KR100375413B1 - Removal Methods of Nitrogen and phosphorus in wastewater using external carbon source - Google Patents

Abstract

The present invention relates to a method for more effectively removing nitrogen (N) and phosphorus (P) in sewage using an organic carbon source provided from the outside.

To this end, the present invention is an anaerobic tank that is selectively supplied with an organic carbon source from the outside in order to release the phosphorus of the second hand influent; A first unit for excessive ingestion of phosphorus released from the anaerobic tank and for oxidizing ammonia nitrogen or organic nitrogen; An oxygen-free tank for degassing and removing nitrate nitrogen by using an organic carbon source supplied from the outside after passing through the first unit described above; A second aerobic tank for performing post-aeration to remove the final residual organic substance and phosphorus which have passed through the anoxic tank; An internal circulation process that internally circulates about 100% of the influent to an anaerobic tank to remove more nitrate nitrogen that may flow out of the second tank of the rear stage; A final settling tank (final needle) for discharging the treated water after discharging the second aeration tank again and discharging the treated water and disposing a portion of the sludge and transferring most of the sludge to the front end of the anaerobic tank; It is characterized by using an external organic carbon source characterized by the above.

Description

Removal Methods of Nitrogen and phosphorus in wastewater using external carbon source}

Nitrogen and phosphorus are mainly derived from agricultural fertilizers, manure from humans or livestock, and synthetic detergents.They are eutrophication, red tides on the coast, and fish toxins in ammonia when large amounts of untreated sewage or factory wastewater flow into lakes including rivers and dams. This may cause dissolved oxygen deficiency in water. In addition, the excessive growth of algae due to the inflow of nitrogen, phosphorus, etc. may lead to the overgrowing of algae in the water purification plant, and the clogging phenomenon of the sand filter, which is the water purification process, shortens the operation time of the filter paper. However, when nitrogen and phosphorus are carried out in a general sewage treatment process, the removal rate is very low, and thus advanced treatment is required.

The present invention relates to a method for simultaneously removing nitrogen and phosphorus from sewage, and in particular, by using an organic carbon source provided from the outside to solve the BOD low load problem, which is a serious problem in sewage, nitrogen (N) and phosphorus (P) are removed. It is about a method that can be removed and processed more effectively at the same time.

Commonly known nitrogen and phosphorus removal methods include the anaerobic-anaerobic-aerobic method (A ² / O method: Anaerobic-Anoxic-Oxic method), M-Bardenpho method, UCT method, VIP method, MLE Law is known.

Among them, the representative A ² / O method uses organic materials in the wastewater as a carbon source for the denitrification process, thus reducing the amount of hydrogen donor and using the alkalinity generated during denitrification in the denitrification tank in the nitrification tank. Can reduce the cost. However, nitrite nitrogen or nitrate nitrogen contained in the return sludge flows into the anaerobic tank, which inhibits the release of phosphorus and finally adversely affects the biological removal effect of phosphorus.

The M-Bardenpho process is an oxygen-free and aeration tank in addition to the existing A ² / O process. In this process, as in the A ² / O process, nitrogen is removed from the aeration tank by returning nitrate nitrogen to the denitrification tank, and phosphorus is removed by the disposal of excess sludge. The removal of phosphorus and nitrogen is influenced by the concentration of organic matter in the influent, since the carbon source consumed for the release of phosphorus in the anaerobic tank and the nitrogen removal in the denitrification tank uses organic matter in the influent sewage. It has the advantage of increasing the phosphorus content while minimizing the sludge production, but the additional cost of the internal circulation pump, and requires a larger reactor than the A ² / O process. It also requires a high BOD / P ratio. In particular, this process has a problem that residual nitrate in the conveying sludge flows into the anaerobic tank, and denitrification bacteria preferentially denitrify using a carbon source, thereby lowering phosphorus emission and consequently lowering phosphorus removal efficiency.

