Target and Enhance Ethanol and Butyrate Production from Anaerobic Fermentation via the pH and Organic Loading Rate Combined Strategy.

The large capacity production and low utilization rate increase the difficulty of fruit and vegetable wastes (FVW) treatment. Efficient and targeted recovery strategies can solve these problems. This study investigated and proposed combined strategies via pH and organic loading rate (OLR) to target and enhance ethanol- and butyrate-dominant acidogenic production in the FVW mixed culture fermentation. Under pH 4.0, OLR 18 gCOD/(L∙d), and mesophilic (35 °C), ethanol-dominant fermentation was formed. The long-term operation (168 days) showed that the highest ethanol yield was 0.33 g/gCOD which was greater than that in other studies. Also, the hydrolysis rate of ethanol-type fermentation reached 74.5%. Besides, butyrate-type fermentation was stable at yield 0.39 g/gCOD following conditions: pH 6.0, OLR 28 gCOD/(L∙d), and 35 °C, of which hydrolysis and acidogenic rate were 78.0% and 62.0%, respectively. The high relative abundance of Lactobacillus, Olsenella, and Bifidobacterium played positive role in achieving ethanol, butyrate, and lactate production among various metabolic pathways. The results revealed the pH value together with OLR was the valid parameter to affect product formation and composition during FVW fermentation.