Hydrogen gas delivery to enhance reductive biodehalogenation of chlorinated solvets in aquifers: a feasibility study

Groundwater contaminants such as chloroethenes (tetrachloroethene, PCE, trichloroethene, TCE, dichloroethene, DCE, and vinyl chloride, VC) affect high-quality water availability worldwide. Chlorinated solvents undergo reductive dechlorination through organohalide respiration (OHR) by anaerobic bacteria such as Dehalococcoides and Dehalogenimonas. Enzymes involved in dechlorination activity are reductases encoded by pceA, tceA, bvcA, vcrA and cerA genes. Microbial dechlorination is a recognized ally in remediation of chloroethenes contaminated sites although biodegradation rate is limited by the amount of electron-donors available to bacteria. Biostimulation with dihydrogen (H2) gas is proposed as a bioremediation strategy that allows to fuel microbial reductive dehalogenation with benefits from some operational points of view and conservation of water quality. Since knowledge of the effectiveness of H2 injection on OHR microbial communities of anaerobic groundwaters is still scarce, the aim of the present work was to investigate the effect of H2 pulses to enhance OHR in a 150-300 mg/L chloroethene-contaminated aquifer. Experimental results at a microcosm-scale level are presented. GC- MS analyses demonstrate chloroethenes transformation by OHR bacteria, evidencing the effect during 2 months’ incubation. OHR biomarkers for tceA, vcrA and cerA reductases and Dehalococcoides and Dehalogenimonas 16S rRNA genes were quantified by Real Time quantitative PCR in the range of 104-107 gene copies/mL. The impact of H2 addition on microbial community is under investigation by 16S rRNA Illumina libraries. Assessment of H2 injections is the base for promising in situ results where biological aspects, including biodegradation rates, will be compared to traditional biostimulation strategies. Acknowledgements: Agritech National Research Center - European Union Next- Generation EU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) - MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.4 - D.D. 1032 17/06/2022, CN00000022). This manuscript reflects only the authors’ views and opinions, neither the European Union nor the European Commission can be considered responsible for them. Nuova Alba, Edison and Tauw supported the research.