The UCT process was created to solve the problems of the A ² / O process and modified Bardenpho processes, and the effect of nitrate was removed by returning the sludge to the anaerobic tank, and the efficiency of phosphorus removal by NO ₃ ^_ contained in the return sludge Inhibitors can be reduced and reactors are smaller than Bardenpho. However, the internal circulation pump costs additionally, and the problem with this process is that keeping the nitrate concentration in the anaerobic tank low determines the overall phosphorus removal efficiency and thus does not tend to sufficiently nitrate.

The VIP process is similar to UCT, but the UCT consists of one complete mixing tank, while the combination of the complete mixing tanks increases the phosphorus excess capacity. The greatest advantage of this process is its high phosphorus removal efficiency and low seasonal influence. In addition, due to the small size of the reaction tank, it takes up less land area, and the nitrate transfer to the anaerobic tank can reduce the alkalinity consumption and reduce the nitrate load in the aerobic tank. However, energy costs are increased because internal circulation pumps are required. In addition, the ability to remove nitrogen decreases at low temperatures.

Other methods, including the A ² / O method described above, can remove nitrogen and phosphorus biologically well in foreign countries such as the United States and Europe, where organic materials are rich in sewage. The relatively low concentration, that is, the low C / N ratio, makes it difficult to obtain efficient TN removal even if the conventional activated sludge process is converted to BNR (Biological Nutrient Removal) process to treat nitrogen and phosphorus. In addition, in order to remove nitrogen biologically, 100 to 300% of the inflow water must be internally circulated from the aeration tank to the anoxic tank front, which is expensive in terms of initial construction and maintenance costs.

The denitrification efficiency in the conventional nitrogen phosphorus removal process presented above is as follows.

That is, the denitrification efficiency of the existing nitrogen removal process can be represented by the MLE process and can be represented by the formula (1).

MLE process

However, for this formula to be established, nitrate nitrogen flowing into the anoxic tank must be denitrated 100%. To this end, the amount of microorganisms in the reactor must be sufficient, and the amount of organic matter necessary for denitrification and the time required for this should be sufficient.

In addition, the denitrification rate according to the return sludge and the internal circulation is shown in the figure below.

Ir + R

In general, when the amount of return sludge is operated at about 50% of the influent, and the internal circulation ratio is assumed to be 100% and 200%, the denitrification efficiency theoretically does not increase directly with the internal circulation rate as 60% and 71.4%, respectively. Do not.

In other words, for the denitrification efficiency according to the internal circulation, the most simple ring MLE process is assumed, but the denitrification efficiency is expressed in most continuous sewage advanced treatment processes such as A ² / O, Bardenpho, and DNR that require internal circulation as well as MLE. Follow (1).

Accordingly, an object of the present invention is to provide a method for more effectively removing nitrogen (N) and phosphorus (P) from sewage using an organic carbon source provided from the outside.

The technical method of the present invention for achieving this object is an anaerobic tank which is optionally supplied with an organic carbon source from the outside to release the phosphorous of the second hand influent; A first unit for excessive ingestion of phosphorus released from the anaerobic tank and for oxidizing ammonia nitrogen or organic nitrogen; An oxygen-free tank for degassing and removing nitrate nitrogen by using an organic carbon source supplied from the outside after passing through the first unit described above; A second aerobic tank for performing post-aeration to remove the final residual organic substance and phosphorus which have passed through the anoxic tank; An internal circulation process that internally circulates about 100% of the influent to an anaerobic tank to remove more nitrate nitrogen that may flow out of the second tank of the rear stage; A final settling tank (final needle) for discharging the treated water after discharging the second aeration tank again to discharge the treated water and disposing of some of the sludge and transferring most of the sludge to the front end of the anaerobic tank; It is characterized by using an external organic carbon source characterized by the above.

