The Influence of Compost on Arsenic Removal from Contaminated Groundwater in Granitic Aquifers

Arsenic is classified as a group 1 human carcinogen according to the World Health Organization. Anthropogenic activities such as mining and wood preservation contribute to arsenic contamination of surface and sub-surface water. Most of the currently available remediation strategies to remove arsenic involve slow processes and produce residues that are difficult to treat or dispose. In this study, with an objective to develop alternative arsenic remediation strategies, we examined removal of arsenic using organic compost as a potential adsorbent. We ran saturated column experiments by injecting 10 mg/L arsenic-spiked synthetic groundwater to compare the arsenic removal between the presence and absence of compost in granitic aquifers. The water analysis showed the compost removed 14 percent (%) of arsenic from the contaminated water within 16 min, while there was no change in arsenic concentration in the experiment without compost. The results illustrated that arsenic treatment using compost is feasible for contaminated groundwater remediation. Different pH evolution was also observed in both experiments. The column with only decomposed granite showed a small decrease in pH, which we believed was caused by a dissolution of silicate minerals in the granite. The column with compost exhibited a more fluctuating pH. An abrupt drop in pH was observed at an early time period and thought to be caused by release of H+ from organic anions after water interacted with the compost. After the initial period, the change in pH was primarily driven by mixing of the water used for column saturation and the injected contaminated groundwater. The major factors identified for arsenic removal are the presence of iron (Fe) and a lower starting pH condition in the compost experiment, which provides more available sorption sites leading to higher arsenic sorption.