JPS63185499A - Methane fermentation method - Google Patents

Abstract

PURPOSE:To generate a high-calorie gas with high efficiency by deproteinizing blood stock, etc., methane-fermenting the stock, circulating the generated gas to agitate the methane-fermentation soln., and removing ammonia and hydrogen sulfide in the course of circulation. CONSTITUTION:Acetic acid, etc., are added to the blood stock or meat stock generated from the aquatic food processing to coagulate and separate protein. When the deproteinized soln. is methane-fermented in a methane fermenter 1, the methane fermentation soln. 5 is agitated by circulating the generated gas. Ammonia is removed by the sulfuric acid 3 in a sulfuric acid tank 22 in the course of circulation, and hydrogen sulfide is removed by the iron oxide 4 in an iron oxide-packed vessel 23. As a result, the blood stock or meat stock which has been difficult to normally methane-ferment heretofore can be used as the raw material in this method, a high-calorie gas can be stably generated with high efficiency from the material, and the separated and recovered protein can be used as a high-quality feed stuff.

Description

[Detailed Description of the Invention] The present invention uses blood juice and broth discharged in the fishmeal production process and other seafood processing processes as raw materials, and can generate fuel gas with a high calorific value at a high rate. This invention relates to a methane fermentation treatment method using methane.

Traditionally, most of the fish iliac bones collected from fresh fish such as sardines, fresh fish dealers, canners, and other processors have been used as feed after undergoing a fishmeal manufacturing process. In this fishmeal manufacturing process, a large amount of blood juice and broth are discharged, and these are generally disposed of as follows.

That is, in the case of blood juice, it is diluted with water, subjected to biodegradation treatment, and then released as purified wastewater that is below the water quality regulation value. On the other hand, in the case of broth, it is either subjected to the above-mentioned biodegradation treatment and then released, or it is heated and concentrated and reused as fish soluble.

However, when treating blood juice or broth using such a method, there are various problems as described below. Now, taking broth as an example, the properties of this broth are generally about 10% solids (wt%), about 9% organic matter, and about 9% organic matter.
BOD is approximately 60,000 mg/j, COD is approximately 11,000
mg/jt, total nitrogen is about 12000mg/J! Since the total carbon content is approximately 48,000 mg/1 and the carbon ratio (C/N ratio) is low at 4, there is a problem that even if biodegradation treatment is performed, it does not decompose quickly and cannot be processed efficiently. . On the other hand, when heating and concentrating to make fisch soluble, there is a problem that the energy cost is high because the water content in the broth is high and a large amount of heat energy is required. Nowadays, with prices down, it is no longer possible to make ends meet. However, if fishmeal is produced using fresh fish as raw material, it is still good because the obtained fish soluble can be used for whole meal production by inputting it into the drying process during fishmeal production. When producing fishmeal using iliac bones as a raw material, the resulting Finsch soluble has quality problems such as oxidation of oil, so it cannot be used to produce whole meal, and it is difficult to process it. The reality is that it hurts my head.

In light of these circumstances, attempts are being made to recover and utilize boiled broth and blood juice as an energy resource by subjecting them to methane fermentation treatment.

However, as mentioned above, broth has a low carbon content and contains many sulfur-containing amino acids, so normal medium-temperature fermentation using a mechanically stirred single-tank methane fermentation tank has an adverse effect on methane-fermenting bacteria. There is a problem in that the concentration of ammonia and hydrogen sulfide that cause methane increases over time, making normal methane fermentation difficult and significantly reducing the amount of gas generated. Moreover, since the BOD value and COD value of the digestive fluid are high, there is also the problem that post-treatment of this digestive fluid is not easy.

Therefore, the present inventors conceived of a processing system that would kill two birds with one stone by separating and recovering colloidal proteins from broth and blood juice, improving the processing efficiency of methane fermentation, and effectively using the separated and recovered proteins as feed. , proceeded with research. However, although the effect of improving methane fermentation is recognized to some extent by simply separating colloidal proteins from boiling liquid, it is not satisfactory because a considerable amount of ammonia and hydrogen sulfide are generated from the nitrogen-containing compounds and sulfur-containing compounds that are still dissolved. However, it is difficult to carry out methane fermentation, and therefore it has become necessary to fundamentally improve the methane fermentation process itself.

