Capturing CO2 with NaOH solution from reject brine via an integrated technology based on bipolar membrane electrodialysis and hollow fiber membrane contactor

Discharges of wastewater and waste gas are two major environmental problems which have drawn great attention. To well use the reject brine and realize continuous absorption of CO2, in this work, a green process for the capture of CO2 by NaOH solution produced from reject brine based on bipolar membrane electrodialysis (BMED) has been proposed. By using the BMED, the maximum concentrations of generated acid and base attained 1.88 mol/L and 2.01 mol/L, respectively, with the current efficiency of 64.71 % and energy consumption of 3.97 kWh/kg NaOH. The acid could be recycled for pH adjustment and the alkali could be directly used for CO2 absorption with the help of hollow fiber membrane contactor (HFMC). The optimization of the gas flow rate, liquid flow rate, liquid temperature, and NaOH concentration has been investigated in CO2 absorption process with a maximum CO2 removal rate of 90.85 %. As for absorption of CO2, the absorbent containing NaOH and Na2CO3 could be directly used in the pretreatment process for reject brine softening. It is noted that the process could be performed without adding extra chemicals and the self-cycle could be achieved. In addition, economic and environmental evaluations verify the feasibility of this process, indicating the prospect of industrial application.