Tailoring Properties of Polyaluminum Coagulants

24 Aluminum coagulants are widely used in water treatment plants to remove turbidity and 25 dissolved substances. However, because high aluminum concentrations in treated water are 26 associated with increased turbidity and because aluminum exerts undeniable human health 27 effects, its concentration should be controlled in water treatment plants, especially in plants 28 that use aluminum coagulants. In this study, the effect of polyaluminum chloride (PACl) 29 coagulant characteristics on dissolved residual aluminum concentrations after coagulation and 30 filtration was investigated. The dissolved residual aluminum concentrations at a given 31 coagulation pH differed among the PACls tested. Very-high-basicity PACl yielded low 32 dissolved residual aluminum concentrations and higher natural organic matter (NOM) removal. 33 The low residual aluminum concentrations were related to the low content of monomeric 34 aluminum (Ala) in the PACl. Polymeric (Alb) /colloidal (Alc) ratio in PACl did not greatly 35 influence residual aluminum concentration. The presence of sulfate in PACl contributed to 36 lower residual aluminum concentration only when coagulation was performed at around pH 6.5 37 or lower. At a wide pH range (6.5–8.5), residual aluminum concentrations <0.02 mg/L were 38 attained by tailoring PACl properties (Ala percentage ≤0.5%, basicity ≥85%). The dissolved 39 residual aluminum concentrations did not increase with increasing the dosage of high-basicity 40 PACl, but did increase with increasing the dosage of normal-basicity PACl. We inferred that 41 increasing the basicity of PACl afforded lower dissolved residual aluminum concentrations 42 partly because the high-basicity PACls could have a small percentage of Ala, which tends to 43 form soluble aluminum–NOM complexes with molecular weights of 100 kDa–0.45 μm. 44 45