Flotation technique with coagulant and polymer application applied to the post-treatment of effluents from anaerobic reactor treating sewage

This paper presents the results of a study performed with a lab-scale batch DAF unit fed with previously coagulated (with FeCl3 and/or cationic polyme r) effluent from a pilot-scale expanded bed anaerobic reactor treating dome stic sewage. The association between ferric chloride and polymers was studi ed, aimed at sludge reduction. Ferric chloride dosages ranging from 15 to 6 5 mg.l(-1) and polymer dosages from 0.25 to 7.0 mg.l(-1) were investigated. Flocculation conditions were kept constant: 20 min of time (Tf) and 80 s(- 1) of mean velocity gradient (Gf). Air requirement was kept to 19.0 g of ai r.m(-3) Wastewater, using 20% recycle ratio and saturation pressure at 450 kPa. When the anaerobic reactor was operating at steady state conditions, i t was possible to reduce the FeCl3 dosage from 65 to 30 mg.l(-1) after appl ying 0.4 mg.l(-1) of non-ionic polymer, before the DAF process. For these d osages, 79% COD removal (residual of 23 mg.l(-1)), 86% total phosphate remo val (residual of 0.9 mg.l(-1)) and 98% turbidity removal (residual of 2.6 N TU) were observed. Furthermore, the use of adequate polymer together with 3 0 mgFeCl(3).l(-1) leads to the production of high rising rate flocs.