Data-Sparse Prediction of High-Risk Schools for Lead Contamination in Drinking Water: Examples from Four U.S. States.

Childhood lead exposure through drinking water has long-term effects on cognition and development, and is a significant public health concern. The comprehensive lead testing of public schools entails high expense and time. In prior work, random forest modeling was used successfully to predict the likelihood of lead contamination in the drinking water from schools in the states of California and Massachusetts. In those studies, data from 70% of the schools was used to predict the probability of unsafe water lead levels (WLLs) in the remaining 30%. This study explores how the model predictions degrade, as the training dataset forms a progressively smaller proportion of schools. The size of the training set was varied from 80% to 10% of the total samples in four US states: California, Massachusetts, New York, and New Hampshire. The models were evaluated using the precision-recall area under curve (PR AUC) and area under the receiver operating characteristic curve (ROC AUC). While some states required as few as 10% of the schools to be included in the training set for an acceptable ROC AUC, all four states performed within an acceptable ROC AUC range when at least 50% of the schools were included. The results in New York and New Hampshire were consistent with the prior work that found the most significant predictor in the modeling to be the Euclidean distance to the closest school in the training set demonstrating unsafe WLLs. This study further supports the efficacy of predictive modeling in identifying the schools at a high risk of lead contamination in their drinking water supply, even when the survey data is incomplete on WLLs in all schools.

Community Perceptions of Arsenic Contaminated Drinking Water and Preferences for Risk Communication in California's San Joaquin Valley.

Due to chronic exposure to elevated levels of arsenic in drinking water, thousands of Californians have increased risk for internal cancers and other adverse health effects. The mortality risk of cancer is 1 in 400 people exposed to above 10 µg/L of arsenic in their drinking water. The purpose of this community assessment was to understand the perceptions and awareness of the residents and public water representatives in rural, unincorporated farming communities of color in San Joaquin Valley, California. In our research, we asked 27 community informants about their (1) available water sources, (2) knowledge about the health impacts of arsenic, and (3) preferences for risk communication and education regarding the health impacts of arsenic-contaminated drinking water. Through our qualitative coding and analysis, we found that most community informants indicated that there was limited community awareness about the health effects of drinking water with elevated arsenic levels. Preferences for risk communication included using in-language, culturally relevant, and health literate health promotion strategies and teaching these topics through the local K-8 schools' science curriculum with a language brokerage approach to transfer student knowledge to family members. Key recommendations include implementing these communication preferences to increase community-wide knowledge about safe drinking water.

Adapting a drinking water treatment technology for arsenic removal to the context of a small, low-income California community.

Small, low-income, and rural communities across the United States are disproportionately exposed to arsenic contaminated drinking water because existing treatment solutions are too expensive and difficult to operate. This paper describes efforts to overcome some barriers and limitations of conventional iron electrocoagulation (Fe-EC) to enable its use in the rural Californian (U.S.) context. Barriers and limitations of Fe-EC's application in rural California considered in this work include: 1) Frequent labor intensive electrode cleaning is required to overcome rust accumulation, 2) Electrolysis durations are long, reducing throughput for a given system size, and 3) Waste needs compliance with California standards. We report results from an investigation for overcoming these limitations via a field trial on a farm in Allensworth, a small, low-income, rural community in California. Our strategies to overcome each of the above barriers and limitations are respectively, 1) operating the Fe-EC reactor at high current density to result in sustained Fe production, 2) operating at high charge dosage rate with external H2O2, and 3) characterization of the arsenic-laden waste, and are discussed further in the paper. Main findings are: (1) Fe-EC removed arsenic consistently below the federal (and state) standard of 10 µg/L, (2) high current density failed to sustain Fe production whereas low current density did not, (3) electrolysis time decreased from > 1 hour to < 2 min with H2O2 dosing of 5 mg/L at higher charge dosage rates, (4) dilution of As-sludge is required to comply with State's non-hazardous waste status, and (5) discrepancies were observed between lab and field results in using current density to overcome labor-intensive electrode cleanings. Finally, implications of overcoming limitations to scale-up of Fe-EC in relevant California communities are discussed.

Superior removal of As(III) and As(V) from water with Mn-doped ß-FeOOH nanospindles on carbon foam.

