Small-scale and household low-cost technologies to provide water free of arsenic for drinking purposes, suitable for isolated rural and periurban areas not connected to water networks in Latin America are described. Some of them are merely adaptation of conventional technologies already used at large and medium scale, but others are environmentally friendly emerging procedures that use local materials and resources of the affected zone. The technologies require simple and low-cost equipment that can be easily handled and maintained by the local population. The methods are based on the following processes: combination of coagulation/flocculation with adsorption, adsorption with geological and other low-cost natural materials, electrochemical technologies, biological methods including phytoremediation, use of zerovalent iron and photochemical processes. Examples of relevant research studies and developments in the region are given. In some cases, processes have been tested only at the laboratory level and there is not enough information about the costs. However, it is considered that the presented technologies constitute potential alternatives for arsenic removal in isolated rural and periurban localities of Latin America. Generation, handling and adequate disposal of residues should be taken into account in all cases.
Arsenic (As) in groundwater for domestic use poses a worldwide threat to public health, most notably in rural areas. The aims of this study were: first, determine groundwater composition in a mining area in central Mexico (Huautla); second, assess As exposure through human groundwater consumption and; third, develop and test a household filter to obtain drinking water for these rural communities. From the 17th century through the 1990s, mines in the area produced Ag-galena and sphalerite from volcanic rock. Groundwater flooded the mines when they were abandoned due to low silver prices. Local households now use the water to meet domestic needs. Water from the mines was found to have high As content (0.04-0.26 mg L(-1)) and Fe, Mn, Pb and Cd were also above Mexican drinking water standards and WHO guidelines. All the population in the Huautla community was exposed to the metalloid through water used in food preparation. The best As removal was obtained with a filter using oxidized commercial fiber (HCl 2N as oxidant). Concentrations in the effluent were below Mexican drinking water standards (0.025 mg As L(-1) water) during the 105-day (2520 h) filter operation, with a maximum As removal efficiency of 95.4%. The household filter was simple, low-cost and may be very attractive for As removal in rural areas in developing countries.
This study evaluated the impact of an abandoned Ag mine on the quality of surface and groundwater. The mining site of Huautla is in south Morelos State, central Mexico. Ag-Pb-Zn and Au-Cu sulfide ores were mined in the district. The ores were characterized by the presence of Ag, galena (PbS), sphalerite (ZnS), and stromeyerite (CuAgS). Ag was the metal of greater interest. Other metals included Cu, Pb, Zn, and Au. Mining activities stopped in the early 1990s when the market price of Ag decreased; the abandoned mines then were flooded by rising groundwater levels. Because of the urgent demand for water by the inhabitants in the area, this water has been used as drinking water and as waterholes for livestock. Water sampling points included abandoned mines (América, Pajáro, Santiago, Tlachichilpa, and San Francisco), dams, and dug wells. The greatest concentrations of As and other toxic chemical elements (Fe, Mn, Pb, Cd, F) were detected in groundwater samples from flooded mines. The presence of these elements was related to the rockwater interaction process. The oxidation of sulfides appears to be the cause of increased metal concentrations in groundwater samples from flooded mine. Other possible water-rock interaction processes that can control the presence of arsenic in groundwater were the adsorption of arsenic in iron oxyhydroxides, the adsorption in carbonates, and/or coprecipitation with calcite. In the case of the San Francisco and América mines, the oxidation conditions, low correlation of As with SO 4 2and Fe 2? , and concentrations of silica indicate that the presence of As in the groundwater could be due also to competition for adsorption sites.
The country of Mexico is facing serious problems with water quality and supply for human use and consumption in rural communities, mainly due to topographic and isolation. In Mexico the average annual precipitation is 1,500 cubic kilometers of water, if 3% of that amount were used, 13 million Mexicans could be supplied with drinking water that they currently do not have access. Considering the limited infrastructure and management in rural communities, which do not receive services from the centralized systems of large cities, a modified pilot multi-stage filtration (MMSF) system was designed, developed, and evaluated for treating collected rainwater in three rural communities, Ajuchitlan and Villa Nicolas Zapata (Morelos State) and Xacxamayo (Puebla State). The efficiencies obtained in the treatment system were: colour and turbidity >93%. It is worth mentioning that the water obtained for human use and consumption complies with the Mexican Standard NOM-127-SSA1-1994.
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