Efficient production of optically pure l-lactic acid from food waste at ambient temperature by regulating key enzyme activity

• A new process for enhancing optically pure l-lactic acid production was reported.
• Synergistic effect between food waste and sludge on hydrolysis was observed.
• Intermittent alkaline fermentation led to exclusively l-lactic acid generation.
• The pilot-scale experiment testified the feasibility of this new technique.

Bio-production of optically pure l-lactic acid from food waste has attracted much interest as it can treat organic wastes with simultaneous recovery of valuable by-products. However, the yield of l-lactic acid was very low and no optically pure l-lactic acid was produced in the literature due to (1) the lower activity of enzymes involved in hydrolysis and l-lactic acid generation, and (2) the participation of other enzymes related to d-lactic acid and acetic and propionic acids production. In this paper, a new strategy was reported for effective production of optically pure l-lactic acid from food waste at ambient temperature, i.e. via regulating key enzyme activity by sewage sludge supplement and intermittent alkaline fermentation. It was found that not only optically pure l-lactic acid was produced, but the yield was enhanced by 2.89-fold. The mechanism study showed that the activities of enzymes relevant to food waste hydrolysis and lactic acid production were enhanced, and the key enzymes related to volatile fatty acids and d-lactic acid generations were severally decreased or inhibited. Also, the microbes responsible for l-lactic acid production were selectively proliferated. Finally, the pilot-scale continuous experiment was conducted to testify the feasibility of this new technique.

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