Design and Parameter Optimization of a Full-Scale Wastewater Reclamation Plant Including Pretreatment, Electrodialysis Reversal, and Ion Exchange in Steel Manufacturing Processes

The daily demand of demineralized water (DMW) in electrolytic galvanizing line (EGL) in China Steel Corporation (CSC) reached approximately 1,600 m3 as the production line was fully in operation. However, the wastewater produced from the EGL was discharged into the cold-rolling mill wastewater treatment plant even though it had potential for reclamation. This study provides details of design and parameter optimization of a full-scale wastewater reclamation plant for the EGL. Three wastewater streams including hot water rinse, pickling rinse wastewater, and condensate water from the EGL were selected for reclamation. The full-scale wastewater reclamation plant was constructed to equip with coagulation, flocculation, sedimentation, and filtration for pretreatment, and electrodialysis reversal (EDR) and ion exchange (IX) processes for desalination. The pretreatment process can reduce the total iron concentrations in the wastewater from 40-70 ppm to <0.1 ppm to protect EDR membranes from fouling. The EDR systems can reduce the conductivity of the pretreated wastewater from ∼800 to 125 μS/cm (i.e., ∼85% desalination rate). The plant is capable of supplying 540 m³/day of reclaimed pure water to the EGL from selected wastewater streams with the total flow rate of ∼770 m3/day (i.e., ∼70% recovery rate). The cost of the reclaimed water was cheaper than the DMW produced by regular processes in CSC. The annual saving of the reclamation system, including pure water cost and wastewater treatment cost, was more than 11.6 million New Taiwan dollars (NT).