KR19980071903A - Nutrient Removal Method of Improved Sewage and Wastewater Using Anaerobic Fermentation Tank - Google Patents

Abstract

The present invention is to efficiently remove nitrogen and phosphorus from sewage and wastewater by supplying organic acid (Volatile Fatty Acid, VFA) produced after fermentation in an anaerobic state by injecting a high concentration of organic waste liquid into the anaerobic fermentation tank , Microbial treatment of inflow and wastewater in the order of anaerobic condition, first anoxic condition and aerobic condition (microbial treatment step), precipitation of the microbial treated discharge water (sedimentation step), precipitation microorganisms after the precipitation ( In the nutrient removal method of sewage and wastewater consisting of a step (return sludge) in the anaerobic conditions of the microbial treatment process, the sludge produced by anaerobic fermentation of high concentration organic waste liquid to dehydrate the sludge produced to produce an organic acid In order to remove the nitric oxide (NOx-N) in the conveying sludge during the process (organic acid production process) and the sludge conveying process. The process of mixing the formed organic acid and the return sludge from the precipitation process under the second anoxic condition (sludge mixing process) is an improved method for removing nutrients from sewage and wastewater using an anaerobic fermentation tank added before the sludge conveying process.

Description

Nutrient Removal Method of Improved Sewage and Wastewater Using Anaerobic Fermentation Tank

The present invention relates to an improved method for removing nutrients from sewage and wastewater using an anaerobic fermentation tank. More particularly, the organic acid (Volatile Fatty Acid (VFA)) produced after fermentation in an anaerobic state by injecting high concentration organic waste into an anaerobic fermentation tank The present invention relates to a method for removing nutrients from sewage and wastewater using an anaerobic fermenter for efficiently removing nitrogen and phosphorus from sewage and wastewater by supplying it to a microbial treatment process.

The degree of purification to be applied to sewage and wastewater should be determined by the condition of the influent to be treated. Unlike sewage in foreign countries, the concentration of organic matter in sewage is low, and the concentration of nitrogen and phosphorus is higher than that of organic sewage. Therefore, in order to purify the sewage and wastewater to secure stable water quality, the selection and operating conditions of a nutrient removal process for removing nitrogen and phosphorus in a relatively high concentration are very important.

In addition, sewage is subject to severe flow rate and concentration change over time, so the selection and operating conditions of the nutrient removal process should be designed in consideration of these factors.

Figure 1 shows the variation of organic load and nitrogen load according to the time of the sewage treatment plant installed fractional sewer pipe. Overall, organic load is higher than nitrogen load and organic load increases when nitrogen load increases, but there are some intervals where nitrogen load and organic load are similar. However, in terms of nutrient removal, organic matters necessary for the removal of nitrogen and phosphorus are insufficient in all sections, and in particular, organic matters are absolutely lacking in the section similar to organic load and nitrogen load. In such a section, appropriate measures such as injecting an external carbon source are required to secure the organic materials needed to remove nitrogen and phosphorus.

Figure 2 is a flow diagram of a conventional method for removing nutrients in sewage and wastewater using phosphorus removal microorganisms and denitrification microorganisms. According to the conventional method, the anaerobic tank (An), the first anoxic tank (Ax) and the aerobic tank (Ox) is addressed, and connected to the aerobic tank (Ox) to the sewage and wastewater flowing into the anaerobic tank (An) through the primary settling cell. By increasing the activity of the phosphorus removal microorganism by mixing the sludge returned from the secondary sedimentation basin, the efficiency of phosphorus removal in the process of passing through the anaerobic tank (An) and the aerobic tank (Ox), and the aeration tank (Ox) discharged water transported to the secondary sedimentation basin at the same time It is a nutrient removal method that promotes denitrification by transporting a part of the product to the first anoxic tank (Ax), while some sludge precipitated in the secondary sedimentation basin and sludge precipitated in the primary sedimentation basin is subjected to gravity concentration in the concentration tank for 1 day. Anaerobic digestion was followed by dehydration. However, in the conventional method, when the carbon material in the sewage is insufficient, denitrification by the denitrification microorganism is not sufficiently performed even by denitrification transport. As a result, an excess amount of nitrate (NOx-N) is present in the conveying sludge. The return sludge remaining with -N) was returned to an anaerobic tank (An) where the growth of the phosphorus-removing microorganism should be ensured, thereby inhibiting the growth of the phosphorus-removing microorganism. In particular, the characteristics of domestic sewage and wastewater are relatively low in organic matter and contain a relatively high concentration of nitrogen, the conventional method was not an efficient nutrient treatment method.

