Anoxic biodegradation of a surrogate naphthenic acid coupled to reduction of nitrite

Abstract

Large volumes of waters contaminated with naphthenic acids (NAs) are produced during the processing of oil sands. Anoxic biodegradation of trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA) coupled to nitrate reduction was reported earlier. Given the generation of nitrite as an intermediate of nitrate reduction, its subsequent use as secondary electron acceptor and its potential inhibitory effect, biodegradation of trans-4MCHCA coupled to nitrite reduction was investigated in the current work.Batch experiments revealed the optimum temperature as 24±2°C and that the nitrite inhibitory effect was severe at 1150mg nitrite L−1. Maximum biodegradation rates in the stirred tank and biofilm reactors were 14.4 and 82.2mgL−1h−1, and the corresponding nitrite reduction rates were 44.2 and 361.6mgL−1h−1, respectively. Using the experimental data, maximum specific growth rate (μm), saturation constant (Ks), and yield (Y) were determined as 0.4h−1, 20.9mg trans-4MCHCA L−1, and 0.3mg biomass (mg trans-4MCHCA)−1, respectively. Comparison of anoxic biodegradation results with nitrate and nitrite demonstrated the superiority of nitrate as an electron acceptor for anoxic biodegradation of NAs.