Method for biologically purifiying concentrated wastewater

Abstract

The invention relates to the field of technologies for biologically purifying wastewater. The claimed method includes the steps of feeding raw wastewater into tanks containing activated sludge and successively providing anoxic, anaerobic and aerobic treatment conditions. Under anoxic conditions, the wastewater undergoes denitrification; under anaerobic conditions, it undergoes dephosphorization; and under aerobic conditions, it undergoes nitrification. Part of the mixed liquor is sent within a nitrate recycle stream to an anoxic tank, providing denitrification, and the remaining part is separated into purified water and activated sludge in a phase separator. The purified water is discharged, and the sludge is sent within an activated sludge recycle stream to the anoxic tank. The nitrate recycle flow rate is determined according to the formula R=(Ntot.raw-NNH4perm.) / Ntot.perm., where R is the nitrate recycle flow rate, Ntot.raw is the permissible total nitrogen concentration in the raw wastewater, Ntot.perm. is the permissible total nitrogen concentration in the purified wastewater, NNH4perm. is the permissible ammonia-nitrogen concentration in the purified wastewater. The technical result is that of purifying concentrated wastewater while reducing the number of mixed liquor recycle streams.

Description

[0001] METHOD OF BIOLOGICAL TREATMENT OF CONCENTRATED WASTEWATER

[0002] The claimed invention relates to the field of technologies for biological treatment of industrial and domestic wastewater, in particular to the treatment of wastewater with activated sludge using aerobic methods, in combination with anaerobic methods.

[0003] Currently, one of the most common and cost-effective methods of wastewater treatment is biological treatment using activated sludge. The main biogenic pollutants in wastewater are suspended solids, ammonium or total nitrogen, phosphates, and organic matter, the concentration of which is determined by determining the biological oxygen demand (BOD) or chemical oxygen demand (COD) in a wastewater sample.

[0004] Suspended solids are removed from the raw wastewater, as a rule, by sedimentation in primary settling tanks; filtration or flotation methods can also be used.

[0005] Nitrification technology is used to remove ammonium compounds from wastewater. Wastewater nitrification involves the biochemical oxidation of ammonia nitrogen by activated sludge in the presence of atmospheric oxygen to form nitrites and nitrates. The process operates under oxidizing conditions, and the tank in which it occurs is called a nitrification tank. This process occurs when the concentration of ammonia nitrogen in the feedwater exceeds 12 mg / dm3. 3 causes an increase in the concentration of nitrate nitrogen in treated wastewater above the standard value, which is about 9 mg / dm3 3When discharging treated wastewater into a reservoir. If the nitrate nitrogen concentration in treated wastewater exceeds the standard, it is necessary to treat the wastewater to reduce the nitrate nitrogen concentration to standard values. This is achieved by denitrifying the wastewater with activated sludge under anoxic conditions in the presence of nitrate nitrogen and organic matter. The process takes place in a denitrifying tank or by creating a zone with anoxic conditions (conditions under which dissolved oxygen concentrations are typically less than 0.8 mg / dm3). 3 , and the concentration of nitrate nitrogen exceeds 12 mg / dm3 3 ).

[0006] To remove phosphorus, biological dephosphation is used, based on the activity of phosphate-accumulating bacteria.

[0007] Organic matter present in wastewater is oxidized by bacteria through biochemical reactions in the presence of either dissolved atmospheric oxygen or the bound oxygen of nitrites and nitrates. The process of removing organic matter in the presence of dissolved atmospheric oxygen occurs in tanks called aerobic tanks or aeration tanks, and the process of oxidation of organic matter is called aerobic. This process is associated with the formation of carbon dioxide.

[0008] The process of organic matter removal also occurs in the presence of bound oxygen from nitrites and nitrates in reservoirs called denitrifying reservoirs, and this process of organic matter removal is called anoxic. This process reduces the concentrations of organic matter and nitrite and nitrate nitrogen, forming molecular nitrogen that diffuses from the reservoir into the atmosphere.

