Biodegradation of two polyethoxylated nonionic surfactants in sequencing batch reactors

Application of surfactants to increase the mobility of hydrophobic contaminants in soils will create a secondary aqueous waste stream containing mobilized contaminant and surfactant that may be biodegraded. Previous research on surfactant biodegradation focused on low surfactant concentrations, typically less than 0.01 % (weightlweight). The goal of this project was to investigate the effect of surfactant concentration, greater than O.Ol%, on the rate and extent of surfactant biodegradation. Two nonionic polyethoxylated surfactants, Neodol 9 1-8 and Makon 12, were selected for study based on their ability to solubilize hydrophobic organic compounds. Investigations were conducted in bench-scale sequencing batch reactors at initial surfactant concentrations of 0.01, 0.025, and 0.05%. The surfactants served as the sole carbon source. The average residual nondegradable fractions of surfactant were 0.35 and 0.15 for Makon 12 and Neodol 91-8, respectively. Although the extent of degradation did not change with initial surfactant concentration, the residual concentration did increase with initial surfactant concentration. Organic carbon removal was best fit by a modified first-order model. The first-order rate constant seemed to decrease exponentially with increasing initial surfactant Concentration. Water Environ. Res., 69, 1282 (1997).