Hybrid process combining electrocoagulation and electrodialysis for chloride ions removal from runoff water loaded with road de-icing salts: Statistical optimization by response surface methodology

Abstract

The aim of this study is to investigate the effects of influential factors on separation of chloride ions from runoff water loaded with road de-icing salts (RRWs) using a hybrid process combining electrocoagulation (EC) and electrodialysis (ED). A concentration of 46.1 mg/L of aluminum ion was released in water while EC was performed at optimal condition (1 A and 4 min) by using aluminum anode. This step resulted in elimination of turbidity and suspended solid by 95 %, and the residual aluminum concentration of 0.01 mg/L was recorded in pretreated water. The supernatant water after settling tank and sand filtration was subjected to ED, where factorial and central composite design methodologies were applied to optimize road de-icing salts separation with minimum energy consumption. Overall, 32 experimental were designed and data points were validated using ANOVA software. The result showed flow rate and electrolysis time have a significant impact on separation factor giving a contribution of 40 % and 23 %, respectively. On the other hand, the percentage of limit current intensity and initial chloride concentration supplied 32 % and 50 % for the energy consumption, respectively. As for optimal point with highest separation and lowest energy consumption, it was found that treatment should be performed under 85 % of limit current intensity with a treatment time of 36 min at a flow rate of 10.9 mL/s. This condition led to achieve an average separation factor of 83 % and energy consumption value of 7.7 kWh/m3 for an initial chloride concentration of 1000 mg/L.