KR100217357B1 - Process for the biological removal of nitrogen and phosphorus - Google Patents

Abstract

The present invention relates to a wastewater treatment method for efficiently removing eutrophic substances such as organic matter, nitrogen, phosphorus and the like from wastewater. According to the present invention, the organic matter is removed from the anaerobic tank and the phosphorus in the form of polymer is eluted in the form of phosphorous acid, the nitrogen oxide is removed in the form of nitrogen gas in the denitrification tank, and the phosphorus in the form of phosphorous in the form of phosphorous acid is removed to the microorganism at the same time. Biologically improved nitrogen and phosphorus, including excess intake, filtration of the aeration tank effluent with an ultrafiltration membrane to release the treated water and obtaining a concentrate, followed by precipitation of the concentrate in the settling tank to discharge the supernatant and return the settling sludge to the denitrification tank. A removal method is provided.

Description

Biological Removal Methods of Nitrogen and Phosphorus

Figure 1 illustrates the process of the present invention to remove nitrogen and phosphorus from wastewater using microorganisms.

The present invention relates to a method for treating municipal sewage or industrial wastewater, and more particularly, to a wastewater treatment method for removing not only organic matter but also eutrophic substances such as nitrogen and phosphorus using microorganisms.

Existing Bottoms Currently Running The wastewater treatment system is mainly operated by the standard activated sludge process, but the organic matter is 90% by the standard activated sludge process. Although it can process more than that, in case of nitrogen and phosphorus, the removal rate is 15-40 each, respectively. , 20 to 40 It only causes nitrogenous or phosphorous appeal and eutrophication and red tide of the sea area.

Therefore, in recent years, the focus has been on the development of a process for increasing the removal rate of nitrogen and phosphorus as a water pollution prevention method, and the process of adding physicochemical treatment to the existing activated sludge process called secondary treatment and the existing activated sludge Processes for removing nitrogen and phosphorus using microorganisms with improved process have been developed.

Generally, ha Nitrogen in the wastewater is mostly ammonia nitrogen and organic nitrogen, and a small amount of nitrite and nitrate nitrogen is present. The composition varies slightly depending on the type of wastewater, the season or the day. Nitrogen removal in conventional conventional treatment plants is carried out by precipitation of organic nitrogen associated with sedimentable substances in the primary sedimentation basin, but soluble and colloidal organic nitrogen and soluble inorganic nitrogen are hardly removed and activated ammonia and organic matter in activated sludge baths Nitrogen is oxidized to nitrite and nitrate nitrogen, some of which are used as part of microbial cell components.

At present, the physicochemical higher-level treatment process for removing nitrogen is sufficient to raise the pH of the wastewater to be treated to 11 or more to degassing the ammonium ions into ammonia to remove them in a gaseous state. There is a breakdown point chlorine treatment method for removing ammonia nitrogen in solution by nitrogen gas, and an ion exchange resin method for removing ammonium ions through an ion exchange resin having excellent selective ion exchange properties. Not only does it take much time, but it is also difficult to use in actual large scale processes due to the control of pH, toxicity of injecting gas, and difficulty in regeneration.

In addition, as a biological higher-order treatment process using a microorganism in the aerobic state using a microorganism such as Nitrobacter, Nitrosomonas (Nitrosomonas) It is a process that oxidizes organic nitrogen or ammonium salt nitrogen in waste water in the form of nitrate, and then reduces and removes nitrate nitrogen with nitrogen gas in the presence of Bacillus, Pseudomonas and Micrococcus under anoxic conditions. Although used in the treatment plant, there is a demand for optimization of the process and improvement of efficiency due to the reliability of the treatment and instability of load variation. Also, ha Phosphorus in wastewater was The degree of the removal of the untreated phosphorus is high, and the physical high-level process for removing the untreated phosphorus includes a process using a polymer membrane and an ion exchange resin, but these processes are expensive and have technical and regeneration difficulties. As a chemical higher order process, ortho-phosphate is agglomerated using lime and metal salt flocculant and then removed by gravity sedimentation. However, this method requires a large amount of chemicals and dehydration of sludge causes a large scale. Not suitable for the device

