Performance evaluation and operating strategies of dissolved-air flotation system treating poultry slaughterhouse wastewater

The wastewater treatment plant at a poultry slaughterhouse (Ceu Azul Alimentos Ltda) comprises a dissolved-air flotation (DAF) system and two upflow anaerobic sludge blanket (UASB) reactors. Diagnosis of the primary treatment unit pointed out the saturation pressure maintained below the recommended values and the non-recycling DAF-effluent as critical points. The DAF system operation, using 24 mg Al3+/l, polyaluminum chloride (PAC) associated with 1.5 mg/l anionic polymer, and the full-industrial effluent pressurization at 300 kPa, accomplished rather low average removal efficiencies of 43 +/- 15%a suspended solids (SS) and 49 +/- 8% oil and grease (O&G). Lab-scale DAF studies showed that by implementing pressurization of 40% recycled DAF-effluent at 450 kPa, using the same chemicals and dosages as in full-scale, would result in 74% SS and 99% O&G removals. By utilizing alternative organic coagulants under proper conditions, the same removal efficiencies would be observed, however, being limited by their costs. The improvement on the DAF system performance would not only avoid instability in the DAF process, but would also ensure the robustness and stability of the UASB process in response to an increase in the industrial production and, moreover, prevent sludge washout, biological activity inhibition and scum layer formation on the top of the reactors. (C) 2007 Elsevier B.V. All rights reserved.