KR20020083611A - Method for removing nutrients of domestic sewage using 2 step aeration and an apparatus used therefor - Google Patents

Abstract

PURPOSE: Provided is a system for removing nutrients of domestic sewage using two step aeration which can remove organic matters in wastewater efficiently by activated sludge process and contact aeration process, and can remove nutrients such as nitrogen and phosphorus by installing denitrification chamber and dephosphorization chamber. CONSTITUTION: The system comprises a flow equalization basin(2) which equalizes flow rate and concentration of wastewater and primarily settles grits; a denitrification tank(3) which reduces NO3-N to nitrogen gas in denitrification tank; an activated sludge tank(4) which nitrifies organic matters and NH3-N in aerobic condition; an intermediate settling tank(5) which separates activated microorganism sludge and disposed water; a contact aeration tank(6) which is packaged with contact media(13) to extend retention time of microorganisms; a dephosphorization tank(8) in which phosphorus is released in anaerobic condition; a chemical precipitation tank(9) in which phosphorus is precipitated by using coagulants; a final settling tank(7) which separates sludge and treated clean supernatant water.

Description

METHOD FOR REMOVING NUTRIENTS OF DOMESTIC SEWAGE USING 2 STEP AERATION AND AN APPARATUS USED THEREFOR}

The present invention relates to a method for removing nutrients from sewage discharged from the home using a two-stage aeration method. More specifically, the present invention uses the activated sludge tank and the contact aeration tank, which is a two-stage aeration method, to introduce organic substances and nutrients nitrogen and phosphorus in the sewage generated at home, and to introduce a separate denitrification tank and dephosphorization tank, stably and efficiently. It is about a method of simultaneous removal.

Since the first urban sewage treatment plant was constructed in 1979, many sewage treatment plants have been constructed and operated all over the country. Most of the existing sewage treatment plants and new sewage treatment plants were intended to remove organic matter and suspended solids, but since 1996, the newly revised discharged water standard was applied, treatment of nutrients nitrogen and phosphorus became an important issue. Therefore, many researchers in Korea have been studying the biological nutrient removal process, but the complete treatment process has not been presented.

Methods of removing nutrients include physical treatment, chemical treatment and biological treatment. As a physical treatment method of removing nitrogen from nutrients, ammonia stripping method which raises pH and blows ammonia into the air and ion exchange method using zeolite are used. The removal of nitrogen by biological treatment methods is the nitrification step of oxidizing ammonia nitrogen in aerobic state to nitrite through nitric acid and the denitrification of nitrified nitric acid to nitrogen gas by denitrification in anoxic state. (Denitrification) step.

Phosphorus removal methods include biological treatment methods using microorganisms to release phosphorus in anaerobic conditions and excess phosphorus intake of phosphorus in aerobic conditions to increase the amount of phosphorus in aerobic conditions; Chemical treatment methods for forming and precipitating and removing phosphorus are widely used.

There are many studies on the treatment process using the above nutrient removal principle in Korea and abroad. Through these studies, the importance of concentration ratio of organic substance and nitrogen and phosphorus for biological treatment of nitrogen and phosphorus is known. TKN / COD is recommended. For the removal of biological nitrogen and phosphorus, it is required to satisfy the TKN / COD ratio below 0.09 (Ekama, GA, Sieebritz, IP, and Marais, GvR (1983). Wat Rec. Tech , Vol. 15, 283-318). However, in the case of domestic sewage, the TKN / COD ratio is usually 0.13 or more due to various reasons such as the inflow of sewage pipes and inflow of groundwater.

Therefore, it is urgently needed to develop a treatment system that can effectively treat sewage organic matter and nutrients in consideration of domestic conditions where sewage characteristics differ from those of other countries.

Therefore, the present inventors not only stably remove organic substances contained in the sewage by introducing a two-stage aeration method in the sewage treatment process, but also separate nitrogenizer and dephosphorization tank to effectively remove nutrients such as nitrogen and phosphorus. The present invention has been completed by developing a method.

