Utilização de ensaios de ecotoxidade no biomonitoramento de efluentes de ETEs industriais, hospitalares e de aterro sanitário, localizadas na região metropolitana de Fortaleza

Abstract

We evaluated the use of ecotoxicity tests with Daphnia magna for the biomonitoring of industrial effluents (real and synthetic), hospital effluent and leachate: real industrial wastewater (Integrated System of Industrial District - SIDI), synthetic industrial wastewater (anaerobic reactor followed by the post-treatments Sequential Batch Reactor - SBR and Advanced Oxidation Process - AOP type H2O2/UV, both treating a wastewater containing the azo dye Reactive Black 5 - RB5), Hospital effluent (Hospital Geral Waldemar de Alcântara - HGWA) and Leachate collected at the output of the stabilization ponds system located at the Metropolitan Sanitary Landfill West of Caucaia - ASMOC and submit to the post-treatment of Submerged Aerated Reactor - SAR. The acute toxicity tests conducted with the leachate indicated that the effluent from ASMOC system showed EC50 of 68%, which could be classified as moderately toxic. Thus, in addition to some physical and chemical parameters that are not complying with the limits defined in the Portaria nº. 154/02 of SEMACE, ecotoxicological results confirm the pollution potential of the leachate to be discharged at the Riacho Garoto, which has low dilution capacity. The post-aerobic treatment performed in SAR showed to greatly contribute in reducing the leachate toxicity in terms of physical-chemical and ecotoxicological characteristics, increasing the EC50 value to 95.04%, and showing to be a good post-treatment option. The results obtained with the real industrial influent and effluent from SIDI revealed that the EC50 increased from 18.05% to 61.90%, switching the classification from very toxic to moderately toxic, respectively. However, the SIDI effluent, considering the physico-chemical properties and toxicity found, associated with the high flow rate of treated wastewater, represents a system with a pollutant load that should be further investigated in the receiving water body. Regarding the hospital wastewater, it was observed that the raw wastewater had a high toxicity, with EC50 of 7.27% (very toxic), while the effluent treated by the sequence of UASB and activated sludge showed EC50 of 30.83% (toxic). Therefore, ecotoxicological tests revealed the toxic character of the effluent in terms of in acute toxicity and it can infer the chronic toxicity that such an effluent can cause in the water body, since it may contain high concentrations of drugs, hormones and other micro-pollutants. The synthetic wastewater containing the azo dye RB5 presented EC50 of 23.02%, classified as very toxic. After treatment in the UASB reactor, the EC50 value increased to 40.34%, i.e. there was a toxicity decrease by the anaerobic treatment. In the post-treatment by SBR, a significant reduction of toxicity was found and the effluent could be classified as non-toxic. However, the UV/H2O2 AOP increased the toxicity, in other words the EC50 decreased to 20.17%, being classified as very toxic. The effect of H2O2 concentration on the ecotoxicological test with D. magna was assessed and showed high toxicity of the residual peroxide, in all dilutions tested, causing death of 100% of the exposed organisms. Therefore, the studies indicated that although the H2O2/UV advanced oxidation process (AOP) has a good prospect for application on recalcitrant compounds, the peroxide residual has to be carefully monitored, not only because it increases the wastewater COD but also because it increases the effluent toxicity. As a general conclusion of this research, it was possible to show the great importance of acute and chronic ecotoxicological tests for the biomonitoring of pollution sources located in Ceará, and also for a better understanding of biological and non-biological processes applied to wastewater treatment.