An object of the present invention is to solve the problems of the conventional method, a method for removing nutrients in sewage and wastewater, which can efficiently remove nutrients including nitrogen and phosphorus from sewage and wastewater having a low concentration of organic matter and a relatively high nitrogen concentration. To provide.

In addition, another object of the present invention is to provide a method for removing nutrients from sewage and wastewater capable of appropriately responding to sewage concentration and load fluctuations and stably securing a target water quality.

1 is an organic material load according to the time of the sewage treatment plant is installed sewage pipe

Nitrogen Load Variation State Diagram.

Figure 2 is a flow chart of a conventional method for removing nutrients of sewage and wastewater

3 is a flowchart of Embodiment 1 of the present invention;

Figure 4 is a schematic diagram of the input and output in the anaerobic fermentation tank used in the present invention.

In order to achieve the above object, the present invention is a step of first sedimentation by introducing wastewater and wastewater (first sedimentation step), the treatment water after the first sedimentation step in the anaerobic condition, the first anoxic condition and aerobic condition Microbial treatment step (microbial treatment step), the secondary precipitated microbial treated discharge water (secondary settling step), the secondary precipitated microorganisms (conveying sludge) after the second settling during the microbial treatment step In the nutrient removal method of sewage and wastewater, including the step of returning to anaerobic condition (sludge conveying step), the step of anaerobic fermentation of organic waste liquid containing primary sludge from the first settling step to produce organic acid (organic acid production step) ) And mixing the organic acid and the conveying sludge from the secondary precipitation process under a second anoxic condition in order to remove the nitric oxide (NOx-N) in the conveying sludge (sludge mixing process). It provides a method for removing nutrients including added phosphorus and nitrogen.

Hereinafter, the configuration of the present invention will be described in detail by the embodiments of the present invention, but the present invention is not limited thereto. In addition, the present invention preferably targets sewage and wastewater, but is not limited thereto.

(Example)

Example 1

A flowchart of Embodiment 1 of the present invention is shown in FIG.

According to FIG. 3, Embodiment 1 of the present invention is a first sedimentation process for removing sedimentable floating material by inflow of sewage and wastewater, and treated water from which primary sedimentation sludge is removed in the first sedimentation process. Microbial treatment process to remove phosphorus, nitrogen and organic substances by treatment of phosphorus removal microorganisms and denitrification microorganisms, and secondary sedimentation of the microbial treated effluent water to secondary sedimentation sludge and external effluent water. A process of producing an organic acid by anaerobic fermentation of a high concentration organic waste liquid including the primary settling sludge (organic acid production step), and the second settled microorganism (return sludge) under the second anoxic condition And a process of removing nitric oxide (NOx-N) by mixing (sludge mixing process) and introducing a return sludge from which the nitric oxide (NOx-N) has been removed into the microorganism treatment process.

In the configuration of the embodiment of the present invention, the process improved and added by the present invention is an organic acid producing process for producing organic acid by fermenting primary precipitated sludge and high concentration organic waste liquor under anaerobic conditions, and second oxygen-free during conveyance of secondary precipitated sludge. It is a sludge mixing process for removing the nitric oxide (NOx-N) by mixing the organic acid under the conditions.

Hereinafter, each process will be described with reference to operating conditions and efficiency.

① 1st precipitation process

In order to remove the sedimentable suspended solids in the sewage and wastewater, the first precipitation was carried out before the microbial reaction process. The residence time in the primary needle battery was maintained at about 1 hour to 1.5 hours. The inventors have found that keeping the first settling residence time as short as possible can maximize the carbon supply by minimizing the removal of BOD, which is an advantageous condition for the purpose of removing nitrogen and phosphorus. In addition, the precipitated sludge was fed to a fermenter in anaerobic conditions which will be described later. As a result of 1.5 hours of retention in the primary sedimentation basin, BOD 20%, SS 20%, TN 10%, and TP10% were removed, and the sediment sludge concentration was about 2%.

② Microbial treatment process

It is a process of removing phosphorus and organic substances by introducing the treated water passing through the primary settler into the microbial reactor consisting of anaerobic tank (An), first anoxic tank (Ax) and aerobic tank (Ox). In the anaerobic tank, the phosphorus removal microorganism is activated by treating the return sludge with the organic acid from the organic acid production process described later, and as a result, phosphorus is released. The residence time in the anaerobic tank was 1 to 2 hours, and 5 to 10 times the concentration of organic acid and organic matter in the treated water was removed.

