CN1587123A - Physiochemical and biochemical interactive city sewage treating method - Google Patents

Abstract

The invention belongs to the technical field of environmental protection, and in particular relates to a physical-chemical-biochemical interactive urban sewage treatment method. The present invention sets pre-anoxic, anaerobic, anoxic, aerobic and other biochemical treatment units in a reactor and a physical and chemical treatment unit that can add flocculants. The physical and chemical units can be used for biochemical treatment under different operating modes. The difference of influent water quality and water quantity and the change of treatment requirements change the reaction conditions of each reaction unit, realize the series or parallel operation of biochemical and physical chemical treatment systems, and effectively remove organic pollutants, suspended solids, and nitrogen at the lowest operating cost. , phosphorus and other nutrients to ensure that the discharge requirements are met.

Description

A Physicochemical-Biochemical Interactive Urban Sewage Treatment Method

technical field

The invention belongs to the technical field of environmental protection, and in particular relates to a physical-chemical-biochemical interactive urban sewage treatment method.

Background technique

Generally speaking, sewage treatment technology can be divided into physical treatment technology, physical chemical treatment technology, biochemical treatment technology and chemical treatment technology, among which biochemical treatment technology of sewage is the most commonly used. There are also many kinds of biochemical treatment technologies, which are mainly classified according to the different conditions of microbial growth conditions and oxygen supply methods. In order to achieve the purpose of nitrogen and phosphorus removal in biological treatment, it is necessary to create anaerobic, anoxic, and aerobic regions in the space or time of the reactor, so as to realize different forms of anaerobic-aerobic phosphorus removal and aerobic-anoxic dephosphorization. Nitrogen, the required hydraulic retention time is longer, and some processes reach more than 12 hours, and the capital construction cost and operating cost are high. At present, biological nitrogen and phosphorus removal processes are widely used in the world. The commonly used ones are: conventional anaerobic/anoxic/aerobic process (A/A/O process), Bardenpho, UCT, VIP, SBR, ICEAS, CASS, UNITANK and Various oxidation ditch processes. With the improvement of sewage treatment and discharge requirements in our country, great progress has been made in the research of sewage treatment process in our country. In addition to the above-mentioned treatment process, my country has also researched and developed the inverted A/A/O process, hydrolysis-anaerobic- Micro-oxygen combined process, high-load activated sludge process, biological aeration filter, high-efficiency composite sewage biological treatment system, intensive treatment process, etc.

There are many physical and chemical treatment methods for water, among which chemical coagulation treatment is the most commonly used and most representative. Due to the large volume of urban sewage, the addition of coagulants results in high operating costs and large sludge production. Therefore, in the past, the use of chemical coagulation alone to treat urban sewage was seldom. In recent years, with the continuous introduction of high-efficiency and cheap chemicals, coupled with the increasingly high requirements for phosphorus removal, chemical coagulation has also begun to receive attention. Tongji University, China North China Design and Research Institute of Municipal Engineering and other units have carried out a pilot study on physical and chemical enhanced primary treatment of Shanghai's combined sewage, adding ferric chloride, polyaluminum sulfate, ferric sulfate and polyacrylamide to the sewage (PAM) used in combination has achieved good results, especially the removal of total phosphorus is stable.

The sewage treatment process that combines physicochemical and biochemical processes is also currently used. Its most notable feature is the addition of chemical coagulants in the process, and the rest are the same or similar to the ordinary activated sludge process. The denitrification effect of this type of process is poor, mainly The purpose is to help remove phosphorus, and the operating cost of sewage treatment is relatively high.

Several main urban sewage treatment processes are as follows:

(1) A/A/O and its improved process

With the increasing eutrophication of water bodies, the nitrogen and phosphorus discharge standards of urban sewage treatment plants are getting higher and higher. At present, the most widely used nitrogen and phosphorus removal process is A/A/O and its improved process. This process is mainly composed of Composed of anaerobic tank, anoxic tank, aerobic tank and secondary sedimentation tank, the removal effect of organic pollutants and suspended solids is good, but there are some disadvantages: ①The removal effect of nitrogen and phosphorus is unstable; ②Influent water quality and quantity The change of the hydraulic pressure has a great influence on the operation effect; ③The designed hydraulic retention time is longer, and the operating cost is higher.