In addition, another technical method of the present invention is the first unit for the excessive intake of phosphorus discharged from the second hand influent and oxidizing ammonia nitrogen or organic nitrogen; Oxygen-free tank for degassing and removing nitrate nitrogen by essentially supplying an organic carbon source from the outside after passing through the first aerobic tank; A second aerobic tank for performing post-aeration to remove the final residual organic substance and phosphorus which have passed through the anoxic tank; In order to release phosphorus, an organic carbon source is supplied from the outside and treated in an anaerobic tank, and then the external organic carbon source is characterized in that the sludge is transferred to and treated by the front end of the first aerobic tank. A first unit for excessively ingesting phosphorus released from the second hand influent and oxidizing ammonia nitrogen or organic nitrogen; Oxygen-free tank for removing the nitrate nitrogen by degassing by supplying an organic carbon source from the outside after passing through the first aerobic tank; A second aerobic tank performing post-aeration to remove the final residual organic material passed through the anoxic tank; An internal circulation process that internally circulates about 100% of the influent into the anoxic tank in order to remove more nitrate nitrogen that may flow out of the second tank of the rear stage; In order to release phosphorus, the organic carbon source is supplied from the outside to be treated in an anaerobic tank, and then the external organic carbon source is characterized in that the sludge is transferred to and treated by the front end of the first aerobic tank.

1 is a process diagram of nitrogen and phosphorus simultaneous removal method of a first embodiment according to the present invention.

Figure 2 is a process diagram of nitrogen and phosphorus simultaneous removal method of a second embodiment according to the present invention.

Figure 3 is a process diagram of nitrogen and phosphorus simultaneous removal method of a third embodiment according to the present invention.

Figure 4 is a process diagram of nitrogen and phosphorus simultaneous removal method of a fourth embodiment according to the present invention.

Hereinafter, with reference to the accompanying drawings an embodiment of the present invention will be described in detail.

First, the biological removal process of nitrogen and phosphorus in sewage is as follows.

Biologically, nitrogen is removed by a two-step reaction.

The first step is nitrification, in which ammonia nitrogen is oxidized to nitrate nitrogen, and the second step is denitrification, which releases nitrate nitrogen to nitrogen gas as an electron acceptor.

Organic nitrogen in sewage is decomposed during anaerobic reaction and decomposed into ammonia nitrogen, and the ammonia nitrogen is converted to nitrite by reducing the ammonia nitrogen to oxidative nitrogen by independent nutrient microorganisms under aerobic conditions. Next, the nitrite is subjected to a two-step reaction in which the nitrite is converted to nitrate.

^{_{NH 4 + + 3/20 2 → NO}} 2 - + 2H + + H 2 O

^{_{NO 2 - - 1/20 2 → NO}} 3 -

These reactions are summarized as follows.

^{_{NH 4 + + 2O 2 → NO}} 3 - + H 2 O + 2H + ... … Formula (2)

Nitrate nitrogen of nitrate ions (NO ₃ ⁻ ) generated in the chemical reaction formula (2) is used as an electron acceptor and is converted into nitrogen gas and degassed into the atmosphere.

The denitrification reaction takes place in an oxygen-free state where there is no dissolved oxygen, and an effective denitrification reaction requires biologically easy organic substances such as methanol. The overall reaction is briefly shown in the following equation (3).

An organic carbon source ^{_{+ 2NO 3 - → N 2 +}} CO 2 + H 2 O ... … Formula (3)

The organic carbon source used here is preferably an organic acid or methanol.

Next, the process of removing phosphorus is as follows.

Biological removal is a method of removal using the phenomenon that activated sludge releases phosphorus in the anaerobic state and ingests excess phosphorus in the aerobic state.

Since phosphorus is needed as an energy carrier in the cells of microorganisms, phosphorus can be removed as much as necessary for biological synthesis, but it can be removed more than the stoichiometric amount required for microbial growth when given anaerobic and aerobic conditions. . Phosphorus accumulation by microorganisms under continuous anaerobic and aerobic conditions is reported to be 4-12%. By discarding these microorganisms, phosphorus removal efficiency of 2.5 to 4 times can be obtained.

