Control of lactic acid production during hydrolysis and acidogenesis of food waste

Lactate accumulation occurs frequently during the hydrolysis and acidogenesis of food waste and produces an unfavorable substrate for anaerobic digestion. The objective of the present study was to reduce lactic acid production during the hydrolysis and acidogenesis of food waste in leachate bed reactor for establishment of the two-phase anaerobic digestion system. The results showed that the hydrolysis and acidogenesis of food waste in batch feeding mode underwent two consecutive stages, namely lactic acid fermentation and mixed acid fermentation. In the lactic acid fermentation stage, lactate constituted 74.4-96.8% of the total organic acids in the leachate. However in semi-continuous mode the content of lactate in the leachate could be reduced less than 0-2% for leach bed reactors operated at feeding loads of 50-150 g/d although lactate accumulation occurred at a feeding load of 200 g/d. Furthermore the organic acid shifted to acetate and butyrate, providing ideal substrates for anaerobic digestion.