutants (preferably chemical oxygen demand (COD), ammonium or phosphate concentration), turbidity, pH, redox potential, conductivity and / or temperature. If the measurement of one or more suitable parameters is performed at two or more locations in the reactor, the locations may, for example, be located at different heights of the reactor. The locations may also be located at the same height of the reactor, for example near the bottom of the reactor or near the effluent decanter. In a preferred embodiment, the extent of plug flow is monitored by one or more online measuring devices located below the effluent decanter system, preferably 0-3 m, more preferably 1-3 m. In a further preferred embodiment, a DTS cable or similar sensor device is used to determine the profile across the reactor levels.

[0121] Alternatively, in another preferred embodiment of the method according to the invention, the degree of plug flow in the reactor during step (a) is monitored by measuring one or more suitable parameters at one or more different locations in the reactor. The one or more suitable parameters are, for example, the concentration of pollutants (preferably chemical oxygen demand (COD), ammonium or phosphate concentration), turbidity, pH, redox potential, conductivity and / or temperature. If the measurement of the one or more suitable parameters is performed at two or more locations in the reactor, the one or more parameters may be measured in-line by an instrument connected to a cable that is moved manually or automatically to different heights in the CAS-VPF or AGS-VPF reactor during step (a). In a further preferred embodiment, a DTS cable or similar sensor device is used to determine the profile across the reactor levels.

[0122] The method for treating wastewater in a biological treatment reactor according to the invention solves the aforementioned drawbacks of the methods known from the prior art. By using a cost-effective structure, the method according to the invention not only ensures that wastewater is distributed to the CAS-VPF and AGS-VPF reactors, but also protects optimal distribution of the wastewater influent across the reactor bottom surface and thus optimal plug flow conditions during VPF reactor operation. This is achieved by actively monitoring the distribution of the wastewater influent across the reactor bottom surface and / or the achieved plug flow conditions. If suboptimal conditions are detected, the distribution pipe is cleaned and / or air accumulated during normal operation is removed from the distribution pipe, preferably without interrupting the wastewater treatment method or interfering with its performance. The present invention effectively eliminates the drawbacks of the prior art and makes it possible to:

[0123] · To obtain a hydraulically superior vertical plug flow regime resulting in equal distribution of wastewater influent across the CAS-VPF and AGS-VPF reactors and performance at maximum capacity of the VPF reactors.

[0124] Monitoring the achieved distribution levels of wastewater influent across the reactor bottom surface and / or the resulting plug flow conditions and correcting suboptimal distribution / plug flow, e.g. through fouling, blockages or air accumulation, before the reactor capacity is affected, preferably without interfering with treatment performance or creating the need to switch off the reactor. This ensures that distribution and plug flow are optimized during reactor operation. - Reducing the volume and construction cost of the VPF reactor by achieving a high exchange ratio. Prevents air from being entrained in the distribution pipe during the aeration stage of the reactor, resulting in suboptimal distribution. · The ability to clear fouling or blockages in the distribution pipes without having to shut down and empty the AGS reactor. ·Cost-effective to build and reduce maintenance costs.

[0125] Thus, even distribution and optimal plug flow are preserved by the method according to the invention. Thus, the AGS-VPF or CAS-VPF reactor can be operated at the practical maximum feasible exchange ratio, providing maximum hydraulic throughput.

[0126] Liquid Distribution Systems

[0127] The present invention also relates to a liquid distribution system. A liquid distribution system is defined herein as a device used to introduce a liquid, preferably an aqueous liquid, into a reactor. The liquid distribution system according to the present invention is preferably used to introduce a liquid into a vertical plug flow (VPF) reactor, in particular a CAS-VPF or AGS-VPF reactor used in the aerobic treatment process of wastewater. The liquid distribution system is placed at or near the bottom surface of the reactor. The liquid distribution system used in the aerobic treatment process of wastewater according to the present invention is also called an inflow distribution system.

