Aplicabilidade do biocarvão de cascas de amendoim (Arachis hypogaea) no tratamento alternativo de água com filtração lenta

Abstract

Despite Brazil's water availability, the population is not entirely supplied with water consistently and qualitatively. This reality is particularly widespread in rural areas, which is reflected in the adoption of alternative and individual measures, such as the use of groundwater through techniques like slow filtration, in order to minimize the social problem of water supply. As a perspective aligned with the Sustainable Development Goals, the application of natural materials to treat water has been extensively observed. Slow filters are conventionally operated with sand and, sometimes, sand and activated charcoal as filter beds. As a contribution to research focused on slow filtration, this study, therefore, aimed to verify the efficiency of applying biochar obtained from peanut shells in the treatment of water intended for human consumption. This verification was based on three pilot systems operated in downward flow, called FA (sand filter), FAC (sand and activated carbon filter), and FAB (sand and peanut shell- -based biochar filter). The water potability guiding parameters were electrical conductivity, apparent and true color, total and thermotolerant coliforms, total iron, pH, temperature, and turbidity, with the main basis for comparison being the limits set by the current Ministry of Health potability ordinance and/or reference. The results showed that the conductivity, even with reductions, did not fit within the allowed limit in all samples. The pH remained constant and within what is established by the ordinance; the temperature also indicated stability. The average removal of apparent color for the three filters – which proved to be similar – was 47.6%; for true color, 25.0%. Coliforms were satisfactorily reduced in the FA, FAC, and FAB filters, with average reductions for total coliforms of 80.9%, 84.5%, and 79.7%, and for thermotolerant coliforms of 92.6%, 100%, and 86.7%, respectively. Regarding total iron decontamination, the values were 84.6%, 89.2%, and 82.4%, respectively. For turbidity, the removal capacity was significant: 65.8%, 67.8%, and 69.5%, respectively. Through statistical tests, the checks indicated similar performance among the filters for all parameters, except true color, with significant differences between raw and treated water. Regarding characterization, the biochar indicated an amorphous nature, low porosity, developed functional groups, stable zeta potential, significant particle size, and small surface area and adsorptive capacity, which was verified through a methylene blue dye test. Thus, the filter made of peanut shell biochar showed efficiency and feasibility for water treatment, when compared to the traditional methodology, since, in addition to reducing impurities and purifying the resource, it is low cost, as well as easy and accessible to apply.