This thesis presents the study of biodegradation factors of a candidate naphthenic acid compound, the trans isomer of 4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA). Low molecular weight components of naphthenic acids such as trans-4MCHCA are known to be toxic in aquatic environments and there is a need to better understand the factors controlling the kinetics of their biodegradation. In this study, a relatively low molecular weight naphthenic acid compound and a microbial culture developed in our laboratory (primarily Alcaligenes paradoxus and Pseudomonas aeruginosa) were used to study the biodegradation of this candidate naphthenic acid. The purpose of the research was to evaluate the kinetic parameters and model the biodegradation of this compound in three bioreactor systems: batch reactors, a continuously stirred tank reactor and immobilized cell reactors.

In batch reactors, the maximum specific growth rate (0.52±0.04 d-1) of the consortium at 23oC and neutral pH was not highly variable over various initial substrate concentrations (50 to 750 mg/L). Batch experiments indicated that biodegradation can be achieved at low temperatures; however, the biodegradation rate at 4oC was only 22% of that at room temperature (23oC). Biodegradation at various pH values indicated a maximum specific growth rate of 1.69±0.40 d-1 and yield (0.41±0.06 mg/mg) at a pH of 10.

Study of the candidate substrate using a continuously stirred tank reactor and the microbial culture developed in the batch experimentations revealed that the kinetics of the candidate naphthenic acid are best described by the Monod expression with a maximum specific growth rate of 1.74±0.004 d-1 and a half saturation constant of 363±17 mg/L. The continuously stirred tank reactor achieved a maximum reaction rate of 230 mg/(L∙d) at a residence time of 1.6 d-1 (39 h).

Two high porosity immobilized cell reactors operating continuously over three months were found to consume trans-4MCHCA