Biodegradation of two polyethoxylated nonionic surfactants in sequencing batch reactors

Abstract

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% (weight/weight). The goal of this project was to investigate the effect of surfactant concentration, greater than 0.01%, on the rate and extent of surfactant biodegradation. Two nonionic polyethoxylated surfactants, Neodol 91‐8 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.