In the first anoxic tank, the nitric oxide (NOx-N) conveyed by internal transport is denitrated. At this time, the organic acids and organic substances in the sewage are removed from the anaerobic tank. Required residence time was maintained at 2 to 3 hours (15 ℃), and the denitrification rate was 3.5 to 5mgNOx-N / gMv · hr at 20 ℃ and 2 to 3.5mgNOx-N / gMv · hr at 15 ℃. .

The aerobic tank oxidizes the phosphorus released from the anaerobic tank, the organic substances that have not been removed from the anaerobic and the first anoxic tank, and converts nitrogen into nitric oxide (NOx-N). The required residence time was maintained at 4 to 5 hours (based on 15 to 20 ° C), and the specific nitrification rate was 2.4 to 3.4 mg NH ₄ -N / gMv · hr (based on 15 to 20 ° C). The MLSS concentration of the reactor was 3,500 mg / L and the aerobic SRT (solid material retention period) was operated for 7-10 days. Nitrified recycle (NRCY) is about 100% (nitrogen removal 60%) relative to the inflow sewage and can be increased to 200% (70% nitrogen removal) for additional nitrogen removal.

③ Second precipitation process

Precipitating and removing microorganisms produced in the microbial treatment process.

Precipitated microorganisms are returned to the microbial treatment process (return sludge), and the amount of returned sludge is 50% of the influent sewage, but it can be calculated by calculating the concentration of secondary sludge and MLSS concentration in the aerobic tank. have. At this time, the nitric oxide (NOx-N) in the conveying sludge is harmful to the phosphorus-removing microorganism, so it must be removed in advance during the next sludge conveying process.

The sludge removed from the secondary sedimentation basin contained excess phosphorus so that it was incinerated after using the mechanical concentration method so as not to be returned to the treatment plant again. The residence time in the secondary sedimentation battery is more than 4 hours and the depth is more than 4 ~ 5m, and it is designed safely for the maximum flow rate of time.

The denitrification rate due to internal breathing in the secondary sedimentation cell was 0.12 to 1 NOx-N / gMv · hr (based on 20 ° C) and was changed according to the SRT (solid material retention period).

④ Sludge Mixing Process

A process for removing nitrates (NOx-N) in the conveying sludge by mixing the return sludge made of the microorganisms precipitated in the secondary precipitation process and the organic acid and the organic material produced in the organic acid production process to be described later in the second anoxic tank (Axr). The return sludge from which the nitric oxide (NOx-N) was removed was added together with the treated water which passed through the primary settling cell to the anaerobic tank during the microbial reaction process.

The residence time in the second anoxic tank (Axr) is 0.5 hours as a standard, and the amount of organic acid to be introduced into the second anoxic tank (Axr) is about 5 (nitrogen oxide (NOx-N) concentration flowing into the second anoxic tank (Axr). COD standard) times.

The specific denitrification rate was 3.6-10 mgNOx-N / gMv · hr (based on 20 ° C).

⑤ Organic acid production process (or anaerobic fermentation process)

Anaerobic fermentation of high concentration organic waste liquids, such as primary sedimentation sludge, manure, septic tank waste, kitchen waste, and livestock meal, removed in the primary precipitation process, to produce organic acids.

Fig. 4 is a schematic diagram of input and output in an anaerobic fermentation tank for producing organic acid from primary sludge, manure, septic tank waste liquor and condensate. After removing sand and contaminants from high concentration organic waste such as manure, septic tank waste, kitchen waste, and livestock meal, fermentation was carried out for less than 6 days in an anaerobic fermentation tank. The present inventors consider that the sludge precipitated in the anaerobic fermentation tank adsorbs a considerable amount of organic acid, so that the desorbent generated after effectively desorbing the organic acid by dehydrating it with a dehydrator after the injection of a dehydrating polymer is effectively used for the second anoxic tank during the sludge mixing process. It was supplied to (Axr) to remove nitric oxide (NOx-N) in the conveying sludge. In addition, the excess organic acid may be introduced into the anaerobic tank (An) together with the sewage and used by the phosphorus removing microorganism.

The concentrations of organic acids obtained through fermentation using anaerobic fermentation tanks are shown in Table 1 on the basis of the inflow rate, and the concentration of organic acids (Volatile Fatty Acid, VFA) contained in the sewage and wastewater was increased by about 50%.

