JPH0218914B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for anaerobically treating human waste using an upflow anaerobic sludge blanket method (hereinafter abbreviated as the UASB method). .

[Conventional technology and its problems]

The UASB method is a method developed in recent years for methane fermentation of wastewater, in which raw wastewater flows upward from the bottom of the reactor (fermenter).
Anaerobic biological treatment that can tolerate high volume loads by forming a sludge bed by flocculating or granulating sludge and securing a high concentration of microorganisms in the reactor without using carriers with bacteria attached. technology, namely methane fermentation method (Journal of the Sewage Works Association Vol. 22, No. 255, 1985/8, pp. 67-77
page).

It is known that this 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 applied to methane fermentation of human waste wastewater. There are none at all.

[Purpose of the invention]

An object of the present invention is to provide a method for methane fermentation of human waste wastewater using the UASB method.

[Structure of the invention]

The present invention provides a method for methane fermentation of human waste water using the UASB method, after diluting the human waste so that the ammonia nitrogen concentration contained in the human waste is 3200 mg/or less and the suspended solid concentration is 5000 mg/or less. This is an anaerobic digestion method for night soil wastewater that is characterized by methane fermentation treatment.

That is, the present invention employs a new method in which human waste is diluted and then subjected to methane fermentation treatment, which has not been used in conventional methane fermentation treatment methods.
This enables processing using the UASB method.

The method of the present invention will be explained in detail below.

In conventional methane fermentation treatment methods for human waste, no consideration has been given to diluting the human waste for treatment in order to retain the human waste in a methane fermentation tank for as long as possible.

The conventional methane fermentation treatment method for human waste wastewater includes a fully mixed digester, a fixed bed upward flow anaerobic reaction tank,
This is a treatment method using a fixed bed type downward flow anaerobic reaction tank or a fluidized bed type anaerobic reaction tank, and in both of these methods, the formation of flocs of methane bacteria, etc. is limited by the ability of methane bacteria to adhere to the carrier. This is a treatment process that uses human waste as a substrate and does not have a particularly large effect on floc formation or adhesion of these bacteria to carriers, making it an inefficient method for diluting human waste wastewater. It was possible to process it as is without doing anything.

Therefore, in the normal human waste methane fermentation method,
A method has been adopted in which, after performing methane fermentation treatment, the material is diluted approximately 10 to 20 times and then subjected to secondary treatment using anaerobic treatment such as activated sludge method or sprinkled bed method.

In contrast to the conventional method, the UASB method does not attach anaerobic bacteria, mainly methane bacteria, to an adhesion medium such as a carrier, but rather self-immobilizes the bacteria themselves (the bacteria is about 0.5 mm to 5 mm thick). A method for carrying out methane fermentation treatment of sewage by forming a sludge blanket using the granules, and passing specific organic sewage through the blanket in an upward flow. It is.

The present inventors conducted an experiment to determine whether this UASB method could be directly applied to the treatment of human waste, and the graph shown in Figure 1 shows the BOD removal rate versus the number of days elapsed when undiluted human waste was treated by the UASB method. As can be seen, it was impossible to treat raw human waste by methane fermentation using the UASB method. In this experiment, BOD 15000 mg/day was applied to a reaction tank with a capacity of 20 at a rate of 0.7/day.
Human waste at a temperature of 33°C was passed through with SS6250mg/ and ammonia nitrogen 6000mg/.

Therefore, we investigated the cause and found that in order to carry out methane fermentation treatment using the UASB method, it is an essential condition that anaerobic bacteria involved in decomposing organic matter into methane gas form granules. Yes, but using undiluted human urine as a substrate
Since this granule (blanket) was not formed when the UASB method was applied, it was thought that there may be a substance in human waste that inhibits granule formation.

Therefore, when we tried to dilute raw human urine 5 times with tap water and treat it using the same UASB method, we found that
As can be seen from the graph of BOD removal rate versus number of days shown in Figure 2, it was found that human waste could be treated by methane fermentation using the UASB method.

