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

Electrocoagulation-Adsorption to remove anionic and cationic dyes from aqueous solution by PV-Energy

The cationic dye malachite green (MG) and the anionic dye Remazol yellow (RY) were removed from aqueous solutions using electrocoagulation-adsorption processes. Batch and continuous electrocoagulation procedures were performed and compared. Carbonaceous materials obtained from industrial sewage sludge and commercial activated carbons were used to adsorb dyes from aqueous solutions in column systems with a 96–98% removal efficiency. The continuous electrocoagulation-adsorption system was more efficient for removing dyes than electrocoagulation alone. The thermodynamic parameters suggested the feasibility of the process and indicated that the adsorption was spontaneous and endothermic (Δ = 0.037 and −0.009 for MG and RY, resp.). The Δ value further indicated that the adsorption process was spontaneous (−6.31 and −10.48; = 303 K). The kinetic electrocoagulation results and fixed-bed adsorption results were adequately described using a first-order model and a Bohart-Adams model, respectively. The adsorption capacities of the batch and column studies differed for each dye, and both adsorbent materials showed a high affinity for the cationic dye.Thus, the results presented in this work indicate that a continuous electrocoagulation-adsorption system can effectively remove this type of pollutant from water. The morphology and elements present in the sludge and adsorbents before and after dye adsorption were characterized using SEM-EDS and FT-IR

Strategies for successful field deployment in a resource-poor region: Arsenic remediation technology for drinking water

Strong long-term international partnership in science, technology, finance and policy is critical for sustainable field experiments leading to successful commercial deployment of novel technology at community-scale. Although technologies already exist that can remediate arsenic in groundwater, most are too expensive or too complicated to operate on a sustained basis in resource-poor communities with the low technical skill common in rural South Asia. To address this specific problem, researchers at University of California-Berkeley (UCB) and Lawrence Berkeley National Laboratory (LBNL) invented a technology in 2006 called electrochemical arsenic remediation (ECAR). Since 2010, researchers at UCB and LBNL have collaborated with Global Change Program of Jadavpur University (GCP-JU) in West Bengal, India for its social embedding alongside a local private industry group, and with financial support from the Indo-US Technology Forum (IUSSTF) over 2012–2017. During the first 10 months of pilot plant operation (April 2016 to January 2017) a total of 540 m3 (540,000 L) of arsenic-safe water was produced, consistently and reliably reducing arsenic concentrations from initial 252 ± 29 to final 2.9 ± 1 parts per billion (ppb). This paper presents the critical strategies in taking a technology from a lab in the USA to the field in India for commercialization to address the technical, socio-economic, and political aspects of the arsenic public health crisis while targeting several sustainable development goals (SDGs). The lessons learned highlight the significance of designing a technology contextually, bridging the knowledge divide, supporting local livelihoods, and complying with local regulations within a defined Critical Effort Zone period with financial support from an insightful funding source focused on maturing inventions and turning them into novel technologies for commercial scale-up. Along the way, building trust with the community through repetitive direct interactions, and communication by the scientists, proved vital for bridging the technology-society gap at a critical stage of technology deployment. The information presented here fills a knowledge gap regarding successful case studies in which the arsenic remediation technology obtains social acceptance and sustains technical performance over time, while operating with financial viability

Arsenic Removal From Drinking Water By Electrocoagulation

Exposure to arsenic through drinking water poses a threat to human health. Electrocoagulation is an emerging water treatment technology that involves electrolytic oxidation of anode materials and in-situ generation of coagulant. Electrocoagulation is an alternative to using chemical coagulants for arsenic removal and thus is beneficial for communities with better access to electricity than to chemicals

Interfacial Chemistry of Trace Elements at Mineral Surfaces in Engineered Water Systems

