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UBC Theses and Dissertations

Aerobic membrane biological reactor treatment of recirculated mechanical newsprint whitewater at high temperatures Tardif, Olivier


The membrane biological reactor (MBR) is a robust and stable biological treatment process which integrates biological oxidation with ultrafiltration for treating wastewaters. A lab scale MBR consisting of a 10 L aerobic reactor, a cross-flow tubular ultrafiltration unit (molecular weight cut-off = 75 kDaltons) and a progressive cavity pump was operated at temperatures ranging from 40 to 55°C, hydraulic retention times (HRT) of 2.8, 1.1 or 0.7 days, a solids retention time of 25 days and a transmembrane pressure of 79 kPa to treat a synthetic closed-mill mechanical newsprint Whitewater. The mixed-liquor volatile suspended solids concentration in the MBR varied with the operating conditions, ranging from 2 to 9 g/L. In another study, the effectiveness of the ultrafiltration component of the MBR alone was investigated. The synthetic Whitewater was ultrafiltered to a concentration factor of 37 using the ultrafiltration unit at a transmembrane pressure of 69 kPa and a cross-flow velocity of 1.7 m/s (same velocity as the MBR). These two treatment processes were assessed for the removal efficiency of total solids (TS), total dissolved solids (TDS), total chemical oxygen demand (TCOD), dissolved chemical oxygen demand (DCOD), dissolved organic carbon (DOC), colour, cationic demand, resin acids (RA) and fatty acids (FA). The MBR achieved similar removal efficiencies for all operating temperatures and hydraulic retention times. It was particularly effective at removing FA (100% removal), RA (average removal > 98%), TCOD (82% average removal), DCOD (78% average removal) and DOC (76% average removal). The reduction of the Whitewater cationic demand was good (64% average removal). The average removal efficiencies for TS (36%) and TDS (27%) were fair, while the MBR was ineffective at removing colour (-5% average removal). Ultrafiltration alone was not nearly as effective at removing the target contaminants from the synthetic Whitewater. The high removal efficiencies of RFA achieved with the MBR may be due to the fact that RFA have a tendency to be adsorbed by the biosolids, which are retained by the ultrafiltration membrane. This and other inherent advantages of the MBR suggest much potential for this process in treating recirculated Whitewater internally in pulp and paper mills.

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