KR100240801B1 - Method for purifying wastewater - Google Patents

Abstract

Disclosed are a wastewater purification method capable of effectively removing organic matter, nitrogen and phosphorus contained in high concentration organic wastewater such as municipal sewage, livestock wastewater and industrial wastewater. In the method for purifying wastewater according to the first embodiment of the present invention, an anaerobic contact tank, a separation tank, a first reaction tank which is a nitrification reaction tank in an aerobic state, a second reaction tank which is a denitrification reaction tank in an oxygen-free state, a third reaction tank in an intermittent aeration state, In the order of the fourth reactor under the intermittent aeration state, the fifth reactor under the aerobic state, and the settling furnace, and returning sludge from the settling tank to the anaerobic contact tank, the sludge separated from the separation tank is introduced into the second reactor, The influent separated in the separation tank is introduced into the first reactor and operated repeatedly. In the wastewater purification method according to the second embodiment of the present invention, an external organic carbon source is injected into the fourth reactor to use as an electron donor for smoothly removing nitrogen and phosphorus. In the wastewater purification method according to the third embodiment of the present invention, in order to improve the pure anaerobic condition, a return sludge denitrification furnace and a pure anaerobic contacting tank are installed and operated instead of the anaerobic contacting tank. The wastewater purification method can be widely applied to purify livestock and industrial wastewater as well as small-scale wastewater.

Description

Wastewater Purification Method

The present invention relates to a method for the purification of high concentration organic wastewater, and particularly, to effectively remove organic matter, nitrogen and phosphorus contained in high concentration organic wastewater such as urban sewage, livestock wastewater and industrial wastewater, which are the main causes of pollution and eutrophication of lakes and rivers. The present invention relates to a method of purifying wastewater that can be removed.

In general, nutrients are inorganic elements necessary for the growth and growth of microorganisms causing organic decomposition, among which nitrogen compounds and phosphates are elements that must be continuously supplied for biological cell formation and life energy acquisition. However, eutrophication occurs when nutrients such as nitrogen and phosphorus increase in rivers, coastal seas and lakes. The eutrophication activates the production of nutrient-containing organisms, thereby changing the ecosystem of nature, causing red tide in the sea area, and algae, etc., in the appeal cause abnormal growth.

This process proceeds smoothly in nature, but when large amounts of domestic sewage, livestock wastewater, and plant drainage flow in, nutrients increase excessively, thus suspending substances are mixed in a large amount, exceeding the natural self-purifying ability. As a result, eutrophication is rapidly progressing and, in severe cases, odors are caused by decay and water pollution is promoted. Therefore, these nutrients in the wastewater should be removed before entering the lake or river, and many studies have been made to efficiently remove them.

In Korea, most sewage treatment and livestock wastewater treatment methods rely on activated sludge method. Most suspended solids and organics can be removed by treatment with activated sludge, but only 20-40% of nutrients such as nitrogen and phosphorus are treated.

Therefore, most of the purpose of wastewater treatment for the protection of the water system is to remove nitrogen and phosphorus, and it is very important to reduce point pollutants that contaminate water systems in the present situation where it is urgent to develop a process that meets the regulatory concentration which will be strengthened in the future. Do.

Processes for the treatment of nutrients such as nitrogen and phosphorus include physicochemical and biological treatments.

First, in the physicochemical treatment method, ammonia degassing, ion exchange using selective adsorption, precipitation of phosphorus using slaked lime and flocculant, and precipitation of struvite formation in which nitrogen and phosphorus are precipitated simultaneously Etc. are used. However, this method, although the treatment is selectively performed, has the disadvantage of being sensitive to temperature and expensive. In addition, the chemical cost and the environment required for operation is difficult to operate because it is specific, and the runoff is unstable in the world as well.

In contrast, in the biological treatment method, in the case of nitrogen, ammonia nitrogen in the dissolved state and nitrogen in the form of organic matter are nitrified by aerobic microorganisms (nitrifiers) under aerobic conditions, and ammonia is converted into nitrate form, Is used as an electron acceptor instead of oxygen by microorganisms under anoxic conditions, which is produced as nitrogen gas and released into the atmosphere (denitrification). These biological treatment methods are effluents are stable, do not require external expenses, including chemical costs, and because they are easy in terms of operation, it is economical in many respects and is used a lot.

