Resource Recovery and Pollution Prevention at Source

摘要

Coated paper and board manufacturers use large quantities of coating colour. Despite good housekeeping and efficient process control, up to 15% of the coating colour produced at some commercial facilities has been reported to go down the drain, contributing BOD, suspended solids and possibly colour to the mill effluent. A large fraction of the suspended solids originating from the coating colour is non biodegradable, and it has to be either managed as waste sludge or as TSS in the treated effluent. BOD associated with waste coating, on the other hand, costs additional aeration demand. It is suggested that coating recovery with or without using processing equipment is techno-economically feasible. There are two options to affect recovery. One option is to use re-concentration equipment (ultrafiltration) to recover coating from dilute waste streams. The other option is to recover waste coating at source, by selectively capturing highly concentrated waste streams or portions of them. This approach, evaluated at a Quebec mill, does not require processing equipment, and involves only minor expenditures. Coating recovered without using re-concentration equipment was blended at up to 5% with the original coating, and the combined coating was tested for viscosity, water drainage, and contamination by large particles or clumps. No significant differences were observed in the combined and original coating samples tested. It is believed that large mills can save millions of dollars a year by recovering waste coating colour while offloading the effluent treatment plant.