Similar results were obtained when raw human waste was diluted with septic tank sludge, waste water, groundwater, river water, seawater, etc. This indicates that the granule formation inhibitors are effective against anaerobic bacteria, including methane bacteria, in raw human urine. This was thought to be due to the concentration being diluted.

Therefore, we investigated factors that inhibit the formation of anaerobic bacterial granules in human urine.

First, after cation exchange treatment of undiluted human urine
When treated using the UASB method, methane fermentation treatment was possible in the same way as the diluted human waste. Therefore, we thought that this might be due to the influence of ammonium ions, which are contained in relatively large amounts as cationic components in night soil, and decided to use undiluted human urine that had undergone cation exchange treatment.
When NH ₄ C was added to various concentrations of ammonia nitrogen and treated by the UASB method, the ammonia nitrogen concentration was
If the ammonia nitrogen concentration is 3,200mg/or less, treatment using the UASB method is possible, but if the ammonia nitrogen concentration is 3,500mg/
It was found that treatment by the UASB method is impossible when the amount is mg/, that is, granules such as methane bacteria are not formed.

Based on this knowledge, when we diluted raw human urine containing 30,000 mg of BOD and 8,000 mg of ammonia nitrogen to 2.5 times or more and tried treating it with UASB, a good granule or blanket of anaerobic bacteria was formed, and methane production was progressing smoothly. I was able to carry out fermentation. Also, raw human urine has a relatively low concentration of BOD10000.
When raw human urine with a concentration of 4000 mg/mg/ammonium nitrogen was diluted to 1.3 times or more and processed by the UASB method, granule formation was sufficient as described above, and the digestion treatment by the UASB method was possible.

From the above results, when human waste is treated by the UASB method, the factor that inhibits the production of granules is ammonia nitrogen, and its concentration is reduced to 3200mg/
It was found that it was necessary to dilute the following:

In addition, while repeating the above experiment, the ammonia nitrogen concentration was diluted to 3200 mg/or less.
We discovered that even when methane fermentation of human waste is carried out using the UASB method, methane fermentation may not proceed smoothly.We further investigated the cause and found that when a large amount of SS is present in human waste, methane fermentation may not proceed smoothly. It was found that the cause was that a large amount of scum was generated in the fermenter, and the granulated bacteria floated to the surface and flowed out along with this scum.

Therefore, we investigated the relationship between the SS concentration in human waste and the generation of scum in a UASB-type methane fermentation tank, and found that the SS concentration in human waste was
By controlling the amount to 5000mg/or less, it is possible to effectively reduce the generation of scum in the methane fermentation tank, and therefore prevent the floating and outflow of granule bacteria accompanying the scum.
It was discovered that granulated bacterial cells could be maintained at a high concentration in the treatment tank.

Therefore, when treating human waste with methane fermentation using UASB, in order to achieve a BOD removal rate of 70% or more, the human waste must be diluted to reduce the ammonia nitrogen concentration.
3,200 mg/in addition to reducing the SS concentration in human waste to 5,000 mg/in or less to suppress the generation of scum in the methane fermenter, thereby preventing the floating and outflow of granulated bacterial cells. It is necessary to prevent this.

Example: Undiluted human urine with BOD 12000 mg/, SS 4000 mg/ from which ammonia was removed by cation exchange treatment has an ammonia nitrogen concentration of 6500 mg/, respectively.
5500mg/, 4500mg/, 3500mg/, 3200mg/
, NH ₄ C was added to give 2500mg/,
These were operated for 6 months at a fermentation temperature of 35°C while passing water at a rate of 1.5/day (residence time 1.33 days) into a UASB reaction tank in which no granulated sludge was present and inoculated with urine digested sludge 1.0. mainly
The BOD removal rate was investigated. The average BOD removal rate during the period when it was determined that a steady state had been reached is shown in Figure 3.

