Implementation of zero-valent iron (ZVI) into drinking water supply - role of the ZVI and biological processes.

Arsenic in drinking water is concerning millions of people around the world, even though many solutions to the problem have come up in recent years. One of the promising solutions for removing arsenic from water is by implementation of a zero-valent iron (ZVI) in the drinking water production. The purpose of this work was to study a treatment of As pollution based on the ZVI, aeration and sand filtration that was monitored for period of 45 months. In applied configuration and conditions ZVI was not able to remove arsenic alone, but it worked as a source of ferrous ions that during its oxidation enabled to co-precipitate arsenic compounds in the sand filter. The results show that after a lag phase of about 6 months, it was possible to achieve water production with an As content from 20 μg L(-1) to below 5 μg L(-1). The treatment also enabled to remove phosphates that were present in groundwater and affected As uptake by hindering its co-precipitation with Fe compounds. Determination of colony forming units on As amended agar helped to find arsenic resistant bacteria at each stage of treatment and also in the sand filter backwash sludge. Bacterial communities found in groundwater, containing low concentration of As, were found to have high As resistance. The results also indicate that the lag phase might have been also needed to initiate Fe ions release by corrosion from elemental Fe by help of microbial activity.