JPS6014997A - Treatment of organic filthy water - Google Patents

Abstract

PURPOSE:To decompose sufficiently org. substances and nitrogen compds. in org. filthy water by subjecting anaerobically digested effluent formed from org. filthy water to biological denitrification together with digested sludge. CONSTITUTION:BOD in the first denitrification tank 6a is increased and denitification reaction is processed with high efficiency by feeding digested sludge S1 discharged from the second digestion tank 2 except that supplied to the first digestion tank 1 as returned sludge, to the first denitrification tank 6a without discharging it to the outside of the system. Also, untreated filthy water L1a is combined with the digested effluent L2 as given by the alternate long and two short dashes line to charge directly to the first denitrification tank 6a. Thus, the ratio of BOD/NH4-N is increased to >=1, and the rate of removal of N in the tank 6a is increased to >=90%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating organic sewage, and in particular, it relates to a method for treating organic sewage, and more specifically, to treat organic matter (130D source) and Sakae C salts (130D source) contained in organic sewage.
This invention relates to a method for treating organic wastewater that can effectively decompose nitrogen compounds, etc.

Anaerobic digestion (hereinafter referred to as digestion) is one of the methods to decompose and remove organic matter and suspended solids contained in organic wastewater (human waste, etc.), and it has been widely used for a long time, but according to recent results, it will be explained later. It has been confirmed that this method generates less sludge than the biological nitrogen removal method. Figure 1 is a flow diagram showing an organic sewage treatment system applying such a digestion treatment method, where 1 shows the first digestion tank, 2 shows the second digestion tank, 3 shows the aeration tank, and 4 shows the settling tank. . In the above system A,
The organic wastewater L1 input into the first digestion tank 1 is subjected to digestion treatment in an anaerobic atmosphere in the first digestion tank 1 and the second digestion IW, 72, so that the substances in the wastewater are solubilized. At the same time, it is decomposed into gases such as 002 and CH, and is discharged from the second digestion tank 2 as a digestion and desorption liquid L2. A portion of the puhi-digested sludge S1 that settles to the bottom of the second digestion tank 2 is returned to the first digestion phase 1 and used as seed sludge, while the remainder is discharged outside the system.

Next, aerobic decomposition is performed by aerating the dehydrated liquid L2, which is put into the aeration tank 3. After washing MZ'+
Pour into Sodium 4 and separate into treated wastewater and sludge S2.

A part of the sludge S2 is returned to the aeration 03 and used as seed sludge, and the remainder is discharged outside the system as surplus sludge Ss.

By the way, in the above-mentioned digestion treatment system, BOD components are sufficiently decomposed and removed, but no consideration is given to the removal of nitrogen-containing compounds, particularly ammonium salts, and the system is discharged with almost no removal.

As a result, the occurrence of bad odors due to the release of ammonia gas and the pollution caused by the enrichment of rivers have become social problems.In addition, in the above-mentioned digestion treatment system, the sludge discharged is There are also two lines of sludge processing equipment for treating two types of sludge, S from the tank, and surplus sludge, S3), and as the equipment becomes multiple vessels, the maintenance and management of the equipment becomes complicated. Therefore, it is necessary to heat the organic wastewater input into the digestion tank to a temperature suitable for the digestion reaction, but since the amount of wastewater input in an organic wastewater treatment system is generally large, heating is not necessary. Heat engineering and Nervo consumption for warming could also be ignored, causing an increase in operating costs.

The present inventors have carried out research in an attempt to solve the various problems in the various digestion treatment systems described above, and first investigated the simultaneous removal of nitrogen compounds, which is the most important issue. However, as for the removal of nitrogen compounds, the biological nitrogen removal method has already been established to some extent, so the first option is to simultaneously remove organic matter and nitrogen compounds by incorporating this method into the above-mentioned digestion treatment system. was considered.

The biological nitrogen removal method uses the following reaction formulas (1) and (2) to convert nitrogen compounds contained in the water to be treated, specifically NH, -N.
) The nitrification reaction shown in (aerobic atmosphere) is followed by the denitrification reaction shown in reaction formulas (3) and (4) in an anaerobic atmosphere.

(1) Nitrification reaction (nitrous acid type) N1 (4++1-!-02→NO2+H20+2H...
・(1) (Nitric acid type) N114++202→NOx +H20+21-I+
...(2)(11) Denitrification reaction (nitrous acid type) 2N02 +6(H) → N2+2I■20+20H-(
η (nitric acid type) 2NO, + 10 (:H) → N2+4H, 0+20H-
-・-(+) The essence of the research that led to the completion of the present invention will be explained below, following the stages of ideological development.

