KR20020048460A - A process for removing a biological nutrient - Google Patents

Abstract

PURPOSE: Provided is a process for removing biological nutrients which performs advanced wastewater treatment using wastewater and sludge without external supply of carbon and reduces amount of sludge epochally. CONSTITUTION: The process for removing biological nutrients adds several steps to existing wastewater treatment process which comprises the steps of primary sedimentation, anaerobic step, aeration and secondary sedimentation. The first is a return step which returns united sludge in the primary and secondary sedimentation steps to the primary sedimentation step. The second is a hydrolysis step which decomposes organic matters by ozone and returns hydrolysis liquid to the primary sedimentation step. The third is an anaerobic steps which mixes return sludge and raw water by agitation. The fourth is a denitrification step which mixes bacteria and the mixture. The last is an aerobic step.

Description

Sewage Treatment Process for Removal of Biological Nutrients {A PROCESS FOR REMOVING A BIOLOGICAL NUTRIENT}

The present invention relates to a sewage treatment process for the removal of biological nutrients, and more particularly, a process combined with a sludge discharge system and a high degree of sewage treatment is used for sewage and sludge without supplying external carbon sources. The present invention relates to a sewage treatment process that significantly reduces the discharge of sludge.

The principle of removing nitrogen and phosphorus from the biological nutrient salts is as follows. First, the removal of phosphorus releases phosphorus while assimilating phosphorus as a storage product in cells with the ability of microorganisms to remove simple enzyme substrates in the anaerobic state, and in the aerobic state, excess phosphorus is stored in the form of multiple phosphates By doing so. Nitrogen removal is classified into two categories. The first is the removal method by assimilation of microorganisms. Second, the nitrification process in which ammonia and organic nitrogen in the influent are converted to nitrate nitrogen and nitrite nitrogen under certain conditions, and the nitrate nitrogen undergoing the nitrification is reduced in the treatment system and discharged to the nitrogen gas into the atmosphere. Denitrification is followed by removal of the compound.

In the prior art, large-scale sewage treatment plants have been designed with a focus on secondary treatment, such as most removal of solids and organics. However, nutrients contained in the sewage, typically nitrogen and phosphorus (P), caused eutrophication, adversely affecting water resources. In particular, in the case of nitrogen, ammonia nitrogen is toxic to fish and shellfish, nitrate nitrogen has a direct impact on the environment ecosystem such as cyanosis. Therefore, attention has recently been focused on the removal of nutrients, such as nitrogen and phosphorus, and the discharge regulation of nutrients in treated water is being implemented, which is gradually being strengthened.

Most of the new sewage treatment plants are designed and operated with advanced treatment such as nitrogen and phosphorus removal in mind. In the case of existing small sewage treatment plants, the improvement of advanced treatment is relatively easy.

However, in the conventional large sewage treatment plant operated mostly by activated sludge method, various problems arise in directly introducing nitrogen and phosphorus removal processes. In other words, the volume of the reaction tank must be increased significantly for proper hydraulic retention time for the advanced treatment, and if the existing process is applied as it is, the organic treatment is insufficient due to the characteristics of domestic sewage, so the advanced treatment can fail. To improve efficiency, operating costs must be continually spent by supplying external carbon sources. Because of this problem, as described below, many techniques for improving the existing activated sludge method have been developed, but the problem still remains.

Conventionally, advanced processing processes developed to simultaneously remove nitrogen and phosphorus include A2 / O method, modified Bardenpho method, VIP (Virginia Initiative Plant) method, and the like.

1 schematically shows a conventional sewage treatment process. Conventional sewage treatment process is composed of a primary sedimentation tank 20, anaerobic tank 21, aeration tank 22 and the final sedimentation tank (23). The primary sedimentation tank 20 is the solid-liquid separation of the introduced raw water and transports the sewage from which the sludge is separated to the anaerobic tank 21 which is the next step. The sludge separated from the primary settling tank 20 is usually sent to a concentration tank (not shown) for disposal. The anaerobic tank 21 decomposes the introduced sewage by the microorganism in the anaerobic state and transfers it to the aeration tank 22 which is the next step. Decomposition by the microorganism is generally made to the organic material. In the aeration tank 22, the organic matter remaining in the sewage is further decomposed by oxygen contained in the aerated gas, and then transferred to the final precipitation tank 23, which is the next step. The final sedimentation tank (23) finally repeats the solid-liquid separation once again, the sludge precipitated is transferred to the concentration tank for disposal, and discharged the clean sewage from which the sludge is separated.

