Aerobic biological wastewater treatment in continuous flow reactor

Abstract

The invention relates to a method for purifying substrate-containing wastewater in a continuous flow-through aerobic bioactive sludge reactor B, in which at least part of the biological sludge (6) and at least part of the substrate-containing wastewater (2) to be purified are adjusted in a selector S under anaerobic or anoxic conditions, optionally after a pretreatment step VB of the supplied wastewater (1), wherein the conditioning comprises first accumulating sludge particles having a settling velocity of at least 2 m / h and subsequently contacting the substrate-containing wastewater with the accumulated sludge particles in a selector S for a contact time of at least 10 minutes wherein the selector S is operated or designed such that during the contact of the sludge with the substrate-containing wastewater, the sludge particles are separated from the sludge particles. The sludge residence time in the selector S is greater than the hydraulic residence time of the sludge / water mixture (3) in the selector, and wherein the sludge / water mixture (3) is fed to an aerobic purification reactor B and subjected to an aerobic treatment B, optionally after an additional anaerobic or anoxic contacting step, wherein the aerobically treated treated wastewater (4) is optionally separated from sludge by sedimentation, flotation or mechanical separation in a secondary sedimentation tank NB, and wherein the selector receives sludge (6) separated from the aerobically treated wastewater and / or at least part of sludge (6 ') from the aerobic purification reactor B.

Description

Technical Field

[0001] The invention belongs to the field of aerobic biological wastewater purification in a continuous flow-through reactor with aerobic granular sludge. Background Art

[0002] In order to protect the aquatic environment, biological treatment of wastewater from residential, urban and industrial activities is an important activity. A large number of biological purification technologies are known, and these technologies can be roughly divided into anaerobic technology and aerobic technology. Both technologies use microorganisms that use pollutants in wastewater as substrates to convert them into less harmful substances. In anaerobic technology, microorganisms (MO) reproduce without adding a large amount of oxygen to the mixture of MO and wastewater. MO mainly converts pollutants into methane gas and promotes MO growth. Examples of such anaerobic technologies are BioBulk, UASB, EGSB and anaerobic MBR. The advantage of this type of technology is that methane gas can be utilized. However, the main disadvantage is that the wastewater treatment performance is quite limited, and aerobic technology is usually required for subsequent treatment to fully protect the aquatic environment. It should be noted that the invention described below does not belong to this anaerobic purification technology.

[0003] In aerobic techniques, oxygen is supplied to the MO in one way or another, such as by surface aerators, by introducing air through bubble aerators or other means. Aerobic MO primarily converts organic carbonaceous contaminants into carbon dioxide and promotes MO growth.

[0004] In addition, there are aerobic technologies in which process conditions are set so that in addition to aerobic MOs, MOs that can remove nutrients such as nitrogen and phosphates from wastewater can also reproduce. Such process conditions generally include so-called anaerobic and anoxic conditions. Under anoxic conditions, in addition to organic pollutants, there are also oxidized nitrogen compounds such as nitrites and nitrates, in which MOs that convert these compounds into harmless nitrogen gas can reproduce. Under so-called anaerobic conditions, the concentration of such oxidized nitrogen compounds is limited or completely absent. Under such conditions, MOs that can store phosphates can reproduce, such as MOs like PAO (phosphate accumulating organisms). It should be noted that although these process conditions often use the term "anaerobic" and are similar to the terminology in anaerobic purification technology, it represents a very different class of MOs and should not be confused with the MOs in the above-mentioned anaerobic purification technology that mainly produces methane. It should be noted that there are also some specific MOs that can convert ammonium and nitrite into nitrogen gas. Such MOs are generally called anaerobic ammonia oxidizers (Anammox (anoxic ammonium oxidizers)). Such MOs cannot reproduce in the presence of carbonaceous pollutants and cannot remove these important pollutants. Therefore, technologies using anaerobic ammonia oxidizers MO do not belong to aerobic wastewater treatment, but often require such aerobic purification technology components as pretreatment to produce nitrite from ammonium or organic nitrogen pollutants.

[0005] A commonly used aerobic wastewater purification technology that has been the most widely used worldwide until recently is the so-called continuous (or circulation) activated sludge system. The so-called Carousel technology described in EP0474296 is an example of such an embodiment. MO grows in the form of sludge flocs, which circulate in the Carousel purification reactor together with the wastewater and are exposed to aerobic and anoxic conditions in this way. Some Carousel embodiments also have an upstream anaerobic reactor to enable PAO MO to grow in the circulating activated sludge. After the MO in the activated sludge (AS) removes pollutants from the wastewater, the AS is separated from the water by sedimentation, flotation, membrane filter or other means, and the AS is returned to aerobic, anoxic and / or anaerobic process conditions. In order for the separation of AS to proceed correctly and quickly, it is very important that the AS has good settling properties. This is why so-called sludge selectors are often used in AS systems, in which the recovered AS is thoroughly mixed with the untreated wastewater to inhibit the growth of so-called filamentous MO with poor settling properties. There are various embodiments of such sludge selectors available, which may include one or more compartments or reactors, are always well mixed and can be operated with or without aeration. In addition, the contact time of the non-aerated sludge selector can be extended by an integrated or continuous non-aerated contact tank to stimulate the growth of PAOs. These sludge selectors (with or without integrated or continuous non-aerated contact tanks) are characterized by the thorough mixing of the activated sludge and water, and the residence time of the sludge in the sludge selector is the same as the residence time of the sludge / water mixture. In other words: the sludge retention time (SRT) is the same as the hydraulic retention time (HRT). Another feature is that all sludge in the control sludge selector has the same SRT, and if the distribution of SRT is unexpectedly limited, this distribution of sludge particles of different sizes is comparable. It should be noted that the invention described below has nothing to do with such sludge selectors where HRT=SRT.

[0006] A new category of aerobic activated sludge systems uses granular sludge instead of flocculated activated sludge. Scientifically speaking, aerobic granular sludge is defined as sludge with a size of at least 0.212 mm and usually less than 6 mm, so that coagulation does not occur during sedimentation, so the sludge volume index (a measure of sludge sedimentation properties) after 5 minutes of sedimentation is comparable to the index after 30 minutes of sedimentation. The main advantage is that aerobic granular sludge settles much faster (4m / h to 40m / h) than flocculated activated sludge (0.5m / h to 2m / h), and if the particles are large enough, the above-mentioned anoxic and anaerobic conditions necessary for nutrient removal will be produced; therefore, even if the granular sludge is aerated and the aerobic MO on the outer layer of the particles decomposes organic carbonaceous pollutants, denitrification and phosphate fixation can be carried out simultaneously deeper inside the particles. Therefore, compared with the activated sludge system, no or much less circulation and advancement are required to expose the sludge to various desired conditions, resulting in energy savings of 20% to 50%. However, this requires that the sludge has a particle size of 0.4 mm, depending on the aeration conditions applied, and preferably has a size greater than 1 mm (and preferably less than 6 mm), otherwise no or only insufficient denitrification capacity can be achieved deep inside the particles. In addition, the construction costs of granular sludge treatment equipment are significantly lower than those of activated sludge systems. On the one hand, due to the rapid sedimentation of the sludge, the required hydraulic retention time in the purification reactor and clarifier is shorter, and on the other hand, due to the good sedimentation characteristics of granular sludge, the amount of MO is much higher. In comparison, activated sludge systems generally use MO concentrations of 3 g / l to 5 g / l, while granular sludge systems are 8 g / l to 20 g / l.

[0007] WO2004 / 024638 describes the first granular sludge technology that is widely used in practice for aerobic purification of wastewater. In order to achieve the transition from activated sludge to granular sludge and maintain the granules during the purification process, there are many important process technology conditions. The granular sludge must be exposed to an "anaerobic" stage (anaerobic here means "without aeration"; strictly speaking, this stage can also be anoxic (in the presence of nitrates)) so that the MO can absorb organic carbonaceous pollutants. In the aerobic treatment process, this absorption is very important because it enables the MO to specifically consume the absorbed carbonaceous pollutants, which is an important condition for achieving granule formation. In addition, this carbon is necessary to convert nitrogen oxide compounds in the anoxic and anoxic parts of the particles into nitrogen. In addition, it is also important to limit the amount of flocculated activated sludge. Since part of the carbon pollutants still remain in the wastewater after absorption in the aforementioned anaerobic stage, this will lead to the growth of a limited amount of activated sludge flocs. In order to produce these important process conditions, WO2004 / 024638 uses a purification reactor with a discontinuous wastewater supply, which belongs to the sequencing batch reactor (SBR) class. In the first stage, wastewater is fed to the reactor from the bottom so that the undiluted wastewater comes into contact with particles that can absorb organic matter. Subsequently, the wastewater supply is stopped and the supply of oxygen-containing gas is started. After aerobic, anoxic and anaerobic bioconversion has sufficiently occurred to purify the wastewater to the desired water quality, the sludge with the worst settling properties is discharged from the reactor together with the flocculent sludge formed. The separation between floccules, sludge with poor settling and sludge with better settling is achieved by discharging the sludge only after a certain degree of sludge settling has occurred and by discharging the sludge from the upper part of the reactor. In the professional literature, this separation is also called selective pressure.

[0008] Since the first practical implementation of aerobic granular sludge and its operating methods and embodiments (as originally described in WO2004 / 024638), this technology is rapidly replacing the use of activated sludge systems due to its many advantages. However, a major disadvantage of the method and embodiment is that it occurs in an SBR, while most of the existing treatment equipment is based on continuous activated sludge. It is not easy to convert from a continuous feed reactor to a discontinuous feed reactor. Due to the many advantages of granular sludge and the above-mentioned scientific insights into the key process conditions required to form granular sludge, many attempts have been made to apply granular sludge to continuous circulation treatment reactors. For example, WO2017 / 025345 describes a process in which a separator is used to separate part of the activated sludge from the aeration tank of a continuous activated sludge system into two parts, namely a faster settling part and a slower settling part, wherein the faster settling part is mixed with the wastewater to be treated and the return sludge in an anaerobic tank.

[0009] US2020 / 0002201 describes a continuous activated sludge system in which part of the activated sludge recovered from the final clarifier to the start of the continuous purification process is treated in an "incubator" before being circulated to the start of the continuous activated sludge system. The disclosed treatment method includes the application of anoxic and anaerobic conditions, in which an additional carbon source is also provided by adding chemicals or by fermenting part of the sludge from the primary sedimentation. In addition, at various locations in the process, separators are used to selectively discharge the slower settling sludge. As with WO2004024638, the process provides all the conditions for achieving particle formation: there is an anaerobic stage, and selection pressure is applied by the separator. However, the published field test results of the process (Shanghai IWA Sustainable Wastewater Treatment and Resource Recovery Innovation Conference (November 2019)) show that the method does not result in a large amount of granulation: only about 30% of all sludge is larger than the scientific particle lower limit of 0.212mm, and more than 90% of the sludge is less than 0.25mm. The cases where granular sludge fractions were found to be large enough to allow simultaneous denitrification as described above (which requires a particle size of at least 0.5 mm to 1 mm) were almost negligible. Therefore, only a small fraction of the potential benefits of granular sludge purification can be realized in a continuous activated sludge process.