First of all, we will start with a system as shown in Figure 2, that is, a nitrification tank 5 between the digestion tank 2 and the ω gas tank 3, and a denitrification tank of 1%! I thought about system B that incorporates J6. All processes after the nitrification tank 5 in this system B are known in principle as biological nitrogen removal methods and equipment. However, when the digestion desorption liquid L2 is nitrified using this system, a small amount of the BOD components remaining in the digestion desorption liquid L2 are oxidized together with NH, which may delay the nitrification reaction itself, and also cause the oxygen consumption will also increase. On the other hand, in the denitrification tank 6, the presence of a hydrogen donor is required in order to advance the denitrification reaction, but since the BOD component that can be used as a hydrogen donor has already been oxidized and decomposed in the nitrification tank 5, a new CI, O
It becomes necessary to introduce a large amount of hydrogen donor such as H into the denitrification process 4'd. As described above, system B shown in FIG. 2 has aspects that are not suitable for practical use.

Therefore, the next idea was to create a system C shown in Fig. 3, in which the first denitrification tank 6a, the nitrification tank 5, and the second denitrification tank 61 were arranged in the order listed after the digestion tanks 1 and 2. Part of the mixed liquid L4 from the nitrification tank 5 is removed.

The denitrification tank 6a is then returned to the denitrification tank 6a, where it is combined with the digestion denitrification 1'iI liquid L2. The processes after the first denitrification tank 6a in the system C are also well known and have been constructed as independent facilities in various places. According to this method, in the first deflation ff1VU6a, the digestion desorption fluid L2
Since the BOD component contained therein is supplied as a hydrogen donor, the nitrate ions and nitrite ions brought in with the nitrifying liquid are reduced by the action of denitrifying bacteria in an anaerobic atmosphere, resulting in so-called denitrification. In addition, nitrogen compounds (N
H4 salt) passes through the first denitrification tank and is introduced into the nitrification tank 5 as a denitrification treatment liquid L6, where it is nitrified in an aerobic atmosphere.

and nitrification liquid L4 (NO, ions, etc. newly generated in the nitrification tank and unreacted NO3 ions, etc. in the first denitrification tank)
Most of the above-mentioned return nitrification liquid is sent to the first denitrification tank 6a.
At the same time, the remainder of the nitrifying liquid L4 enters the second denitrification lamb, but since the content of NOs ions etc. is a little low here, the amount of BOD components such as CH3011 to be replenished is small and easy. Denitrification treatment can be performed at low cost. After decomposing the remaining 130D component by aeration treatment, treated water L7 and sludge S are obtained from settled Gm4.

It is discharged as.

However, in the above-mentioned system C, since the BOD component of the digested and desorbed liquid L2 has decreased considerably due to the digestion process, it is necessary as a hydrogen donor provided for the denitrification reaction in the first denitrification 'IW6a. Although this is improved over system B, it has the disadvantage that the denitrification reaction does not proceed sufficiently.

The present invention aims to solve these problems, and its primary purpose is to sufficiently decompose tE2'16y (BOD component) and nitrogen compounds in organic wastewater, and furthermore, it A second purpose is to reduce energy, particularly energy consumed for preheating organic wastewater.

Therefore, the method for treating organic sewage of the present invention achieves the above object and subjects the aerobic digestion-depleted 1'1ffl liquid produced by anaerobic digestion of organic sewage to biological nitrogen removal treatment together with the digested sludge. Alternatively, the basic gist is to add l30D increasing components other than the digested sludge together with the above-mentioned digested sludge, etc. to perform biological nitrogen removal treatment (= l) By heating the organic wastewater using treated wastewater, we succeeded in making effective use of energy.

In other words, the reason why the removal of nitrogen compounds in the method shown in FIG. Further supplementary addition of donor will be necessary. However, it is inappropriate to add large amounts of valuable substances such as CH and OH because it increases the cost of treating organic wastewater. Therefore, the present inventors focused on the digested sludge discharged from the second digestion tank 2 and measured the physical properties when mixed with the digested and desorbed liquid, and the results shown in Table 1 were obtained. For comparison, the properties of the digested fluid alone were measured at the same time.

Table 1 As shown in Table 1, it was found that the concentration of BOD increased significantly by mixing digested sludge with the digested and desorbed fluid. On the other hand, in order to progress the denitrification reaction well, BOD/N
It is considered desirable to increase the H, -N ratio as much as possible, but if the BOD/NH, -N ratio shown in Table 1 increases from 0.25 to 0.85, the t, -S ratio will increase. , it was strongly expected that the crab removal effect would be improved. According to the results of the denitrification treatment experiments, the nitrogen removal rate of the former was only 26 on average, whereas in the present invention, in which the digested desorption liquid and digested sludge were mixed, the nitrogen removal rate rose to 86q6 on average.

From such preliminary experimental data, we have come to believe that it is effective to mix and use digested sludge as a hydrogen donor.

Next, the present invention will be explained based on examples. FIG. 4 is a flow sheet of an embodiment, showing the system D of the present invention. In this example, the digested sludge S discharged from the second digestion tank 2,
Of the sludge, other than that supplied to the first digestion tank 1 as return sludge, this is not discharged outside the system and is subjected to the first denitrification m6 a.
The BOD in the first denitrification tank 6a is
By increasing the BOD/NH4-N ratio (and increasing the BOD/NH4-N ratio), the denitrification reaction can proceed efficiently, and the nitrogen removal rate has been successfully improved.