In case of treating phosphorus by biological treatment method, the waste water is alternately maintained under anaerobic and aerobic conditions, and under anaerobic conditions, phosphorus is released from microorganisms (in bacterium, Acinetobacter, etc.), and in subsequent aerobic conditions, the microorganisms over-phosphorus Ingestion is followed by the removal of phosphorus from the wastewater by removing certain amounts of microorganisms. In this case, the degree of ingestion of the microorganisms in the aerobic condition in excess of phosphorus depends on the amount and type of organic matter introduced into the anaerobic conditions. In particular, the amount of phosphorus released in the pure anaerobic state is enhanced, and the intake of phosphorus in the subsequent aerobic state is improved, thereby increasing the throughput.

Therefore, in the nitrogen and phosphorus removal process, anaerobic-aerobic-anaerobic-aerobic reactors are separately arranged to induce organic matter oxidation and nitrification reactions and microorganisms to ingest phosphorus in the aerobic reactors according to the characteristics of the respective reactors, and anaerobic and anoxic reactors. Induces the release of phosphorus and the denitrification which releases nitrate nitrogen into nitrogen gas and releases it into the atmosphere.

In general, in the process of treating nutrients as described above, in order to improve the sedimentation of the sludge and to suppress the release of phosphorus, an aerobic reactor is placed before the precipitation tank. An example of such a method is the Bardenpho process disclosed in US Pat. No. 3,964,988 to Barnard et al. Single system A / O process, A ² / O process (Reference: Hong, S., Kisenbauer, KS and Fox, VG (1981), An innovative biological nutrient removal system.In: FM Saunders, ed., Proceedings in 1981 National Conference of Environmental Engineering, Environmental Engineering Division, ASCE, Atlanta, Georgia).

These processes operate in steady-state so that the wastewater passes through the reactors under anaerobic and aerobic conditions by arranging reactors separately with or without oxygen. However, these processes have the drawback of excessive power consumption because the internal circulation must be maintained at about four times the wastewater inflow in order to increase the efficiency of the wastewater treatment.

Another example of such a method is the DEPHANOX process (G. Bortone et al. (1997), Wat. Sci. Tech. Vol 35, No. 10, pp. 87-94). In this process, anaerobic contacting tanks and separation tanks are used for the microorganisms to adsorb organic matter and induce the release of phosphorus in the anaerobic contacting tank, the organic matter and microorganisms adsorbed in the separation tank are separated into the subsequent denitrification tank and the nitrogen is not adsorbed. The compound is nitrified in a separate reactor and sent to a subsequent denitrification tank for denitrification by the microorganisms that adsorb the organics. That is, the DEPHANOX process is a process in which denitrification and nitrification are performed in separate sludges and reactors, and excess phosphorus is consumed by microorganisms in a subsequent aerobic reactor.

However, since DEPHANOX process does not have internal circulation and denitrification is performed only in a single denitrification tank during subsequent treatment after nitrification, high nitrogen removal efficiency cannot be expected. In particular, when the C / N (CODcr / T-N) ratio of influent water is low, such as urban sewage in Korea, nitrogen removal is drastically reduced, and an external carbon source needs to be injected to improve the denitrification rate.

The present invention has been made to solve the conventional problems as described above, the object of the present invention is organic matter and nutrition such as livestock wastewater including urban sewage and industrial wastewater (wastewater with toxic and low C / N ratio) To provide a recipe for wastewater that is effective in treating salts.

1 is a schematic diagram showing a wastewater purification process according to a first embodiment of the present invention.

2 is a schematic diagram showing a purification process of wastewater according to a second preferred embodiment of the present invention. And

3 is a schematic diagram showing a purification process of wastewater according to a third embodiment of the present invention.

<Description of the code | symbol about the principal part of drawing>

1: anaerobic contact tank 2: separation tank

3: first reactor 4: second reactor

5: third reactor 6: fourth reactor

7: fifth reactor 8: settling tank

9: medium or carrier 10: external organic carbon source

In order to achieve the above object, the present invention,

Anaerobic contact tank, separation tank, first reaction tank which is a nitriding reaction tank under aerobic state, second reaction tank which is a denitrification reaction tank under anoxic state, third reaction tank under intermittent aeration state, fourth reaction tank under intermittent aeration state, fifth reaction tank under aerobic state, and The sludge is returned from the settling tank to the anaerobic contacting tank, the sludge separated from the separation tank is introduced into the second reactor, and the inflow water separated from the separation tank is introduced into the first reactor. Provides a method for the purification of wastewater consisting of repetitive operations.

