Ex situ bioremediation method for the treatment of groundwater contaminated with PAHs

The present study was carried out with the objective of integrating physical and biological methods for the treatment of polycyclic aromatic hydrocarbons (PAHs)-contaminated groundwater and to assess its efficiency. The aquifer in Kirchseeon region, Germany, is contaminated with PAHs due to product loss of tar oil which was used in large amounts for treating the railway sleepers produced in this area. Six pumping wells, two recharge wells and fifteen observation wells were installed for this study as a part of the ex situ biodegradation treatment plant. Zoogloea, Leptothrix, Sphingomonas, Novosphingobium and Comamonadaceae were the indigenous bacteria that facilitated degradation of the PAHs. In the bioreactors, 95 % of naphthalene and methylnaphthalene and 90 % of total PAHs were removed. During this remediation process, 700,000 m(3) of PAHs-contaminated groundwater was purified to almost drinking water quality. Also, 7,000 kg of dense non-aqueous phase liquid (DNAPL) and 950 kg of PAHs were removed from the pumped groundwater. The remediated groundwater is recharged back into the aquifer through two recharge wells located 600 m from the study site. The observation wells show a decrease in contamination of up to 95 %. Thus, this field scale study showed that using indigenous bacteria to remediate PAHs-contaminated groundwater is a viable option.