(2) SBR and its modification process

SBR and its variant process realize anaerobic, anoxic and aerobic in time series to achieve the function of denitrification and phosphorus removal. The reaction and sedimentation process are concentrated in one pool, which has the advantages of less processing structures, small footprint and flexible operation. and other characteristics, but it also has some disadvantages: ①SBR and its variants both use decanters. Due to the limitation of the water output of the decanters, it is impossible to treat a large amount of water in a single tank, so this process is not suitable for large-scale sewage treatment plants; ②The volume utilization rate of the reactor is low, and the water head loss is large; ③The utilization rate of the system equipment is low, and the control is complicated; ④Affected by the reaction time, the reaction conditions of anaerobic, anoxic and aerobic cannot be fully guaranteed; ⑤The effluent is not continuous, and subsequent treatment difficulty.

(3) UNITANK process

The UNITANK process is actually very similar to the three-ditch oxidation ditch process. Although the secondary settling tank and the sludge return system can be omitted, they have ① no obvious independent anaerobic and anoxic areas, which affect the nitrogen and phosphorus removal effect; ② The sludge concentration in the reaction tank is unbalanced. In the later stage of the reaction cycle, the sludge concentration on the inlet side is low, and the sludge concentration on the sedimentation side is high. ③The number of UNITANK process equipment is large, the utilization rate of the equipment is low, and the control is complicated; ④The outlet weir is fixed, and the initial outlet The amount of water is difficult to determine and requires reflux.

Contents of the invention

The purpose of the present invention is to propose a flexible physical-chemical-biochemical interactive urban sewage that can generally adapt to various water quality and treatment requirements in view of the ubiquitous treatment problems of low organic matter concentration, low carbon-to-nitrogen ratio, and high nitrogen-phosphorus concentration in urban sewage Approach.

A physical-chemical-biochemical interactive urban sewage treatment method proposed by the present invention adopts an interactive reactor composed of a biochemical treatment unit and a physical-chemical treatment unit, wherein the biochemical treatment unit consists of a pre-anoxic pool 1, an anaerobic pool 2, and an anoxic pool 3 , aerobic pool 4, and post-aeration pool 5 are connected successively through the water holes of the partition wall. The physical and chemical treatment unit is composed of flocculation pool 6. The post-aeration pool 5 is connected with flocculation pool 6 through pipelines and valves. The biochemical treatment unit The pre-anoxic tank 1 is connected to the return sludge pipeline, the anaerobic tank 2 of the biochemical treatment unit is connected to the water inlet pipeline, the post-aeration tank 5 of the biochemical treatment unit is connected to the sedimentation tank 7, and one end of the physical and chemical treatment unit is connected to the water inlet pipe. The other end is connected to the sedimentation tank 7, and at the same time, the biochemical treatment unit and the physical and chemical treatment unit are connected through pipes and valves; the urban sewage enters the physical, chemical, biochemical and biochemical interactive reactor after being treated with grit, and the biochemical treatment unit is selected according to the difference in water quantity and quality. , Physical and chemical treatment units in series, parallel, or simultaneous biological nitrification and denitrification operation mode, biochemical treatment, physical and chemical treatment of sewage, and finally the mixed solution in the reactor enters the sedimentation tank for mud-water separation, and part of the precipitated sludge returns to the pre-anoxic pool, partly discharged as excess sludge, of which:

(1) When the influent water volume is 0.7-1.5 times of the design flow rate, the chemical oxygen demand of the influent water is 70mg/L-800mg/L, the biochemical oxygen demand is 30mg/L-400mg/L, and the suspended solids are 150mg/L When L-300mg/L, Kjeldahl nitrogen is 20mg/L-60mg/L, and total phosphorus is 2mg/L-8mg/L, the reactor adopts a series operation mode, and the pre-anoxic pool (1), anaerobic Pool (2), anoxic tank (3), aerobic tank (4), post-aeration tank (5), flocculation tank (6), and sedimentation tank (7) are connected in sequence through pipelines;

(2) When the influent flow rate is greater than 1.5 times the design flow rate, the chemical oxygen demand of the influent water is 70mg/L-400mg/L, the biochemical oxygen demand is 30mg/L-200mg/L, and the suspended solids are 150mg/L- 300mg/L, when the Kjeldahl nitrogen is 10mg/L-40mg/L, and the total phosphorus is 1mg/L-5mg/L; The oxygen tank (3) and the aerobic tank (4) are connected in sequence, and are connected in parallel with the flocculation tank (6) of the physical and chemical treatment unit through pipelines;

(3) When the influent flow rate is 0.7-1.0 times of the design flow rate, the chemical oxygen demand of the influent water is 100mg/L-300mg/L, the biochemical oxygen demand is 50mg/L-150mg/L, and the suspended solids are 150mg/L When L-300mg/L, Kjeldahl nitrogen is 20mg/L-60mg/L, and total phosphorus is 2mg/L-4mg/L, the simultaneous biological nitrification and denitrification operation mode is adopted, and the anaerobic pool (2) in the reactor, after The aeration tank (5) and the sedimentation tank (7) are connected successively.