[0009] The "Anaerobic-Anoxic-Oxidative Process" (or "A2 / O Process") [1] is known from the prior art. It involves deeper phosphorus removal through the creation of alternating anaerobic-aerobic conditions during biological treatment. Wastewater enters a zone with anaerobic conditions, where phosphorus is displaced from the sludge cells. The sludge mixture then sequentially enters a zone of anoxic and then aerobic, or oxidic, conditions, where intensive phosphorus accumulation in the cell body is observed, and the phosphorus content in the sludge increases. Anoxic conditions are created by the influx of nitrates and nitrites from the aerobic zone, where they are formed from ammonium nitrogen in the presence of atmospheric oxygen under the action of activated sludge. The influx of nitrates and nitrites from the aerobic (oxidic) zone to the anoxic zone is accomplished through the organization of a recirculation cycle.A disadvantage of this technology is the low dilution rate of the initial wastewater by the return recirculation flow, which results in a high sludge load for concentrated wastewater sent for treatment. The high BODload on activated sludge, measured in terms of total BOD, exceeds 400 mg BOD per gram of activated sludge dry matter per day, reducing the effectiveness of biological treatment.

[0010] A five-section Bardenfo biological treatment process is known [2], including anaerobic, first - anoxic and aerobic zones, second - anoxic and aerobic zones, and also a phase separator in the form of a secondary clarifier. The original wastewater sequentially enters the anaerobic, first - anoxic and aerobic zones, second - anoxic and aerobic zones, and also into a phase separator in the form of a secondary clarifier. To ensure the condition for the dephosphotation process to occur, the return of activated sludge from the phase separator to the anaerobic zone is ensured. To ensure the condition for the denitrification process to occur in the first anoxic zone, the return of the sludge mixture with nitrates and nitrites after the first aerobic zone is ensured. The sludge mixture with nitrates and nitrites after the first aerobic zone is a product of the biochemical transformation of ammonium compounds in the first aerobic zone. Oxidizing conditions in the aerobic (oxide) zone are ensured by supplying atmospheric oxygen to this zone.

[0011] From the first oxidizing zone, in addition to returning the sludge mixture to the first anoxic zone, a portion of the treated wastewater at the original flow rate is sequentially sent for treatment with activated sludge in the second anoxic zone, to the second aerobic zone, and to a phase separator, where the sludge mixture is separated into purified wastewater and settled sludge. The purified wastewater is discharged, and the settled sludge is recirculated to the beginning of the anaerobic zone.

[0012] The second anoxic zone provides additional denitrification, consuming nitrate as an electron acceptor produced in the aerobic section and organic carbon as an electron donor during the oxidation-reduction reaction. In the final aerobic stage, gaseous nitrogen is released into the atmosphere. This stage ensures minimal phosphorus release into the secondary clarifier. The disadvantages of this treatment process include the large capacity of the facility, the high energy costs associated with wastewater recycling, and the additional costs of reagents, which must be added to the treated wastewater before the second anoxic zone as organic carbon.

[0013] 5 The University of Cape Town (UCT) treatment technology is known, or the UCT process, the wastewater treatment sequence of which is shown in Fig. 1. When treating wastewater using this technology, the initial wastewater 1 with a flow rate Q is sequentially fed for treatment with activated sludge in zones with anaerobic 3, anoxic 2 and aerobic 4 conditions. After treatment, the sludge mixture is fed for separation of sludge and treated wastewater in a phase separator 5, which can be, for example, a secondary settling tank. Treated wastewater 6 is sent to the outlet, and the sludge settled in the phase separator 5 is returned to the anoxic zone 2 with a recycle flow rate 7 of activated sludge (0.5-1.0) * Q. The excess portion of the activated sludge 8 is removed from

[0014] 15 systems and is sent for dewatering and disposal. Also, after the aerobic zone, part of the wastewater with nitrate recycle 9 (1.0-2.0)*Q is sent to the beginning of the anoxic zone 2. After the anoxic zone 2, part of the sludge mixture, called anoxic recycle 10, with a flow rate of (1.0-2.0)*Q is sent to the beginning of the anaerobic zone 3.

