FACTORS THAT AFFECT THE DEGRADATION OF NAPHTHENIC ACIDS IN OIL SANDS WASTE-WATER BY INDIGENOUS MICROBIAL COMMUNITIES

The acute toxicity of wastewater generated during the extraction of bi tumen from oil sands is believed to be due to naphthenic acids (NAs). To determine the factors that affect the rate of degradation of repres entative NAs in microcosms containing wastewater and the acute toxicit y of treated and untreated wastewater, the effects of temperature, dis solved oxygen concentration, and phosphate addition on the rate of (CO 2)-C-14 release from two representative naphthenic acid substrates, (l inear) U-C-14-palmitic acid (PA) and (bicyclic) decahydro-2-naphthoic acid 8-C-14 (DHNA), were monitored. Tailings pond water (TPW) containe d microorganisms well adapted to mineralizing both PA and DHNA: PA was degraded more quickly (10-15% in 4 weeks) compared to DHNA (2-4% in 8 weeks). On addition of phosphate, the rate of NA degradation increase d up to twofold in the first 4 weeks, with a concurrent increase in th e rate of oxygen consumption by oil sands TPW. The degradation rate th en declined to levels equivalent to those measured in flasks without p hosphate. The observed plateau was not due to phosphate Limitation. De creases in either the dissolved oxygen concentration or the temperatur e reduced the rate. Phosphate addition also significantly decreased th e acute toxicity of TPW to fathead minnows. In contrast, Microtox(R) a nalyses showed no reduction in the toxicity of treated or untreated TP W after incubation for up to 8 weeks at 15 degrees C.