JPS61187995A - Treatment of organic sewage - Google Patents

Abstract

PURPOSE:To suppress the increase in liquid temp. by discharging part of the sludge in an anaerobic digestion tank to the outside of the system according to the degree of increase in the liquid temp. while monitoring the liquid temp. in a biological treatment process including nitrification and denitrification. CONSTITUTION:Part 16 of the sludge in the anaerobic digestion treatment tank 13 for org. sewage is discharged to the outside of the system according to the degree of increase of the liquid temp. while the liquid temp. in the biological treatment state is monitored in a treatment method for the org. sewage in which the anaerobic digestion process in the tank 13 and the biological treatment process including the nitrification and denitrification in the digestion tank 1 and denitrification tanks 3, 6 are operated by being cyclically combined. The control of the increase in the liquid temp. is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control method capable of suppressing an excessive rise in liquid temperature during treatment of organic wastewater.

[Conventional technology]

Organic matter (BOD source) and solid matter contained in organic wastewater are decomposed through a series of biological aerobic treatments such as the trickling filter method and activated sludge method, and the treated water is sent to rivers, lakes, oceans, etc. is released into the river. On the other hand, water pollution phenomena (for example, red tide) caused by nutrient salts (salts such as N and P) contained in organic wastewater have recently become a social problem, but the biological treatment method described above is However, it is not possible to completely decompose and remove these salts, so these nutrients Jl! ! As a result of research into developing a method suitable for treating organic wastewater containing a large amount of organic waste, a treatment method using nitrification and denitrification was proposed.

FIG. 2 is a flow diagram showing the basic treatment process of the above treatment method, which is called the nitrification solution circulation method. Since the nitrifying solution is circulated in this method, the explanation of the flow is the same regardless of which process is started, but for the sake of convenience, it will be explained from the nitrifying process.

The nitrification tank 1 is maintained in an aerobic atmosphere with oxygen gas 2. In the nitrification tank 1, NHa/-N in the raw water is nitrified by the nitrification reactions (1) and (2) shown below, but at the same time, biological oxidative decomposition of organic matter contained in the organic wastewater is also progressing. There is.

(Nitrite m type) NHa + (3/2)02 -NO2- + H2
0+2H' ・・・・・・・・・(1) (Nitric acid type) NH4+202 + NO3-+H70+2H・ ・・・・・・・・・(2)
The first denitrification tank 3 contains circulating fluid 4 returned from the nitrification tank 1.
At the same time, raw water 5 is introduced. In the first denitrification tank 3, denitrification reactions (3) and (4) shown below proceed. Of the treated water treated in the nitrification tank 1, the water other than the circulating fluid 4 is transferred to the second denitrification tank 6. It is led to a settling tank 8 via a reaeration tank 7.

(Nitrous acid type) 2NOr+6[H] → N2 +2H20+20H−・・・・・・・・・(3)
(Nitric acid type) 2 NO3−+ 10 [H] → N2 + 4 H20+ 20 H−−・−・・−・・
- Organic matter contained in the raw water 5 or circulating fluid 4 is used as the hydrogen donor in (4) denitrification reactions (3) and (4), and the effluent treated in the first denitrification tank 3 is sent to the nitrification tank 1.
be led to. The treated water 9 obtained in the settling tank 8 is subjected to advanced treatment if necessary, and part of the settled sludge is removed as surplus sludge 10, and the rest is led to the first denitrification tank 3 as return sludge 11. Organic wastewater is treated by cyclically repeating each of these processes.

[Problems to be solved by the invention] By the way, in the conventional organic wastewater treatment method as described above, aerobic biological decomposition of organic matter is carried out in a nitrification tank, which causes the liquid temperature to rise. Especially when driving in the summer, the temperature may reach 40 degrees Celsius or more. Therefore, there is a risk that the activities of microorganisms and protozoa in the nitrification tank will be inhibited, and in order to prevent this, it is necessary to pour dilution water as shown at reference numeral 12 in FIG. 2. However, if a large amount of dilution water is injected, the processing load in subsequent processes will increase due to the increased amount of processed water.

Additionally, a refrigerator or the like may be used to suppress the rise in liquid temperature, but in this case there is a problem that maintenance costs and the like increase.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a treatment method that can suppress the rise in liquid temperature when treating organic wastewater.

[Means for Solving the Problems] The treatment method of the present invention that meets the above objectives is a cyclic combination of an anaerobic digestion process of organic wastewater and a biological treatment process including nitrification and denitrification. A method for treating organic sewage that operates in a biological treatment process, in which the liquid temperature is monitored during the biological treatment process, and a portion of the sludge in the anaerobic digestion tank is pulled out of the system according to the degree of rise in liquid temperature. There is a summary in .

[Function] Next, the structure and the function and effect of the present invention will be explained while tracing the research history that led to the completion of the present invention.

As mentioned above, the reason why the temperature of the liquid in the system increases in the nitrification/denitrification process is due to the heat of the biological decomposition reaction of organic matter in the nitrification tank. With this in mind, it is necessary to prevent the oxidative decomposition of organic matter in order to suppress the rise in liquid temperature, which will be explained below. In other words, the organic matter should be removed by some method.

Therefore, the present inventors obtained a guideline that it is sufficient to prevent the contamination of organic matter by a physical method before starting the nitrification/denitrification process. In other words, the sludge in which organic matter has been adsorbed is extracted from the anaerobic digestion tank, and this means breaking away from the conventional idea of removing organic matter through biological treatment. It was completed as a result of intensive research based on guidelines.

