MICROBIAL-DEGRADATION OF ACRYLONITRILE WASTE EFFLUENTS - THE DEGRADATION OF EFFLUENTS AND CONDENSATES FROM THE MANUFACTURE OF ACRYLONITRILE

Effluents from the manufacture of acrylonitrile are difficult to biodegrade. They contain eight major organic components: acrylonitrile, acrylamide, acrylic acid, acrolein, cyanopyridine, fumaronitrile, succinonitrile and maleimide. Bacteria have been isolated that grow on acylonitrile, acrylamide, acrylic acid, cyanopyridine or succinonitrile as the sources of carbon and nitrogen, or which can biotransform acrolein, fumaronitrile or maleimide. Mixed cultures of the bacteria were grown in mixed batch and continuous culture on the eight major components of the waste, and complete degradation of all the components was demonstrated (Wyatt & Knowles, Biodegradation, 6, 93-107, 1995). Effluents from Stripper Column Bottoms (SCB) from acrylonitrile (AN) manufacture were biodegraded by continuous mixed cultures of the bacteria, with a 75% reduction in Chemical Oxidation Demand (COD) and over 99% removal of detectable toxic components of the wastes. Effluents from Wastewater Column Bottoms (WWCB) from AN manufacture, which are stronger than the SCB effluents, were more resistant to biodegradation and had to be diluted 10-fold to enable 75% removal of COD but with a low biomass yield in the fermenter. Condensates of the WWCB and SCB were prepared by distillation to decrease the ammonia and tar content. The mixed bacterial continuous culture, as obtained in the earlier studies, was able to degrade the WWCB condensate, reducing the COD by 80%. The SCB condensate could also be biodegraded in continuous culture, with removal of 90% of the GOD. In both cases the microbial culture became floccular. A mixed condensate of the AN,castes was prepared by employing a recycle system on the AN manufacturing plant, to reduce the levels of ammonia rand cyanide in the effluent. A mixed bacterial continuous culture, prepared as previously, reduced the COD front 3600 to 850-900 ppm, and removed cyanide and all detectable toxic components of the effluent. A two-stage laboratory-scale activated sludge system, was used to degrade the mixed condensate. The process was floccular, and a biomass recycle was employed. Overall, a reduction in COD of 80%,was obtained, but no nitrification was observed in this simple system. Gel filtration studies of the residual COD showed that it had a molecular weight of greater than 700, and was probably due to polymerization of monomeric material present in the effluents caused by their storage prior to biotreatment.