Drinking Water in the Rural Developing World: Improving Ion Flux in Capacitive Deionization and Understanding Technical Interventions

Today, a billion people lack access to safe drinking water. Climate change, a host of/nunsustainable practices, and emerging contaminants threaten to exacerbate the problem./nFor the developing-world communities disproportionately affected, limited infrastructure and/nresources often preclude the developed-world solutions. New technologies will be necessary./nUnfortunately, even mature technologies often fail in these settings. This work presents two/nefforts: one to advance understanding of robust technical interventions and one to improve/nwater treatment technology for such settings./nIn the Poshiir River watershed study, we built comparative case studies of single-village/npiped-water drinking water schemes in rural Maharashtra. In-depth datasets were built from/ndirect technical observations, evaluation of records at national, district, and local levels, and/nstructured interviews with scheme users and administrators. Redundant information sources/nwere used to triangulate and assess confidence in our factual findings, which were formalized/nin novel node-network models of each scheme-village pair. Hypotheses were developed and/nmapped onto these networks via process tracing. We theorize that resilience of a scheme/nis dependent on healthy, positive feedback loops within these social-technical networks. We/nalso took early steps toward typological theories on scheme failures./nIn the course of the Poshiir study, we developed a method for rigorously and objectively/nreconciling data from disparate sources. For a number of queries on a given topic, the/nmethod takes the array of agreements and disagreements between all sources as inputs; it/ngenerates most-probable values for the validity of each source's response, as well as mean/nvalidities for the sources themselves. Early tests of the method with a verifiable dataset/nprovide meaningful results, and application to the Poshiir study have returned consistent/nscores when assessing comparable cases. While further investigation is certainly required,/nthe method appears promising./nWe also sought to improve the effective flow rate for capacitive deionization (CDI), a/ntreatment technology for removing ionic species from brackish water. We first proposed two/nnovel powering arrangements that would accomplish this by increasing effective ion mobility:/noptimal powering profiles and pulse-charged CDI. We developed a theoretical model and/ngoverning equations that would allow us to measure internal ion drift rates from externally/nobservable variables. We then designed, built, and tested a prototype CDI cell capable of operating/nin either mode. We performed experimental work, as well as numerical simulations for/npulse-charged CDI over a range of realistic conditions, capturing a set of crucial timescales./nWe find that practical restrictions required to avoid redox reactions in pulse-charged CDI/nensure that optimal powering profiles will always offer the greater benefit./nProviding safe drinking water access in the developing world will require a new generation/nof technologies. These must be paired, however, with an improved understanding of how to/nimplement such projects, such that infrastructure proves resilient and impacts prove permanent./nI am optimistic that the work presented here may contribute, incrementally, to each/nof these efforts.

Advisor: Gadgil, Ashok J