Biological treatment of the components of solid oligomeric waste from a nylon-6 production plant

Abstract

On partial analysis of the solid oligomeric waste of a nylon-6 production plant, it was found to contain ε-caprolactam, 6-aminocaproic acid (6-ACA) and its linear and cyclic oligomers. Out of four bacterial isolates capable of utilizing caprolactam as the sole growth substrate, Alcaligenes faecalis was found to be the most potent and utilized 90% of caprolactam in 24 h. In shake flask experiments, when the solid waste after solubilization was treated with a consortium of bacteria of four different genera, except the cyclic oligomers, all the other constituents were found to be degraded. A reduction of the chemical oxygen demand (COD) of the solid waste to the level of 63–66% was obtained when it was treated with either a consortium of the bacterial isolates or only a single isolate, A. faecalis. Alcaligenes faecalis could bring about a decrease of 95% in the caprolactam content of the solid waste, while 6-ACA and its linear oligomers were almost completely degraded. Alcaligenes faecalis cells adapted on solid waste could degrade the linear oligomers at a faster rate as compared to cells adapted on caprolactam. However, cyclic oligomers could not be degraded in either case. When solid waste, partially hydrolysed with acid to yield 6-ACA as the major constituent, was treated with the consortium of bacterial isolates, a 95% reduction in the COD was achieved.