Quantitation of Arsenic Removal in Microelectrolysis (ME) Reactors: Effects of Mixing, Active Media Composition, and Active Media Regeneration

Abstract

Landfill gas condensate is formed within a landfill gas collection system or during landfill gas (LFG) purification carried out to produce renewable natural gas (RNG). LFG condensates formed during RNG production have been found to contain high levels of arsenic which may result in exceedances of applicable discharge limits. Arsenic species in LFG condensates are predominantly methylated and/or thiolated organoarsenicals which are much more difficult to remove with conventional treatment techniques. Microelectrolysis (ME) treatment using zero-valent iron (ZVI) and activated carbon (AC) achieves high levels of arsenic removal in LFG condensate samples. This study evaluates the efficacy of ME reactors operating at different mixing modes, impeller types, and, to some extent, electrochemically augmented ME treatment of LFG condensate. Other aspects of ME treatment optimization explored in this thesis include acid regeneration of ME treatment media, its performance longevity, and the assessment of several commercially available ZVI and GAC products. Experimental results show a range of ME treatment performance across different reactor types, with typical arsenic removal between 80% and 97%. A single initial dose of ZVI was found to be cyclable for at least 15 cycles for maintained ME treatment performance so long as GAC is either replaced periodically or more mass is added after each cycle. Preliminary data for electrochemical augmentation of ME treatment in batch and flow recirculation reactors with a ME mixing zone suggests that the addition of an external voltage enhances ME treatment, but further testing is required to verify these findings.