Caracterização e proposta de tratamento de efluentes gerados por mecânicas automotivas

Abstract

The demand for automotive repair services performed in the mechanic’s workshops grows with the increase in the number of vehicles that circulate on the streets daily. Such workshops generate liquid effluents and solid waste that if discarded incorrectly increase the sources of pollution and contamination of the environment. The effluents generated in the workshops represent a serious environmental problem due to its high COD (Chemical Oxygen Demand) and oils and greases, necessitating, therefore, an improvement of is treatment. When confronted with this reality, this work had as objective the characterization of effluents generated in automotive mechanics, as well as its treatment with a view to reuse or disposal in nature. For this, the effluents were collected in four automotive mechanics of the city of Bagé (RS) and in an automotive mechanic of the municipality of Bento Gonçalves (RS). The characterization of the effluents was done with respect to the following parameters: temperature, pH, turbidity, oils and greases, COD, biochemical oxygen demand (BOD), electrical conductivity and dissolved solids. The effluents were treated by preliminary treatment (oil and water separation box) and primary (coagulation, flocculation and filtration) treatment. In the preliminary treatment, a retention box was constructed with a view to the separation of oil and grease from the aqueous phase in a pseudo-continuous system. The aqueous phase was subjected to the primary treatment, which consisted of the addition of aluminum polychloride (PAC) as a coagulant and anionic polymer as a flocculating agent. The process of coagulation and flocculation gave rise to two phases: the clarified and the sludge. The clarified was filtered and after characterized with respect to the physicochemical parameters mentioned above and the possible framing in a class of CONAMA resolution n°. 357/2005 (BRASIL, 2005) will characterize it for a possible reuse or, CONAMA n° 430/2011 (BRASIL, 2011) and CONSEMA n° 355/2017 (RIO GRANDE DO SUL, 2017) for the discharge of effluents into receiving bodies. Were observed in the ray materials from the mechanical workshops in the city of Bagé (RS) and Bento Gonçalves (RS) a high COD (above 50.000 mg/L), high electrical conductivity values (greater than 500 μS) and high turbidity (above 890 NTU) as well as high oil and grease contented (above 30%), demonstrating the need to treat these effluents. The retention box reduced turbidity by approximately 83% and by 87% the amount of oil presented in the effluent. After the filtration process, removal percentages increased to about 99,5% turbidity, 27,5% electrical conductivity, 38% dissolved solids and 99,8% COD. Based on this, the treated effluent has values of pH, oil and greases, turbidity and dissolved solids acceptable to CONAMA Resolution 357/2005 (reuse class II) (BRASIL, 2005), and the values of temperature and COD of the treated effluent are within the range acceptable by Resolution CONSEMA n° 355/2017 (RIO GRANDE DO SUL, 2017).