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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2016)

Millions of people in rural West Bengal, India, are exposed to groundwater containing toxic concentrations of arsenic, unpleasant levels of iron and non-negligible fecal contamination. Before publicly-provided piped water becomes widely available, a promising approach to address this unacceptable situation is to treat groundwater in small decentralized plants that sustain themselves by selling water to households at an affordable price. This approach hinges on two hypotheses: first, that groundwater can be treated for all contaminants –arsenic, iron, and microorganisms– at very low-cost and with locally available materials and labor; second, that a large fraction of households –ideally all households– will purchase treated water. This dissertation examines these two hypotheses in detail. First, it analyzes the concurrent removal of arsenic and bacteria from contaminated groundwater using iron electrocoagulation (Fe-EC), a simple and robust process suitable for operation in resource-limited settings. Second, it investigates household water practices and drivers of behavior change in rural West Bengal.

Fe-EC relies on the dissolution of an Fe(0) anode to produce strong oxidants and Fe(III) precipitates with a high sorption affinity for arsenic. Building on previous work, a computational model is used to investigate the combined effects of pH and operating conditions (Fe dosage rate and O2 recharge rate) on arsenic removal by Fe-EC. A relationship is established between the impact of operating conditions and the process limiting arsenic removal (As(III) oxidation versus As(V) adsorption), which depends on the pH and the O2 concentration. The robustness of the trends predicted by the model, which operates at constant pH, is evaluated against lab experiments reproducing more realistic conditions where pH increases during treatment –as a result of groundwater equilibrating with atmospheric CO2. The results provide a nuanced understanding of the levers that an operator might use to optimize Fe-EC performance in a range of groundwaters under economic constraints.

Bacteria attenuation by Fe-EC is investigated in detail using a series of laboratory experiments. After showing that Fe-EC can attenuate bacteria in synthetic Bengal groundwater without detriment to arsenic remediation, the impact of operating parameters (Fe dosage and dosage rate), groundwater composition (pH, HCO3-, Ca, Mg, Si, P, and natural organic matter (NOM)), and bacteria type are systematically investigated, with a focus on elucidating the mechanisms of bacteria attenuation. The results show that attenuation is primarily due to bacteria encapsulation in Fe(III) flocs and removal by gravitational settling, while inactivation by germicidal reactive oxidants remains limited in the presence of HCO3- and at pH>7. Fe(III) precipitates are found to adhere to the surface of bacterial cells, primarily through interactions with bacterial phosphate groups, resulting in bacteria enmeshment in precipitate flocs. The effect of major groundwater ions is interpreted in light of this mechanism: Ca and Mg reduce attenuation by complexing bacterial phosphate groups; Si and NOM, which do not strongly compete with phosphate groups for sorption to Fe(III) precipitates, do not affect attenuation; by contrast, P decreases attenuation significantly, except in the presence of bivalent cations, which can bridge between P sorbed to precipitates and bacterial phosphate groups. Finally, Fe-EC is shown to be equally effective towards Gram-positive and Gram-negative bacteria, smooth and rough alike, likely due to the universal presence of phosphate moieties on bacterial cell walls. Altogether, results show that Fe-EC can effectively remove all types of bacterial contamination from a range of groundwaters.

Results of a 501-household survey about water practices in the arsenic-affected district of Murshidabad, in West Bengal, India, are presented. 53% of the surveyed population was found to use alternatives to shallow groundwater including domestic filters, water purchased from small private entrepreneurs, government tubewells, and municipal piped water. The analysis shows that following socioeconomic status, risk perception of gastric illness and dissatisfaction with iron are the primary predictors of the use of alternatives, prevailing over arsenic risk perception. This finding indicates that households react to readily noticeable water problems more than to an invisible contaminant with long-term effects. The factors affecting the choice amongst available alternatives are investigated. The results show that purchased water does not currently provide universal access and that it only reduces, but does not eliminate, arsenic ingestion. Overall, the findings suggest that the provision of treated water through small independent entrepreneurs can be an interim, but partial, solution to the arsenic crisis until piped water becomes widespread in rural West Bengal.