[0010] A similar process is described in WO2019 / 195918. Again, the sludge is circulated from the secondary settling to a separate compartment, a separate reactor or a series of reactors with anoxic conditions, after which the sludge is mixed with raw wastewater in another compartment, a separate reactor or a series of reactors to be exposed to anaerobic conditions. WO2019 / 195918 also applies selection pressure by discharging less settled sludge into the sludge treatment line. The above-mentioned shortcomings of US2020 / 0002201 seem to play a role here as well.

[0011] There is an ongoing need in the art to further implement and optimize the process as described in WO2004 / 024638 and to achieve extensive granular sludge formation in a continuous flow-through system as described above. Summary of the invention

[0012] Through experiments, the inventors have determined that despite the use of the above-mentioned sludge selector in the context of the Carrousel technology, and whether or not the non-aerated tanks are integrated or subsequently used (as described in the prior art) and by mixing the sludge with untreated wastewater in an anaerobic tank, whether or not an anoxic stage is performed first, the above-mentioned continuous system is not able to achieve a large part of the sludge conversion and maintain the desired particle size of at least 0.4 mm to 1.0 mm on an industrial scale. However, in the study, the inventors determined that there is a correlation between the distribution of the particle size and sludge residence time of individual sludge particles with different settling properties or sizes and their exposure level to readily biodegradable organic substrates (rbCOD) in anoxic or anaerobic contact tanks or selectors. Subsequently, the inventors took advantage of this unexpected discovery and developed an improved method and apparatus implementation for a continuously fed, flow-through aerobic biological purification reactor based on WO2004 / 024638 and WO2017 / 025345, wherein by deploying such sludge retention time and rbCOD exposure distribution, normal activated sludge can be converted into sludge with a large amount of granule formation, and for the first time in practice it is possible to match the advantages that could previously only be achieved in granular sludge technology using SBR.

[0013] In practice, according to the inventors, this can be achieved by using a selector under anaerobic or anoxic conditions before aerobic purification, which actively provides or controls the sludge with larger size and / or higher sedimentation rate in the selector to contact the substrate-containing wastewater for a longer time (i.e., longer contact time than the sludge with smaller size and / or lower sedimentation rate). For example, this can be achieved by applying (i) multiple stages with discrete or discontinuous flow rate changes, (ii) an increased flow gradient (i.e., a continuously increasing flow rate) or a combination of (i) and (ii) in the selector. In these two ways, a distribution of sedimentation rates is achieved (allowing portions with lower and higher sedimentation rates), while increasing the contact time and substrate concentration of larger particles in contact with the wastewater. This is an improvement on the method in WO2017 / 025345. The function of the selector is to allow at least a large portion of the larger sludge particles to have a longer residence time than the hydraulic residence time of the conditioned sludge / water mixture, and preferably to expose the larger sludge particles to a higher substrate concentration. In doing so, the embodiment (i) with discrete flow rate variation is preferred. More advantageously, this can be achieved in the following ways: (a) a continuous mode, which provides a flux variation in the flow direction of the selector at a constant water / sludge flow rate; and / or (b) a semi-batch mode, in which the variation of the flow rate in the selector is achieved by changing the water / sludge flow rate. The different embodiments (i)(a) and (i)(b) and (ii) are further explained in the detailed description and the figures.

[0014] The inventors have also found that it is more advantageous to first accumulate (i.e., concentrate) sludge particles with a settling velocity of at least 2 m / h, preferably at least 2.5 m / h, and more preferably at least 3 m / h, preferably in the selector S, but the accumulation step can also be performed in a separate tank before the selector. The accumulation of these rapidly settling sludge particles can be achieved by adjusting the sludge supply flow rate in the upward flow or upstream setting so that the rapidly settling sludge is concentrated at the bottom of the tank or selector. After accumulation, the substrate-containing wastewater is contacted with the accumulated sludge particles in the selector for a contact time of at least 10 minutes, and the operation or design of the selector S makes the sludge retention time in the selector S greater than the hydraulic retention time of the sludge / water mixture in the selector. Conveniently, the contact time is 10 minutes to 120 minutes, preferably 20 minutes to 90 minutes. This initial accumulation step stimulates the growth of rapidly settling sludge in the selector.

[0015] It is advantageous to saturate the sludge with substrate from the substrate-containing wastewater, preferably to the extent that at least 60%, preferably at least 75%, more preferably at least 80% of the readily biodegradable substrate (rbCOD) in the wastewater is removed from the wastewater (i.e., adsorbed by the accumulated sludge). In addition, the inventors have found that it is advantageous to limit the contact time between the substrate-containing wastewater and the accumulated sludge, so that preferably most of the substrate has been adsorbed by the sludge when the rbCOD level reaches a steady state.

[0016] In the advantageous wastewater treatment using aerobic granular sludge technology, the present invention particularly relates to a method for purifying substrate-containing wastewater in a continuous flow-through aerobic biological activated sludge reactor, wherein, optionally after a pretreatment step VB of the supplied wastewater 1, at least a portion of the biological sludge is conditioned with at least a portion of the substrate-containing wastewater to be purified in a selector under anaerobic or anoxic conditions (whether or not after a conventional pretreatment step of the received wastewater), wherein the conditioning comprises first accumulating a sedimentation velocity of at least 2 m / h, preferably at least 2.5 m / h, more preferably at least 3 m / h. sludge particles, and contacting the substrate-containing wastewater with the accumulated sludge particles in the selector S for a contact time of at least 10 minutes, wherein the selector S is operated or designed so that the sludge retention time in the selector S during the contact of the sludge with the substrate-containing wastewater is greater than the hydraulic retention time of the sludge / water mixture in the selector, wherein during the contact of the accumulated sludge with the substrate-containing wastewater, preferably at least 20 wt% of the sludge in the selector has a retention time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector, and preferably larger sludge particles are contacted with the highest substrate concentration,

[0017] Thereafter, the sludge / water mixture leaving the selector (whether or not after a final additional anaerobic or anoxic step) is fed to an aerobic purification reactor and subjected to (conventional) aerobic purification,

[0018] In this process, the treated (purified) wastewater is separated from the sludge after aerobic purification.

[0019] In this way, sludge particles with larger size and / or faster settling properties have a longer contact time with the higher concentration of substrate-containing wastewater than sludge particles with smaller size or slower settling properties. By using a selector, the conditioned sludge / water mixture (whether or not after the final additional anaerobic or anoxic step) is fed to the aerobic purification reactor, wherein at least 20 wt% of the sludge comprises granular sludge. Preferably, the proportion of granular sludge is at least 25 wt%, preferably at least 30 wt%, most preferably at least 40 wt%, especially at least 50 wt%; and preferably at least 20 wt% of this granular sludge (i.e. sludge with a size of at least 0.212 mm) in the aerobic biological purification reactor B, or more preferably at least 25 wt%, preferably at least 30 wt%, most preferably at least 40 wt%, especially at least 50 wt% of this granular sludge has a particle size of at least 0.4 mm to 1.0 mm.

[0020] The sludge separated from the aerobically treated wastewater can be returned (as return sludge 6) to the selector. This return establishes the continuity of the wastewater treatment and ensures the formation and maintenance of an effective size distribution of granular sludge. Similarly, or in combination with receiving the return sludge 6, the selector can also receive sludge 6' from bioreactor B during the accumulation period. In a preferred embodiment, the sludge 6' is fed to the selector, while the (return) sludge 6 from the aerobic treatment is fed to reactor B. In other words, in the above method, the sludge is treated in the selector under anaerobic or anoxic conditions, so that larger sludge particles are in contact with higher substrate concentrations in the selector, and their contact is more than that of smaller sludge particles, while the larger sludge particles in the bioreactor B have a longer contact time with the substrate-containing wastewater than the smaller sludge particles. In practice, the substrate concentration varies greatly due to fluctuations in the wastewater composition and the absorption of MO in the selector. Preferably, at least the largest 10 wt% of the sludge particles are in contact with the highest substrate concentration in the selector for a time at least 20% longer than the average contact time of the sludge, and this substrate concentration is preferably at least 50% higher than the substrate concentration contacted by the smallest 15 wt% of the sludge particles.

[0021] In the context of the present invention, the above-mentioned improved settling velocity distribution and the increase in contact time of larger particles with the wastewater and substrate contact concentration - and their related characteristics - are achieved by using a selector preferably within 200 days of the start of deployment of the process, more preferably within 150 days. Fig.11A As shown, without the use of selectors, these goals cannot be achieved after the startup phase.

[0022] In one embodiment, the sludge / water mixture in the selector is subjected to discrete changes in flow rate and / or flow rate gradients under anaerobic or anoxic conditions. In a specific embodiment, the discrete changes in flow rate are achieved by discrete changes in flux in the flow direction of the selector and / or discrete changes in the flow rate of the supplied wastewater and / or the return sludge.

[0023] The term "discrete change" in the context of the present invention refers to a (distinguishable) discontinuous change in flow rate.

[0024] In a particular embodiment, the selector has a first step, which separates a portion of sludge into a faster settling portion and a slower settling portion under anaerobic or anoxic conditions, wherein a mixture of wastewater and a faster or slower settling portion is selected, and the mixture is separated into a faster settling portion and a slower settling portion again in at least the second, next step in the selector. In order to separate in different steps of the selector, it is preferred to apply a selection based on sedimentation rate at any time in the upflow column, wherein the upflow velocity of the wastewater through the different steps of the selector can be adjusted separately and independently as a parameter. In doing so, a discontinuous or discrete change in flow velocity is achieved. This can be achieved, for example, by an upflow column with concentrically arranged compartments, which together form the selector. The upflow velocity in each step of the selector is preferably 1m / h to 25m / h. Preferably, the upflow velocity in each step of the selector is lower than the upflow velocity in the previous step, preferably 25% to 50% of the upflow velocity in the previous step in each case. Preferably, the selector has at least a third step, wherein the faster or slower settling portion from the second step is further separated into a faster or slower settling portion, after which the sludge-treated wastewater stream and the sludge are fed to a conventional purification reactor, and wherein the remainder is returned to the previous step of the selector. The third step is preferred to avoid the accumulation of sludge that settles too quickly. Such multiple sludge separation steps based on the variation of the settling velocity / flow rate in the anaerobic selector preferably result in at least 20% of the sludge in the selector having a residence time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector. The following objectives are also achieved: at least the largest 10wt% of the sludge particles are in contact with the highest substrate concentration in the selector for a time that is at least 20% longer than the average contact time of the sludge, and the highest substrate concentration is at least 50% higher than the substrate concentration contacted by the smallest 15wt% of the sludge particles. Figure 2 schematically shows such an embodiment.

[0025] In another embodiment, the selector is a semi-batch step, wherein the sludge is contacted with the wastewater in the reactor under anaerobic or anoxic conditions, and wherein the feed rate is varied.

[0026] In another specific embodiment, the selector separates by creating a gradient (increasing or decreasing) in flow rate, thereby causing the selector to continuously separate downstream sludge according to settling velocity, so that the residence time of the sludge in the selector increases with increasing settling velocity. To achieve this goal, the gradient can be adjusted accordingly. Figure 3 Such embodiments are schematically shown in Figures 6 to 6. In these cases, a continuous increase in flow rate is provided.

