The anaerobic biodegradation of Linear Alkylbenzene Sulfonate (LAS) was studied in Upflow Anaerobic Sludge
Blanket Reactors (UASB). One reactor was fed with easily degradable substrates and commercial LAS solution
during a period of 3 months (Reactor 1), meanwhile a second reactor was fed with a commercial LAS solution
without co-substrate (Reactor 2) during 4 months. Both reactors were operated with an organic loading rate of
4–5 mg-LAS/l∗day and a hydraulic retention time of one day. The LAS biodegradation was determined by full
mass balance. LAS was analysed by HPLC in the liquid phase (influent and effluent streams of the reactors) as
well as in the solid phase (granular sludge used as biomass). The results indicate a high level of removal (primary
biodegradation: 64–85%). Biodegradation was higher in the absence of external co-substrates than in the presence
of additional sources of carbon. This indicates that the surfactant can be partially used as carbon and energy source
by anaerobic bacteria. Under the operating conditions used, inhibition of the methanogenic activity or any other
negative effects on the biomass due to the presence of LAS were not observed. The methanogenic activity remained
high and stable throughout the experiment.