In the anaerobic contact tank, the first reactor, the second reactor, the third reactor, the fourth reactor, and the fifth reactor, a stirring system for improving the contact between the microorganism and the influent is operated.

An external organic carbon source may be injected into the fourth reactor to use as an electron donor for smoothly removing nitrogen and phosphorus from the influent. Preferably, the external organic carbon source consists of an organic material containing methanol and acetate.

In the first reactor, the third reactor, the fourth reactor, and the fifth reactor, an aeration system capable of increasing dissolved oxygen in water is operated. The first reactor is operated with a medium or a carrier for nitrification of the influent.

Instead of the anaerobic contacting tank, a return sludge denitrification furnace and a pure anaerobic contacting tank are installed and operated, and the inflow water is introduced stepwise in the return sludge denitrification furnace.

Preferably, the separation tank is composed of a precipitation tank, a floating tank or a centrifugal reaction tank.

According to the purification process of the wastewater according to the present invention as mentioned above, it is possible to maximize the treatment of nitrogen and phosphorus which is the main cause of eutrophication. In other words, in the case of toxic sewage and wastewater, the anaerobic contacting tank is contacted with microorganisms to adsorb toxic substances in sewage and wastewater to the microorganisms. Since only two reactors are transported, the effect on nitrifying bacteria, which are relatively weak in toxicity, is reduced, so that the nitrification reaction can proceed without difficulty in the first reactor.

In addition, as for the wastewater having a low C / N ratio, as the external organic carbon source is supplied to the fourth reactor in anoxic state where there is little organic matter, the efficiency of denitrification can be improved. In addition, by using a carrier or a medium, the slow growth nitride can be concentrated, so that the time required for the nitrification reaction can be shortened, and as a result, the volume of the reaction tank can be reduced. It can be widely applied to livestock and industrial wastewater including small domestic wastewater.

Hereinafter, the wastewater purification process of the present invention will be described in detail with reference to the accompanying drawings.

Municipal sewage to be treated using the present invention has a low C / N ratio of 6-7 or less and has the characteristic that the toxic substances are intermittently introduced. Table 1 below shows the characteristics and adsorption experiments of the average small urban sewage (sewage discharged from a group residence such as a dormitory) obtained by the inventors through several measurements.

Table 1. Small-scale urban sewage characteristics and adsorption test results

Item City sewage (inflow) After adsorption by microorganism TCODcr (organic) 315mg / ℓ 37mg / ℓ SCODcr 195mg / ℓ 34mg / ℓ BOD ₅ 150mg / ℓ 18mg / ℓ T-N (nitrogen) 47mg / ℓ 39mg / ℓ Toxicity Ceriodaphnia dubia (C ₅₀ ) 72.2% 89% Toxicity Nitrifier (Inhibition%) 43% 11%

As shown in Table 1, the domestic small municipal sewage has a low C / N ratio, and the toxicity by Nitrifier was inhibited by 43% of Nitrifier when the wastewater was introduced. In addition, in the toxicity test by Ceriodaphnia dubia (a kind of water flea), 50% of Ceriodaphnia dubia was observed to be killed when the amount of raw water added was 72.2%. This means the presence of toxic substances in sewage and wastewater in residential areas such as dormitories.

The concentrations of organic matter and nitrogen after separating the municipal sewage from the activated sludge and anaerobic contact were reduced as shown in Table 1 above, and the toxic substances causing growth inhibition in nitride bacteria were also reduced. Therefore, the sewage and wastewater after anaerobic contact separation improves the nitriding reaction by nitride bacteria.

1 is a schematic diagram showing a wastewater purification process according to a first embodiment of the present invention.