This thesis research consists of two independent research projects that both studied interfacial chemical processes affecting trace elements at mineral surfaces. The objectives of Project 1 were to 1) quantify the impact of water chemistry on As(III) adsorption on lepidocrocite, 2) develop a surface complexation model to describe equilibrium As(III) and As(V) adsorption to lepidocrocite and 3) elucidate the mechanism of Fe(II)-mediated As(III) oxidation at the lepidocrocite-water interface. Arsenic is a regulated element that can be found at high concentrations in groundwater resources that are used as drinking water sources. Iron (oxyhydr)oxides are one of the most abundant groups of minerals in soils and aquifers, and their presence can significantly affect the behavior of arsenic. Iron (oxyhydr)oxides are also commonly used as adsorbents in engineered system to remove arsenic from drinking water. In addition to adsorbing arsenic, Fe(III) minerals can participate in As(III) oxidation to As(V), which can reduce arsenic\u27s mobility and enhance its adsorption. Advances in the understanding of the environmental chemistry of arsenic are important to the development of water treatment technologies. The adsorption of arsenic to lepidocrocite strongly depends on water chemistry. Experiments that pursued objectives in Project 1 examined As(III) and As(V) adsorption to lepidocrocite as a function of pH, total As(III) concentration, iron loading, Fe(II) and competing adsorbate presence. For the arsenic concentrations and Fe loadings studied, As(V) adsorption decreases substantially with increasing pH, while As(III) adsorption is less sensitive to pH changes, characterized by a stable level of high adsorption between pH 6-9. For As(III), the presence of oxygen promoted the overall arsenic adsorption via partial As(III) oxidation. A surface complexation model, optimized for both adsorption isotherms and adsorption edges, was able to describe the adsorption of both As(III) and As(V) to lepidocrocite over a broad range of conditions. The concentration and oxidation states of dissolved arsenic measured over the course of a reaction provided information on As(III) oxidation. When dissolved oxygen and Fe(II) were not present, As(III) was not oxidized by the Fe(III) in lepidocrocite. At both oxic and anoxic conditions, As(III) was oxidized to As(V) in systems that contained lepidocrocite together with Fe(II); this oxidation led to overall enhanced arsenic adsorption at near neutral pH. With oxygen, the pH-dependent generation of oxidants from the Fenton reaction drove the As(III) oxidation. In the absence of oxygen, the As(III) was probably oxidized by Fe(III) in lepidocrocite that had become more reactive upon reaction with Fe(II). The two reaction pathways could occur individually or in combination. Findings in Project 1 provide a deeper understanding of arsenic behavior in engineered water systems and are instrumental to manipulating the conditions under which arsenic is removed via adsorption. The objectives of the second project were to 1) investigate the impact of water chemistry on trace element mobilization from shales during shale-fluid contact and 2) to identify the dominant mobilization pathways. The rapid development and expansion of hydraulic fracturing operations for enhanced energy recovery can affect water quality. The flowback and produced waters after injection of a fracking fluid could contain high total dissolved solids and trace elements mobilized from contact with shales. The concentrations of specific elements depend on the geochemistry of the formation, fluid composition, and time of shale-fluid contact. An understanding of shale-bound element mobilization will facilitate wastewater management associated with hydraulic fracturing practices. Experiments in Project 2 were performed to evaluate trace element mobilization from shales over a range of fluid chemistries with core samples from the Eagle Ford and Bakken formations that are currently producing natural gas and oil via hydraulic fracturing. Samples were characterized with regard to their mineralogy, surface area and total carbon prior to experiments. The fluid chemistry was varied in pH, oxidant level, solid:water ratio, and temperature. Analytical results from experiments and chemical equilibrium modeling were integrated to identify dominant mobilization pathways. The Eagle Ford samples used in this research were rich in carbonates and quartz with minor amounts of kaolinite, albite, pyrite and 5 wt % total organic carbon. The release of most elements strongly depended on pH, which was primarily controlled by carbonate dissolution. The introduction of oxygen and other oxidants (H2O2) significantly increased the amount of sulfate over time; the sulfate generated had a direct impact on Ba concentrations due to the formation of BaSO4 as a secondary phase. For these Eagle Ford samples, trace elements (such as As and U) mobilized from rock-fluid contact had low concentrations in all the conditions studied. Major mineral phases in the Bakken Formation samples included quartz, K-feldspar, illite, dolomite and pyrite. One sample with 18.7 wt % total organic carbon was naturally enriched in redox-sensitive trace elements (including regulated elements such as As and U). For all the water chemistry variables studied (pH, oxidant level, solid:water ratio, temperature, salinity and chemical additive presence), pH and the oxidant level were properties that dominated the behavior of most elements. The addition of chemical additives (HCl, citrate, and persulfate) affected element release mainly by altering system pH or redox conditions. The abundance of dolomite relative to pyrite determined the system pH when sufficient oxidants (such as oxygen and oxidizing chemical additives) were present. The lack of acid-neutralizing minerals, in case of sulfide mineral oxidation, may lead to a significant decrease in the pH. The knowledge gained in Project 2 provides insight on the key factors that dominant shale-bound element mobilization during rock-fluid interactions, and is helpful for understanding and managing produced and flowback water related issues associated with hydraulic fracturing

