Activated Sludge Treatment of Wastewater from a Nylon 6 Manufacturing Plant

Abstract

The activated sludge treatment of wastewater containing ɛ-caprolactam from a Nylon 6 manufacturing plant was investigated by basic studies and operation of a full-scale treatment plant. Activated sludges were obtained from several municipal and industrial wastewater sources, or were prepared by mixing ɛ-caprolactam-utilizing bacteria (Bacillus sp. and Achromobacter sp.) with a municipal activated sludge. However, bulking phenomena were soon observed in the acclimatization of ordinary activated sludges, even when started from a very low concentration of ɛ-caprolactam. On the other hand, the activated sludge synthesized from ɛ-caprolactam-utilizing bacteria showed better results as regards sludge volume index (SVI), BOD removal, and transparency of treated water. Wastewater from the Nylon 6 manufacturing plant, which contained ɛ-caprolactam, was treated by this synthesized activated sludge in a bench-scale apparatus consisting of a 4 m3 aeration basin and a 1.4 m3 sedimentation basin. The optimum BOD loading was estimated to be 0.35-0.40 kg BOD/kg MLSS/day for this wastewater. Production of excess activated sludge was 10% of the BOD loaded. In 1974, based on this preliminary experiment, a wastewater treatment facility consisting of a 2,500 m3 aeration basin and a 1,250 m3 sedimentation basin was constructed near the Uji Nylon 6 manufacturing plant (Unitika Ltd), to treat 5,000 m3 of wastewater (BOD 300-400 mg/l) per day. The treatment plant operates successfully, producing treated water with a BOD below 10 mg/l.