JPH0312955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for treating organic wastewater that decomposes and separates and removes organic substances contained in organic wastewater.

In general, as a method for treating domestic wastewater such as sewage, human waste, kitchen waste, etc. or their decomposition products, and wastewater containing organic substances such as agricultural, livestock, and fishery waste such as orange peel, ultrafiltration membranes are used.・It is known that organic substances are separated from wastewater using a separation membrane such as a reverse permeation membrane, but this treatment method has a slow separation speed and concentration polarization occurs during the treatment, making it difficult to separate organic substances. There were disadvantages such as a decrease in membrane permeability and an increase in energy consumption to prevent the decrease.

Also known is an anaerobic digestion method that uses anaerobic microorganisms to decompose and remove organic components in wastewater. This anaerobic digestion method ferments wastewater containing, for example, fats, proteins, polysaccharides, or their decomposition products, and converts them into lower organic substances such as volatile fatty acids.
Next, methane is gasified and fermented to decompose it into methane gas, carbon dioxide, etc., such as a reaction in which acid is mainly produced by facultatively anaerobic microorganisms (acid fermentation), and a reaction in which methane is produced by obligately anaerobic microorganisms (methane gasification fermentation). ), but this method does not require any particular external energy except when it is necessary to maintain the digestion temperature, and it produces less sludge, so it is recommended from an energy-saving perspective. Although it is excellent, the reaction rate is slow and the biochemical process is long, so the processing time is long and the processing equipment is large, and it is also sensitive to large changes in external environmental conditions such as organic load. However, there were some inconveniences such as the reaction stopping.

Therefore, the present inventor discovered that the rate of acid fermentation is approximately 10 times faster than the rate of subsequent methane gasification and fermentation, and that the organic substances in wastewater are complex, such as fats, proteins, polysaccharides, and other decomposed products of these. Even if it is a mixture, acid fermentation can produce volatile fatty acids such as acetic acid, alcohols, aldehydes, ketones, ammonia, carbon dioxide, hydrogen, water, and a small number of low-molecular-weight organic compounds that are liquid or gaseous at room temperature. Focusing on the fact that it not only concentrates and decomposes substances, but also removes surface-active substances such as alkyl sulfuric acid, we developed a separation membrane that separates lower organic substances produced by this acid fermentation from the treated liquid. As a result of research for
By using a hydrophobic porous membrane that vibrates at high frequencies, it is possible to efficiently separate and concentrate the low-molecular-weight organic substances mentioned above, without relying on the slow methane gasification fermentation mentioned above. We have come to the knowledge that organic wastewater can be treated, and have come to form the present invention.

Furthermore, in anaerobic digestion, the pH of the reaction solution is usually
When the concentration is around 6.8, or when the residence time of the proliferating bacteria in the system increases and the concentration increases, methane gasification fermentation occurs, and the concentration of lower organic substances produced by acid fermentation, that is, low molecular weight organic substances, increases. As a result of our study, we found that if anaerobic fermentation is performed with the dissolved oxygen concentration in organic wastewater at 0.1 to 0.0001 mg/d, acid fermentation will occur. It was found that methane gasification and fermentation could be suppressed. Then, we determined the dissolved oxygen concentration in this organic wastewater.
As a means to adjust the amount to 0.1 to 0.0001 mg/, when methane gasification and fermentation occurs, oxygen is supplied to adjust the dissolved oxygen concentration in the organic wastewater.

That is, the method for treating organic wastewater according to the present invention involves fermenting wastewater containing organic substances with microorganisms in an anaerobic atmosphere to produce lower organic substances, and converting the lower organic substances into hydrophobic substances subjected to high frequency vibration. It is characterized in that it is stably separated, concentrated, and removed from the system using a porous membrane.

In the present invention, examples of microorganisms used for anaerobic fermentation include facultative anaerobes such as Pseudomonas, Clostridium, and denitrifying bacteria;
There are thermophilic anaerobic bacteria that ferment alcohol, acetic acid, and cellulose.