[0015] 20 Anaerobic conditions in anaerobic zone 3 are ensured by the absence of dissolved and bound oxygen in the initial wastewater 1, as well as by returning the sludge mixture with denitrified wastewater after anoxic zone 2 with anoxic recycle 10. In this case, in anaerobic zone 3, the concentration of organic matter decreases, phosphorus is released, and the concentration of ammonium nitrogen remains unchanged. After anaerobic zone 3, the sludge mixture enters anoxic zone 2. Nitrate recycle 9 is also fed to this zone, that is, a portion of the wastewater after aerobic zone 4 with an increased concentration of nitrites and nitrates formed in aerobic zone 4 from ammonium compounds under the action of atmospheric oxygen in the presence of activated sludge. Due to the creation of anoxic conditions, the concentration of organic compounds decreases and nitrites and nitrates are transformed into molecular nitrogen. The concentration of ammonium compounds remains virtually unchanged.This sludge mixture, with reduced concentrations of organic compounds, reduced concentrations of nitrate and nitrite nitrogen due to denitrification, and reduced concentrations of ammonium nitrogen due to dilution by 2-3 times with nitrate recycle, then enters the aerobic zone (aeration zone) 4. In this zone, in the presence of atmospheric oxygen, the biochemical oxidation of ammonium nitrogen to nitrates and nitrites occurs. After aerobic zone 4, part of the sludge mixture, the so-called nitrate recycle 9, is again sent to the beginning of the anoxic zone 2, and part is sent to phase separator 5 to separate purified wastewater 6 from activated sludge.

[0016] The disadvantage of this method is the increased energy consumption for providing three recycles: anoxic, nitrate and activated sludge recycle, as well as the lack of recommendations for the treatment of wastewater with a content of total or ammonium nitrogen in the original wastewater of over 35-40 mg / dm3. 3, with the discharge rate into the reservoir at a level of 9-10 mg / dm3 3 by total nitrogen.

[0017] The task that the specified technical solution is aimed at solving is to develop a multi-stage method for biological treatment of wastewater using anaerobic, anoxic and aerobic conditions with a minimum number of sludge mixture recycles and ensuring the possibility of treating wastewater with increased concentrations of ammonium compounds in the original wastewater, including up to 50 mg / dm3 3 and above.

[0018] The technical result of the claimed invention consists in ensuring the required degree of purification of concentrated wastewater with a concentration of ammonium compounds in the original wastewater of over 50 mg / dm3. 3 at the rate of discharge of wastewater into a reservoir with a total nitrogen concentration of 9-10 mg / dm3 3 , while reducing the number of sludge mixture recycles.

[0019] The technical result is achieved by the first version of the method for biological treatment of concentrated wastewater with activated sludge, including stages of treatment under anoxic, anaerobic and aerobic conditions, which includes stages in which the initial wastewater is fed into tanks with activated sludge, in which anoxic, anaerobic and aerobic treatment conditions are sequentially provided.In this case, denitrification of wastewater is carried out under anoxic conditions, dephosphotation is carried out under anaerobic conditions and nitrification is carried out under aerobic conditions, after which part of the sludge mixture is sent as part of the nitrate recycle to a tank with anoxic conditions, thereby ensuring denitrification in it, and the other part of the sludge mixture is separated into purified wastewater and activated sludge in a phase separator, after which the purified wastewater is discharged, and the activated sludge is sent as part of the activated sludge recycle to a tank with anoxic conditions, and the nitrate recycle flow rate is determined by the formula R = (No6in.ncx. - NNH4flon.) / Mtotal.add., where R is the nitrate recycle flow rate, Mtotal.init. is the concentration of total nitrogen in the original wastewater, Mtotal.add. is the permissible concentration of total nitrogen in the purified wastewater, H4add. - permissible concentration of ammonium nitrogen in treated wastewater.

[0020] After separation of the sludge mixture in the phase separator, excess activated sludge can be removed for disposal.

[0021] A secondary gravity settling tank, separator, aero separator, or flotation unit can be used as a phase separator.

