JPH0218915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for treating human waste wastewater by an upflow anaerobic sludge bed method.

[Conventional technology]

The upflow anaerobic sludge bed method (hereinafter abbreviated as UASB method) is a method developed in recent years as a method for methane fermentation of wastewater. A sludge bed is formed by flocculating or granulating the sludge (bacteria) without using a carrier for bacteria to adhere to, and a higher volume load is applied to ensure a high concentration of microorganisms in the fermenter. This is an anaerobic microbial treatment technology that allows for the treatment of liquids, and the equipment is equipped with a distribution inlet pipe to uniformly flow the liquid to be treated at the bottom in order to prevent short circuits of the liquid to be treated at low loads, and , equipped with a gas-solid-liquid three-phase separation device at the top (Journal of the Japan Sewage Works Association)
Vol. 22, No. 255, 1985/8, pp. 67-77).

It is known that this UASB method may or may not be adopted depending on the quality of the waste liquid, and there have been no reports to date on whether this method can be used for methane fermentation of night soil wastewater. There are none at all.

[Purpose of the invention]

An object of the present invention is to provide a method for treating human waste water using the UASB method.

[Structure of the invention]

In the present invention, human waste wastewater is subjected to acid fermentation in an acid fermentation tank, and the SS contained therein is removed as scum.
When performing methane fermentation treatment by passing water in an upward flow into a sludge bed type methane fermentation reaction tank having a solid-liquid separation section, carbon dioxide gas is absorbed into the effluent from the acid fermentation tank. A method for treating human waste wastewater, characterized in that the wastewater is supplied to a person, and an apparatus for carrying out the method.

Conventional methane fermentation treatment of human waste waste requires a fully mixed digester that can retain human waste for a long time, a fixed bed upward flow anaerobic reaction tank, and A fluidized bed anaerobic reactor is used. All of these treatment methods utilize the ability of these bacteria to adhere to carriers to form flocs (approximately 0.5 mm or less in diameter) of anaerobic bacteria such as methane bacteria, and human waste is used as a substrate. Since there is no adverse effect on the formation of flocs of these bacteria or their adhesion to carriers, it has been possible to treat human waste wastewater as it is without diluting it, although this is inefficient.

On the other hand, in the UASB method, in order to increase the retention power or amount of anaerobic bacteria such as methane bacteria in the fermenter, the bacteria self-immobilize without using a carrier or other adhesion medium for the bacteria. Seshime, that is, bacterial cells
A method in which granules aggregated into granules of about 0.5 mm to 5 mm are formed, a sludge bed (sludge blanket layer) is formed by the granules, and wastewater is passed through the sludge bed in an upward flow for methane fermentation. , is a method that can treat specific organic wastewater with high efficiency.

The present inventors have demonstrated that methane fermentation can be carried out with high efficiency for specific organic wastewater.
I tried applying human urine directly to the UASB method, but
It was discovered that the granule, in which the bacterial cells that form the sludge bed aggregate into granules, floats up together with the scum and is washed away, making it impossible to achieve the intended purpose.

Therefore, two UASB reactors are connected in series, and the first stage UASB reactor performs acid fermentation and flotation separation by scum formation of SS in urine, and the second stage UASB reactor performs the SS concentration. almost
When the acid-fermented human waste reduced to less than 5,000mg was processed, methane fermentation was successfully carried out without any granules flowing out in the subsequent UASB reaction tank. However, more than 2500 mg/volatile organic acid remained, and the BOD removal rate did not exceed 70% compared to the BOD concentration used as the sample urine.
The average removal rate was 68%. Although this result is a sufficiently satisfactory processing result, it is effective to further increase the BOD removal rate in order to reduce the load on the subsequent UASB method, perform advanced processing, and lower processing costs. We thought that this was the case, and further investigated the reason for the high residual rate of volatile organic acids.

In the two-stage treatment method, the first stage fermenter does not necessarily need to be a UASB reaction tank, but
It is necessary to use an upflow reaction tank to promote acid fermentation and scum generation. Therefore, since it is necessary to form a large-diameter floc of the inflowing SS, it is possible to prevent the disintegration of the floc and to promote the generation of scum by gently stirring only with the generated gas without using gas agitation or mechanical agitation. In order to remove the gas, the generated gas only rises in the first stage reaction tank in a short period of time, and sufficient gas-liquid contact does not occur, so that the carbon dioxide in the generated gas is absorbed into the acid fermentation liquid. It will not be absorbed sufficiently. As a result, the acid concentration in the subsequent UASB reaction tank is insufficient to neutralize the ammonia in the human waste, and if the volatile organic acid concentration becomes 0, the estimated value is 8.7, which is the preferred pH for methane-fermenting bacteria. The value is significantly different from the conditions (6.9 to 8.2).

In fact, when we started a human waste treatment experiment by filling the latter-stage UASB reaction tank with Granule, a highly active methane-fermenting bacterium, we found that immediately after the start of the experiment, the methane-fermenting bacterium was active, resulting in a large amount of volatile organic acids. The concentration of volatile organic acids in the effluent treated water was low, and the BOD removal rate was 80% higher. However, as time passed, the concentration of volatile organic acids in the treated water increased, and the concentration of volatile organic acids in the treated water reached a steady state of about 2,700 mg/.