In addition, as a hydrophobic porous membrane, for example, as shown in the schematic diagram shown in FIG. The polyvinylidene fluoride membranes 3, 3 are clad through membranes 2, 2 which have been radicalized polytetrafluoroethylene membranes, etc. to form a hydrophobic porous membrane X, and this porous membrane X is coated with carbon fiber, etc. By using a conductor as an electrode material and connecting this electrode 5 to a high frequency power source to apply a high frequency drive to the radicalized films 2, 2, harmonic microwaves are generated on the surfaces of the films 3, 3. The one that is made to do so is used. These detailed configurations can be found in Japanese Patent Application No. 58-221443 (Japanese Unexamined Patent Publication No. 60-60), which was previously filed by the applicant of this patent.
This is similar to the "flat plate membrane separation device" disclosed in No.-114303).

Here, the electromagnetic field characteristics of the surface of the hydrophobic porous membrane Depending on the characteristics, it can be adjusted by changing the radicalization conditions of the polytetrafluoroethylene membrane, etc., that is, the thickness of the radicalized membranes 2, 2, and the way they are combined. In addition, in order to radicalize the polytetrafluoroethylene membrane,
This can be carried out by performing forced electrolytic treatment with active oxygen in the gas phase or in an organic solution.

Generally, a flowing potential is generated when a liquid moves with respect to the surface of a solid, but in the present invention, by appropriately combining the polytetrafluoroethylene membrane 1 and the membranes 2 and 2 that have been subjected to radicalization treatment, etc. , by adjusting the electromagnetic field characteristics and reversely using the flowing potential to promote the separation of the lower organic substances and water separated by the above-mentioned high-frequency vibration, by combining the potential change during movement within the hydrophobic porous membrane X. You can also. For this purpose, electrodes 6, 6 may be provided to provide a potential difference on both sides of the porous membrane X in FIG. 3.

Fermentation by microorganisms in an anaerobic atmosphere is carried out by introducing organic wastewater into anaerobic fermenters A ₁ and A ₂ as shown in Figures 1 and 2.
The aforementioned facultative anaerobic microorganisms are inoculated in the form of digested sludge, and acid fermentation is performed in the presence of a small amount of dissolved oxygen of about 0.1 to 0.0001 mg/d. In this state, lower organic substances such as acetic acid, alcohol, and ketone in the acid fermentation solution are in a state of hydrogen bonding with water polymers in the solution.

Therefore, when this treated liquid is supplied to the membrane separation concentration tank sections B ₁ and B ₂ equipped with a hydrophobic porous membrane X and the porous membrane X is vibrated at high frequency, the lower The organic substances are then separated, concentrated and passed through the porous membrane X to be removed from the wastewater.

At this time, the connection relationship between the anaerobic fermenters A ₁ , A ₂ and the membrane separation concentration tank sections B ₁ , B ₂ is as shown in FIG. Alternatively, as shown in FIG. 2, the product may be supplied to the membrane separation concentration tank section B ₂ during fermentation, and the membrane separation concentration tank section B ₂ may be supplied to the membrane separation concentration tank section B ₂ .
A circulation method may be adopted in which only the lower organic substances are separated in the fermenter A 2 and the rest is returned to the fermenter A ₂ . In either type, lower organic substances are separated and concentrated in the membrane separation concentration tank sections B ₁ and B ₂ , and the separated and concentrated lower organic substances are removed from the system to form organic wastewater. Processing takes place.

As described above, the present invention skillfully combines and combines the anaerobic fermentation method and the membrane separation method to convert wastewater containing organic substances into wastewater containing lower organic substances, and to convert the wastewater into wastewater containing lower organic substances with high efficiency. As a result, the biochemical process can be shortened, and as a result, the processing equipment can also be made smaller. When separating and concentrating lower organic substances from dilute acidic fermentation liquid, the energy consumption is approximately
1/600, which greatly contributes to so-called energy saving.Also, unlike separation using normal ultrafiltration or reverse filtration membranes, the concentration of the separated product is extremely high, and it is easy to store and handle in small quantities. Furthermore, it is far superior to methane gasification and fermentation in that it removes propionic acid, ethanol, etc. that cannot normally be removed by methane gasification and fermentation.