According to the conventional activated sludge process, the removal rate of nitrogen is 10 to 40% and the removal rate of phosphorus is 5 to 20%, which is only a very low level.

On the other hand, the sludge treatment technology has been attracting a lot of attention in a situation where it is not easy to treat landfills, the demand is also increasing. Sludge free systems have been recognized as a very suitable technology in this respect. However, certain techniques for sludge disintegration are inherent, and even more so in combination with sludge-free systems and advanced sewage treatment.

The present invention has been invented to solve the problems in the prior art as described above, in accordance with the characteristics of domestic sewage lacking organic matter necessary for denitrification and phosphorus release by configuring a process combined with a sludge discharge system and advanced treatment of sewage Its purpose is to provide a sewage treatment process for the removal of biological nutrients, which performs advanced treatment using sewage and sludge without supplying external carbon sources, and at the same time significantly reduces the discharge of sludge.

1 is a schematic diagram showing a conventional sewage treatment process.

2 is a schematic view showing a sewage treatment process according to the present invention.

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

1: raw water 2, 6, 7, 10: conveying sludge

3: hydrolysis liquid 4: sludge

5 mixture 9 discharge

11: settling and anaerobic tank 12: anaerobic bath

13: Exhalation tank 14: Final sedimentation tank

15: hydrolysis bath 16: disposal

20: primary sedimentation tank 21: anaerobic tank

22: aeration tank 23: final sedimentation tank

Sewage treatment process for the removal of biological nutrient salts of the present invention for achieving the above object, in the sewage treatment process consisting of the first precipitation step, anaerobic step, aeration step and the final precipitation step,

The final sedimentation step and the sludge precipitated from the first settling step further includes a conveying step (a) to be returned to the first settling step, the return sludge of the first settling step is 0.1 to 0.5 times the raw water and the final The sludge returned from the precipitation step is 0.2 to 1.0 times the raw water and the sludge returned to the first precipitation step is operated under the condition of 0.35 to 1 times the raw water.

Hydrolysis step (b) for decomposing the organic matter by ozone oxidation to the confluence of the sludge conveyed in the conveying step (a), and conveying the hydrolysis liquid to the first precipitation step may further include, The sludge of the first precipitation step introduced into the hydrolysis step is 0.1 to 0.5 times the raw water and the return sludge of the final precipitation step is 0.2 to 1.0 times the raw water and the sludge returned to the first precipitation step is 0.35 to 1 times the raw water. The residence time in the hydrolysis step of the mixture is operated under the condition of 2.0 ~ 12.0 hours.

In addition, by the addition of mechanical stirring to the primary precipitation step comprises the precipitation and anaerobic step (c) configured to mix the conveyed sludge and raw water, the aeration step is divided into the front end of the microorganisms by mechanical agitation in an oxygen-free state The denitrification step (d) configured to mix with the mixture may be configured to include an exhalation step (e) configured to maintain an aerobic state at the rear end of the divided aeration step.

In addition, sludge may be returned from the denitrification step (d) to the precipitation and anaerobic step (c), from the exhalation step (e) to the denitrification step (d), and from the final settling step to the denitrification step (d). , The return sludge of the denitrification step (d) flowing into the precipitation and anaerobic step (c) is 0.5 to 3 times the raw water, and the return sludge of the aerobic step (e) flowing into the denitrification step (d) is 1 of the raw water. ~ 3 times and the final sludge return sludge can be operated under the conditions of 0.25 ~ 0.5 times the raw water. In addition, the residence time in the precipitation and anaerobic step (c) of the mixed solution is 0.5 to 3 hours, the residence time in the denitrification step (d) is 1 to 3 hours and the residence time of the mixture in the aerobic step (e) It is preferable to make 3.0 to 7.0 hours.

In addition, the sludge of some of the mixture returned to the first precipitation step may be configured to be disposed immediately before the first precipitation step.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation of the present invention.

2 is a schematic view showing a sewage treatment process according to the present invention. Conventionally, the raw water passing through the screen and the flow adjustment tank passes through the settling and anaerobic tank, and a considerable amount of the organic material useful for denitrification is transferred to the anaerobic digester in the form of primary sludge. On the other hand, in the present invention, the conventional primary precipitation tank 20 is modified to be an anaerobic tank so that a considerable amount of organic matter that can be lost is used for denitrification and phosphorus release, and a hydraulic retention time suitable for advanced processing without additional reactor is added. To keep it.

As shown in FIG. 2, the hydrolysis solution 3 passed through the return sludge 2 and the hydrolysis tank 15 of the raw water 1 and the anoxic tank 12 flows into the precipitation and anaerobic tank 11. The precipitation and anaerobic tank 11 share the function as an anaerobic tank, and promote the reaction between the microorganism and the substrate through mechanical mixing.

