Evaluating the impact of recycled fiber content on effluent recycling in newsprint manufacture

This paper investigates the effect of using recycled fiber (RCF) in newsprint production on the effluent quality and its treatability using membrane operations for internal and external recycling and reuse. Increased chemical usage in RCF for deinking had significant impact on the silica and sodium content of the effluent which in turn limits the membrane's operation. Increasing the RCF content from 0% to 50% is estimated to increase the silica content from 4 to 119 mg L−1 and sodium content from 135 to 500 mg L−1. A process model was developed to calculate the impact of these excess chemicals on the greenhouse gas (GHG) emission and brine disposal for an integrated membrane plant design producing 4 ML day−1 of recycled water. As the ratio of RCF increased from 0% to 50% in the mill process, the operating pressure increased for nanofiltration (NF) and reverse osmosis (RO). Additionally, organics presence in the feed increased the NF operating pressure above the simulated value and reduced the silica removal efficiency by 15%. Incorporation of lime coagulation pretreatment was found to be essential to operate RO at high recoveries with relatively GHG emissions. Without pretreatment, as RCF content increased from 0% to 50%, RO recovery decreased from 80% to 22% and the expended GHG increased from 0.9 to 3.5 kgCO2 m−3. Although the excess sodium concentration limits the brine disposal for irrigation purposes, a partial blending of the treated wastewater with other process streams resulted in the reduction of sodium absorption ratio by 20%.