    Cover page: Improving Access to Safe Water in West Bengal, India: From Arsenic and Bacteria Removal to Household Behavior Change
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    Globally, 200 million people drink groundwater contaminated with fluoride concentrations exceeding the World Health Organization's recommended level (WHO-MCL = 1.5 mg F-/L). This study investigates the use of minimally processed (dried/milled) bauxite ore as an inexpensive adsorbent for remediating fluoride-contaminated groundwater in resource-constrained areas. Adsorption experiments in synthetic groundwater using bauxites from Guinea, Ghana, U.S., and India as single-use batch dispersive media demonstrated that doses of ∼10-23 g/L could effectively remediate 10 mg F-/L. To elucidate factors governing fluoride removal, bauxites were characterized using X-ray fluorescence, X-ray diffraction, gas-sorption analysis, and adsorption isotherms/envelopes. All ores contained gibbsite, had comparable surface areas (∼14-17 m2/g), had similar intrinsic affinities and capacities for fluoride, and did not leach harmful ions into product water. Fluoride uptake on bauxite -primarily through ion-exchange- was strongly pH-dependent, with highest removal occurring at pH 5.0-6.0. Dissolution of CaCO3, present in trace amounts in India bauxite, significantly hindered fluoride removal by increasing solution pH. We also showed that fluoride remediation with the best-performing Guinea bauxite was ∼23-33 times less expensive than with activated alumina. Overall, our results suggest that bauxite could be an affordable fluoride-remediation adsorbent with the potential to improve access to drinking water for millions living in developing countries.
      Cover page: Factors Governing the Performance of Bauxite for Fluoride Remediation of Groundwater
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2017)
      Iron electrocoagulation (Fe-EC) has been shown to effectively remove arsenic from contaminated groundwater at low cost and has the potential to improve access to safe drinking water for millions of people. Understanding how operating conditions, such as the Fe dosage rate and the O2 recharge rate, affect arsenic removal at different pH values is crucial to maximize the performance of Fe-EC under economic constraints. In this work, we improved upon an existing computational model to investigate the combined effects of pH, Fe dosage rate, and O2 recharge rate on arsenic removal in Fe-EC. We showed that the impact of the Fe dosage rate strongly depends on pH and on the O2 recharge rate, which has important practical implications. We identified the process limiting arsenic removal (As(III) oxidation versus As(V) adsorption) at different pH values, which allowed us to interpret the effect of operating conditions on Fe-EC performance. Finally, we assessed the robustness of the trends predicted by the model, which assumes a constant pH, against lab experiments reproducing more realistic conditions where pH is allowed to drift during treatment as a result of equilibration with atmospheric CO2. Our results provide a nuanced understanding of how operating conditions impact arsenic removal by Fe-EC and can inform decisions regarding the operation of this technology in a range of groundwaters.
        Cover page: How do operating conditions affect As(III) removal by iron electrocoagulation?
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2016)
        Iron electrocoagulation (Fe-EC) is a low-cost process in which Fe(II) generated from an Fe(0) anode reacts with dissolved O2 to form (1) Fe(III) precipitates with an affinity for bacterial cell walls and (2) bactericidal reactive oxidants. Previous work suggests that Fe-EC is a promising treatment option for groundwater containing arsenic and bacterial contamination. However, the mechanisms of bacteria attenuation and the impact of major groundwater ions are not well understood. In this work, using the model indicator Escherichia coli (E. coli), we show that physical removal via enmeshment in EC precipitate flocs is the primary process of bacteria attenuation in the presence of HCO3(-), which significantly inhibits inactivation, possibly due to a reduction in the lifetime of reactive oxidants. We demonstrate that the adhesion of EC precipitates to cell walls, which results in bacteria encapsulation in flocs, is driven primarily by interactions between EC precipitates and phosphate functional groups on bacteria surfaces. In single solute electrolytes, both P (0.4 mM) and Ca/Mg (1-13 mM) inhibited the adhesion of EC precipitates to bacterial cell walls, whereas Si (0.4 mM) and ionic strength (2-200 mM) did not impact E. coli attenuation. Interestingly, P (0.4 mM) did not affect E. coli attenuation in electrolytes containing Ca/Mg, consistent with bivalent cation bridging between bacterial phosphate groups and inorganic P sorbed to EC precipitates. Finally, we found that EC precipitate adhesion is largely independent of cell wall composition, consistent with comparable densities of phosphate functional groups on Gram-positive and Gram-negative cells. Our results are critical to predict the performance of Fe-EC to eliminate bacterial contaminants from waters with diverse chemical compositions.
          Cover page: Bacteria attenuation by iron electrocoagulation governed by interactions between bacterial phosphate groups and Fe(III) precipitates
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2017)
          Shallow groundwater containing toxic concentrations of arsenic is the primary source of drinking water for millions of households in rural West Bengal, India. Often, this water also contains unpleasant levels of iron and non-negligible fecal contamination. Alternatives to shallow groundwater are increasingly available, including government-built deep tubewells, water purchased from independent providers, municipal piped water, and household filters. We conducted a survey of 501 households in Murshidabad district in 2014 to explore what influenced the use of available alternatives. Socioeconomic status and the perceived likelihood of gastrointestinal (GI) illness (which was associated with dissatisfaction with iron in groundwater) were the primary determinants of the use of alternatives. Arsenic knowledge was limited. The choice amongst alternatives was influenced by economic, social, and aesthetic factors, but not by health risk perceptions. The use of purchased water was rarely exclusive and was strongly associated with socioeconomic status, suggesting that this form of market-based water provision does not ensure universal access. Demand for purchased water appeared to decrease significantly shortly after free piped water became available at public taps. Our results suggest that arsenic mitigation interventions that also address co-occurring water problems (iron, GI illness) could be more effective than a focus on arsenic alone.