Arsenic pollution of water is one of the severest environmental challenges threatening human health. Iron-based nanomaterials have been demonstrated effective in arsenic removal. However, they generally suffer from low removal efficiency towards highly toxic As(III), loss of active sites owing to agglomeration, and poor reusability. Herein, we report a carbonized melamine foam supported Mn(IV)-doped ß-FeOOH nanospindles(CF@Mn-FeOOH NSp) for tackling the technical hurdles. The designed CF@Mn-FeOOH NSp appears as a free-standing monolith through a low-cost and straightforward hydrothermal method. The atomic-scale integration of Mn(IV) into ß-FeOOH enables an oxidation-adsorption bifunctionality, where Mn(IV) serves as oxidizer for As(III) and Fe(III) acts as adsorber for As(V). The maximal adsorption capacity for As(V) and As(III) can reach 152 and 107 mg g-1, respectively. Meanwhile, As in simulated high arsenic groundwater can be decreased to below 10 µg L-1 within 24 h. By simple "filtrating-washing", 85% and 82% of its initial adsorption capacity for As(V) and As(III) can be easily recovered even after 5-cycles reuse. Kinetics and isotherm adsorption study indicate that the arsenic adsorption behavior is mainly through chemical bonding during single-layer adsorbing process. The as-prepared CF@Mn-FeOOH offers a scalable, efficient, and recyclable solution for arsenic removal in groundwater and wastewater from mines and industry.

Safety and effectiveness of a non-electric infant warmer for hypothermia in Rwanda: A cluster-randomized stepped-wedge trial.

BACKGROUND: Neonatal hypothermia is a common source of morbidity and mortality in low resource settings. We developed the Dream Warmer, a low cost, re-usable non-electric infant warmer to prevent and treat hypothermia. METHODS: We conducted a cluster-randomized stepped-wedge trial. The primary aim was to assess the effect on overall euthermia rates of introducing the warmer compared to standard of care in rural Rwandan hospitals. The secondary aims were to assess effects of warmer introduction on mortality, as well as the safety and feasibility of the warmer. Ten district hospitals participated in the study from November 19th 2019 to July 15th 2020. Patients were eligible to use the warmer if they were 1) hypothermic (temp < 36·5 °C) or 2) or at risk of hypothermia (weight < 2·5 kg or estimated post menstrual age < 35 weeks) when Kangaroo Mother Care was not available. An encounter was defined as the data from an individual infant on a single day. Trial of a Non Electric Infant Warmer for Prevention and Treatment of Hypothermia in Rwanda [NCT03890211]. FINDINGS: Over the study period, 3179 patients were enrolled across the ten neonatal wards, yielding 12,748 encounters; 464 unique infants used the warmer 892 times, 79% eligible due to hypothermia. Because of limited study nurse resources, the warmer was used in only 18% of eligible encounters. Despite this low rate of warmer use, the rate of euthermia rose from 51% (95% CI 50-52%) of encounters pre-intervention to 67% (66-68%) post-intervention; p < 0·0001. Among the encounters in which the warmer was used, only 11% (9-13%) remained hypothermic. While mortality rates pre- and post-intervention did not change, mortality rate among those who used the warmer was significantly lower than among those who did not (0·9% vs 2·8%, p = 0·01). Use of the warmer did not affect hyperthermia rates. There were no safety concerns or instances of incorrect warmer use. INTERPRETATION: Introduction of the warmer increased rates of euthermia with no associated safety concerns.

Rapid and Efficient Arsenic Removal by Iron Electrocoagulation Enabled with in Situ Generation of Hydrogen Peroxide.

Millions of people are exposed to toxic levels of dissolved arsenic in groundwater used for drinking. Iron electrocoagulation (FeEC) has been demonstrated as an effective technology to remove arsenic at an affordable price. However, FeEC requires long operating times (∼hours) to remove dissolved arsenic due to inherent kinetics limitations. Air cathode Assisted Iron Electrocoagulation (ACAIE) overcomes this limitation by cathodically generating H2O2 in situ. In ACAIE operation, rapid oxidation of Fe(II) and complete oxidation and removal of As(III) are achieved. We compare FeEC and ACAIE for removing As(III) from an initial concentration of 1464 µg/L, aiming for a final concentration of less than 4 µg/L. We demonstrate that at short electrolysis times (0.5 min), i.e., high charge dosage rates (1200 C/L/min), ACAIE consistently outperformed FeEC in bringing arsenic levels to less than WHO-MCL of 10 µg/L. Using XRD and XAS data, we conclusively show that poor arsenic removal in FeEC arises from incomplete As(III) oxidation, ineffective Fe(II) oxidation and the formation of Fe(II-III) (hydr)oxides at short electrolysis times (<20 min). Finally, we report successful ACAIE performance (retention time 19 s) in removing dissolved arsenic from contaminated groundwater in rural California.

Long-term electrode behavior during treatment of arsenic contaminated groundwater by a pilot-scale iron electrocoagulation system.

