Electroneutralization with simultaneous highly-efficient desalination exemplified by acidic brackish wastewater

Abstract

Chemical neutralization has commonly been employed for the treatment of acidic brackish wastewater through the addition of external alkaline chemicals. However, this approach can potentially compromise the health of aquatic environment and resource sustainability. In this study, an innovative electroneutralization stack incorporating highly-efficient desalination was developed as a green solution for acidic hot-spring discharge treatment. Two distinct stack configurations, i.e., AECE and AEBP, were designed to evaluate the performance of simultaneous neutralization and desalination under different operating conditions. The results demonstrated the effectiveness of neutralizing acidic discharges while concurrently achieving a significant reduction in salinity. The brine solution produced during the process also presented the possibility of being harnessed as a valuable resource. Notably, the design parameters for the process were determined using a first-order kinetic model integrated with the Nernst-Planck equation. The maximum rate constants for sulfate and chloride removal were found to be 0.129 min−1 and 0.125 min−1 for AECE, and 0.039 min−1 and 0.042 min−1 for AEBP, respectively. The corresponding chloride-to-sulfate selectivities were observed to range from 0.42 to 1.00 for AECE, and from 0.15 to 1.21 for AEBP. Furthermore, the optimal operational conditions were identified through a comprehensive multi-objective assessment, resulting in process energy consumption ranging from 1.5 to 2.2 kWh/m3, while maintaining a clean water productivity of ∼30 L/m2/h. Significantly, in comparison to conventional chemical neutralization methods, the developed electroneutralization process demonstrated a substantial reduction in operating costs by 2 to 5-fold, along with a remarkable decrease in CO2 emissions (by approximately 4-fold) and the avoidance of sludge generation.