Temporal hydrochemical and microbial variations in microcosm experiments from sites contaminated with chloromethanes under biostimulation with lactic acid

Abstract

The objective of our research is to identify the sequence of degradation processes leading to microbial speciation of microorganisms involved in degradation of CT and CF under natural attenuation and lactic acid biostimulation conditions. To this end, a comparative study of two types of microcosm experiments was carried out to analyze two scenarios: natural attenuation and lactic acid biostimulation. Experiments were carried out with water and sediment from a field site located at a petrochemical complex whose hydrochemical background inhibited the natural attenuation of carbon tetrachloride and chloroform. A significant result of our work was that these experiments allowed us to identify the CT abiotic degradation processes, among which the abiotic degradation induced by the biogenic activity of Dechlorosoma suillum should be noted. Although this is an abiotic degradation, the metabolism of this microorganism generates green rust precipitates, which in turn favor the abiotic reductive dechlorination of CT. Other relevant result was the identification of the biotic reductive dechlorination of CF by a bacterium of the Clostridiales order. This result presented the particularity that an apparent absence of isotopic fractionation was observed because a mixture of chloroform of different origins was produced. Our research showed that these processes were more efficient, in terms of faster degradation rates, when biostimulation with lactic acid was carried out. This biostimulation could therefore be an efficient remediation strategy at sites contaminated by chloromethanes, especially in cases where a complex pollution history results in a rich hydrochemical background that makes it difficult natural attenuation.