| Summary: | Eleven metal coagulants and one polyelectrolyte were assessed on their suitability for assisting a dissolved air flotation (DAF) system in treating poultry processing wastewater. The DAF unit was designed to maximize the microbubble production by varying the pressure, temperature, hydraulic retention time, and air flow parameters. The maximum microbubble flow from the designed system produced 30 mL of air per L of water. This value was considered low compared to other systems, but attempts to increase the microbubble volume in the current system beyond this value resulted in the coalescing of microbubbles due to turbulent conditions. Jar tests were used to identify the best coagulant available and were based on the removal efficiency of total suspended solids (TSS) and volatile suspended solids (VSS). These results were compared to increases in water clarity measured by optical density. Preliminary tests determined that a combination of 800 mg/L of ferric chloride and 900 mg/L of Floccin 1115 would provide the best treatment by removing at least 98% of the TSS and 97% of the VSS while providing a 97% increase in water clarity. Final flotation tests displayed 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 COD (chemical oxygen demand), and nearly 100% removal of FOGs (fats, oils, and greases). 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. The combination of these two coagulants was also determined impractical, costing nearly twice the current treatment costs of the processing plant. Due to limited alkalinity and excess phosphate in the wastewater, overdosing was a potential issue but could easily be addressed in future work.
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