Reuse of effluent from a wastepaper wash-deinking process

Prerequisite for success of any wastepaper recycling technology based on a wash-deinking process is the reuse of effluents. Characteristics of effluent from a laboratory scale newsprint wash-deinking plant, are presented in relation to the recycling ratio of the effluent after clarification by chemical treatment and sedimentation. The recycling ratios used varied from 0 to 95%. The deinking process operating under any recycling ratio was stabilized after a short time from the start and the parameters BOD5, COD, Total Solids (TS), conductivity, hardness and sludge yield reached steady state conditions values following first order kinetics. It was found that the increase of the recycling ratio from 0 to 95% increased the BOD of the effluent from 17 to 206 mg/L, the COD from 41 to 670 mg/L, the Total Solids from 620 to 1294 mg/L and the Conductivity from 185 to 1315 μS/cm, while it decreased the hardness (expressed as calcium carbonate) from 413 to 303 mg/L and the sludge yield from 28.2% to 23.8%. The total recycling (95%) of the treated deinking effluent was shown to increase the yield of the deinked pulp by 5% and to have no detrimental effects on the brightness of deinked pulp.