Enhanced Aerobic Biodegradation of Naphthalene in Soil: Kinetic Modelling and Half-Life Study

To demonstrate the potential use of bioremediation in polycyclic aromatic hydrocarbons contaminated soil using naphthalene as a model pollutant, a laboratory study with the objectives of investigating, evaluating and comparing the methods of natural attenuation, biostimulation, bioaugmentation, and combined biostimulation and bioaugmentation was performed. The study dealt with naphthalene biodegradation in soil using inorganic NPK fertilizer and mixed culture of Alcaligenes, Aeromonas, Micrococcus, and Serratia as source of biostimulation and bioaugmentation, respectively. Each treatment strategy contained 4% (w/w) naphthalene in soil as a sole source of carbon and energy. After 4 weeks of remediation, the results revealed that natural attenuation, biostimulation, bioaugmentation, and combined biostimulation and bioaugmentation exhibited 44%, 69.5%, 77.5%, and 85% naphthalene degradation, respectively. Also, the total hydrocarbon-degrading bacteria (THDB) count in all the treatments increased throughout the remediation period. The highest bacterial growth was observed for combined biostimulation and bioaugmentation treatment strategy. A first-order kinetic model was fitted to the biodegradation data to evaluate the biodegradation rate and the corresponding half-life time was estimated. The model revealed that naphthalene contaminated-soil microcosms under combined biostimulation and bioaugmentation treatment strategy had higher biodegradation rate constants, as well as lower half-life times, than other remediation systems. Therefore, the kinetic parameter values showed that the degree of effectiveness of these bioremediation strategies in the cleanup of naphthalene contaminated soil is in the following order: natural attenuation < biostimulation < bioaugmentation < combined biostimulation and bioaugmentation. Thus, the present work will contribute to the development of strategies for in situ treatment of polycyclic aromatic hydrocarbons contaminated soils.