Field Testing of an Affordable Zero-Liquid-Discharge Arsenic-Removal Technology for a Small-Community Drinking Water System in Rural California

Arsenic contamination in groundwater threatens public health, particularly in small, low-income communities lacking affordable treatment solutions. This study investigated the field implementation of novel air cathode assisted iron electrocoagulation (ACAIE) technology for arsenic removal in Allensworth, California, where groundwater arsenic concentrations exceeded 250 µg/L. Over four months, a pilot-scale ACAIE system, operating at 600 L/h, consistently reduced arsenic levels to below the EPA’s maximum contaminant level of 10 µg/L. Laboratory experiments informed the optimization of charge dosage and flow rates, which were validated during field testing of the ACAIE 600 L/h system. The in-situ generation of hydrogen peroxide at the cathode speeded up the reaction kinetics, ensuring high arsenic removal efficiency while allowing high throughput, even with a compact reactor size. An economic analysis demonstrated a treatment cost of USD 0.02/L excluding labor, highlighting the system’s affordability compared to conventional methods. Adding labor costs increased the treatment cost to USD 0.09/L. The regeneration of air cathodes extended their operational life, addressing a key maintenance challenge, thus reducing the costs slightly. Intermittent challenges were encountered with filtration and secondary contaminant removal; these issues highlight opportunities for further operational improvements. Despite these challenges, ACAIE’s low operational complexity, scalability, and cost-effectiveness make it a promising solution for underserved small communities. These findings provide critical insights into deploying sustainable arsenic remediation technologies that are tailored to the needs of rural, low-resource communities

Coupling of Oxidation-Reduction Reactions of Chromium, Iron and Manganese: Implications for the Fate and Mobility of Chromium in Aquatic Environments

Both within the United States and internationally, hexavalent chromium (Cr(VI)) is a contaminant of concern in drinking water supplies. The U.S. Environmental Protection Agency is considering a Cr(VI)-specific standard. Thus improved technologies for Cr(VI) removal in drinking water are needed. Iron electrocoagulation for Cr(VI) removal was examined at conditions directly relevant to drinking water treatment, and humic acid (HA) affects the performance of electrocoagulation in multiple ways. The success of the chromium treatment or remediation also relies on the stability of the Cr(III)-containing solids with respect to reoxidation under groundwater conditions. Manganese is ubiquitous in aquatic and terrestrial environments, and the redox cycling of manganese may significantly impact the fate and transport of chromium. Coupling of redox reactions of chromium, iron and manganese involves multiple interaction pathways that occur in the aqueous phase as well as at solid-water interfaces. A mechanistic and quantitative understanding of these processes is needed to establish input parameters for kinetic and transport models and to enable decision-making for chromium treatment strategies. Iron electrocoagulation (EC) is a technology that can successfully achieve low concentrations of Cr(VI) in treated drinking water. In our research we have applied iron electrocoagulation (EC) with iron serving as the sacrificial anode to treat simulated drinking water solutions. Experiments have evaluated the effects of pH, dissolved oxygen, and common anions on Cr(VI) removal during batch EC treatment. In addition, the presence of humic acid (HA) inhibited the rate of Cr(VI) removal in electrocoagulation, with slower Cr(VI) removal at higher pH. This is due to dissolved oxygen competing with Cr(VI) for the oxidation of Fe(II) released from the anode. As determined using dynamic light scattering and wet chemistry experiments, the presence of HA resulted in the formation of Cr(III)-Fe(III)-HA colloids during electrocoagulation, which is difficult to remove in following water treatment steps of sedimentation and granular media filtration. Characterization of the solids by X-ray diffraction indicates that the iron oxides produced are lepidocrocite at pH 8, with more ferrihydrite in the presence of HA. Building on previous knowledge of MnO2 as an oxidant for Cr-containing solids, we systematically evaluated the rates and products of the oxidation of Cr(III) in iron oxides by MnO2. We found that Cr(III) dissolution from CrxFe1-x(OH)3 greatly influenced the Cr(VI) production rates. A multi-chamber reactor was used to assess the role of solid-solid mixing in CrxFe1-x(OH)3-MnO2 interactions. A dialysis membrane divided the reactor into two chambers, eliminating the possibility of direct contact of the solids in each chamber but allowing dissolved species to diffuse across the membrane. The Cr(VI) production rate was much lower in multi-chamber experiments (CrxFe1-x(OH)3||MnO2) than in completely mixed batch experiments under the same condition, indicating that the redox interaction is greatly accelerated by mixing of the two solids. The model was first established to predict Cr(VI) release in Cr(OH)3||MnO2 multichamber experiments, as dissolved Cr(III) concentration in equilibrium with Cr(OH)3 is higher at low pH and it’s easy to observe the behavior of Cr(VI) dynamics with more Cr(VI) generation. While solid phase Mn(IV) is well known oxidants of Cr(III)-containing solids, the localized oxidation of adsorbed Mn(II) by dissolved oxygen can also promote the oxidation of Cr(III) contained within CrxFe1-x(OH)3. The promotional effects was likely due to Mn redox cycling in which oxidized forms of Mn species were generated as oxidants of CrxFe1-x(OH)3 that were more potent than O2

