JPS6154290A - Single-phase fermenting method by immobilized microbe - Google Patents

Abstract

PURPOSE:To accelerate methane fermentation and to reduce remarkably the number of days for retaining waste water in a fermenter by cultivating and propagating microbes capable of fermenting methane and immobilized on a carrier, and bringing the obtained immobilized microbes into contact with waste water contg. org. materials. CONSTITUTION:When waste water contg. org. materials is methane-fermented, microbes immobilized on a carrier and capable of fermenting methane are firstly cultivated and propagated, and the obtained immobilized microbes are brought into contact with said waste water to carry out single-phase methane fermentation. Consequently, the microbe concn. in a fermenter is increased, the number of days for retaining waste water in the fermenter is remarkably reduced, and excess sludge is reduced. When sludge digested at moderate temps. is used as said seed sludge, the culture of microbes and contact with waste water are appropriately carried out at 20-45 deg.C, preferably at 35-40 deg.C, and at 6.5-8.5pH, preferably at 7.0-8.0pH. When sludge digested at high temps. is used, said process is appropriately carried out at 45-60 deg.C, preferably at 50-55 deg.C, and at 6.5- 8.5pH, preferably at 7.0-8.0pH.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a single-phase methane fermentation method using immobilized microorganisms.

Generally, in the methane fermentation method, acid-producing bacteria and methane-producing bacteria are separated from among the microorganisms involved in methane fermentation, and each of these is cultured under optimal conditions.In the acid production process, organic matter is removed by the action of the acid-producing bacteria. decomposes to obtain lower fatty acids,
In the methane production process, there is a method in which acid is decomposed by the action of methanogenic bacteria to obtain methane and carbon dioxide, and there is a method in which fermentation is carried out in one step without separating microorganisms as described above. In this specification, the former method will be referred to as a two-phase methane fermentation method, and the latter method will be referred to as a single-phase methane fermentation method. This invention relates to the latter, that is, improvements to the single-phase methane fermentation method.

Prior art and its problems Methane fermentation is an excellent energy production method that can recover methane gas at the same time as wastewater treatment. In particular, the single-phase methane fermentation method, in addition to the above points, produces less waste and Since it is easy to operate, it is advantageous as an energy-saving method. However, in the conventional single-phase methane fermentation method, the growth rate of methane-producing bacteria is slow, and when the number of days the wastewater stays in the tank is shortened, organic acids accumulate, which directly or indirectly lowers the pH and causes methane production. This requires a retention period of 10 to 30 days to inhibit the growth of the producing bacteria.For this reason, this fermentation method is not practical as an energy production process; Improvements were desired.In view of this point, a method has been proposed in which lower fatty acids or lower alcohols are added to sludge containing methane-fermenting bacteria to promote the growth of bacteria (Japanese Patent Publication No. 56-38117). However, the reality is that satisfactory results have not yet been obtained.

Means for Solving the Problems This invention was made for the purpose of providing a methane fermentation method that can meet the above-mentioned demands for improvement. In fermentation, first, microorganisms with methane fermentation ability immobilized on a carrier are cultured and grown, and then the immobilized microorganisms are brought into contact with organic matter-containing wastewater.

When medium-temperature, digested sludge from a sewage treatment plant is used as the seed sludge, the culture of immobilized microorganisms and the contact of the immobilized microorganisms with organic matter-containing wastewater are carried out at a temperature of 20-45°C, preferably 35-45°C.
40°C, pH 6.5-8.5 preferably 7.0-8.0
carried out under the following conditions.

In addition, when using high-temperature digested sludge, culture of immobilized microorganisms and contact of immobilized microorganisms with organic matter-containing wastewater are carried out at a temperature of 45 to 60°C, preferably 50 to 55°C, and a pH of 6.5 to 8.
．． 5 preferably under conditions of 7°0 to 8.0°.

Examples of microorganisms having methane fermentation ability include Methanococcus fj, Methanococcus fj, Methanococcus spp.
Methanobacterium H, a bacterium belonging to the genus rcina)
vlethan.

Examples include bacteria belonging to the genus Bacterium.

Immobilization of microorganisms is carried out as follows by a known entrapping method in which microorganisms are wrapped in a gel-like carrier. That is, after a predetermined amount of microbial cells are mixed into an aqueous solution of a gel base, the mixed solution is cooled or brought into contact with a gelling agent, and the resulting gel is formed into particles or films of a desired size.

In addition, when polyacrylamide is used as a gel substrate, acrylamide monomer, a crosslinking agent, an m-merization accelerator, and a polymerization initiator are added to a solution containing a predetermined amount of microbial cells, and the monomers are polymerized. Mold it like this. Carrageenan, sodium alginate, polyvinyl alcohol, polyacrylamide, polyurethane, etc. are used as the gel base, potassium chloride, calcium chloride, magnesium chloride, etc. are used as the gelling agent, and N is used as the crosslinking agent.

