Dissolved air flotation for treating wastewater of the nuclear industry: preliminary results

Preliminary testing of dissolved air flotation (DAF) for wastewater treatment is presented. A combined coagulation-flocculation/DAF column system is used to remove oil and Co-60 from nuclear industry wastewater. In this work, operational conditions and coagulant/flocculant concentrations are optimized by varying pH. Determinations of air-solids ratio (G/S), retention time (theta), pressure (P), volume of depressurized air-water mixture (V), turbidity and Co-60 concentrations are reported. The effect of the treatment on the efficiency of separation of oily residues is also discussed. The results establish that the coagulant/flocculant system, formed by a modified polyamine (25 mgL(-1)) and a slightly cationic polyacrylamide (1.5 mgL(-1)), under specific operational conditions (pH = 7, mixing intensity Im(1) = 300 s(-1) and Im(2) = 30 s(-1)), allowed the destabilization of colloidal matter, resulting in resistant flocs. It was concluded that by using G/S = 0.3, theta = 15 min, P = 620 kPa and V = 0.0012 m(3), the greatest percentage removals of oil, turbidity, total cobalt and Co-60 were obtained. These preliminary results then show that dissolved air flotation represents a good alternative for treatment of nuclear industry wastewater contaminated with radionuclides.