Environmental evaluation of bipolar membrane electrodialysis for NaOH production from wastewater: Conditioning NaOH as a CO2 absorbent

Abstract Post-combustion CO2 capture by reaction with a strong alkali such as NaOH appears a promising strategy to mitigate CO2 emission. This study proposes bipolar membrane electrodialysis (BMED) as a technology for the reclamation of NaOH from glyphosate neutralization liquor and its subsequent use as an absorbent for CO2 capture. The proposed method produces a NaOH solution for further reaction with CO2 while recovering the glyphosate from the wastewater. A NaOH solution with a concentration of ∼1.45 mol L-1 and purity of ∼96.5% was obtained. Accordingly, a current efficiency of 80.8%, 76.2%, 68.7% and 69.0% at current densities of 30, 40, 50 and 60 mA cm-2 was observed, respectively. In addition, the lowest energy utilization recorded as 2.15 kW h kg-1 was obtained by the BMED process at a low current density of 30 mA cm-2, resulting in a better performance in view of energy saving. A glyphosate recovery of ca. 98.2% was also achieved. The environmental impact of the BMED process was evaluated in terms of the amount of CO2 emissions produced and the total amount of CO2 captured taking into account of the CO2 production through BMED process. The results demonstrate that a promising CO2 capture (up to 530.65 g CO2 kg-1 NaOH) can be only achieved if the electricity resources originate from renewable sources such as wind, hydroelectric, as well as solar photovoltaics or nuclear energy. However, the utilization of non-renewable energy resources for NaOH production by BMED process imposes a risk on producing a significant emission of CO2, which makes the application of BMED unviable for a CO2 capture scenario.