JP4865294B2 - Decomposition method of organic waste - Google Patents

Description

  The present invention relates to a method for decomposing organic wastes such as sewage, animal manure, and garbage in a microbiologically efficient and odorless manner with less excess sludge.

  Numerous methods have been proposed for the treatment of industrial waste including domestic waste such as factory waste water, domestic waste water, animal manure, and garbage, and domestic waste, and the representative method is the activated sludge treatment method. Are known. However, this method oxidizes and decomposes organic matter by aerobic respiration by aerobic microorganisms in an environment with a high dissolved oxygen content (DO), and there are problems such as generation of a large amount of excess sludge and generation of sewage malodor. . Moreover, although the decomposition method under anaerobic conditions is also known, since it produces a large amount of fermentation products, hydrogen sulfide, etc., there is a problem of generating a bad odor.

  Therefore, the present inventor paid attention to an electron acceptor that is a respiration factor of a microorganism group that decomposes organic matter, controls the amount of dissolved oxygen in a minute amount, and performs a final aeration process step including the electron acceptor. A system for returning the supernatant liquid to the wastewater inflow process was developed, and the volume of excess sludge was significantly reduced and bromination-free in all treatment processes (Patent Documents 1 and 2). In addition, the group of microorganisms that coexist and proliferate in the presence of a slight oxygen amount and an electron acceptor other than oxygen, and the organic matter decomposition process by these microorganisms were studied, and an effective utilization method was proposed (Patent Document 3).

JP 2002-361279 A JP 2004-188281 A JP 2004-248618 A

  The present invention has been proposed as a result of further research on the above-mentioned new organic waste treatment method. That is, in Patent Document 3, microorganisms appearing in a microaerobic treatment tank are described, but these are microorganisms identified by isolation culture, and the entire volume of the microorganism group that inhabits the treatment tank. It cannot be said that it was what grasped. For this reason, it is insufficient as a condition for stably maintaining the state of the microorganism group in the treatment tank and stably decomposing the organic waste.

Therefore, the present inventor performs a gene analysis (metagenome analysis) on the microorganism group that inhabits the treatment tank, thereby finely analyzing the microorganism that appears in the treatment tank in the microaerobic state to generate a microorganism group. In addition to pursuing an ideal biofilm, we have created a conditional method for generating such a biofilm. As a result, even if the conditions of the organic waste to be treated change, an efficient and stable decomposition treatment can be performed, the generation of odor can be suppressed, and the amount of generated sludge can be greatly suppressed. It provides a method for decomposing and treating radioactive waste.

As means for solving the above-mentioned problem, in the invention of claim 1, the waste water of the organic waste stored in the inflow tank is aerated in the reaction tank, and then the treated water in the precipitation tank In the method for decomposing organic waste, separating the sludge, re-aeration treatment of the separated sludge in the sludge digestion tank, and returning the supernatant water of the re-aeration process to the inflow tank as an electron acceptor liquid,
The aeration treatment in the reaction tank is treated under the conditions of dissolved oxygen amount of 0.1 to 3 mg / L, oxidation-reduction potential of 0 to 300 mV in the presence of the electron acceptor liquid,
The organic waste is decomposed in the reaction tank in a state in which a biofilm of a microbial group in which at least 20% of denitrifying bacteria are generated.
Moreover , in invention of Claim 2, the said biofilm is produced | generated in the said inflow tank and / or the said sludge digestion tank, It is characterized by the above-mentioned.
The invention of claim 3 is characterized in that the oxidation-reduction potential is adjusted by the amount of dissolved oxygen and the supply amount of the electron acceptor liquid.
In the invention of claim 4, the denitrifying bacterium is an acid borax-like bacterium.
In the present invention, the treatment tank is a tank for microbiologically decomposing organic waste, and an aeration tank provided with an oxygen supply device in the tank is a typical example. Only one treatment tank may be used, but usually a plurality of treatment tanks are used in combination.

  Although denitrifying bacteria depend on the organic waste to be treated, they are acid borax-like bacteria, Klebsiella, Pseudomonas, Acinetobacter, Bacillus, etc. Among them, acid borax-like bacteria increase. The microorganism group includes other types of microorganisms such as nitrate bacteria, sulfur-oxidizing bacteria, and sulfur-reducing bacteria, but the ratio of denitrifying bacteria is the largest.

  A biofilm of a microorganism group mainly driven by nitrate respiration is generated by a microorganism group mainly composed of denitrifying bacteria. Thereby, the growth rate of microorganisms can be reduced without lowering the metabolic activity of the microorganism group, and as a result, the generation of excess sludge can be suppressed. Moreover, it is one of the causes of bad odor and can suppress the generation of hydrogen sulfide produced by sulfate-reducing bacteria. The generated small amount of hydrogen sulfide is oxidized by the action of sulfur-oxidizing bacteria that oxidize to sulfuric acid, and the odorless state is maintained.

