Avaliação ecotoxicológica de efluentes de estações de tratamento de esgoto aeróbio e anaeróbio

Abstract

As consequence of the population and industrial growth, the pollution of receiving waters can cause a shortage of water resources with an adequate quality and the need for more complex treatment to the water. Given this issue is necessary to monitor effluents in receiving waters. To determine acute toxicity using microcrustaceans Daphnia magna, it is evaluated the mortality or immobility of the body exposed to the test substance for 48 hours. This study aimed to assess the acute ecotoxicity of samples of raw sewage and treated effluent, from two sewage treatment plants (STP) through the bioassays with microcrustaceans Daphnia magna. For that, were defined collection points: tributary of the sandbox and effluent of the secondary clarifier of STP treatment aerobic and; tributary of the sandbox and effluent from facultative ponds before application of chloride gas and effluent from facultative ponds after application of chloride gas of STP treatment anaerobic. The sensitivity of the bodies was evaluated using as reference substance potassium chloride and the results were expressed in effective concentration that causes mobility to 50% for the tested organisms (CE50). The CE50 determined by the sensitivity test was 722.4 mg KCl.L-1, standard deviation (σ) of ± 25.3 and coefficient of variation (CV) of 3.5%. The results demonstrates that the samples of the tributary of the sandbox presents toxicity in a single sample (FT 4) and the effluent of the secondary clarifier of STP treatment aerobic did not show toxicity (FT 1). However it was not possible to verify if the treatment of STP aerobic was efficient for the reduction of toxicity, because the only sample that was considered the time of detention, the tributary have presented FT 1. For the STP treatment anaerobic, it was verified that the tributary of the sandbox present toxicity in all samples tested. For the effluent, there was little difference between the toxicity factors of effluents from facultative ponds before the application of chloride gas and after the application of chloride gas, demonstrating that the chlorine could be possibly evaporated from the samples due to the elevated temperatures. For STP treatment anaerobic, it was possible to verify that the toxicity was reducted along the time of treatment, being reducted from FT4 to FT1. However, for more complete evaluation is required acute toxicity bioassays using others organisms and chronic toxicity testing to verify the real impact of evictions in the receiving bodies.