Effect of pH on volatile fatty acids (VFAs) in rice wash

The study investigated the characteristics of rice wash in fermentation, component and odd/even proportion of volatile fatty acids (VFAs), to contribute new knowledge by developing quantitative relationship between VFAs and polyhydroxyalkanoates. The fermentation experiments were conducted with and without controlling pH. Rice wash produces primarily even fatty acids in the system with uncontrolled pH. The change in VFAs in rice wash with pH was investigated. It was found that the maximum concentration of VFAs was 3,156.68 mg/L without controlling pH with concentrations of acetic acid, propionic acid, butyrate and valerate being 974.46; 361.97; 1,082.51, and 737.73 mg/L, respectively. Even fatty acids reached the maximum value of 2,056.97 mg/L. When pH was changed from 4 to 8, the dominant fatty acid changed from butyrate to propionic acid. The results showed that when pH was changed from acidic to alkaline, the proportion of odd fatty acids increased gradually. When pH was less than 4, 5, and 6, the ratios of odd to even fatty acids were 1:2.5, 1:2, and 1:3. When pH was 8, the proportion of odd to even fatty acids was 1:1. The study results can provide guidelines for comprehensive utilization of solid wastes and waste treatment.