Effects of engineering injection and supplement mode of in-situ biogeochemical transformation enhancement EVO-FeSO4 on the remediation of tetrachloroethylene contaminated aquifer.

Traditional in situ biogeochemical transformation suffers from competition among crucial microorganisms and inadequate formation of reactive minerals, thus leading to the accumulation of toxic intermediates. In this study, three regulation schemes were proposed to solve these problems from the perspective of engineering mode. Results showed intermittent injection mode effectively reduced the accumulation of toxic intermediates but the reduction rate of tetrachloroethylene was decreased. And periodical supplementation of carbon and sulfur sources accelerated the removal of tetrachloroethylene but failed to reduce the accumulation of toxic products. While, regular supplementation of sulfate effectively weakened the competition of methanogens and increased the iron sulfide proportion on the surface of the minerals, thus reducing the accumulation of toxicity. Based on the results, this study obtained an effective engineering approach for practical site application. In addition, the main forms of active minerals capable of β-eliminating contaminants during biogeochemical transformation were identified in this study, including FeS, FeS2, and Fe3S4. Furthermore, the engineered regulatory mechanism of this study was summarized through the analysis of microbial community structure and mineral morphology. The amendment promotes the production of minerals and thus controls the transformation pathway of contaminants by altering the abundance of sulfate-reducing bacteria and dissimilatory iron reducing bacteria. This mechanism can provide a basis for subsequent theoretical studies.