Removal of chlorine-contaminated groundwater by two-stage ozonation and biostimulation methods

Trichloroethene (TCE) contamination is a critical environmental hazard, and the substrate options for its biostimulated remediation are limited. This study applied an ozonation-and-biostimulation process to remove TCE from groundwater. The substrate used, denoted as Transferred Energy Element (TEE), was composed of natural organic materials and had a low viscosity (2.914 cP). Ten batch experiments were conducted through the application of micro-nano bubbles (MNBs) and substrates (TEE and EOS® [emulsified oil substrate]). MNBs with an average diameter of 157.5-180.8 nm effectively degraded TCE and dichloroethane within 6 min. Biostimulation using the TEE substrate effectively degraded both TCE and vinyl chloride pollutants and reached a steady state after 25 days. The two-stage dechlorination procedure with MNB treatment as the first stage enhanced TCE removal via biostimulation. MNBs reduced the TCE concentration in the first 20 min, but increased the chloride (Cl^-) concentration over the following five days (∼80 mg/L). The procedure with biostimulation as the first stage and 20 min ozonation as the second stage reduced the Cl^- concentration by ∼10 mg/L. The Cl^- concentrations rebounded after day 25 in the EOS environment. X-ray diffraction revealed that the released Na⁺ from the TEE settled with Cl^- as minerals in the soil. The novel two-stage method for TCE removal was found to be more effective than solo MNB treatment or biostimulation.