The process of removing phosphorus biologically is a process of removing phosphorus using intracellular phosphorus accumulating microorganisms such as Acinetobacter, Bacillus, Pseudomonas, Micrococcus, etc. By culturing the microorganisms under anaerobic conditions, the microorganism in the anaerobic state is unable to obtain energy through a normal tricarboxylic acid cycle as in the aerobic state, so that the polymer phosphate is used. The microorganism metabolizes by using the energy released by the hydrolysis of the macromolecular phosphoric acid and converting it into phosphate, and this energy is used to actively transport extracellular organic matter into the cell. After being stored as poly-β-hydroxybutyrate and being in aerobic state, it is sent to the normal tricarboxylic acid circuit to obtain adenosine triphosphate, which is then absorbed by the extracellular phosphoric acid and stored as polymeric phosphoric acid. In this process, excess accumulation of phosphorus occurs. Phosphorus content in cells is considerably low when the growth of microorganisms is fast, but increases under conditions where the growth of microorganisms is poor due to nutrient imbalance. In other words, an inverse relationship is established between the synthesis of the polymeric phosphoric acid and the nucleic acid. Phosphorus bioremoval is the over-accumulation of phosphorus in activated sludge and removal of this sludge. To accumulate macromolecular phosphorus in the cell, it is necessary to create a temporary compression state and the accumulation of phosphorus in the cell is over-plus. And by a mechanism called Luxury-Uptake. The over-plus is a phenomenon in which the microorganisms are rapidly ingested when phosphorus is supplied again after the supply of phosphorus is insufficient, and the luxuri-uptake refers to phosphorus intracellularly in a state in which limited elements other than phosphorus are restricted. When there is enough energy to move, it means excessive phosphorus. Intracellular accumulation of phosphorus occurs when the supply of substrate from the outside is greater than the amount of substrate required, and the stored compound is used when the supply of energy from the outside is less than the cell minimum. As described above, the biological phosphorus removal method utilizes such excess phosphorus by using phosphorus accumulating microorganisms to release the macromolecular phosphoric acid stored in the anaerobic state and ingest excess phosphoric acid as an intracellular storage material for growth in the aerobic state. As a treatment process for removing phosphorus through the removal of phosphorus, it is advantageous for a large amount of treatment, but the stability of the treatment is insufficient.

Conventional processes for the simultaneous removal of nitrogen and phosphorus have been developed such as PhoStrip, Bardenpho, Anaerobic / Aerobic (A ₂ / O), UCT processes, etc. As a process for stably removing phosphorus, a part of the return sludge is eluted from the final sludge of the activated sludge process in an anaerobic tank, and the coagulation and precipitation of lime is added to remove phosphorus. However, when nitrification is made in the aeration tank, the release of phosphorus is inhibited due to the effect of nitrogen oxides, chemical costs are high, and the microorganisms of activated sludge are killed.

The anaerobic / aerobic (A ₂ / O) process installs anaerobic, anaerobic and aeration tanks where the return sludge is mixed with the incoming wastewater in the anaerobic tank, resulting in the absorption of organics and release of phosphorus in the anaerobic state, followed by the nitrification process in the aerobic tank. The wastewater passed through the wastewater is returned and denitrification occurs.In the aeration tank, the process of removing phosphorus by sludge disposal after excessive ingestion of phosphorus in microorganisms is relatively simple but difficult to set operating conditions and difficult to remove stable phosphorus. Have.

In the UCT process, an anaerobic tank, an anoxic tank, and an aeration tank are installed to bring the return sludge into the anoxic tank to increase the efficiency of phosphorus removal, but the sedimentation and concentration of sludge is reduced.

In the modified Bardenpho process, the reaction tank is installed in the order of anaerobic tank, first anaerobic tank, first aeration tank, second anaerobic tank, and second aeration tank, and the return sludge flows into the anaerobic reactor, and denitrification reaction occurs in the first and second anaerobic tanks. Phosphorus is removed through the excess sludge treatment of the aeration tank. This process has a very high nitrogen removal rate, a high proportion of phosphorus in the sludge and a relatively stable treatment (Barth, EF, Project officer, Summary Report: Workshop on Biological Phosphrous Removal in Municipal Wastewater Treatment, USEPA (1982); and Barnard , JL, Biological Nutrient Removal Without the Addition of Chemicals, Water Research 9, 485 (1975)).

Among the methods developed above, the PhoStrip process is disclosed in US Patent No. 4,141,822 to Gilbert V. Levin et al. And Korean Patent Application No. 89-908 to Kim Chang-Hee (notice no. 91-3004). The anaerobic / expiratory method is disclosed in Korean Patent Application No. 82-1616 (Notification No. 87-107) to Matsuo Yoshidaka et al.

