Water Qualities and Products Generated in Dechlorination Process Using Ultra-high Lime with Aluminum Method

Abstract

Feasibility of dechlorination using ultra-high lime with aluminum process (UHLA) has been demonstrated by previous studies. However, the negative influences of UHLA on water qualities (pH, conductivity, and residual calcium concentration) after dechlorination and the products generated in dechlorination process have not been thoroughly analyzed. In this study, changes of water qualities at various dechlorination conditions were investigated, and favorable conditions for Friedel’s salt formation were explored by X-ray diffraction analysis. The pH and conductivity after dechlorination increased with the improvement of chloride removal effect. The calcium ion concentration in effluent also fluctuated with different dosages of CaO. At the maximum chloride removal efficiency of 71.4%, the pH, conductivity, and calcium ion concentration in effluent were 12.8, 10.9 ms/cm, and 22.7 mg/L, respectively. X-ray diffraction analysis for precipitants indicated that Friedel’s salt with the highest purity was also generated at the optimal dechlorination efficiency. The high dechlorination efficiency of 80.5% was achieved with the development of a stepwise addition strategy. Chemical costs for treating one ton of wastewater containing 500 mg/L chloride were $3.96.