[0022] The technical result is achieved by a second variant of the method for biologically treating concentrated wastewater with activated sludge, including treatment stages under anoxic, anaerobic, and aerobic conditions. This method involves feeding the feedstock wastewater into activated sludge tanks, where anoxic, anaerobic, and aerobic treatment conditions are sequentially achieved. Denitrification of the wastewater occurs under anoxic conditions, dephosphorization occurs under anaerobic conditions, and nitrification occurs under aerobic conditions. The sludge mixture is then separated into purified wastewater and the remaining sludge mixture in a device with pressure hollow fiber ultrafiltration membranes, after which the purified wastewater is discharged, and the remaining sludge mixture is sent as part of the nitrate recycle to a tank with anoxic conditions, thereby ensuring denitrification in it, while the flow rate of the nitrate recycle is determined by the formula R = (No6m.Mcx.-NNH4flon.) / Mtotal.where: R is the nitrate recycle rate, Mtotal.isch is the total nitrogen concentration in the original wastewater, Mtotal.add. is the permissible total nitrogen concentration in the treated wastewater, Mmn add. is the permissible ammonium nitrogen concentration in the treated wastewater. After separation of the sludge mixture in a device with pressure hollow fiber ultrafiltration membranes, the excess remaining sludge mixture can be removed for disposal.

[0023] The essence of the claimed method is explained by figures, which depict the following: Fig. 1 - a diagram of the UCT process, Fig. 2 - an illustration of an example of implementing the first version of the claimed method, Fig. 3 - an illustration of an example of implementing the second version of the claimed method.

[0024] The numbers indicate the following:

[0025] 1 - initial wastewater,

[0026] 2 - anoxic zone,

[0027] 3 - anaerobic zone,

[0028] 4 - aerobic zone,

[0029] 5 - phase separator,

[0030] 6 - purified water,

[0031] 7 - activated sludge recycling,

[0032] 8 - excess sludge,

[0033] 9 - nitrate recycling,

[0034] 10 - anoxic recycling,

[0035] 11 - feed pump,

[0036] 12 - pressure hollow fiber membrane module.

[0037] Both variants of the method of biological treatment of concentrated wastewater with activated sludge, including stages of treatment under anaerobic, anoxic and aerobic conditions, consist of stages in which the initial wastewater is fed into tanks with a sludge mixture, in which anoxic, anaerobic and aerobic treatment conditions are successively provided.

[0038] The first variant of the method is implemented using a water treatment plant that contains hydraulically interconnected tanks with a sludge mixture (a tank with an anoxic zone (first), a tank with an anaerobic zone (second), a tank with an aerobic zone (third)), a phase separator, an aeration system, and pumping equipment for moving the sludge mixture to create recirculation flows.

[0039] A secondary gravity settling tank, separator, air separator, or flotation unit can be used as a phase separator. The aeration system necessarily includes air blowers or compressors connected to distribution ducts and aerators located at the bottom of the aerobic tank.

[0040] In the first tank, denitrification of the incoming wastewater is carried out under anoxic conditions, achieved by recycling the sludge mixture after treatment in the aerobic (third) tank. After denitrification is complete, the wastewater is fed to the anaerobic (second) tank.

[0041] In the second tank, dephosphorization (release of bound phosphorus phosphates) of the incoming wastewater occurs under anaerobic conditions, created by the complete removal of nitrates and nitrites (in the first tank) through their reduction to molecular nitrogen in the anoxic tank. This tank is free of dissolved oxygen from the air and the bound oxygen of nitrates and nitrites, and the release of phosphorus phosphates occurs. After the dephosphorization process is complete, the wastewater is fed to the aerobic (third) tank.

[0042] In the third tank, wastewater is nitrified under aerobic conditions. Phosphorus-accumulating organisms released in the second tank with the anaerobic zone also grow here by absorbing phosphorus. Aerobic conditions are maintained by introducing atmospheric oxygen into the aerobic tank via compressors or blowers through air ducts and aerators. Organic matter concentrations are reduced, and ammonia nitrogen is converted into nitrate and nitrite nitrogen to achieve the specified maximum permissible concentrations of total nitrogen and ammonia nitrogen in the treated wastewater.

