Traditional geological and biological processes require the injection of dissolved substrates to enhance biodegradation. However, continuous substrate injection results in clogging aquifer due to excess growth of microbes near an injection well. To overcome this problem, research on slow substrate-release technology has been conducted recently. In this study, a substance emulsified with oil, humic acid and distilled water was prepared to promote the biological anaerobic dechlorination and natural attenuation of trichlorethylene (TCE).
In other studies, chemical surfactants used for oil emulsification are not economical because they have to maintain a critical micelle concentration or higher. In this study, humic acid was used instead of surfactant to minimize the limitations of the existing method and the environmental load. Humic acid is a substance that exists in nature and can play a sufficient role because it has both hydrophilic and hydrophobic groups. The method for manufacturing microsized-oil droplet (MOD) was optimized using distilled water, corn oil, and humic acid. In order to evaluate the applicability of the TCE dechlorination process of the manufactured MOD, a lab-scale batch reactor experiment was conducted. Four factors were evaluated in the experiment; 1) TCE dechlorination evaluation in the presence or absence of MOD, 2) appropriateness of humic acid as a substitute for surfactant, 3) TCE dechlorination in the presence or absence of inactivator of native microbial activity, and 4) MOD concentration effects on TCE dechlorination.
Batch reactors were constructed using site groundwater and soil in which Dehalococcoides were present. humic acid did not affect on the TCE dechlorination, suggesting that humic acid may be appropriate as a substitute for surfactant. Without MOD, TCE was decomposed into dichlorethylene (DCE), but the other by-products of TCE dechlorination was not detected. With MOD, DCE, vinyl chloride (VC), and ethylene (ETH) were sequentially observed. Through this result, it was confirmd that the MOD effectively supplies electrons to the complete dechlorination of TCE to ETH. However, when an excess of MOD was supplied, there was a limitation forming unfavorable conditions for anaerobic digestion in which the dechlorination reaction did not proceed and propionic acid was accumulated after DCE was generated. Therefore, if an appropriate amount of MOD is supplied, MOD can be effectively used as a natural reduction activator to promote biodegradation in an aquifer contaminated with TCE.