Batch and continuous biodegradation of three model naphthenic acids in a circulating packed-bed bioreactor.

Generation of process waters contaminated by naphthenic acids is a serious environmental concern associated with processing of the oil sands. This together with the necessity for sustainable use of water highlights the need for development of effective technologies such as bioremediation for treatment of these contaminated waters. In this work, a circulating packed bed bioreactor and a culture developed in our laboratory were used to study batch and continuous biodegradation of trans-4-methyl-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans-4-methyl-cyclohexane acetic acid (4-MCHAA), and mixture of these three naphthenic acids. Experimental results revealed that the biodegradability of the naphthenic acids was influenced by both carbon number and the spatial arrangement of the alkyl side branch. The maximum biodegradation rate of trans-4MCHCA observed during the continuous operation (209 mg/Lh at a residence time of 0.15 h) was significantly higher than those reported for CSTR and packed-bed bioreactors. The biodegradation rates of cis- and trans-4-MCHAA were much lower than trans-4MCHCA, with the maximum biodegradation rates determined for the two isomers being 4.2 and 7.8 mg/Lh, respectively (residence time: 3.3 h).