Therefore, the present inventors configure the reaction tank with anaerobic tank, denitrification tank, aeration tank and sedimentation tank to improve the removal rate of phosphorus as well as organic matter and nitrogen while taking advantage of the simple anaerobic / aerobic (A ₂ / O) process. After the sludge concentration was fixed at, the nitrogen was removed from the denitrification tank, the microorganisms ingested excess phosphorus in the aeration tank, and the sludge containing phosphorus was concentrated by ultrafiltration to reduce the volume of the settling tank during the removal of phosphorus. Increasing the speed improves the shortcomings of the existing process and improves the stability and efficiency of the dephosphorization process to complete the present invention.

Therefore, an object of the present invention is to provide an efficient and economical It is to provide a method for biological removal of nitrogen and phosphorus in the waste water. That is, an object of the present invention is to provide a combination of anaerobic-aerobic activated sludge process by microorganisms, It provides a method for efficiently and economically removing contaminants such as organic matter, nitrogen and phosphorus in waste water under high removal rate.

Hereinafter, the present invention will be described in detail.

The present invention improves the anaerobic / aerobic (A ₂ / O) process for the simultaneous removal of nitrogen and phosphorus, by connecting the reaction treatment tank in the order of anaerobic tank, denitrification tank, aeration tank and sedimentation tank To remove organic matter, nitrogen and phosphorus in the waste water Provide a wastewater treatment method.

In the present invention, since the carrier mounted on the anaerobic tank suppresses the discharge of sludge and suspended matter in the anaerobic tank effluent to maintain a constant sludge concentration in the anaerobic tank, it is not necessary to supply the conveying sludge, thus, nitric acid and nitrite ions, which have been a conventional problem. This solves the problem of prolonging the residence time and lowering the treatment efficiency. In addition, aeration tank effluent is subjected to an ultrafiltration membrane before it is introduced into the sedimentation tank so that a substantial portion of the effluent is preferably 80. By discharging the degree as the final treated water, the capacity of the final sedimentation tank into which the remaining agricultural water is introduced is greatly reduced to about 1/5, and the stability of the treated water quality and the phosphorus removal rate are increased.

Hereinafter, the present invention will be described in detail with reference to the process diagram shown in FIG.

Inflow water (6) such as municipal sewage, animal husbandry wastewater, food production wastewater, papermaking wastewater, and dairy wastewater is introduced into an anaerobic tank (1) equipped with a carrier (7). Since the carrier in the anaerobic tank suppresses the discharge of sludge and suspended matter in the anaerobic tank effluent, the sludge concentration in the anaerobic tank is kept constant, so the supply of the return sludge is not necessary. Here, the organic matter is removed, and under the anaerobic conditions, the macromolecular phosphorus in the microbial cell is converted into the phosphate form and released. The conditions in the reactor are preferably free of oxygen and bound oxygen, which are electron acceptors. Concentration is 1-3 Of It is preferred that the redox potential value, which is below and used as a measure of anaerobic level, is maintained between -200 and -300 mA.

75 in the anaerobic treatment tank Or more, preferably 80 Removes organic matter from 32 to 38 , Preferably 35 The treatment is carried out at a temperature of 1 to 3 hours, preferably 2 hours. Examples of the carrier to be mounted in the anaerobic tank include activated carbon, porous sponge carrier, ceramic carrier and ciliated or ring carrier made of polyethylene (PE) or polypropylene (PP), of which PE or PP carrier is preferable. Do. In addition, it is preferable to use a carrier in the amount of ⅓-의 of an anaerobic treatment tank volume.

The outflow water 8 from the anaerobic tank 1 flows into the denitrification tank 2 together with the return sludge 16 and the aeration tank return liquid 10 of the final settling tank 5. In the denitrification tank (2), in order to reduce and remove nitrogen in the state of nitric oxide, it prevents the inflow of outside air and operates in anoxic conditions without dissolved oxygen, and when free oxygen is present, respiration of microorganisms using combined oxygen such as nitrogen oxide Rather, breathing using free oxygen is preferred and free oxygen acts as a deterrent to the denitrification reaction, so the denitrification tank 2 must be completely sealed, and a gas outlet and agitator are installed at the top of the denitrification tank 2 to completely mix. This can be done and at the same time facilitate the discharge of the generated gas. In the denitrification tank 2, nitrogen in the form of nitric oxide is reduced and removed in the form of nitrogen gas for a contact time of 2 to 4 hours. Meanwhile, the carbon sources required for the denitrification reaction use organic materials in raw water without additional input of organic carbon sources such as methanol.

