JP4311264B2 - Anaerobic treatment method - Google Patents

Description

Anaerobic present invention to reduced solubilization by treatment with methane fermentation of anaerobic treatment how, in particular organic waste liquid single-phase type processes by methane fermentation of organic waste liquid in the presence of a sludge containing anaerobic microorganisms it relates to the sex how to process.

  The anaerobic digestion method, which treats slurried high-concentration organic wastewater such as organic sludge, human waste, and food wastewater in the presence of anaerobic microorganisms by single-phase methane fermentation, is also called anaerobic digestion. It is a method that has been done from. In this method, an organic substance is converted into methane gas in an anaerobic tank by anaerobic microorganisms through steps of liquefaction, low molecular weight formation, organic acid production, and methane production. In the single-phase methane fermentation, the acid-generating phase and the methane-forming phase occur in parallel in a single phase, and it is divided into two tanks, a fermentation tank and a desorbed liquid separation tank, as in the conventional anaerobic treatment of sewage sludge. Even in the case of two-stage treatment, if the acid generation phase and the methane generation phase occur in parallel in each tank, they are included in the one-phase processing.

  In such anaerobic treatment, a large amount of sludge mainly composed of undegraded substances and anaerobic microorganisms is generated. Since this sludge is mainly composed of living cells, it is biologically stable, and it is difficult to significantly reduce the volume by biological treatment. Conventionally, it is mechanically dehydrated for incineration, landfill, etc. Had been processed by.

As a method for reducing the volume of sludge produced by anaerobic treatment, Patent Document 1 discloses an organic material in which anaerobically digested sludge is heated at 100 to 180 ° C. and then returned to the anaerobic digester. A method for treating activated sludge is described.
However, such conventional methods can reduce the volume of sludge, but the conditions of solubilization treatment are severe at high temperatures, so that non-biodegradable organic substances are generated and the chromaticity and COD of the treatment liquid are increased. As a result, the quality of the treated water deteriorates, and a device having high heat resistance and pressure resistance is required, and there is a problem that the energy consumption is large and the cost is high.

On the other hand, as a method for reducing the volume of excess sludge produced by aerobic treatment (activated sludge treatment) of organic waste liquid, Patent Document 2 describes a method of treating sludge with ozone and returning it to an aeration tank. Yes.
However, this method relates to an aerobic treatment, and the possibility of application in an anaerobic treatment is not disclosed.
JP-A-1-224100 JP-A-6-206088

An object of the present invention is to solve the above problems, and to suppress the deterioration of treated water, and to reduce the sludge volume at a low energy consumption and low cost by a simple apparatus and operation. it is to propose a anaerobic how to process the liquid.

The present invention
Anaerobic treatment process in which organic wastewater is converted to methane gas through the steps of liquefaction, low molecular weight, organic acid production and methane production in the presence of sludge containing anaerobic microorganisms. When,
A reforming step for reforming sludge produced in the anaerobic treatment step into an easily biodegradable modified sludge by ozone treatment with an ozone usage of 0.005 to 0.04 g-O ³ / g-VSS; ,
An anaerobic treatment method including a return step of returning the modified sludge to the anaerobic treatment step.

  In the present invention, the organic effluent to be treated is an effluent (including sludge) containing organic matter to be treated by anaerobic treatment. A slurry containing a solid is suitable for processing, but may be a liquid containing no solid. In addition, non-biodegradable organic substances, inorganic substances, cellulose, paper, cotton, wool cloth, solid matter in human waste may be contained. Such organic effluents include sewage, sewage initial sludge, human waste, septic tank sludge, food factory effluent, beer waste yeast and other industrial effluents, and sludge such as excess sludge generated when these effluents are treated. Can be given.

  The anaerobic treatment process is a process of methane fermentation of organic wastewater in the presence of sludge containing anaerobic microorganisms in an anaerobic treatment tank, where the acid-generating phase and the methane-forming phase occur in a single phase. This is a methane fermentation process, and includes a case where a fermentation tank and a desorbed liquid separation tank are separated to perform a two-stage process in which an acid generation phase and a methane generation phase are performed in each. For this reason, sludge containing acid producing bacteria and methanogenic bacteria is used as sludge containing anaerobic microorganisms. In this process, the organic substance is converted into methane gas by the steps of liquefaction → low molecular weight → organic acid production → methane production by anaerobic microorganisms in the anaerobic treatment tank.

  As conditions for methane fermentation, any temperature condition in which a medium temperature methanogen having an optimum temperature around 35 ° C. and a high temperature methanogen having an optimum temperature around 55 ° C. are allowed to grow. Medium-temperature methanogens have a slow growth rate and therefore a long residence time (SRT), but they can be treated at a relatively low temperature, so that the equipment for warming and keeping warm becomes simple. On the other hand, in the case of high-temperature methanogens, heating and heat retention facilities are required, but since the growth rate is fast, the residence time is shortened, and processing in a short time becomes possible.