FIG. 1 is a flowchart showing one embodiment of the present invention that realizes this concept. A conceptual explanation will first be given with reference to this figure, and then a detailed explanation will be provided. Incidentally, the same reference numerals are given to the same steps as those shown in FIG. 2, and the explanation thereof will be omitted. Anaerobic digestion tank 1
3, mixed sludge is formed as the anaerobic digestion process progresses. This mixed sludge is formed by adsorbing organic matter in the raw water 5 introduced into the anaerobic digestion tank 13 to activated sludge. After a portion 16 of this mixed sludge is drawn out from the anaerobic digestion tank 13, a portion of the residual liquid becomes the anaerobic digestion tank effluent 14. The subsequent cycles have been described above, so they will be omitted here.

The return destination of the returned sludge was the first denitrification tank 3 in FIG. 2, but it is now the anaerobic digestion tank 13, so a new reference number 15 has been added.

This will be explained in more detail with reference to FIG.

The feature of the present invention is that a portion 16 of the mixed sludge in the pneumatic digestion tank 13 is drawn out as described above.

As a result, some of the organic matter in the mixed sludge (organic matter in the raw water 5) is removed. Therefore, the aerobic effluent 14 with reduced organic matter content is transferred to the first denitrification tank 3. Nitrification tank 1. It will be guided to the second denitrification tank 6 and the like. Anaerobic effluent 14
Since the organic matter content of the liquid is reduced, the amount of organic matter decomposed during the nitrification/denitrification process is also reduced, and therefore the reaction heat generated during the nitrification/denitrification process can be reduced, which ultimately reduces the rise in liquid temperature. Can be suppressed. Therefore, there is no need to pour dilution water or use other cooling means as in the conventional case. Also, when the liquid temperature rises slowly, such as in winter, or when you want to maintain the liquid temperature above 35°C, it is not necessary to pull out the mixed sludge. When the organic matter (hydrogen source) necessary for denitrification is insufficient, the mixed sludge 16
Treated water with a high C/N ratio by subjecting it to an ammonia dripping method may be returned to the nitrification process. In other words, the supernatant liquid produced by lime coagulation and precipitation of the dehydrated filtrate of the mixed sludge 16 that has been drawn out. After removing NH3 by ammonia dripping, the supernatant liquid is returned to the nitrification process. By applying the ammonia dripping method in this way, it becomes possible to maintain the C/N ratio of the treatment liquid at a value convenient for nitrification. Further, P removal can also be performed at the same time. Further, since the solid content after dewatering the mixed sludge 16 that has been pulled out contains organic matter, it can be used as a fertilizer or, after drying, as an incineration material. In other words, conventionally, this solid content would be decomposed during the nitrification/denitrification process and converted into thermal energy, but in the present invention, this solid content is stored as fertilizer or incineration material as described above. . That is, according to the present invention, energy efficient treatment of organic wastewater can be achieved. Furthermore, since the amount of oxygen supplied to the nitrification tank 1':J can be reduced, maintenance costs such as the cost required for aeration of the oxygen can also be reduced.

In this embodiment, the anaerobic digestion tank 13 is used to generate the mixed sludge, but the mixed sludge can be formed more effectively if an anaerobic stirring tank is used. In addition, when carrying out the nitrification/denitrification process, the first denitrification tank 3° nitrification tank 1. Second denitrification tank6. Although the re-aeration tank 7 is used in the described order, there is no need to limit it in this way, and in short, it is sufficient to realize a biological treatment process including nitrification and denitrification, and anaerobic digestion 4
P! 13 and the first denitrification J7e3, and the mixed sludge may be pulled out from there.

[Example] Below, the results of Examples of the present invention will be described in comparison with those of conventional methods.

FIG. 3 is an explanatory diagram showing the distribution ratio of energy contained in human waste when the treatment method according to the present invention is applied to human waste in comparison with a conventional method.

Human waste costs 90.00 as shown in reference number 17 in Figure 3.
It has an energy of 0 to 1IO,000 Kcan/kl in the form of organic and inorganic substances. This energy is split between energy released during the biological treatment process (used to raise the temperature of the liquid above) and energy recovered as sludge. The latter, that is, the energy recovered as sludge, is conventionally 46, as indicated by reference numeral 18 in FIG.
000 Kca/min, whereas in the case of the present invention, the cost is 54,800 Kca9. as shown in 19. It was flat. Note that 20 is the energy used to raise the liquid temperature in the conventional method.

21 indicates the energy used to raise the liquid temperature according to the present invention.

[Effects of the Invention] Since the present invention is configured as described above, it has the effect of being able to control the rise in liquid temperature when treating organic wastewater.

[Brief explanation of drawings]

Fig. 1 is a flow diagram showing one embodiment of the present invention, Fig. 2 is a flow chart showing the basic processing process of the nitrification liquid circulation method, and Fig. 3 shows the energy distribution ratio in the case of the present invention and the conventional method. FIG. l...Nitrification tank 2...Oxygen gas 3...First denitrification tank 4...Circulating fluid 5...Raw water
6...Second denitrification tank 13...Anaerobic digestion tank

Claims (1)

[Claims] This is a method for treating organic wastewater that operates by cyclically combining the anaerobic digestion process of organic wastewater with a biological treatment process including nitrification and denitrification, and the temperature of the liquid during the biological treatment process is monitored. A method for treating organic sewage characterized by drawing out a portion of sludge in an anaerobic digestion tank to the outside of the system according to the degree of rise in liquid temperature.