[Effect of pH value on fermentation pathways of biodegradable organic waste]

Batch reactors were set up to evaluate the effect of pH value on the anaerobic fermentation of biodegradable organic waste. The results show that pH=7 of fermentative media is favorable for the microbial growth and proliferation, thereby promoting hydrolysis and acidogenesis of particulate biodegradable organic waste. The predominant fermentation types are diverse at different pH value, butyric acid fermentation dominates at pH=7, and at the later phase of pH= 8, propionic acid fermentation dominates at the later phase of pH=5. Lactic acid is produced at the early phase of fermentation, but gradually degrades at pH=5 and pH=7, while remains constant at pH=8. The predominant metabolic pathway shifts from alcohol-forming pathway to acid-forming pathway except for pH=5, where alcoholic fermentation still dominates at the later phase. The first-order hydrolysis constants k(h) for pH 5, 7 and 8 are equal to 0.000 8 h(-1), 0.000 9 h(-1) and 0.0002 h(-1), respectively. The soluble total organic carbon is mainly composed of acidogenic products after 100 h, 300 h and 600 h for pH=7, 5 and 8, respectively.