| Arsenic in (anaerobic) groundwater is one of the main flobal groundwater quality problems. Intermittent introduction of aerated water in extraction wells can in principle reduce the As load in the pumped water due to oxidation of Fe(II) and Mn(II) followed by formation of metal hydroxides which wil contain As through adsorption/coprecipitation phenomena. These reaction occur at the transition zone between oxic and anoxic groundwater, which is one of the topics to be addressed in the TRIAS programme. Redox, buffering of compounds and distribution of compounds over solid and solution are other TRIAS priorities. The problem is extremely complex both from a chemical as well as from a physical/hydrological point of view. The system is chemically multi-component, and conditions change in space and time around the well. Both the ratio and the absolute concentration level of the elements which show strong chemical interaction (Fe, Mn, As, P, Ca), vary largely in relevant groundwater systems. The chosen approach addresses the chemical interactions with varying degree of sophistication. The main factors which control the chemical behaviour will be derived in part I and be used to construct a simplified reaction framework which will be used in part II. In part II a 3D reactive transport model, using network and percolation theory will be developed. In part II also experiments will be done which focus on aspects of transport of As with the colloids that are formed in situ and formation of an iron hydroxide filter around the well. Another important aspect is research in the (co) precipitation aboveground ex-situ, to remove As. The outcome of the research will be useful to design improved strategies for As removal either ex-situ or in-situ. |