[0027] In each of these embodiments, particles having a settling velocity of at least 2 m / h, preferably at least 2.5 m / h, more preferably at least 3 m / h are first accumulated and then contacted with the substrate-containing wastewater. The sludge is contacted with the substrate-containing wastewater in the selector, and the sludge retention time during the contact in the selector is greater than the hydraulic retention time; preferably, at least 20 wt% of the sludge in the selector has a retention time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector. Preferably, the proportion of granular sludge (sludge with a size of at least 0.212 mm) in the aerobic biological purification reactor B is even at least 25 wt%, preferably at least 30 wt%, most preferably at least 40 wt%, and in particular at least 50 wt%; and preferably, at least 20 wt% of this granular sludge (i.e. sludge with a size of at least 0.212 mm), or more preferably, at least 25 wt%, preferably at least 30 wt%, most preferably at least 40 wt%, and in particular at least 50 wt% of this granular sludge has a particle size of at least 0.4 mm to 1.0 mm. In addition, preferably, it is also achieved that the larger sludge particles in the selector are more in contact with the higher substrate concentration than the smaller sludge particles. Those skilled in the art will be able to adjust the feed rate and flow rate parameters to achieve these goals.

[0028] In any of these embodiments, the accumulation of sludge in the selector can be prevented by regularly increasing the degree of mixing or flow rate within an adjustable time to guide the faster settling sludge to the downstream aerobic reactor. In addition, in any of these embodiments, the proportion of sludge flocs can be further reduced by extracting at least a portion of the discarded excess sludge from the position where the proportion of the worst settling sludge particles in the selector is the largest. Preferably, this mixing occurs at a frequency of no more than 2 times per hour, more preferably no more than 1 time per hour, and even more preferably no more than 1 time per 4 hours. The duration of this mixing depends on a variety of factors, including the hydraulic retention time, and is preferably at least 5 minutes, more preferably at least 15 minutes to 30 minutes.

[0029] The present invention is capable of maintaining and forming granular sludge in any type of flow-through purification reactor, including purification reactors in which the sludge comprises a mixture of biological sludge and biofilm carriers and / or growths and / or ballast materials. Such carriers / growths / materials are used in some types of reactors to better settle the sludge and utilize natural, organic, inorganic or mixed materials suspended in the sludge for the purpose of forming biofilms on the biological sludge or agglomerating on the biological sludge. Therefore, in the context of the present invention, reactor B may comprise a mixture of biological sludge and suspended biofilm carriers.

[0030] Description of the process and implementation scheme

[0031] Below, various possible workings and embodiments of the present invention will be described, all of which are aimed at achieving granulation by improving the distribution of sludge residence time - as described above. Those skilled in the art will recognize that the common point of the methods and embodiments is that a significant distribution of sludge residence time is achieved, and that this distribution is combined with the contact of the sludge with untreated wastewater or contaminated side streams so that the largest sludge particles are exposed to longer contact times and higher substrate contact concentrations. Those skilled in the art will also recognize that the methods do not exclude variants, alternatives and other embodiments that achieve the same effect, and that such embodiments and similar methods are part of the same invention. Each of the following embodiments also includes a first accumulation or concentration and subsequent saturation steps as described above.

[0032] Figure 1A The basic principle of the improved continuous flow-through biological purification according to the present invention is shown. If necessary, the wastewater 1 is first pretreated in a primary settling tank VB and then fed to a selector S via 2 where it is mixed with sludge 6. From the selector S, the wastewater / sludge mixture flows to the biologically activated sludge treatment reactor B, after which the sludge from the purified wastewater / sludge mixture 4 is preferably separated from the treated wastewater in a secondary settling tank NB5 and at least partially (as 6) returned to the selector. Optionally, the selector receives at least a portion of the sludge 6' from the reactor B ( Figure 1B ), while at least part of the sludge 6 separated in the settler NB is returned to the reactor B. Part of the sludge produced during the purification process is discharged from the process. This excess sludge discharge 7 can be carried out at different process locations or a combination of locations. Although in Figure 1A and 1B The accumulation is carried out in the selector, but alternatively, the accumulation step can also be carried out in a separate tank or device before the selector S.

[0033] Those skilled in the art will appreciate that the pretreatment VB may have various embodiments, such as but not limited to screens, sieves, filters, cyclones, gravity settlers, inclined plate settlers, flotation devices, etc. The biological purification reactor B may be any conventional embodiment of a continuous flow activated sludge reactor, including but not limited to oxidation ditch, plug flow, CSTR, Bardenpho, UCT, etc. Such biological purification reactors also typically have compartments or sub-reactors in which aerobic, anoxic, and anaerobic conditions are maintained.

[0034] In the context of the present invention, stream 6 is interchangeably referred to as biological sludge, sludge and return sludge. Sludge stream 6' is the sludge from reactor B that is specifically sent to selector S; Figure 1B In Figures 2 to Fig.10 In the present invention, stream 6 is understood to mean stream 6 and / or 6'. Fig.10 As detailed in , in the method according to the invention, at least a portion of the return sludge may originate from conventional wastewater treatment.

[0035] In this embodiment, the desired accumulation and sludge retention time distribution is achieved by changing the flux toward the flow direction. The selector S is preferably a compartmented upflow reactor with concentrically oriented compartments, such as Figure 2A , wherein the effective volume of compartment Sa is less than the effective volume of Sb, and also less than the effective volume of Sc. In an alternative form (in FIG. 2B ), the selector applies three adjacent and connected compartments Sa, Sb and possibly Sc, which have adjusted volumes, wherein the effective volume of compartment Sa is smaller than the effective volume of Sb. Figure 2A and 2B It is also possible to work with only compartments Sa and Sb. Sludge 6 or 6' is introduced horizontally at the bottom of compartment Sa, where it contacts at least a portion of the wastewater 2. The remainder of the wastewater 2 is introduced at the bottom of another compartment. Due to the vertical flow in compartment a, a significant sludge residence time distribution is intentionally achieved, because the sludge residence time of each sludge particle is determined by its respective settling properties. Particles whose settling characteristics (sedimentation velocity) are much lower than the vertical flow velocity will leave compartment a with the upward flow, and the time they stay in this compartment will not exceed the residence time of water in this compartment. However, sludge particles whose settling properties are higher than the liquid velocity stay in the compartment longer than water, and the sludge particles with the fastest settling velocity accumulate at the bottom of compartment Sa and flow from there to compartment Sb. MO is very important for the formation of granular sludge, because the sludge is in contact with nutrient-rich water and under anoxic or anaerobic conditions, MO will preferentially absorb substrates, so the sludge particles with the best settling properties will gain a biological selection advantage, thereby growing towards granular sludge and maintaining a granular sludge state.

[0036] The sludge particles will then enter compartment Sb through the overflow or underflow of compartment Sa, depending on their settling velocity. The fluid velocity in compartment Sb is lower than in compartment Sa. This in turn imposes a significant sludge residence time distribution on the sludge, and it is also important that the sludge with the best settling properties will have more contact time and be exposed to the more concentrated wastewater. Finally, particles with a settling velocity comparable to the liquid velocity stay in the compartment as long as the liquid and have a relatively short contact time with the less undiluted wastewater in the lower part of the compartment. The faster settling part, together with the sludge particles with the best settling velocity from the bottom of compartment a, can stay longer in the lower part of compartment Sb and absorb more substrate. A similar effect occurs in compartment Sc, which is fed from compartment Sb through the bottom and overflow. Here, individual sludge particles with a faster settling velocity are in contact with the most concentrated wastewater for the longest time. It goes without saying that the selector can be extended to more compartments (Sd, Se, ...) according to the same principle.

[0037] In order to prevent sludge particles from forming in the last compartment (in Figure 2A and 2B In the compartment Sc), the sedimentation accumulation is too fast, and the compartment is preferably mixed continuously or intermittently with a stirrer M. This mixing can be achieved by using a mechanical stirrer or propeller, or by introducing a gas or by adjusting the size of the latter compartment so that the vertical liquid flow rate generated is greater than the liquid flow rate in the compartment a. Although this gas can also be oxygen or an oxygen-containing gas, the selector is considered to be an anaerobic or anoxic reactor because the gas in the last compartment can reduce the effective anaerobic contact time of the selector at most.

[0038] The dimensions within the compartments and the rates generated are selected so that the above-mentioned target levels of sludge accumulation and sludge residence time distribution occur.

[0039] exist Figure 2 In the schematic diagram, in addition to compartment Sa, two additional compartments Sb and Sc are shown. Based on the information given here, those skilled in the art will recognize that in order to implement the present invention, at least one additional compartment Sb is necessary, but more additional compartments (Sb, Sc, Sd, Se...) can also be used to further optimize performance and operational robustness. As the number of additional compartments increases, the possibility of further increasing and controlling the sludge retention time distribution also increases. This also applies to the method of compartmentalization and how to achieve the desired flow pattern and mixing in the relevant compartments. For example, a quadrilateral tank is preferably designed with compartment Sa and only one additional compartment Sb. Optionally, the overflow from the additional compartment is transferred to the lower part of another (preferably adjacent) compartment via a pipe.

[0040] Incidentally, the inflow of wastewater 2 can also be done from the bottom of the compartment, and the supply of return sludge 6 and / or sludge 6' is located at the liquid level in the compartment. In this case, the partition walls between the compartments do not need to have openings at the bottom between the compartments. Figure 2C This is shown only for compartment Sa. The liquid velocity of the wastewater 2 in compartment Sa is chosen so that the sludge particles in 6 are flushed into compartment Sb. Sludge particles with a higher settling velocity will stay longer in this compartment Sa before being flushed away by the upward flow of wastewater, compared to particles with a lower settling velocity. Thus, the desired contact time and substrate contact concentration profile are also achieved. Figure 2A As shown, several compartments with wastewater supply at the bottom can appear in succession.

[0041] Figure 3 Another preferred variant is shown, in which the selector S is designed with an inclined bottom v, so that the liquid velocity increases with the flow. The wastewater 2 and the (return) sludge 6 and / or 6' are in close contact with each other on the inlet side, wherein the wastewater is preferably evenly distributed at the bottom, or this is optionally achieved by a mixer M. The water / sludge mixture then flows to the right (in the direction of the inclined bottom v), so that the liquid velocity gradually increases. The sludge particles with the fastest settling speed can gather around the bottom at the beginning of the selector, and then move to the beginning of the selector through the inclined bottom v as the flow rate increases. Sludge particles with a slower settling speed have a shorter residence time in the selector through 3. In this way, the desired sludge residence time distribution is obtained.

[0042] Those skilled in the art will recognize that this preferred variant can also be integrated into a circulating or plug flow activated sludge system for use, such as Figure 4A , 4B and 4C shown. Figure 4B and 4C is a side view, Figure 4A It is a top view. Figure 4B Shows Figure 3 A preferred variant of how this is achieved is by providing a riser or deflection baffle between sections a and a' of the circulating activated sludge system. The deflection baffle increases the flow velocity over the deflection baffle, and sludge particles having a sufficiently high settling velocity (i.e., the settling velocity is higher than the flow velocity) flow upstream of the deflection baffle, or at least flow slowly downstream, thereby coming into contact for a longer time with the wastewater entering before or at the beginning of the deflection baffle. The agitator or impeller is run regularly for a period of time. Depending on preference, the (return) sludge 6 and / or sludge 6' can be supplied before the baffle (as shown in Figure 4b) or after (as described below, as shown in Figure 6b) or at any other location, for example through an existing return sludge inlet. In this embodiment, it is important to obtain sufficient anaerobic time in sections a to a' for the sludge to hydrolyze and adsorb organic pollutants. Figure 4CIt is shown how the same purpose can be achieved by tilting the bottom of the depressions of segments a and a' in the flow direction. Of course, this can also be applied in segments of a plug flow system.