Their response is as follows.

In the anaerobic state, microorganisms consume organic materials and accumulate in the body in the form of poly-β-hydroxybutyrate (PHB). The energy required for the synthesis of PHB is supplied as the poly-P accumulated during the aerobic period is decomposed, and the decomposed phosphate (ortho-P) is released into the aqueous solution. The scheme is shown below.

Anaerobic: poly-P → ortho-P (energy release)

Organics → PHB (Energy Accumulation)

During exhalation, phosphate phosphorus in the water is excessively ingested by the phosphorus ingesting organism and stored in the body in the form of polyphosphoric acid. That is, under aerobic conditions, microorganisms accumulate large amounts of phosphorus granules of polyphosphoric acid in the body. When microorganisms ingest a large amount of phosphorus and accumulate in the body at high density, it is possible to remove phosphorus by disposing of sludge.

During expiration: ortho-P → poly-P (energy accumulation)

PHB + O ₂ → CO ₂ + H ₂ O (energy release)

That is, while anaerobic releasing a large amount of phosphorus, during exhalation, the phosphorus intake more than the amount released by the microorganisms can remove the phosphorus in the sewage.

As described above, in order to biologically remove nitrogen and phosphorus, an organic material used as a large amount of organic carbon source is required. The external carbon source (organic material) provided here includes chemicals such as methanol, ethanol, acetic acid, food processing companies or Organic acids produced by fermenting organic waste liquids and food waste generated in a alcohol factory may be effective. When using chemicals such as methanol can be very expensive. However, the present invention uses the organic acid produced by fermenting the organic waste liquid and food waste generated in a food processing company or a alcohol factory.

The characteristics of the present invention is that the treatment method is arranged in anaerobic No. 1, anoxic, and No. 2 processes to be able to denitrate most of the nitrate nitrogen generated in the first unit by supplying an external organic carbon source from the anoxic tank immediately after the end. In addition, large internal circulation is unnecessary.

In other words, it is theoretically possible to denitrate up to 100% by receiving the organic acid necessary for denitrification from the anoxic tank immediately after the nitrate nitrogen converted in the first reactor.

The presence of internal circulation has many advantages in terms of the rate of removal of contaminants when compared with the absence of internal circulation.

If there is an internal circulation, the following diagram is used to represent the equation required for reactor analysis.

Sewage concentration (mg / L) is Co, concentration of pollutants entering the reactor (mg / L) is Ci, reactor actual residence time (HRT _real , hr), pollutant removal rate (mg / L, hr) r When the reaction rate constant (/ hr) is expressed as k, the BNR relation equation is expressed as follows.

Based on the above equation, when the sludge return (R) is 1/2 of the influent (Q) and there is no internal circulation and the internal circulation changes by 100-300%, Ci and HRT are as follows.

In order to remove more contaminants, it is necessary to have a high contaminant concentration in the reactor or to secure a large residence time in the reactor.

However, as can be seen from the above table, the concentration of the actual pollutant inflow into the reactor is Co》 Ce, so the internal circulation is relatively small, and the actual reactor residence time (HRT _real ) is also increased. There is a disadvantage that decreases.

Figure 1 shows a process diagram of the nitrogen and phosphorus simultaneous removal method of the first embodiment according to the present invention, Figure 1 is anaerobic, No. 1, anoxic, No. 2 process does not require internal circulation.

In anaerobic tanks, an external carbon source may be selectively supplied to release phosphorus sufficiently, but if the sewage is rich in organic matter, it is not necessary to supply an external carbon source.

In the following first vessel, excess phosphorus released from the anaerobic tank is oxidized and oxidizes ammonia nitrogen or organic nitrogen.

In the following anoxic tank, nitrate nitrogen is degassed and removed by using an organic carbon source supplied from the outside.

In the following Unit 2, post-aeration is carried out to cleanly remove the last remaining organic matter.

