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

ABSTRACT

The aim of this research was to identify the sequence of degradation processes that leads to the selective enrichment of microorganisms involved in the degradation of carbon tetrachloride and chloroform under conditions of natural attenuation and lactic acid biostimulation. To this end, a comparative study using microcosm experiments was conducted to analyze these two scenarios. The authors used groundwater and sediment collected from a field site located at a petrochemical complex to create the microcosms. Chemical, compound-specific isotope and microbial analyses were performed. A significant finding of this work was the abiotic degradation of carbon tetrachloride. Another result was the identification of biotic reductive dechlorination of chloroform by a bacterium of the Clostridiales order. This study showed that biostimulation with lactic acid produced faster degradation rates of carbon tetrachloride and chloroform. Lactic acid acted as an electron donor and promoted a decrease in the concentration of other electron acceptors such as nitrate and sulfate, which competed with chloromethanes. Thus, biostimulation could be an efficient remediation strategy for sites contaminated with chloromethanes, especially when a site's complex pollution history results in chemical background concentrations that are high in compounds that could potentially reduce natural attenuation.

KEYWORDS:

• Biostimulation with lactic acid
• biotic and abiotic degradation
• chloromethanes
• Clostridiales order
• compound-specific isotope analysis (CSIA)
• Dechlorosoma suillum sp.
• DGGE
• microcosm
• natural attenuation

Acknowledgments

We are indebted to the Catalan Water Agency and members of Clariant Ibérica S.A. of Tarragona and INTECSON S.L. of Reus for their support and cooperation while carrying out this fieldwork. We also thank members of the Department of Geochemistry, Petrology, and Geological Prospecting at the University of Barcelona and particularly members of the hydrogeology group. We are grateful to members of the Scientific Technical Services at the University of Barcelona for their help in analyzing the samples.

Funding

This research was supported by projects CTM 2005-07824 and CGL 2008-02164/BTE of the Spanish Ministry of Education and Science and Clariant Ibérica S.A.