Effect of aluminum speciation and pH on in-line coagulation/diatomite microfiltration process: Correlations between aggregate characteristics and membrane fouling

Abstract

a b s t r a c t a r t i c l e i n f o7+ ), were employed to explore the role of Al speciation. Floc characteristics, including particle size and fractal structure under different coagulants and water pH levels, were investigated using a laser diffraction particle sizing device. The results indicated that in the dosage range of 1.0-11.0 mg/L, coagulation/DMM could effectively remove particles (97-100%) and DOC (40-80%), and as pH increased from 3.0 to 10.0, its purification efficiency was higher and more stable than separate coagulation. AS contributed to large and loosely structured flocs and thus alleviated the flux declines most effectively, leading to a flux reduction of about 50%, while the reductions for PACl and Al 13 were 71% and 73%, respectively. Neutral pH was found most conducive to the hybrid process and alkaline pH (9.0) led to relatively larger flux than strong acidic pH (3.0), especially for AS coagulation system. As pH changed, Al 13 led to the least variation in flux declines while both the removal efficiency and filtration flux fluctuated most obviously for AS coagulation system.

Charge Neutralization Mechanism Efficiency in Water with High Color Turbidity Ratio Using Aluminium Sulfate and Flocculation Index

“…The most important mechanisms to explain the coagulation of inorganic iron and aluminium salts are sweep flocculation, adsorption and charge neutralization [6]. Sweep flocculation is more broadly used in the conventional process, which prioritizes the sedimentation of large flocs formed by larger dosages of coagulant and coagulation pHs, while adsorption and charge neutralization is more broadly used in direct filtration, using lower dosages of coagulant and coagulation pHs, which are necessary for the formation of stronger microflocs, leading to improved filtration conditions [3,7,8]. Coagulation diagrams are an important operation selection tool in water treatment plants [23].…”

Jar Tests for Water Treatment Optimisation

“…If the idea suggested by Filipenska et al (2019) that the floc size increases with increasing M-O distance in a hydrated metal ion is accepted, then the order of floc size Ti > Zr > Fe > Al would correspond to M-O distances of 2.34 > 2.19 > 2.00 > 1.89 Å, respectively, as reported by Persson (2010). Pre-polymerised metal salts, particularly PACls of different Al species, prepared in a laboratory were mostly reported to form smaller flocs than their monomeric versions (Jiao et al, 2016;Shi et al, 2007;Wang et al, 2009Wang et al, , 2016. However, commercially available pre-polymerised products (e.g., PAX-16, PAX-XL1, PAX-XL9, or PIX 115) formed larger flocs than their corresponding metal salts (Gregory & Dupont, 2001;Gregory & Yukselen, 2001).…”

“…For example, Shi et al (2007) and Wang et al (2009) suggested that the smaller size of flocs formed by PACl compared to aluminium chloride may be related to the reconformation of the long humic acid molecules around the preformed Al species. Wang et al (2016) reported that the size of fulvic acid comprising flocs prepared by using different coagulants decreased in the order aluminium sulphate > PACl > Al 13 polymer, which was ascribed to the different coagulation mechanisms. Additionally, Jiao et al (2016), who used aluminium sulphate and nano-Al 13 for the formation of Al-NOM flocs, reported a larger floc size for aluminium sulphate.…”

A Comprehensive Review on the Progress of Coagulation for Natural Organic Matter Removal in Water Treatment

“…For pH far from the optimum value (>11 or <3), small particles do not aggregate and remain in the water due to their low destabilization potential (J. Wang et al, 2016). The destabilization occurs through charge neutralization.…”