Flocculation-Flotation vs. MBR for High MLSS Secondary Clarification

Rendering plants produce high strength wastewater with high TSS, FOG, BOD and TKN. At one such plant it was decided to install a primary DAF followed by an anaerobic-anoxic-aerobic treatment system for TSS, FOG, TKN and BOD removal. Since wastewater is a high strength (TSS up to 10,000, FOG up to 3,000, TKN up to 350 and BOD up to 6,000 mg/l, respectively, bioreactors will produce high MLSS up to 11,000 mg/l. Pilot scale studies tested the feasibility of using either flocculation-flotation or membranes for MLSS removal. Only a small space was available inside the building, making it necessary to operate solid/liquid separation at an HRT of 5 GPM/ft2, and a solids loading of up to 15 lb/ft2/hr. Currently engineers consider that it is impossible to clarify aerobic MLSS at loading over 10 lb/ft2/hr unless membrane separations are use d. After the pilot studies where solid/liquid separations were achieved with the GEM flotation System, full scale System was installed in 2012 and is operating for the last three years. This manuscript describes the pilot study and full scale installation of the GEM flotation System at this plant.