Leaching from High Capacity Arsenic-Bearing Solid Residuals under Landfill Conditions

Abstract

Arsenic is a naturally occurring contaminant in ground water. The link between human exposure to elevated levels of arsenic and the increase in cancerous and non-cancerous diseases is well documented. Consequently, arsenic removal from drinking water has been thoroughly investigated.Lowering the maximum contaminant limit of arsenic (from 50 to 10 ppb) will burden small water utilities, who either lack the financial or technical ability to comply. Adsorption onto solid media has been one of the most attractive options for small water utilities (EPA, 2001), but this process generates huge amounts of arsenic bearing solid residuals (ABSRs) complicating further this matter.Numerous studies have suggested that the Toxicity Characteristics Leaching Procedure (TCLP) does not properly reflect the actual leaching behavior of ASBRs under landfills (Ghosh et al., 2004). This work focuses on testing different arsenic iron- oxide and non- iron- based sorbents, likely to be used for arsenic removal, and assessing the long term behavior of these sorbents under landfill conditions. Our results indicate that microbial processes play a major role in the mobilization of As from granular ferric hydroxide (GFH). Long term operation of GFH sorbent showed that Fe (III) was reduced to Fe(II) and As(V) was reduced to As(III) under anaerobic/reducing conditions. Under semi batch landfill simulation experiments, our results show that non iron based media leached arsenic above the Toxicity Characteristics limit (TC) and it was observed that sorbate (As) might leach at a faster rate than the sorbent itself. It is thought that arsenic mobilization from iron-based sorbent occurs mostly due to iron reduction and its subsequent dissolution. However, measured arsenic leaching rates from the sorbents used in this study are comparable with that of the ferric hydroxide media, which indicates that the mechanism of arsenic mobilization might be independent of the possible dissolution of the sorbent. Despite the fact that non- iron based media may have a higher arsenic adsorption capacity, they leach arsenic at a higher rate than iron based media under our simulated landfill conditions.