[0043] After the nitrification process is complete in the third aerobic tank, a portion of the sludge mixture is sent to a phase separator, where the treated wastewater and activated sludge are separated. From the phase separator, the treated wastewater is discharged, for example, into a reservoir, while the activated sludge (activated sludge recycle) is sent to the first tank. Another portion of the sludge mixture (nitrate recycle) from the third tank is also sent to the first tank, where anoxic conditions are created. Excess sludge, if any, is removed from the nitrate recycle of the sludge mixture, as it contains the maximum number of phosphorus-accumulating organisms. The activated sludge (activated sludge recycle) is returned to the tank with the anoxic zone after the sludge mixture passes through the phase separator.

[0044] Ensuring anoxic conditions during the first cycle of implementation of the first version of the cleaning method is carried out in advance, at the stage of commissioning works.

[0045] The residence time of the sludge mixture in the anoxic zone of the first and aerobic zone of the third reservoir can be taken based on the specified degree of nitrification processes in the aerobic zone and the complete course of the denitrification process in the anoxic zone, and the residence time of the sludge mixture in the anaerobic zone of the second reservoir is not less than 30 minutes.

[0046] The second variant of the method is implemented using a water purification plant that contains hydraulically interconnected tanks with a sludge mixture (a tank with an anoxic zone (first), a tank with an anaerobic zone (second), a tank with an aerobic zone (third)), a phase separator, which is a pressure ultrafiltration membrane apparatus consisting of a feed pump and a pressure hollow fiber membrane module, an aeration system, as well as pumping equipment for moving the sludge mixture in order to create a recirculation flow.

[0047] The aeration system necessarily includes air blowers or compressors connected to distribution air ducts and aerators located at the bottom of the aerobic tank.

[0048] The processes taking place in the first, second and third reservoirs are similar to those carried out in the first version of the claimed method.

[0049] The second variant of the claimed method differs from the first in that, after the nitrification process is complete in the third tank under aerobic conditions, the entire sludge mixture is sent to a pressure ultrafiltration membrane unit, where it is separated into treated wastewater and the remaining sludge mixture. The treated wastewater is then discharged, for example, into a reservoir, while the remaining sludge mixture (nitrate recycle) is sent to the first tank to create anoxic conditions at the rate of nitrate recycle. This treatment scheme eliminates the need for anoxic recycle and activated sludge recycle, due to the use of a phase separator in the form of a pressure ultrafiltration membrane unit. Any excess remaining sludge mixture, if any, is collected from the nitrate recycle, as it contains the maximum amount of phosphorus-accumulating organisms.

[0050] Ensuring anoxic conditions during the first cycle of implementing the second version of the cleaning method is carried out in advance, at the stage of commissioning works.

[0051] The residence time of the sludge mixture in the anoxic zone (first) and aerobic zone (third) of the reservoirs can be taken based on the specified degree of nitrification processes in the aerobic zone and the complete course of the denitrification process in the anoxic zone, and the residence time of the sludge mixture in the anaerobic zone (second) of the reservoir is not less than 30 minutes.

[0052] For the first and second variants of the claimed method, the volumetric flow rate of nitrate recycle Q B When returning the sludge mixture after aerobic treatment to the anoxic zone, it is necessary to take into account the required recycle coefficient R, in relation to the initial flow rate Oin, and can be determined using the formula:

[0053] Q B= QB*R, while the value of the recycling coefficient R is taken to be equal to no less than the ratio of the difference in the concentrations of total nitrogen total in the source waters and the permissible concentration of ammonium nitrogen yn4 доп in treated waters to the permissible concentration of total nitrogen in treated wastewater total.add, which can be determined by the formula

[0054] R = (No6iu.ncx _ NNH4flon) / Total additional (1)

[0055] Calculation of the activated sludge recycling rate for the first embodiment of the method is carried out using a known method, such as in the cited analogs of the claimed method. Examples of the implementation of the claimed method's variants are provided for the treatment technology for domestic wastewater with the parameters listed in Table 1. The initial wastewater quality parameters presented in Table 1 are typical for wastewater from small settlements, including shift settlements, and individual enterprises whose water supply systems typically consume low amounts of water, at a level of 100-120 liters per day per resident.