Therefore, it is an object of the present invention to provide a sewage nutrient removal method suitable for the characteristics of domestic sewage.

Another object of the present invention is to provide a sewage nutrient removal device suitable for the domestic sewage properties.

1 is a block diagram of a nutrient removal system of sewage using a two-stage aeration method according to the present invention.

<Description of the symbols for the main parts of the drawings>

1: Nutrient removal system of sewage using two-stage aeration

2: primary settling tank and flow adjusting tank 3; Denitrification tank

4: activated sludge tank 5: intermediate sedimentation tank

6: contact aeration tank 7: final precipitation tank

8: dephosphorization tank 9: chemical treatment tank

10: Mixer for Mixing 11: Blower

12; Air Supply Unit 13: Media

In order to achieve the above object, the nutrient removal method of sewage using the two-stage aeration method according to the present invention is to equalize the concentration and flow rate of the sewage discharged from the home to facilitate the subsequent treatment and to settle the sedimentable suspended matter first. Primary precipitation and flow rate adjustment steps to remove; A denitrification step of reducing nitrified nitrate nitrogen to nitrogen gas from anoxic state using organic matter of sewage through an aerobic activated sludge stage or a contact aeration stage; An activated sludge step of nitrifying organic substances and ammonia nitrogen in sewage with nitrite nitrogen and nitrate nitrogen using aerobic microorganisms and oxygen; An intermediate precipitation step of separating the activated microorganism and the treated water in the activated sludge step; Contact aeration step of prolonging the residence time of the microorganisms by filling the media to increase the concentration of the microorganisms; A dephosphorization step of maximally releasing phosphorus in the sludge introduced in the intermediate precipitation step in an anaerobic state and returning the sludge from which the phosphorus is released to the denitrification step; Chemical treatment step of chemically precipitating and removing phosphorus contained in the supernatant via the dephosphorization step using a flocculant; And a final settling step for finally separating the microorganisms removed from the contact aeration step and the treated water.

The two-stage aeration method according to the present invention is a method of improving the sewage treatment efficiency and improving the responsiveness to changes in the water quality of the raw water. By maintaining the concentration high, it is a treatment system that can secure stable treatment efficiency even in a shocking situation where the quantity or concentration of inflowing water suddenly increases. In addition, in terms of nutrient removal, it is also responsible for improving phosphorus removal efficiency in the activated sludge stage and improving nitrification in the contact aeration stage.

Hereinafter, the present invention will be described in more detail with reference to a block diagram of a nutrient removal method of sewage using a two-stage aeration method shown in the accompanying drawings.

1 is a block diagram of a nutrient removal method of sewage using a two-stage aeration method according to the present invention, where the solid line represents the flow of waste water, the dotted line represents the flow of sludge.

The sewage nutrient removal system 1 according to the present invention is largely composed of two paths, namely, a movement path of a workpiece and a conveyance and movement path of sludge.

First of all, due to the characteristics of sewage discharged from the home, the concentration of sewage varies greatly with time and season, and the flow rate varies greatly depending on the time of day. A primary settling and flow rate adjusting step (2) for firstly settling out; A denitrification step (3) of reducing nitrate nitrogen sufficiently nitrified through nitrification in the activated sludge stage (4) and the contact aeration stage (6) to nitrogen gas in an oxygen-free state using sewage organic matter; Oxygen contained in the continuously supplied air and organic matter contained in the processed materials introduced by the proliferation and decomposition of aerobic microorganisms maintaining a constant concentration in the reaction step are removed, and nitrifying microorganisms Nitrification occurs by oxidizing nitrogen, nutrient nitrogen, into ammonia nitrogen ---> nitrite nitrogen ---> nitrate nitrogen, and also releases phosphorus in the dephosphorization step (8). An activated sludge step (4) which flows into the reaction step to cause excessive intake of phosphorus in the workpiece to remove phosphorus; An intermediate precipitation step (5) for separating the microorganisms grown in the activated sludge step (4) and the treated object; Sludge is equipped with media that can secure a large amount of microorganisms and minimize impact load or sludge loss for secondary removal of organic substances that are not completely treated in the activated sludge stage (4) and perfect nitrification of ammonia nitrogen. A contact aeration step 6 which has sufficiently extended the residence time of the; A final precipitation step 7 of finally separating the microorganisms detached from the media of the contact aeration step 6, the non-attachment microorganisms, and the treated object; A dephosphorization step 8 designed to release phosphorus in the settling sludge introduced in the intermediate precipitation step 5 in an anaerobic state; Through the process consisting of a chemical treatment step (9), which discharges the supernatant containing the discharged phosphorus to chemically precipitate and remove it using a flocculant (Alum, Lime and polymer flocculant, etc.). It was configured to be discharged to.

