BACKGROUND: Anaerobic treatment of distillery wastewater, purified terephthalic acid (PTA) wastewater and synthetic glucose wastewater was conducted and the soluble microbial products (SMPs) in the anaerobic effluent were investigated. RESULTS: Gas chromatography-mass spectrometry (GC-MS) analysis showed that apart from the degradation residuals, the long chain alkanes, esters and acids totally accounted for the majority of the low molecular weight (MW) SMPs in the effluents. The sum of protein and polysaccharide SMPs in the effluent increased from 50 to 323 mg L-1 when organic loading rate (OLR) was increased from 2.5 to 10.5 kg m(-3) d(-1); when influent COD changed from 5000 to 10 000 mg L-1, the sum increased from 54 to 98 mg L-1 at about the same OLR of 5 kg m(-3) d(-1). CONCLUSION: The results showedthat SMPs made up an important proportion of organic compounds in the anaerobic effluents; the main low MW SMPs were long chain alkanes, esters and acids. The protein and polysaccharide SMPs increased with the increasing OLR, while higher influent concentrations led to higher concentrations of SMPs at the same OLR. From the variation of protein and polysaccharide SMPs along the height of the anaerobic reactors, it could be inferred that the methanogens might have contributed more in SMP consumption. (C) 2010 Society of Chemical Industry