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The new arsenic in drinking water regulation will require many utilities to implement technologies for arsenic removal. Of the US Environmental Protection Agency (USEPA) identified treatment options, adsorption onto solid media seems to be the most attractive for small treatment facilities, especially in the arid Southwest. The arsenic bearing solid residuals from these adsorption processes are to be disposed in non-hazardous landfills. The Toxicity Characteristic Leaching Procedure (TCLP) test defines whether a waste is hazardous or non-hazardous (w.r.t. landfill disposal) and most solid residuals pass the TCLP. However, the TCLP may not correctly estimate the leaching potential of arsenic residuals. The TCLP poorly simulates the alkaline pH, anaerobic microbial activity, mineralogical aging, high phosphate, and concentrated organic characteristics of landfills. These same conditions are expected to favor mobilization of arsenic from metal oxide adsorbents. This study quantifies leaching of arsenic and other contaminants from solid residuals under landfill conditions and compares this to the leaching observed using the TCLP. Activated Alumina (AA) and Granular Ferric Hydroxide (GFH) have been identified as the adsorbents that will be most widely used for arsenic removal. Consequently, this research focused on leaching from these two residuals. Initially, small volume batch experiments were used to quantify the extent of arsenic sorption as a function of pH and arsenic to solid mass ratio. The results indicate arsenic partitions significantly more strongly to the aqueous phase in the pH range and high arsenic loadings that characterize landfill conditions than in the conditions created in the TCLP. Computer simulation results are compared to the observed results from laboratory trials. This model effort indicates potential mechanistic underpinnings for the observed behavior and allows prediction of leaching potentials under a wider range of conditions. The work indicates that significantly greater arsenic leachate concentrations can be expected than those predicted by TCLP results for both activated alumina and GFH. It further indicates the more challenging WET procedure may also underestimate arsenic mobilization in certain cases. Includes 27 references, figures.

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Edition: Vol. - No. Published: 06/16/2002 Number of Pages: 16File Size: 1 file , 370 KB