[0056] Table 1. Quality indicators of raw wastewater and requirements for its treatment

[0057] In the first case, when implementing the first variant of the claimed method (Fig. 2), using, for example, a gravity secondary clarifier as a phase separator 5, the initial wastewater 1 with a flow rate Q with the quality indicators presented in Table 1 is successively fed for treatment with activated sludge to zone 2 with anoxic, zone 3 with anaerobic, and zone 4 with aerobic conditions. After treatment, the sludge mixture is fed for separation of sludge and purified wastewater to phase separator 5, which is a secondary clarifier. Purified wastewater 6 is sent to the outlet, and the settled sludge is returned to the anoxic zone 2 with the flow rate of activated sludge recycle 7. The excess portion of activated sludge 8 is removed from the aerobic zone 4 and sent for dewatering and disposal. Also, after the aerobic zone 4, a portion of the wastewater with nitrate recycle 9 is sent to the beginning of the anoxic zone 2.

[0058] The treatment of the initial wastewater is carried out in a steady state with an activated sludge concentration of 3-5 g / dm3 3 and formed biocenoses of nitrifying, denitrifying and phosphorus-accumulating microorganisms.

[0059] Wastewater treatment is carried out as follows. Initial wastewater 1 with the parameters presented in Table 1, at a flow rate Q, enters the tank in which anoxic zone 2 is formed. Nitrate recycle 9 enters the same tank after the tank with aerobic zone 4. The flow rate of nitrate recycle 9 depends on the concentration of total nitrogen in the initial wastewater, the permissible concentration of total nitrogen and ammonium nitrogen in the treated wastewater, is determined by formula (1) and is 13 times the initial flow rate Q. Also, activated sludge recycle 7 enters this tank from phase separator 5 at a flow rate equal to 0.5...1.0 of the initial flow rate. As a result of creating anoxic conditions in the first tank under the action of activated sludge, a decrease in the concentration of organic compounds occurs due to the growth of microorganisms and a complete transformation of nitrate and nitrite nitrogen into molecular nitrogen.Ammonium nitrogen present in the original wastewater does not change, but its concentration decreases by 14 times and is about 10 mg / dm3. 3 After anoxic zone 2, the sludge mixture enters a tank where anaerobic zone 3 has formed. This zone is free of dissolved oxygen and the bound oxygen of nitrates and nitrites. Phosphorus is released from the phosphates, and the sludge mixture enters a tank where aerobic zone 4 has formed.

[0060] Aerobic zone 4 is formed by supplying oxygen to the sludge mixture tank from an air source, such as compressors or blowers, through a distribution system connected to aerators located at the bottom of the tank. The aeration system ensures an oxygen concentration of at least 4-6 mg / dm3 at the surface of the sludge mixture in the initial part of zone 4. 3 , and at the end of zone 4, an oxygen concentration of about 0.8-1.0 mg / dm3 is provided. 3In the aerobic zone, molecular nitrogen formed in anoxic zone 2 is removed, phosphorus released in anaerobic zone 3 is absorbed by phosphorus-accumulating bacteria, and organic matter concentrations are finally reduced. Ammonia nitrogen is converted into nitrate and nitrite nitrogen to achieve the specified maximum permissible concentrations of total nitrogen and ammonia nitrogen in the treated wastewater. Excess activated sludge 8 with elevated phosphate content is removed from aerobic zone 4 for dewatering and disposal.

[0061] After the aerobic zone 4, the sludge mixture with a flow rate of (1.5-2.0)*Q is also sent to the gravity-type phase separator 5, from where the purified wastewater 6 with a flow rate of Q is sent to the outlet, and the activated sludge via the activated sludge recycle 7 (with a flow rate of 0.5-1.0)*Q is sent to the entrance of the anoxic zone 2.

