A dissolved air flotator that treats wastewater from the manufacture of electrical equipment: Analysis and operational improvement

This study investigated the efficiency of three chemical coagulants in reducing the turbidity and solids concentration of wastewater produced in an electrical equipment industry, associating the use of coagulants with improving the performance of the dissolved air flotation (DAF) unit already in place at the industry's wastewater treatment plant (WWTP). The experimental protocol was based on preliminary Jar-Test trials to define the coagulant dosages that would allow the greatest reduction in turbidity, without correcting the initial pH of the wastewater. This was followed by on-site tests in which the coagulant dosages were added before treatment in the DAF. In the preliminary stage, the coagulants tested were aluminium sulphate (Al2(SO4)3), ferric chloride (FeCl3) and aluminium polychloride (PAC). The dosages that provided the highest turbidity removal efficiencies were 4, 35 and 40 mg L-1 for the PAC, FeCl3 and Al2(SO4)3 coagulants, respectively. In the on-site tests, only the PAC and aluminium sulphate coagulants were tested. The dosage of 40 mg L-1 of Al2(SO4)3 showed greater efficiency in removing ST and TSS. Turbidity removal was more effective using PAC at a dosage of 4 mg L-1. Due to the better performance in the on-site tests, a comparative cost analysis was carried out for the PAC and Al2(SO4)3 coagulants, with PAC being chosen as the most economical coagulant alternative for operating the existing DAF in the industrial WWTP.