JPH035796B2 - - Google Patents

Description

[Detailed description of the invention]

A. Field of Industrial Application The present invention relates to stabilizing means for immobilizing anaerobic fermentation microorganisms using a substance that gels with polyvalent metal ions as a carrier. B. Prior Art Polyacrylic acid gels and alginate gels cross-linked with calcium ions are widely used as materials for immobilizing microorganisms. However, in anaerobic fermentation, cross-linked calcium is removed due to the production of lower fatty acids in the initial stage, the gel strength is weakened, microorganisms are washed out, the gel collapses, and it cannot withstand long-term use. There is a method of adding a large amount of calcium ions to the fermentation stock solution to prevent calcium desorption from the gel, but there is a risk that the microorganisms will be out of the adaptation range for the calcium ion concentration, and furthermore, the solution after fermentation will become extremely hard water. Unfavorable for processing. Gel preservation can also be achieved by adding a large amount of water-soluble calcium salt in advance during gel preparation, but calcium ions are quickly eluted into the fermentation liquid and the gel strengthening effect is temporary. Furthermore, anaerobic microorganisms lose their physiological activity in extremely concentrated calcium ion solutions. C Problems to be Solved by the Invention The present invention solves the problem of low strength stability of microorganism immobilization carriers, which was unavoidable in the past in various fields that utilize the above-mentioned anaerobic microorganisms, especially in the water treatment field.
The purpose of the present invention is to provide a new method for stabilizing an immobilized microorganism carrier that can solve all of the drawbacks such as not being able to withstand long-term use, changing the liquid properties of the fermentation liquid, and losing physiological activity of microorganisms. D Means for Solving the Problems According to the present invention, a stabilization method is provided for immobilizing anaerobic fermentation microorganisms using a substance that gels with polyvalent metal ions as a carrier. In the process of intensive research into microbial immobilization technology, the present inventors discovered that the initial stage of fermentation was improved by adding sparingly soluble calcium carbonate to the carrier material in advance as a countermeasure against rancidity and deactivation during anaerobic fermentation. They discovered and announced that it neutralizes the produced fatty acids and prevents rancidity and deactivation [Honda, Murakami, Sano; Water Treatment Technology Vol. 27, No. 9, p. 619 (1986)]. Although it has been successfully utilized, simply adding an arbitrary amount of calcium carbonate cannot prevent the disintegration of the carrier. The solubility of calcium carbonate is extremely small (0.052 g/or Ca 0.5 mmol/30
°C) The concentration of calcium ions (Ca10 to 100 mmol/) required for solidification of alginate sol is only about 1/100, and contact with calcium carbonate alone has no effect on gelling and crosslinking. Too much calcium carbonate makes the gel brittle and easily crumbles from the beginning. However, in anaerobic fermentation, a two-step reaction of organic matter → lower fatty acids → (methane + carbon dioxide) takes place in succession, so when the initial stage reaction occurs within the carrier, calcium carbonate decomposes and becomes fatty acid calcium. , sequentially, the fatty acids generate methane and carbon dioxide and disappear, and at the same time regenerate calcium carbonate. This calcium carbonate recycling reaction mechanism was previously proposed by the inventors [Sano, Honda; Energy Resources Research Society Preliminary Lectures 5-1, 99 (1985)]; ―→ ←――― Methanated fatty acid calcium has not been numerically demonstrated. Therefore, the present inventors tested the disintegration properties of the carrier gel by increasing and decreasing the amount of calcium carbonate, and obtained the new finding that the life of the gel carrier can be significantly extended within a certain range of the amount of calcium carbonate added. . The present invention was completed based on this knowledge. Hereinafter, a method for stabilizing an immobilized microorganism carrier by incorporating a sparingly soluble carbonate of the present invention will be described in detail. In the method for stabilizing an immobilized microorganism carrier according to the present invention, the carrier gel used may be any substance that can be crosslinked into a gel by polyvalent metal ions, and typical examples thereof include sodium polyacrylate, alginic acid, and the like. In the method of the present invention, an anaerobic microorganism-containing carrier sol is prepared by stirring and mixing an anaerobic microorganism and a poorly soluble carbonate with a carrier sol. The amount of microorganisms at this time is appropriately determined depending on the type of carrier and the purpose of use.
The thus obtained anaerobic microorganism-containing carrier sol is then subjected to a crosslinking reaction using calcium ions to obtain an anaerobic microorganism-immobilized gel. The shape of the resulting gel can be any shape, such as bead-like, film-like, flake-like, granular, lump-like, etc., and its size is also not particularly limited, but granules are preferably 0.5 mm or more. It is appropriate that the distance is about 2 to 5 mm. The gel preservation mechanism by the poorly soluble carbonate of the present invention will be explained below using calcium carbonate as an example. The amount of calcium ions released by calcium carbonate is around 0.5 mmol, so the gel crosslinking effect is so small that it can be ignored. However, lower fatty acids are produced from organic matter within the carrier during the initial stage of anaerobic fermentation, and when the pH inside the carrier drops to 6 or less, calcium carbonate becomes solubilized and reacts with the lower fatty acids to produce fatty acid calcium. Since fatty acid calcium has a high solubility, calcium ions inside the carrier rapidly increase and can sufficiently support crosslinking of the carrier. On the other hand, free fatty acids are neutralized by calcium, so the PH inside the carrier does not drop and falls within the optimal activity range of methane-fermenting bacteria, and the fatty acids are actively decomposed into methane and carbon dioxide. After methane production, calcium is regenerated into calcium carbonate again by decomposed carbon dioxide. In the present invention, the amount of calcium carbonate added to the carrier material is 1 to 30 g/carrier, preferably 1 to 30 g/carrier.
10g/carrier (Example 1). Further, even when magnesium carbonate, iron carbonate, etc. or a mixture thereof is used, the range of addition amount is almost the same (Example 2). The same effect can be expected in principle as long as the carbonate used in the present invention is a metal that has crosslinking properties and forms a poorly soluble carbonate. However, since additives that have a significant effect on the physiological activity of anaerobic microorganisms cannot be used, the additives are actually limited to calcium carbonate, magnesium carbonate, iron carbonate, or a mixture thereof. E. Examples Hereinafter, an example of a method for stabilizing an immobilized microorganism carrier by mixing the hardly soluble carbonate of the present invention and a water treatment test example using the immobilized microorganism obtained thereby will be given as an example. Example 1 Commercially available sodium polyacrylate (degree of polymerization 22,000~
A microorganism-containing sol is prepared by preparing an 8% aqueous solution of 66000) and adding and mixing digested sludge from a sewage treatment plant (MLSS 10%, MLVSS 6%) and calcium carbonate. At this time, the concentration of sodium polyacrylate is approximately 4%.
becomes. The microorganism-containing sol is dropped into a 1.5% calcium chloride solution from a syringe and stirred for about 1 hour to cause a crosslinking reaction, thereby producing a microorganism-containing gel. The obtained gel particles had a diameter of 0.4 cm to 0.5 cm. These gel particles are filled into an anaerobic fermentation tank, and artificial sewage consisting of peptone, glucose, etc. is passed through it.
A digestion test was conducted using a mesophilic digestion method to examine the disintegration properties of the gel particles. The results are shown in Table 1. The degree of disintegration was calculated by assuming that the particles that did not pass through a sieve screen with a mesh size of 0.3 cm in water remained in their original shape.

