In-situ treatment of nitrate polluted groundwater by chemoautotrophic denitrification: flow-through tank experiments

Nitrate in groundwater can be converted microbially into N₂. However, the lack of anoxic conditions (oxygen concentrations < 50 μmol/L) in the aquifer linked with the limitation of microbial available organic and inorganic electron donors may lead to insufficient denitrification in aquifers and nitrate concentration above the drinking water limit of 50 mg/L can be observed. In view of the increasing drinking-water scarcity associated with climate change and the continuing increase in nitrate concentrations in near-surface aquifers, it is urgently necessary and prudent to develop practicable and cost-effective methods to reduce nitrate to harmless N₂.
Faced with the increasing nitrate pollution in groundwater, we want to develop a new cost-effective in-situ remediation technology by hydrogen/methane coupled denitrification. We hypothesize that the simultaneous injection of the two water soluble electron donors H₂ and CH₄ into groundwater may significantly enhance the rate of nitrate consumption by activation of denitrifying chemolithoautotrophic microorganisms that are already present in the groundwater.
Here we show the experimental set-up of the 2D-model aquifer (6 m x 1,8 m), the sampling strategy and show first results of the methane injection experiment. Measurements are performed along the flow direction and at several depths. Concentration profiles and stable isotope composition of methane (δ¹³C) and nitrate (δ¹⁵N) linked with oxygen concentrations shed light on the hydrogen-methane coupled denitrification potential in the model aquifer.