1, the apparatus for performing the wastewater purification process according to the first embodiment of the present invention is anaerobic contact tank (1), separation tank (2), first, second, third, arranged in series , Fourth and fifth reactors (3,4,5,6,7), and precipitation tanks (8). Separation tank (2) is composed of a settling tank, flotation tank or centrifugal reaction tank. In the first reactor 3, a medium or a carrier 9 for nitrifying the influent water introduced into the first reactor 3 via the anaerobic contacting tank 1 and the separation tank 2 is disposed. The operation method of the wastewater purification apparatus configured as described above is continuously and repeatedly operated in the form as indicated by the arrow in FIG. 1.

First, when sewage and wastewater flow into the anaerobic contacting tank 1, organic matter of sewage and wastewater is adsorbed to the floating microorganisms and adsorption of toxic substances is induced. In addition, the anaerobic contact tank (1) maximizes the release of phosphorus from the bacteria (Acinetobacter, etc.) by using the organic acid flowing in the waste water. Next, in the separation tank 2, the influent of organic matter, microorganisms and toxic substances adsorbed with toxic substances, and nitrogen compounds such as ammonia with low toxic substances and poor adsorption are separated relatively.

Microorganisms separated from the inflow water in the separation tank (2) flows into the second reaction tank (4), which is a denitrification reaction tank under anoxic state, and at the same time, the inflow water treated in the separation tank (2) is low in organic matter and toxic substances and contains nitrogen such as ammonia. In many states, a compound flows into the 1st reaction tank 3 which is a nitriding reaction tank under an aerobic state. In the first reactor 3, a medium or a carrier 9 is provided to increase the nitrification efficiency by attaching and growing nitrifying bacteria with slow growth. Thereby, the nitrification reaction of the inflow water which flowed into the 1st reaction tank 3 advances.

In the second reactor (4), the denitrification reaction is induced under an oxygen-free state in which air is not injected by mixing the suspended microorganisms that adsorb organic matter and the sewage in which the nitrate is rich in the first reactor (3). Inflow water denitrated in the second reactor 4 is continuously introduced into the third reactor 5 and the fourth reactor 6 under intermittent aeration. In the third reactor 5 and the fourth reactor 6, the aeration and non-aeration in the reactor in the intermittent aeration state are operated alternately at regular intervals. At this time, the aeration and non-aeration time can be flexibly adjusted according to the sewage and waste water properties, such as 1 hour / 1 hour, 2 hours / 2 hours, 2 hours / 1 hour. Therefore, in the third reactor 5 and the fourth reactor 6, nitrification and denitrification reactions can be simultaneously performed with the removal of organic matter. It may also remove phosphorus by inducing release and intake by phosphorus bacteria.

In the fifth reactor 7, which is an aerobic reactor, degassing reaction of the final organic matter and nitrogen gas is performed. Next, part of the sludge settled in the settling tank 8 is returned to the anaerobic contacting tank 1 and the remainder is drawn into the waste sludge for subsequent treatment.

2 is a schematic diagram showing a purification process of wastewater according to a second preferred embodiment of the present invention. The purification process of the wastewater according to the second embodiment of the present invention shown in FIG. 2 is the present invention shown in FIG. 1 except that the external organic carbon source 10 is supplied into the fourth reactor 6, which is an anoxic reactor. The same as the purification process of the wastewater according to the first embodiment of the.

Referring to FIG. 2, when there is little organic matter in sewage and wastewater, the external organic carbon source 10 is supplied as an electron donor into the fourth reactor 6 so that nitrogen and phosphorus may be smoothly removed. In this case, the external organic carbon source 10 may be used as long as it is an economical organic material including methanol and acetate. Therefore, organic matter produced by fermenting sediment sludge in municipal sewage, including livestock wastewater, can also be injected.

3 is a schematic diagram showing a purification process of wastewater according to a third embodiment of the present invention. The wastewater purification process according to the third embodiment of the present invention shown in FIG. 3 is performed except that the return sludge denitrification furnace 1a and the pure anaerobic contact tank 1b are installed instead of the anaerobic contact tank 1. It is the same as the wastewater purification process according to the first embodiment of the present invention shown in FIG.

The wastewater purification process is performed by determining the concentrations of dissolved oxygen and nitrates (electron acceptors) that may be present in the return sludge and influent water in the wastewater purification process according to the first and second embodiments of the present invention shown in FIGS. 1 and 2. In short, it is a process to improve pure anaerobic condition.

