Anaerobic Co-Biodegradation Of Linear And Cyclic Model Naphthenic Acids Under Denitrifying Conditions

Abstract

Large volumes of oil sand process water are generated as part of the Clarke caustic hot water process used for extraction of bitumen from shallow oil sand reserves. These process waters contain naphthenic acids in high concentrations (40-120 mg/L), which are persistent in the environment for decades. The toxic nature of naphthenic acids has been found to endanger aquatic biota and terrestrial habitat. Reclamation of these oil sand process waters has also come to the forefront due to the increasing future demand for water consumption in the oil sand industry and the need for sustainable use of water. Bioremediation as a cost effective technology for treatment of these process affected waters is gaining impetus. In earlier works, the biodegradation of single naphthenic acids was studied in the batch and continuous modes. In this work, biodegradation of individual naphthenic acid as well as co-biodegradation of mixture of naphthenic acid (linear and cyclic) namely octanoic acid, trans 4-methylcyclohexanecarboxylic acid (4MCHCA) and a mixture of octanoic acid and 4MCHCA used to study in batch and continuous mode. The batch studies were completed to evaluate the kinetics of biodegradation process in anaerobic conditions. Mixed culture was used to conduct the biodegradation process. Nitrate ions were utilized to replace the oxygen as electron acceptor to oxidize the organic substrate. The production of nitrite was observed during biodegradation process, which indicated that denitrifying process was happening. However, at the end of the process, concentration of nitrite decreased and reached to zero, suggesting that nitrite was utilized together with nitrate for additional electron acceptor. The method was suggested as an efficient treatment for both naphthenic acids and nitrate as water pollutants. In addition, the effect of temperature in cobiodegradation, ranged from 100C to 350C, was also monitored. The maximum removal rates of the cyclic naphthenic acid (trans-4MCHCA) were found to be lower than that of octanoic acid (linear) irrespective of the presence of the other compound in the mixture.