Biological treatability and inhibitory effects of a textile waste containing caprolactam

Abstract

A biological treatability study was undertaken on a high-strength textile waste containing caprolactam. Caprolactam is a cyclic amide which is used as a monomeric unit in the production of nylon. The compound exhibits some unique properties and has been shown to be phytotoxic. The focus of this research was concerned with the inhibitory effect of caprolactam and the development of biokinetic growth constants. Lab-scale, continuous-flow, conventional activated-sludge reactors operated at cell residence times (θc) of 5, 10 and 15 days were utilized in the kinetic studies. Short-term batch experiments, involving both caprolactam standards and wastewater, were used in the development of inhibition curves. The inhibitory effects were analyzed by comparing specific utilization rate to chemical oxygen demand (COD). Influent wastewater characteristics, after a 1:18 dilution, were as follows: COD 2000 mg/L, caprolactam 1000 mg/L, total Kjeldahl nitrogen (TKN) 120 mg/L. Percent reductions achieved at the 5, 10 and 15 day θc</sub values were, respectively, as follows: COD, 49, 89, 96; caprolactam, 65, 96, 100; and TKN, 15, 41, 53. Complete inhibition, under batch conditions, was observed at initial COD concentrations in the range of 800 to 1900 mg/L. The results suggested that primary degradation of caprolactam occurred readily at all cell residence times considered, with intermediate degradation products being responsible for the residual COD in treated effluent. Success in treating the wastewater appears to be dependent upon in-house improvements to reduce waste stream strength and/or dilution of the waste stream