Hydrogen fermentation of food waste without inoculum addition

A novel batch process that produces H2 without inoculum addition was devised based on two facts: (1) the abundant indigenous microflora found within organic solid wastes and (2) batch H2 production completion times being in the same range with hydraulic retention times at continuous processes. Food waste successfully served not only as a substrate but also as a source of H2-producing microflora when heat (90 °C for 20 min), acid (pH 1.0 for 1 d), or alkali (pH 13.0 for 1 d) treatment was applied. Among the three pretreatments, the heat treatment showed the best performance. The role of the pretreatment was the selection of microbial population rather than the enhancement of hydrolysis. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis showed that lactic acid bacteria were the most abundant species in untreated food waste while H2-producing bacteria were dominant in the pretreated food wastes. The increase of pretreatment temperature depressed the lactate production while increased the H2/butyrate production. Repeated batch operation performances were impressive and reliable, achieving a very high H2 yield of 2.05 mol H2/mol hexoseconsumed with a margin of 17% error. As this invented method is simpler than those of existing continuous systems, and does not require a start-up period, this method is thought to be practically applicable.