[0128] Accordingly, the present invention also relates to a liquid distribution system comprising one or more distribution pipes, each of which is provided with one or more nozzle outlets arranged to provide an even distribution of the influent wastewater across the bottom surface of the reactor, and a vertical vent pipe connected to each distribution pipe.

[0129] The liquid distribution system of the present invention corresponds to a preferred embodiment of the wastewater inflow distribution system used in the wastewater treatment method of the present invention, said method being as described above.

[0130] The length of the vertical vent pipe depends on the height of the reactor, in particular on the height of the liquid level during operation of the reactor with the liquid distribution system. During operation, the vertical vent pipe or pipes of the liquid distribution system must extend above the operating liquid level of the reactor with the liquid distribution system in order to release the air or oxygen entrained in the corresponding distribution pipe or pipes. The height of the vent pipe above the reactor liquid surface depends on the maximum pressure that will be generated in the distribution pipes when supplying the maximum designed value for the water flow.

[0131] As mentioned above, the vertical aeration pipes ensure that the air entrained during the aeration phase of the treatment cycle is released into the corresponding distribution pipes, which is very important since such air entrainment would otherwise cause unequal distribution of the wastewater, resulting in a significantly reduced plug flow characteristic, lower achievable exchange ratios and larger required reactor volumes.

[0132] The use of the liquid distribution system according to the invention in the method for treating wastewater in a biological treatment reactor according to the invention as well as some advantages of said method due to the liquid distribution system have been described in detail above. It should be noted that the preferred embodiments of the wastewater inflow distribution system in the method of the invention correspond to the preferred embodiments of the liquid distribution system of the invention. Some preferred embodiments will now be described in more detail.

[0133] The connection between the vent pipe and the distribution pipe should be such that air can escape from the distribution pipe and the cleaning device can be injected into the distribution pipe through the vent pipe. Cleaning of the distribution pipe via the vent pipe has also been described in more detail above. Some options for the connection of the vent pipe (8) and the distribution pipe (3) are shown in Figure 9.

[0134] In a preferred embodiment of the liquid distribution system according to the invention, the one or more nozzle outlets on each distribution pipe are directed downwards. In another preferred embodiment, the liquid distributor system according to the invention comprises two or more distribution pipes. In another preferred embodiment, each distribution pipe in the liquid distribution system comprises two or more nozzle outlets.

[0135] As described above for the method according to the invention, the size of the distribution pipe or pipes of the liquid distribution system and the number and size of the nozzle outlets on each distribution pipe depend on the wastewater composition, the wastewater flow and the reactor size. Typically, the diameter of the distribution pipes is 100-1000 mm. The number of distribution pipes depends on the wastewater characteristics and the size of the VPF reactor. Smaller reactors may only be equipped with one or two distribution pipes, whereas larger reactors can have tens or even more than 100. To ensure that good plug flow conditions are obtained, the number of distribution pipes in the reactor and the distance between them, as well as the number of nozzle outlets per distribution pipe and the distance between them, should be determined so that the total number of nozzle outlets does not exceed m of the reactor bottom surface. 2 The optimum number depends on the wastewater characteristics and the target quality of the treated wastewater. In one embodiment, the number of m of the bottom surface of the reactor is in the range of 0.5-50. 2 In some embodiments, there are 0.25-50 nozzle outlets per nozzle, and in other embodiments, there are 0.25-25 nozzle outlets per nozzle.

[0136] Preferably, each distribution pipe of the liquid distribution system is connected to a distribution pipe manifold, also called a header.

[0137] Additionally, each vent pipe of the liquid distribution system preferably includes a removable end cap with a vertically positioned opening, or a U-shaped bend with an open end that directs potential water spray toward the water surface and away from walkways, access podiums, and the like.

[0138] In another preferred embodiment of the liquid distribution system, two or more vertical vent pipes are bundled together to reach the same location on the reactor wall or to reach an access platform, walkway or platform at the top of the reactor.

