BIOREMEDIATION OF PETROLEUM HYDROCARBONS USING COMPOST AMENDMENTS AND PHYTOREMEDIATION

This research investigated the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aged petroleum-contaminated soils. One hundred percent organic compost tea (mushroom compost extract) and solid compost was evaluated for their ability to increase the biodegradation rates of recalcitrant PAHs compounds: naphthalene, phenanthrene, anthracene, fluoranthene and pyrene, in aged soils. The decrease in toxicity levels of residual compounds and subsequent phytoremediation was also investigated.

In laboratory treatments using compost tea, 95% naphthalene, and 75% phenanthrene, anthracene, fluorene, and pyrene were biodegraded within 48 days. Evidence for biodegradation of the PAHs was based on the detected known intermediate transformation products such as hydroxylated PAHs and organic acids. Additionally, a greater than four orders of magnitude increase in the microbial numbers was observed in the compost tea treated soils: 1.73 x10² to 2.72x10⁶ CFU g^-1 in compost tea amended soils compared to 9.40x10³ CFU g^-1 in the unamended control. In a 12-week greenhouse study, phytoremediation with maize (zea mays) and willow trees (Salix spp.) was applied as a polishing step for the compost extract treated soils with initial total PAH concentrations in the range of 100 – 2000 mg g^-1. After 4 weeks of treatment, initial concentrations decreased by 100% for naphthalene and 90% for pyrene with the application of compost tea compared to 95% naphthalene and only15% pyrene loss in the no amendment controls. After six weeks, the treated soils were planted with maize seedlings and young willow trees. Although none of the willows survived, maize grew in the contaminated soils that had been pre-treated with compost tea. The latter plant tolerated a higher residual PAH concentration in the aged soils. Pyrene concentrations in planted compost tea treatments reduced from 31 ppm (week-4) to 17 ppm (week-12). The residual concentrations for the other four compounds were < 0.5ppm. In the no amendment control, pyrene decreased from 112 ppm (week-4) to a residual concentration of 53 ppm (week-12). High residual concentrations were also observed for phenanthrene (88ppm) and anthracene (330 ppm).