Assuming that the quantity of raw water 1 is Q, the return sludge 2 in the settling and anaerobic tank 12 to the anaerobic tank 11 is in the range of about 0.5 to 3.0 [Q], and the hydrolyzate 3 is returned. Is operated to be in the range of about 0.35 to 1.0 [Q]. The residence time of the mixture in the precipitation and anaerobic tank 11 is about 0.5 to 3.0 hours.

In the sedimentation and anaerobic tank 11, residual ozone in the hydrolysis solution 3 is first reduced, and nitrate nitrogen contained in the return sludge 2 of the oxygen-free tank 12 is reduced. Volatile acid is then produced under anaerobic conditions, and phosphorus release by microorganisms takes place as the carbon source.

The oxygen-free tank 12 is a modification of the existing aeration tank, it is formed in the front end after dividing the aeration tank into a partition. An aerobic tank 13 was formed at the rear end of the aeration tank divided by the partition wall so that the transport sludge 6 could be transported to the oxygen-free tank 12. In the oxygen-free tank 12, the mixed liquid 5 transferred from the settling and anaerobic tank 11 and the final conveying sludge 7 of the final settling tank 14 are also introduced and operated with oxygen-free stirring. When oxygen contained in the return sludge 6 of the aerobic tank 13 is depleted preferentially, denitrifying microorganisms in the anoxic tank 12 are easily biodegradable organic substances contained in the mixed solution 5 transferred from the anaerobic tank (Readily Biodegradable COD). Denitrification is carried out using) as a carbon source. For complete denitrification, the sludge 2 of the anaerobic tank 12 is returned to the sedimentation and anaerobic tank 11 again.

When the quantity of raw water is Q, the return sludge 6 of the aerobic tank 13 is conveyed at about 1.0-3.0 [Q], and the final return sludge from the final settling tank 14 is maintained in order to maintain the microorganism density | concentration of a reaction tank appropriately. 7) is returned to about 0.2 to 1.0 [Q], and the hydraulic residence time of the mixture in the oxygen-free tank 12 is operated to be about 1 to 3 hours.

The aeration tank 13 conveys the conveying sludge 6 to the anoxic tank 12 in order to improve the efficiency of denitrification and phosphorus release. In the aerobic tank 13, an additional nitrification process, phosphorylation by microorganisms, and oxidation of residual organic matter occur in an aerobic state. The aerobic tank 13 according to the present invention can be operated with a relatively short hydraulic residence time as compared with a conventional activated sludge tank. That is, decomposable organic matter contained in the mixture is already almost depleted through the anaerobic stage and the anaerobic tank 12 in the precipitating and anaerobic tank 11, and the aerobic tank 13 actually serves as nitrification and phosphorus intake. Since it is only responsible for, it is possible to shorten the hydraulic residence time of the mixture in the aerobic tank 13. The hydraulic residence time of the aerobic tank 13 is preferably about 3.0 to 7.0 periods.

The final sedimentation tank 14 discharges the treated water after finally separating the mixture 8 through the sewage treatment process. The final conveyed sludge 7 precipitated at this time is returned to the anoxic tank 12 in order to maintain an appropriate concentration of microorganisms. At the same time, the final conveying sludge 10 is returned to the hydrolysis tank 15 in order to efficiently use the organic matter contained therein for denitrification and phosphorus release. In the above, the final conveying sludge 10 may be configured to be directly returned to the sedimentation and anaerobic tank 11 without the hydrolysis tank 15. Here, it demonstrates centering on the Example with which the hydrolysis tank 15 is provided.

The hydrolysis tank 15 decomposes the introduced sludge through oxidation with ozone, and the dissolved and dissolved organic matter is returned to the anaerobic precipitation and anaerobic tank 11 to be used as a carbon source useful for denitrification and phosphorus release. . The sludge 4 of the settling and anaerobic tank and the return sludge 10 of the final settling tank 14 flow into the hydrolysis tank 15. In the hydrolysis tank 15, when the quantity of raw water 1 is Q, the sludge 4 conveyed from the sedimentation and anaerobic tank is about 0.1 to 0.5 [Q], and the sludge conveyed from the final sedimentation tank 14 ( 10) is about 0.2 to 1.0 [Q], and the hydraulic retention time of the mixture in the hydrolysis tank 15 is operated to be about 2.0 to 12.0 hours.