The latter is then returned to the denitrification step (3) of the sludge separated from the workpiece in the intermediate precipitation step (5) to the denitrification action and to maintain the appropriate microbial concentration in the activated sludge step (4) ; A sludge migration path 15 for transporting the sludge separated from the workpiece in the intermediate precipitation step 5 to the dephosphorization step 8 to release the phosphorus contained in the sludge; A sludge migration path 16 which partially returns the sludge separated from the workpiece in the final precipitation step 7 to the denitrification step 3; A sludge migration path 17 for transferring the object including the phosphorus released in the dephosphorization step 8 and the sludge from which the phosphorus is released to the denitrification step 3; A sludge movement path 19 for transporting sludge containing suspended solids precipitated in the first precipitation and flow rate adjusting step 2 to a sludge treatment process; In the sludge treatment process through the sludge transfer path 20 which is returned to the active sludge stage 4 of the sludge separated from the workpiece in the intermediate precipitation step 5 to maintain the proper microbial concentration and to transfer the excess surplus sludge remaining. The transfer was configured for final disposal.

Sludge return and transfer is directly related to nutrient removal efficiency, and how much sludge is returned or moved from one reaction step to another is characterized in each nutrient removal process. In the present invention, by introducing a two-stage aeration method, a sludge conveying and moving path is provided for the purpose of improving nutrient removal efficiency.

The role and operation of each reactor of the nutrient removal device of sewage using the two-stage aeration method according to the present invention will be described in detail as follows.

Sewage, which is to be treated, varies widely according to the lifestyle, dietary culture, and regional characteristics, and changes in the properties and flow rates of the treated materials in biological treatment of nutrients have a lot of adverse effects on microorganisms, resulting in poor treatment efficiency. Can be obtained. Therefore, the primary sedimentation tank and the flow regulating tank (2) are responsible for equalizing the concentration and flow rate of the sewage introduced and improving the removal efficiency of subsequent biological treatment by first removing the sedimentable suspended solids contained in the sewage. do. The role of the primary sedimentation tank and the flow rate adjusting tank (2) depends on the size of the sewage treatment plant. However, when the sewage treatment plant is large, the inflow flow rate is automatically equalized because the distance from the sewage generation site to the treatment plant and the arrival time are lengthened sequentially. It is designed to act as the primary sedimentation tank rather than the flow control tank, and when the size of the treatment plant is small, the sewage from the sewage treatment area flows in a short time, so it is designed to play the role of the flow control tank rather than the primary sedimentation tank.

The to-be-processed material which passed through the primary sedimentation tank and the flow adjusting tank 2 flows into the denitrification tank 3. In the denitrification tank 3, the settling sludge of the intermediate settling tank 5 is introduced through the moving path 14, the settling sludge of the final settling tank 7 is introduced through the moving path 16, and phosphorus is released from the dephosphorization tank 8. Sludge is introduced through the sludge movement path 17. The denitrification tank 3 is equipped with a mixing mixer 10 for the smooth mixing of the object and the microorganism, and is reduced to nitrogen gas through two steps by denitrifiers. The first step is nitric acid, the process is switched to the (N ₂₎ and nitrogen gas (NO ₃ ^-) The nitrous acid (NO ₂ ^{- -)} in a process of transition, the second step is nitrite goes through two intermediates (NO ₂₎ . These two steps are commonly called dissimilation, and the paths of this reaction that are commonly known are:

