Ozonation followed by coagulation/flocculation and flotation as post-treatment of the effluent from an anaerobic baffled reactor treating domestic sewage

This paper reports on the use of ozonation and dissolved air flotation as a post-treatment of the effluent from an anaerobic baffled reactor treating domestic sewage. After preliminary essays, the present experiment was performed fixing coagulant doses and, to all of them, some ozone doses were investigated. Later, the pH value and the ozone dose which provided the best removal efficiencies of all the parameters involved were tested, changing the coagulant dose and varying, for each of them, two ozone doses: the zero one and the optimum. Considering the best conditions of coagulation/flotation (ferric chloride dose of 65 mg.L⁻¹: and pH around 5.5), the ozone dose application of 6 mg.L⁻¹ led to a significant level in the removal efficiency of COD (80.4%), BOD (79.0%), total phosphate (93.4%), apparent color (91.9%) and turbidity (97.0%), demonstrating that the system seems to be efficient and capable of promoting a high degree of sewage post-treatment, reducing the coagulant dose until 30%, with a consequent reduction in the sludge generation.