Coupling of Oxidation-Reduction Reactions of Chromium, Iron and Manganese: Implications for the Fate and Mobility of Chromium in Aquatic Environments

Both within the United States and internationally, hexavalent chromium (Cr(VI)) is a contaminant of concern in drinking water supplies. The U.S. Environmental Protection Agency is considering a Cr(VI)-specific standard. Thus improved technologies for Cr(VI) removal in drinking water are needed. Iron electrocoagulation for Cr(VI) removal was examined at conditions directly relevant to drinking water treatment, and humic acid (HA) affects the performance of electrocoagulation in multiple ways. The success of the chromium treatment or remediation also relies on the stability of the Cr(III)-containing solids with respect to reoxidation under groundwater conditions. Manganese is ubiquitous in aquatic and terrestrial environments, and the redox cycling of manganese may significantly impact the fate and transport of chromium. Coupling of redox reactions of chromium, iron and manganese involves multiple interaction pathways that occur in the aqueous phase as well as at solid-water interfaces. A mechanistic and quantitative understanding of these processes is needed to establish input parameters for kinetic and transport models and to enable decision-making for chromium treatment strategies. Iron electrocoagulation (EC) is a technology that can successfully achieve low concentrations of Cr(VI) in treated drinking water. In our research we have applied iron electrocoagulation (EC) with iron serving as the sacrificial anode to treat simulated drinking water solutions. Experiments have evaluated the effects of pH, dissolved oxygen, and common anions on Cr(VI) removal during batch EC treatment. In addition, the presence of humic acid (HA) inhibited the rate of Cr(VI) removal in electrocoagulation, with slower Cr(VI) removal at higher pH. This is due to dissolved oxygen competing with Cr(VI) for the oxidation of Fe(II) released from the anode. As determined using dynamic light scattering and wet chemistry experiments, the presence of HA resulted in the formation of Cr(III)-Fe(III)-HA colloids during electrocoagulation, which is difficult to remove in following water treatment steps of sedimentation and granular media filtration. Characterization of the solids by X-ray diffraction indicates that the iron oxides produced are lepidocrocite at pH 8, with more ferrihydrite in the presence of HA. Building on previous knowledge of MnO2 as an oxidant for Cr-containing solids, we systematically evaluated the rates and products of the oxidation of Cr(III) in iron oxides by MnO2. We found that Cr(III) dissolution from CrxFe1-x(OH)3 greatly influenced the Cr(VI) production rates. A multi-chamber reactor was used to assess the role of solid-solid mixing in CrxFe1-x(OH)3-MnO2 interactions. A dialysis membrane divided the reactor into two chambers, eliminating the possibility of direct contact of the solids in each chamber but allowing dissolved species to diffuse across the membrane. The Cr(VI) production rate was much lower in multi-chamber experiments (CrxFe1-x(OH)3||MnO2) than in completely mixed batch experiments under the same condition, indicating that the redox interaction is greatly accelerated by mixing of the two solids. The model was first established to predict Cr(VI) release in Cr(OH)3||MnO2 multichamber experiments, as dissolved Cr(III) concentration in equilibrium with Cr(OH)3 is higher at low pH and it’s easy to observe the behavior of Cr(VI) dynamics with more Cr(VI) generation. While solid phase Mn(IV) is well known oxidants of Cr(III)-containing solids, the localized oxidation of adsorbed Mn(II) by dissolved oxygen can also promote the oxidation of Cr(III) contained within CrxFe1-x(OH)3. The promotional effects was likely due to Mn redox cycling in which oxidized forms of Mn species were generated as oxidants of CrxFe1-x(OH)3 that were more potent than O2