Temperature effects on flocculation, using different coagulants

Abstract

Temperature is known to affect flocculation and filter performance. Jar tests have been conducted in the laboratory, using a photometric dispersion analyser (PDA) to assess the effects of temperature on floc formation, breakage and reformation. Alum, ferric sulphate and three polyaluminium chloride (PACI) coagulants have been investigated for temperatures ranging between 6 and 29 degrees C for a suspension of kaolin clay in London tap water. Results confirm that floc formation is slower at lower temperatures for all coagulants. A commercial PACl product, PAX XL 19, produces the largest flocs for all temperatures; and alum the smallest. Increasing the shear rate results in floc breakage in all cases and the flocs never reform to their original size. This effect is most notable for temperatures around 15 degrees C. Breakage, in terms of floc size reduction, is greater for higher temperatures, suggesting a weaker floc. Recovery after increased shear is greater at lower temperatures implying that floc break-up is more reversible for lower temperatures.

Polyacrylamide in Agriculture and Environmental Land Management

“…At cool temperatures from 6 to 29 °C, flocculation for a variety of inorganic and polymer compounds tended to be slower and flocs tend to be smaller than at higher temperatures (Fitzpatrick et al, 2004;Hanson and Cleasby, 1990). Furthermore, floc strength seems to vary with the shear conditions of the flow media in which flocs are formed.…”

“…Furthermore, floc strength seems to vary with the shear conditions of the flow media in which flocs are formed. The larger flocs formed at higher temperatures are more easily disrupted and less capable of reformation than flocs formed at lower temperatures (Fitzpatrick et al, 2004;Yeung and Pelton, 1996;Yeung et al, 1997).…”

Measuring Floc Structural Characteristics

“…The ratio of the two gives the flocculation index (FI), which gives a good measurement of aggregation. The PDA has been widely used in closed loop systems to measure dynamic floc size, similar to those mentioned for the light scattering techniques (Burgess and Phipps, 2000;Fitzpatrick et al, 2003;Yukselen and Gregory, 2004;McCurdy et al, 2004). Whilst the other sizing methods give an absolute value for floc size, the PDA gives a combined value that increases with increasing particle size and number.…”

Enhancement of Quality of Secondary Industrial Wastewater Effluent by Coagulation Process: A Case Study

“…The efficiency increased to 73.5% at 15˚C and to 79.4% at 48˚C. Fitzpatrick and et al [17] studied the effect of temperature on flocculation using different coagulant. However, their results are different.…”