Effect of Rice Bran on Continuous Organic Waste Decomposition Processes

The mirobial decomposition process of househole waste, mainly food waste, is considered an environmentally friendly way to treat organic wastes. However, there are some problems which often occur, such as low conversion rate and bad smell generation, especially in the early stage of continuous operation systems. Rice bran has been known empirically as an acclerator or improving material for the microbial decomposition process of organic wastes. Unfortuantely, little information about the detailed findings has been obtained so far. This study intended to analyze the effect of rice bran as an activating agent in organic waste decomposition in order to minimalize the problems. Firstly, the effect of rice bran was confirmed. Reactor weight, temperature, moisture content, pH, and microbe number were measured and used as the parameters to confirm the effect of rice bran addition in the decomposition process. It was observed that the total waste reduction during the process was larger in the case of rice bran addition than that of the blank, i.e. without rice bran addition. The other parameters also showed similar tendencies, indicating that rice bran is surely capable of activating the decomposition process. Then, the growth accelerating effect for microorganisms in the composting process was examined by a cultivation test using trypticase-soy liquid medium. The microbe number in the medium with rice bran addition was higher than the medium without rice bran. Secondly, the factors contributing this effect were searched. Although we could narrow down the number of candidate constituent, among them magnesium was one of the major candidates, the precise identification was not possible, possibly because the effect of each nutrient on the microbes varies depending on the kind of microbial strain, and not a single but a combination of multiple nutrients may cause this effect. However, it was confirmed as a whole that rice bran shows a good influence on the growth of many micorbes in the composting process and accelerates the performance of decomposition.