Treatment of pulp and paper industrial effluent using physicochemical process for recycling

Abstract

Physicochemical treatment, consisting of a combination of primary settling, coagulation- flocculation-aided clarification (alum, lime and magnesium sulfate as coagulants) and activated carbon adsorption, was employed for the treatment of pulp and paper mill wastewater. Treatability studies were undertaken to assess the feasibility of recycling the effluents from a paper mill. The results of laboratory scale investigation showed that the hydraulic retention time (HRT) of four hours for plain settling was effective to reduce 30% of the pollution load from pulp and board mill wastewater (PBMWW). The chemical secondary treatment reduced turbidity (89%), Chemical Oxygen Demand (84%), total suspended solids (90%) and color (89%) at the mass loading of 3400 mgl-1 of magnesium sulfate (MgSO4), when primary-treated effluent was subsequently treated by the coagulation-flocculation process. The combination of primary settling and lime coagulation (optimum dosage of 1400 mgl-1) resulted in a turbidity removal of 94%, a COD (Chemical Oxygen Demand) reduction of 86%, a Total Suspended Solids (TSS) removal of 93% and color removal of 91.6% at an initial pH of 11. The combination of this primary settling and coagulation-flocculation treatment trial indicated that the pollutant reduction efficiency of alum was better than the other two coagulants (MgSO4, lime), because the plain settling and coagulation-flocculation process with alum (optimum dosage of 1200 mg/L) resulted in a turbidity removal of 98%, COD reduction of 93%, TSS removal of 98% and color removal of 96% at the pH 6.0 with the sludge volume index of 156 mg/L. This chemically-treated water required further treatment with activated carbon in a batch reactor for up to four hours to meet the paper mill water quality standards. Pollutant reductions at the rate of 99.5%, 99.1%, 99.4% and 99.5% were obtained for turbidity, COD, TSS and color, respectively, with the combination of the sedimentation, coagulation-flocculation process and activated carbon adsorption meeting the production process quality standards. The study revealed that a hybrid end-of-pipe physicochemical treatment was effective in reducing the pollutant load of paper mills effluent and meeting the discharging standards.