Settling behaviour of polymer flocculated water-treatment sludge I: analyses of settling curves

Abstract

Publication informationSeparation and Purification Technology, 35 (1): 71-80Publisher ElsevierLink to online version http://dx.doi.org/10.1016/S1383-5866(03)00132-1 Item record/more information http://hdl.handle.net/10197/3182 Publisher's statementThis is the author's version of a work that was accepted for publication in Separation and Purification Technology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Separation and Purification Technology, 35 (1): 71-80 DOI:10.1016/S1383-5866(03)00132-1 Publisher's version (DOI)http://dx.doi.org/10.1016/S1383-5866(03)00132-1Some rights reserved. For more information, please see the item record link above.--1-- **************************************************************** AbstractSettling behaviour of polymer conditioned water-treatment sludge was investigated in this study for the purpose of a better understanding of a so-called "CML30 method", which was developed in previous study to evaluate the optimum polymer dosage in sludge conditioning.The "CML30 method" is on the basis of a 30 min settling test in 100 ml measuring cylinders.In this study, the series of settling tests in 100, 500 and 1000 ml measuring cylinders were respectively performed and the settling curves (interfacial height to dose and time) were the main focuses for presentation and analyses in great detail in this paper. According to the experimental data presented in this study, settling behaviour may be controlled by both the growth of large sized floc and progressively decreased viscosity. The "speed-up" phenomenon in small polymer dose range obviously enhances the settlement and plays a critical role for the settling set in a 100 ml measuring cylinder at a special dose and at the settling time interval 5-30 min. It is such special observation that leads to the success of socalled ad hoc "CML30 method". However, sludge settling behaviour could be controlled by the formation of networked structure which is involved in excess polymer during the large --2--range (say over 10 mg/l for the case tested) of polymer doses. The higher liquid viscosity values derived from excess polymer will increase the drag force for the resistance of the settlement. In addition, wall effects are likely to interplay with the internal networked structure in large dosed region.

A study of dual polymer conditioning of aluminum-based drinking water treatment residual

“…Actually, settling characteristics of polymer conditioned sludge has been extensively studied and evidenced by the deteriorative settlement in overdose range due to the large but less compacted flocs and increased viscosity in the settling environment. [7,9] However, this appears not to be the case in the current study.…”

Settling behaviour of polymer flocculated water-treatment sludge II: effects of floc structure and floc packing

“…As noted, D F is a quantitative measurement of floc structure (referred to floc mass) and a description of how the original particles are organized within the floc interior. Yet, the change of floc structure may be considered as one of the factors to control the settling behaviour, especially during underdose range as illustrated in an earlier paper [6]. However, it is noted that the fact that D F hardly changes with dosages above 2.0 mg/l (see Table 2) does not appear to influence the position of the interfacial height in the "CML30 method".…”

“…7 is the "gap" between volume fractions in overdosing range. The reason this "gap" occurs is unclear but is associated with the viscosity feature of supernatant in bulk solution [6]. In addition, Johnson et al [17] emphasized that untrapped colloidal material can also affect settling velocity by clogging pores and altering the flow conditions around and within settling aggregates.…”

“…In particular, the interaction between polymer and water treatment sludge, commonly known as alum sludge, is complex and the settling behaviour of this suspension is a physicochemical process. In spite of the efforts described in an earlier paper [6] which provides ample information focused on the detailed analyses of settling curves, it is inadequate in view of the complexity of the settling process. In this paper, by making use of the image analysis system, floc structural characteristics such as floc size, density and fractal dimension are examined in greater detail in terms of their response to the polymer dosage.…”

Exploitation of Fenton and Fenton-like reagents as alternative conditioners for alum sludge conditioning

“…However, considerable differences in the settling behaviour can be observed between the sludge conditioned with the polymers and those conditioned with the Fenton's reagent. This may be explained by the polymer particle size-bridging mechanism which significantly increases the size of sludge particles (Zhao;Ma et al, 2007). Figure 6 provides a qualitative description of the effectiveness of the different conditioners on the sludge conditioning as compared with that of the raw sludge.…”