Evaluating coagulation pretreatment on poultry processing wastewater for dissolved air flotation

Eleven metal coagulants and one polyelectrolyte were assessed for their suitability in assisting a dissolved air flotation (DAF) system aimed at treating poultry processing wastewater. Preliminary jar tests determined that a combination of 800 mg/L of FeCl(3) (ferric chloride) and 900 mg/L of Floccin 1115 would provide the best treatment by removing at least 98% of the total suspended solids (TSS) and 97% of the volatile suspended solids (VSS), while providing a 97% increase in water clarity. Final flotation tests suggested that the flocculated particles could be carried to the surface with 40% recycle ratio of the DAF. The resulting supernatant indicated 94.7% increase in clarity (± 1.4%), 97.3% reduction in TSS (± 0.5%), 96.6% reduction in VSS (±1.1%), 91% reduction in chemical oxygen demand (COD), and nearly 100% removal of fats, oils, and greases (FOGs). Despite the high removal efficiencies, flotation was found not to be critically necessary for treatment because the high concentration of coagulants caused settling of the flocs to occur just as rapidly. Potential coagulant overdosing is suspected at the higher end of the tested coagulant concentrations due to limited alkalinity in the wastewater. However, lack of residual metal (coagulant) ions in water may be linked to reactions leading to phosphate precipitation. The exact effect of the competing phosphate reaction on treatment efficiency is not clearly evident from this present study.