Petroleum-contaminated soil contains various hazardous materials such as aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs). This study focused on PAHs since they are potentially toxic, mutagenic, and carcinogenic. Bioremediation of PAHs was carried out by adding tamarind leaf inoculums into petroleum-contaminated soil. Tamarind and other leguminous leaves have been reported to contained several PAH-degrading microorganisms. To minimize the amount of leaves added, the preparation of tamarind leaf inoculums was developed by incubating tamarind leaves with a sub-sample of contaminated soil for 49 days. After that, the efficiency of tamarind leaf inoculums was tested with two soil samples collected from a navy dockyard and railway station in Samutprakarn and Bangkok, respectively. These soil samples had different levels of petroleum contamination. Bioaugmentation treatment was carried out by mixing contaminated soil with the inoculum at the ratio of 9:1. For navy dockyard soil, the concentration of phenanthrene was decreased gradually and reached the undetectable concentration within 56 days in the inoculated soil; meanwhile 70-80% of fluoranthene and pyrene were remained at the end of treatment. For railway station soil, which had lower petroleum contamination, PAH degradation was more rapid, for example, the concentration of phenanthrene was below detection limit after 28 days. Besides PAHs, the amounts of several hydrocarbons were also reduced after treatment. At the same time, numerous phenanthrene-degrading bacteria, which were used as representatives of PAH degraders, could be observed in both inoculated soils. However, higher numbers of bacteria were found in railway station soil, which corresponded with the lower amount of PAHs and higher amount of soil nutrients. The results showed that inoculum prepared from tamarind leaves could be used to degrade PAHs as well as clean-up petroleum contaminated soil.
