A novel three-stage treatment train for the remediation of trichloroethylene-contaminated groundwater

Abstract

This study used a novel three-stage treatment train that was composed of chemical oxidation, anaerobic bioremediation and a passive reactive barrier (PRB) to remediate trichloroethylene (TCE)-contaminated groundwater. Batch oxidation and biodegradation experiments and a continuous column study were used to evaluate the compatibility of different technologies and the feasibility of the removal of TCE by the treatment train. The results of batch experiments show that high concentrations of TCE (50 mg L À1 ) were removed completely by the addition of 5000 to 50 000 mg L À1 persulfate during 24 to 96 h of reaction. Ferrous ion-activated persulfate may result in a residue of TCE due to the rapid consumption of persulfate by ferrous ions. Significant inhibition of soil bacteria was observed upon the addition of persulfate in concentrations greater than 20 000 mg L À1 . Both low pH and the oxidative stress of persulfate were responsible for the adverse effect on indigenous microorganisms. The results of a microcosm study reveal that the presence of high concentrations of sulfate (up to 50 000 mg L À1 ) had no adverse effect on TCE removal. Sulfate significantly enhanced the dechlorination of vinyl chloride via sulfate reduction, which demonstrates that sulfate produced from persulfate oxidation could be utilized by indigenous bacteria to achieve the complete dechlorination of TCE. The addition of 5000 to 50 000 mg L À1 bioremediation reagent improved the degradation of TCE. Dechlorinating bacteria, Dehalococcoides, and the reductive dehalogenase, vcrA, of Dehalococcoides were detected during TCE biodegradation. The results of a column study show that the proposed treatment train removed TCE and its byproducts effectively and there was no problem with the connection of chemical oxidation and anaerobic bioremediation in the novel treatment train technology. The use of 10 000 mg L À1 of persulfate and the bioremediation reagent, and the PRB that can continuously release 6000 mg L À1 of persulfate are suggested to operate the treatment train. The proposed treatment scheme will provide a more effective alternative for the remediation of contaminated sites in the future.

Remediation of trichloroethene (TCE)-contaminated groundwater by persulfate oxidation: a field-scale study

“…However, co-metabolic biodegradation of TCE under aerobic conditions is limited if no extra carbon source is added. 1,22,23 Because TCE contamination was first detected in 2006, the results indicate that natural attenuation mechanisms at this site did not decrease TCE concentrations to the groundwater control standard. Therefore, more active remediation technologies are required for this site.…”

“… 24 Decreases of 2.5 to 6.0 pH units caused by persulfate have been observed in aqueous and soil slurry systems. 1 In general, pH plays an important role in affecting the performance for the degradation of contaminants in persulfate systems. Hussain et al 24 found that acid conditions (pH 2.0 and pH 4.0) are favorable to the degradation of p -chloroaniline (PCA) in a zero-valent iron-activated persulfate system.…”

“…Chlorinated solvents, such as trichloroethene (TCE), are mainly used for industrial production, degreasing and dry cleaning and are released into the environment because of leakage from storage tanks and the use of improper disposal procedures. 1,2 Since TCE is a possible human carcinogen and has acute toxicity to humans, the contamination of groundwater with TCE is of concern. The US Environmental Protection Agency (EPA) has set a maximum contaminant level (MCL) of 5 mg L À1 for drinking water to protect public health.…”

“…6,7 Because persulfate is a stable oxidant that persists in the subsurface for a long time, it is a useful oxidant for soil and groundwater remediation. 1,8,9 Many studies of persulfate oxidation focus on the development of activation methods, 2,[10][11][12] the feasibility of contaminant removal, 5,6 the effect of pH on pollutant degradation [13][14][15] and the mechanism and kinetics of contaminant removal. 12,16,17 Studies involving the application of persulfate are fewer.…”

“…Persulfate is activated by activators such as heat or ferrous ions to generate powerful sulfate free radicals (SO 4 − ˙) (reaction ( 2 )): 1,5 S 2 O 8 2− + activators → 2SO 4 − ˙ or SO 4 − ˙ + SO 4 2− , E 0 = 2.7 V …”