Treatment of thermomechanical pulping (TMP) whitewater in thermophilic (55degrees C) anaerobic-aerobic moving bed biofilm reactors

Thermomechanical pulping whitewater was treated in an anaerobic followed by an aerobic Kaldnes moving bed biofilm reactor at 55 degrees C. The anaerob ic reactor was mixed by gas circulation and the aerobic reactor was mixed b y aeration. The anaerobic reactor was started with mesophilic inoculum, whi le the aerobic reactor was started without inoculation. The reactors were o perated on molasses water for one and a half years before the experiment wa s started. Total biomass concentrations (suspended and attached) were 3.3 g VSS/L in the anaerobic reactor and 1.6 g VSS/L in the aerobic reactor when starting feeding the reactors with TMP whitewater. After 7 months of opera tion the biomass concentrations had reached 5.5 and 6.5 g VSS/L in the anae robic and aerobic reactors, respectively. The CODsol removals in the anaero bic reactor were around 30 % at loading rates up to 7 kg CODsol/m(3)d, and over-all CODsol removals of about 60 % were achieved. The results show that the anaerobic-aerobic moving bed biofilm process could be feasible for the thermophilic treatment of thermomechanical pulping whitewater. (C) 1999 Pu blished by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.