[0043] As with the preferred variant described above, changes in the wastewater flow rate during the day are advantageous for further distribution of the sludge retention time, and in order to prevent accumulation of the best settled sludge particles in the selector, an agitator or impeller may be operated periodically.

[0044] In another preferred variant, the sludge residence time distribution in a circulation or plug flow system is obtained by applying a partial widening of the channel width, resulting in a change in the liquid velocity and the best settling sludge particles settling to the bottom. Figure 5 This is an intermediate form between discontinuous flow rate change and continuous flow velocity gradient.

[0045] For installation of the selector in existing situations, it may be difficult or not cost-effective to apply the previously proposed preferred variants. In such cases, the preferred variant shown in FIG6 is advantageous. Operation and Figure 4a or 4b The operation is the same, but here the liquid velocity is increased by placing a deflection baffle d before the wastewater and return sludge enter. Since the flow velocity is reduced immediately after this baffle, larger particles will settle to the bottom here and come into contact with the food. Also, in the above integration, in this variant it is important to obtain sufficient anaerobic time in sections a to a' for the sludge to hydrolyze and adsorb organic pollutants.

[0046] In another preferred variant, Figure 7 As shown, wastewater 2 is distributed at the bottom of the selector S, and (return) sludge 6 and / or sludge 6' is introduced through a pipe with side openings at at least 3 different heights. Through these openings, the sludge comes into contact with the wastewater. Since the faster settling sludge particles come into contact with the wastewater at a deeper depth in the selector, the desired sludge residence time distribution is obtained.

[0047] In another preferred variant, Fig. 8A and 8BIt is schematically shown that the desired accumulation and distribution of sludge residence time in the selector S is obtained by using at least two selector compartments Sa and Sb, in which the supply of wastewater 2 and sludge 6 and / or sludge 6' is alternately carried out with the discharge of conditioned sludge, wherein the desired settling rate of the accumulated sludge and the distribution of sludge residence time in the selector S are obtained by supplying wastewater 2 to the compartments at the bottom of the compartments, and wherein the discharge of conditioned sludge can be achieved by applying a flow rate change and / or applying mixing, and / or by extracting at least a portion of the sludge / wastewater at the level of the bottom of the compartment (3a), while optionally providing sludge 6 and / or 6' at the liquid level in the compartment (6b) and / or somewhere between the bottom level (6a) and the liquid level of the compartment.

[0048] Using these two selector compartments Sa and Sb with alternating wastewater and sludge supply, a stirrer M can be used. This embodiment is as Fig. 8A As shown. Wastewater 2 is introduced at the bottom of the compartment. Return sludge 6 and / or sludge 6' is supplied at one or more heights between the bottom of the compartment and the liquid level. Fig. 8A In the diagram, only the option of supplying sludge at the bottom is shown, but this option of dividing according to 6a and 6b and optionally further supplying sludge in between ( Figure 8B ) can also be applied there. During the accumulation period, the selector is fed with sludge 6 and / or 6' at a flow rate such that the flow rate is at least 2 m per square meter of selector cross section per hour. 3 Wastewater is supplied and no agitator / propeller is used. The water / sludge mixture overflows through outlet 3 and sludge particles with a settling rate higher than 2m / h accumulate. After accumulation, the supply of wastewater 2 is started and no agitator / propeller is used during this supply phase. The wastewater supply stratifies the sludge bed according to the settling properties. The smallest sludge particles move upward with the flow, while heavier and larger particles move countercurrently and contact the substrate-containing wastewater for a longer time. The regulation here is carried out by discontinuous changes in the upstream and / or flow rate. After the desired anaerobic contact time is reached, wastewater or sludge is continued to be supplied for the desired time, but now the agitator M is in operation to supply the sludge / water mixture 3 to the continuous flow-through bioreactor. In order to maintain the continuity of wastewater treatment, at least 2 compartments are operated alternately to ensure that the wastewater continuously enters the selector. In addition, similar to the previously described variant, without using a mixer M, larger sludge particles can also be transported to the reactor B by using a pump, an Archimedean screw, an air lift, coarse bubbles, etc.

[0049] The above described variants can also be configured and operated without the use of a stirrer M. Figure 8B . As in the above variant, sludge 6 and / or sludge 6' may be supplied at the bottom level (6a), the liquid level (6b) or somewhere in between the compartment, but instead of using an agitator, the compartment may also be equipped with at least one sludge / wastewater outlet, which is at the bottom level (3a) and the liquid level (3b) of the compartment or alternatively or additionally, somewhere in between. During the above-mentioned cumulative sludge supply (sludge is introduced at heights 6a, 6b or between the two) and preferably saturated, the sludge / wastewater is removed from the selector compartment through 3b. After the anaerobic contact time is reached, the wastewater or sludge is continued to be supplied for a required period of time, but now the sludge / wastewater is removed from the compartment through 3a, so that the mixture 3 containing larger sludge particles is supplied to the continuous flow-through bioreactor. In this variant, the removal of conditioned sludge / wastewater from the compartment can also be effectively achieved by supplying sludge to the selector compartment through 6b.

[0050] The advantage of the embodiment of alternate operation is that when the accumulated sludge is saturated, when preferably reaching the degree as above, it is possible to easily stop supplying substrate-containing wastewater. Saturation degree or saturation rate can be followed by monitoring substrate or rbCOD concentration, for example, in reactor outlet 3, or on the top of sludge / water mixture in selector; When measurement result shows that there is no significant further adsorption of biodegradable substrate (rbCOD), it is possible to stop supplying wastewater. Alternatively, it is possible to achieve the same purpose by measuring conductivity, pH, VFA concentration, BOD concentration, P concentration, extinction, color or other parameters that change with substrate adsorption. Such measurement can also be used in other embodiments above-mentioned, to adjust flow conditions, so that the accumulated sludge amount can adsorb the biodegradable substrate in the wastewater supplied.

[0051] By means of the embodiments detailed above and shown in Figures 2 to 8, as well as all possible variants described above, the sludge can be fed continuously to the bioreactor B.

[0052] Those skilled in the art will recognize that if continuous supply of sludge from the selector S to the bioreactor B is not necessary for the operation of the bioreactor, the same advantages of the process of the present invention can be achieved using only one intermittently operated selector tank / compartment and without providing a flow rate difference (e.g., a deflection baffle). Fig. 9A In this preferred variant, the selector S is first filled with a certain flow rate of (return) sludge 6 and / or 6', so that the flow rate is equal to or higher than 2m per square meter of selector cross section per hour. 3wastewater. During this feeding process, sludge particles that settle fast enough accumulate in the selector, while other sludge particles are flushed out through 3. Then, the feed 2 is fed vertically to the selector S, during which the faster settling sludge particles in the accumulated sludge are concentrated to the bottom of the selector and exposed to the maximum substrate concentration of the wastewater. During the feeding process, the substrate in the wastewater is absorbed by the sludge. Initially, the easily degradable substrates (such as fatty acids) present in the fed wastewater are almost completely absorbed by the larger sludge particles accumulated at the bottom of the selector. Therefore, this substrate is no longer available for use by the smaller sludge particles higher up in the selector. Only when the MO in the larger sludge particles is completely saturated with substrate and the sludge particles can no longer absorb the substrate, the substrate can be used by the MO in the sludge particles higher up in the selector. This is in Fig. 9A The sludge in the figure marked as "area a" is in contact with the substrate, while the sludge in "area b" is not. The height of area a increases with time. This Fig. 9B The horizontal axis is the time since the wastewater was supplied, and the vertical axis shows the height of the substrate front (the boundary e between areas a and b). Once the substrate front reaches the top of the selector, the maximum effective contact time between the sludge and the wastewater is reached ( Fig. 9B At the time dt in the reactor, the agitator M is started, and the sludge is flushed into the reactor B through the agitator M, and then the above steps are repeated.

[0053] For all the preferred variants mentioned, the (return) sludge 6 and / or 6' can also be introduced into the selector intermittently or at different flow rates.

[0054] It goes without saying that all the above preferred variants can also be used in a sludge return line parallel to the purification reactor using only a portion of the return sludge. In this case, the proportion of return sludge treated in the selector S is preferably greater than 30 wt%, more preferably greater than 50 wt%, most preferably greater than 70 wt%.

[0055] All previously proposed preferred variants are preferably combined with the separation and discharge of the smallest or worst settling sludge particles in the sludge discharge 7. Mechanical or gravity separators can be used, and such separators are usually located in the return sludge, in the selector S, but can also be used in parallel with the bioreactor B, or between B and the final settling tank NB. By using such separators in combination with the optimization of the residence and contact time distribution in the selector S, the granulation in the continuous purification is further promoted.

[0056] Preferably, this sludge discharge of the smallest and worst settling sludge particles accounts for at least 30 wt% of the total amount of sludge discharged from the continuous purification process (surplus sludge), more preferably at least 40 wt% of the surplus sludge, more preferably at least 60 wt%. Preferably, the average size of the smallest sludge particles separated and thus discharged is at most 0.4 mm, even more preferably at most 0.2 mm. This increases the proportion of granular sludge.

[0057] As mentioned above, this selective emission (see Figure 1A and 1B ) can be performed at various locations in the activated sludge system, such as between the activated sludge reactor B and the secondary settling tank NB, in the final settling tank NB, in the return line of the activated sludge system, and also in the anaerobic selector S. All embodiments of the selector S preferably also have a device for separating and discharging the smallest or worst settling sludge particles. In one variant, the device such as the discharge is located at the top of the selector S. For example, Fig. 9A It is shown how the selective discharge is carried out at the top of the sludge bed in selector c. The upper part of this tank contains particularly the smallest size sludge, and by discharging from the upper part of the tank, the smallest particles are thus separated from the larger sludge particles closer to the bottom of the tank. Figure 2b shows the sludge discharge 7 occurring in the upper part of compartment Sb, where the concentration of the smallest sludge is highest, Fig. 9A It is shown how the smallest sludge e is discharged via the sludge discharge 7.

[0058] List of implementation plans

[0059] A method for purifying substrate-containing wastewater in a continuous flow-through aerobic biological activated sludge reactor B, wherein, optionally after a pretreatment step VB of the supplied wastewater 1, at least a portion of the biological sludge 6 is conditioned with at least a portion of the substrate-containing wastewater 2 to be purified in a selector S under anaerobic or anoxic conditions,

[0060] wherein the conditioning comprises first accumulating sludge particles having a settling velocity of at least 2 m / h, and then contacting the substrate-containing wastewater with the accumulated sludge particles in a selector S for a contact time of at least 10 minutes, wherein the selector S is operated or designed such that during the contact between the sludge and the substrate-containing wastewater, the sludge retention time in the selector S is greater than the hydraulic retention time of the sludge / water mixture 3 in the selector,

[0061] And wherein, optionally after an additional anaerobic or anoxic contact step, the sludge / water mixture 3 is supplied to an aerobic purification reactor B and subjected to aerobic treatment B, wherein the treated wastewater 4 after aerobic treatment is optionally separated from the sludge by sedimentation, flotation or mechanical separation in a secondary sedimentation tank NB, and wherein the selector receives the sludge 6 separated from the aerobically treated wastewater and / or (at least a portion of) the sludge 6' from the aerobic purification reactor B.

