Remediation of groundwater contaminated with trichloroethylene (TCE) using a long-lasting persulfate/biochar barrier

Groundwater contamination by chlorinated solvents causes potential threats to water resources and human health. Therefore, it is important to develop effective technologies to remediate contaminated groundwater. This study uses biodegradable hydrophilic polymers, hydroxypropyl methylcellulose (HPMC), hydroxyethyl cellulose (HEC) and polyvinyl pyrrolidone (PVP) as binders to manufacture persulfate (PS) tablets for the sustained release of persulfate to treat trichloroethylene (TCE) in groundwater. The release time for different tablets decreases in the order: HPMC (8-15 days) > HEC (7-8 days) > PVP (2-5 days). The efficiency with which persulfate is released is: HPMC (73-79%) > HEC (60-72%) > PVP (12-31%). HPMC is the optimal binder for the manufacture of persulfate tablets and persulfate is released from a tablet of HPMC/PS ratio (wt/wt) of 4/3 for 15 days at a release rate of 1127 mg/day. HPMC/PS/biochar (BC) ratios (wt/wt/wt) between 1/1/0.02 and 1/1/0.0333 are suitable for PS/BC tablets. PS/BC tablets release persulfate for 9-11 days at release rates of 1243 to 1073 mg/day. The addition of too much biochar weakens the structure of the tablets, which results in a rapid release of persulfate. TCE is oxidized by a PS tablet with an efficiency of 85% and a PS/BC tablet eliminates more TCE, with a removal efficiency of 100%, due to oxidation and adsorption during the 15 days of reaction. Oxidation is the predominant mechanism for TCE elimination by a PS/BC tablet. The adsorption of TCE by BC fits well with the pseudo-second-order kinetics and the pseudo-first-order kinetics, which describes the removal of TCE by PS and PS/BC tablets. The results of this study show that a PS/BC tablet can be used in a permeable reactive barrier for long-term passive remediation of groundwater.