Biodegradation of polycyclic aromatic hydrocarbons in petroleum-contaminated soil by the addition of tamarind leaves composted contaminated soil

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) are considered as environmental pollutant due to its widespread distribution and potential health threat. This research aimed to develop PAHs bioremediation in petroleum-contaminated soil by using tamarind leaves which have been proven to be a source of effective degrading microorganisms in preparation of a seed culture for the treatment system. A 2 g soil reactor was set up by using contaminated soil collected from Phrachulachomklao Royal Navy Dockyard mixed with tamarind leaves at the ratio of 9:1. Moisture content, temperature and aeration in the reactor were adjusted to the optimal conditions. At 49 days of incubation, degradation rate seemed to be the highest in which 18% phenanthrene, 24% fluoranthene and 9% pyrene were degraded. Biodegradative efficiency was increased 5%, 4%, and 1% respectively after 56 days while only 1-3% of these PAHs were eliminated in the control. The scale-up experiment was furtherachieved in 20 g. reactor. The tamarind leaves-soil mixture incubated for 49 days was used as a seed culture by using the ratio of 9:1 (contaminated soil: seed culture). The experimental results were observed in the soil collected from two contaminated sites: Phrachulachomklao Royal Navy Dockyard and Bangkoknoi Railway Station. Phenanthrene degrading bacteria were determined as representative of PAHs degraders by detecting colonies surrounded with clear zones on CFMM agar plates after spraying with phenanthrene solution. The highest numbers of phenanthrene degrading bacteria were observed in Bangkoknoi Railway Station's soil mixed with seed culture. However, numerous phenanthrene degraders were found in the soil mixed with seed culture. Thus the seed culture prepared from leaves composting in contaminated soil provided highly effective PAHs degradation in both of the soils collected from different contaminated sites.