Treatment of petrochemical wastewater by rotating biological contactor.

A laboratory scale study has been conducted to assess the efficiency of rotating biological contactor (RBC) to treat the synthetic wastewater from a petrochemical industry producing acrylonitrile. The attached biomass was acclimatised by gradually increasing cyanide concentration from 5 to 40 mg l(-1) with simultaneous increase in the concentration of chemical oxygen demand (COD) and ammonium nitrogen (NH4+-N). During acclimatization COD removal varied between 80-88 percent (%) while cyanide removal was more than 99%. The RBC was operated at varying hydraulic loading rates from 0.011 to 0.027 m3 m(-2) d(-1). The performance of the RBC was monitored for various parameters like COD, 5-day biochemical oxygen demand at 20-degree centigrade (degrees C) [BOD5], cyanide, ammonium nitrogen etc., for all hydraulic loadings. At all hydraulic loadings the cyanide removal remained more than 99%. The removals obtained in terms of percentage, for cyanide, COD, BOD5 and NH4+-N were greater than (>) 99, 95.2, 99.1 and 77, respectively at hydraulic loading of 0.011 m3 m(-2) d(-1). The effect of substrate/cyanide ratio on the performance of the process at five different ratios, 100/1, 80/1, 60/1, 40/1 and 20/1, showed more than 99% cyanide removal at ratio 20/1. The effect of COD/nitrogen (N) ratio was studied at four different ratios, 12/1, 10/1, 8/1 and 6/1, showed cyanide removal remained unaffected. The variation of biomass concentration within the system was also studied.