Biological removal of organic nitrogen and fatty acids from metal-cutting-fluid wastewater

Abstract

The anaerobic, anaerobic/aerobic (anaerobic followed by aerobic) and straight aerobic treatments of a simulated metal-cutting-fluid wastewater were evaluated in terms of the removal of organic nitrogen (primarily alkanolamines and heterocyclic compounds) and fatty acids, the two major constituents of many water-based metal-cutting fluids. The organic nitrogen was not well adsorbed on activated carbon but was degraded through the anaerobic/aerobic or straight aerobic treatment. It was also found that an acclimation period was necessary before the organic nitrogen could be anaerobically degraded. 2-Methylhexanoic, heptanoic, 3,5,5-trimethylhexanoic and benzoic acid, which were found in the wastewater, were degraded well both anaerobically and aerobically. The wastewater also contained a group of unidentified organic compounds that consisted of five gas chromatographic peaks (probably branched C 8–C 10 fatty acids or their esters). These unidentified organics were partially degraded and persisted in the effluents, contributing to the non-biodegradable portion of organics. Several low molecular weight fatty acids (acetic acid, propanoic acid, 2-methylpropanoic acid, butanoic acid, 3-methylbutanoic acid and pentanoic acid) were produced during the periods when the influent chemical oxygen demand (COD) loading was varied to study the response of an anaerobic reactor to the variation. The anaerobic/aerobic treatment produced an effluent similar to that of the straight aerobic treatment with respect to fatty acid concentrations.