Clean Water Technology, Inc.

Flocculation - Flotation pretreatment improves operation of MBR installed to treat snack food manufacturing wastewater

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Abstract
Large food manufacturing company has facilities to produce their well known brand name dairy based products in rural Indiana. As is commonly case with dairy wastewater, significant amount of proteins, sugars, oil and some suspended solids are present. Company installed membrane bioreactor (MBR) System to treat such wastewater for possible reuse.

The MBR performed poorly due to membrane fouling. Manufacturer suggested that in addition to screen other primary pretreatment is needed to reduce FOG and organic TSS as low as possible prior to MBR treatment. Classical DAF and advanced hybrid centrifugal – dissolved air flotation (GEM) were pilot tested. Both systems performed well, but GEM removed FOG and TSS to lower amount and produced drier sludge. The full scale GEM System has been installed in June 2010. Dual high molecular weight flocculants and GEM flotation remove TSS below 50 mg/l, FOG below 2 mg/l and produce sludge with 20% solids. Data are currently collected to evaluate how such pretreatment improves operation of the MBR.

Keywords: snack food wastewater, MBR fouling, pretreatment, DAF vs. GEM Flotation

Introduction
At their rural Indiana facility, large food manufacturing company currently uses a Membrane Bio-Reactor (MBR) [GE ZENON] to treat their wastewater stream. The water from the plant is collected in an approximately 200,000 gallon outdoor Equalization Tank (EQ Tank). The water is collected from the manufacturing and cleaning of machinery used for the production of Coffee Mate, milk, chocolate milk as well as other similar brand name products. The influent water was shown to be very turbid and cloudy, containing high levels of Total Suspended Solids (TSS) and Fats, Oils and Grease (FOG). From the EQ tank, the water is pumped through a basket screen and continues to a 500 GPM aerobic MBR for further treatment – removal of BOD.

GE Zenon ZeeWeed aerobic MBR combines suspended growth bioreactor with reinforced hollow fibers ultrafiltration. MBR combines aeration and solid liquid separation into a simple, small footprint, efficient system. Poor settling that often happens in conventional aerobic activated sludge bioreactors used to treat high strength industrial wastewater is thus eliminated. Membranes can also handle more biosolids than clarifiers. ZeeWeed process can typically be operated at mixed liquor suspended solids (MLSS) concentrations as high as 8,000 to 12,000 mg/l. Elevated biomass concentration allows for treatment of high strength industrial wastewater.

ZeeWeed ultrafiltration membranes use permeate pump to apply vacuum and draw treated water through the hollow fiber reinforced UF modules. Intermittent air flow is introduced to the bottom of the membrane modules, producing turbulence that scours the external surface of the hollow fibers. This scouring action transfers rejected solids away from the membrane surface, significantly reducing membrane fouling and flow rate loss. Such design allows operation at significantly higher TSS than standard pressure driven UF membrane modules.

A primary treatment system for reduction of TSS and FOG was not installed prior to the MBR system. The MBR is used to reduce BOD and TSS and separate effluent water from biosolids through a external membrane tank system. The waste biosolids (mixed liquor) solids from MBR are sent to a centrifuge for sludge thickening which is achieved through the addition of polymer.

The amount of FOG in the plant effluent has caused continuous membrane fouling, with significant decrease in flow rate and increase in cleaning cost with time. Plant engineers decided to compare performance of classical dissolved air flotation (DAF) and advanced hybrid centrifugal – dissolved air flotation system (the GEM) as primary treatment choices to remove as much FOG and TSS as possible, while producing as dry sludge as feasible.

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