Profiled characterization of aluminum during drinking water treatment.

摘要

Aluminum present in alum as well as naturally occurring aluminum in raw water is transferred into various forms (speciation) during drinking water treatment. Speciation of aluminum during drinking water treatment is essential to understand the behavior of aluminum and aluminum species removal during water treatment and also to identify the factors influencing residual aluminum in treated waters. Determination of trace levels of aluminum present in drinking water is becoming increasingly important since literature suggests that aluminum present in drinking water is more bio-available compared to aluminum from other sources.; This study examined (i) the profile and characterization of aluminum at the Buffalo Pound Water Treatment Plant (BPWTP); and (ii) the factors influencing residual aluminum at BPWTP.; Aluminum speciation study at the BPWTP indicated that (i) raw water total aluminum varied considerably between the aluminum speciation periods namely September–November 1997 and October–December 1998; (ii) alum addition increased raw water total aluminum levels; (iii) total, suspended, and particulate aluminum formed due to the use of alum was subsequently removed by clarifier and filtration (more than 90%) and (iv) particulate aluminum was the dominant species of total aluminum. Suspended form of aluminum was the predominant species of raw water total aluminum. Organic aluminum appeared to be the predominant species of soluble aluminum through (raw to treated) the BPWTP during September–November 1998. However, there was a shift in this condition during October–December 1998, i.e., inorganic aluminum dominated in soluble aluminum.; Analysis of eight-year plant data showed that (i) dissolved organic carbon (DOC) present in the raw water played a major role in controlling efficacy of alum coagulation at BPWTP; and (ii) when alum/DOC was less than 7, insufficient alum addition led to incomplete coagulation resulting in colloidal material mostly organic aluminum in particulate form in the treated water. Particulate aluminum increased in treated water. But this increase in particulate aluminum did not influence the turbidity of treated water.; Pilot scale speciation study showed that when the alum/DOC ratio was 5.3, most of the total aluminum in the filtered water was in the form of particulate aluminum. Such an increased particulate aluminum level did not influence the finished water turbidity. Soluble organic aluminum also did increase when the alum/DOC ratio was 5.3. Al speciation study conducted during jar testing showed that organically bound aluminum increased two times (compared to raw water levels) in the finished water when the alum/DOC = 1.37. If adequate mixing and settling times and optimum pH (pH of near minimum theoretical solubility of Al) are maintained during alum coagulation at a full-scale plant, it is possible to avoid both an increase in soluble and organically bound aluminum.