Alternatives for treating recirculated newsprint whitewater at high temperatures

Four treatment alternatives were investigated for the removal of dissolved and colloidal substances at high temperatures from a simulated closed-system mechanical newsprint whitewater: (i) sequenching batch reactor treatment (SBR), (ii) ultrafiltration (UF), (iii) biological treatment followed by UF (SBR⊕UF) and (iv) membrane bioreactor (MBR) treatment. Contaminants investigated included resin and fatty acids (RFA), dissolved organic carbon (DOC), dissolved chemical oxygen demand (DCOD) and total dissolved solids (TDS). Ultrafiltration alone yielded excellent FA removals at temperatures ranging from 20 to 60°C, but only fair removals (9 to 42%) of TDS, dissolved COD, DOC and RA. Removal efficiencies were generally enhanced when using a membrane of a smaller pore size but did not vary with temperature. The SBR was effective at removing contaminants at temperatures ranging from 20 to 40°C (up to 100% of the RA, 96% of the FA, 76% of the DCOD and 34% of the TDS were removed). However, the performance of the SBR was poor at 45 and 50°C. Batch ultrafiltration of SBR pre-treated whitewater enhanced the removal of target contaminants, compared to SBR treatment alone. The MBR was judged to be the preferable treatment process at high temperatures. It yielded consistent removal efficiencies at temperatures ranging from 40 to 55°C, removing up to 100% of RA and FA, 84% of DCOD and 37% of TDS.