To this end, instead of the anaerobic contacting tank 1 shown in Figs. 1 and 2, a conveying sludge denitrification furnace 1a and a pure anaerobic contacting tank 1b are provided. In the conveying sludge denitrification furnace 1a, a small amount of organic matter in the influent sewage flowing into the conveying sludge denitrification furnace 1a by a stepwise injection is used to minimize the concentration of the conveying sludge and the electron acceptor in the influent. The pure anaerobic contact tank 1b improves the pure anaerobic state. At this time, the influent sewage is mainly introduced into the pure anaerobic contact tank (1b) to maximize the adsorption of organic matter by the sludge and the release of phosphorus by the phosphorus bacteria.

In all wastewater purification processes of the present invention as described above, a reaction vessel including an anaerobic contacting tank is equipped with a stirring facility for improving contact between the microorganisms and the wastewater, and the dissolved oxygen in the aerobic reaction tank can be increased. Aeration system is provided.

Wastewater treatment process according to the present invention can be treated with organic matter and nutrients in the wastewater even if the C / N ratio is lower than the conventional treatment process. In addition, even if some toxic substances in the influent can be treated. In particular, it is possible to effectively treat the wastewater flowing into the sewage and wastewater treatment plant of Korea, it is possible to shorten the hydraulic retention time by nitrification using a medium or a carrier.

According to the purification step of the wastewater according to the present invention as described above, it is possible to maximize the treatment of nitrogen and phosphorus which is the main cause of eutrophication. In other words, in case of toxic sewage and wastewater, the anaerobic contact tank is contacted with microorganisms to adsorb toxic substances in the sewage and wastewater to the microorganisms, and the microorganism is separated from the separation tank so that only concentrated microorganisms are denitrification reaction tanks under anoxic state. Since only two reactors are transported, the effect on nitrifying bacteria, which are relatively weak in toxicity, is reduced, so that the nitrification reaction can proceed without difficulty in the first reactor.

In addition, as for the wastewater having a low C / N ratio, as the external organic carbon source is supplied to the fourth reactor in anoxic state where there is little organic matter, the efficiency of denitrification can be improved. In addition, by using a carrier or a medium, the slow growth nitride can be concentrated, so that the time required for the nitrification reaction can be shortened, and as a result, the volume of the reaction tank can be reduced. It can be widely applied to clean domestic and industrial wastewater as well as small scale domestic wastewater.

Claims (10)

Anaerobic contact tank, separation tank, first reaction tank which is a nitriding reaction tank under aerobic state, second reaction tank which is a denitrification reaction tank under anoxic state, third reaction tank under intermittent aeration state, fourth reaction tank under intermittent aeration state, fifth reaction tank under aerobic state, and The sludge is returned from the settling tank to the anaerobic contacting tank, the sludge separated from the separation tank is introduced into the second reactor, and the inflow water separated from the separation tank is introduced into the first reactor. A method for the purification of wastewater consisting of repetitive operations. According to claim 1, wherein the anaerobic contact tank, the first reactor, the second reactor, the third reactor, the fourth reactor and the fifth reactor in the stirring apparatus for improving the contact between the microorganism and the influent water is arranged Waste water purification method characterized in that the operation. The method of claim 1 or 2, wherein an external organic carbon source is introduced into the fourth reactor to operate as an electron donor for smoothly removing nitrogen and phosphorus from the influent. 4. The method of claim 3, wherein the external organic carbon source consists of an organic material containing methanol and acetate. The method of claim 1, wherein an aeration system capable of increasing dissolved oxygen in the water is disposed in the first reactor, the third reactor, the fourth reactor, and the fifth reactor. The method of claim 1 or 5, wherein the first reaction tank is provided with a medium or a carrier for nitrifying the influent. The wastewater purification method according to claim 1, wherein a return sludge denitrification furnace and a pure anaerobic contact tank are installed and operated in place of the anaerobic contact tank, and the return sludge is introduced in a stepwise manner. The method of claim 1, wherein the separation tank comprises a settling tank. The method of claim 1, wherein the separation tank comprises a floating tank. The method of claim 1, wherein the separation tank comprises a centrifugal reaction tank.