Análisis experimental mediante plantas piloto para el tratamiento de aguas, aplicando tecnologías de biofiltración en el sector rural

Abstract

The availability and quality of water sometimes is not appropriate for consumption without prior treatment. This situation occurs commonly in rural areas of developing countries, where inhabitants in some cases consume water directly from the source without treatment. In most of cases, the use of a centralized drinking water system is impossible due to the large distance between the houses and on other occasions due to the topographic location that limits its implementation. It is in this context this doctoral thesis intends to determine a conventional low cost method for water treatment, to be implemented in single-family homes or in small dispersed settlements in the rural sector. The most appropriate treatment to be implemented in rural areas is biofiltration, which is based on a system of filters made of ceramics, sand, gravel, biofuels, fibers and other materials that favor the removal of pollutants from the water. These materials are efficient as those used commercially in large centralized water treatment systems. They are inexpensive in their preparation, and maintenance. Another advantage is the use of materials from the zone for water treatment which are efficient. The water treatment process has been developed experimentally in full-scale pilot plants in certain rural areas of southern Ecuador. These pilots are capable of supplying the population with a minimun provision considered for hydration of a person of 7.5 L/day, a value recommended by the World Health Organization. These pilot plants were configured according to the local availability of filter materials and the type of water to be treated. Several biofiltration pilots were carried out which are briefly described. Firstly, a pilot plant was built for the elimination of Total Coliforms (TC) and Escherichia coli (E. coli) from water, by direct filtration in beds made up of ceramic spheres, silica sand and activated carbon cartridge. The efficiency in the elimination of the TC was superior to 70% in the ceramic filters, in the sand filters superior to 90% and in the activated carbon filters they were able to eliminate up to 100%. In the case of E. coli, all filter materials eliminate up to 100% with respect to the influent. The main mechanisms that allowed bacteria to be eliminated were the inactivation produced by clay minerals, as well as adhesion (where chemical and physical interactions are generated between the surface of the material and the bacteria). The cost of the ceramic material was USD 0.78/kg, this makes it a competitive material in the market. Another pilot system was built to remove Pb2+, Fe2+ and Mn2+ from a natural water, with the use of ceramics from natural clays and combined with agricultural by-products such as rice husks and birseed seeds. The removal of Pb2+, Fe2+ and Mn2+, the material with the best efficiency was the ceramic obtained from natural clay added with birdseed seeds, obtaining a removal greater than 76%, 31% and 79%, respectively. In the case of Zn2+, the material with the highest efficiency was obtained from the combination of natural clay with rice husk with removal values higher than 76%. A biochar type filter material obtained from agricultural by-products (such as peanut shell, corn cob and chonta fruit) was also elaborated and analyzed, for the lead and cadmium removal from water. The biochar with the best efficiency to remove Pb2+ and Cd2+ was obtained from the peanut shell with an adsorption capacity of 2.528 mg/g and 0.314 mg/g, respectively. The rest of the biochar worked efficiently, but with lower efficiency values than that obtained with the peanut shell biochar. It was found that the removal occurred by adsorption on biochar, although it is also promoted by chemical reactions, complexation and ion exchange. It was found that adsorption is a low cost technology (USD 0.35/kg) and easy to implement in drinking water treatment systems. The socioeconomic benefit of the proposed technologies is very relevant for developing countries. In addition to improve the microbiological characteristics of the water, serious diseases can be avoided in children and adults due the consumption of unhealthy water. On the other hand, technology is transferred to rural sectors, even turning out to be attractive for local ceramic producers. Finally, an added value is given to clay materials, arid materials and by-products of agricultural origin, thereby achieving a sustainable use of agricultural residues or by-products, which otherwise would have to be managed, incurring significant costs.