N'-methylenebisacrylamide or the like is used, β-dimethylaminopropionitrile or the like is used as a polymerization accelerator, and potassium persulfate or the like is used as a polymerization initiator.

Methane fermentation by contacting immobilized microorganisms with organic matter-containing wastewater may be either batch fermentation or continuous fermentation.

Further, as the fermenter, a mechanically stirred fermenter, a fixed bed fermenter, a fluidized bed fermenter, etc. are used.

Examples of wastewater containing organic matter include wastewater containing municipal waste, sewage sludge, sludge from valves, food processing wastewater such as alcohol distillation waste, and human waste.

Effects of the Invention According to the methane fermentation method of the present invention, microorganisms capable of methane fermentation are immobilized on a carrier and the immobilized microorganisms are grown. In addition to significantly reducing the number of days that sludge remains in the tank, the use of immobilized microorganisms also reduces excess sludge. Therefore, the methane fermentation method according to the present invention is an excellent practical process.

EXAMPLES Next, examples of the present invention will be shown to illustrate the effects of the present invention.

Example 1 (1) Preparation of immobilized methane-fermenting bacteria
/I, dipotassium hydrogen phosphate 30/l.

A synthetic wastewater consisting of 2a/1 potassium dihydrogen phosphate, 5(]/l ammonium carbonate, 3(]/11 sodium carbonate, 19/l ferric chloride hexahydrate) was prepared, and this was used as a culture medium. Medium-temperature stratified sludge from a sewage treatment plant was acclimatized to pH 7 to 8 at a temperature of 37°C in a culture medium, and 100ml of the obtained acclimatized sludge was concentrated to 2Qml.This concentrated sludge was sterilized and kept at a temperature of 40°C. It was mixed with 180 ml of a 4% carrageenan aqueous solution, and the mixed solution was dropped into a 2% potassium chloride aqueous solution at a concentration of 1.51.A bead-shaped gel with a diameter of about 4 mm containing the methane-fermenting bacteria was thus formed.

Then, the obtained immobilized bacteria were incubated in a medium with the above composition at a temperature of 37°C.
The cells were cultured for 24 hours at p) -17 to 8 for proliferation.

(2) Production of methane The above synthetic wastewater 1/ and the grown immobilized methane-fermenting bacteria were placed in a mechanically stirred fermenter with an actual volume of 21, and the temperature was 37°C while stirring.
24 It at pl-17~8 at °C;? Intermittent batch fermentation was performed. Then, the synthetic wastewater was supplied once a day so that the organic matter load was one predetermined shift, and continuous fermentation was performed. The wastewater was supplied by stopping the stirring for 10 minutes, then drawing out the culture solution corresponding to the supplied amount from the tank, and then introducing the wastewater into the tank. The volume of fermentation liquid was adjusted so that the total volume including carrier beads was 11.

When continuous fermentation was carried out in this way, the organic matter load was 11
Even in KO/m 3 ・day, the organic matter is 2.5!
It was possible to obtain a methane-containing gas containing 50 to 55% of methane gold at a generation rate of 6.51/l/day without leaving 7//L.

Example 2 (1) Preparation of immobilized methane-fermenting bacteria High-temperature digested sludge from a sewage treatment plant was acclimatized with alcohol distillation waste liquid at a temperature of 51°C and pH 7 to 8, and the obtained acclimatized sludge 100
After concentrating 111/ to 20 ml, the concentrated sludge was suspended in sterilized physiological saline 14 Qm/. Alcohol distillation waste liquid is 280g// of Philippine molasses and 1 urea.
．． Alcohol fermentation for 24 hours using a medium consisting of 4 g//
haromyces cerevisiae I
This is a waste liquid obtained by boiling the fermented liquid after carrying out FQ Q 224) for about 4 hours to scatter the alcohol. The BOD of this waste liquid was 33000 m (+/1).

Acrylamide monomer 159 and N,N-methylene bisacrylamide 0.89 were added to the suspension of methane-fermenting bacteria.
2Q+n1 of 5% β-dimethylamine propionitrile and 20 ml of 2.5% potassium persulfate were added. Next, the mixed solution was injected into four vats of 10 cm x 10 cm, and left at a temperature of 25 °C for 15 minutes to obtain a polyacrylamide gel by polymerizing the monomers.
This gel was cut into cubes with sides of about 5 mm.

In this way, methane-fermenting bacteria were immobilized.

Then, the obtained immobilized bacteria were cultured in the alcohol distillation waste liquid for 24 hours at a temperature of 51 DEG C. on points 17 to 8 for proliferation.

(2) Methane production A fluidized bed fermenter with an actual volume of 11 shown in the attached drawing was used as the fermenter. The same phase mainly consists of a small-diameter flow section (2) with a jacket (1) and a large-diameter settling section (3) for bacterial cell sedimentation connected above this, and the flow section (2) has temperature and I ) H control display device (4) is provided, and the sedimentation section (3)
is equipped with a cylindrical gas separation chamber (5) for separating the generated gas from the fermentation liquid. Then, wastewater containing wastewater is supplied to the bottom of the tank, and treated wastewater is overflowed from the top of the tank. Further, a part of the waste water at the top of the tank is circulated to the bottom of the tank, and the content of the generated gas is measured with a wet gas meter (6).

