Mass Balance of Arsenic in Microelectrolysis Treatment of Arsenic-Containing Landfill Gas Condensate and Initial Study of Formation of Volatile Arsenic Species

Abstract

The behavior of arsenic in treated landfill gas condensate from the BioEnergy Washington facility at the Cedar Hills Regional Landfill in King County, WA was studied with the goal to quantify the mass balance of arsenic typical for microelectrolysis (ME) treatment and identify the extent of volatilization and speciation of arsenic species that may be formed in ME treatment. Microelectrolysis treatment successfully removes arsenic at >90% from the condensate, but mass balance experiments demonstrate little to no arsenic retained by ME solid reaction media. Therefore, an analytical method based on the formation of colored complexes between arsines and silver diethyldithiocarbamate (AgDDC) was tested to examine the generation of arsines and, to a lesser extent, stibines. These gases are formed in highly reducing conditions induced by sodium borohydride and milder reduction occurring in the ME treatment, converting the dissolved arsenic. AgDDC absorbance data that comprise the spectra of individual arsine/AgDDC complexes, their characteristic maxima and kinetic profiles of concentration-dependent absorbance development and, in some important cases, fading strongly indicate that the arsenic volatiles formed upon the borohydride reduction of the condensate are dominated by methylated arsines. These results need to be confirmed and expanded for ME treatment of BEW process water. Further work is needed to determine the extent of As volatiles’ removal by oxidative and reductive processes, adsorption, and thermal treatment.