Remoção de ferro e manganês de águas de abastecimento utilizando sistemas de filtração rápida descendente.

Abstract

The presence of metals such as iron and manganese in drinking water sources represents a challenge for water treatment systems due to their negative impacts on public health, aesthetic water quality, and treatment process efficiency. The Nova Camará Dam, located in the municipality of Alagoa Nova, Paraíba, Brazil, is responsible for supplying water to several municipalities in the Brejo Paraibano region. However, the seasonal occurrence of iron and manganese in the source water has been observed, posing additional challenges to the clarification and filtration stages of conventional water treatment. In this context, the present study aimed to evaluate and optimize the rapid downward filtration process for the removal of iron and manganese in water intended for public supply, as well as auxiliary water quality parameters such as turbidity and apparent color. For this purpose, bench-scale filtration systems were constructed with different combinations of filter media, including sand, anthracite, and granular activated carbon (GAC). The optimization of the filtration process was carried out by analyzing the influence of filter bed depth and filtration rate using a Central Composite Design (CCD) associated with Response Surface Methodology (RSM), a statistical approach that enables the development of predictive models and the identification of optimal operational regions. The results indicated that the filter composed of sand and anthracite achieved manganese removal higher than 81,71% under optimal clarification conditions (pH 9.0, polyaluminum chloride (PAC) dosage of 35 mg L⁻¹, and chlorine dosage of 10 mg L⁻¹), with a filter bed depth of 50 cm and a filtration rate of 200 m³ m⁻² day⁻¹. However, the turbidity of the filtered effluent did not comply with the limits established by Brazilian drinking water regulation (GM/MS Ordinance No. 888/2021). In contrast, filters containing GAC met the manganese standard in approximately 50% of the analyzed samples, highlighting the filtration and adsorption properties of this material. In addition, these filters showed satisfactory turbidity removal performance, with values ranging from 0.7 to 1.7 NTU. It was also observed that both filter bed depth and filtration rate significantly influenced iron and manganese removal. For filters containing GAC, due to the predominance of adsorption mechanisms, further studies focusing on mass transfer phenomena are recommended. Finally, it can be concluded that the optimization of the rapid filtration stage is an important strategy for improving water treatment systems in the presence of metals such as iron and manganese.