A part of the sludge contained in the hydrolysis liquid 3 returned from the hydrolysis tank 15 to the precipitate and the anaerobic tank 11 is discarded 16 during the conveyance. Thus, the amount of sludge released is significantly reduced compared to the conventional sewage treatment process.

Hereinafter, the present invention will be described through examples.

The sewage treatment process according to the present invention and the conventional activated sludge method (continuous inflow, continuous aeration) were compared through laboratory scale experiments (0.1 ton daily treatment). Table 1 shows the sewage treatment efficiency according to the experimental results over four weeks.

Item Raw water concentration (ml / L) Treatment process according to the present invention Existing Treatment Process Removal efficiency (%) Removal efficiency (%) COD _cr 150 98 98 Total nitrogen 38.5 90 35 A total person 5.5 82 19 Surplus sludge 0.96 ^* 85 0

* Sludge Generation (g / day)

As shown in Table 1, the removal efficiency of total nitrogen and total phosphorus in the sewage treatment process according to the present invention showed a drastically improved result compared to the conventional sewage treatment process. The amount of excess sludge generated is 1% of the average inflow. In the conventional sewage treatment process, the sludge loss occurs somewhat during the digestion and concentration process, but in the sewage treatment process, the sludge loss is not at all. However, according to the sewage treatment step of the present invention, since sludge reduction treatment is included, most of the sludge is removed except for components that are not decomposable, such as sand, in the primary sludge.

As described in detail above, by using the sewage treatment process for the removal of biological nutrient salts of the present invention, it is possible to effectively remove nitrogen, phosphorus, etc., while minimizing the cost of improving the existing process, as well as to reduce sludge generation. There is an effect that can be significantly reduced.

Claims (10)

In the sewage treatment process consisting of the first settling step, anaerobic step, aeration step and the final settling step, Sewage treatment process for the removal of biological nutrient salts, characterized in that it further comprises a return step (a) of the sludge precipitated from the final precipitation step and the first precipitation step is returned to the first precipitation step. The method of claim 1, The sludge conveyed in the first precipitation step is 0.1 to 0.5 times the raw water and the sludge conveyed in the final precipitation step is 0.2 to 1.0 times the raw water and the sludge conveyed to the first precipitation step is 0.35 to 1 times the raw water. Sewage treatment process for the removal of nutrients. The method of claim 1, Further comprising a hydrolysis step (b) for decomposing organic matter by ozone oxidation to the confluence of the sludge conveyed in the conveying step (a), and returning the hydrolysis liquid to the first precipitation step. Sewage treatment process for the removal of biological nutrients. The method of claim 3, wherein The sludge of the primary precipitation step introduced into the hydrolysis step is 0.1 to 0.5 times the raw water and the return sludge of the final precipitation step is 0.2 to 1.0 times the raw water and the sludge returned to the primary precipitation step is 0.35 to 1 of the raw water. And, the residence time in the hydrolysis step of the mixture is a sewage treatment process for the removal of biological nutrients, characterized in that 2.0 to 12.0 hours. The method according to claim 2 or 4, And a settling and anaerobic step (c) configured to mix the conveyed sludge and the raw water by adding mechanical stirring to the primary settling step. The method of claim 5, The denitrification step (d) is configured to divide the aeration step and to mix the microorganism and the mixture by mechanical agitation in anoxic state at the front end thereof. The rear end of the divided aeration step sewage treatment process for the removal of biological nutrients, characterized in that it comprises an aerobic step (e) configured to maintain an aerobic state. The method of claim 6, Sludge is returned from the denitrification step (d) to the precipitation and anaerobic step (c), from the aerobic step (e) to the denitrification step (d), and from the final settling step to the denitrification step (d). Sewage treatment process for the removal of biological nutrients. The method of claim 7, wherein The return sludge of the denitrification step (d) flowing into the precipitation and anaerobic step (c) is 0.5 to 3 times the raw water, and the return sludge of the aerobic step (e) flowing into the denitrification step (d) is 1 to 1 of the raw water. Sewage treatment process for the removal of biological nutrients, characterized in that 3 times and the final sludge return sludge is 0.2 ~ 1.0 times the raw water. The method of claim 8, The residence time in the precipitation and anaerobic step (c) of the mixture is 0.5 to 3 hours, the residence time in the denitrification step (d) is 1 to 3 hours and the residence time of the mixture in the aerobic step (e) is 3.0. Sewage treatment process for the removal of biological nutrients, characterized in that ~ 7.0 hours. The method of claim 9, Sewage treatment process for the removal of biological nutrients, characterized in that the sludge of some of the mixture returned to the first precipitation step is disposed so that just before the first precipitation step.