Influence of Nonionic Surfactants on Fungal and Bacterial Degradation of Hexane

Batch solubility and microcosm studies were conducted to examine the role of nonionic surfactants (Brij 30, Brij 35, Triton X-100, and Tween 80) on fungal and bacterial degradation of hexane, a model volatile organic compound with a high Henry's law constant. The apparent solubility of gas phase hexane was not observed as a linear correlation in respect to surfactant concentration due to the insufficient mass transfer at the gas-liquid interface. The hexane partitioning to micellar phase was related to the unique structure of surfactants with different lengths of hydrophobic alkyl or hydrophilic polyoxyethylene chains. Microcosm test results revealed that most tested surfactants below critical micelle concentration (CMC) improved the fungal and bacterial growth, but surfactants at high concentration (5 CMC) adversely affected biodegradation kinetics. The observed low hexane removal was possibly attributed to the toxicity of surfactants at elevated concentration, the preferential utilization of a surfactant as substrate, and the partitioning of hexane into micellar phase. The results from this study suggest that low concentrations of Brij 30 and Tween 80 are favorable to enhance both the solubility and bioavailability of hexane with fungi as working consortium, while Brij 30 and Triton X-100 below their CMC hold promising potential for bacterial degradation of hexane without having significant biodegradation of the surfactant.