  The proportion of the denitrifying bacteria in the microorganism group depends on the treatment conditions of the organic waste, but it should be at least 20%, preferably 40% or more. This is because a microorganism group having 20% or less denitrifying bacteria is a so-called activated sludge treatment method mainly composed of aerobic microorganism groups. Denitrifying bacteria have a symbiotic relationship with other microorganisms such as nitrifying bacteria, sulfate-reducing bacteria, and sulfur-oxidizing bacteria, and the occupancy rate of denitrifying bacteria is naturally adjusted by the balance of mutual metabolic relationships.

  The biofilm of the microorganism group is naturally generated by flowing organic waste into the treatment tank and setting the dissolved oxygen amount, the electron acceptor liquid, and the oxidation-reduction potential to the following conditions. That is, when a necessary amount of oxygen is maintained by aeration or aeration and then left to stand, among the microorganisms contained in the organic waste, denitrifying bacteria mainly act to form a microbial population. And the biofilm is formed with the secretory substance which they discharge | emit, and the symbiotic state of the microorganism group mainly of denitrifying bacteria is formed. In this way, factors necessary for the growth of microorganisms are ensured in the biofilm, the metabolic activity is activated, the environment is protected from environmental changes outside the biofilm, and a stable symbiotic form of the microorganism group is maintained.

  In order to generate and maintain the biofilm of the microorganism group, the amount of dissolved oxygen in the treatment tank is set to 3 mg / L or less, preferably 1 mg / L or less. Beyond this, it becomes a so-called activated sludge treatment method with oxygen driving. The dissolved oxygen may be 0, which means that the microbial group is exhausting oxygen (unlike anaerobic aeration where no oxygen is supplied), but the minimum respiratory factor of the microbial group is 0.1 mg / L. An oxygen amount exceeding is preferred. The dissolved oxygen is used as a part of an electron acceptor liquid described later, and includes a portion used for oxidation of other bacterial cells (for example, nitrification by nitric acid bacteria). The amount of dissolved oxygen can be determined, for example, by controlling the amount of aeration in the treatment tank.

  The electron acceptor liquid is an inorganic solution containing oxygen and nitrates of respiratory factors necessary for the decomposition of organic substances consumed by microorganisms as an energy source. In addition, chemical substances such as sulfate, iron and manganese Is included. This electron acceptor fluid is produced microbiologically. That is, the substance is naturally generated in the metabolic activity of the microorganism group, and is distinguished from artificially synthesized products and purified products.

  Oxygen is preferentially consumed as a preferred respiratory factor. However, when dissolved oxygen reaches about 0.1 mg / L, the microorganism group consumes nitrate and sulfate as a respiratory factor that replaces oxygen and the final electron acceptor. start. In order, nitrates with high redox potential are consumed, and then sulfates are consumed. And denitrification is performed by nitrate respiration of the denitrifying bacteria which are the main body of the microorganism group. In addition, hydrogen sulfide is generated by sulfate-reducing bacteria that perform sulfuric acid respiration as described above. Although hydrogen sulfide is one of the causes of bad odor, in the present invention, nitrate respiration is dominant in the whole symbiotic bacteria group, and hydrogen sulfide is hardly generated. In addition, the odorless state seems to be maintained by the action of sulfur-oxidizing bacteria that oxidize hydrogen sulfide to sulfuric acid.

  The electron acceptor liquid preferably contains 5-500 mg / L nitrate, 5-700 mg / L sulfate, and 0.1-3 mg / L oxygen. When nitrate and sulfate are 5 mg / L or less, nitrate respiration and sulfate respiration by the microorganism group described above are not efficiently promoted. Conversely, when the nitrate is 500 mg / L or more and the sulfate is 700 mg / L or more, the microorganisms are inactivated by these substances. The nitrate and sulfate are preferably 100 mg / L or less.

  The oxidation-reduction potential is 300 mV or less and is adjusted in the range of 0 mV to 300 mV. The oxidation-reduction potential is an index for constituting a microorganism group (symbiotic bacteria group) mainly composed of nitrate respiration by maintaining oxygen (dissolved oxygen), nitrate, and sulfate constituting the electron acceptor within the above range. Is. When the oxidation-reduction potential is 0 mV or less, oxygen as an electron acceptor is insufficient, and the balance of the microorganism group is inclined toward the sulfur compound-using bacteria. In addition, at 300 mv or more, since there is too much oxygen as an electron acceptor, the balance of the microorganism group is inclined toward the oxygen-using bacteria (becomes activated sludge).

  If necessary, the oxidation-reduction potential can be adjusted by adjusting the oxygen supply amount, introducing a predetermined electron acceptor liquid, introducing a buffer solution (such as a wastewater treatment medium) having a predetermined oxidation-reduction potential, and the like. In the present invention, when the organic matter-containing waste is decomposed by microorganisms, the amount of dissolved oxygen and the amount of electron acceptor liquid supplied can be controlled so that the inside of the treatment tank becomes a microorganism group mainly composed of denitrifying bacteria. .

