In-mill removal of TMP whitewater contaminants by biological treatment in an aerobic biokidney used in conjunction with microfiltration and laccase treatment

SUMMARY: The suitability of an aerobic in-mill biokidney for purification of TMP newsprint white water was investigated. The effects of microfiltration and laccase treatment on the quality of biologically treated white water were also studied. The biokidney showed high (71-92%) removal efficiency for COD, BOD, carbohydrates and lignans. The removal efficiency was moderate (50-66%) for TOC and TS, and low (25-35%) for lipophilic extractives and lignin-like material while the amount of suspended solids (SS) increased by 67% as some of the biomass from the biokidney went into the white water. Microfiltration of biologically treated white water removed a minor part of the remaining contaminants of TMP origin and the bulk of the biomass from the biokidney. The treatment of biologically treated white water with laccase before microfiltration gave a large improvement in removal efficiency for all contaminants originating from the TMP but the material present in the laccase solution caused an increase in COD, BOD and TS. The biomass-based SS from the biokidney and the dissolved material in the laccase solution had a more detrimental effect on the mechanical and optical properties of handsheets prepared with untreated and treated white water than the wood-based contaminants.