Treatment of a low strength complex wastewater of chemical oxygen demand (COD) around 500 mg/L was studied in a 10 L capacity laboratory scale anaerobic baffled reactor (ABR). It was operated at hydraulic retention times (HRTs) of 20, 15, 10, 8 and 6 h. Corresponding organic loading rates (OLRs) were 0.6, 0.8, 1.2, 1.5 and 2 kg COD/m(3) d. At every HRT (or OLR), pseudo steady state (PSS) was achieved. Even at maximum OLR of 2 kg COD/m(3) d, COD and biochemical oxygen demand (BOD) removals exceeded 88%. Removal of particulate fraction of organics was found to be greater than Soluble fraction. Compartment-wise studies of various parameters revealed that if the OLR was larger, the number of initial compartments played significant role in the removal of organics. The values of volatile fatty acids (VFA) demonstrated that hydrolysis and acidogenesis were the main biochemical activities in the initial few compartments. Based on the tracer studies, dead space in the ABR was found to range from 23% to 34%. The flow pattern in the AN was classified as intermediate between plug flow and perfectly mixed flows. Observations from scanning electron micrographs (SEM) also suggested that distinct phase separation takes place in an ABR. Study of organic and hydraulic shock loads revealed that ABR was capable of sustaining the type of shock loads generally experienced at a sewage treatment plant (STP). (C) 2008 Elsevier Ltd. All rights reserved.