An estimated 300,000 people in California rely on public water systems that are out of compliance regarding carcinogenic arsenic (As). Low income, minority communities bear a disproportionate burden of high As levels in drinking water, above the EPA-Maximum Contaminant Level (MCL) of 10 μg/L. In addition, aquifers containing As(III) are often co-contaminated by manganese (Mn), for which the EPA secondary MCL is 500 μg/L. Effective and affordable As and Mn removal from drinking water is critical to ensure the health and economic well-being of marginalized communities relying on such aquifers. Air Cathode Assisted Iron Electrocoagulation (ACAIE) is a novel water treatment method with applicability to rural communities. Similar to iron electrocoagulation (Fe-EC), ACAIE relies on the electrical dissolution of an Fe anode to produce Fe(II) in solution. However, ACAIE systems employ a carbon-based gas-diffusion cathode to produce H2O2 in the electrolyte. Depending on the charge dosage rate (CDR), ACAIE can generate equimolar H2O2 and Fe(II), facilitating rapid formation of reactive, nanoscale Fe (oxyhydr)oxides that bind to dissolved contaminants and can be later removed by filtering or settling. This study investigated the effect of CDR (6, 600 and 1500 C/L/min) and pH (4, 7 and 10) in ACAIE in a synthetic California groundwater matrix on removal of 1500 μg/L As(III) and 1000 μg/L Mn(II). Decreasing As(III) removal was observed with increasing pH, whereas Mn(II) removal increased with pH. CDR had a modest effect at pH 7, with increasing CDR decreasing As removal, but increasing Mn removal. EPA-MCL for As was achieved at pH 4 and 7, and at pH 7 and 10 for Mn. Characterization of the precipitate by Fe K-edge X-ray absorption spectroscopy showed pH and CDR did not impact the structure of Fe(III) precipitates, which were present as highly disordered hydrous ferric oxide. The XAS data indicated &gt;90% of the As(III) had been oxidized to As(V) in each ACAIE experiment. Despite the highly oxidizing conditions in ACAIE, Mn(II) was not as effectively oxidized as As(III), and was present mostly as Mn(II) (~60%), with some Mn(III) (~40%). The difference in Mn(II) and As(III) oxidation in ACAIE can be explained by the selectivity and reaction rates of the Fenton-type reactive intermediates. Overall, our results indicate that ACAIE can be an effective method for As and Mn co-removal, but the pH range for optimal removal is limited to circumneutral waters.

Inverse trends of As(III) and Mn(II) removal in air cathode iron electrocoagulation

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.