Hotspot analysis and improvement schemes for capacitive deionization (CDI) using life cycle assessment

The ultimate goals for the advancement of capacitive deionization (CDI) are high performance and low environmental impact. The aim of this study was to obtain comprehensive knowledge on the improvement of CDIs from environmental aspects. Life cycle assessment (LCA) was utilized to evaluate the environmental friendliness of the CDIs. Five lab-scale design schemes, including CDI, membrane capacitive deionization (MCDI) and scale-up MCDI stacks, were investigated in this study. A technical performance indicator of productivity (L/h/m(2)) was also employed to elucidate the efficiency of water production of the CDIs. The LCA results of the CDI stacks indicated that electricity consumption had a relatively lower overall impact (as low as 9.7%) compared to material or chemical usages (ranges from 52% to 89.8%). This result suggested that changing key materials or chemicals in improved stacks could decrease their associated impacts. Our results further pointed out the importance of the management of chemical use of N-methyl-2-pyrrolidone (NMP), the substitute for N, N-Dimethylacetamide (DMAC) in the basic CDI stack. The scale-up MCDI stacks exhibited the highest productivity of 3.62 L/h/m(2), implying that CDI has the potential to be an efficient water technology. LCA was demonstrated to support future improvement decisions for CDI with favorable environmental performance.