[0062] 1. The method according to embodiment 1, wherein in the selector, the sludge 6 and the wastewater 2 are subjected to discrete changes in flow rate and / or flow rate gradients under anaerobic or anoxic conditions.

[0063] 2. A method according to embodiment 2, wherein the discrete change in flow velocity is achieved by a discrete change in the flux in the flow direction of the selector and / or by a discrete change in the flow rate.

[0064] 3. A method according to any one of the preceding embodiments, wherein the accumulated sludge is saturated with substrate-containing wastewater in the selector, preferably to the extent that at least 60%, preferably at least 75% and more preferably at least 80% of the readily biodegradable substrate (rbCOD) is adsorbed by the sludge.

[0065] 4. A method according to any of the preceding embodiments, wherein during contacting the accumulated sludge with the substrate-containing wastewater, at least 20 wt% of the sludge in the selector S has a residence time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector, and wherein preferably at least 40%, more preferably 50% to 90% of the sludge in the selector has a residence time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector.

[0066] 5. A method according to any of the preceding embodiments, wherein during contacting the accumulated sludge with the substrate-containing wastewater, at least 20%, preferably at least 40%, more preferably 50% to 90% of the sludge in the selector has a residence time in the selector that is at least 40% longer than the hydraulic retention time of the sludge / water mixture in the selector.

[0067] 6. A method according to any one of the preceding embodiments, wherein the selector adjusts the sludge-wastewater mixture so that at least 20%, more preferably 40% to 100% of the sludge in the aerobic biological purification reactor B is granular sludge with a minimum particle size of 0.212 mm.

[0068] 7. A method according to any one of the preceding embodiments, wherein the selector adjusts the sludge-wastewater mixture so that the proportion of granular sludge is at least 25wt%, preferably at least 30wt%, most preferably at least 40wt%, and in particular at least 50wt%; and preferably at least 20wt% of this granular sludge (i.e., sludge with a size of at least 0.212mm) in the aerobic biological purification reactor B, or more preferably at least 25wt%, preferably at least 30wt%, most preferably at least 40wt%, and in particular at least 50wt% of this granular sludge has a particle size of at least 0.4mm to 1.0mm.

[0069] 8. A method according to any one of the preceding embodiments, wherein at least 10 wt % of the largest sludge particles are in contact with the maximum substrate concentration in the selector for a time that is at least 20% longer than the average contact time of the sludge, and wherein the maximum substrate concentration is at least 50% higher than the substrate concentration contacted by 15 wt % of the smallest sludge particles in the selector.

[0070] 9. A method according to any of the preceding embodiments, wherein in addition to or instead of the return sludge 6 from the secondary settling tank NB or the sludge 6' from the biologically activated sludge reactor B, the selector S is supplied with a sludge portion received from a mechanical or gravity separator, which is arranged to selectively discharge the slowest settling sludge in the biological purification or in the return sludge to the sludge treatment line.

[0071] 10. The method according to any of the preceding embodiments, wherein the concentration of rapidly biodegradable substrates is increased by dosing an external carbon source, by a side stream from a sludge treatment line that is part of a treatment plant using the biological purification reactor, or by pre-treating the wastewater in whole or in part by hydrolysis or fermentation.

[0072] 11. A method according to any of the preceding embodiments, wherein the selector S is an upflow reactor having a set of concentric compartments, having an inner first compartment Sa and at least one or more additional compartments (Sb, Sc, etc.) concentrically surrounding the inner compartment, the additional compartments being connected to the previous compartment at the bottom and the top, wherein the supply of (return) sludge 6 and / or sludge 6' is located in the lower part of the first compartment Sa, and each subsequent compartment has an inlet for the wastewater 2 entering the bottom, so that the sludge and wastewater are in contact with each other, whereby the selector provides a vertical flow ('upflow') in the compartment.

[0073] 12. A method according to any one of embodiments 1 to 11, wherein the selector S is an upflow reactor having three adjacent and interconnected compartments Sa, Sb and optionally Sc, the compartments having adjusted volumes, wherein the effective volume of compartment Sa is smaller than the effective volume of Sb, wherein the biological sludge 6 and the substrate-containing wastewater 2 to be purified flow sequentially from Sa to Sb and from Sb to Sc, the compartments being fluidly connected to the previous compartment at the bottom and top, wherein the supply of (return) sludge 6 and / or sludge 6' is located at the bottom of the first compartment Sa, and each subsequent compartment has an inlet for the wastewater 2 entering the bottom, so that the sludge and wastewater are in contact with each other, whereby the selector provides vertical flow ('upflow') in the compartments.

[0074] 13. A method according to any one of embodiments 1-11, wherein the selector S is an upflow reactor having a plurality of, preferably three, adjacent and interconnected compartments Sa, Sb and optionally Sc, the compartments having adjusted volumes, wherein the effective volume of compartment Sa is smaller than the effective volume of Sb, wherein sludge 6 and / or sludge 6' and substrate-containing wastewater 2 to be purified flow sequentially from Sa to Sb and from Sb to Sc, the compartments being connected to the previous compartment at the top, wherein the inlet for the wastewater 2 is located at the bottom of the compartment, and the inlet for the return sludge 6 and / or sludge 6' is located at the liquid level, whereby the selector provides vertical flow ('upflow') in the compartment.

[0075] 14. A method according to any of the preceding embodiments, wherein the selector S comprises at least two compartments Sa and Sb, in which the supply of wastewater 2 and (return) sludge 6 or sludge 6' is alternately carried out with the discharge of conditioned sludge, and wherein the sludge is discharged by alternating the liquid level (6b) in the compartment and / or somewhere between the bottom level (6a) of the compartment and the liquid level at a rate preferably per hour per m2. 2 The cross-sectional area of ​​the selector is at least 2m 3 The flow rate of the wastewater provides sludge 6 or sludge 6' to accumulate the desired sludge, and wherein the desired distribution of sludge residence time in the selector S is obtained by supplying wastewater 2 to the compartment at the bottom of the compartment, and wherein the discharge of the conditioned sludge can be achieved by applying a flow rate change and / or applying mixing and / or by extracting at least a portion of the sludge / wastewater at the bottom level (3a) of the compartment.

[0076] 15. A method according to embodiment 15, wherein the selector S operates intermittently.

[0077] 16. The method according to any one of the preceding embodiments, wherein the change in the flow rate in the selector is achieved by changing the feed flow rate of the wastewater.

[0078] 17. The method according to any of the preceding embodiments, wherein the variation of the flow rate in the selector is achieved by changing the feed rate of the sludge 6 and / or sludge 6'.

[0079] 18. The method according to any of the preceding embodiments, wherein the selector S is also fed with a portion of return sludge and / or excess sludge from another purification line.

[0080] 19. The method according to any of the preceding embodiments, wherein the selector S is followed by or integrated with a granular sludge reactor operating on the sequencing batch principle.

[0081] 20. The method according to any of the preceding embodiments, wherein the formation of granular sludge is accelerated and / or its maintenance is supported by adding a carrier material having an average size of 0.05 mm to 2.5 mm and a relative density or specific gravity equal to or greater than the wastewater.

[0082] 21. The method according to any one of the preceding embodiments, wherein the sludge in reactor B comprises a mixture of biological sludge and suspended biofilm carriers. DETAILED DESCRIPTION

[0083] The present invention relates to a method for purifying substrate-containing wastewater in a continuous flow-through aerobic biological activated sludge reactor B, wherein, optionally after a pretreatment step VB of the supplied wastewater 1, at least a portion of the biological sludge 6 is conditioned with at least a portion of the substrate-containing wastewater 2 to be purified in a selector S under anaerobic or anoxic conditions,

[0084] wherein the conditioning comprises first accumulating sludge particles having a settling velocity of at least 2 m / h, and contacting the substrate-containing wastewater with the accumulated sludge particles in a selector S for a contact time of at least 10 minutes, wherein the selector S is operated or designed so that the sludge retention time in the selector S is greater than the hydraulic retention time of the sludge / water mixture 3 in the selector, thereby achieving contact of larger or faster settling sludge particles with the highest substrate concentration,

[0085] and wherein the sludge / water mixture 3 is fed to an aerobic purification reactor B and subjected to an aerobic treatment B, optionally after an additional anaerobic or anoxic contacting step,

[0086] wherein the treated wastewater 4 after aerobic treatment is optionally separated from the sludge by sedimentation, flotation or mechanical separation in a secondary settling tank NB, and wherein the selector receives (at least a portion of) the sludge 6 separated from the aerobic treated wastewater and / or the sludge 6' from the aerobic purification reactor B. The selector is preferably operated or designed so that during the contact of the sludge with the substrate-containing wastewater, the residence time of at least 20 wt% of the sludge in the selector is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector.

[0087] In particular, the present invention relates to a method for purifying substrate-containing wastewater in a continuous flow-through aerobic biological purification reactor B, wherein at least a portion of the biological sludge 6 is conditioned with at least a portion of the substrate-containing wastewater 2 to be treated in a selector S under anaerobic or anoxic conditions (whether or not after a conventional pretreatment step VB of the supplied wastewater), wherein the conditioning comprises first accumulating sludge particles having a settling velocity of at least 2 m / h, and contacting the substrate-containing wastewater with the accumulated sludge particles in the selector S for a contact time of at least 10 minutes, after which contact time the substrate-containing wastewater is contacted with the remaining sludge particles in the selector S, and the operation or design of the selector S is such that the sludge retention time in the selector S is greater than the hydraulic retention time of the sludge / water mixture in the selector, thereby achieving contact of larger or faster settling sludge particles with the highest substrate concentration,

[0088] so that, preferably during the period of contact between the sludge and the substrate-containing wastewater, at least 20% of the sludge in the selector has a retention time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector,

[0089] wherein the sludge / water mixture 3 (with or without any additional anaerobic or anoxic contact time) is fed to an aerobic purification reactor B and subjected to (conventional) aerobic purification,

[0090] The treated (purified) wastewater 4 after aerobic treatment is separated from the sludge by a sedimentation vessel NB, flotation or mechanical separation.

[0091] and wherein the selector receives (at least a portion of) the sludge 6 separated from the aerobically treated wastewater and / or the sludge 6' from the aerobic purification reactor B. A portion of the sludge (preferably the sludge particles with the worst settling) can be removed as sludge discharge 7. Figure 1A and 1B .

[0092] In the context of the present invention, the terms "purified" wastewater and "treated" wastewater are used interchangeably. Throughout the specification and claims, the term "residence time" is to be understood as the average residence time, unless explicitly stated otherwise.

