Assessment of Bioremediation Potential for PAH Contaminated Site in Auckland

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a unique class of pollutants that are of extreme environmental concern due to their toxic and carcinogenic effects on human and animal health. As a result, there is a great interest in the removal of these pollutants from the environment that have accumulated from various industrial and anthropogenic sources. Bioremediation is a promising treatment technology that aligns with Te Ao Maori and mana whenua’s values of “pare kore” (zero waste), which focuses on the use of microorganisms to degrade organic pollutants into less harmful by-products. A study was undertaken to determine the bioremediation potential of a PAH contaminated site in Auckland, New Zealand, focusing on the stimulation of native organisms within the soil and minimising disruption to the land. Soil contaminated with numerous PAHs and heavy metals were amended with glucose, nutrients, external microbes, and oxygen to determine if biodegradation of the PAH, phenanthrene within the aged soil could be enhanced. At least a 15% reduction of phenanthrene in all soil samples was observed, with degradation in the control (non-amended) samples indicating that natural biodegradation could occur on the site. The order of phenanthrene degradation potential was found to be glucose > oxygen > nutrients > microbes > control. Trends in the population of PAH-degrading bacteria and DNA concentration within the soil indicated that substrates other than PAHs were preferentially utilised for microbial growth, however evidence of a synergetic relationship between PAH- and non-PAH-degrading microbes could be observed where microbes altered the soil environment which stimulated PAH degradation. The native bacteria within the glucose amended soil were found to belong to the genera Pedobacter, Thiobacillus, Flavobacterium, and the native fungi within the soil were found to belong to the genera: Microdochium, Mortierella, and Stachybotrys. Further research focusing on increased treatment time, optimising hybrid soil amendments containing a mixture of nutrient and glucose and analysing the effectiveness of adding amendments in-situ in a pilot-scale will be required to help determine if biodegradation would be feasible in full-scale. Additionally, measuring the levels of other PAHs, heavy metals, and toxicity, and analysing the trends and change in microorganism growth through DNA sequencing will help to better understand the degradation pathways occurring during the bioremediation process.