Impacts of System Operation and Organic Loading Rate on Membrane Fouling and Sludge Production in Pilot-Scale Flat-Plate MBR Treatment of Potato Processing Wastewater

A two-year research study was undertaken to demonstrate and optimize the performance of a two and three-stage high-rate membrane bioreactor (MBR) system treating primary clarified potato processing wastewater. Organic loading rates (OLRs) ranged from 1.4 to 6.7 kg COD/m3·d (0.8 to 3.9 kg BOD/m3·d), F:Ms from 0.15 to 0.66 kg COD/kg MLSS·d (0.1 to 0.46 kg BOD/kg MLVSS·d), and hydraulic retention times (HRTs) from 0.5 to 2.3 d. Even at high loading rates and low HRTs, the MBR process produced excellent effluent quality, with effluent concentrations less-than-detectable on a consistent basis for BOD, TSS, and NH3-N (i.e., removals were virtually 100 percent for these parameters). Nitrogen removal averaged 96 percent in three-stage operation at an HRT of only 17.5 h for an influent TKN concentration of 230 mg/l, without the need for a specific unaerated anoxic stage.Increased operating temperature (from mechanical friction at increased aeration intensity and exothermic aerobic biological activity) helped enhance performance and lower sludge production at higher loading rates. Venturi aeration was used in the initial pre-aeration stage(s) to provide adequate oxygen transfer. This type of aeration combined with the high volumetric power densities applied in the initial stage of the process provided enhanced shear of the biological floc which also appeared to aid in decreasing sludge production.Membrane fouling was not significantly impacted by the enhanced shear and relatively high loading rates. This was presumably due in part to the staging of the process (i.e., more plug flow), and lower volumetric power densities in the membrane tank (which enhanced biological reflocculation).