Avaliação físico-química e toxicológica de tecnologias para o tratamento de efluentes de laticínios

Abstract

No Brazil, effluents generated by dairy industries cause pollution in rivers when discharged into them without proper treatment. Thus, the present work aimed to apply and compare different treatments in the effluent of a dairy industry that produces cheese in physical-chemical and ecotoxicological terms. The raw effluent from the industry was collected by a composite sample and characterized in physical-chemical terms. A physical-chemical treatment (coagulation) was applied to the raw effluent, evaluated by experimental design with three independent variables (pH, settling time and dosage of the natural coagulant Urera baccifera extract). Photo-ozonation was also applied on the raw effluent and after the physical-chemical treatment. To evaluate the ecotoxicological effects of raw and treated effluents leakage tests with Eisenia fetida, immobility/mortality test with Artemia salina and MTT cytotoxicity test with mammalian cell culture were applied. Regarding the results of the physical-chemical analyses, the raw effluent showed high values of COD (5551.56 mg/L), BOD5 (2942.33 mg/L), oils and greases (1133.00 mg/L), solids total suspended (6836.00 mg/L) and turbidity (506 UNT), with basic pH (9.93), demonstrating the need to carry out the treatment of this effluent before its release into the environment .The experimental planning evaluating the natural coagulant U. baccifera showed that this presented very satisfactory results in the reduction of turbidity (0.02 UNT), oils and greases (240.00 mg/L) and sedimentable solids (<0.1 mg/L), being defined the best treatment in the conditions of pH of 9.92, coagulant dosage of 14 mL/ 100ml and settling time of 12.8 min. However, due to the characteristic of natural coagulant, both the treatment with coagulation, and the treatment with coagulation followed by photo-Ozonization, were not efficient in the reduction of COD, DBO5, total solids, volatile and fixed. Treatment only with photo-ozonization resulted in the best physicochemical results in terms of oil and grease reduction (163.60 mg/L), DBO5 (903.21 mg/L), COD (1771.00 mg/L), total solids (5808.00 mg/L) and fixed solids (929.0 mg/L). Regarding ecotoxicity, the raw effluent was toxic for the bioindicator A. salina and the treatments on this raw effluent were not effective to reduce its toxicity. For the bioindicator E. fetida, the crude effluent treated with coagulant U. baccifera followed by photo-ozonization presented toxicity and, for the culture of macaque kidney cells, only the extract of U. baccifera alone resulted in cytotoxicity. Therefore, it is understood that other treatments should be applied to the raw effluent and the use of U. baccifera extract as a natural coagulant may be promising, because, in addition to reducing physico-chemical parameters of the raw dairy effluent, did not result in an increase in or generation of toxicity to E. fetida and the mammal culture used in this study.