Processos oxidativos avançados em efluente de tratamento de sementes e avaliação da ecotoxicidade

Abstract

In agriculture, there is a constant search for increased productivity and for this, there is a growing use of products to carry out seed treatment before planting with fungicides, insecticides, inoculants, among other products. After treatment, the machines and equipment are sanitized, generating a liquid waste of a composition that is not very well known, which can generate environmental impacts. Thus, the aim of this study was to characterize and evaluate the toxicity of this effluent generated in washing soybean seed treatment machines, suggesting treatment methods. The applied treatment was a combined coagulation process followed by heterogeneous photocatalysis and ozonation. The coagulation process was carried out in a Jar Test, using 50 mL of aluminum sulfate coagulant (0.01g mL1) for each 500 mL of effluent. The parameters were programmed so that fast agitation remained at 100 rpm for 30 seconds and slow agitation at 25 rpm for 10 minutes. The settling time was 120 minutes. In the photocatalysis process, TiO2 was used as catalyst in the proportion of 0.2 g to 100 mL, remaining for 180 minutes in the photocatalytic reactor. Finally, during ozonation, the effluent remained for another 210 minutes at room temperature, while oxygen and ozone were continuously bubbled into the jacketed photoreactor. The analyzes identified a high amount of soluble, total and total sedimentable solids in the raw effluent, as well as a high chemical oxygen demand (COD). After the treatments there was a significant decrease in the concentration of sedimentable solids of 95.22%, while the total solids and total dissolved solids decreased only 25.26% and 9.14%, respectively. On the other hand, COD reached a removal rate of 31.55%. Despite the reduction in the physicochemical parameters of the effluent, it still showed high toxicity to the bioindicators Artemia salina L. (immobility/mortality test) and Eisenia fetida (leakage test), and in some cases showed acute toxicity (mortality) to the organisms. The results confirm the risk that this effluent poses to the environment, showing the importance of continuing the investigation of new treatment technologies, in order to provide the reduction of physicochemical parameters and final toxicity.