In the present invention, when adopting the tandem operation mode, its control conditions are as follows: all urban sewage enters the anaerobic pool 2, the anoxic pool 3, and the aerobic pool 4 in the biochemical treatment unit in sequence, and reacts with chemical agents, and the biochemical treatment unit stay in the physical and chemical treatment unit for 4-8 hours; then enter the flocculation tank 6 in the physical and chemical treatment unit, fully mix with the flocculant, and stay in the physical and chemical treatment unit for 0.5-1 hour; finally the mixed solution enters the sedimentation tank for mud-water separation, and the sedimentation time is 2-4 Hours, the settled sludge returns to the pre-anoxic tank 1 for endogenous denitrification to remove nitrate nitrogen, the reflux ratio is 25-100%, the sludge after removing nitrate nitrogen and stabilized by anoxic enters the anaerobic tank.

In the present invention, when adopting parallel operation, its control conditions are as follows: the sewage is divided into 2 stocks, and one stream of sewage enters the anaerobic pool 2, the anoxic pool 3, and the aerobic pool 4 in the biochemical treatment unit, and reacts with chemical agents , the influent flow is 50%--80% of the total influent, and the water is discharged from the 4th end of the aerobic tank, and stays in the biochemical treatment unit for 4-6 hours; a stream of sewage enters the physical and chemical treatment unit, fully mixed with the flocculant, and flocculated The time is 0.5-1.5 hours, and the water intake is 20%-50% of the total water intake; after the two streams of sewage are treated, they are mixed into the sedimentation tank for mud-water separation. The sedimentation time is 1.5-3 hours, and part of the sludge is returned to the pre-sludge Oxygen tank, the sludge return ratio is 25-80%, part of the returned sludge is returned to the chemical flocculation tank, the sludge return ratio is 0--25%.

In the present invention, when the simultaneous nitrification and denitrification operation mode is adopted, the control conditions are as follows: all the sewage enters from the anaerobic tank 2, aerates through the rear aeration tank 5, and then enters the sedimentation tank 7 for mud-water separation, and simultaneously nitrifies and denitrifies The running time is 6-10 hours, the settling time is 3-5 hours, the flocculation tank 6 is used together as the post-aeration tank 5 for aeration, the sludge returns to the pre-anoxic tank (1), and the sludge return ratio is 50%-100 %, dissolved oxygen is 0.6mg/L-1.0mg/L.

In the present invention, the flocculant is one of polysilicon, polysilicon and aluminum, and the dosage is 20mg/L--80mg/L.

In the present invention, the physical-chemical-biochemical interactive reactor is composed of a pre-anoxic tank, an anaerobic tank, an anoxic tank, an aerobic tank, a post-aeration tank, a flocculation tank and a sedimentation tank. The pre-anoxic tank is used for anoxic denitrification of return sludge, and the denitrification carbon source is mainly from sludge components, or added by some urban sewage; the anaerobic tank is used for anaerobic phosphorus release during systemic biochemical phosphorus removal; The anoxic tank is used for denitrification and denitrification of the system; the aerobic tank is used for aerobic reaction processes such as organic matter degradation, ammonia nitrogen nitrification, and phosphorus absorption in the system; the post-aeration tank is used for simultaneous nitrification and denitrification in the front-end process Short-term high-intensity aeration promotes sedimentation; the flocculation tank is used as an auxiliary physicochemical treatment unit to enhance the phosphorus removal effect of the system when the system biochemical physicochemical series is running, and can also be operated as a biochemical unit to strengthen post-aeration. When running in parallel for biochemical and physical chemistry, as a separate physical and chemical treatment unit, it undertakes the physical and chemical treatment of part of the sewage.

The present invention is characterized by the comprehensiveness and flexibility of the reaction system.

