Flotação por ar dissolvido no pós-tratamento de efluente de indústria de produtos lácteos visando ao reúso

Abstract

Dissolved air flotation (DAF) consists on a physical process used for water and wastewater clarification. On wastewater treatment, DAF is used to suspended solids, fats, fibers and other low density solids removal. Its use in a wide range of industrial wastewaters can be highlighted, as well as post-treatment for sanitary sewage. The aim of this work was to evaluate FAD preceeded by coagulation-floculation as pos-treatment in an dairy industry, in order to achieve quality for non potable water reuse. Firstly, a conventional DAF laboratorial test equipment was manufactured, in order to evaluate the potential performance of comercial coagulants ferric chloride 38%, Klaraid IC 1176L and Novfloc 1540 associated with Polfloc D150 floculation auxiliar. For such purpose, a strategy sequence of experimental planning for operational condiction optimization was developed. Secondly, an enlarged FAD module with augmented range for the operational parameters capacity and air dissolved measurement was proposed and manufactured. This module was used for modeling and optimal operational conditions determination through 24 central composite rotational design using ferric chloride 38% and Klaraid IC1176L, varying coagulant dosage, pH, saturation pressure, and recirculation rate. After that, the identified optimal condition was tested in real scale in an industrial plant. The three coagulants presented similar potencial performance considering the operational conditions on conventional batch test equipment for the evaluated removals of turbity, COD ans TSS, as well as final pH. On a second step, taking into account the regression models and optimized conditions, indicate by the Statistica desirability function, in the following predicted results were found: 100% turbity removal, 82.4% COD removal and 4.2 final pH for ferric chlorid 38% (with coagulant dosage of 680 mg L-1, 5.1 inicial pH, 520 kPa of saturation pressure, 36.7% of recirculating rate) and 99,5% turbity removal, 87.8% COD removal and 5,9 final pH for Klaraid IC1176L (with coagulant dosage of 633 mg L-1, 5,9 of inicial pH, 545 kPa of saturation pressure, 37% of recirculating rate), both using 10 mg L-1 of Polfloc D150 dosage. It was possible to carry out a testing in an industrial flotation unit the coagulant Klaraid IC1176L with Polfloc D150 on the following conditions: coagulant dosage of 587 mg L-1, floculation auxiliar dosage of 13.3 mg L-1 and inicial pH of 6.1. In the analised results, removal of 93.8% on turbity, 74.8% on COD, 72% of TSS and final pH of 5,5 were obtained. The final quality of the treated wastewater on field conditions was close to the demanded quality for water reuse in activities such as car washing, floor washing, garden irrigation and toilet flushing.