| Abstract | The effect of linear alkylbenzene sulfonate (LAS) in activated sludge system, focusing on its influence in COD removal efficiency was studies. Experiments have been done at different LAS concentrations, varying from 20 to 120 mg/L in continuous activated sludge process and at 20 and 40 mg/L of MBAS (Methylene blue active substance) in batch-fed activated sludge process. OECD (organization for Economic Co-operation and Development) synthetic sewage with 230-300 mg/L of COD was used throughout this experiment. In the batch activated sludge process, at 1500 mg/L of MLSS the synthetic sewage was biologically degraded mainly within the first 2 h. ninety three (93), 88 and 80% COD removal efficiencies were achieved within 3 h. corresponding to 0, 20, 40 mg/L of MBAS. In the continuous activated sludge process with 2 h. detention and 2500 mg/L of MLSS, the COD removal efficiency were 84.68, 81.33, 74.25% which corresponded to 30, 70, 120 mg/L of MBAS and 1.81, 2.25, 2.73 kg COD/ kg MLSS-d of organic loadings. The COD removal was not a result of adsorption onto the sludge since less MBAS concentration was detectable upon extraction of the sludge. The results showed that increasing LAS concentrations at the same time as increasing organic loading affected COD removal efficiency. LAS as high as 120 mg/L showed no inhibitory effect on the growth late of microorganisms in the continuous activated sludge system. It can degrade very fast and achieve 98% of MBAS removal at this concentration. In the batch-fed activated sludge system, no inhibitory effect on the growth rate of microorganism was observed at LAS concentrations as high as 40 mg/L. |