The invention can effectively remove organic pollutants, total Kjeldahl nitrogen, suspended solids and part of phosphate through physical, chemical and biochemical interactive reactions. After being treated by the method of the present invention, effluent COD≤60mg/L, 5-day biochemical oxygen demand BOD _5≤20mg /L, suspended solid SS≤20mg/L, total nitrogen TN-N≤20mg/L, NH ₃ - N≤8mg/L (temperature>12°C), NH ₃ -N≤15mg/L (temperature≤12°C) and other indications can all meet or exceed the national "Urban Sewage Treatment Plant Pollutant Discharge Standard" (GB18918-2002) The primary standard (B standard) requirements.

Description of drawings

Fig. 1 is a schematic diagram of the layout of the interactive reactor of the present invention.

Numbers in the figure: 1 is the pre-anoxic tank, 2 is the anaerobic tank, 3 is the anoxic tank, 4 is the aerobic tank, 5 is the post-aeration tank, 6 is the flocculation tank, and 7 is the sedimentation tank.

Detailed ways

Example 1:

When the water quality and water quantity are normal, the series operation mode is selected. The specific steps are: introduce the urban sewage treated by sand settling in a certain place into the interactive reactor, the influent water enters the anaerobic pool 2, and the mixed solution in the aerobic pool is pushed through the wall. The flow pump returns to the anoxic tank 3; the return sludge enters the pre-anoxic tank 1, and the sewage flows through the anaerobic tank 2, the anoxic tank 3, the aerobic tank 4, and the post-aeration tank 5 in turn, and flows out of the flocculation tank 6 for reaction device, through the settling tank 7 water outlet. The average temperature of influent water is 22°C, and the average pH value is 7.37. The hydraulic retention time of sewage in the reactor is 9h, the average sludge reflux ratio is 100%, the average mixed liquid reflux ratio is 200%, the sludge concentration is maintained at 3.5g/L, and the average sludge age is 10d.

After testing, the average value of COD _Cr is 335mg/L when entering water, and the average value is 42mg/L when effluent, with a removal rate of 87.5%; The rate is 92%; the average value of ammonia nitrogen is 30mg/L when entering water, the average value of effluent is 3.4mg/L, and the removal rate is 88.7%; the average value of TN is 35mg/L when entering water, and the average value is 12mg/L when effluent , and the removal rate was 65.7%. The average value of TP in the water inlet is 3.89mg/L. When no flocculant is added, the average value of the water outlet is 1.1mg/L, and the removal rate is 71.7%. , the average TP concentration in the effluent is less than 0.5mg/L.

Example 2:

For combined sewage pipelines during heavy rains, or when the water volume increases during heavy rains due to pipe network leakage and other reasons in separate pipelines, the mode of parallel connection of physicochemical and biochemical processes is run. At this time, except that the sewage is treated through the unit anaerobic pool 2, anoxic pool 3, and aerobic pool 4 (running in an aerobic mode), the water is discharged to the secondary sedimentation tank (to keep the organic load of the biological treatment system unchanged), and the overloaded part of the sewage The flow is diverted to the rear aeration tank 5 and the flocculation tank 6, and after physical and chemical strengthening treatment, it is merged into the secondary sedimentation tank.

The urban sewage treated by sand settling in a certain place is introduced into the interactive reactor. The average water temperature of the incoming water is 26.5°C, and the average pH value is 7.44. The hydraulic retention time of sewage in the biochemical treatment unit is 5.6h, the average sludge return ratio is 100%, the average mixed liquid return ratio is 150%, the sludge concentration is maintained at about 3.0g/L, and the average sludge age is 15d. The hydraulic retention time of the physical and chemical treatment unit is 0.4h, and the average sludge return ratio is 25%.

After testing, the average value of COD _Cr is 123mg/L when entering the water, and the average value is 38mg/L when the water is discharged, and the removal rate is 69%. The removal rate is 82%; the average value of ammonia nitrogen is 18mg/L when entering water, the average value of effluent is 3.9mg/L, and the removal rate is 78.2%; the average value of TN is 21mg/L when entering water, and the average value is 14.2mg/L L, the removal rate was 32.4%. The average value of TP in the water inlet is 2.4mg/L, and when the dosage of polysilicon ferrosilicon flocculant is 30mg/L, the TP in the outlet water can be kept below 0.6mg/L.

Example 3:

When the influent COD and TN concentrations are not high or the water volume is not large, the sewage treatment runs in parallel mode. At this time, 70% of the influent water enters the rear aeration tank 5 and the flocculation tank 6 to make full use of the chemical biological flocculation, and achieve the purpose of removing organic matter and phosphorus within a reaction time of less than 1 hour, and 30% of the sewage enters the pre-aeration tank in turn. Anoxic pool 1, anaerobic pool 2, anoxic pool 3, and aerobic pool 4 are used for organic matter degradation and denitrification. At this time, pre-anoxic pool 1, anaerobic pool 2, anoxic pool 3, and aerobic pool 4 also Partial operation is possible, and some units are on standby.