[Table] Even without the addition of calcium carbonate, sufficient crosslinking occurs and gelatinization occurs in the initial stage, but as soon as sewage water is passed through, calcium ions begin to be washed out and collapse occurs. If there is too much calcium carbonate, the gel particles become brittle and easily collapse from the beginning. Example 2 A microorganism-containing sol was prepared in the same manner as in Example 1, and added carbonate was mixed at a ratio of 3 g/gel. The gel disintegration rate after gelation was tested. The results are shown in Table 2. *Acrylic acid-based water-absorbing resin gel was used.

【table】

[Table] Example 3 The gel on which the anaerobic microorganisms obtained in Example 1 were immobilized was filled into an anaerobic fermenter, and artificial sewage (0.4 g of peptone as organic matter/0.8 g of glucose/0.02 g of potassium phosphate as nutrients) (containing sodium bicarbonate to adjust pH to approximately 7) was added continuously, and anaerobic digestion was performed according to the mesophilic digestion method (37°C) to examine changes over time in the ability to decompose organic matter. The results are shown as line 1 in FIG. As a result of a comparative test, the organic matter decomposition ability without the addition of poorly soluble carbonates was shown as line 2.
The amount of organic matter in the supplied artificial sewage is shown as line 3. In Fig. 1, the vertical axis indicates products manufactured by Shimadzu Corporation;
The concentration of organic matter in water (mg/) measured using a total organic carbon measuring device is shown, and the horizontal axis shows the number of days of continuous operation (days) since the start of the test. From FIG. 1, as is clear from the comparison between line 1 in the case of addition of poorly soluble calcium carbonate and line 2 in the case of no addition (disintegration stopped after 15 days), the gelation stabilization method of the present invention shows that It is clear that the immobilized microbial gel can stably and sustainably exhibit the desired organic matter decomposition ability over a long period of time.

[Brief explanation of the drawing]

Figure 1 is a graph examining the daily change in organic matter decomposition ability of immobilized microbial gel.

Claims (1)

[Claims] 1. In anaerobic fermentation, when using a substance that gels with polyvalent metal ions, such as polyacrylic acid gel or alginate gel, as a carrier material for immobilizing anaerobic fermentation microorganisms, calcium, magnesium, iron carbonate or these 1. A method for stabilizing an immobilized microbial carrier, the method comprising containing a mixture of the following in a gel.