The present invention was made based on the above-mentioned circumstances, and uses broth and blood juice as raw materials, which have hitherto been difficult to normally perform methane fermentation processing, and then stabilizes gas with a high calorific value at a high rate. The purpose is to provide an innovative methane fermentation treatment method that can generate methane.

In order to achieve this objective, the methane fermentation treatment method of the present invention involves circulating the gas generated when methane fermentation is carried out in a methane fermentation tank of a liquid obtained by deproteinizing blood juice or broth. The gist is that the methane fermentation liquid is gas-stirred and that ammonia and hydrogen sulfide are removed during the gas circulation.

13F11 As in the present invention, when the generated gas is circulated and the methane fermentation liquid is stirred, and ammonia and hydrogen sulfide are removed during the gas circulation, the ammonia and hydrogen sulfide generated in the methane fermentation liquid are removed. Since it is circulated in a stirred gas and removed during the circulation, the concentration of harmful ammonia and hydrogen sulfide in the methane fermentation tank is significantly reduced. Therefore, methane-fermenting bacteria become actively active and normal methane fermentation continues, resulting in the stable generation of high-calorie gas at a high rate, and the BOD and COD values of digestive juices.
The value also becomes extremely small.

Hereinafter, the methane fermentation treatment method of the present invention will be explained in detail with reference to Examples.

FIG. 1 is a flowchart of a methane fermentation process according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a methane fermentation tank equipped with a gas circulation device used in the present invention. According to the methane fermentation treatment method of the invention, first, blood juice or broth as a raw material is diluted to about twice the amount with water. The blood juice used as a raw material is the liquid discharged from the storage pit and transport pinto, and contains exudate from the fish body, blood, internal organs, pieces of meat, etc. The broth used as a raw material is the liquid discharged from the cutter, and contains fish body exudates, blood, internal organs, pieces of meat, etc. Contains extracts, blood, internal organs, meat juice components (proteins), and bone components. The properties of this broth are as described above, and approximately 80% of the solid matter is crude protein.

After diluting the raw material broth, etc., approximately 1% by volume of acetic acid is added to the diluted solution. When acetic acid is added in this manner, the colloidal proteins in the diluted solution are brought to a state where they are approximately at the isoelectric point, so that they rapidly aggregate. In this example, acetic acid, which is preferred as a flavoring agent, is added to aggregate proteins, but other organic acids such as formic acid or inorganic acids may also be added to aggregate proteins, provided the raw materials are of low concentration. , the aggregates may be separated directly by diluting several times.

Once the proteins have aggregated, the aggregates are then centrifuged in a high speed centrifuge. The aggregates separated and collected in this way contain about 83% water, and are pre-dried to remove about 50% water.
%, it can be processed into pellets. When this is dried, most of the attached acetic acid evaporates and a small amount of acetic acid remains as a feed flavoring agent, yielding a valuable high-protein feed (about 80% crude protein).

When the protein removal treatment is performed as described above, about 15% of nitrogen-containing compounds and sulfide-containing metals harmful to methane fermentation are removed, and the content is reduced from about 6,500 mg11 to about 5,500 mg/j.
However, as mentioned above, the raw material liquid still contains a considerable amount of soluble proteins, sulfur-containing amino acids, etc. Even if it is placed in a stirring single-tank methane fermentation tank and subjected to medium temperature fermentation, it is difficult to carry out methane fermentation normally.

Therefore, in the present invention, the protein-removed solution is introduced into a solubilization tank and subjected to acid fermentation for 5 days, and then introduced into a methane fermentation tank equipped with a gas circulation device as shown in Fig. 2 for 20 days. The gas circulation device 2 attached to this methane fermentation tank 1, which performs methane fermentation using a medium temperature or high temperature fermentation method, has a sulfuric acid tank 22 and an iron oxide filling tank 23 connected in series in the middle of a circulation pipe 21, as shown in the figure. Both ends of the circulation pipe 21 are connected to the top and bottom of the methane fermentation tank 1, respectively. Therefore, the gas generated in this methane fermentation tank 1 passes through the circulation pipe 21 from the top and comes into contact with the sulfuric acid 3 in the sulfuric acid tank 22, and then comes into contact with the iron oxide 4 in the iron oxide filling tank 23 to produce methane. Returning to the bottom of the fermentation tank 1, the methane fermentation liquid 5 is bubbled and circulated while stirring the gas.