Iron electrocoagulation (Fe-EC) is an effective technology to remove arsenic (As) from groundwater used for drinking. A commonly noted limitation of Fe-EC is fouling or passivation of electrode surfaces via rust accumulation over long-term use. In this study, we examined the effect of removing electrode surface layers on the performance of a large-scale (10,000 L/d capacity) Fe-EC plant in West Bengal, India. We also characterized the layers formed on the electrodes in active use for over 2 years at this plant. The electrode surfaces developed three distinct horizontal sections of layers that consisted of different minerals: calcite, Fe(III) precipitates and magnetite near the top, magnetite in the middle, and Fe(III) precipitates and magnetite near the bottom. The interior of all surface layers adjacent to the Fe(0) metal was dominated by magnetite. We determined the impact of surface layer removal by mechanical abrasion on Fe-EC performance by measuring solution composition (As, Fe, P, Si, Mn, Ca, pH, DO) and electrochemical parameters (total cell voltage and electrode interface potentials) during electrolysis. After electrode cleaning, the Fe concentration in the bulk solution increased substantially from 15.2 to 41.5 mg/L. This higher Fe concentration led to increased removal of a number of solutes. For As, the concentration reached below the 10 µg/L WHO MCL more rapidly and with less total Fe consumed (i.e. less electrical energy) after cleaning (128.4 µg/L As removed per kWh) compared to before cleaning (72.9 µg/L As removed per kWh). Similarly, the removal of P and Si improved after cleaning by 0.3 mg/L/kWh and 1.1 mg/L/kWh, respectively. Our results show that mechanically removing the surface layers that accumulate on electrodes over extended periods of Fe-EC operation can restore Fe-EC system efficiency (concentration of solute removed/kWh delivered). Since Fe release into the bulk solution substantially increased upon electrode cleaning, our results also suggest that routine electrode maintenance can ensure robust and reliable Fe-EC performance over year-long timescales.

Performance of a Nonelectric Infant Warmer in Rwandan Health Centers.

Background. Neonatal hypothermia remains a challenge in resource-limited settings. Methods. We conducted a prospective mixed-methods cohort study in rural Rwandan health centers to assess the performance of an infant warmer we designed for low-resource settings. All hypothermic infants were eligible for enrollment. Outcomes. Safety: incidence of adverse reactions. Effectiveness: attainment of euthermia, rate of temperature rise. Feasibility: correct use of warmer, signs of wear. Interviews of caregivers and nurses. Findings. Of 102 encounters, there were no adverse reactions. Of 80 encounters for hypothermia when infants on warmer for ≥1 hour, 79 achieved euthermia; 73 in ≤2 hours. Of the 80 encounters, 64 had temperature rise ≥0.5°C/h. Of the 102 encounters, there were no instances of the warmer being prepared, used, or cleaned incorrectly. Five out of the 12 warmers exhibited wear. Interview participants were predominantly positive; some found time for readiness of warmer challenging. Interpretation. The warmer performed well. It is appropriate to study in larger scale.

Iron detection and remediation with a functionalized porous polymer applied to environmental water samples.

Iron is one of the most abundant elements in the environment and in the human body. As an essential nutrient, iron homeostasis is tightly regulated, and iron dysregulation is implicated in numerous pathologies, including neuro-degenerative diseases, atherosclerosis, and diabetes. Endogenous iron pool concentrations are directly linked to iron ion uptake from environmental sources such as drinking water, providing motivation for developing new technologies for assessing iron(ii) and iron(iii) levels in water. However, conventional methods for measuring aqueous iron pools remain laborious and costly and often require sophisticated equipment and/or additional processing steps to remove the iron ions from the original environmental source. We now report a simplified and accurate chemical platform for capturing and quantifying the iron present in aqueous samples through use of a post-synthetically modified porous aromatic framework (PAF). The ether/thioether-functionalized network polymer, PAF-1-ET, exhibits high selectivity for the uptake of iron(ii) and iron(iii) over other physiologically and environmentally relevant metal ions. Mössbauer spectroscopy, XANES, and EXAFS measurements provide evidence to support iron(iii) coordination to oxygen-based ligands within the material. The polymer is further successfully employed to adsorb and remove iron ions from groundwater, including field sources in West Bengal, India. Combined with an 8-hydroxyquinoline colorimetric indicator, PAF-1-ET enables the simple and direct determination of the iron(ii) and iron(iii) ion concentrations in these samples, providing a starting point for the design and use of molecularly-functionalized porous materials for potential dual detection and remediation applications.

Addressing technical barriers for reliable, safe removal of fluoride from drinking water using minimally processed bauxite ores.

