Role of Aluminum Speciation in the Removal of Disinfection Byproduct Precursors by a Coagulation Process

Abstract

Humic acid (HA) was extracted and separated into different molecular weight (MW) fractions, then coagulated by aluminum chloride and polyaluminum chloride (PACl). The removal of disinfection byproduct (DBP) precursors and the aluminum speciation variation of the coagulants were investigated in detail. In particular, the role of aluminum speciation in the removal of DBP precursors was discussed. During the coagulation process, AlCl 3 hydrolyzed into dominating in situ Al 13 species at pH 5.5. The in situ Al 13 species exhibited better removal ability for haloacetic acid (HAA) precursors than PACl. At pH 7.5, in situ hydrolyzed Al 13 species of AlCl 3 decomposed into dimeric Al species. In this case, preformed Al 13 of PACl had a high removal ability of HAA precursors. Specially, the greatest reduction of HAA precursors with a low MW (<30 kDa) was through charge neutralization at pH 5.5, and that of HAA precursors in high MW (>30 kDa) fractions was through adsorption at pH 7.5. Different from HAA precursors, the in situ Al 13 species did not have a high removal ability of trihalomethane (THM) precursors. Therefore, PACl exhibited a better removal ability of THM precursors than AlCl 3 at different pH values. In the different MW fractions, the greatest reduction of THM precursors was through charge neutralization at pH 5.5.

Coagulation behaviors of aluminum salts towards fluoride: Significance of aluminum speciation and transformation

“…PACl contains a serial of Al species, of which Al 13 ([AlO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ ) is the dominant species [18,19]. Al 13 can also be in situ generated in AlCl 3 coagulation at pH 5.5, with the in situ Al 13 species exhibiting better removal of haloacetic acid precursors than preformed PACl does, as indicated from our previous study [20]. AlCl 3 is also observed to be more effective than PACl in removing turbidity and dissolved organic matter in eutrophic water, and this is not only attributed to the generation of in situ Al 13 species but to AlCl 3 functioning as a pH control agent [21].…”

“…PACl contains more Al species as compared to AlCl 3 [20], and more complicated mechanisms involve in the removal of fluoride. First, polymeric Al species exhibits higher positive charge than monomeric Al does [14] and shows stronger attraction towards fluoride.…”

Influence of Selected Coagulants of Indicator and Dioxin-Like PCB Removal from Drinking Water

“…Higher efficiency is explained by the fact that polyaluminium chloride solutions contain more polycationic and polymerized products of controlled prehydrolysis than aluminium sulphate. In the pH range of natural waters and with their alkalinity, hydrolysis of aluminium cations present in aluminium sulphate occurs almost immediately after their contact with treated water, therefore the precipitation of aluminium hydroxide occurs faster than the desired reaction of colloids and organic pollutant anions neutralization [2]. The obtained results suggest that in case of removal from water indicator and dioxin-like PCB using polyaluminium chlorides, their alkalinity is important, which should amount to approx.…”

“…10 and 3% of Al 2 O 3 . The application of polyaluminium chlorides as coagulants for organic pollutant removal, is recommended by many authors [1,2]. Higher efficiency is explained by the fact that polyaluminium chloride solutions contain more polycationic and polymerized products of controlled prehydrolysis than aluminium sulphate.…”

“…These substances can be divided into several categories, one of which is classifications into organic micropollutants (e.g. polycyclic aromatic hydrocarbons, polychlorinated biphenyls, surfactants, pesticides), and inorganic micropollutants, primarily heavy metals [1,2].…”