At this time, the pH remained stable at approximately 8.2 due to neutralization equilibrium between the residual volatile organic acid concentration and ammonia, but the BOD removal rate remained low at 67%.

The reason for this is that the BOD removal rate is high at the stage immediately after the start of the experiment when the bacteria are highly active, and when the concentration of volatile organic acids in the treated water is low, the PH of the treated water, that is, the PH in the reaction tank, is lower than that of the methane-fermenting bacteria. Therefore, the activity of methane-fermenting bacteria decreased, and as this activity decreased, the organic acid concentration in the treated water gradually increased, reaching a steady state at 2700 mg/mL. be done.

In fact, the pH of the treated water immediately after the start of the experiment was high, reaching the highest level.
Reached 8.4.

From the above results, in the two-stage UASB method, in which organic acid fermentation and SS removal of night soil wastewater are performed in the first stage, and UASB treatment is performed in the second stage, when external pH control is not performed, found that the liquid in the fermenter was maintained at a pH below 8.2, at which methane fermentation could occur, due to the residual presence of volatile organic acids in the subsequent UASB reaction.

From the above results, the pH in the UASB methane fermentation tank can be reduced by adding inorganic acids that do not provide nutrients to methane fermentation bacteria to the latter stage UASB methane fermentation tank.
If it can be controlled so that it does not rise above 8.2, that is, if the PH in the UASB methane fermenter can be maintained at the preferred PH conditions for methane fermenting bacteria (PH 6.9 to 8.2) in any case. We conducted various studies based on the idea that it might be possible to accelerate the decomposition of volatile organic acids and reduce the concentration of volatile organic acids in the processing liquid.

Then, we investigated the possibility of using carbon dioxide gas as an inorganic acid to be added.

That is, acid fermentation is carried out by passing human waste water with an ammonia nitrogen concentration of 3000 mg/into an upflow acid fermenter with a fermentation section volume of 2.0 at a rate of 1.5 per tank volume at a temperature of 30°C to 37°C. At the same time, the scum that floated up was removed to produce an acidic fermentation liquid with an SS content of 4500mg/, which was then fed to a UASB reaction tank with a fermentation section volume of 2.0 while pressurizing carbon dioxide gas to a pH of 6.5 to 8.1. Liquid flow rate 3/day, temperature 30℃~37℃
When methane fermentation was carried out in the treated water, methane fermentation could be carried out stably with a volatile organic acid content of 120 mg/in the treated water, and the BOD removal rate in this case was 85%.

In addition, when methane fermentation is performed in the same way without injecting carbon dioxide gas into the acid fermentation liquid, the volatile organic acid content in the treated water is 2500 mg/, and the BOD removal rate is 68.
It was %.

The gas generated in the acid fermentation tank or methane fermentation tank contains a large amount of carbon dioxide gas, and this gas is used as a neutralizer for the acid fermentation liquid to prevent the pH from increasing after the reaction in the subsequent UASB reaction tank. Can be used.

That is, when the gas generated in the acid fermenter was circulated through acid-fermented human urine to absorb carbon dioxide gas, and then methane fermentation was carried out using the UASB method, results similar to those obtained when carbon dioxide gas was pressurized were obtained.

Next, the present invention will be explained based on the drawings.

FIG. 1 is a schematic flow diagram showing the human waste wastewater treatment apparatus of the present invention, in which an acid fermenter is used as an acid fermenter.
This shows the case where a tank of the same shape as the UASB reaction tank is used.

Human waste wastewater is first introduced into the acid fermentation tank 1 from a waste water introduction pipe 10 by a pump 4 through a distribution inlet 6 provided at the bottom of the acid fermentation tank 1. In this acid fermenter, acid fermentation mainly proceeds, but methane fermentation also partially proceeds, generating digestive gas. The generated gas adheres to the SS in the human waste water introduced as it ascends through the acid fermentation tank, floats up with the SS, and forms a scum layer. The formed scum layer is continuously or intermittently removed by a scum scraping device 8 provided on the water surface of the gas-solid-liquid separation section 7 in the upper part of the acid fermenter. In the acid fermentation tank, even when the air and water temperatures are low, such as during the winter, methane fermentation partially proceeds and gas is generated.
It is preferable to provide heating equipment so that the human waste can be heated to 25°C to 40°C and then introduced into the acid fermentation tank.

The acidic fermentation liquid is drawn out from below the water surface of the gas-solid-liquid separator 7 and introduced into the lower part of the carbon dioxide absorption device 3.
The gas containing carbon dioxide separated at the upper part of the acid fermentation tank is circulated and aerated into the acid fermentation liquor from the blower 5 through the aeration tube installed at the bottom of the carbon dioxide absorption tower, and after the acid fermentation liquor absorbs carbon dioxide gas, it is carbonated. Gas absorption device 3
It is pulled out from the top of the UASB methane fermentation tank 2, introduced into the UASB methane fermentation tank 2 through the distribution inflow pipe 6 provided at the bottom of the UASB methane fermentation tank 2, and methane fermentation is performed in an upward flow. The methane-fermented human waste water is separated into gas, solid, and liquid in the gas-solid-liquid separation section 7', and the gas is collected in the center and drawn out through the pipe 9', after which methane is separated. On the other hand, the treated liquid overflows from the upper part of the methane fermentation tank and is discharged from the treated water discharge gutter 11, and the separated solids (mainly flocs) are allowed to settle downward.

