Discontinuous method for purifying waste water

Abstract

The invention relates to a discontinuous method for purifying waste water (1), comprising the following repeating method steps: • supplying waste water (1) into at least one activated sludge reactor (300) via at least one intake; • aerating the reactor content; • terminating the aeration in order to settle the sludge; • drawing off clarified water (5) and excess sludge, wherein, prior to being supplied into the at least one activated sludge reactor (300), a solids fraction (2) is removed from the waste water (1) in the form of a primary sludge substrate, the solids fraction (2) undergoes a conditioning process in order to obtain an activated sludge having a granulated structure (4D), and the granulated sludge (4D) is supplied as needed to the at least one activated sludge reactor (300). The invention also relates to a device for this purpose.

Description

[0001] Discontinuous process for the treatment of wastewater

[0002] The invention relates to a discontinuous process for the purification of wastewater, in which the following steps are repeatedly carried out:

[0003] • Feeding wastewater into an activated sludge reactor;

[0004] • Ventilation of the reactor contents;

[0005] • Stop aeration to allow sludge to settle;

[0006] • Removal of clear water and excess sludge.

[0007] The process described above is a so-called SBR (Sequence Batch Reactor) process, in which – in contrast to continuously operating wastewater treatment plants, where the respective inflow and outflow correspond to the currently occurring wastewater volume – a predetermined amount of wastewater is collected and then pumped into an activated sludge reactor in a short period of time. The wastewater is treated in the activated sludge reactor essentially without any further wastewater input. After completion of a treatment cycle, the activated sludge reactor is partially emptied. Clarified water is withdrawn from the upper section of the activated sludge reactor, and a small amount of sludge is withdrawn from a lower section of the activated sludge reactor, which is usually disposed of.

[0008] Compared to continuously fed activated sludge processes, the SBR process offers several decisive advantages. The treatment process in this process takes place independently of hydraulic fluctuations in the influent flow. Furthermore, the reaction times can be easily adapted to varying influent concentrations without structural modifications. This minimizes fluctuations in the effluent concentrations. The temporarily elevated substrate concentrations increase bacterial metabolism. Furthermore, the prevention of bulking sludge and the selection of floc-forming bacteria can be achieved through the periodic alternation between nutrient supply during the filling phases and nutrient deficiency at the end of the reaction phases. Sedimentation of the activated sludge takes place under flow-free conditions and can be easily monitored if necessary.

[0009] A key feature of any SBR process is that a predetermined amount of activated sludge always remains in the activated sludge reactor, so that the reactor's usable capacity—i.e., the amount of wastewater added per treatment cycle—represents only a fraction of the total capacity of the activated sludge reactor. In conventional SBR processes, approximately half to two-thirds of the total capacity of the activated sludge reactor is constantly retained as activated sludge, while the remainder is used to feed wastewater. After the wastewater has been added, the activated sludge reactor is aerated in the usual way to carry out nitrification. If necessary, denitrification can be carried out by an anaerobic process section prior to aeration. After aeration is complete, a settling phase follows to form a layer of clear water above the activated sludge. The clear water is then drained off.In order to keep the amount of biomass and sludge and thus the sludge concentration in the activated sludge reactor constant, a certain amount of sludge must also be removed as excess sludge.

[0010] Such discontinuous wastewater treatment based on SBR technology can be found, for example, in EP 2 426 090 A2 or WO 96 / 16909 A1.

[0011] DE 196 20 158 A1 describes a process and device for the biological treatment of wastewater using an aeration stage with activated sludge containing nitrifying microorganisms. A portion of the return sludge is stabilized under nitrifying conditions in a separate sludge treatment stage before being returned to the aeration stage and retained to increase the sludge age. EP 2 792 646 A1 describes a discontinuous wastewater treatment process in which activated sludge is taken from an aeration tank and separated in a special hydrocyclone into a lighter fraction with a predominantly aerobic ammonium-oxidizing bacteria and a heavier fraction of anaerobic ammonium-oxidizing bacteria.

[0012] A key factor for the cycle times and thus the throughput of such an activated sludge plant is the duration of the settling phase, during which the sludge settles at the bottom of the reactor, and a layer of clear water forms above this activated sludge, which is then subsequently removed. The longer this settling phase lasts, the longer the cycle times and the reduced throughput.

[0013] It is therefore an object of the invention to reduce the duration of this settling phase in order to increase the throughput of the plant.

[0014] This object is achieved according to the invention in that a solid fraction in the form of preferably filtered primary sludge is removed from the wastewater before being fed into the at least one activated sludge reactor, this solid fraction is subjected to conditioning so that an activated sludge with a granulate structure is obtained, and this granulate sludge is fed to the at least one activated sludge reactor as activated sludge if required.

