LAUSR

Abstract The influence of biotic processes that occur in anaerobic conditions in landfills on arsenic (As) release from As-laden waste and the dependence of these processes on leachate composition was evaluated using incubations of an As-bearing water treatment residual comprised of the iron-oxide E33 adsorbent. This adsorbent, which is mainly goethite, was incubated with an As(V) and sulfate reducing bacterium, Bacillus benzoevorans HT1, and an Fe(III) and As(V) reducing bacterium, Shewanella putrefaciens CN32, in synthetic leachate with composition similar to landfill leachate. The influence of leachate composition on biotic As release was evaluated by studying systems prepared with a leachate solution that incorporated elevated concentrations of phosphate, bicarbonate, sulfate or silicate. The total As released under biotic conditions was two orders of magnitude higher than that in the abiotic control and during the initial stages of the incubations we observed most of the arsenic as As(III), consistent with the dissimilatory reduction of As(V). At later times, however, trends differed based upon whether the system was equilibrated with CN32 or HT1. Under the baseline leachate conditions, CN32-mediated As release was further promoted by reductive dissolution of goethite, while HT1-mediated As release was limited via indirect reductive goethite dissolution controlled by dissimilatory sulfate reduction. Biotic incubations with elevated anions identified As release behavior that reflected the influence of the different anions. Elevating phosphate not only promoted rapid As release via enhanced As(V) bioreduction in the first 2 days of incubation, but also incurred secondary As release from iron sulfide phases, which were secondary mineral phases generated from Fe(III) reduction. Increasing bicarbonate stimulated As release as it exchanged with sorbed As at the goethite surface thereby increasing the availability of As(V) for bioreduction. Elevating sulfate and silicate both decreased biotic As release as they appeared to inhibit Fe(III) bioreduction. Overall, our results identified that biotic As release mechanisms were related to bacteria metabolic diversity and leachate composition. Such information can assist in evaluating As risk assessment and As-laden waste management in biologically active environments, such as landfills.