Treatment of Food Ingredients Manufacturing Effluent by Physicochemical–Biological Two-Stage Wastewater Treatment System

A physicochemical (PC) and biological two-stage wastewater treatment system has successfully treated food ingredients manufacturing effluent in the USA for decades. The first-stage PC treatment is accomplished by a circular high-rate Supracell dissolved air flotation (DAF), which has a diameter of 8 feet (2,400 mm), and is made of 304-stainless steel. The second-stage treatment is accomplished by a conventional aerobic biological package plant. The DAF is rated at 148 GPM (34 m 3 /h) design capacity and is installed in a small building on top of a sludge storage tank due to DAF’s short DT (3–5 minutes), compact overall size, and shallow depth of 23.5 in (600 mm). So the DAF footprint is almost zero. In a real full scale treatment, the DAF influent came from an equalization tank, containing milk-based powdered total suspended solids (TSS) residues 475–640 mg/L, coconut oil FOG 100–250 mg/L, 5-day BOD 1,700–2,500 mg/L, etc. With DAF’s first-stage pretreatment (operated at 148 GPM, 27% recycle pressurization mode, with alum or polymer coagulation), pollutant reductions were: TSS 53%–77%; FOG 60%–100% and 5-day BOD 39%–66%. DAF effluent went to the second-stage aerobic biological package plant for additional treatment. The second-stage effluent quality was excellent: TSS 20 mg/L and 5-day BOD20 mg/L, meeting the sewer discharge requirements. The second-stage effluent went to the sewerage system of publicly owned treatment works (POTW) for final polishing. The floated sludge solids were analyzed to be 5.4% (using alum), or 9% (using polymer) which met the requirement of sludge thickening. For technology transfer from the USA to developing countries, this chapter also introduces the DAF process description, technology status, applications, advantages, disadvantages, reliability, chemical requirements, residuals, design criteria, and predicted performance in general. Any manufacturer’s DAF in any shape should also be feasible for food waste treatment. Specific design and operational procedures of the Supracell DAF are presented. PC and biological technologies available for the food waste treatment are reviewed and reported. Further research for possible recovery and reuse of harvested food solids and proteins as the animal foods are suggested.