A laboratory scale rotating biological contactor (RBC) was used to study the biodegradation of synthetic wastewater similar to the one from the petrochemical industry producing acrylonitrile (ACR). The study was carried out at hydraulic retention time (HRT) of 30 h for simultaneous removal of cyanide (CN), acetonitrile (ACN), and ACR in petrochemical wastewater stream. The attached biomass was acclimatised by gradually increasing CN, ACN, and ACR concentration from 5 to 40, 41 to 113, and 45 to 142 mg L(-1), respectively, with simultaneous increase in the concentration of chemical oxygen demand (COD) and ammonium nitrogen at HRT of 30 h. During acclimatisation the percent removal of COD, CN, ACN, and ACR were 90-95, > 99, 80-94, and 80-88, respectively. The performance of RBC was monitored for various parameters like COD, 5-day biochemical oxygen demand at 20 degrees C (BOD(5)), CN, ACN, ACR, ammonium nitrogen, etc. The removals obtained in terms of percentage, for CN, ACN, ACR, and COD were 97, 81, 89, and 95, respectively, at HRT 30 h. The quantitative shocks consisting of increase in influent substrate concentration with subsequent increase in concentration of other parameters proportionally were studied. The variation of biomass concentration within the system was also studied.