[0015] According to the invention, a solid fraction is removed from the raw wastewater, preferably by microfiltration and / or microsieving. This solid fraction, referred to as the primary sludge substrate, contains microorganisms that provide hydrolytic enzymes important for wastewater treatment. According to the invention, this primary sludge substrate is treated, with particular attention being paid to obtaining activated sludge with a granular structure that has a higher specific gravity than the activated sludge typically obtained from the incoming raw wastewater in the activated sludge reactor. This treatment particularly preferably takes place in at least one breeding reactor.

[0016] Due to its higher specific gravity, the resulting granular sludge has the advantage of quickly settling to the bottom of the tank after the aeration phase in both the breeding reactor and the activated sludge reactor. Furthermore, due to its granular structure, it is little to not disturbed even when fresh wastewater is added, which, under optimal conditions, allows the breeding reactor and the activated sludge reactor to be filled and drained simultaneously. This further reduces cycle time and allows for a corresponding increase in throughput.

[0017] Investigations by the applicant have shown that the solids content of the biomass is approximately 2.5 times that of the comparable volume of activated sludge used in a conventional reactor. A further advantage of the process according to the invention is that the more stable degradation processes result in an increase in the material conversion rates, even under fluctuating inflow conditions. This is because the selection or reduction of the wastewater constituents during the conversion of the organic components of the primary sludge substrate results in extensive hydrolysis of the substrate-storing organisms, preferably in the breeding reactor. This results in lower sludge loading with better and increased degradation performance.

[0018] The use of activated sludge with a granular structure has become well-known in continuously operated wastewater treatment plants. However, this granular sludge has the disadvantage that an undesirably high proportion of suspended matter remains in the treated wastewater. Therefore, the process according to the invention provides that only a portion of the activated sludge in the activated sludge reactor is replaced with granular sludge during each treatment cycle. This maintains the above-described advantages of granular sludge while simultaneously reducing the proportion of suspended matter in the treated clear water to a minimum.

[0019] The different terms used are explained in more detail below: In the context of this application, "primary sludge" or "primary sludge substrate" refers to a solid fraction that is removed from the raw wastewater, for example, by microfiltration and / or microsieving, and then subjected to conditioning. This conditioning produces a substrate sludge that forms the basis for the granular sludge. According to the invention, this granular sludge is introduced into the breeding reactor or activated sludge reactor as needed, and thus becomes part of the activated sludge contained therein, which degrades the organic contaminants in the wastewater using microorganisms (biocenosis).

[0020] In a preferred embodiment of the process, the solid fraction is separated from the untreated raw wastewater by microfiltration and / or microsieving before the wastewater is fed to pretreatment and / or directly to at least one breeding reactor and / or activated sludge reactor. Using the microfiltration process, an initial separation of solids from the wastewater occurs, whereby the excess primary sludge can be separated and disposed of without further dilution in the inlet to the breeding reactor and / or activated sludge reactor. The primary sludge substrate is then subjected to conditioning to produce a substrate sludge concentrate, which forms the basis for the formation of activated sludge with a granular structure.

[0021] It is particularly preferred that, in order to condition the primary sludge substrate, it is mixed with at least one alkaline conditioning agent in a first step, then the conditioned substrate sludge is concentrated, and this conditioned substrate sludge is then fed to at least one breeding reactor, wherein a granulate sludge is produced in the at least one breeding reactor, which granulate sludge is fed as activated sludge to the at least one activated sludge reactor as required.

[0022] A two-stage concentration of the conditioned substrate sludge has proven particularly effective in this regard. Initially, the substrate sludge is separated via a perforated partition wall in at least one mixing chamber, and in a second step, further concentration is carried out by settling the substrate sludge in at least one separation chamber. This results in a substrate sludge concentrate particularly suitable for the production of granular sludge, which produces a rapidly growing granular structure in the at least one breeding reactor. According to the invention, this granular structure is fed as activated sludge to the at least one activated sludge reactor as required.

[0023] To further increase throughput rates, a further embodiment of the invention provides for at least two activated sludge reactors to be fed via a breeding reactor. These two activated sludge reactors are preferably operated acyclically to each other to achieve a quasi-continuous wastewater treatment process. Depending on the influent load, the activated sludge reactors can be fed alternately one after the other or in parallel from the breeding reactor at the end of each cycle. This offers the advantage that the breeding reactor can be operated continuously (if there is sufficient wastewater production) and the downstream activated sludge reactors can be operated discontinuously. This achieves maximum hydraulic throughput at different usable volumes.

