Application of Persulfate Oxidation to Remediation of Contaminated Soil and Groundwater
Date Issued
2011
Date
2011
Author(s)
Fang, Shyang-Chyuan
Abstract
The purposes of this study are to explore the applicability and relevance to implement persulfate oxidation as a remedial means for soil and groundwater contaminated by petroleum hydrocarbons in Penghu area. This study consisted of three main work tasks including two laboratory and one pilot-scale demonstrations. Prior to oxidation testings, priority heavy metals content of the testing soils collected from the project area was evaluated through bench-scale chemical oxidation experiments.
As in the tests for the the study site, a gasoline service station, it was observed that at pH of groundwater less than 4.0, heavy metal as nickel was detected at a concentration of 1.19 mg/L in groundwater, exceeding the regulatory standard of 1.0 mg/L. When pH elevated to a level above 6.0, nickel concentration was declined to a concentration of 0.719 mg/L. It appeared that decrease in nickel concentration was attributed to the pH increases in groundwater; therefore, it appeared that decrease in pH in groundwater during oxidation treatment process was the main cause to trigger the increase of nickel concentration.
As in the field pilot tests for power plant remediation, Results obtained from the bench- and pilot-scale tests reveal that persulfate is a more persistent oxidant than hydrogen peroxide and sulfate radical (SO4-‧) has longer reaction time than hydroxyl radical (OH-‧). Furthermore, it was observed that persulfate was subject to less impact by radical scavengers as CO32-, HCO3-, and Cl- than was hydrogen peroxide, and it thereby, had less soil oxidant demand in the aqueous system onsite. Data obtained from bench-scale experiments showed that persulfate oxidation provided better removal efficiency for petroleum hydrocarbons than Fenton-like reaction. Results of bench experiments revealed that nearly 90% of total petroleum hydrocarbons (TPHd) in the soil matrix was reduced through persulfate oxidation, as opposed to 41% through Fenton-like reaction. The subsequent pilot-scale testing showed that persulfate activated by either ferrous ion or hydrogen peroxide could effectively reduce TPHd concentration to below the regulatory standard within two weeks of testing period. In the course chemical oxidation, heat, low pH, and gas generated during oxidation process would not only enhance desorption of the contaminants but also elevate the solubility of the chemicals of concern. Persulfate oxidation in the pilot test was observed to elevate the solubility of TPHd by two orders of magnitude, from 1.34 mg/L in groundwater to 289 mg/L in leachate collected from the soil treatment cells. Statistical analysis of the pilot testing performed at a power-plant indicated that 71.7% of diesel fuel was reduced through persulfate oxidation, 23.5% of diesel fuel was recovered from leachate as free product, and less than 5% of diesel fuel remained in the soil.
Nickel has poor sorption selectivity to soil as compared to other divalent metals and has strong tendency to dissolve in groundwater as pH declines, causing secondary site contamination, particularly in the area where the aquifer consists of nickel-rich soil. Therefore, treatability of chemical oxidation for groundwater remediation should be carefully evaluated and planned prior to implementation to prevent from adverse site impact.
Subjects
in-situ chemical oxidation (ISCO)
sodium persulfate
nickel
heavy metals,
secondary contamination
groundwater pollution
Type
thesis
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