Removal of Petroleum Hydrocarbon from Water by Combined Cultivation of <i>Azolla</i> and Bacteria

Background: Pollution of water resources with petroleum hydrocarbons causes adverse effects on ecosystems and human health. Physico-chemical methods for removing thin layers of oil on the water surface are not cost-effective. Azolla is one of the plants that grows and reproduces on the surface of water and has many roots that can be a suitable place for microbial growth and decomposition of oil compounds. Objectives: The aim of this study was to remove petroleum hydrocarbons from water by co-culture of Azolla and bacteria. Methods: Commercial diesel fuel was used as a source of total petroleum hydrocarbon (TPH) pollution in water. Isolated bacteria from diesel fuel-contaminated soil were identified by biochemical test results according to standard methods. Experiments were conducted in separate runs, including culturing bacteria alone, Azolla alone, and co-culture of Azolla-bacteria. Concentrations of 100, 500, and 1000 mgL-1 of TPH in water and contact times of 5.0, 10.0, and 15.0 days were examined. Results: In the case of Azolla culture alone, the mean TPH removal was 40%. In the case of bacteria culture alone and TPH concentration of 1000 mgL-1, the minimum removal was 35% for Pseudomonas aeruginosa and the maximum was 60% for Alcaligenes faecalis. In the case of co-culture with TPH concentration of 1000 mgL-1, the minimum removal was 80% for P. aeruginosa-Azolla and the maximum was 100% for A. faecalis-Azolla. In the case of co-culture, the removal was 100% for TPH concentrations of 100 and 500 mgL-1 at contact times of 5.0 and 10.0 days, respectively. Conclusions: Co-culture of Azolla and bacteria was effective for the complete removal of petroleum hydrocarbons (100 and 500 mgL-1) from water. This method can be used to clean up and remove petroleum hydrocarbons from water.