When the methane fermentation liquid 5 is stirred with the circulating gas in this way, harmful ammonia and hydrogen sulfide generated in the methane fermentation liquid 5 are retained in this stirring gas, and are directly transferred to the circulation pipe 2.
During the circulation, ammonia is removed as ammonium sulfate by contact with sulfuric acid 3 in a sulfuric acid tank 22, and hydrogen sulfide is removed as iron sulfide by contact with iron oxide 4 in an iron oxide filling tank 23. be done. Therefore, when this gas circulation is repeated, the concentration of ammonia and hydrogen sulfide decreases significantly, and the amount of ammonia in the methane fermentation liquid 5 is about 270.
It remains almost constant at 0 mg/J, and hydrogen sulfide in the circulating gas is about 7
It decreases to 8 ppm. Therefore, methane-fermenting bacteria are active and normal methane fermentation continues, so high-calorie gas is stably generated at a high rate of approximately 0.6311/g (decomposition rate of approximately 63%). I come to do it.

In this embodiment, a sulfuric acid tank 22 and an iron oxide filling tank 23 are installed in the middle of the above-mentioned circulation pipe 21 as the gas circulation device 2, and ammonia and hydrogen sulfide are removed separately. Alternatively, a gas circulation system with only one tank filled with iron sulfate may be used to remove ammonia and hydrogen sulfide at the same time. Rather than directly returning the gas to the methane fermentation tank, part or all of it may be returned to the methane fermentation tank via a solubilization tank.

The digestion gas obtained in the above manner contains 70% methane,
It has a composition of 29% carbon dioxide gas and 1% other substances, and has a large calorific value of about 6000 Kcal/N-nf, so it can be used directly as a fuel or converted into electricity and used as alternative energy for fishmeal production and other purposes. Can be done.

On the other hand, digestive juice has a BOD of about 4000 mg/j or less,
The BOD removal rate by methane fermentation is as high as about 90% or more, and the COD is about 2000 mg 71 or less. Therefore, this digestive fluid can be diluted with water and easily purified using the normal activated sludge method, etc.
It is sufficient to discharge the wastewater as wastewater whose water quality is below the water quality regulation value through purification treatment.In some cases, it is also possible to carry out transpiration treatment using a blower method, taking advantage of the fact that the temperature of the digestive fluid is relatively high at approximately 35°C. .

For reference, if we calculate the income and expenditure for one year when 60 tons of fish juice per day is subjected to methane fermentation using the method of the present invention and the recovered protein is converted into feed, it is as follows: 43,400,000 yen/year
Therefore, considering the cost of 35,000,000 yen/year required for conventional heating and concentration, the annual
This will result in a profit of 0,000 yen.

Expenditure Acetic acid 44,000,000 yen/year Running cost 22,600,000 yen/year Income Recovered protein feed
44,000,000 yen/annual deduction 43.4
00,000 yen/year Also, it is clear from the above explanation that according to the methane fermentation treatment method of the present invention, it is possible to use fish juice and blood juice as raw materials, which were conventionally difficult to undergo normal methane fermentation treatment. From this, a gas with a large calorific value can be stably generated at a high rate, and the separated and recovered protein can also be used as high-quality feed. Therefore, the present invention is a useful invention that greatly benefits the fishery processing industry, particularly the fishmeal manufacturing industry, and is also an excellent invention in terms of pollution prevention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart of a methane fermentation process according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a methane fermentation tank with a gas circulation device used in the present invention. 1... Methane fermentation tank, 2... Gas circulation device, 21.
... Circulation pipe, 22... Sulfuric acid tank, 23... Iron oxide filling tank, 3... Sulfuric acid, 4... Iron oxide, 5... Methane fermentation liquid.

Claims (1)

[Claims] (1) When carrying out methane fermentation in a methane fermentation tank with a liquid obtained by removing protein from blood juice and broth discharged during the seafood processing process,
A methane fermentation processing method characterized in that the generated gas is circulated to stir the methane fermentation liquid, and ammonia and hydrogen sulfide are removed during the gas circulation.