When the medium temperature methanogen is mainly used, the growth rate is slow, so the sludge residence time in the anaerobic treatment tank is 10 days or longer, preferably about 15 to 30 days. On the other hand, when a high-temperature methanogen is mainly used, the growth rate is fast, so it is possible to set a residence time shorter than the above range (for example, a minimum residence time of 5 days or more). Organic matter load is 0.6 to 1.6 kg-VSS / m ³ · day, MLSS concentration in anaerobic treatment tank is 5,000 to 100,000 mg / l, preferably 30,000 to 60,000 mg / l, anaerobic The anaerobic treatment can be performed at a temperature of 30 to 38 ° C or 45 to 60 ° C.

  The anaerobic treatment step can be combined with a solid-liquid separation step using a solid-liquid separation device such as a membrane separation device, a decanter, or a filtration device. In the solid-liquid separation step, the liquid in the anaerobic treatment tank is subjected to solid-liquid separation, the separation liquid is discharged as a treatment liquid, and the concentrated sludge is returned to the anaerobic treatment tank. When membrane separation is used, various membrane types such as hollow fiber, tubular, and flat membrane can be used. Moreover, since the purpose of membrane separation is to separate solids, membranes having a relatively large pore size such as MF and UF are preferred.

In reformer a portion of biological sludge reforming step from processing system in such anaerobic treatment step is a step of modifying the more readily biodegradable ozone treatment. When extracting biological sludge, it is preferable to extract the concentrated sludge separated by the solid-liquid separator and perform the reforming treatment. However, the biological sludge may be extracted from the anaerobic treatment tank in a mixed solution state. In some cases, these reformers can be provided in the anaerobic treatment tank.

The ozone treatment is performed by bringing sludge into contact with ozone. As a contact method, a method of introducing digested sludge into an ozone treatment tank and blowing ozone, a method of mechanical stirring, a method of using a packed bed, or the like can be employed. As ozone, ozone gas, ozone-containing air, ozonized air, or the like can be used. The amount of ozone ^{0.005~0.04g-O 3 / g-VSS} , preferably shall be the ^{0.01~0.03g-O 3 / g-VSS} . When a packed bed is used, the SV of the packed bed is preferably ¹ to 10 hr ⁻¹ , desirably 3 to 6 hr ⁻¹ .

The amount of sludge that is pulled out from the anaerobic treatment tank and reformed is at least equal to, or preferably twice or more, the amount of solids charged into the anaerobic treatment tank in order to ensure the sludge volume reduction effect. For example, in the case of an anaerobic treatment tank staying for 15 days, the circulation ratio can be set to 1/15 day ⁻¹ or more, preferably 2/15 day ⁻¹ or more. The upper limit of the circulation ratio is 1/15 or less, preferably 1/15 to 1/50 of the total amount of sludge retained in the anaerobic treatment tank per day from the viewpoint of ensuring effective anaerobic treatment (solid content weight). ) Is preferable.

By making the amount of sludge extracted in this way more than 1 times the amount of solids to be charged, the volume of sludge as a whole treatment system can be increased, and all the retained sludge in the anaerobic treatment tank By setting it as 1/15 or less of quantity, anaerobic processing can be effectively performed in the state which maintained sludge activity as the whole anaerobic processing tank highly.
In the case of a two-stage treatment in which the anaerobic treatment tank is divided into two parts, a fermentation tank and a desorbed liquid separation tank, the sludge extraction for the reforming treatment may be performed from either the first stage or the second stage.

  The return process is a process of returning the sludge modified in the reforming process to the anaerobic treatment process. When the sludge is extracted from the anaerobic treatment process, the extraction and the return can be combined to form a circulation process. When reforming is performed in the anaerobic treatment tank, the liquid in the anaerobic treatment tank is circulated.

  The treatment method using the anaerobic treatment apparatus of the present invention is an anaerobic treatment step, in which an organic effluent is introduced into an anaerobic treatment tank, mixed with sludge containing anaerobic microorganisms, and subjected to anaerobic treatment. Wake up. Here, the organic substance is converted into methane gas through the steps of liquefaction, molecular weight reduction, organic acid generation, and methane generation. The liquid in the anaerobic treatment tank is subjected to solid-liquid separation in a solid-liquid separator, the separated liquid is discharged as a treatment liquid, and the concentrated sludge is returned to the anaerobic treatment tank.

In reformer part of the liquid or concentrated sludge containing sludge of the anaerobic treatment tank, modified into a more readily biodegradable ozone treatment. In the anaerobic treatment process, the number of microorganisms increases due to the growth of microorganisms in the sludge, but there is a limit to the volume reduction by digestion even if the living bacteria are concentrated and returned to the anaerobic treatment tank.