[0093] After initial accumulation of rapidly settling sludge in selector S, the substrate-containing wastewater is contacted with the accumulated rapidly settling sludge for a contact time sufficient to allow the larger particles of the accumulated sludge to absorb the readily biodegradable substrate and become saturated with the concentrated substrate-containing wastewater before the wastewater is contacted with the remaining sludge in the selector. Saturation can be measured, for example, by monitoring P release from the sludge, the amount of readily biodegradable organic matter in the selector effluent, or changes in the redox curve, conductivity, pH, extinction, color, or other parameters that vary with substrate absorption.

[0094] In the above method, the accumulated sludge is separated based on the difference in sedimentation rate under anaerobic or anoxic conditions in a selector, and the larger sludge particles (characterized by a higher sedimentation rate) are controlled to obtain a longer contact time with the wastewater, and the larger sludge particles are contacted with a higher substrate concentration in the wastewater compared to the smaller sludge particles. This can be achieved by, for example, applying (i) multiple stages with discrete or discontinuous flow rate changes, (ii) an increasing flow rate gradient (i.e., a continuously increasing flow rate) or a combination of (i) and (ii) in the selector.

[0095] In one embodiment, the sludge / water mixture in the selector is subjected to discrete changes in flow rate and / or flow rate gradients under anaerobic or anoxic conditions. In a specific embodiment, the discrete changes in flow rate are achieved by discrete changes in flux in the selector flow direction and / or discrete changes in the flow rate of the supply wastewater and / or return sludge.

[0096] Advantageously, starting from conventional activated sludge, granular sludge is produced by the above method, preferably within 200 days after the start-up of the method, more preferably within 100 days after the start-up of the method. As described above, since granular sludge settles significantly faster than sludge flocs, significantly smaller settlers can be used and / or significantly more sludge can be retained during the purification process, thereby providing a more extensive purification of the wastewater. In the proposed process, granular sludge is obtained in a continuous flow-through wastewater purification process, and smaller settling volumes or higher upflows can be used, while still maintaining effective separation of sludge and treated water. In addition, the volume of anoxic tanks or anoxic compartments between the anoxic zone and the aerobic zone in the aerobic treatment reactor can be reduced, or such anoxic tanks / compartments are not required, and there is no need to circulate water / sludge from the aerobic zone to the anoxic zone and the anoxic zone, while still removing nitrogen compounds from the wastewater in large quantities.

[0097] In one embodiment, the anoxic reactor compartment or reactor zone between the anoxic and aerobic steps (a) and (b) may be excluded.

[0098] As mentioned above, the present invention particularly relates to a method for continuous flow-through wastewater purification, wherein wastewater 1 is optionally pretreated in a primary settling tank VB, and the pretreated wastewater 2 is subsequently:

[0099] (a) contacting with biological sludge 6 and / or 6' in a selector S under anaerobic conditions to obtain a mixture of wastewater and sludge, wherein the selector S controls and / or ensures that the sludge retention time is greater than (extends) the hydraulic retention time, preferably until at least 20% of the accumulated sludge in the selector has a retention time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector,

[0100] (b) wherein the stream 3 containing the sludge conditioned in the selector is subsequently conveyed to an aerobic purification reactor B, and

[0101] (c) wherein sludge is optionally separated from the wastewater (by settling in a secondary settling tank NB, flotation or mechanical separation) to obtain treated wastewater 5, and wherein the selector receives (at least a portion of) sludge 6 separated from the aerobically treated wastewater and / or sludge 6' from the aerobic purification reactor B. Preferably, a portion of the sludge particles having the worst settling may be removed from the treatment process as stream 7. This sludge removal 7 may be performed at a different location or a combination of multiple locations within the treatment process.

[0102] In the above step (a), the fast settling biological sludge entering S is first accumulated or concentrated, and then the substrate-containing wastewater is contacted with the accumulated sludge particles in the selector S for a contact time of at least 10 minutes, and then the stream 3 containing the sludge conditioned in the selector is transported to the aerobic purification reactor B. "Fast settling biological sludge" refers to sludge having a settling velocity of at least 2 m / h, preferably at least 2.5 m / h, and more preferably at least 3 m / h. The contact time is preferably 10 to 120 minutes, more preferably 20 to 90 minutes.

[0103] In this way, the selector controls the larger, faster settling sludge particles to be in contact with the higher concentration of substrate-rich wastewater for a longer time compared to the smaller, slower settling sludge particles. As a result, the MOs in these larger sludge particles can absorb more and longer substrates than the smaller sludge particles with shorter residence times and less contact with high substrate concentrations. This provides a competitive advantage for the growth of MOs, stimulating granule growth and subsequently forming and stably maintaining granular sludge in the continuous flow-through purification process.

[0104] Preferably, at least 40%, more preferably 50% to 90% of the sludge in the selector has a residence time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector during contacting of the sludge with the substrate-containing wastewater.

[0105] If no pretreatment is required, wastewater streams 1 and 2 are identical and can be interchanged.

[0106] In one embodiment, preferably at least 40%, more preferably 50% to 90% of the sludge in the selector has a residence time in the selector that is at least 40% longer than the hydraulic retention time of the sludge / water mixture in the selector during contacting the sludge with the substrate-containing wastewater.

[0107] Preferably, the selector adjusts the sludge-wastewater mixture so that the proportion of granular sludge in the aerobic biological purification reactor B is at least 25wt%, preferably at least 30wt%, most preferably at least 40wt%, and especially at least 50wt%; and preferably at least 20wt%, or more preferably at least 25wt%, preferably at least 30wt%, most preferably at least 40wt%, and especially at least 50wt% of this granular sludge (i.e., sludge with a size of at least 0.212mm) in the aerobic biological purification reactor B has a particle size of at least 0.4mm to 1.0mm.

[0108] In a preferred embodiment, the improved granular sludge size distribution and sludge residence time distribution according to the present invention is achieved by using a selector S which applies discrete or discontinuous flow rate changes, preferably a selector S with different compartments (Sa, Sb, etc.) and their own flow rates, wherein the flow rate in a subsequent compartment is always 25% to 50% of the flow rate in the previous compartment.

[0109] More preferably, the selector S is an upflow reactor with a collection of concentric compartments, with an inner first compartment Sa and at least one or more concentrically surrounding additional compartments (Sb, Sc, etc.), which are always in fluid communication with the previous compartment at the bottom and top, wherein the supply of (return) sludge 6 and / or sludge 6' is located in the lower part of the first compartment S, and each subsequent compartment has an inlet for the wastewater 2 entering the lower part, so that the sludge and wastewater 1 are in contact with each other, whereby the selector provides a vertical flow ("upflow") in the compartments. The diameters of the different compartments can be selected by a person skilled in the art to achieve the desired difference in flow rate between adjacent compartments. In this way (a1), the mixture is selected according to the settling rate, and the first part of the sludge S1 (including the slower settling sludge) is brought to the second compartment through the overflow, while the second part of the sludge S2 (including the faster settling sludge) is collected at the bottom and brought to the second compartment through the connection at the bottom, wherein the faster settling sludge S2 in the second compartment is preferably brought back into contact with the wastewater at a lower flow rate, and the process of separating the faster settling sludge S3 at the bottom and in communication with the third compartment from the slower settling sludge S4 entering the third compartment through the overflow is repeated. In this way, the contact time of the faster settling sludge with the wastewater is increased, and it is also achieved that the largest sludge particles experience the highest substrate concentration and can preferentially adsorb the substrate to form granular MO. Reference Figure 2A for further explanation.

[0110] In one embodiment, the selector S is an upflow reactor having three adjacent and interconnected compartments Sa, Sb and optionally Sc, the compartments having adjusted volumes, wherein the effective volume of compartment Sa is smaller than the effective volume of Sb, wherein biological sludge 6 and / or sludge 6' and substrate-containing wastewater 2 to be purified flow successively from Sa to Sb and from Sb to Sc, the compartments always being fluidly connected to the previous compartment at the bottom and top, wherein the supply of (return) sludge 6 and / or sludge 6' is located in the lower part of the first compartment, and each subsequent compartment has a wastewater inlet into the lower part 2, so that the sludge and wastewater 1 are in contact with each other, whereby the selector provides vertical flow ("upflow") in the compartments. Reference Figure 2B For further explanation.

[0111] In the method according to the invention, the variation of the flow rate in the selector is achieved by varying the feed rate of the wastewater 2. The inventors have found that fluctuations in the wastewater flow rate 2 during the day can further improve the sludge retention time distribution. In particular, during periods of low supply, the best settled sludge particles accumulate around the bottom of the different compartments, thereby having the greatest contact with the wastewater with the highest concentration and the lowest dilution. This makes the sludge retention time distribution of the sludge in the selector more thorough.

[0112] In the method according to the invention, the variation of the flow rate in the selector is achieved by varying the flow rate of the sludge 6 and / or the sludge 6' fed to the selector.

[0113] In a preferred embodiment, granulation is further stimulated not only by influencing the distribution of sludge age in the selector, but also by increasing the substrate concentration in the supplied wastewater (by adding a suitable external carbon source or pre-treating the supplied wastewater by processes such as hydrolysis, fermentation, etc.) to promote the growth of granulated MO. In this way, the proportion of rapidly biodegradable substrates (such as fatty acids) is preferably increased to at least 15% of the total substrate concentration, or more preferably to at least 25% of the total substrate concentration. In one embodiment, the concentration of the substrate is increased by adding an external carbon source, a side stream from a sludge treatment line (which is part of a treatment plant using a biological purification reactor) or by pre-treating all or part of the wastewater by hydrolysis or fermentation.

[0114] There is no restriction on the source of wastewater. The wastewater treated according to the method of the present invention generally contains organic nutrients (organic matter), also referred to as substrate-containing wastewater in the context of the present invention. Generally, the biochemical oxygen demand (BOD) in the wastewater entering is at least 50 mg / l, for example 100 mg / l to 10000 mg / l. Any type of wastewater, such as sewage or water in industrial production processes, can be treated according to the present invention. Therefore, the method according to the present invention can also be referred to as wastewater treatment. The wastewater treated according to the method of the present invention can be pre-treated before step (a), for example, wastewater that has been treated at the primary level known in the art, although the primary treatment is not always necessary for the effective operation of the method. Typical wastewater pretreatment technologies include one or more of the following: purification, removal of coarse suspended solids, removal of grease and primary sedimentation.

[0115] In one embodiment, the proportion of rapidly biodegradable fatty acids in the wastewater source is less than 10 wt% to 15 wt% of the total substrate / nutrients, and / or the fatty acid concentration in the supplied wastewater fluctuates, so that the proportion is less than 10 wt% to 15 wt% at least 20% of the time. The inventors have found that low fatty acid concentrations and their variations complicate continuous wastewater treatment based on granular sludge technology; the use of a selector according to the present invention makes continuous wastewater purification based on granular sludge technology easy to manage.

[0116] The selector S according to the present invention is part of the anaerobic zone. In a preferred embodiment, the selector S forms the (only) anaerobic zone. The conditions in the selector S are called "anaerobic" because no oxygen is added. As mentioned above, the conditions in the selector S can also be anoxic. Under anaerobic conditions, in addition to organic pollutants, there are also oxidized nitrogen compounds, such as nitrites and nitrates, and MOs that convert these compounds into harmless nitrogen can multiply. Under anaerobic conditions, the concentration of such oxidized nitrogen compounds is limited or completely absent. Under such conditions, MOs that store phosphates can multiply. In the anaerobic zone, the conditions and residence time of the wastewater allow the sludge particles to absorb organic nutrients from the incoming wastewater. These organic nutrients are usually stored in microorganisms in the form of polymers (e.g., poly-β-hydroxybutyrate (PHB)). In the anaerobic zone of the step, the typical average residence time of the mixture of sludge and water is 15 minutes to 5 hours, preferably 30 minutes to 2 hours.

