Arsenic (As) is a highly toxic metalloid that has been identified at high concentrations in groundwater in certain locations around the world. Concurrent microbial reduction of arsenate (AsV) and sulfate (SO42-) can result in the formation of poorly soluble arsenic sulfide minerals (ASM). The objective of this research was to study As biomineralization in a minimal iron environment for the bioremediation of As-contaminated groundwater using simultaneous AsV and SO42- reduction. A continuous-flow anaerobic bioreactor was maintained at slightly acidic pH (6.25-6.50) and fed with AsV and SO42-, utilizing ethanol as an electron donor for over 250 d. A second bioreactor running under the same conditions but lacking SO42- was operated as a control to study the fate of As (without S). The reactor fed with SO42- removed an average 91.2% of the total soluble As at volumetric rates up to 2.9 mg As/(L∙h), while less than 5% removal was observed in the control bioreactor. Soluble S removal occurred with an S to As molar ratio of 1.2, suggesting the formation of a mixture of orpiment- (As2S3) and realgar-like (AsS) solid phases. Solid phase characterization using K-edge X-Ray absorption spectroscopy confirmed the formation of a mixture of As2S3 and AsS. These results indicate that a bioremediation process relying on the addition of a simple, low-cost electron donor offers potential to promote the removal of As from groundwater with naturally occurring or added sulfate by precipitation of ASM.

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Water scarcity is especially impactful in remote and impoverished communities without access to centralized water treatment plants. In areas with access to a saline water source, point-of-use desalination by solar-driven membrane distillation (MD) is a possible method for mitigating water scarcity. To evaluate the applicability of MD, a comprehensive process model was developed and used to design an economically optimal system. Thermal energy for distillation was provided by solar thermal collectors, and electricity was provided using photovoltaic collectors. Distillation was performed using sweeping-gas membrane distillation. The cost of water in the optimized system was approximately $85/m 3. Membrane modules and solar thermal collectors made up the largest portion of the cost. Neither thermal nor electrical energy storage was economical within current technologies. The model developed provides a template to optimize MD membrane characteristics specialized for point-of-use applications.