Remoção de detergentes em efluentes de usina elétrica a gás por tratamento físico-químico

Abstract

The generation of electricity by the Usina Elétrica a Gás de Araucária (UEGA) requires the use of large amount of water for producing steam and for replacement of losses from open cooling system. This system consists of a cooling tower with a air circulation and has an average replacement at 24 325 m3.h-1, when the plant is operating at full load. The water used for replacement of this system is already a reuse water, collected and treated by the Sanepar industrial Water Treatment Plant (WTP). However, due to the shortage of this resource and the increase in pressure for its use, it is considered the application of treatment that enables the reuse of cooling tower waste water (purge) or at least an economy by reducing the volume currently discharge. In the water used by UEGA persist detergents (linear alkyl benzene sulfonate - LAS) due to the large use of these by the general population. In the cooling tower, due to the agitation of the water and the presence of detergents, are formed foams that generate operational annoyances. This study aims to test two surfactants removal methods to avoid foaming in the cooling tower as a sectoral treatment and to internal reuse. It was evaluated the processes of coagulation/ flocculation/ sedimentation and coagulation/ flocculation/ flotation separately using aluminum sulfate as coagulant. The physical-chemical analysis of COD and turbidity, to characterize the effluent, were held at the Laboratório de Tratamento de Águas Residuárias - LATAR, while the analysis of LAS and total dissolved solids were made at the UEGA’s Laboratory, following the methodology of Standard Methods for the Examination of Water and Wastewater and standards of the Associação Brasileira de Normas Técnicas (NBR). The optimum removing conditions in the sedimentation were obtained by adjusting the concentration of the coagulant and the pH, obtaining better removal of LAS at a concentration of 400 mg.L-1 of aluminum sulphate at pH 7. The removal of LAS in flotation under the same conditions was similar to that of sedimentation, approximately 30%. Besides the removal of LAS, it was observed COD removal of 26% for sedimentation and 56 % for flotation. An average increment of 341 % in turbidity and 9% in the TDS for the sedimentation, while for flotation the average increment was 79% in turbidity and 49 % in the TDS. Thus, the best condition for the treatment of gas power plant - UEGA effluent was obtained at pH 7 and the concentration of Al2 (SO4) 3 400 mg.L-1, using sedimentation as solids separation method for 30 minutes.