Globally, it is estimated that 94 – 220 million people are exposed to high levels of naturally occurring arsenic through groundwater used as a primary source of drinking water. High levels of arsenic refer to concentrations above the EPA and WHO allowable limit of 10 µg/L. Arsenic is a potent carcinogen that also causes skin lesions, ulcers, gangrene, and cardiovascular, neurological, and immunological diseases. While technologies exist that can effectively remove arsenic from drinking water sources, they have proved to be unsustainable in resource poor communities such as rural South Asia. Despite past investments in remediation projects, solutions were not installed with long-term sustainable societal placement strategies, resulting in failure of the technologies over time. In the U.S., the most affected communities tend to be small, rural, low-income, and marginalized communities lacking the technical, managerial, and financial capacity to implement and maintain arsenic remediation systems.

The purpose of this dissertation is to present insights from the lab to field trajectory, in the development and scale-up process, of novel arsenic remediation technologies for safe drinking water. First, the 10,000 LPD capacity ECAR (ElectroChemical Arsenic Remediation) plant at a high school in rural West Bengal, India, is used as a case study to shed light on the critical project efforts for ensuring a sustainable safe water system. The lessons learned from the field, with a focus during the commissioning phase (last six months) of the project, elucidate both the technical and social obstacles that were overcome working alongside a multidisciplinary and international team. From April 2016 to January 2017, a total of 540,000 liters of arsenic-safe water was produced, consistently and reliably reducing arsenic concentrations from initial 252 ± 29 to final 2.9 ± 1 µg/L. The ultimate commercialization of ECAR was based on its contextual design, a rigorous educational campaign and trust building, supporting local livelihoods, and complying with local regulations within a defined Critical Effort Zone (CEZ) period. Also key to the project was the financial support from a funding source focused on invention maturation into commercial systems. In short supply is the knowledge of how to transition from successful field testing to a scalable successful business model leading to large scale impact. The lessons from successfully crossing the “valley of death” are much less understood and much less reported on, than either of the two sides of that valley. This work bridges a knowledge gap between case studies of successful technology field testing on one hand, and those reporting on technologies with good social acceptance, having achieved robust performance over long-term operation and implemented through a financially viable business model.

The takeaways from deployment of ECAR in rural India are then leveraged for development of a next generation system for the context of the Central Valley of California, requiring a higher throughput and more compact design. In the ECAR, or conventional iron electrocoagulation (Fe-EC) process, two large 1,250-liter tanks require aeration, and the entire treatment train spans a spatial footprint of 1,400 ft2 to treat 500 liters per hour (LPH) of water contaminated with 250 µg/L arsenic. Adapting Fe-EC with a carbon-based air diffusion cathode allows for modularized electrochemical reactors to meet large throughput demands and treats 600 LPH of comparably arsenic contaminated water within a spatial footprint of about 120 ft2.

Next, the performance of ACAIE (air cathode assisted iron electrocoagulation), or air-EC, in a synthetic California groundwater matrix, for co-removal of arsenic (As(III)) and manganese (Mn(II)) is investigated in the laboratory. The coulombic dosage rates (CDRs) reach over 300 times greater than at the ECAR plant, with a large dynamic range, from 6 to 1500 C/L/min, as well as a wide pH range from 4 to 10. Systematically varying these operating conditions and utilizing molecular-scale techniques, the reaction products are characterized to uncover the As(III) and Mn(II) removal mechanisms in air-EC. CDR did not have a major impact on removal efficiencies, but inverse trends with respect to pH were found for As(III) and Mn(II) removal. The MCL for As was reached at pH 4 and 7, while the secondary MCL for Mn was reached only at pH 10. Under the optimal pH values, removal was achieved in electrolysis times as short as 24 seconds. Furthermore, complete As(III) oxidation to As(V) was achieved, while only ~40% of Mn(II) was oxidized to Mn(III), indicating that As(III) more strongly competes for the reactive oxidant species in the system. Lastly, the As(V) was bound in binuclear, bidentate inner-sphere complexes with the electrolytically generated Fe(III) (oxyhydr)oxides, which is the dominant binding mode in conventional Fe-EC.

In the final section, we investigate the endpoints of the Fenton reaction that allow for effective and simultaneous As and Mn removal in air-EC, which relies on effective H2O2 generation at the cathode. Using Faradaic Efficiency (FE) as a performance metric, the efficacy of H2O2 production was assessed in both new and used modified gas diffusion layers (GDLs) to investigate the impact from air-EC operating conditions in a complex synthetic groundwater matrix. While operating at a high current density of 50.8 mA/cm2, the FE values are high at ~80%, whereas at a low current density of 0.20 mA/cm2, the FE yields are only ~30%. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are used to elucidate morphological attributes of the GDL base, newly modified- and used cathodes, and respective atomic compositions. Synchrotron-based XAS and X-ray fluorescence mapping were performed to obtain the elemental distribution of iron, calcium, chloride, and sulfur present on the cathode after use in the air-EC system. Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to offer potential mechanistic explanations for efficiencies and losses in H2O2 production, showing the reduction of defects in the carbon lattice. The loss of catalytic oxygen reduction reaction (ORR) sites contributed to the lower FE for H2O2 production. These results elucidate the role of groundwater composition in the fouling of the cathode in air-EC. While the ionic composition of the arsenic-contaminated groundwater will vary across aquifers, the air-EC system can be designed as a two-chamber system to minimize fouling from the anodically generated Fe precipitates.

The lessons learned from the field in India will continue to inform the development and deployment of ACAIE within the Central Valley of California. Work remains to better understand the stability of the As- and Mn-laden precipitates and potential remobilization of contaminants once in typical landfill conditions. At the cathode, effective and simple regeneration methods must be further investigated to increase lifespan while minimizing maintenance costs. Finally, long-term operation of the air-EC system must be optimized in the field, as well as the implementation of a sustainable business model contextual to rural California.