[0062] Purified wastewater 6 from the gravity-type phase separator 5 is directed to the outlet by gravity, and the recycle of activated sludge 7 and nitrate recycle 9 is ensured by the operation of pumping equipment.

[0063] When implementing the second variant of the claimed method, in the case of using (Fig. 3) a pressure ultrafiltration apparatus with hollow fiber membranes as a phase separator for purified wastewater and sludge mixture, the wastewater is purified in the following manner.

[0064] The initial wastewater 1 with a flow rate Q and the quality indicators presented in Table 1 are successively fed for treatment with activated sludge to zone 2 with anoxic, zone 3 with anaerobic, and zone 4 with aerobic conditions. After treatment in the specified zones, the sludge mixture is fed for separation of the treated wastewater to phase separator 5, which is an apparatus with pressure hollow fiber ultrafiltration membranes, consisting of a feed pump 11 and a pressure hollow fiber membrane module 12. Treated wastewater 6 is sent to the outlet, and the remaining sludge mixture (treated water and activated sludge) is returned to the anoxic zone 2 with the flow rate of nitrate recycle 9. According to this treatment scheme, it is not necessary to provide anoxic and sludge recycles. Periodically, the excess portion of the remaining sludge mixture is removed from the phase separator 5 and sent for dewatering and disposal.Treatment of the initial wastewater is carried out in a steady state with an activated sludge concentration of 8-10 g / dm3. 3 and formed biocenoses of nitrifying, denitrifying and phosphorus-accumulating microorganisms.

[0065] Wastewater treatment is carried out as follows. The initial wastewater 1 with the parameters presented in Table 1, at a flow rate Q, enters the tank in which an anoxic zone 2 is formed. Nitrate recycle 9 enters the same tank after the phase separator 5. The flow rate of nitrate recycle depends on the concentration of total nitrogen in the initial wastewater, the permissible concentration of total nitrogen and ammonium nitrogen in the treated wastewater, is determined by formula (1) and is 13 of the initial flow rates Q. As a result of creating anoxic conditions in the first tank under the action of activated sludge, a decrease in the concentration of organic compounds occurs due to the growth of microorganisms and the complete transformation of nitrate and nitrite nitrogen into molecular nitrogen. Ammonium nitrogen present in the initial wastewater does not undergo changes, while its concentration decreases by 14 times and is about 10 mg / dm 3After anoxic zone 2, the sludge mixture enters a tank where anaerobic zone 3 has formed. This zone is free of dissolved oxygen and the bound oxygen of nitrates and nitrites. Phosphorus is released from the phosphates, and the sludge mixture enters a tank where aerobic zone 4 has formed.

[0066] Aerobic zone 4 is formed by supplying oxygen to the sludge mixture tank from an air source, such as compressors or blowers, through a distribution system connected to aerators located at the bottom of the tank. The aeration system ensures an oxygen concentration of at least 4-6 mg / dm3 at the surface of the sludge mixture in the initial part of zone 4. 3 , and at the end of zone 4, an oxygen concentration of about 0.8-1.0 mg / dm3 is provided. 3 .

[0067] In aerobic zone 4, the removal of molecular nitrogen formed in anoxic zone 2 occurs, the absorption of phosphorus by phosphorus-accumulating bacteria released in anaerobic zone 3, the final reduction of organic matter concentrations and the transformation of ammonium nitrogen into nitrate and nitrite nitrogen to the specified values ​​of maximum permissible concentrations of total nitrogen and ammonium nitrogen in treated wastewater.

[0068] After aerobic zone 4, the sludge mixture, at a flow rate equal to 14 times the initial flow rate, is sent to phase separator 5, which is a pressure ultrafiltration apparatus consisting of a feed pump 11 and a pressure hollow fiber membrane module 12. After phase separator 5, purified wastewater 6 at the initial flow rate is sent to the outlet, and the remaining sludge mixture is returned to anoxic zone 2 with a nitrate recycle flow rate 9 equal to 13 times the initial flow rate. Periodically, the excess portion of the remaining sludge mixture is removed from phase separator 5 and sent for dewatering and disposal.

