Effect of pH and Fermentation Time on Yield and Optical Purity of Lactic Acid from Kitchen Wastes Fermentation
pH和发酵时间对厨余垃圾发酵产乳酸及光学特性的影响

Batch experiments were carried out to analyze the effect of pH and fermentation time on the yield of total lactic acid and the distribution of L- and D-lactic acid among total lactic acid during the non-sterilized fermentation of kitchen wastes. The results show that the concentration of reduced sugar (calculated as organic carbon) is low and accounts for 0.35% of the TOC of fermentation liquid. The maximum total lactic acid production rate and yield is 0.59g?(L?h)-1 and 0.62g per gram VS at pH 7, respectively. The proportion of lactic acid (calculated as organic carbon) among the TOC reaches 78% and 89% at controlled pH 7 and 8, respectively. The L-lactic acid is the predominant isomer form at pH 8. Lactic acid concentration depends on pH, fermentation time and interaction from the response surface analysis. pH and fermentation time have a significant effect on the optical purity of lactic acid. At acidic conditions, the ratio of L-lactic acid to the total lactic acid increases with the fermentation time before 120h, and the ratio reaches 0.9 at 120h. At acidic conditions, the ratio keeps at above 0.86 in the whole experimental fermentation time and obtains the maximum value(0.93) at 48h. It decreases with fermentation time at pH 7. To obtain high lactic acid yield and optical purity simultaneously, it is suggested that pH control at 8.