Electrocoagulation using zinc electrodes

The aim of this research was to test the use of a new material for the construction of electrodes, zinc, as an alternative in the treatment of wastewater of a small dairy industry using electrocoagulation in real conditions. We performed the electrocoagulation tests in a batch, in a 150 mm diameter glass reactor with four zinc plates (100 mm × 130 mm × 15 mm). The connection was in parallel and monopolar, and constant direct current was applied. We collected samples of wastewater from a dairy industry for the application of treatment by electrocoagulation. The operational variables were electrolysis time, pH, and electrical current density. A central composite design (CCD) with three factors, electrical current density (I), electrolysis time (t), and initial pH with the two-level composite factorial using α = 1.6818 was composed of eight cubic points, six central points, and six axial points. The levels of operating parameters I, t, and initial pH used were 50.0 and 116.7 mA·m−2; 26.2 and 73.8 min; 4.2 and 7.8, respectively. We tested the treatment for final chemical oxygen demand (COD), total solids and their fractions, and turbidity. The conditions for treating dairy wastewater were electric current density 82.6 A·m−2, electrolysis time around 10 min, and initial sample pH of approximately 3.0. This operating condition allowed a difference with reduction value of 50.4% in COD, 99.8% in turbidity, 24.2% in total fixed solids (TFS), 9.6% in volatile dissolved solids, 73.4% in total suspended solids, and 79.9% in volatile suspended solids. The negative effects of the zinc electrode were that the TFS in 17.7%, fixed dissolved solids in 64.6%.