Throughout the developing world, over 200 million people drink groundwater containing fluoride concentrations surpassing the World Health Organization's maximum recommended contaminant level (WHO-MCL) of 1.5 mg F-/L, resulting in adverse health effects ranging from mottled tooth enamel to debilitating skeletal fluorosis. Existing technologies to remove fluoride from water, such as reverse osmosis and filtration with activated alumina, are expensive and are not accessible for low-income communities. Our group and others have demonstrated that minimally-processed bauxite ores can remove fluoride to safe levels at a fraction of the cost of activated alumina. We report results from testing for some technical challenges that may arise in field deployment of this technology at large scale, particularly in a sufficiently robust manner for application in development contexts. Anticipating possible modes of failure and addressing these challenges in advance in the laboratory is particularly important for technologies for vulnerable communities where the opportunity to re-launch pilot projects is limited and small failures can keep solutions from the people that need them most. This work addresses three potential technical barriers to reliable removal of fluoride from drinking water with bauxite ore from Visakhapatnam, Andhra Pradesh, India. We evaluate competition from co-occurring ions, adsorption reversibility, and potability of the product water with regards to leaching of undesirable ions during treatment with various adsorbent materials including raw and thermally activated bauxite, and synthetic gibbsite (a simple model system). Under the conditions tested, the presence of phosphate significantly impacts fluoride adsorption capacity on all adsorbents. Sulfate impacts fluoride adsorption on gibbsite, but not on either bauxite adsorbent. Nitrate and silicate (as silicic acid), tested only with gibbsite, do not affect fluoride adsorption capacity. Both thermally activated bauxite and gibbsite show non-reversible adsorption of fluoride at a pH of 6. Raw bauxite leached arsenic and manganese in a TCLP leaching test at levels indicating the need for ongoing monitoring of treated water, but not precluding safe deployment of bauxite as a fluoride remediation technology. Understanding these phenomena is crucial to ensure field deployment over large diverse geographical areas with aquifers varying in groundwater composition, and for ensuring that the appropriate engineering processes are designed for field implementation of this innovation.

Effective Remediation of Groundwater Fluoride with Inexpensively Processed Indian Bauxite.

India represents one-third of the world's fluorosis burden and is the fifth global producer of bauxite ore, which has previously been identified as a potential resource for remediating fluoride-contaminated groundwater in impoverished communities. Here, we use thermal activation and/or groundwater acidification to enhance fluoride adsorption by Indian bauxite obtained from Visakhapatnam, an area proximate to endemic fluorosis regions. We compare combinatorial water treatment and bauxite-processing scenarios through batch adsorption experiments, material characterization, and detailed cost analyses. Heating Indian bauxite above 300 °C increases available surface area by > 15× (to ∼170 m2/g) through gibbsite dehydroxylation and reduces the bauxite dose for remediating 10 ppm F- to 1.5 ppm F- by ∼93% (to 21 g/L). Additionally, lowering groundwater pH to 6.0 with HCl or CO2 further reduces the average required bauxite doses by 43-73% for ores heated at 300 °C (∼12 g/L) and 100 °C (∼77 g/L). Product water in most examined treatment scenarios complies with EPA standards for drinking water (e.g., As, Cd, Pb, etc.) but potential leaching of Al, Mn, and Cr is of concern in some scenarios. Among the defluoridation options explored here, bauxite heated at 300 °C in acidified groundwater has the lowest direct costs ($6.86 per person per year) and material-intensity.

Optimization of Secondary Air Injection in a Wood-Burning Cookstove: An Experimental Study.

Nearly 40% of the world's population regularly cooks on inefficient biomass stoves that emit harmful airborne pollutants, such as particulate matter (PM). Secondary air injection can significantly reduce PM mass emissions to mitigate the health and climate impacts associated with biomass cookstoves. However, secondary air injection can also increase the number of ultrafine particles emitted, which may be more harmful to health. This research investigates the effect of secondary air injection on the mass and size distribution of PM emitted during solid biomass combustion. An experimental wood-burning cookstove platform and parametric testing approach are presented to identify and optimize secondary air injection parameters that reduce PM and other harmful pollutants. Size-resolved measurements of PM emissions were collected and analyzed as a function of parametric stove design settings. The results show that PM emissions are highly sensitive to secondary air injection flow rate and velocity. Although increasing turbulent mixing (through increased velocity) can promote more complete combustion, increasing the total flow rate of secondary air may cause localized flame quenching that increases particle emissions. Therefore, biomass cookstoves that implement secondary air injection should be carefully optimized and validated to ensure that PM emission reductions are achieved throughout the particle size range.

