Breakage and Regrowth of Al-Humic Flocs - Effect of Additional Coagulant Dosage

Abstract

The growth, breakage and regrowth of flocs formed by aluminum sulfate (alum) with humic acid (HA) in water at neutral pH was investigated by jar testing with continuous optical monitoring. Various initial dosages of alum and different breakage shears were investigated to compare the floc strengths and to explore the growth of flocs and regrowth of broken flocs. In all cases there was significant irreversibility of floc breakage when no additional coagulant was added. On the other hand, when a small additional dosage of alum was added to the suspension during floc breakage, the size of regrown flocs was higher than that before breakage. The result did not change with the variation of the initial dosage of alum, and the intensity and duration of floc breakage, provided that the additional coagulant was added shortly before the end of the breakage process. It seems that aluminum hydroxide is better able to form flocs, when newly precipitated, rather than after an extended period of high shear.

Effect of dosage strategy on Al-humic flocs growth and re-growth

“…As researched by our previous paper [10], the additional dosage of alum can improve the size of flocs whether the flocs is broken or not. Also the result was supported in this paper.…”

“…3, the FSD of flocs before and after breakage with same d 50 was nearly the same, while the grown and re-grown ability were significantly different. Surface activity was brought forward in our previous papers [10,18], and here we put forward "active point". A schematic diagram is shown to explain the variation of flocs activity in flocs formation, breakage process (Fig.…”

“…During the jar test, the pH of final solution was maintained at 7.0 by prior addition of a predetermined amount of 0.1 M HCl or NaOH. Initial dosage of 0.2 mM was used here since the zeta potential was near 0 mV [10]. The temperature was maintained at 25 ± 1 • C.…”

“…Normally, sweep coagulation is the dominant mechanism at optimal dosage of alum, and it is difficult for broken flocs to fully regrow to their initial size before breakage. Our previous research [10] indicated that there was significant irreversibility of floc breakage when no additional coagulant was added. When a small additional dosage of alum was added to the suspension during floc breakage, the size of re-grown flocs was a little higher than that before breakage according the floc monitoring results of flocculation index.…”

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

“…Zeta potentials for coagulation with 2.0 and 5.0 mg/L of Al 13 were À6.25 and 0.15 mV, respectively. Previous research of Yu et al [35] revealed that effective onset of coagulation corresponded with dosage where zeta potential had risen to about À8 mV, so it could be speculated that 2.0 mg/L of Al 13 was sufficient enough to destabilize the colloids efficiently through charge neutralization.…”