Biogeochemical evaluation of disposal options for arsenic-bearing wastes generated during drinking water treatment

Arsenic contamination of drinking water sources threatens the health of over 50 million people around the world. Sustainable implementation of arsenic removal technologies requires disposal options for produced wastes that limit the release of arsenic. Arsenic contamination is particularly severe in Bangladesh and India, where access to landfills is limited and most wastes are disposed on the ground nearby arsenic removal units. To address concerns with arsenic release under these disposal conditions, this research characterized the stability of arsenic wastes during two alternative disposal strategies. Stabilization of wastes in concrete and mixing wastes with cow dung were tested using arsenic-bearing ferric iron wastes generated during the removal of arsenic from groundwater in West Bengal, India. Under a range of leaching tests, 4.2). Through the characterization of arsenic within the cement matrix by microXRF, arsenic was found to remain primarily associated with iron, consistent with the initial state of the waste. These results show that concrete stabilization can be a viable disposal option to limit arsenic release when low pH can be avoided. Cow dung mixing has been recommended based on the ability of microorganisms to create volatile arsine gases that can be subsequently diluted to safe levels in the atmosphere. However, little is known about the extent of volatilization or the microbial communities responsible for this transformation. Cow dung mesocosms with varying levels of methanogenic inhibition were used to study the impact of methanogenesis on arsenic volatilization under anaerobic conditions. Arsenic volatilization was primarily due to the activity of methanogens, but was not a significant transformation pathway. Less than 0.02% of the total arsenic was released to the gaseous phase. Instead, more arsenic (<4%) was leached into the aqueous phase. These results highlight that cow dung disposal may increase the potential for arsenic release into the aqueous phase and is ineffective in producing volatile arsenic gases. Taken together, these studies characterized the important microbial and geochemical determinants of arsenic fate in non-landfill disposal conditions and provide additional insight on arsenic transformations over a broader range of environmental conditions.