Bundschuh, and 9 co-authors, reported in 2010 that current information about the contamination of ground- and surface-water resources by arsenic from geogenic sources in Latin America is presented together with possible emerging mitigation solutions. The problem is of the same order of magnitude as other world regions, such as SE Asia, but it is often not described in English. Despite the studies undertaken by numerous local researchers, and the identification of proven treatment methods for the specific water conditions encountered, no technologies have been commercialized due to a current lack of funding and technical assistance.
Emerging, low-cost technologies to mitigate the problem of arsenic in drinking water resources that are suitable for rural and urban areas lacking centralized water supplies have been evaluated. The technologies generally use simple and low-cost equipment that can easily be handled and maintained by the local population. Experiences comprise (i)coagulation/filtration with iron and aluminum salts, scaled-down for small community and household-scale-applications, (ii) adsorption techniques using low-cost arsenic sorbents, such as geological materials (clays, laterites, soils, limestones), natural organic based sorbents (natural biomass), and synthetic materials. TiO2-heterogeneous photocatalysis and zerovalent iron, especially using nanoscale particles, appear to be promising emergent technologies. Another promising innovative method for rural communities is the use of constructed wetlands using native perennial plants for arsenic rhizofiltration.
Small-scale, simple reverse osmosis equipment (which can be powered by wind or solar energy) that is suitable for small communities can also be utilized.
The individual benefits of the different methods have been evaluated in terms of:
i) size of the treatment device,
ii) arsenic concentration and distribution of species, chemical composition and grade of mineralization in the raw water,
iii) guidelines for the remaining As concentration,
iv) economical constrains, and
v) complexity of installation and maintenance, and infrastructure constraints (e.g. electricity needs).
The main features and limitations of the emerging As removal technologies investigated in Latin America over the last few decades are analyzed. Technologies rely on adaptation and improvement of methods involving simple physicochemical processes like adsorption, coagulation/precipitation and ion
exchange, all of them being more suitable for As(V) removal, which usually implies a preliminary oxidation step.
The technologies best suited for application at the community level will be those that are robust, operate well under a wide range of environmental conditions, and can be effectively operated and maintained by people without extensive technical training. For rural communities in Latin America, small-scale and household level As removal systems are the only feasible short-term solution. Specific reactants used in coagulation/sorption processes for As removal are suitable for addition to small volumes of water and can be easily applied at a household level.
Natural geological materials like iron oxides and hydroxides, calcite, clays, and soils may yield effective, simple and low-cost As removal at the household level and for small communities. The As removal efficiency of natural geological materials (e.g. zeolites) may be artificially improved, but this reduces direct
availability to the communities and increases costs. Natural organic materials are also the basis for suitable low-cost technologies. Sorption agents coming from plants and animal residues are more attractive for small-scale, rural, household applications, while the use of As-tolerant and As accumulating plants is more suitable for community applications, since care must be paid to the growth, harvest, and disposal of the specimens.
Procedures using zerovalent iron from diverse materials are affordable and easy to operate and maintain. They require daily attention, but most of them are nevertheless adequate for family use and furthermore, sunlight may be used to improve their effectiveness. Relatively inexpensive UV lamps can be used if solar radiation is not sufficient and there is access to electricity.
Other alternatives, like desalination and capacitive deionization, require electricity that may be produced from environmental-friendly sources like wind or sunlight. Emergent small-scale RO is adequate at a community level since no specially trained technicians are needed. Since experiences with innovative emerging As removal processes in Latin America remain scarce, and are generally limited to laboratory studies, there is a great need for further research to determine how the technologies for As removal described previously can be effectively applied as As mitigation interventions in rural and urban isolated communities. Their use in a regular treatment, however, depends upon the economic level of the communities and the continuous availability of the reactants at the contaminated sites. The effectiveness of the specific reactants should be tested, like many of the treatment options, with the untreated water of every site.
Social knowledge and acceptability of treatment technologies by the local population are important issues in Latin America. The role of women must be considered in particular, since they are the primary procurers and users of the water. To provide them fast and easy technologies to get clean and
safe water can result in a better profit of their time, which can be devoted to educational and leisure activities with their children.
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