Furthermore, in the present invention, in addition to inputting the digested sludge, BOD increasing components (hydrogen donors) other than the digested sludge, such as untreated organic sewage L1a, are added to the digested and desorbed liquid L2 as shown by the two-dot chain line.
By directly charging the nitrogen into the first denitrification tank Q6a, it is possible to increase the BOD/NH, -N ratio in the first denitrification tank 6a to 1 or more, thereby increasing the nitrogen removal rate to 90% or more. It can be increased up to. Furthermore, the first denitrification tank 6a
The NO2 ions and NO3 ions that were not completely removed are decomposed and removed in the second denitrification tank 6b.

It is also necessary to introduce a hydrogen donor into the second denitrification tank 6b, but the amount of hydrogen donor required here is only a little less than terol (D).
Te CHB OH etc. may also be used.

Furthermore, in the present invention, the organic wastewater L1 can also be heated using the heat retained in the treated water L7. In other words, the biological nitrogen removal reaction is an oxidation reaction (
This is a combination of a nitrification reaction (nitrification reaction) and a reduction reaction (denitrification reaction) under anaerobic conditions, and when 1 kg of nitrogen is removed, approximately 10,000 kcal of heat is generated. As a result, the temperature of the treated water L7 rises to about 35°C. Therefore, the fourth
A heat exchanger 7 is installed as shown by the two-dot chain line in the figure, and the treated water L
The organic wastewater L1 is heated by exchanging heat between the organic wastewater L1 and the organic wastewater L1. This is traditionally necessary.

The prospect of omitting the heating treatment of organic sewage in the digesters 1 and 2 was obtained. Furthermore, the treated water L7 obtained by heating the organic sewage water becomes L8 and is discharged outside the system.

By the way, the above explanation was based on the flowchart shown in FIG. 4, but the concrete example of implementation equipment is a mud tank reaction tank with a depth of 10 m, and its operating conditions are a DO amount of 0.
It is recommended that the MLSS be 2 to 1.1 Inl/1% or more than 15000 Inl/1.

Incidentally, it is actually possible to remove organic matter and nitrogen compounds all at once using only the biological nitrogen removal equipment described above, but in this case, the amount of sludge generated is 20 times or more compared to the method of the present invention. sludge treatment requires a great deal of labor and cost.

In contrast, the method of the present invention generates approximately the same amount of sludge as the conventional digestion method, and can be said to be an excellent method in this respect as well. This is because when decomposing BOD components, aerobic bacteria generate less sludge than decomposition by aerobic bacteria; in other words, in the method of the present invention, most of the BOD components are decomposed in the digestion tank. This is because there is very little risk of relying on aerobic decomposition in subsequent biological nitrogen removal equipment.

Since the present invention is configured as described above, it is possible to obtain the effects summarized below.

(1) By combining digestion treatment and biological nitrogen removal treatment, organic matter (BOD components) and nitrogen compounds (N
H, salts) can be efficiently and completely removed, and even if discharged outside the system, it will not cause environmental pollution.

(2) Since organic wastewater, which is the liquid to be treated, can be heated using the amount of heat generated during the biological nitrogen removal process, it is economical because it requires less energy for heating, especially in cold regions during the winter. It is true.

(3) Since the digested sludge was used as a hydrogen donor for the denitrification reaction, the denitrification reaction could be carried out economically, and the sludge discharged from the system was consolidated into surplus sludge, making sludge treatment easier. Ta.

(4) Most of the organic matter (BOD components) is decomposed in the digestion process, and nitrogen compounds are decomposed and removed in the biological nitrogen removal process, so there is less reliance on the action of aerobic bacteria throughout the system, and organic matter and As a method for removing nitrogenated metals all at once, we were able to provide a method that generates less sludge.

[Brief explanation of the drawing]

FIG. 1 is a flow explanatory diagram showing the digestion processing system, and FIG.
FIG. 3 is a flow explanatory diagram of a reference example system that combines a digestion process and a biological nitrogen removal process, and FIG. 4 is a flow explanatory diagram showing an embodiment of the present invention. 1... 1st digestion tank 2... 2nd digestion tank 3... aeration tank 4... settling cypress 5... nitrification tank 6.6a, 6b... denitrification tank 7...
·Heat exchanger

Claims (4)

[Claims] (1) A method for treating organic sewage, which comprises subjecting an anaerobic digestion solution produced by anaerobic digestion of organic sewage to biological nitrogen removal treatment together with digested sludge. (2) The anaerobic digestion desorbed liquid produced by anaerobic digestion of organic wastewater is subjected to biological nitrogen removal treatment together with the digested sludge, and the A method for treating organic sewage characterized by heating the organic sewage. (3) Organic sewage characterized by subjecting the anaerobic digestion desorbed liquid produced by anaerobic digestion of organic sewage to biological nitrogen removal treatment together with digested sludge and BOD-increasing components other than the digested sludge. processing method. (4) The anaerobic digestion solution produced by anaerobic digestion of organic sewage is subjected to biological nitrogen removal treatment together with digested sludge and BOD increasing components other than the digested sludge, and the biological nitrogen is A method for treating organic wastewater, comprising heating the organic wastewater by heat exchange with treated wastewater after removal.