            Cover page: Determinants of the use of alternatives to arsenic-contaminated shallow groundwater: an exploratory study in rural West Bengal, India
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2015)
            Technologies addressing both arsenic and microbial contamination of Bengal groundwater are needed. Fe electrocoagulation (Fe-EC), a simple process relying on the dissolution of an Fe(0) anode to produce Fe(III) precipitates, has been shown to efficiently remove arsenic from groundwater at low cost. We investigated Escherichia coli (E. coli) attenuation by Fe-EC in synthetic Bengal groundwater as a function of Fe dosage rate, total Fe dosed, pH, and presence of natural organic matter (NOM). A 2.5 mM Fe dosage simultaneously achieved over 4-log E. coli attenuation and arsenic removal from 450 to below 10 μg/L. E. coli reduction was significantly enhanced at pH 6.6 compared to pH 7.5, which we linked to the decreased rate of Fe(II) oxidation at lower pH. 3 mg/L-C of NOM (Suwanee River fulvic acid) did not significantly affect E. coli attenuation. Live-dead staining and comparisons of Fe-EC with chemical coagulation controls showed that the primary mechanism of E. coli attenuation is physical removal with Fe(III) precipitates, with inactivation likely contributing as well at lower pH. Transmission electron microscopy showed that EC precipitates adhere to and bridge individual E. coli cells, resulting in large bacteria-Fe aggregates that can be removed by gravitational settling. Our results point to the promising ability of Fe-EC to treat arsenic and bacterial contamination simultaneously at low cost.
              Cover page: Escherichia coli Attenuation by Fe Electrocoagulation in Synthetic Bengal Groundwater: Effect of pH and Natural Organic Matter
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2015)
              Mixed-valent iron nanoparticles (NP) generated electrochemically by Fe(0) electrocoagulation (EC) show promise for on-demand industrial and drinking water treatment in engineered systems. This work applies multiple characterization techniques (in situ Raman spectroscopy, XRD, SEM, and cryo-TEM) to investigate the formation and persistence of magnetite and green rust (GR) NP phases produced via the Fe(0) EC process. Current density and background electrolyte composition were examined in a controlled anaerobic system to determine the initial Fe phases generated as well as transformation products with aging. Fe phases were characterized in an aerobic EC system with both simple model electrolytes and real groundwater to investigate the formation and aging of Fe phases produced in a system representing treatment of arsenic-contaminated ground waters in South Asia. Two central pathways for magnetite production via Fe(0) EC were identified: (i) as a primary product (formation within seconds when DO absent, no intermediates detected) and (ii) as a transformation product of GR (from minutes to days depending on pH, electrolyte composition, and aging conditions). This study provides a better understanding of the formation conditions of magnetite, GR, and ferric (oxyhydr)oxides in Fe EC, which is essential for process optimization for varying source waters.
                Cover page: Production and Transformation of Mixed-Valent Nanoparticles Generated by Fe(0) Electrocoagulation
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2019)
                Most residents of the developing world do not have access to safely managed sanitation services, and large financial investments are required to address this need. Here we evaluate surcharges on water/sewerage tariffs as an option for supporting these investments in low-income neighborhoods. We investigated willingness-to-pay (WTP) for a pro-poor sanitation surcharge among customers of two urban water utilities in Kenya. Applying qualitative and quantitative methods, we conducted semi-structured in-depth interviews, focus-group discussions, and a double-bounded contingent valuation method for measuring WTP. We varied scenarios quasi-experimentally to study the effects of messaging and surcharge characteristics and evaluated factors associated with WTP. Our study finds that mean WTP was 290 KES (USD 2.9) per month, about 8% of the average water bill; median WTP was 100 KES (USD 1). In a multivariate analysis, WTP was significantly higher among customers that were younger, wealthier, shared toilets, and had higher water bills. WTP was also higher among customers that trusted the utility and distrusted the county government. Of our randomized scenarios, only the bill type was found to significantly influence WTP; WTP was higher if the surcharge was presented as a proportion of the customers’ last water bill vs a flat amount. Our findings suggest that in a sector that struggles to provide universal access to sanitation services, cross-subsidies may offer a means to support financing of safe sanitation for low-income households. These results indicate there are opportunities for cross-subsidies in urban Kenya that may be relevant for a wider understanding of surcharge payments that support basic services for low-income citizens.
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2014)
                  Millions of people in rural South Asia are exposed to high levels of arsenic through groundwater used for drinking. Many deployed arsenic remediation technologies quickly fail because they are not maintained, repaired, accepted, or affordable. It is therefore imperative that arsenic remediation technologies be evaluated for their ability to perform within a sustainable and scalable business model that addresses these challenges. We present field trial results of a 600 L Electro-Chemical Arsenic Remediation (ECAR) reactor operating over 3.5 months in West Bengal. These results are evaluated through the lens of a community scale micro-utility business model as a potential sustainable and scalable safe water solution for rural communities in South Asia. We demonstrate ECAR's ability to consistently reduce arsenic concentrations of ~266 μg/L to <5 μg/L in real groundwater, simultaneously meeting the international standards for iron and aluminum in drinking water. ECAR operating costs (amortized capital plus consumables) are estimated as $0.83-$1.04/m(3) under realistic conditions. We discuss the implications of these results against the constraints of a sustainable and scalable business model to argue that ECAR is a promising technology to help provide a clean water solution in arsenic-affected areas of South Asia.
                    Cover page: Electro-chemical arsenic remediation: Field trials in West Bengal
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