Solubilization and fermentation in a modified VFA-potential method

The VFA-potential method is a fermentation technique for estimating the total volatile fatty acids (VFA) availability in wastewater. The VFA-potential was conceived as a measurement of the readily fermentable COD, because fermentation utilizes this COD as a substrate. However, anaerobic hydrolysis can also be a potential source of fermentable matter. In this work, the VFA-potential method has been modified and simplified to avoid nitrogen gas usage. In the modified method, several conventional BOD flasks are completely filled with wastewater and subsequently opened at scheduled times. This procedure keeps oxidation-reduction potential (ORP) at very low levels while reducing the laboratory equipment required. COD fractionation of initial wastewater was carried out. Analysis of total suspended solids (TSS), soluble phosphate, ammonia nitrogen, total and soluble COD, and individual VFA were obtained throughout the VFA-potential test, to evaluate hydrolysis and fermentation. The mean ratio between VFA-potential and the initial total COD was 0.23 mg VFA-COD/mg COD. The VFA to phosphate ratio was in the range of 14.6-22 mg VFA-COD/mg P, which is in accordance with the recommended value for biological phosphorus removal (20 mg/mg). A strong hydrolysis of solids was detected throughout the degradation of TSS and soluble COD. The observed behavior of TSS, soluble COD, and VFA is compatible with a partial utilization of hydrolyzed COD for fermentation. Phosphorus and nitrogen solubilization are described, as well as pH and alkalinity behavior, throughout the test.