Removal of linear alkylbenzene sulfonate by anaerobic and aerobic reactors treating domestic sewage

This study evaluated the removal and behavior of linear alkylbenzene sulfonate (LAS) in pilot-scale integrated anaerobic-aerobic wastewater treatment systems, which were tested at different effluent recirculation rates (0%, 50%, and 100%). The systems combined UASB reactors and anaerobic filters with activated sludge reactors and submerged aerated biofilters treating typical domestic sewage. LAS concentrations, loads, adsorption, and chromatographic profiles of homologues and positional isomers were investigated to better understand the mechanisms that govern surfactant removal under different hydraulic conditions. The influent LAS concentrations ranged from 2.55 ± 0.34 to 3.43 ± 1.31 mg L^-¹. Aerobic units consistently showed higher LAS removal efficiencies than anaerobic units, achieving a peak removal of 75 ± 17% and an overall system removal of 68 ± 38% at a recirculation rate of 50%. Conversely, higher recirculation rates increased hydraulic loading and promoted LAS desorption in anaerobic units, resulting in higher LAS loads during some treatment stages. Chromatographic analyses indicated that aerobic units selectively biodegraded LAS positional isomers, while adsorption was the dominant process in anaerobic sludge. The results demonstrate that LAS removal in integrated anaerobic-aerobic systems is governed by interactions among hydraulic conditions, adsorption/desorption processes, and aerobic biodegradation, providing practical insights for optimizing surfactant removal in wastewater treatment systems.