Fate of linear alkylbenzene sulfonate (LAS) in activated sludge plants

Monitoring data were collected in a pilot-scale municipal activated sludge plant to assess the fate of the C12-homologue of linear alkyl benzene sulfonate (LAS-C12). The pilot-plant was operated at influent LAS-C12 concentrations between 2 and 12 mg/l and at sludge retention times of 10 and 27 days
Monitoring data were collected in a pilot-scale municipal activated sludge plant to assess the fate of the C-12-homologue of linear alkyl benzene sulfonate (LAS-C-12). The pilot-plant was operated at influent LAS-C-12 concentrations between 2 and 12 mg l(-1) and at sludge retention times of 10 and 27 days. Effluent and waste sludge concentrations varied between 5 and 10 mug l(-1) and between 37 and 69 mug g(-1) VSS, respectively. In the sludge samples only 2-8% was present as dissolved LAS-C-12, whereas the remaining 92-98% was found to be adsorbed to the sludge. In spite of this high degree of sorption, more than 99% of the LAS-C-12 load was removed by biodegradation, showing that not only the soluble fraction but also the adsorbed fraction of LAS-C-12 is readily available for biodegradation. Sorption and biodegradation of LAS-C-12 were also investigated separately. Sorption was an extremely fast and reversible process and could be described by a linear isotherm with a partition coefficient of 3.21 g(-1) volatile suspended solids. From the results of biodegradation kinetic tests it was concluded that primary biodegradation of LAS-C-12 cannot be described by a (growth) Monod model, but a secondary utilisation model should be used instead. The apparent affinity of the sludge to biodegrade LAS-C-12 increased when the sludge was loaded with higher influent concentrations of LAS-C-12. (C) 2003 Elsevier Ltd. All rights reserved.