The denitrification reaction is a reaction to generate alkaline. The production of alkalinity becomes an important factor in the treatment process that can offset the alkalinity consumption by nitrification to some extent in the activated sludge tank 4 and the contact aeration tank 6. The optimum pH of denitrification in the denitrification tank (3) depends on the type of microorganisms in the denitrification tank (3) or the characteristics of the sewage, but in general, pH 7-8 is most suitable. Operation was possible without any additional chemicals or adjustments.

The workpiece to be processed via the denitrification tank 3 flows into the activated sludge tank 4. In the activated sludge tank 4, aerobic microorganisms and nitrifier microorganisms (Nitrifiers) are present in a large amount, and the organic materials in the inflowed to-be-processed object are supplied to the air supply device 12 that supplies air by using the air generated in the blower 11. It is used for oxidizing action of microorganism, cell synthesis and proliferation with oxygen sent continuously by the reaction.

In addition, the activated sludge tank 4 in the ammonium nitrogen nitrite nitrogen by nitrifying ^{microorganism-nitrate} quality again (NO ₃ ^-), (NO ₂₎ caused a nitrification reaction is oxidized by an H ⁺ is generated from the reaction of alkali Nitty is consumed which causes the pH to drop.

The product to be processed via the activated sludge tank 4 flows into the intermediate sedimentation tank 5. The intermediate sedimentation tank is an essential reaction tank that keeps the concentration of microorganisms in the activated sludge tank constant by returning the sludge settled in the sedimentation tank to prevent the loss of microorganisms in the activated sludge tank and removing excess microorganisms grown in the activated sludge tank. . The microorganisms and the to-be-processed materials flow into the intermediate sedimentation tank (5), and the microorganisms form flocs in an entangled state with each other to precipitate by gravity, and the treated to-be-treated sludge and the solids of the to-be-processed materials are located in the upper layer. Separation takes place. Precipitated sludge is transferred to the respective reactors through the sludge migration paths 14, 15, and 20.

The sludge returned through the sludge migration path 14 enters the denitrification tank 3, undergoes denitrification reaction, and enters the activated sludge tank 4 to maintain constant Liquor Suspended Solids (MLSS) in the activated sludge tank. It will play a role. The sludge introduced into the dephosphorization tank 8 through the sludge migration path 15 is discharged with phosphorus in the sludge, and the excess sludge released through the sludge migration path 20 is transferred to a sludge treatment process and disposed of. The excess sludge is determined according to the residence time of the activated sludge tank 4 in an amount excluding the return amount for maintaining the optimum microbial concentration (Mixed Liquor Suspended Solids, MLSS) among the microorganisms grown in the activated sludge tank (4). .

The object to be processed via the intermediate settling tank 5 flows into the contact aeration tank 6. In the contact aeration tank 6, the filter medium 13 is filled. The filled media consists of a myriad of pores to which microorganisms can attach, and is made of a physicochemically safe material. The microorganisms attached to the filter medium 13 in large quantities oxidize organic matter and multiply the cells, achieve more perfect oxidation of ammonia nitrogen which is not completely oxidized in the activated sludge tank 4, and cope with the impact load of the influent sewage. It is designed to play a buffering role. When the interior is anaerobic due to the growth of the microorganisms attached to the filter medium 13, the microbial membrane is detached. In order to prevent this in advance, the backwashing method using the air supply device 12 performs a backwashing method of the air supply device 12. You can get good results if you do 2-3 times consecutively by hardening and stopping air volume.