The fermenter with the above configuration was filled with the immobilized methane fermenting bacteria and the alcohol distillation waste liquid, and the temperature was 51°C and the pH was 7 to 8.
After daily batch fermentation, alcohol distillation waste liquid was continuously supplied to carry out continuous fermentation. Then, the reaction rate was examined by gradually increasing the amount of alcohol distillation waste liquid supplied.

As a result, the maximum BOD load is approximately 15Kg/m3・d
ay, and the BOD of the treated wastewater at this time is approximately 2000mg// (the BOD of the raw water is 3300Qm (
1/l), and approximately 0.71 methane could be recovered per 1 g of BOD.

Example 3 (1) Preparation of immobilized methane-fermenting bacteria.
Temperature 37 with alcohol distillation waste liquid of 53000 mg/l
Acclimated sludge 1 which was acclimatized at pI-17 to 8 at ℃ and 1!7
After concentrating and binding 00n+1 to 20m/bin, this concentrated sludge was mixed with a sterilized 2% sodium alginate aqueous solution kept at a temperature of 40'C if! 218Qml, and the mixed solution was mixed with 1.
51 O, 1M calcium chloride aqueous solution. In this way, bead-shaped gels with a diameter of about 4 mm were formed that contained methane-fermenting bacteria.

The immobilized bacteria thus obtained were then cultured in the alcohol distillation waste liquid for 24 hours at a temperature of 37° C. and a pH of 7 to 8 for proliferation.

(2) Production of methane In Example 2, a fluidized bed type Hikari fermentation with an actual volume of 11 was filled with the alcohol distillation separate liquid and the immobilized methane fermentation bacteria, and the temperature was 37°C and the temperature was 24. After carrying out time-batch fermentation, the above-mentioned alcohol distillation waste liquid was supplied, and the supply amount was gradually increased to increase the BOD load and the reaction rate was investigated.

As a result, the BOD load could reach a maximum of 8 kg/m3·day, and methane-containing gas with a methane content of 60% could be provided at a generation rate of 91//·day. The BOD of treated wastewater at this time was 1300+++g/
l (Raw water BOD Ha33000111 g/l
), and the amount of sludge produced is approximately 0.04 [I MLSS/(
It was 1.BOD.

Example 4 (1) Preparation of immobilized methane-fermenting bacteria A gel containing methane-fermenting bacteria was formed in the same manner as in Example 3, and the methane-fermenting bacteria were grown.

(2) Production of methane After performing batch fermentation using the same fermentation tank and operation as in Example 3, peptone 0.87 (1/1), meat nitrate,
67! II/! ', Urine No., 2(]/l, Disodium hydrogen phosphate 0.179//, Sodium chloride 5
0mg/l, potassium chloride 201T1g/l, magnesium sulfate 201nQ/l, calcium chloride 20mg//
The reaction rate was investigated by supplying a synthetic wastewater of 50% by volume, gradually increasing the supply amount, and increasing the 80D load.

As a result, the BOD load is maximum r5K (1/113・da
At this time, methane-containing gas with a methane content of 60% can be obtained at a generation rate of 3.5//l) day, and 80D of treated wastewater is 100+ng/l.
(The BOD of raw water was 1000n+ (]/l).

[Brief explanation of the drawing]

The drawing shows the fluidized bed type Hikari 5 fermentation layer used in Examples 2 to 4! ! FIG. (2)...Flowing section, (3)...Settling section, (5)...
・Gas separation member. 2 Rakido Iku 3゛ Gorge S descending section 577゛ Also divided S material

Claims (6)

[Claims] (1) In methane fermentation of organic matter-containing wastewater, immobilization is characterized by first culturing and multiplying microorganisms with methane fermentation ability immobilized on a carrier, and then bringing the immobilized microorganisms into contact with organic matter-containing wastewater. Single-phase methane fermentation method using microorganisms. (2) The methane fermentation method according to claim 1, wherein the operation is carried out at a temperature of 20 to 45°C and a pH of 6.5 to 8.5. (3) The methane fermentation method according to claim 2, wherein the methane fermentation method is operated under conditions of humidity of 35 to 40°C and pH of 7.0 to 8.0. (4) The methane fermentation method according to claim 1, wherein the methane fermentation method is operated under conditions of a temperature of 45 to 60°C and a pH of 6.5 to 8.5. (5) The methane fermentation method according to claim 4, wherein the methane fermentation method is operated under conditions of a temperature of 50 to 55°C and a pH of 7.0 to 8.0. (6) The methane fermentation method according to any one of claims 1 to 5, wherein the immobilization of microorganisms is carried out by an entrapment method.