The denitrification tank effluent (9), which has undergone the denitrification process, is introduced into the aeration tank (13), where nitriding bacteria, nitrosomonas and nitrobacter, convert ammonia nitrogen into nitrite nitrogen and nitrate nitrogen, and contain it in water. Phosphorus in the form of regular phosphate is ingested and accumulated in the form of macromolecular phosphate in the body. The residence time in the aeration tank is 3 to 5 hours, preferably 3 hours, here 30 to 40 Is processed.

Subsequently, the aeration tank effluent 12 containing the excess phosphorus sludge flows into the ultrafiltration membrane 4 made of polyolefin. The ultrafiltration membrane 4 is a tubular type having a low scale generation rate and easy to clean. It is preferred that the molecular weight cut-off value is 20,000, and most of the influent is preferably 80 By designing the discharge to the treated water 18, the size of the final sedimentation tank 5 can be preferably reduced to 1/5 or less as compared with the conventional anaerobic / aerobic (A ₂ / O) process. The treated water passed through the ultrafiltration membrane had a chemical demand (COD) and a biological demand (BOD) of 3, respectively. Of It is a degree and always maintains a constant water quality regardless of the water quality of the aeration tank effluent 12. Concentrated concentrated water flowing out of the ultrafiltration membrane (approximately 20 13) is introduced into the sedimentation tank (5) containing sludge containing excessive phosphorus and reduced in size compared to the sedimentation tank in the conventional anaerobic / aerobic (A ₂ / O) process. In the settling tank 5, sludge is precipitated using gravity, and the residence time is appropriate for 2-3 hours in which the state of the sludge does not become anaerobic. 10 out of the sludge 15 discharged after the supernatant was discharged as treated water The degree is conveyed so that the concentration of mixed liquor suspended solids (MLSS) in the mixed liquid of the denitrification tank 2 can be kept constant, and the remaining sludge 17 is discharged out of the system as surplus sludge.

This invention will be described in more detail based on the following examples. The following examples are intended to specifically illustrate the invention and are not intended to limit the scope of the invention.

EXAMPLE

In the present Example, the municipal sewage having the composition shown in Table 1 was treated using the treatment apparatus configuration as shown in FIG. 1 and the experimental conditions for each process as shown in Table 2, and the results as shown in Table 3 were obtained. .

Comparative Example

In order to compare the treatment efficiency by the wastewater treatment method of the present invention, the municipal sewage was treated by the conventional A / O process using experimental conditions for each process shown in Table 4, and the results as shown in Table 5 were obtained.

While the present invention has been described above in connection with specific embodiments, it should be understood that changes, modifications, and modifications apparent to those skilled in the art without departing from the scope of the present invention fall within the scope of the present invention. .

Claims (4)

A wastewater treatment method for removing eutrophication materials including organic substances, nitrogen and phosphorus, the method comprising the steps of: introducing influent into an anaerobic tank equipped with a carrier to remove organic substances and eluting phosphorus in the form of a polymer in the form of ortho phosphate; Flowing the effluent of the anaerobic tank into the denitrification tank together with the aeration tank return liquid and the return sludge of the settling tank to remove the nitric oxide in the form of nitrogen gas; Inflowing the treated water after denitrification into an aeration tank to nitrate ammonia nitrogen and ingesting phosphorus in the form of phosphate to the microorganism; A part of the aeration tank effluent is returned to the denitrification tank, and the remaining is separated and concentrated by an ultrafiltration membrane to release the treated water as recycled water to obtain a high concentration of phosphorus containing excess phosphorus; And introducing the ultrafiltration membrane concentrate into the final settling tank and subjecting the gravity settling to discharge the supernatant and returning some of the precipitated sludge to the denitrification tank and releasing the remaining sludge out of the system. Wastewater treatment method. The method according to claim 1, wherein the carrier is mounted in the anaerobic tank to suppress the discharge of sludge in the anaerobic tank and at the same time reduce the concentration of suspended matter in the effluent. The method according to claim 1, wherein a polyolefin-based ultrafiltration membrane is used as the ultrafiltration membrane. The method according to claim 1, wherein the return sludge of the settling tank is returned to the denitrification tank.