Effect of Al(III) speciation on coagulation of highly turbid water

Abstract

In Taiwan, the turbidity of raw water for fresh water treatments can sometimes reach as high as 40 000 NTU due to intensive rainfall, especially in typhoon seasons. In response, water works often apply large quantities of coagulants such as polyaluminium chloride (PACl). In this study, simulated and natural highly turbid water was coagulated with two PACls, a commercial product (PACl-1) and a laboratory product (PACl-E). The Al species distributions of PACl-1 and PACl-E under various pH conditions were determined, and the corresponding coagulation efficiency was evaluated. The PACl-E has a wider range of operational pH, while the efficiency of PACl-1 peaks at around neutral pH. For simulated water up to 5000 NTU, the PACl-E was superior to PACl-1 at low dosage and in the pH range studied. Similar results were discovered with natural water, except that when the turbidity was extremely high, the coagulation efficiency of PACl-E decreased significantly due to the presence of large amounts of organic matter. The coagulation of PACl-E was closely related to the content of polycationic aluminium (Al 13 ) while that of PACl-1 was dictated by the amount of Al c . The sludge from PACl-E coagulation had better dewaterability when the optimum dosage was applied. The experimental results suggest that for natural water up to 5000 NTU, PACl containing high Al 13 species is recommended for coagulation. In cases when the water contains high organic matter, efficient coagulation depends upon enmeshment by amorphous aluminium hydroxide.

Evaluation of enhanced coagulation coupled with magnetic ion exchange (MIEX) in natural organic matter and sulfamethoxazole removals: The role of Al-based coagulant characteristic

“…Under the same dosage, zeta potential was in the sequence of Al 13 > PACl > AS, which had a good correlation with the content of Al b (as shown in Table 1). This is consistent with the published literature which indicates that the active Al 13 species in the pre-hydrolyzed aluminum salts is the most highly charged [28]. It should be noted that zeta potentials for PACl and Al 13 became positive as their concentrations increased to 5.0 mg/L and above, which might lead to re-stabilization of the colloidal matters.…”

Effect of coagulation mechanism on membrane permeability in coagulation-assisted microfiltration for spent filter backwash water recycling

“…This could be explained by the variation of hydrolyzed Al species with pH. The PACl applied in this study contained a large fraction of monomeric Al species, which formed hydrolyzed Al(OH) 3 at neutral pH [27]. Our work also indicated that the amounts of hydrolyzed Al(OH) 3 was a critical factor in determining the coagulation mechanism [35].…”

“…Researchers have also suggested that the enhancement of membrane permeability was strongly related to the strength and size distribution of the flocs [22][23][24][25][26]. For Al-based coagulation, the property of the flocs is dictated by the mechanism of coagulation induced by various hydrolyzing Al species [27]. Mechanisms of coagulation by hydrolyzing these include charge neutralization of negatively charged colloids and incorporation of impurities into an amorphous hydroxide precipitate (i.e., sweep flocculation) [28].…”

Application of a Low Cost Ceramic Filter for Recycling Sand Filter Backwash Water

“…The initial flux at this pressure was measured to be approximately 1000 L/m 2 /d and remained constant until day 14. In Run-3, the TMP was further increased to 3.0 kPa and operated continuously for 5 days (days [15][16][17][18][19] 2 and 3), and <0.1 mg/L (except day 2), respectively, which were approximately 99.4% of the average removal from the raw SFBW. In Run-2, feed water turbidity, Fe, and Mn were measured as 319-770 NTU, 14-78.5 mg/L, and 2.4-10.15 mg/L, respectively.…”

“…The consistency of the filtration flux largely depends on the size and structure of the flocculants formation, which eventually dependson the operating conditions such as pH and coagulant dosages [14][15][16]. For alum coagulation, size and structure of the flocculants are induced by various hydrolyzing Al species [17]. The application of an alum coagulant in a coagulation/microfiltration process has beeninvestigated in the recent past [18][19][20].…”