Study on the reuse of anaerobic digestion effluent in lactic acid production

Abstract

Abstract A novel process for reuse of anaerobic digestion effluent in lactic acid fermentation was investigated to resolve wastewater pollution in lactic acid industry. A series of experiments were performed and the results showed that anaerobic digestion effluent directly reused did not affect liquefaction of raw materials, but inhibited lactic acid fermentation instead. Further experimental studies proved that excess ammonia-nitrogen, Zn2+, Fe2+, S and Mn2+ in the anaerobic digestion effluent could inhibit lactic acid fermentation and their corresponding critical inhibition concentrations were 100 mg/L, 1 mg/L,1 mg/L, 2.5 mg/L and 1 mg/L, respectively. In this paper, the activated carbon treatment was adopted to process the anaerobic digestion effluent, and these inhibitors had been effectively removed. The removal rate of metal ions reached 75%, and that for ammonia-nitrogen was over 80%. Application of the treated anaerobic digestion effluent in lactic acid fermentation, there was 129.59 ± 3.13 g/L of lactic acid, which was comparable to the control (130.09 ± 2.12 g/L). This new process is of significance to the realization of no-waste manufacturing, energy saving and emission reduction in lactic acid industry. It can be concluded that a cleaner way to produce lactic acid is realized.