[0139] As also mentioned above, in the liquid distribution system, each vent line is preferably equipped with a water level gauge, a pressure gauge and / or a temperature sensor (preferably a distribution temperature sensing (DTS) cable).

[0140] The present invention also relates to the use of the liquid distribution system according to the invention in a process for the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor. The present invention in particular relates to the use of the inflow distribution system according to the invention in a process for the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor according to the invention. In a preferred embodiment, the liquid distribution system is used in a process for the aerobic treatment of wastewater in an AGS-VPF reactor or a CAS-VPF reactor.

[0141] The liquid distribution system according to the present invention overcomes the above-mentioned shortcomings of existing wastewater distributors: it not only ensures that wastewater is distributed to the CAS-VPF or AGS-VPF reactors using a cost-effective construction, but also allows monitoring of the distribution of wastewater influent across the reactor surface during AGS-VPF source reactor operation without interrupting the wastewater treatment process or disturbing its performance, and also ensures optimal distribution and plug flow by allowing accumulated air to be removed from the distribution pipes during normal operation.

[0142] Facilities for treating wastewater

[0143] The invention also relates to an installation for carrying out the method according to the invention, i.e. the treatment of wastewater in a biological treatment reactor. Said method is described in detail above. The installation comprises a liquid distribution system according to the invention. Said liquid distribution system is also described in detail above.

[0144] The equipment according to the invention comprises a reactor having a liquid inlet system at the bottom of the reactor, a liquid outlet system at the top of the reactor, and a gas inlet at the bottom of the reactor, the liquid inlet system comprising one or more distribution pipes, each of said one or more pipes comprising one or more nozzle outlets arranged to provide an even distribution of liquid across the bottom surface of the reactor, and a vertical vent pipe connected to each distribution pipe, the vertical vent pipe terminating above the operating water level of the reactor for releasing air entrained in the distribution pipes.

[0145] It should be noted that the equipment used in the preferred embodiments of the method according to the invention, as explained in detail above, corresponds to the preferred embodiments of the equipment according to the invention. Some preferred embodiments will now be explained in more detail.

[0146] In a preferred embodiment, the liquid inlet system comprises two or more distribution pipes. Preferably, each distribution pipe of the liquid inlet system comprises two or more nozzle outlets. Further, it is preferred that one or more of the nozzle outlets in each distribution pipe are directed downwards.

[0147] In the installation according to the invention, in the liquid inlet system, the distance between the nozzle outlets in the distribution pipe is in the range of 0.5-10 m and / or the distance between the nozzle outlets in the distribution pipe is in the range of m of the bottom surface of the reactor. 2 Preferably there are 0.5-50 nozzle outlets per nozzle.

[0148] Preferably, each distribution pipe in the liquid inlet system is connected to a distribution pipe manifold. Also, each vent pipe is preferably equipped with a removable end cap with a vertically positioned opening, or a U-shaped bend with an open end. In a preferred embodiment, each vent pipe is equipped with a water level gauge, a pressure gauge and / or a temperature sensor, preferably a distributed temperature sensing (DTS) cable.

[0149] Preferably, the installation further comprises means for determining a suitable parameter profile across the reactor from the bottom to the top of the reactor. Suitable parameters are for example the concentration of pollutants (preferably chemical oxygen demand (COD), ammonium or phosphate), turbidity, pH, redox potential, conductivity or temperature. Said means may for example be an analyzer or probe for determining said parameters. The determination of the suitable parameter profile is described in detail above for the method of the invention and the preferred embodiments described for the method of the invention apply analogously to the installation of the invention. Thus, the installation according to the invention preferably comprises an analyzer or probe for determining a suitable parameter profile. Suitable parameters are preferably the concentration of pollutants (preferably chemical oxygen demand (COD), ammonium or phosphate), turbidity, pH, redox potential, conductivity and / or temperature.

