Household food waste has been treated in various ways, such as landfill, incineration, composting and fermentative process for the conversion to animal feed. However none of these processes are totally successful to handle the increasing amount of food waste. One of the main reasons that inhibits the efficient treatment of food waste is its high moisture content, normally over 80 percent. Therefore this study is aimed at biological treatment of the liquid fraction of food waste which is separated from the highly-wet food waste, and further recycling of the biomass as animal feed.
High salt concentration and low pH are known as inhibitory factors in biological treatment of food waste. Saccharomyces carlsbergensis0644 and Bacillus sp.B1 were selected for this experiment after tolerance tests for high NaCl and low pH environment.
The selected Bacillus sp. has high α-amylase activity and S.carlsbergensis shows easy-flocculating and bottom fermenting characteristics that ensure its high recovery rate of the biomass. These two strains were found to be tolerant even at 3% NaCl concentration, also the growth were not completely inhibited by low pH conditions.
To determine the optimum operating factors for continuous operation, several batch tests were performed. It was found that co-culture of S.carlsbergensis and Bacillus sp. was mostly efficient in soluble COD removal. Aeration rate and HRT was determined at 150 mL/min ad 1.5 day respectively for the continuous operation. Four hybrid reactors were operated under acrated and anacrobic conditions. The reactors were operated for three phases at different substrate loading levels, started from sCOD 5000 ㎎/L and increased by 5000 ㎎/L up to 15000 ㎎/L. The reactor of S.carlsbergensis and Bacillus sp. co-culture showed 48% sCOD removal rate which was almost 10% higher than that of the control reactor. Also high ethanol production was monitored in the anaerobic reactor. The high concentration ethanol in the effluent can be used afterwards. as a good carbon source in various wastewater treatments. For further use of the biomass from the continuous reactors, the protein concentration of S,carlsbergensis was analyzed. It was 50.61%, in dry matter basis, which seems high enough as protein supplement for animal.