However bacteria in the sludge by performing more reforming the ozone treatment in the reformer is killed, it is decomposed with other organic materials, low molecular weight organic material and some inorganic substances generated, the easily biodegradable Reformed. Such modified sludge is used and decomposed as a substrate for anaerobic microorganisms by circulating to an anaerobic treatment tank.
As a result, the volume of sludge is reduced, and the amount of sludge discharged as excess sludge is reduced.

  Even if all the sludge discharged as surplus sludge from the anaerobic treatment process is reformed and circulated, the sludge in the anaerobic treatment tank will increase, because it will be utilized and the sludge will grow. The sludge must be discharged as surplus sludge, and the discharged sludge cannot be brought close to zero. Therefore, if more sludge is extracted than the amount of sludge generated as surplus sludge so that the amount of excess sludge is zero, and this is reformed and circulated, the amount of excess sludge extracted and the amount of proliferated sludge are balanced. The amount of sludge increased will approach zero. Even in this case, in order to avoid accumulation of mineralized sludge, it is desirable to discharge a minimum amount of digested sludge.

  When excessive sludge is reformed in this way, digestion efficiency is reduced, but an anaerobic treatment tank is usually operated with an SRT of about 15 days, so the SRT is shortened by the reforming process. However, it is possible to operate with sufficient margin, and the decrease in efficiency is not so serious.

  The treatment liquid in the anaerobic treatment step can be discharged as it is into sewage or the like, but it may be discharged after an aerobic biological treatment or other post-treatment.

According to the anaerobic treatment method of the present invention , the organic drainage is converted into methane gas through the steps of liquefaction, low molecular weight, organic acid generation and methane generation in the presence of sludge containing anaerobic microorganisms. the sludge produced in the anaerobic treatment step of Ru is methane fermentation by methane fermentation, by ozone treatment in the ozone amount ^{0.005~0.04g-O 3 / g-VSS} , easily biodegradable modification sludge Since the anaerobic treatment is carried out by reforming to the above, it is possible to reduce the volume of sludge while suppressing deterioration of treated water quality such as an increase in chromaticity and COD. Further, energy consumption can be reduced as compared with the conventional processing method, and it is not necessary to use a device having high heat resistance and pressure resistance, and therefore, processing at low cost is possible.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system diagram showing an anaerobic treatment apparatus of an embodiment, FIG. 2 is a system diagram showing an anaerobic treatment apparatus of a reference example , and FIG. 1 shows concentrated sludge obtained by concentrating an anaerobic treatment liquid using a solid-liquid separator. FIG. 2 shows an example of reforming the mixed solution in the anaerobic treatment tank.

In FIG. 1, 1 is an anaerobic treatment tank, 2 is a membrane separation apparatus as a solid-liquid separation apparatus, and 3 is a reforming tank.
In the treatment apparatus of FIG. 1, the anaerobic treatment tank 1 introduces organic drainage from the liquid passage 4 to be treated, and returns sludge returned through the return sludge passage 5 and anaerobic biological sludge in the anaerobic treatment tank 1. It mixes and it is comprised so that anaerobic processing may be performed, stirring gently with the stirrer 6. FIG. By the anaerobic treatment performed here, the organic matter in the liquid to be treated is decomposed by acid-producing bacteria and methanogenic bacteria. Digestion gas containing the generated methane gas is discharged from the exhaust gas passage 7.

  The membrane separation device 2 is configured such that a part of the mixed solution in the anaerobic treatment tank 1 is taken out from the communication path 11, pressurized by the pump 12 and guided to the membrane separation device 2, and membrane separation is performed by the separation membrane 13. ing. The permeated liquid 14 and the concentrated sludge 15 are separated by membrane separation performed here. The permeate 14 is discharged out of the system from the treatment liquid path 16 as a treatment liquid. A part of the concentrated sludge 15 is taken out from the concentrated liquid take-out path 17 and introduced into the reforming treatment tank 3, and a part or all of the remaining part is returned from the return sludge path 5 to the anaerobic treatment tank 1. When surplus sludge is generated, it is discharged from the surplus sludge discharge path 18 outside the system.

  An ozone treatment tank is used as the reforming tank 3, and the sludge is reformed by passing the concentrated sludge 15 through the packed bed 21, blowing ozone from the ozone generator 22, and performing ozone treatment. The modified sludge is returned to the anaerobic treatment tank 1 from the modified sludge passage 23 and subjected to anaerobic treatment. Thus, the solid content modified to be readily biodegradable by the modification is digested in the anaerobic treatment tank 1, and the excess sludge generated from the treatment system is reduced in volume.