[0069] Purified wastewater 6 and nitrate recycle 9 are provided by the operation of the feed pump 11 of the phase distributor 5, which is a pressure ultrafiltration apparatus.

[0070] Thus, the claimed invention makes it possible to achieve a technical result consisting in ensuring the required degree of purification of concentrated wastewater with a concentration of ammonium compounds in the original wastewater of up to 50 mg / dm3 and higher at a rate of discharge into a reservoir of wastewater with a concentration of total nitrogen at the level of 9-10 mg / dm3, with a reduction in the number of recycles of the sludge mixture.

[0071] LIST OF USED SOURCES

[0072] 1. Volume 9: Advanced Biological Treatment Processes. L. K. Wang, N. K. Shammas, and Y. T. Hung (eds.) 738 pp. (2009). P.224, fig.7.5.

[0073] 2. Pat. U.S. No. 3964998 B2

[0074] 3. Volume 9: Advanced Biological Treatment Processes. L. K. Wang, N. K. Shammas, and Y. T. Hung (eds.) 738 pp. (2009). P.225, fig.7.7.

Claims

CLAUSES OF THE INVENTION 1. A method for biological treatment of concentrated wastewater with activated sludge, including stages of treatment under anoxic, anaerobic and aerobic conditions, comprising the steps of feeding the initial wastewater into tanks with activated sludge, in which anoxic, anaerobic and aerobic treatment conditions are sequentially provided, wherein denitrification of the wastewater is carried out under anoxic conditions, dephosphotation is carried out under anaerobic conditions and nitrification is carried out under aerobic conditions, after which part of the sludge mixture is sent as part of a nitrate recycle to a tank with anoxic conditions, thereby ensuring denitrification in it, and the other part of the sludge mixture is separated into purified wastewater and activated sludge in a phase separator, after which the purified wastewater is discharged, and the activated sludge is sent as part of an activated sludge recycle to a tank with anoxic conditions, wherein the nitrate recycle flow rate is determined by the formula K = (1Mob Щ.origin.- k1N4add.) / total.add., where R is the nitrate recycle flow rate, total.origin. is the concentration of total nitrogen in the original wastewater, Mtotal.add. is the permissible concentration of total nitrogen in the treated wastewater, Ымнadd. is the permissible concentration of ammonium nitrogen in the treated wastewater.

2. The method according to paragraph 1, in which, after separating the sludge mixture in the phase separator, excess activated sludge is removed for disposal.

3. The method according to any one of paragraphs 1-2, in which a secondary gravity-type settling tank or separator, or an aero-separator, or a flotation unit is used as a phase separator.

4. A method for biological treatment of concentrated wastewater with activated sludge, including stages of treatment under anoxic, anaerobic and aerobic conditions, comprising stages in which the initial wastewater is fed into tanks with activated sludge, in which anoxic, anaerobic and aerobic treatment conditions are provided sequentially, while under anoxic conditions denitrification of the wastewater is carried out, under anaerobic conditions dephosphotation is carried out and under aerobic conditions nitrification is carried out, then the sludge mixture is separated into purified wastewater and the remaining sludge mixture in an apparatus with pressure hollow fiber ultrafiltration membranes, after which the treated wastewater is discharged, and the remaining sludge mixture is sent as part of the nitrate recycle to a tank with anoxic conditions, thereby ensuring denitrification in it, while the nitrate recycle flow rate is determined by the formula K = (Mtotal.initial - Mmn4add.) / Mtotal.add., where: R is the nitrate recycle flow rate, Mtotal.initial is the concentration of total nitrogen in the original wastewater, Mtotal.add. is the permissible concentration of total nitrogen in the treated wastewater, Mmn add. is the permissible concentration of ammonium nitrogen in the treated wastewater.

5. The method according to claim 4, in which, after separating the sludge mixture in an apparatus with pressure hollow fiber ultrafiltration membranes, the excess remaining sludge mixture is discharged for disposal.

Images