The urban sewage treated by sand settling in a certain place is pumped into the interactive reactor, the average temperature of the influent water is 25°C, and the average pH value is 7.32. The hydraulic retention time of sewage in the biochemical treatment unit is 5.6h, the average sludge return ratio is 100%, the average mixed liquid return ratio is 150%, the sludge concentration is maintained at around 3.0g/L, and the average sludge age is 20d. The hydraulic retention time of the physical and chemical treatment unit is 0.5h, and the average sludge return ratio is 50%.

After testing, the average value of COD _Cr is 90mg/L when entering the water, and the average value is 28mg/L when the water is discharged, and the removal rate is 68.9%. The rate is 78.5%; the average value of ammonia nitrogen is 12mg/L when entering water, the average value of effluent is 3.6mg/L, and the removal rate is 71%; the average value of TN is 12.7mg/L when entering water, and the average value is 7.6mg when effluent /L, the removal rate was 12.1%. The average value of TP in the water inlet is 1.5mg/L, and when the dosage of polysilicon aluminum flocculant is 20mg/L, the TP in the outlet water can be kept below 0.6mg/L.

Example 4:

Run the simultaneous nitrification and denitrification mode when the water volume is normal and the pollutant concentration is low. At this time, the anaerobic pool 2, the anoxic pool 3, and the aerobic pool 4 are all operated according to low oxygen to achieve the purpose of simultaneous nitrification and denitrification, and the post-aeration pool 5 and the flocculation pool 6 are operated according to aerobic conditions.

The urban sewage after grit settling treatment is pumped into the interactive reactor, the average temperature of the influent water is 22°C, and the average pH value is 7.32. The theoretical hydraulic retention time of sewage in the biochemical treatment unit is 7.6h, the average sludge reflux ratio is 100%, no mixed liquid reflux is required, the sludge concentration is maintained at about 2.5g/L, the average sludge age is 18d, and the dissolution of the reactor The oxygen concentration is controlled at 0.6mg/L-1.0mg/L, and the dissolved oxygen concentration in the rear aeration tank is controlled at 3mg/L-4mg/L.

After testing, the average value of COD _Cr is 145mg/L when entering water, and the average value is 38mg/L when leaving water, with a removal rate of 73.8%; the average value of SS is 129mg/L when entering water, and the average value of effluent is 15mg/L The rate is 88.4%; the average value of ammonia nitrogen is 18mg/L when entering water, the average value of effluent is 2.6mg/L, and the removal rate is 85%; the average value of TN is 22.7mg/L when entering water, and the average value is 8.4mg when effluent /L, the removal rate is 63%. The average value of TP in water inflow is 1.5mg/L, and the average value of TP in water outflow is below 1.0mg/L.

Claims (5)

1, a kind of Physiochemical and biochemical interactive city sewage treating method, it is characterized in that adopting the biochemical treatment unit, the interactive reactor that physicochemical treatment unit is formed, wherein the biochemical treatment unit is by pre-anoxic pond (1), anaerobic pond (2), anoxic pond (3), Aerobic Pond (4), back aeration tank (5) is connected to form by the water hole of partition wall successively, physicochemical treatment unit is made up of flocculation basin (6), back aeration tank (5) links to each other with flocculation basin (6) with valve by pipeline, the unitary pre-anoxic pond of biochemical treatment (1) links to each other with the returned sluge pipeline, the unitary anaerobic pond of biochemical treatment (2) links to each other with inlet channel, biochemical treatment aeration tank, unitary back (5) links to each other with settling tank (7), physicochemical treatment unit one end links to each other with water inlet pipe, the other end links to each other with settling tank (7), be connected with valve by pipeline between biochemical treatment unit and the physicochemical treatment unit simultaneously, municipal effluent enters the Physiochemical and biochemical interactive reactor after handling through sand setting, difference according to the water yield and water quality, select the biochemical treatment unit, the physicochemical treatment unit series connection, in parallel, or while biological nitration denitrification operation scheme, sewage is carried out biochemical treatment, materialization is handled, mixed solution in the final reactor enters settling tank and carries out mud-water separation, sedimentary sludge part is back to pre-anoxic pond, part is as excess sludge discharge, wherein:

(1) when amount of inlet water be design discharge 0.7-1.5 doubly, the influent quality chemical oxygen demand (COD) is 70mg/L-800mg/L, biochemical oxygen demand (BOD) is 30mg/L-400mg/L, suspended solids is 150mg/L-300mg/L, kjeldahl nitrogen is 20mg/L-60mg/L, when total phosphorus is 2mg/L-8mg/L, reactor adopts the series operation mode, pre-anoxic pond (1), anaerobic pond (2) in the reactor, anoxic pond (3), Aerobic Pond (4), aeration tank (5), back, flocculation basin (6), settling tank (7) link to each other successively by pipeline;

(2) when flooding velocity 1.5 times greater than design discharge, the influent quality chemical oxygen demand (COD) is 70mg/L-400mg/L, and biochemical oxygen demand (BOD) is 30mg/L-200mg/L, and suspended solids is 150mg/L-300mg/L, kjeldahl nitrogen is 10mg/L-40mg/L, when total phosphorus is 1mg/L-5mg/L; Reactor adopts the parallel running mode, and the unitary anaerobic pond of reactor state biochemical treatment (2), anoxic pond (3), Aerobic Pond (4) link to each other successively, and in parallel by pipeline with the flocculation basin (6) of physicochemical treatment unit;

(3) when flooding velocity be design discharge 0.7-1.0 doubly, the influent quality chemical oxygen demand (COD) is 100mg/L-300mg/L, biochemical oxygen demand (BOD) is 50mg/L-150mg/L, suspended solids is 150mg/L-300mg/L, kjeldahl nitrogen is 20mg/L-60mg/L, when total phosphorus is 2mg/L-4mg/L, adopt biological nitration denitrification operation scheme simultaneously, anaerobic pond in the reactor (2), aeration tank (5), back, settling tank (7) link to each other successively.

2, Physiochemical and biochemical interactive city sewage treating method according to claim 1, when it is characterized in that adopting the series operation mode, its control condition is as follows: make municipal effluent all enter anaerobic pond (2), anoxic pond (3), Aerobic Pond (4) in the biochemical treatment unit successively, stopped 4-8 hour in the biochemical treatment unit; Enter the flocculation basin (6) in the physicochemical treatment unit then,, stopped 0.5-1 hour in physicochemical treatment unit with the flocculation agent thorough mixing; Last mixed solution enters settling tank and carries out mud-water separation, sedimentation time is 2-4 hour, precipitating sludge is back to pre-anoxic pond (1) and carries out endogenous denitrification removal nitric nitrogen, and reflux ratio is 25-100%, and the mud of removing after nitric nitrogen and process anoxic are stablized enters anaerobic pond.

3, Physiochemical and biochemical interactive city sewage treating method according to claim 1, when it is characterized in that adopting the parallel way operation, its control condition is as follows: sewage is divided into 2 strands, one sewage enters anaerobic pond (2), anoxic pond (3), the Aerobic Pond (4) in the biochemical treatment unit, flooding velocity is the 50%--80% of total inflow, from the terminal water outlet of Aerobic Pond (4), in the biochemical treatment unit, stopped 4-6 hour; One sewage enters physicochemical treatment unit, and with the flocculation agent thorough mixing, flocculation time is 0.5-1.5 hour, and flooding quantity is the 20%--50% of total inflow; Two strands of sewage are mixed into settling tank after treatment and carry out mud-water separation, and sedimentation time is 1.5-3 hour, and part mud is back to pre-anoxic pond, and return sludge ratio is 25-80%, and partial reflux mud is back to chemical flocculation basin, and return sludge ratio is 0--25%.

4, Physiochemical and biochemical interactive city sewage treating method according to claim 1, when it is characterized in that adopting simultaneously the nitration denitrification operation scheme, its control condition is: sewage is all entered from anaerobic pond (2), through after aeration tank (5) aeration, enter settling tank (7) again and carry out mud-water separation, nitration denitrification is 6-10 working time hour simultaneously, sedimentation time is 3-5 hour, flocculation basin (6) together carries out aeration as aeration tank, back (5), mud is back to pre-anoxic pond (1), return sludge ratio is 50%-100%, and dissolved oxygen is 0.6mg/L--1.0mg/L.

5, the method for Treating Municipal Sewage according to claim 1, its feature also are described flocculation agent for gathering a kind of of ferrosilicon, poly-sial, and dosage is 20mg/L--80mg/L.

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