[0150] The invention further relates to the use of the installation according to the invention in the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor. In particular, the installation according to the invention is used in the method for treating wastewater according to the invention.

[0151] The invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible and fall within the scope of protection defined in the appended claims.

Claims

1. 1. A method for treating wastewater in a biological treatment reactor, comprising: (a) introducing wastewater inflow into the bottom of the reactor while simultaneously decanting treated wastewater effluent exiting at an operating level at the top of the reactor; (b) an aeration step; (c) a settling step for settling the biomass; Including, Step (a) is carried out under vertical plug flow conditions achieved by introducing wastewater influent into said reactor through an inlet distribution system comprising one or more distribution pipes, said one or more pipes preferably including one or more nozzle outlets oriented downwards and arranged to provide an even distribution of the influent wastewater across a bottom surface of said reactor, and discharging treated wastewater effluent through an effluent decanter system configured to discharge the treated wastewater effluent evenly across an operating water level at the top of said reactor; A method wherein during step (a), the even distribution of influent wastewater across said distribution pipes and / or the degree of plug flow within the reactor are monitored, and when suboptimal distribution or suboptimal plug flow is detected, the influent distribution system and / or the outlet decanter system are cleaned by removing fouling and / or blockages.

2. The method of claim 1 , wherein the inlet distribution system comprises two or more distribution pipes connected to a common manifold or header.

3. The inflow distribution system comprises: (i) draining the reactor and manually cleaning one or more of the distribution pipes and their nozzles; or (ii) lifting one or more distribution tubes for manual cleaning; or (iii) inserting an internal pipe cleaning device (e.g., a pipe pig, a cleaning robot, or a hydrojet) into the header; or (iv) temporarily increasing the flow rate through the inlet distribution system; The method according to claim 1 or 2, wherein the washing is carried out by

4. 3. The method of claim 1 or 2, wherein in step (a), a vertical vent pipe is connected to each distribution pipe, the vertical vent pipe terminating above the operating water level of the reactor to release air or oxygen entrained in the distribution pipe.

5. 5. The method of claim 4, wherein the inlet distribution system distribution pipes are cleaned by entering a high pressure lance or alternative mechanical or hydro-mechanical device at the top of the reactor through the vent pipe connected to the distribution pipe.

6. A method according to any one of the preceding claims, in which a grid with a header is routed above the water level, optionally using the entry of a cleaning device placed in said header.

7. 7. The method of any one of claims 1 to 6, wherein during step (a), the degree of plug flow in the reactor is monitored by determining a profile of a suitable parameter across the reactor from the bottom to the top of the reactor at various times during step (a).

8. 8. The method according to claim 7, wherein the suitable parameter is a pollutant concentration, preferably chemical oxygen demand (COD), ammonium or phosphate, turbidity, pH, redox potential, conductivity or temperature.

9. 9. The method of any one of claims 1 to 3, 6 to 8, wherein step (a) monitors even distribution of the wastewater influent across two or more distribution pipes by measuring flow rate and / or pressure in said distribution pipes.

10. 9. The method according to any one of claims 4 to 8, wherein in step (a) even distribution of the wastewater influent across the distribution pipe is monitored by measuring the water level and / or pressure and / or temperature or other suitable parameters in said vent pipe.

11. 11. The method according to any one of claims 1 to 10, wherein in step (a) the wastewater influent across the distribution pipe is evenly distributed to produce a plug flow to such an extent that at least 30%, preferably more than 50%, 60% or 70% of the reactor volume is displaced towards a treated wastewater effluent decanter system without significant breakthrough of raw wastewater.

12. The method according to any one of claims 1 to 11, wherein at least 70% of the biomass particles in the reactor have a particle size of at least 0.2 mm, preferably in the range of 0.2-50 mm.

13. 12. The method of any one of claims 1 to 11, wherein at least 70% of the biomass particles in the reactor have a diameter of 0.2 mm or less.

