Diverting electron fluxes towards sulfate reduction using linoleic acid in a mixed anaerobic culture

Abstract

Sulfate (1500  mg/L) reduction and glucose (1870  mg/L) degradation was examined in the presence of five varying linoleic acid (LA) levels (100  –  1000  mg/L) at 37  ±  2°C and pH 7·0  –  7·2. The sulfate reduction and methane formation data suggest that LA selectively inhibited methane producing bacteria (MPB). The quantity of sulfate removed increased with increasing LA dosage. Approximately 1375  mg/L (92%) sulfate was removed in cultures fed with high concentrations of LA (1000  mg/L), which was 68% more than that removed in glucose and sulfate controls. The quantity of sulfate removed in cultures fed with 100, 300, 500 and 700  mg/L LA were 62%, 66%, 77%, and 84%, respectively. Initial sulfate degradation rates increased with increasing LA levels in the cultures. High LA levels (1000  mg/L) attributed to approximately a sevenfold increase in the initial sulfate degradation rates compared to cultures containing sulfate plus glucose. The highest initial sulfate removal rate (0·19  µg/(mgVSS  min)) was observed in cultures receiving 1000  mg/L LA. Initial glucose degradation rates decreased with increasing LA concentrations. The rates for the cultures receiving 1000  mg/L LA were 2·53  µg/(mgVSS  min) while the degradation rate for cultures containing 100  mg/L LA was 5·40  µg/(mgVSS  min). Methane formation decreased when sulfate and LA were added. Methane formation was lowest in cultures receiving elevated LA concentrations. The percent electron flow fluxes increased towards sulfidogenesis and decreased towards methanogenesis with increasing LA levels. Less than 0·6% electron flow was diverted to methanogenesis in cultures containing high levels of LA (≥700  mg/L) while ≤ 45% was diverted to sulfidogenesis. Acetate and propionate were the major volatile fatty acids (VFAs) detected during glucose degradation. The amount of sulfate reduced in the cultures receiving only LA or sulfate and no other carbon source was comparable (approximately 10%), which suggests that LA did not contribute to electrons during the course of experiment for sulfate reduction.