Effects of different temperatures and pH values on volatile fatty acids production during codigestion of food waste and thermal-hydrolysed sewage sludge and subsequent volatile fatty acids for polyhydroxyalkanoates production

Abstract

The effects of temperature (35 °C and 55 °C) and pH (uncontrolled, 7 and 10) on volatile fatty acid (VFA) yields from anaerobic codigestion of food waste, and thermal-hydrolysed sewage sludge were investigated in this study. The results revealed that optimal conditions for VFA production occurred at 35 °C at pH 7 and at 10 and 55 °C at pH 7. The dominant bacterial genera associated with VFA production significantly differed when the temperature and pH were altered, including Prevotella, Lactobacillus, Bifidobacterium Megasphaera, Clostridium XlVa, and Coprothermobacter. A temperature of 35 °C at pH 7 favoured mixed acid-type fermentation, while a temperature of 35 °C at pH 10 and 55 °C at pH 7 favoured butyric acid-type fermentation. The maximal polyhydroxyalkanoate content accounted for 54.8% of the dry cell at 35 °C with pH 7 fermentative liquids and comprised 58.9% 3-hydroxybutyrate (3HB) and 41.1% 3-hydroxyvalerate (3HV).