Shifting product spectrum by pH adjustment during long-term continuous anaerobic fermentation of food waste.

Anaerobic fermentation is widely used to recover different products from food waste, and in this study, the evolution of fermentation products and microbial community along with pH variation was investigated thoroughly using four long-term reactors. Lactic fermentation dominated the system at pH 3.2-4.5 with lactic acid concentration of 5.7-13.5 g/L, and Lactobacillus was the superior sort. Bifidobacteria increased significantly at pH 4.5, resulting in the increase of acetic acid. Butyric acid fermentation was observed at pH 4.7-5.0. Bifidobacterium, Lactobacillus, and Olsenella were still dominant, but the lactic acid produced by them was converted to volatile fatty acids (VFAs) rapidly by Megasphaera, Caproiciproducens, Solobacteria, etc. Mixed acid fermentation occurred at pH 6.0 with the highest concentration 14.2 g/L of VFAs, and the dominant Prevotella and Megasphaera converted substrates to VFAs directly. On the whole, pH 4.5 and 4.7 led to the highest hydrolysis rate of 50% and acidification rate of 45%.