Next, examples of the present invention will be described.

Example 1 A wastewater treatment device was configured as shown in Figure 1, and organic wastewater was collected by concentrating excess sludge at a sewage treatment plant using a centrifuge to a solid content concentration of 5%, and analyzed. As a result, the acetic acid concentration was 300mg/
It was hot. Digested sludge containing Pseudomonas bacteria collected as microorganisms from the digestion tank of a sewage treatment plant was inoculated into this organic wastewater as a seed, kept at 38℃, and air diluted 2000 times with nitrogen gas was blown into the mixture and stirred. By fermenting for 2 days in an anaerobic atmosphere, an acid fermentation solution containing 3000 mg of acetic acid was obtained. During this period, no generation of methane gas was observed. This acid fermentation treatment liquid was introduced into the membrane separation concentration tank section _B1 , and the hydrophobic porous membrane X having the above-mentioned configuration was installed in the membrane separation concentration tank section _B1.
(membrane surface area 50cm ² ), and this porous membrane
Apply a high frequency drive of about 455KHz, 250V,
Low-molecular organic substances were separated by generating harmonic microwaves of around 2 GHz on the membrane surface.

As a result, it was possible to separate low-molecular organic substances containing about 10% of water and mainly acetic acid at a rate of 12 to 13 ml/min with a small energy usage of about 1.2 W min.

Example 2 The processing equipment was connected to form a circulating flow between the anaerobic fermenter section A ₂ and the membrane separation concentration tank section B ₂ as shown in FIG. The wastewater collected in the same manner was filled into the fermenter A ₂ , and immediately after seeding, it was supplied to the membrane separation concentration tank section B ₂ to start membrane separation. From half a day later, the rate was approximately 0.1 ml/hour on average. We were able to separate low-molecular organic substances. During this period, no methane gas was observed to be generated. After completing the fermentation and membrane separation in 10 days, we examined the concentration of organic substances in the treated solution and found that approximately 50% of the organic substances initially present had been digested and removed. The conventional method of methanation, in which acid-fermenting bacteria and methanogenic bacteria coexist and ferment in one phase, requires 20 days to perform the same amount of treatment, but the time is significantly reduced. Obtained.

Here, as in this example, the treatment liquid is transferred to the fermenter _A2.
By forming a circulating flow between the membrane separation and concentration tank section _B2 , fermentation inhibition and methane fermentation caused by lower organic substances, which are fermentation products, are prevented during the fermentation process, and the reaction is accelerated and the reaction time is reduced. It is possible to shorten the processing time, and even if the processing device is downsized, sufficient processing capacity can be obtained.

[Brief explanation of drawings]

Figures 1 and 2 of the drawings are flow sheets of different embodiments of the method for treating organic wastewater according to the present invention, and Figure 3 is a schematic diagram for explaining the internal configuration of the membrane separation concentration tank section. be. A ₁ , A ₂ : Anaerobic fermentation tank, B ₁ , B ₂ : Membrane separation concentration tank part, X : Hydrophobic porous membrane, 1 : Polytetrafluoroethylene membrane, 2 : Radicalization of polytetrafluoroethylene membrane, etc. Treated membrane, 3; Polyvinylidene fluoride membrane, 5, 6; Electrode.

Claims (1)

[Claims] 1. Lower organic substances are produced by fermenting wastewater containing organic substances by microorganisms in an anaerobic atmosphere, and the lower organic substances are produced by a hydrophobic porous membrane subjected to high frequency vibration. A method for treating organic wastewater, which is characterized by separating, concentrating, and removing it from the system. 2. The method for treating organic wastewater according to claim 1, wherein the fermentation of the wastewater containing organic substances by microorganisms is carried out in an anaerobic atmosphere with a dissolved oxygen concentration of about 0.1 to 0.0001 mg/. . 3. The method for treating organic wastewater according to claim 1, wherein the fermentation is acid fermentation.