The sludge separated from the object in the intermediate settling tank 5 is transferred to the dephosphorization tank 8 which is anaerobic through the sludge migration path 15. In the anaerobic dephosphorization tank (8), microorganisms decompose organic substances in wastewater using energy obtained by hydrolysis of polyphosphates stored in cells to lower BOD.The microorganisms absorb the carbon source produced in this cell and acetoacetate ( Acetoacetate is produced and stored in the form of polyhydroxybutyrate (PHB), which releases phosphorus out of the cell. Symbolic water containing the released phosphorus is transferred to the chemical treatment tank (9) to form a chemically precipitated precipitate using a chemical flocculant (Lime, Alum, polymer flocculant, etc.). The precipitated sludge removed and discharged (18), and the phosphorus released from the dephosphorization tank (8) is transferred to the denitrification tank (3) via the sludge migration path 17, and the polyhydroxybutyl in the aerobic activated sludge tank (4) The phosphorus is ingested excessively while using the carbon source stored in the rate (PHB) form, and the excess phosphorus is stored in the cell with polyphosphate to finally remove the excess sludge in the intermediate precipitation tank 5.

The workpiece which has passed through the contact aeration tank 6 flows into the final settling tank 7. Treated materials and microorganisms (microorganisms removed from the media and microorganisms not attached to the media) that flow into the final settling tank (7) are separated into the treatment and sludge by gravity and the sludge deposited is the sludge return path. It is conveyed to the denitrification tank 3 through 16, and the processed to-be-processed object is discharged | emitted finally.

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited thereto.

Example

The nutrient removal process of sewage using the two-stage aeration method of FIG. 1 was made of transparent acrylic that looks inside the reactor on a laboratory scale, and the sewage discharged from the apartment was directly collected. Table 1 summarizes the reactor and specifications of the sewage treatment process used in this experiment.

TABLE 1

Reactor and instrument standard Residence time Remarks Primary settling tank and flow rate adjusting tank Denitrification tank Intermediate settling tank Contact aeration tank Final settling tank Mixer blower for mixing tank 5.0 L1.25 L2.5 L1.25 L1.8 L0.4 L2.0 LM6GA30ASPP-200GJH 12hr3hr6hr3hr2hr1hr48hr Rectangular (Sewage Sludge Type) Rectangular (Sewage Sludge Type) Cylindrical (Hopper Angle 60 °) Rectangular (Sewage Sludge Type) Cylindrical (Hopper Angle 60 °) Cylindrical (Hopper Angle 60 °) 60 rpm 210 L / min capacity

The amount of sample used in the experiment is 10 L per day and the residence time of the dephosphorization tank is long because the inflow flow rate is small. The blower was used to supply air to the activated sludge tank and the contact aeration tank, and the raw water supply was injected evenly five times a day using a metering pump to ensure accuracy. Natural sludge was used and the sludge was returned to the correct amount by installing a timer using a metering pump.

Comparative example

The sewage treatment process of Namyangju-si, which does not adopt the two-stage aeration method, and the sewage treatment efficiency of the present invention are shown in Table 2 below. The sewage treatment plant in Namyangju-si adopts activated sludge method adopted by most sewage treatment plants in our country.The treatment process is primary sedimentation tank-> activated sludge tank-> secondary sedimentation tank (final sedimentation tank)-> disinfection tank. -> It consists of discharge.

TABLE 2

BOD T-N T-P Concentration (mg / L) % Removal Concentration (mg / L) % Removal Concentration (mg / L) % Removal Existing system enemy 192 - 39.7 - 6.47 - Treated water 10 94.8 15 62.2 2.0 69.1 Invention enemy 225 - 56 - 9.8 - Treated water 6.6 94.9 12.8 77.1 1.7 82.6

The results of the experiment summarized in Table 2 are the average concentration during the operation period according to the present invention, and the sewage treatment plant treated with the sewage treatment process of the influent BOD 225 mg / L, TN 56 mg / L, and TP 9.8 mg / L in this sewage treatment process. BOD 6.6 mg / L, 12.8 mg / L, and 1.7 mg / L, which satisfactorily satisfy 20, 40, and 8 mg / L of BOD, TN, and TP, which are the effluent standards, are shown. And nitrogen, which is a nutrient compared to conventional sewage treatment processes. Excellent in removal of phosphorus. Therefore, if the sewage treatment process is applied to the sewage treatment plant, it can have a better effect than the conventional sewage treatment process.