Acid fermenter 1 and UASB methane fermenter are both
It is preferable to maintain the temperature at 25° C. to 40° C., and the amount of liquid to be passed is preferably 0.5 to 6 per day per each reaction tank. Note that the amount of liquid passed may differ based on the temperature of each fermenter, the BOD concentration of human waste water, the activity of microorganisms, etc.

The amount of carbon dioxide absorbed in the carbon dioxide absorption tower varies depending on the content of ammonia nitrogen in the human waste wastewater, but it is preferable to absorb the carbon dioxide to a pH of 6.5 to 8.1. It is preferable to absorb carbon dioxide gas under pressure of about atmospheric pressure.

The reason why the treatment efficiency of night soil wastewater treatment using the UASB reaction tank according to the present invention has been improved is that, in addition to being able to reduce the concentration of volatile organic acids remaining in the treated water as described above, the It has an improving effect. In other words, due to the high pH and the resulting inhibitory effect of free ammonia, we were able to overcome the drawback that granule formation by methane bacteria, which is the most important factor for the UASB method to be established as a methane fermentation process, is not sufficiently achieved. It is. This has extremely important significance when adopting the UASB method. When the human waste water after acid fermentation was passed through the subsequent UASB reaction tank without any pH neutralization, the granulated sludge filled at the beginning of the treatment was retained with sufficient activity, but At least no increase in granulated sludge was observed there. Therefore, according to this method, it is necessary to obtain granulated methane fermentation sludge when starting up the operation of the treatment equipment, but obtaining it requires considerable expense. On the other hand, in the method of the present invention, although the methane fermentation sludge initially filled was not granulated, the methane fermentation sludge gradually progressed to granulation in the subsequent UASB reaction tank, and eventually PH
A granulated sludge layer three times larger than that without neutralization was formed, and it was possible to start up the UASB process for human waste treatment without using granulated sludge. In addition, in terms of treatment performance, the total residence time of the two-stage human waste treatment UASB process operated without PH neutralization by carbon dioxide gas absorption was 2.5 days, whereas the total residence time of the method of the present invention was 2.5 days. The total residence time achieved was 1.5 days, making it possible to achieve even higher load and faster treatment processes, and as mentioned above, the treatment yield was even more excellent. The processing time for such human waste wastewater is 20 to 30 times that of the conventional human waste anaerobic digester, which takes an average of 30 days. , it is possible to achieve high-speed processing, and its practical effects are extremely large.

[Brief explanation of drawings]

FIG. 1 is a flow diagram schematically showing the human waste wastewater treatment apparatus of the present invention. 1... Acid fermenter, 2... UASB methane fermenter,
3... Carbon dioxide absorption tower, 6, 6'... Distribution inflow pipe,
7, 7'... Gas-solid-liquid separation section, 9, 9'... Produced gas discharge pipe, 11... Treated water discharge gutter.

Claims (1)

[Scope of Claims] 1 Human waste wastewater is preliminarily fermented in an acid fermentation tank and the SS contained therein is removed as scum, and then the sludge has a distribution inflow pipe at the bottom and a gas-solid-liquid separation section at the top. When carrying out methane fermentation treatment by passing water in an upward flow through a bed type methane fermentation reaction tank, the method is characterized in that carbon dioxide gas is absorbed into the effluent from the acid fermentation tank and then supplied to the methane fermentation reaction tank. How to treat human waste water. 2. The method for treating human waste wastewater according to claim 1, which uses gas produced in an acid fermenter as the carbon dioxide gas. 3. The method for treating human waste wastewater according to claim 1, which uses gas produced in a methane fermentation tank as the carbon dioxide gas. 4. An acid fermenter having a distribution inflow pipe for human waste wastewater at the bottom, a gas-solid-liquid separation section and a removal device for scum floating in the gas-solid-liquid separation section at the top;
A night soil system in which a distribution inflow pipe for introducing the acid fermentation liquid produced in the acid fermentation tank at the bottom is connected to a sludge bed type methane fermentation tank having a gas-solid-liquid separation section at the top. A sewage treatment device, characterized in that a carbon dioxide gas absorption tank for the acid fermentation liquid is provided on the piping that leads the acid fermentation liquid to the bottom of the methane fermentation tank. Sewage treatment equipment. 5. The human waste sewage treatment device according to claim 4, wherein the carbon dioxide absorption device is piped to introduce the carbon dioxide-containing gas produced in the acid fermentation tank. 6. The human waste sewage treatment device according to claim 5, which is constructed by piping so as to introduce the carbon dioxide-containing gas produced in the methane fermentation tank into the carbon dioxide absorption device.