Effect of Ozone on the Formation and Breakup of Flocs in Raw Waters with High Algae Content

Abstract

The effect of ozone on the formation, breakup and re-formation of flocs generated using ferric sulphate has been investigated using conventional jar test procedure and by continuous optical monitoring using raw water. Using a range of different dosage of coagulant, the breakage of flocs was followed at a high stirring speed, corresponding to average shear rate (G) of about 518 s(-1). Most of the breakage occurred within a few seconds of increasing the shear rate. After breakage the stirring rate was reduced to the original value of 50 rpm (G approximately equals 23 s(-1)) to allow the flocs to re-grow. It was found that only limited re-growth of flocs occurred indicating irreversibility of the floc breakup process. For preozonated samples, the re-growth of flocs occurred to a much greater extent with lower residual turbidity. The findings show that the use of preozonation (1.25 and 1.50 mg/L) provides beneficial results to both improve turbidity removal and reduce coagulant requirement. Furthermore, better re-formation of flocs is achievable.

Impact of ozonation on particle aggregation in mature fine tailings

“…This result is consistent with previous studies (Chheda and Grasso, 1994;Jekel, 1994;Valdes et al, 2002). Ozonation of organic matter is known to break high molecular weight organic matter into smaller, more polar and oxygen-rich compounds, resulting in an increase in the substrate's contents of hydroxyl, carbonyl, and carboxylic groups (Chandrakanth and Amy, 1998;Yukselen et al, 2006). This environment favors the association of aluminum, magnesium, and calcium to clay particles, the formation of insoluble aluminum and calcium complexes, and adsorption of insoluble particles to alum flocs Edwards and Benjamin, 1992;Yan et al, 2007).…”

“…According to the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, a weakening of surface charge would weaken electrostatic repulsive forces among the particles and enhance particle aggregation (Hidalgo Alvarez et al, 1996). The reduction of surface charge by ozonation has been well documented in previous studies (Liu et al, 2007;Yukselen et al, 2006) and is probably due to the desorption of organic coating on the surface of MFT fine particles (Bonneville and Smith, 2001;Farvardin and Collins, 1989;Jekel, 1991), as discussed in the previous section.…”

“…This environment favors the association of aluminum, magnesium, and calcium to clay particles, the formation of insoluble aluminum and calcium complexes, and adsorption of insoluble particles to alum flocs Edwards and Benjamin, 1992;Yan et al, 2007). This effect of ozone likely contributed to a reduction in negative surface charge of the MFT particles and a consequent particle destabilization (Jekel, 1991(Jekel, , 1994Liu et al, 2007;Yukselen et al, 2006).…”

Pilot Scale Comparison of Enhanced Coagulation with Magnetic Resin Plus Coagulation Systems

“…The parameter of floc strength is difficult to define and measure but is related to the interaction between the components of the floc and the number of bonds within the floc (32). The change in floc size with breakage rpm was greater for the resin pretreated system compared with conventional coagulation.…”