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Groundwater is one of the primary sources of water for both drinking and industrial use in northeastern Mexican territory, around 46% of the total, due to the lack of precipitation during the year and solar radiation index. The presence of arsenic in brackish soil and groundwater is a severe health issue, specifically in semi-arid and arid regions in the north of Mexico. Additionally, it represents the only source of drinking water in communities far from big cities, mainly due to the absence of hydric infrastructure. This work presents a new approach to treating polluted water with arsenic. The system based on activating jute fiber with nanoparticles of zero-valent iron immobilized over graphene oxide will allow nZVI particles to preserve their unique qualities for water sanitization. A dynamic flow test was designed to determine the effectivity of activated jute fibers as a water sanitation system. The results showed a reduction in the total arsenic content from 350 ppb to 34 ppb with a filtrate flow of 20 mL/min. The above represents 90% adsorption by the activated fiber. The analyzed sample corresponds to contaminated groundwater taken from Coahuila, Mexico. This sanitation system could be applied to low-income populations lacking robust infrastructure, such arsenic treatment plants. [ABSTRACT FROM AUTHOR]

The paper deals with the removal of arsenic (As), hydrated silica (HS), and coexisting ions from groundwater by electrocoagulation (EC) using a laboratory-scale up-flow reactor with sacrificial iron anodes (1018 steel, >99% wt. Fe). Natural groundwater, taken in the northern region of Mexico, contained 25.7 μg L−1 As, 237.8 mg L−1 HS, 1.43 mg L−1 F−, 45.0 mg L−1 SO 4 2−, 0.61 mg L−1 PO 4 3−, pH 8.62, and 577 μS cm−1 conductivity. The effect of current densities (4 ≤ j ≤ 8 mA cm−2) and mean linear flow velocities (1.1 ≤ u ≤ 4.6 cm s−1) on the pollutant's removal was systematically addressed. The best EC trial that showed the lowest overall cost and complied with the WHO guideline (<10 μg L−1 As) was obtained at j = 6 mA cm−2 and u = 2.3 cm s−1, reaching residual concentrations of As and HS of 4.6 μg L−1 and 150.0 mg L−1, respectively. A large amount of HS was found after electrolysis; therefore, a second EC was applied to reduce the HS concentration further. This time, residual concentrations of HS and As of 37.0 mg L−1 and 1.2 μg L−1 were obtained, with electrolytic energy consumption and overall cost of EC of 0.872 kWh m−3 and 0.178 USD m−3, respectively. XRF, EDS, XRD, and FTIR analyzes on flocs indicate that hydrated silica reacts with iron, forming iron silicates with divalent cations as flocs. Arsenic and PO 4 3− are abated by adsorption on flocs. The modest removal of F− and SO 4 2− (44% and 12%, respectively) is due to its weak adsorption on flocs. [Display omitted] • Hydrated silica (HS) and As elimination from groundwater by electrocoagulation (EC). • An EC reactor equipped with 1018 steel as electrodes provides the iron coagulant. • As concentration after EC meets WHO guideline (<10 μg L−1), with 74% HS removal. • HS reacts with Fe forming iron silicates as flocs, while As adsorbs on aggregates. • Best EC was obtained at 6 mA cm−2 and 2.3 cm s−1, with 0.178 USD m−3 overall cost. [ABSTRACT FROM AUTHOR]

This paper deals with the elimination of hydrated silica, arsenic, and phosphates from real groundwater collected in central Mexico (arsenic 22 μg L−1, hydrated silica 161 mg L−1, sulfate 50 mg L−1, phosphate 0.41 mg L−1, pH 7.6 and conductivity 508 μS cm−1) by electrocoagulation (EC), using a cascade-shaped up-flow reactor with a six-cell stack open to the atmosphere at the top. Aluminum plates were used as electrodes. The influence of both current density (4 ≤ j ≤ 10 mA cm−2) and mean linear flow rates (1.2 ≤ u ≤ 4.8 cm s−1) in the EC reactor on the removal efficiency of hydrated silica, arsenic, and phosphates were examined. The best removal of arsenic after EC (reaching a residual concentration, C As = 1.5 μg L−1) was obtained at j = 10 mA cm−2 and u = 1.2 cm s−1, meeting the World Health Organization (WHO) recommendation (<10 μg L−1), while the residual concentrations of hydrated silica, phosphates and sulfates were C hs = 42 mg L−1, C PO 4 3 − = 0.03 mg L−1 and C SO 4 2 − = 35 mg L−1, respectively. The experimental conditions at j = 10 mA cm−2 and u = 1.2 cm s−1, produced a large amount of coagulant (85.4 mg L−1), so this condition was repeated in a second round of the EC process to further reduce the concentration of hydrated silica. This time, C hs = 2.6 mg L−1 and C SO 4 2 − = 30 mg L−1 were obtained with the complete abatement of arsenic and phosphates. The total cost of the EC was 1.093 USD m−3, which included the electrolytic energy consumption, the price of aluminum, the costs of pumping and confinement of sludge, emphasizing that the calculation was based on Mexican costs. SEM-EDS, XRD, XRF and FTIR analyses on flocs revealed that the coagulant reacted with silica forming aluminum silicates, while arsenic and phosphates were removed by adsorption on flocs. The partial removal of sulfates (40%) is associated with weak adsorption on aggregates. • Elimination of hydrated silica, arsenic, phosphate and sulfate from groundwater. • Cascade-shaped up-flow electrocoagulation (EC) reactor with aluminum electrodes. • High coagulant doses are formed at current densities of 10 mA cm−2. • Silica reacts with coagulant to form aluminosilicates and silicates as flocs. • WHO guideline for As was satisfied after EC. [ABSTRACT FROM AUTHOR]

• Abatement of arsenic and hydrated silica from groundwater by electrocoagulation, EC. • Serpentine reactor, with aluminum electrodes, opened at the top to favor H 2 release. • Important aluminum doses are produced at current densities higher than 6 mA cm−2. • Silica reacts with aluminum to yield aluminosilicates as flocs. • WHO and Mexican guidelines for As and hydrated silica were fulfilled after EC. This paper concerns with the elimination of arsenic and hydrated silica from deep well water, collected form the septentrional area of Guanajuato in Mexico (arsenic 23 μg L−1, hydrated silica 154 mg L−1, sulphate 160 mg L−1, phosphate 0.3 mg L−1, pH 7.5 and conductivity 550 μS cm−1) by electrocoagulation (EC) using an up-flow electrochemical reactor, opened to the atmosphere, with a six-cell stack in a serpentine array. Aluminum plates were used as electrodes. The efficiencies of arsenic and hydrated silica removal at different current densities (4 ≤ j ≤ 7 mA cm-2) and mean linear flow rates (1.2 ≤ u ≤ 4.8 cm s−1) were examined. The best EC was obtained at 7 mA cm-2 and 1.2 cm s−1, which satisfies the WHO guideline for arsenic (< 10 μg L−1) and permits the abatement of hydrated silica, giving values of electrolytic energy consumption and overall cost of EC of 1.64 kW h m-3 and 0.387 USD m-3, respectively. SEM-EDS, FXRD, XRD and FTIR analyses on the flocs revealed that they are structured mainly by aluminosilicates due to the reaction between aluminum and silica. While arsenates, sulfates and phosphates are removed by adsorption on aluminum flocs. [ABSTRACT FROM AUTHOR]