| Arsenic contamination of water supplies is recognized as a global issue. The need for affordable and reliable arsenic removal technology is especially pressing in third world countries, such as Bangladesh, where inhabitants are ingesting high levels of arsenic contaminated water daily. This technology is also important for the treatment of industrial wastes, where arsenic levels can be orders of magnitude higher than in contaminated drinking water.;It was determined that neither the addition of sulfate, nor the addition of limestone to the bench-scale reactors had an effect on arsenic removal. However, experiments examining the effects of biotic versus abiotic conditions found a statistically significant (20--40%) increase in arsenic removal in the biotic systems as opposed to those that had been sterilized. These results indicate the importance of biological activity in anaerobic bioreactors, but also serve as a clear indication that this is not the primary removal mechanism in these model systems.;Results from the experiments examining the effects of inlet arsenic concentration indicated that the reactor solids were capable of adsorbing a fixed amount of arsenic and that this adsorption in directly related to the life expectancy of these systems. These findings suggest that the mechanism behind arsenic removal in the bench-scale reactors is adsorption to the reactor contents.;X-ray absorption spectrometry analysis of spent reactor solids from both the Trail system and the bench-scale reactors identified arsenite, arsenate and an arsenic (III)-sulfur compound that could not be identified as either orpiment or realgar, signifying that the formation of thioarsenite species plays a role in these systems. Notably, the results indicated that the formation of insoluble arsenic sulfides---orpiment and realgar---does not appear to play a major role in arsenic removal.;This thesis aimed to determine if the performance of a field-scale biological reactor that is successfully operating in Trail, BC could be reproduced at a bench-scale level and from there to determine, which mechanisms are responsible for the observed arsenic removal within these systems; elucidation of the mechanisms would allow for the optimization of these systems as well as the assessment of the practicality of using bioreactors as an effective and economical means by which to remove arsenic from industrial effluent and possibly even drinking water supplies. A redesign of an earlier model system was able to greatly improve result reproducibility. Arsenic removal in the bench-scale models was then assessed as a function of biotic versus abiotic conditions, sulfate addition, limestone addition as well as variations in the inlet arsenic concentration (25 mug/L, 50 mug/L, 100 mug/L and 1000 mug/L). An investigation into the stability of the spent reactor solids was also conducted to determine whether or not this material requires classification as hazardous waste upon the decommissioning of the units.;Leachability results from the examination of reactor solids from both the Trail reactor system as well as the bench-scale systems were variable. In some instances, leachable arsenic concentrations were above the hazardous waste leachate criteria of 2.5 mg/L set out by the Ontario Ministry of the Environment. Accordingly, it is advised that all spent solids be analyzed prior to disposal. |