Degree of increase of organic acid by anaerobic fermentation tank (mgVFA / L) division Existing concentration Concentration after anaerobic fermentation Sewage (Based on BOD 150mg / L) 30 45 excretions 5,000 7,000 Septic tank waste liquid 1,500 2,300 Money (money) - 10,000

Example 2

The present inventor omitted the first settling process on the basis of the experimental results that the shorter the residence time of the first settling process of Example 1 is advantageous to the removal of nutrients, the sewage and wastewater flows directly into the microbial reaction tank, the manure in the organic acid production process Only high concentration organic wastes, such as septic tank waste, kitchen waste and livestock meal, were added to the anaerobic fermentation tank. All other processes were performed similarly to Example 1.

Example 2 is a preferred method for saving and maintaining facility costs, especially in small treatment plants.

Example 3

The present inventors supplemented acetic acid with an external carbon source during the sludge mixing process of Example 1 when the organic acid produced in the anaerobic fermentation tank was insufficient in the organic acid production process of Example 1. All other processes were performed similarly to Example 1.

When treating general sewage according to the practice of the present invention, the water quality of the treated water is BOD 10-15 mg / L, TN 10-15 mg / L, TP 0.5-1.0 mg / L based on 15 ° C. It is possible to produce stable water quality which can be changed according to septic tank waste liquid, kitchen waste, livestock powder and acetic acid usage. In particular, it is possible to freely change the concentration of TN and TP below the above concentration, in general, TN production of 5 mg / L, TP can be produced below 0.5 mg / L. Table 2 shows the water quality of treated water according to the concentration of inflow and wastewater and the return rate.

As described above, the present invention can efficiently remove nutrients (nitrogen and phosphorus) from sewage and wastewater with relatively high nitrogen, and can appropriately respond to sewage concentration and load fluctuations, and stably secure the target water quality. Sewage and wastewater treatment.

In addition, the present invention increases the non-denitrification rate by using an anaerobic fermentation tank and utilizes a portion of the liquid waste phosphorus manure or the wastewater being treated, thereby making it easy to maintain and inexpensive maintenance costs.

Claims (9)

Microbial treatment (microbial treatment) in order of anaerobic, first anoxic and aerobic conditions, precipitation of the microbial treated effluent (sedimentation process), precipitation microorganisms after the precipitation (returning) In the nutrient removal method of sewage and wastewater consisting of the step of returning the sludge) to the anaerobic conditions of the microbial treatment process (sludge conveying step), a process of dehydrating the sludge produced by anaerobic fermentation of high concentration organic waste liquid to generate organic acid (Organic acid production step) and a step of mixing the produced organic acid and the return sludge from the precipitation step under a second anoxic condition in order to remove nitrates (NOx-N) in the transport sludge during the sludge conveying step (sludge mixing) Process for removing nutrients from sewage and wastewater using anaerobic fermentation tank added before the sludge conveying process. The method according to claim 1, wherein the anaerobic fermentation tank to which the first settling process is added in order to classify the inflow and wastewater into the first settling sludge and the treated water discharged to the microbial treatment process before the microbial treatment process is first settled. To remove nutrients from wastewater and wastewater. 3. The improved nutrient removal method of sewage and wastewater using an anaerobic fermentation tank according to claim 2, wherein the residence time of the primary precipitation process is about 1 to 1.5 hours. The method for removing nutrients from sewage and wastewater using an anaerobic fermentation tank according to claim 2 or 3, characterized in that anaerobic fermentation of the primary sedimentation sludge from the primary sedimentation step in the organic acid production step. The method of claim 1 or claim 2, wherein the high concentration organic waste liquid is selected from the group consisting of manure, septic tank waste, kitchen waste and livestock meal improved nutrients for sewage and wastewater using an anaerobic fermentation tank. The improved nutrient removal method of sewage and wastewater using an anaerobic fermentation tank according to claim 1 or 2, wherein the sludge removed in the precipitation step is mechanically concentrated and then dehydrated and incinerated. The improved nutrient removal method of sewage and wastewater using an anaerobic fermentation tank according to claim 1 or 2, wherein acetic acid is further mixed in the sludge mixing process. The method for removing nutrients from sewage and wastewater using an anaerobic fermentation tank according to claim 1 or 2, wherein a part of the organic acid produced in the organic acid producing step is returned under anaerobic conditions during the microbial treatment step. The improved nutrient removal of sewage and wastewater using an anaerobic fermentation tank according to claim 1 or 2, wherein a process of mixing the dewatering polymer with the sludge is added before dewatering the sludge produced by the anaerobic fermentation during the organic acid production process. Way.