[0024] It can also be planned to operate at least two activated sludge reactors in series, so that the wastewater is treated in two stages. This reduces the suspended solids concentration in the treated wastewater to a minimum.

[0025] When feeding the granular sludge into the activated sludge reactor, it has been shown that, when introduced via the bottom or a side wall of the activated sludge reactor, it acts as a hydraulic barrier layer, preventing sludge clouds from rising when the activated sludge reactor is filled with raw wastewater. This allows the discharge and / or filling of the activated sludge reactor to occur more quickly than with conventional activated sludge reactors.

[0026] The invention is explained in more detail below using a non-limiting embodiment with the accompanying figure.

[0027] Fig. 1 is a schematic representation of a device for conditioning primary sludge, and

[0028] Fig. 2 is a schematic representation of a wastewater treatment plant according to the invention.

[0029] Figure 1 shows a plant 100 for conditioning primary sludge. A solid fraction 2 is extracted from the raw wastewater 1 via a filtration device 110, which in this case is designed as a belt filter system. This solid fraction 2 forms the primary sludge substrate, which is fed to a conditioning tank 120 via suitable pipelines. Excess primary sludge can be fed to a sludge treatment plant 115 or a digestion tower if necessary.

[0030] In this conditioning tank 120, the primary sludge substrate 2 is mixed with at least one alkaline dosing agent 3 while monitoring the pH value, temperature and nitrate and / or ammonium concentration by means of suitable measuring devices 124 and introduced into a mixing chamber 130 as substrate sludge 4A.

[0031] In this mixing chamber 130, the substrate sludge 4A is thickened and concentrated. Mixing in the mixing chamber 130 can be achieved mechanically and / or hydraulically by blowing in air in a mixing area 131 of the mixing chamber 130. Pre-thickening within the mixing chamber 130 occurs via a perforated partition wall 132, which separates the mixing area 131 from a thickening area 133. In this embodiment of the invention, measuring devices 134 for determining the organic matter content, in particular a COD probe, are arranged in the thickening area 133.

[0032] The excess water 5 is drained off via an overflow 135, while the thickened and conditioned substrate sludge 4B is transferred to a concentration chamber 140 with measuring devices 144A, in particular for monitoring the dry matter content. In this chamber, the substrate sludge 4B is further separated from the excess water 5 by settling, with the excess water 5 being fed, for example, to a buffer tank. The substrate sludge 4C concentrated and conditioned in this way is finally introduced into a breeding reactor 200. Before the substrate sludge 4C is introduced, the properties of the substrate sludge 4C are checked again using another measuring device 144B, in particular a COD probe.

[0033] In the breeding reactor 200, a coarse-grained, compact and heavy activated sludge with a granular structure, called granular sludge 4D, is produced by setting suitable environmental parameters, which - as shown in Fig. 2 - is then fed to one or more activated sludge reactors 300 as needed for the discontinuous purification of the wastewater 1.

[0034] Here, the breeding reactor 200 is preferably designed in a cylindrical shape, with the substrate sludge 4C being fed particularly preferably via a sludge inlet 210 provided in the bottom region of the breeding reactor 200. In order to obtain the activated sludge in granular form 4D required according to the invention, the breeding reactor 200 is equipped with numerous sensors and measuring devices 224, with the aid of which the water temperature, pH value, oxygen levels, and / or the acid buffer capacity are monitored.

[0035] Particularly preferred is a sludge level meter with an optical measuring device, with which the specific sludge weight of the granular sludge 4D contained in the breeding reactor 200 can be determined. By adding alkaline dosing agents 3, which are usually introduced into the breeding reactor 200 in pasty or liquid form via dosing pumps as required, an activated sludge 4D with a granular structure is obtained, which preferably has a specific sludge weight of at least 10 kg / m 3 and has a particle size of more than 1 mm (diameter).

[0036] Activated sludge with these physical properties allows for sludge settling times of less than 1 minute per meter of settling height, reducing the sludge index (ISV) from 100 ml / g according to the state of the art to less than 30 ml / g. This sludge index (ISV) is a measure of the settling properties of the sewage sludge from an activated sludge reactor.

[0037] An embodiment of the wastewater treatment plant 1000 according to the invention can be seen in Fig. 2. It is provided that at least one activated sludge reactor 300 is connected to at least one breeding reactor 200 via a sludge line 400A, through which the activated sludge with granular structure 4D grown in the breeding reactor 200 is introduced into the activated sludge reactor 300. Additionally, a filling line 400B is provided, through which excess water 5 can be transferred from the breeding reactor 200 to the activated sludge reactor 300 if necessary.

