Evaluation of the performance of titanium and zirconium salts as coagulants in industrial wastewater treatment: pollutant removal, sludge production, and sludge characteristics

Abstract In this study, titanium tetrachloride (TiCl 4 ), zirconium tetrachloride (ZrCl 4 ), and zirconium oxychloride (ZrOCl 2 ·8H 2 O) were evaluated using jar test experiments as coagulants and compared with traditional aluminum sulfate (Al 2 (SO 4 ) 3 ·18H 2 O) and ferric chloride (FeCl 3 ) for industrial wastewater treatment. The effects of the initial pH of 4–10 and initial coagulant doses of 10–100 mg/L on chemical oxygen demand (COD) and total suspended solids (TSS) removal were investigated. The performances of the five coagulants were also assessed in terms of the settled sludge volume, the sludge volume index (SVI), and removal efficiencies of metals, color, and total phosphorus (TP) under optimum conditions. In addition, the contents of the residual sludge produced for all five tested coagulants under optimum conditions were determined. The results showed that the maximum removal efficiency of COD (69.33%) was achieved using 100 mg/L TiCl 4 at pH 8. The maximum removal efficiency of TSS (98.32%) was achieved using 50 mg/L Al 2 (SO 4 ) 3 ·18H 2 O at both pH 8 and 10. The settled sludge volume and SVI generated by TiCl 4 were lower than that for the other four tested coagulants. ZrCl 4 , ZrOCl 2 ·8H 2 O, FeCl 3 , and Al 2 (SO 4 ) 3 ·18H 2 O resulted in 128.13, 92.39, 72.26, and 69.66 mL/g SVI, while that using TiCl 4 was 48.84 mL/g. Ti- and Zr-based coagulants achieved better removal efficiencies of TP, Zn, and Cu than FeCl 3 and Al(SO 4 ) 3 ·18H 2 O. The residual sludge from using Ti and Zr coagulants had a very high TP content. The results indicated that Ti- and Zr-based coagulants could be used as alternatives to traditional coagulants for industrial wastewater treatment.