The nutrient removal method of sewage using the two-stage aeration method according to the present invention is a treatment process that can stably and reliably remove the organic material in the sewage by introducing the activated sludge tank and the contact aeration tank, which is a two-stage aeration method. By laying man-made separately, it is an excellent sewage treatment facility that can satisfy the contents of nitrogen and phosphorus, which are nutrients in sewage, below the discharge water quality standard of sewage treatment plant, and also cope with future anticipated regulations.

Claims (9)

A first precipitation and flow rate adjustment step of equalizing the concentration and flow rate of sewage discharged from the home to facilitate subsequent treatment and to settle and remove precipitated suspended solids first; A denitrification step of reducing nitrified nitrate nitrogen to nitrogen gas from anoxic state using organic matter of sewage through an aerobic activated sludge stage or a contact aeration stage; An activated sludge step of nitrifying organic substances and ammonia nitrogen in sewage with nitrite nitrogen and nitrate nitrogen using aerobic microorganisms and oxygen; An intermediate precipitation step of separating the activated microorganism and the treated water in the activated sludge step; Contact aeration step of prolonging the residence time of the microorganisms by filling the media to increase the concentration of the microorganisms; A dephosphorization step of maximally releasing phosphorus in the sludge introduced in the intermediate precipitation step in an anaerobic state and returning the sludge from which the phosphorus is released to the denitrification step; Chemical treatment step of chemically precipitating and removing phosphorus contained in the supernatant via the dephosphorization step using a flocculant; A method for removing nutrients from sewage using a two-stage aeration method, including a final precipitation step of finally separating the microorganisms separated from the contact aeration step and the treated water. The two-stage aeration system according to claim 1, further comprising a primary settling step and a flow adjusting step for controlling the flow rate when the sewage treatment plant is small and serving as the primary settling role when the scale is large. Method of removing nutrients from sewage using the method. The denitrification step according to claim 1, comprising a denitrification step designed to remove nitrogen in the sludge by denitrification by introducing inert nitrified sludge through the activated sludge step and the contact aeration step and the sludge released phosphorus in the dephosphorization step. Sewage nutrient removal method using a two-stage aeration method characterized in that. The method for removing nutrients from sewage using a two-stage aeration method according to claim 1, wherein the activated sludge step and the contact aeration step are sequentially installed through an intermediate precipitation step. 2. The two-stage aeration method according to claim 1, further comprising a dephosphorization step of releasing phosphorus in the settling sludge introduced from the intermediate precipitation step in an anaerobic state and returning the sludge from the discharged phosphorus to the denitrification step. How to remove nutrients from sewage using. The method of claim 1, further comprising a chemical treatment step of chemically precipitating and removing phosphorus contained in the supernatant via the dephosphorization step using a flocculant. The process according to claim 1, further comprising: a route for returning the treated material nitrified in the activated sludge step from the intermediate precipitation step to the denitrification step; A route for transferring the sludge precipitated in the intermediate precipitation step to an anaerobic dephosphorization step to release phosphorus; A route for returning sludge from the dephosphorization stage to the denitrification stage; A method for removing nutrients from sewage using a two-stage aeration method, comprising a path for returning sludge denitrated and nitrified sludge from the final aeration step to denitrification. Characterized in that it comprises an air supply device for supplying air to the primary settling tank and flow adjusting tank, denitrification tank, activated sludge tank, intermediate settling tank, contact aeration tank, dephosphorization tank, chemical treatment tank, final settling tank, and activated sludge tank and contact aeration tank. Sewage nutrient removal device using a two-stage aeration method. 9. The apparatus for removing sewage nutrients using the two-stage aeration method according to claim 8, wherein the activated sludge tank and the contact aeration tank are continuously disposed through an intermediate sedimentation tank.