Naphthenic acids (NAs) comprise a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. NAs are present in wastewaters at petroleum refineries and in the process waters of oil sands extraction plants where they are primarily retained in large tailing ponds in the Athabasca region of Northern Alberta. The toxicity of these waters, primarily caused by NAs, dictates the need for their treatment.Bioremediation is considered as one of the most cost-effective approaches for the treatment of these wastewaters. Ex-situ bioremediation conducted in a bioreactor optimizes the microbial growth and activity by controlling environmental conditions resulting in efficient conversion of the contaminants to less harmful compounds. In this work, a circulating packed bed bioreactor (CPBB), with improved mixing, mass transfer and biomass hold-up has been used to study biodegradation of several model NA compounds: namely trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans- 4-methyl-cyclohexane acetic acid (4MCHAA), and octanoic acid as well co-biodegradation of these naphthenic acids with octanoic acid, using a mixed culture developed in our laboratory. The biodegradation rates achieved for trans-4MCHCA in the CPBB are far greater than those reported previously in the literatures. The maximum biodegradation rate of trans-4MCHCA observed during batch operation was 43.5 mg/L-h, while a rate of 209 mg/L-h was achieved during continuous operation. Although cis-4MCHAA is more resistant to biodegradation when compared with trans-4MCHCA, the experimental results obtained from this study indicated both isomers were effectively biodegraded in the CPBB, with the maximum biodegradation rates being as high as 2.25 mg/L-h (cis-4MCHAA) and 4.17 mg/L-h (trans-4MCHAA) during batch operations and 4.17 mg/L-h(cis-4MCHAA) and 7.80 mg/L-h (trans-4MCHAA) during the continuous operation. Optimum temperature for biodegradation of 4MCHAA was determined as 25 aC. Furthermore, the biodegradation rate of single ring NAs (trans-4MCHCA and 4MCHAA) were found to be significantly improved through utilization of octanoic acid as a co-substrate. For example, the maximum biodegradation rate of trans-4MCHCA obtained during batch operation with the presence of octanoic acid was 112 mg/L-h, which was 2.6 times faster than the maximum value of 43.5 mg/L-h when trans-4MCHCA was used as a sole substrate. Similarly, the highest biodegradation rates of cis-4MCHAA and trans-4MCHAA were 16.7 and 28.4 mg/L-h in the presence of octanoic acid, which were 7.4 and 6.8 times higher than the maximum rates of 2.25 and 4.17 mg/L-h in the absence of octanoic acid.

Naphthenic acids (NAs) comprise a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. NAs are present in wastewaters at petroleum refineries and in the process waters of oil sands extraction plants where they are primarily retained in large tailing ponds in the Athabasca region of Northern Alberta. The toxicity of these waters, primarily caused by NAs, dictates the need for their treatment.Bioremediation is considered as one of the most cost-effective approaches for the treatment of these wastewaters. Ex-situ bioremediation conducted in a bioreactor optimizes the microbial growth and activity by controlling environmental conditions resulting in efficient conversion of the contaminants to less harmful compounds. In this work, a circulating packed bed bioreactor (CPBB), with improved mixing, mass transfer and biomass hold-up has been used to study biodegradation of several model NA compounds: namely trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans- 4-methyl-cyclohexane acetic acid (4MCHAA), and octanoic acid as well co-biodegradation of these naphthenic acids with octanoic acid, using a mixed culture developed in our laboratory. The biodegradation rates achieved for trans-4MCHCA in the CPBB are far greater than those reported previously in the literatures. The maximum biodegradation rate of trans-4MCHCA observed during batch operation was 43.5 mg/L-h, while a rate of 209 mg/L-h was achieved during continuous operation. Although cis-4MCHAA is more resistant to biodegradation when compared with trans-4MCHCA, the experimental results obtained from this study indicated both isomers were effectively biodegraded in the CPBB, with the maximum biodegradation rates being as high as 2.25 mg/L-h (cis-4MCHAA) and 4.17 mg/L-h (trans-4MCHAA) during batch operations and 4.17 mg/L-h(cis-4MCHAA) and 7.80 mg/L-h (trans-4MCHAA) during the continuous operation. Optimum temperature for biodegradation of 4MCHAA was determined as 25 aC. Furthermore, the biodegradation rate of single ring NAs (trans-4MCHCA and 4MCHAA) were found to be significantly improved through utilization of octanoic acid as a co-substrate. For example, the maximum biodegradation rate of trans-4MCHCA obtained during batch operation with the presence of octanoic acid was 112 mg/L-h, which was 2.6 times faster than the maximum value of 43.5 mg/L-h when trans-4MCHCA was used as a sole substrate. Similarly, the highest biodegradation rates of cis-4MCHAA and trans-4MCHAA were 16.7 and 28.4 mg/L-h in the presence of octanoic acid, which were 7.4 and 6.8 times higher than the maximum rates of 2.25 and 4.17 mg/L-h in the absence of octanoic acid.