[0117] As mentioned in the introduction, in the prior art, granular sludge is defined as sludge with a size of at least 0.212 mm (usually less than 6 mm) and does not coagulate during the sedimentation process, so the SVI after 5 minutes of sedimentation is equivalent to the SVI after 30 minutes of sedimentation. Flocculent sludge has a smaller size. Although a small amount of flocculent sludge may be present in the wastewater purification system according to the present invention, the method is intended to reduce the proportion of flocculent sludge. Since the flocculent sludge has a shorter residence time in the selector S and is less in contact with the substrate in the selector - of course not in contact with the substrate with the highest substrate concentration in the selector - the growth of flocculent sludge is not promoted and the proportion of flocculent sludge is still less. In the present method, the proportion of flocculent sludge with a size of 0.212 mm or less is preferably limited to a maximum of 50% by weight, preferably less than 40% by weight, and more preferably less than 30% by weight. The process operates smoothly with such a limited amount of flocculent sludge and, moreover, the amount of flocculent sludge can be further reduced by removing, in particular via the sludge discharge 7, sludge with poor settling properties (residual sludge discharged from the purification system to prevent sludge accumulation due to continued sludge growth), for example by extracting this sludge as far as possible from the inlet of the secondary settling tank, or by extracting this sludge at a place in the selector where the proportion of faster settling sludge is small, or by applying a gravity or mechanical separator in the return sludge or in parallel with the aerobic reactor or selector and removing the minimum sludge obtained thereby.

[0118] In the context of the present invention, the terms "faster settling sludge" and "heavy sludge" are considered synonyms, as are the terms "slower settling sludge" and "light sludge". Settling rate or settling velocity is generally determined in the art. A practical measure of settling rate known in the art is the sludge volume index (SVI). The SVI is defined as the volume (in ml) occupied by 1 gram of sludge after a certain settling time. For granular sludge according to the present invention, the ratio of the SVI after 5 minutes of settling (SVI-5) to the SVI after 30 minutes of settling (SVI-30) has a typical value of less than 3, typically 1 to 2.5, more typically about 1.5, while the SVI-5 / SVI-30 ratio of conventional flocculated sludge is greater than 3.

[0119] In view of the presence of microorganisms, the sludge present in the system according to the invention can also be called "activated sludge". The microorganisms required for the method according to the invention can be found in the sludge of conventional wastewater treatment plants. They do not need to be separated, because the conditions set by the invention control these microorganisms to remain as part of the granular sludge.

[0120] The mixture of wastewater and sludge leaving the selector S is subsequently transferred to an aerobic reactor B, to which oxygen molecules are supplied (aeration), for example using an aerator known in the art. The average residence time of the mixture of sludge and water in the aerobic reactor B can vary greatly, depending on, for example, the amount and type of pollutants in the incoming wastewater and the desired degree of purification, and is generally 1 to 30 hours, preferably 2 to 20 hours. The average residence time of the sludge also depends on the amount and type of pollutants in the incoming wastewater and the desired degree of purification, and is generally 3 to 40 days, preferably 5 to 20 days. The aeration rate in the aerobic zone is such that the dissolved molecular oxygen concentration in the wastewater in the reactor B is preferably at least 0.5 mg / l, more preferably at least 1 mg / l, while preferably not higher than 5 mg / l, more preferably not higher than 10 mg / l. The present invention does not involve modifying conventional aerobic reactors and aerobic conditions herein.

[0121] In addition to aerobic zones or compartments, the reactor B may also have zones and compartments where anoxic conditions occur, which may be used to achieve denitrification and further remove nitrogen compounds from the wastewater.

[0122] Subsequently, the biologically purified wastewater is preferably separated from the mixture of sludge and water from reactor B. This is usually achieved by sedimentation (secondary sedimentation in a secondary sedimentation tank NB), but can also be achieved by mechanical separation, flotation, filtration or other means. This sedimentation and separation step of separating the sludge from the treated water is common in conventional wastewater treatment plants. Since there is granular sludge instead of flocculated sludge, the sedimentation tank can be much smaller than the conventional tank required for the sedimentation of flocculated sludge (for example, about one-fourth the area for the same wastewater input), or filtration can be achieved with a higher filtration flux. The incoming mixture of water and sludge from reactor B stays in the sedimentation tank or similar separator for a sufficient period of time. Once the sludge has been separated from the water, the biologically treated wastewater is clean enough to be discharged into the environment, although for some applications and / or locations, additional further treatment may be required, such as filtration or removal of, for example, metals.

[0123] The water treated according to the invention discharged from a clarifier or similar separator is the main product of the process according to the invention. Compared to the incoming wastewater, the purified water is freed from organic matter (organic nutrients). The treated water can be discharged into the environment, further purified or used as required.

[0124] In the above method, the sludge is subjected to natural selection so that, starting from conventional activated sludge, the formation of granular sludge occurs preferably within 200 days after start-up, more preferably within 150 days after start-up, and granular sludge always accounts for the majority of the sludge during the purification process. By initially starting the purification process with sludge that already contains at least part of granular sludge, the formation of a large part of granular sludge can be accelerated and supported. Preferably, the proportion of granular sludge in the sludge added to the system during the start-up is at least 15% by weight, and the sludge concentration is 3 kg / m 3 , preferably greater than 0.6kg / m 3 More preferably, the start-up is carried out with a sludge of which more than 50% is already granular sludge.

[0125] In addition, by continuously or occasionally adding solids or chemicals to which sludge particles can adhere to increase their size or weight in the sludge, the formation and stable maintenance of granular sludge can be accelerated and supported. This solid support material preferably has a size of 0.05mm to 2.5mm and a specific gravity comparable or greater than that of wastewater. This material can be, for example, granular sludge from another reactor, activated sludge of screening, classified sand, plastic particles or other natural or synthetic materials. For example, a specific gravity of at least 1.05kg / l is added to the sludge. MO is the sludge that will adhere to the material, causing the density of the sludge particles to increase, thereby increasing the sedimentation rate. A similar effect is achieved by adding liquid chemicals (such as iron salts, aluminum salts, calcium salts, etc.) so that the salt in the sludge / water mixture reacts to form a solid.

[0126] The present invention can also be used in parallel with conventional treatments that do not form granular sludge or do not allow large amounts of granules to form. Fig.10 . Wherein the purification line L1 is a conventional purification, its bioreactor includes one or more compartments or reactors capable of achieving different combinations of aerobic, anoxic and anaerobic process conditions. In the figure, this is represented as B1, B2 and B3, but it can also be more or less parts. The purification line L2 is a method according to the present invention. By connecting the discharge sludge line from L2 to L1, the purification line according to the present invention also has a synergistic effect on the operation, sludge properties and MO of the conventional purification line. This is achieved by not discharging the sludge (7) from the purification line L2 to the sludge treatment, but transferring it in whole or in part to one or more bioreactor components (line 8). After all, this discharge sludge has better biomass properties, larger size and stronger simultaneous denitrification capacity than the conventional sludge in the conventional line, and therefore will improve the sludge properties and operation in the conventional line. This synergistic effect can be further enhanced by transporting a portion of the return sludge 6 and / or sludge discharge 7 from the conventional line L1 to L2 via line 9. In this way, part of the sludge of the conventional line is also affected by the selector S of line L2. As a result of the connection of the two purification lines described above, improved results and larger sludge particles are also obtained in line L1, without the need to treat all wastewater and sludge with the innovative selector S and without the need to convert L1 into a purification device according to the invention. In one embodiment, the method according to the invention comprises the step of feeding the waste sludge 7 (as 8) to a conventional treatment device, preferably a treatment device without the means to obtain granular sludge. In another embodiment, the method according to the invention comprises the step of feeding excess sludge or part of the return sludge from a conventional purification device.

[0127] In another variant, the same synergistic effect can be obtained by arranging the selector according to the invention after or integrated with an aerobic granular sludge (AGS) reactor operated as a sequencing batch system (SBR) and connecting the selector to a continuous flow conventional system (as described above). Fig.10 . The purification line L3 comprises a selector according to the invention as well as an AGS SBR. The sludge discharge (7) from the S-AGS-SBR in L3 is conveyed to the conventional line L1 via line 10. As with the previously described synergistic connection, the sludge discharge (7) or part of the return sludge (6) from the conventional line can also be conveyed to the selector S (via line 9).

[0128] Based on the above, the present invention is also characterized in that in an embodiment, the selector S is also fed with return sludge and / or a portion of the sludge discharge from another purification line, or the selector S is arranged after or integrated with a granular sludge reactor operating according to the sequencing batch principle. Therefore, it is preferred that the selector S is fluidly connected or integrated with the granular sludge reactor operating according to the sequencing batch principle.

[0129] In a preferred embodiment, the method is operated in parallel with one or more other wastewater purification process lines, wherein the selector S receives the biological sludge 6 and / or the sludge 6' and a portion of the biological sludge 9 from these other parallel wastewater purification process lines, and wherein optionally a portion of the biological sludge 6 is directed to these other parallel wastewater purification process lines.

[0130] Example

[0131] The advantages of the present invention have been clearly demonstrated in the operation of the pilot plant. The pilot plant consists of a series of six 0.075m 3 Up to 0.15m 3 Mixed anaerobic compartment (selector S A To S F ) selector zone, a series of 6 mixed anoxic / aerobic reactor compartments (reactor B A To B F )(1m each 3 ), and 0.32m 3 The last reactor compartment B FA partially submerged manifold is also included for periodic discharge of sludge after the settling period, designed to increase retention of the better settled sludge. A portion of the return sludge can also be discharged as excess sludge. Positive displacement pumps are used for recirculation of mixed liquor (from the aerobic zone to the anoxic zone) or return sludge (from the clarifier to the anaerobic selector). The return sludge can be distributed between the anaerobic selector and the first aerobic / anoxic compartment. The mixed aerobic / anoxic compartments are equipped with independently controllable fine and coarse bubble aeration. The sludge in all mixed compartments is suspended by mechanical agitation. With this pilot, multiple configurations of the flow-through granular activated sludge system configuration were tested.

[0132] The inventors first ran the pilot in a configuration that represented the prior art. The prior art was believed to be a multi-stage activated sludge process with a plug flow anaerobic selector and using selective sludge discharge. The configuration was as follows:

[0133] 1. Wastewater and return sludge flow into the selector tank S A , and flow through the selector pool S in sequence B , S C , S D , S E and S F The working volume of each pool is 0.075m 3 ;

[0134] 2. Reactor B A : Hypoxia;

[0135] 3. Reactor B B To B E : Aerobic, operated at a dissolved oxygen concentration (DO) of 2 mg / l;

[0136] 4. Reactor B F : Aerobic, equipped with a submerged manifold for selective sludge discharge, with the sludge settling selection criterion set at 3m / h; and

[0137] 5. Clarifier.

