Estudo analítico sobre a eficiência de caixas de gordura: desenvolvimento de protótipo em concreto e análise da influência do tempo de detenção hidráulica na sua eficiência

Abstract

Grease traps are devices used for the retention of fatty effluents from kitchens, industries and other environments. Greases from these environments should not be discharged into the sewerage connection, as they can clog public pipes, hinder the treatment of effluents and cause damage to the receiving bodies. There are no Brazilian standards that require the installation of these devices, although some municipalities have already regulated and imposed its use. Several studies indicate that the grease trap models presented in the NBR 8160 from 1999 does not exhibit appropriate efficiencies for the function. The present study consists in the development and construction of a grease trap prototype (GTP) in reinforced concrete with baffles to carry out efficiency tests. These experiments’ objective was to verify the influence of the hydraulic retention time (HRT) in the efficiency of the equipment and to obtain numerical relation between these two indicators. To change HRTs for the same prototype, adjustments were made to the entry flows by varying the mixing level inside the affluent reservoir. The tests used synthetic blends of edible soybean oil in the proportion of 150 g/L (grams per liter), simulating common fatty domestic effluents. HRTs of 4, 7.6 and 11.8 minutes were tested, checking the concentration of oil in each effluent mixture to verify the percentage of soybean oil retained by the GTP. As results, efficiencies of 64.0% were obtained for test 1 (HRT of 4 minutes), 83.8% for test 2 (HRT of 7.6 minutes) and 89.2% for test 3 (HRT of 11.8 minutes), all of which are higher than the efficiency of prefabricated grease traps tested in other bibliographies. With these results, an equation that represents the numerical relationship between each HRT and efficiency analyzed in the tests was found. It was observed an optimum time of 10 minutes for hydraulic detention of the GTP, obtaining the prototype’s most advantageous TDH x efficiency ratio.