Caracterização e avaliação do aproveitamento de resíduos sólidos do tratamento preliminar da estação de tratamento de esgoto de uma instituição de ensino

Abstract

The treatment of sewage generates some types of by-products such as biogas, sludge, treated effluent, coarse solids, sand and scum. The first three have been evaluated for different purposes such as energy production, nutrient supply, soil conditioning, making sorbents to remove contaminants and manufacturing lightweight aggregates. However, the latter, due to their great heterogeneity and contamination with different pollutants, have been little studied, being sent to landfills, with a large occupation of areas and reduced cell life. Thus, with the accomplishment of the present work, the objective was to characterize and evaluate the potential use of the grated material (retained in the perforated plates) of the sewage treatment station of UFLA (ETE-UFLA) in the production of sand for civil construction and fertilization of soils. To achieve the objectives, the waste from the preliminary treatment was separated by lift stations (“Veterinary lift station” x “Guava lift station” - sewage with different characteristics - coming from the south and north portions, respectively, of the university campus) and by treatment stage (coarse and fine screen), in addition to carrying out the following evaluations: mass, gravimetric and granulometric characterization; obtaining mass/specific weight, total, fixed and volatile solids, macro and micronutrients; evaluation of the presence of total and thermotolerant coliforms and microplastics in the samples; and evaluation of fertilization in pots (compared to soil without fertilization and soil with NPK fertilization). Based on the results found, it was verified that most of the preliminary treatment residues are classified as “others”, having important soil composition. The residue presents soil characteristics of medium texture (to clayey) and with the presence of macro and micronutrients, which is why it provided greater plant production of elephant grass in relation to the chemical treatment. In this by-product, there is the presence of microplastics, while the segregated sand presents organic matter and pathogenic organisms. Treatment with chemical products provided a greater reduction in the volatile solids content, although the values achieved are low and are close to simpler treatment (with maintenance at room temperature and use of tap water), while chlorination allowed the non-detection of pathogens in the concentration of 8 g/L of calcium hypochlorite. It generates 0.013-0.023 L/m3 of waste in the period with the highest presence of students, and the time of year (number of users) and the lift station (Veterinary generates more waste) interfere in the sampled amount.