[0138] After the primary clarification stage, the pilot plant was fed with municipal wastewater. The primary effluent contained on average 425 mg / l chemical oxygen demand (COD), 8.1 mg / l phosphorus (P), 6 mg / l P, 51 mg / l ammonium (N) and 110 mg / l total suspended solids (TSS). The influent flow rate was 250 l / h to 500 l / h, and the sludge recirculation coefficient from the clarifier to the anaerobic selector was 0.5 to 1.0. From the reactor B E To B A The flow rate of the anoxic cycle was equal to the combined influent and return sludge flow rates. Before starting the experiment, the reactor was inoculated with Aerobic granular sludge from the reactor. During the experiment, the sludge settling characteristics and sludge size distribution were monitored. In order to distinguish between flocculent sludge and granular sludge, the sludge samples were classified using a 200 μm sieve and then the dry solids level of the classified fraction was measured.

[0139] The experiment was repeated using the same configuration and similar flow rates and wastewater composition, but now using two 0.375 m 3 The selector S A and S B . The two selector tanks are operated in an anti-parallel cycle. First, the selector is fed with return sludge from the clarifier at a height of 50% of the selector liquid height, with sludge having an accumulated settling rate of at least 3 m / h. The feed flow rate corresponds to a surface load of about 3 m / h and the sludge / water mixture overflows from the top water level of the selector (3b in Figure 8). Afterwards, the selector is fed with wastewater, which is introduced horizontally at the bottom and flows upward through the accumulated sludge while overflowing from the top (3b in Figure 8). Finally, before repeating the accumulation cycle, the conditioned sludge is replaced by feeding sludge at the top of the selector (6b in Figure 8) while discharging the sludge / water mixture at the bottom of the selector (3a in Figure 8). The pilot plant is again inoculated with sludge from Aerobic granular sludge in reactor.

[0140] Fig.11a The sludge volume index and the sieve fraction are plotted over time after inoculation with aerobic granular sludge in a flow-through pilot plant, where (a) is a prior art configuration; and (b) is a configuration according to FIG8b. Fig.11A It can be seen that the particle level in the sludge decreased and the SVI 30 In two months the typical levels of granular sludge increased to those of flocculated sludge. It is clear that the granular MO was replaced by flocculated growth MO. The total sludge amount also decreased from about 6 g / l TSS to about 2.5 g / l TSS. Using the selector according to the invention, in contrast to the first described experiment, the particle amount did not drop substantially and a particle size of 1 mm was maintained throughout the experiment: Fig.11b Not only did particles make up a large portion of the total sludge volume over a period of more than 400 days, but the total sludge volume increased from about 4 g / l TSS to about 6 g / l TSS to 7 g / l TSS, which is significantly higher than the experiment with the prior art configuration. In addition, after the first decline caused by equipment problems, the percentage of particles in the total sludge volume remained at a high level of 60% to 80%, and showed an increase after the initial decline. In addition, Fig. 11B The amount of smaller particles decreased, while the amount of larger particles increased. e SVI 30The concentration of sludge was maintained at 40 to 70 ml / g, which is consistent with sludge having good settling properties. In addition, the sludge concentration was maintained at about 4 to 5 g / l TSS.

Claims

1. A method for purifying substrate-containing wastewater in a continuous flow-through aerobic biological activated sludge reactor B, wherein: Optionally after a pretreatment step VB of the supplied wastewater 1, at least a portion of the biological sludge 6 is conditioned with at least a portion of the substrate-containing wastewater 2 to be purified in a selector S under anaerobic or anoxic conditions, wherein the conditioning comprises first accumulating sludge particles having a settling velocity of at least 2 m / h, and then contacting the substrate-containing wastewater with the accumulated sludge particles in the selector S for a contact time of at least 10 minutes, and wherein the selector S is operated or designed so that during the contact between the sludge and the substrate-containing wastewater, the sludge retention time in the selector S is greater than the hydraulic retention time of the sludge / water mixture 3 in the selector, and wherein, optionally after an additional anaerobic or anoxic contact step, the sludge / water mixture 3 is supplied to an aerobic purification reactor B and subjected to aerobic treatment B, wherein the treated wastewater 4 after aerobic treatment is optionally separated from the sludge by sedimentation, flotation or mechanical separation in a secondary sedimentation tank NB, and wherein the selector receives (at least a portion of) the sludge 6 separated from the aerobically treated wastewater and / or the sludge 6' from the aerobic purification reactor B.

2. The method according to claim 1, wherein: In the selector, the sludge 6 and the wastewater 2 are subjected to discrete changes in flow rate and / or flow rate gradients under anaerobic or anoxic conditions.

3. The method according to claim 2, wherein: The discrete variation of the flow velocity is achieved by a discrete variation of the flux in the flow direction of the selector and / or by a discrete variation of the flow rate.

4. A method according to any one of the preceding claims, wherein: The accumulated sludge is saturated with substrate-containing wastewater in the selector, preferably to the extent that at least 60%, preferably at least 75% and more preferably at least 80% of the readily biodegradable substrate (rbCOD) is adsorbed by the sludge.

5. A method according to any one of the preceding claims, wherein: During the period of contacting the accumulated sludge with the substrate-containing wastewater, at least 20 wt% of the sludge in the selector S has a residence time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector, and wherein, preferably at least 40%, more preferably 50% to 90% of the sludge in the selector has a residence time in the selector that is at least 20% longer than the hydraulic retention time of the sludge / water mixture in the selector.

6. A method according to any one of the preceding claims, wherein: During contacting the accumulated sludge with the substrate-containing wastewater, at least 20%, preferably at least 40%, more preferably 50% to 90% of the sludge in the selector has a residence time in the selector that is at least 40% longer than the hydraulic retention time of the sludge / water mixture in the selector.

7. A method according to any one of the preceding claims, wherein: The selector adjusts the sludge-wastewater mixture so that at least 20%, more preferably 40% to 100% of the sludge in the aerobic biological purification reactor B is granular sludge with a minimum particle size of 0.212 mm.

8. A method according to any one of the preceding claims, wherein: The selector adjusts the sludge-wastewater mixture so that the proportion of granular sludge is at least 25wt%, preferably at least 30wt%, most preferably at least 40wt%, and especially at least 50wt%; and preferably at least 20wt% of this granular sludge (i.e., sludge with a size of at least 0.212mm) in the aerobic biological purification reactor B or more preferably at least 25wt%, preferably at least 30wt%, most preferably at least 40wt%, and especially at least 50wt% of this granular sludge has a particle size of at least 0.4mm to 1.0mm.

9. A method according to any one of the preceding claims, wherein: At least 10 wt % of the largest sludge particles are in contact with the highest substrate concentration in the selector for a time that is at least 20 % longer than the average contact time of the sludge, and wherein the highest substrate concentration is at least 50 % higher than the substrate concentration that 15 wt % of the smallest sludge particles are in contact with in the selector.

10. A method according to any one of the preceding claims, wherein: In addition to or instead of the return sludge 6 from the secondary settling tank NB or the sludge 6' from the biologically activated sludge reactor B, the selector S is also fed with a sludge portion received from a mechanical or gravity separator, which is arranged to selectively discharge the slowest settling sludge in the biological purification or in the return sludge to the sludge treatment line.

11. A method according to any one of the preceding claims, wherein: The concentration of rapidly biodegradable substrates is increased by dosing an external carbon source, by a side stream from a sludge treatment line as part of a treatment plant using the biological purification reactor, or by pre-treating the wastewater in whole or in part by hydrolysis or fermentation.

12. A method according to any one of the preceding claims, wherein: The selector S is an upflow reactor with a collection of concentric compartments, having an inner first compartment Sa and at least one or more further compartments (Sb, Sc, etc.) concentrically surrounding the inner compartment, the further compartments being connected to the previous compartment at the bottom and the top, wherein the supply of (return) sludge 6 and / or sludge 6' is located in the lower part of the first compartment Sa, and each subsequent compartment has an inlet for the wastewater 2 entering the bottom, so that the sludge and wastewater are in contact with each other, whereby the selector provides a vertical flow ('upflow') in the compartments.

13. The method according to any one of claims 1 to 11, wherein: The selector S is an upflow reactor having three adjacent and interconnected compartments Sa, Sb and optionally Sc, which have adjusted volumes, the effective volume of compartment Sa being smaller than the effective volume of Sb, wherein biological sludge 6 and substrate-containing wastewater 2 to be purified flow sequentially from Sa to Sb and from Sb to Sc, wherein the compartments are fluidically connected to the previous compartment at the bottom and top, and wherein the supply of (return) sludge 6 and / or sludge 6' is located at the bottom of the first compartment Sa, and each subsequent compartment has an inlet for the wastewater 2 entering the bottom, so that the sludge and wastewater are in contact with each other, whereby the selector provides vertical flow ('upflow') in the compartments.

14. The method according to any one of claims 1 to 11, wherein: The selector S is an upflow reactor having a plurality of, preferably three, adjacent and interconnected compartments Sa, Sb and optionally Sc, the compartments having adjusted volumes, wherein the effective volume of compartment Sa is smaller than the effective volume of Sb, wherein sludge 6 and / or sludge 6' and substrate-containing wastewater 2 to be purified flow sequentially from Sa to Sb and from Sb to Sc, the compartments being connected to the previous compartment at the top, and wherein the inlet for the wastewater 2 is at the bottom of the compartment, and the inlet for the return sludge 6 and / or sludge 6' is at the liquid level, whereby the selector provides vertical flow ('upflow') in the compartments.

15. A method according to any one of the preceding claims, wherein: The selector S comprises at least two compartments Sa and Sb in which the supply of wastewater 2 and (return) sludge 6 or sludge 6' is alternately carried out with the discharge of conditioned sludge and wherein the sludge is discharged by means of a flow rate of 100% by a flow rate of 200% by ...100% by a flow rate of 1 2 The cross-sectional area of ​​the selector is at least 2m 3 The flow rate of the wastewater provides sludge 6 or sludge 6' to accumulate the desired sludge, and wherein the desired distribution of sludge residence time in the selector S is obtained by supplying wastewater 2 to the compartment at the bottom of the compartment, and wherein the discharge of the conditioned sludge can be achieved by applying a flow rate change and / or applying mixing and / or by extracting at least a portion of the sludge / wastewater at the bottom level (3a) of the compartment.

16. The method according to claim 15, wherein: The selector S operates intermittently.

17. A method according to any one of the preceding claims, wherein: The change of the flow rate in the selector is achieved by changing the supply flow rate of the wastewater.

18. A method according to any one of the preceding claims, wherein: The change of the flow rate in the selector is achieved by changing the feed rate of the sludge 6 and / or sludge 6'.

19. A method according to any one of the preceding claims, wherein: The selector S is also fed with return sludge and / or a portion of excess sludge from another purification line.

20. A method according to any one of the preceding claims, wherein: The selector S is followed by a granular sludge reactor operating on the sequencing batch principle or is integrated with the latter.

21. A method according to any one of the preceding claims, wherein: The formation of granular sludge is accelerated and / or its maintenance is supported by the addition of a carrier material having an average size of 0.05 mm to 2.5 mm and a relative density or specific gravity equal to or greater than that of the wastewater.

22. A method according to any one of the preceding claims, wherein: The sludge in reactor B contained a mixture of biological sludge and suspended biofilm carriers.

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