The hydraulic retention time (HRT) of the sewage is about 7 to 10 hours, and the solid retention time (SRT) is about 7 to 15 days.

Figure 2 shows the nitrogen and phosphorus simultaneous removal method of the second embodiment according to the present invention, the overall process is the same as Figure 1 but in order to remove more nitrate nitrogen that can flow out of the second stage of the second stage of the influent 100% internal circulation can be done. The reason for 100% internal circulation is to remove nitrogen since some of the nitrogen components may be included in the external organic carbon source solution supplied to the anoxic tank.

Figure 3 shows the nitrogen and phosphorus simultaneous removal method of the third embodiment according to the present invention, the entire process is the same as Figure 1, but does not flow into the first anaerobic tank without flowing into the anaerobic tank.

In anaerobic tanks, an external source of organic carbon must be supplied to ensure sufficient phosphorus release.

Figure 4 shows the nitrogen and phosphorus simultaneous removal method of the fourth embodiment according to the present invention, the same as Figure 3 but about 100% of the influent to remove more nitrate nitrogen that can flow out of the second stage of the second tank It can give internal circulation.

As described above, as a result of performing the sewage treatment process using the present invention, the following results were obtained.

As shown in the above results, the present invention solves the BOD low load problem, which is a serious problem in sewage using an organic carbon source provided externally, and simultaneously removes nitrogen (N) and phosphorus (P) more effectively than the existing invention. It is possible to solve the food waste problem by using organic acid generated by fermenting organic waste liquid and food waste generated from food processing company or alcohol factory instead of methanol. It is a beneficial invention that brings savings.

Claims (4)

delete An anaerobic tank in which an organic carbon source is selectively supplied from the outside to release phosphorus in the second hand influent; A first unit for excessive ingestion of phosphorus released from the anaerobic tank and for oxidizing ammonia nitrogen or organic nitrogen; An oxygen-free tank for degassing and removing nitrate nitrogen by using an organic carbon source supplied from the outside after passing through the first unit described above; A second aerobic tank for performing post-aeration to remove the final residual organic substance and phosphorus which have passed through the anoxic tank; An internal circulation process that internally circulates about 100% of the influent to an anaerobic tank to remove more nitrate nitrogen which may flow out of the second tank of the rear stage ; A final settling tank (final needle) for discharging the treated water after discharging the second aeration tank again and discharging the treated water and disposing a portion of the sludge and transferring most of the sludge to the front end of the anaerobic tank; Nitrogen, phosphorus removal method of sewage using an external organic carbon source, characterized in that. A first unit for excess intake of phosphorus released from the second hand influent and for oxidizing ammonia nitrogen or organic nitrogen; An oxygen free tank for degassing and removing nitrate nitrogen by essentially supplying an organic carbon source from outside after passing through the first unit described above; A second aerobic tank for performing post-aeration to remove the final residual organic substance and phosphorus which have passed through the anoxic tank; The method for removing nitrogen and phosphorus from sewage using an external organic carbon source, characterized in that the organic carbon source is supplied from the outside in order to discharge phosphorus, treated in an anaerobic tank and then transported and treated with sludge to the front end of the first aerobic tank . A first unit for excessively ingesting phosphorus released from the second hand influent and oxidizing ammonia nitrogen or organic nitrogen; Oxygen-free tank for removing the nitrate nitrogen by degassing by supplying an organic carbon source from the outside after passing through the first aerobic tank; A second aerobic tank performing post-aeration to remove the final residual organic material passed through the anoxic tank; An internal circulation process of internally circulating about 100% of the influent to the anoxic tank in order to remove more nitrate nitrogen which may flow out of the second tank of the rear stage; The method for removing nitrogen and phosphorus from sewage using an external organic carbon source, characterized in that the organic carbon source is supplied from the outside in order to discharge phosphorus, treated in an anaerobic tank and then transported and treated with sludge to the front end of the first aerobic tank .