The treatment apparatus of FIG. 2 is configured to draw a part of the mixed liquid in the anaerobic treatment tank 1 from the sludge extraction passage 24 as drawn sludge and introduce the drawn sludge into the reforming tank 3 to perform the reforming process. Is done. The reforming tank 3 is configured to perform a high-pressure pulse discharge process as a reference example, and applies a high-pressure pulse from the power supply device 27 between the + electrode 25 and the − electrode 26 to perform discharge, thereby reforming sludge. The concentrated sludge from the membrane separator 2 is returned to the anaerobic treatment tank 1.

  In FIG. 1 and FIG. 2, the membrane separation device 2 is used as the solid-liquid separation device, but other solid-liquid separation devices such as a precipitation device and a centrifugal separation device can also be employed. In FIG. 1, the return of the sludge from the return sludge path 5 can be omitted.

Reference Example 1 and Comparative Example 1
Using an jar fermenter with an effective volume of 2 liters, an anaerobic treatment tank with a liquid volume of 1.2 liters and 80 ml of raw mud concentrated to about 2% by weight of excess sludge from the sewage treatment plant as TS Each was supplied by syringe. A membrane separation device having a flat membrane module with a molecular weight cut off of 30,000 and a membrane area of 177 cm ² is connected to the anaerobic treatment tank, and the liquid in the tank is filtered 80 ml per day while circulating with a pump. It was circulated so that the amount was constant. The anaerobic treatment tank was controlled at a temperature of 35 ° C., and about 50 ml of UASB granules were added as seed sludge.

In Reference Example 1, a high-pressure pulse discharge device was used as the reforming treatment tank, and once a day, 80 ml of sludge having the same amount as the raw mud supply was drawn out with a syringe and introduced into a 150 ml capacity cell, and a tungsten / thorium alloy. Between the positive electrode made of stainless steel and the negative electrode made of stainless steel, a high pressure pulse discharge was performed for 10 minutes at an electrode interval of 5 mm, an applied voltage of 30 kV, and a pulse interval of 50 Hz, and then returned to the anaerobic treatment tank.

A comparative example 1 that was not subjected to any reforming treatment was also tested at the same time to compare changes in sludge concentration in the tank. FIG. 3 shows the daily change of the gas generation amount, and FIG. 4 shows the daily change of the TS concentration. From these results, it can be seen that in Reference Example 1, the sludge decomposition rate is higher than in Comparative Example 1, and the volume is reduced to such an extent that substantially no excess sludge is produced.

Example 1
In Example 1 , an ozone treatment tank was used as the reforming treatment tank in Example 1, and once a day, 80 ml of sludge having the same amount as the raw mud supply amount was drawn out with a syringe, and the ozone injection rate was 0.05 g-O ^3. After the ozone treatment under the condition of / g-TS and the reforming treatment, it was returned to the anaerobic treatment tank.
The test was performed in the same manner as in Reference Example 1, and the change in the sludge concentration in the tank was compared with Comparative Example 1 in which no ozone treatment was performed.

As a result, similarly as in Reference Example 1, Example was subjected to ozone treatment 1 is the sludge concentration in the anaerobic digestion tank was stable at 1.8% by weight TS, Comparative Example 1 is increased continuously It reached 5% by weight or more on the 30th day from the start of operation. From these results, as in Reference Example 1, it is clear that Example 1 also has a higher sludge decomposition rate than Comparative Example 1, and has reduced the volume to such an extent that there is substantially no excess sludge. .

It is a systematic diagram which shows the anaerobic processing apparatus of embodiment of this invention. It is a systematic diagram which shows the anaerobic processing apparatus of a reference example . It is a graph which shows the daily change of the gas generation amount of the reference example 1 and the comparative example 1. FIG. It is a graph which shows the daily change of TS density | concentration of the reference example 1 and the comparative example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anaerobic treatment tank 2 Membrane separation device 3 Reforming tank 4 Processed liquid path 5 Return sludge path 6, 22 Stirrer 7 Exhaust gas path 11 Connection path 12 Pump 13 Separation membrane 14 Permeate 15 Concentrated sludge 16 Process liquid path 17 Concentration Liquid discharge path 18 Excess sludge discharge path 21 Packed bed 22 Ozone generator 23 Reformed sludge path 24 Sludge extraction path 25 + Pole 26 -Pole

Claims (1)

Anaerobic treatment process in which organic wastewater is converted to methane gas through the steps of liquefaction, low molecular weight, organic acid production and methane production in the presence of sludge containing anaerobic microorganisms. When,
A reforming step for reforming sludge produced in the anaerobic treatment step into an easily biodegradable modified sludge by ozone treatment with an ozone usage of 0.005 to 0.04 g-O ³ / g-VSS; ,
An anaerobic treatment method including a return step of returning the modified sludge to the anaerobic treatment step.

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