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 mg/L 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 mg/L) 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.
Highlights
Water pollution is increasing at an alarming pace due to industrialization as its prime reason.A quarter of children born in developing countries die before the age of five due to pollution-related diseases
As chemically-treated water is further treated by activated carbon, similar results were reported by Shawwa, Smith and Sego in [41] by using activated petroleum coke in the adsorption process
The most important result is that the combination of sedimentation, coagulation and adsorption resulted in water quality where the color was no longer visible (i.e.,
Summary
Water pollution is increasing at an alarming pace due to industrialization as its prime reason. A quarter of children born in developing countries die before the age of five due to pollution-related diseases. About 30,000 people die from water-related diseases each day [1]. Rapid increase in population growth demands the establishment of new industries demanding the use of freshwater. This phenomenon has been associated with problems such as the overexploitation of natural resources, water pollution and a shortage of fresh water. One of the main industries utilizing huge amounts of water, natural resources and the consequent generation of considerable amounts of polluted water from various unit processes, is the pulp and paper industry [2]
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