The present invention satisfies the above conditions limit is, garbage decomposition purification treatment, garbage decomposing compost, domestic wastewater treatment, animal manure processing, industrial organic waste treatment can be carried out in the like. As typical examples, as proposed by the present inventor in Japanese Patent Laid-Open No. 2002-361279, an inflow tank for storing wastewater raw water, a reaction tank for performing aeration treatment of wastewater from the inflow tank, Organic wastewater treatment equipped with a sedimentation tank that deposits sludge and collects sludge from the sedimentation tank and re-aerates to digest and reduce excess sludge, and returns the supernatant to the inflow tank. Applicable to equipment. In other words, efficient and stable decomposition treatment is possible by forming a biofilm of the microorganism group mainly composed of the denitrifying bacteria in all or some of the inflow tank, reaction tank and sludge digestion tank. It becomes. In particular, the volume of sludge generated in the sludge digestion tank can be reduced as compared with the prior art, and the supernatant water can be used as a high-quality electron acceptor liquid.

  According to the present invention described above, in the decomposition treatment of organic waste, a biofilm of a microorganism group mainly composed of denitrifying bacteria is generated in the treatment tank, and the dissolved oxygen concentration and the supply of the electron acceptor liquid are controlled. Therefore, even if the conditions (for example, BOD, COD) of the organic waste to be treated are changed, an efficient and stable decomposition process is taken, so that the decomposition of the organic matter is accelerated and no odor is generated. Since organic matter is decomposed by microorganisms mainly composed of nitrate respiration, the amount of generated sludge can be greatly reduced.

  Domestic wastewater with an average inflow organic matter amount of 100 mg / L and inflow water amount of 500 t / day was treated under the following conditions. The processing apparatus is composed of the above-described inflow tank, reaction tank, sedimentation tank, and sludge digestion tank. The results are shown in Table 1. In Table 1, the influent water is the quality of the inflow tank, and the treated water is the quality of the supernatant water of the precipitation tank. Table 2 shows measured values of nitrate, sulfate, oxygen amount, and oxidation-reduction potential in the reaction tank at this time.

  Wastewater from a food processing plant having an average inflow organic matter amount of 1000 mg / L and an inflow water amount of 200 t / day was treated by the same treatment apparatus as in Example 1 under the following conditions. The results are shown in Table 3. The measured values of nitrate, sulfate, oxygen amount and oxidation-reduction potential in the reaction vessel are as shown in Table 4.

  As is clear from the above examples, according to the present invention, it is understood that the quality of the treated water is greatly purified compared to the inflow water (waste water before treatment). Also, almost no bad odor was observed. Furthermore, it can be seen that the supernatant water of the sludge digester contains appropriate amounts of nitrate and sulfate, and is a high-quality electron acceptor-containing solution.

  The treated water of the reaction tank of Example 2 was collected, and a metagenomic analysis of microorganisms surviving in the biofilm was performed. In addition, the metagenome analysis of microorganisms that survive in the reaction tank is also performed for the conventional activated sludge method that consists of an inflow tank, a reaction tank, and a precipitation tank, and aerated the inflow tank and the reaction tank with a dissolved oxygen amount of 3 mg / L or more. It was. Metagenome is named for all genome groups in the soil microbial population, including microorganisms that cannot be cultivated. Metagenome analysis is an analysis of the entire microbial flora genome without going through the process of culturing. To do. The analysis results (classification of microorganisms by comparison of the base sequence of 16S rRNA gene in the small subunit of ribosome) are shown in Table 5.

  As shown in the above table, in the method of the present invention, acid borax-like bacteria (49.2%), which belong to proteobacteria and are a kind of denitrifying bacteria, remarkably appear, and chloroflexus-like bacteria that are sulfur-oxidizing bacteria ( 16.2%) has disappeared. Incidentally, in the activated sludge method, sulfur-oxidizing bacteria account for 23.5%. The above classification is based on the phylum classification divided into similar gene sequences by metagenomic analysis, but the bacteria belonging to the same phylum have not always have common microbiological properties. Absent.

Claims (4)

Raw organic wastewater stored in the inflow tank is aerated in the reaction tank, then the treated water is sludge separated in the settling tank, and the separated sludge is aerated again in the sludge digestion tank. In the organic waste decomposition method of returning the supernatant water of the aeration treatment as an electron acceptor liquid to the inflow tank,
The aeration treatment in the reaction tank is treated under the conditions of dissolved oxygen amount of 0.1 to 3 mg / L, oxidation-reduction potential of 0 to 300 mV in the presence of the electron acceptor liquid,
A method for decomposing organic waste, comprising decomposing organic waste in a state where a biofilm of a microorganism group in which denitrifying bacteria account for at least 20% is generated in the reaction tank .   The organic waste decomposition method according to claim 1, wherein the biofilm is generated in the inflow tank and / or the sludge digestion tank.   The organic waste decomposition method according to claim 1 or 2, wherein the oxidation-reduction potential is adjusted by the amount of dissolved oxygen and the supply amount of the electron acceptor liquid.   The method for decomposing organic waste according to any one of claims 1 to 3, wherein the denitrifying bacterium is an acid borax-like bacterium.