From this result, the influence of ammonia nitrogen concentration on BOD removal ability is as follows: NH ₄ -N is 2500 mg/
It was found that the amount changed significantly between 3500mg/. In addition, in a treatment experiment of human waste with a NH ₄ -N concentration of less than 2500 mg/N, granules with a particle size of 1 to 2 mm were formed by methane bacteria, and the sludge concentration in the UASB reaction tank was over 50,000 mg/N, but with an NH 4 -N concentration of over 3500 mg/ In the UASB reaction tank through which human waste with _{a -N} concentration was passed, granulation of sludge did not occur even after 6 months of operation, and floc-like sludge was present, and the sludge concentration was as low as 4000 mg/day. Ta. That is, when the NH ₄ -N concentration was 3500 mg/or more, a sufficient concentration of methane bacteria could not be maintained in the UASB reactor, and therefore only a low performance with a BOD removal rate of 36% or less was obtained.

We further investigated the permissible ammonia nitrogen concentration for granule formation, assuming other conditions were the same, and found that up to 3200 mg/NH ₄ -N would require approximately 3 months of operation, as shown in Figure 3. It was found that granulation of sludge was achieved and the BOD removal rate was over 77%, which is a rapid increase compared to cases with higher NH ₄ -N concentrations. The amount of methane gas generated at this NH ₄ -N3200mg/ is 4.46/NH ₄ -
The amount of methane gas generated was 1.25/about 3.6 times that of treated human waste 1 when N3500mg/N, which was sufficient.

Next, SS concentration 7000mg/human waste (BOD20000mg/, ammonia nitrogen concentration 3000mg)
mg/(concentration adjusted by cation exchange),
SS concentration is 6000mg/, 5000mg/, 4000 respectively
mg/, 3000mg/, 2000mg/, 1000mg/
(7-fold dilution) and UASB
Using reaction tank (2), the BOD volume load is 8
A treatment experiment was conducted by passing human waste at each dilution level so that the rate was constant at 3 kg/m ³ days. A similar treatment experiment was also conducted for the undiluted product. The residence time at this time is 2.5 in the UASB reaction tank that processes undiluted human urine.
The UASB reaction tank processes human urine diluted 7 times per day.
It was 0.36 days. The fermentation temperature was the same in all cases at 35°C. Figure 4 shows the average BOD removal rate expressed as the SS of input human waste during the approximately 7 months of operation, when the treatment is thought to have finally stabilized. SS concentration in human urine is 5,000mg/
The BOD removal rate in the following cases is high at over 80%, in which case the amount of methane gas generated per day was as high as 7.8/day, while the SS concentration was 6,000 mg/day.
In the above cases, the BOD removal rate decreases extremely (25
% or less), and the amount of methane gas generated was also low at 1.7/day. This is because when using the UASB method to treat human waste with a high SS of 6000 mg/min or more, a large amount of scum is generated and all the granules that have been formed float to the surface, making it impossible to increase the sludge concentration in the UASB reaction tank. It was due to something.

[Brief explanation of drawings]

Figure 1 shows the relationship between the number of days that has passed and the BOD removal rate when undiluted human waste is processed using the UASB method, and Figure 2 shows the relationship between the number of days that has passed and the BOD removal rate when human waste that has been diluted 5 times is processed using the UASB method. A diagram showing the relationship between the BOD removal rate, Figure 3. A diagram showing the relationship between the ammonia nitrogen concentration (mg/) in human waste and the BOD removal rate when human waste is treated by the UASB method, Figure 4.
The figure shows the relationship between the SS concentration (mg/) in human waste and the soluble BOD removal rate when the human waste is processed by the UASB method.

Claims (1)

[Claims] 1. In a method of treating human waste water by methane fermentation using an upflow anaerobic sludge blanket method, the concentration of ammonia nitrogen contained in human waste is
3200mg/or less and suspended solids concentration is 5000
An anaerobic digestion method for night soil wastewater, which is characterized by diluting it to less than mg/mg and then subjecting it to methane fermentation treatment.