An anaerobic filter was used to examine the treatability of wastewater formulated to simulate that from the manufacture of detergents. The detergent element was a mixture (1:1:1 v/v) of concentrated washing up liquid, a non-biological hand washing detergent and a fabric softener and, thus contained a combination of cationic surfactants, anionic surfactants, non-ionic surfactants and amphoteric surfactants. A concentration of 2 ml/l caused a deterioration in the performance of the digester which was pronounced after 7 days. When the packing of the filter was modified to include two layers of granular activated carbon, 320 g in total, the reactor was capable of treating a feed containing 10 ml/l. The amount of detergent removed during this second trial was greater than the Langmuir monolayer capacity of the carbon, indicating that both adsorption and degradation were occurring. The results also showed that, at detergent concentrations greater than 1 ml/l, the theoretical COD removal was lower than the actual COD removal. This was compatible with there being an element of adsorption by the activated carbon. (C) 2003 Elsevier Ltd. All rights reserved.