Treatment of Arsenic Contaminated Groundwater using Oxidation and Membrane Filtration

ii I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. Abstract Arsenic is a known carcinogen, causing cancers of the skin, lungs, bladder and kidney. Current research suggests that drinking water is the most common pathway for long-term low dose exposure. Arsenic contaminated drinking water has caused serious health problems in many countries including: Nanofiltration (NF) is a promising technology for arsenic removal since it requires less energy than traditional reverse osmosis membranes. Several studies have shown that nanofiltration is capable of removing the oxidized form of arsenic [As(V)] while the reduced form of arsenic [As(III)] is poorly removed. To exploit this difference it has been suggested that a pretreatment step which oxidizes the As(III) to As(V) would improve the performance of membrane filtration, but this has never been demonstrated. The research had three objectives: The first was to investigate the ability of NF membranes to treat arsenic contaminated groundwater and evaluate the influence of the membrane type and operating conditions. Secondly, the effectiveness of a solid phase oxidizing media (MnO 2) to oxidize arsenite to arsenate was investigated. Lastly, the MnO 2 was combined with NF membrane filtration to determine the benefit, if any, of oxidizing the arsenic prior to membrane filtration. A pilot membrane system was installed to treat a naturally contaminated groundwater in Virden, Manitoba, Canada. The groundwater in Virden contains between 38 and 44 μg/L of arsenic, primarily made up of As(III), with little particulate arsenic. In the first experiment three Filmtec ® membranes were investigated: NF270, NF90 and XLE. Under all conditions tested the NF90 and NF270 membranes provided insufficient treatment of Virden's groundwater to meet Canada's recommended Interim Maximum Acceptable Concentration (IMAC) of 25 μg/L. The XLE membrane provided better arsenic removal and under the conditions of 25 Lmh flux and 70% recovery produced treated water with a total arsenic concentration of 21 μg/L. The XLE membrane is therefore able to sufficiently treat Virden's ground water. However treatment with the XLE membrane alone is insufficient to meet the USEPA's regulation of 10 μg/L or Canada's proposed Maximum Allowable Concentration (MAC) of 5 μg/L. The effects of recovery and flux on total arsenic passage are consistent with accepted membrane theory. Increasing …