[0038] The breeding reactor 200 further comprises an outlet 235 through which excess water 5 can be drained off if necessary, an aeration device 230 and a sludge discharge 220 for removing excess sludge.

[0039] Thus, in addition to the flocculated activated sludge 4E normally present in the activated sludge reactor 300, there is a second activated sludge fraction in the form of granular sludge 4D, with both activated sludge fractions 4D and 4E actively participating in the purification of the raw wastewater 1. The addition of granular sludge 4D significantly improves the settling rate of the sewage sludge after the aeration phase in the activated sludge reactor 300, while at the same time, the flocculated activated sludge 4E keeps the suspended solids concentration low in the purified wastewater 6, which is discharged from the activated sludge reactor 300 via an outlet 310 after completion of the purification and settling cycle. Furthermore, the activated sludge reactor 300 has an outlet 320 for removing excess sludge. Likewise, the activated sludge reactor 300 is equipped with numerous measuring devices 324 that allow monitoring and control of the wastewater treatment process.Finally, an aeration device 330 and an overflow 335 are arranged on the activated sludge reactor 300.

[0040] While conventional granular sludge processes usually require downstream facilities to remove suspended matter due to an increased suspended matter concentration, such downstream facilities are not necessary in plants for the process according to the invention.

[0041] It is understood that the present invention is not limited to the above-mentioned embodiments. In particular, it can be provided that more than one breeding reactor feeds more than one activated sludge reactor. This, with appropriate process control, enables a quasi-continuous treatment process that can also be quickly adapted to varying wastewater inflow loads.

Claims

PATENT CLAIMS Discontinuous process for the purification of wastewater (1), comprising the repetitive process steps • Feeding of wastewater (1) into at least one activated sludge reactor (300) via at least one inlet, • Aerating the reactor contents, • Terminating aeration to settle sludge (4D, 4E), • Removal of clarified water (6) and excess sludge, characterized in that a solid fraction in the form of a primary sludge substrate (2) is removed from the wastewater (1) before it is fed into the at least one activated sludge reactor (300), this solid fraction is subjected to conditioning so that an activated sludge with a granular structure (4D) is obtained, and this granular sludge (4D) is fed to the at least one activated sludge reactor (300) as activated sludge as required. A batch process according to claim 1, characterized in that the solid fraction (2) is removed from the raw wastewater (1) by means of microfiltration and / or microsieving.A discontinuous process according to claim 1 or 2, characterized in that, for conditioning, the solid fraction (2) is first treated with at least one alkaline conditioning agent (3), followed by concentration of the conditioned substrate sludge (4A), and this conditioned substrate sludge (4C) is subsequently fed to at least one breeding reactor (200), wherein a granular sludge (4D) is produced in the at least one breeding reactor (200), which, if required, is fed to the at least one activated sludge reactor (300) as activated sludge.A discontinuous process according to claim 3, characterized in that the concentration of the conditioned substrate sludge (4A) is carried out in two stages, wherein first a separation of the substrate sludge (4A) takes place in at least one mixing chamber (130) via a perforated partition (132), and in a second step a further concentration takes place in at least one separation chamber (140) by settling the substrate sludge (4C). A batch process according to claim 3 or 4, characterized in that the granular sludge (4D) produced in the at least one breeding reactor (200) is fed to the at least one activated sludge reactor (300) as activated sludge as required. A batch process according to any one of claims 1 to 3, characterized in that at least two activated sludge reactors (300) are fed via a breeding reactor (200). A batch process according to any one of claims 1 to 6, characterized in that the granular sludge (4D) has a specific sludge density of at least 10 kg / m³. 3and has a particle size of over 1 mm (diameter). Device (1000) for carrying out a discontinuous process for the purification of wastewater (1) according to one of claims 1 to 7, with at least one activated sludge reactor (300), characterized in that at least one filtration device (110), preferably by means of microfiltration and / or microsieving, is provided for the removal of a solid fraction (2) from the wastewater (1), wherein the at least one filtration device (110) is connected to a device (100) for conditioning the solid fraction (2), wherein the device (100) for conditioning the solid fraction (2) is configured to produce granular sludge (4D), and the device (100) for conditioning the solid fraction (2) is connected to the at least one activated sludge reactor (300).Device (1000) according to claim 8, characterized in that the device for conditioning the solid fraction comprises at least one breeding reactor (300) for producing granular sludge (4D). Device (1000) according to claim 8 or 9, characterized in that the device (100) for conditioning the solid fraction (2) comprises at least one device for conditioning (120) and at least one device for concentrating (130, 140) the solid fraction (2).

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