Determinants of the use of alternatives to arsenic-contaminated shallow groundwater: an exploratory study in rural West Bengal, India.

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.

How do operating conditions affect As(III) removal by iron electrocoagulation?

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.

Factors Governing the Performance of Bauxite for Fluoride Remediation of Groundwater.

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.

Measuring and Increasing Adoption Rates of Cookstoves in a Humanitarian Crisis.

Traditional smoky cooking fires are one of today's greatest environmental threats to human life. These fires, used by 40% of the global population, cause 3.9 million annual premature deaths. "Clean cookstoves" have potential to improve this situation; however, most cookstove programs do not employ objective measurement of adoption to inform design, marketing, subsidies, finance, or dissemination practices. Lack of data prevents insights and may contribute to consistently low adoption rates. In this study, we used sensors and surveys to measure objective versus self-reported adoption of freely-distributed cookstoves in an internally displaced persons camp in Darfur, Sudan. Our data insights demonstrate how to effectively measure and promote adoption, especially in a humanitarian crisis. With sensors, we measured that 71% of participants were cookstove "users" compared to 95% of respondents reporting the improved cookstove was their "primary cookstove." No line of survey questioning, whether direct or indirect, predicted sensor-measured usage. For participants who rarely or never used their cookstoves after initial dissemination ("non-users"), we found significant increases in adoption after a simple followup survey (p = 0.001). The followup converted 83% of prior "non-users" to "users" with average daily adoption of 1.7 cooking hours over 2.2 meals. This increased adoption, which we posit resulted from cookstove familiarization and social conformity, was sustained for a 2-week observation period post intervention.

Bacteria attenuation by iron electrocoagulation governed by interactions between bacterial phosphate groups and Fe(III) precipitates.

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.

Reducing Ultrafine Particle Emissions Using Air Injection in Wood-Burning Cookstoves.

In order to address the health risks and climate impacts associated with pollution from cooking on biomass fires, researchers have focused on designing new cookstoves that improve cooking performance and reduce harmful emissions, specifically particulate matter (PM). One method for improving cooking performance and reducing emissions is using air injection to increase turbulence of unburned gases in the combustion zone. Although air injection reduces total PM mass emissions, the effect on PM size distribution and number concentration has not been thoroughly investigated. Using two new wood-burning cookstove designs from Lawrence Berkeley National Laboratory, this research explores the effect of air injection on cooking performance, PM and gaseous emissions, and PM size distribution and number concentration. Both cookstoves were created using the Berkeley-Darfur Stove as the base platform to isolate the effects of air injection. The thermal performance, gaseous emissions, PM mass emissions, and particle concentrations (ranging from 5 nm to 10 µm in diameter) of the cookstoves were measured during multiple high-power cooking tests. The results indicate that air injection improves cookstove performance and reduces total PM mass but increases total ultrafine (less than 100 nm in diameter) PM concentration over the course of high-power cooking.

Formation of macroscopic surface layers on Fe(0) electrocoagulation electrodes during an extended field trial of arsenic treatment.

Extended field trials to remove arsenic (As) via Fe(0) electrocoagulation (EC) have demonstrated consistent As removal from groundwater to concentrations below 10 µg L(-1). However, the coulombic performance of long-term EC field operation is lower than that of laboratory-based systems. Although EC electrodes used over prolonged periods show distinct passivation layers, which have been linked to decreased treatment efficiency, the spatial distribution and mineralogy of such surface layers have not been investigated. In this work, we combine wet chemical measurements with sub-micron-scale chemical maps and selected area electron diffraction (SAED) to determine the chemical composition and mineral phase of surface layers formed during long-term Fe(0) EC treatment. We analyzed Fe(0) EC electrodes used for 3.5 months of daily treatment of As-contaminated groundwater in rural West Bengal, India. We found that the several mm thick layer that formed on cathodes and anodes consisted of primarily magnetite, with minor fractions of goethite. Spatially-resolved SAED patterns also revealed small quantities of CaCO3, Mn oxides, and SiO2, the source of which was the groundwater electrolyte. We propose that the formation of the surface layer contributes to decreased treatment performance by preventing the migration of EC-generated Fe(II) to the bulk electrolyte, where As removal occurs. The trapped Fe(II) subsequently increases the surface layer size at the expense of treatment efficiency. Based on these findings, we discuss several simple and affordable methods to prevent the efficiency loss due to the surface layer, including alternating polarity cycles and cleaning the Fe(0) surface mechanically or via electrolyte scouring.

Escherichia coli Attenuation by Fe Electrocoagulation in Synthetic Bengal Groundwater: Effect of pH and Natural Organic Matter.

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.