Treatment of efluents of soybean oil refnery by dissolved air flotation

The aim of this work was to evaluate the performance of coagulants combined with three polyelectrolytes (anionic, cationic and non ionic) using dissolved air flotation (DAF) in the treatment of effluents of the soybean oil refinery. This study was conducted at laboratory-scale to find, through the coagulation diagram, the best limits of pH and coagulant concentration. With those limits, the dosage of flocculants was varied to achieve the optimum dosage. For that, some parameters were fixed: time and rapid mix gradient (1 min and 150 s(-1)), time and slow mix gradient (10 min and 40 s(-1) -5 min and 20 s(-1)), pressure in saturation chamber (450 kPa) and ascension velocity (1.67 cm min(-1)) for two flotation tests. After the flotation tests, samples of treated effluent were collected for comparison with crude effluent. The removal percentage obtained of chemical oxygen demand (COD) was 93.7 and 95.1% and of oil and greases (O&G) was 94.2 and 99.8% for the test 1 and 2, respectively. Despite excellent efficiencies of removal, the treated effluent did not present characteristics for reuse in cooling towers, because the COD was above 75 mg L-1O2.