14. A liquid distribution system comprising one or more distribution pipes with one or more nozzle outlets positioned to provide an even distribution of influent wastewater across a bottom surface of the reactor, and a vertical vent pipe connected to each distribution pipe.

15. The liquid dispensing system of claim 14 comprising two or more distribution pipes.

16. 16. A liquid dispensing system according to claim 14 or 15, wherein each distribution pipe comprises two or more nozzle outlets.

17. A liquid dispensing system according to any one of claims 14 to 16, wherein the one or more nozzle outlets face downwards.

18. A liquid distribution system according to any one of claims 14 to 17, wherein the distance between the nozzle outlets in the distribution pipe is in the range of 0.5 to 10 m.

19. A liquid distribution system according to any one of claims 14 to 18, wherein each distribution pipe is connected to a distribution pipe manifold.

20. A liquid dispensing system as claimed in any one of claims 14 to 19, wherein each vent pipe is fitted with a removable end cap having a vertically positioned opening, or a U-shaped bend having an open end.

21. A liquid dispensing system according to any one of claims 14 to 20, wherein each vent pipe is equipped with a water level gauge, a pressure gauge and / or a temperature sensor, preferably a Dispensing Temperature Sensing (DTS) cable.

22. Use of a liquid distribution system according to any one of claims 14 to 21 in a method for the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor.

23. The use according to claim 22, wherein the process for treating wastewater is a process according to any one of claims 1 to 13.

24. An installation comprising a reactor having a liquid inlet system at the bottom of the reactor, a liquid outlet system at the top of the reactor, and a gas inlet at the bottom of the reactor, 14. An installation for carrying out the method according to any one of claims 1 to 13, wherein the liquid inlet system comprises one or more distribution pipes, each of which is provided with one or more nozzle outlets arranged to provide an even distribution of liquid across a bottom surface of the reactor, and a vertical vent pipe is connected to each distribution pipe, the vertical vent pipe terminating above the operating water level of the reactor for releasing air entrained in the distribution pipes.

25. 25. The arrangement of claim 24, wherein the liquid inlet system comprises two or more distribution pipes.

26. 26. An arrangement as claimed in claim 24 or 25, wherein each distribution pipe of the liquid inlet system is provided with two or more nozzle outlets.

27. An installation as claimed in any one of claims 24 to 26, wherein the nozzle outlet or outlets in each distribution pipe face downwards.

28. The distance between the nozzle outlets in the distribution pipe is in the range of 0.5 to 10 m, and / or the m of the bottom surface of the reactor ２ 28. The installation according to any one of claims 24 to 27, wherein there are 0.5 to 50 nozzle outlets per nozzle.

29. An installation according to any one of claims 24 to 28, wherein each distribution pipe is connected to a distribution pipe manifold.

30. 30. An arrangement as claimed in any one of claims 24 to 29, wherein each vent pipe is fitted with a removable end cap having a vertically positioned opening, or a U-shaped bend having an open end.

31. An installation according to any one of claims 24 to 30, wherein each vent pipe is equipped with a water level gauge, a pressure gauge and / or a temperature sensor, preferably a distributed temperature sensing (DTS) cable.

32. 32. The installation of any one of claims 24 to 31, further comprising means for determining a profile of a suitable parameter across the reactor from the bottom to the top of the reactor.

33. 33. The installation of claim 32, wherein the suitable parameter is a contaminant concentration, turbidity, pH, redox potential, conductivity or temperature.

34. 34. The installation according to claim 32 or 33, wherein the installation is equipped with analyzers or probes for measuring contaminant concentration, turbidity, pH, redox potential, conductivity and / or temperature.

35. Use of an installation according to any one of claims 24 to 34 in the aerobic treatment of wastewater in a vertical plug flow (VPF) biological treatment reactor.

36. The use according to claim 35, wherein the process for treating wastewater is a process according to any one of claims 1 to 13.

Images