|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Integrated research on agricultural waste reclamation|
Because soybean cooking waste has such a high COD value, it is one of the most difficult of all food industry wastes to treat in Japan. Consequently, there are many devices to treat soybean cooking waste via mechanical, chemical, or biological methods.
In 1970, an industrial co-operative was formed to treat this waste. It was established by nine members from a miso factory at Maruko, Nagano Prefecture (4). This is the sole factory in Japan where SCP is being made from agro-industrial waste, except for factories that make torula yeast from spent sulphite liquor.
As shown in Figure 1, soybean cooking waste is sent to the factory by tank trucks or pipelines directly from the miso factory cookers. After the pH value is adjusted to 4.0 in a serving tank, the waste is transferred into a Waldhof continuous fermenter of 15 kl capacity. In the fermenter, Torulopsis xylinus is cultivated, with an anti-foaming agent, at 30°Cat a dilution rate of 0.3 - 0.4 hr(-1) without any other nutrient supplements. Maximum production of dehydrated yeast is 800 kg when 80 tons of waste are supplied and COD is reduced by 70 - 75 per cent. For purpose of lowering production costs, the yeast milk, after washing and heating at 80°C for 30 min., is often delivered to neighborhood farms.
At present, this method has problems that must be solved: (i) the 70 - 75 per cent COD reduction rate should be raised still further; (ii) microbial contamination, originating mainly during transportation of the waste in tank trucks, must be eliminated; and (iii) the process, although small in scale, requires trained technologists to conduct it properly, resulting in higher costs to the consumer.