Feasibility of an Energy Saving Membrane Process for the Treatment of Alkaline Peroxide Mechanical Pulping Plants´ Effluent

According to our previous study, it is believed that ultrafiltration with polyethersulfone (PES) flat-sheet membrane is suitable for the concentration process of alkaline peroxide mechanical pulping (APMP) plant´s effluent. So we scaled up the concentrating experiment to a pilot-scale. Specifically, the cross flow velocity and volume reduction factor were optimized again for a higher flux and a lower system energy consumption. A mathematical model was established to obtain the optimal parameters. An estimation of energy and water saving effect were also developed. The optimal ultrafiltration conditions obtained were: molecular weight cut-off at 10,000 Dalton, trans-membrane pressure at 3 bar, feed temperature at 50°C, cross-flow velocity at 2 m/s, and volume reduction factor at 0.9. The average permeate flux under these conditions was 43.21 1/m²h. The total solids content was increased from 25.47 g/l in the feed to 128.36g/l in the concentrate. The permeate had low total solids content of 1103 g/l, Chemical Oxygen Demand of 9180 mg/l, and Biochemical Oxygen Demand of 5870 mg/l. Such qualities would allow the permeate to be reused in the APMP process after lightly biochemical treatment. With this new concentration process, about 62017 kWh energy can be saved and 22.5 m³ effluent discharge can be reduced for each ton of pulp produced.