Moisture Distribution in Sludges

Abstract

By studying the drying characteristic curve, the moisture in sludge is classified into four categories: free moisture, interstitial moisture, surface moisture and bound moisture. The effects of three dewatering procedures: gravity drainage, vacuum filtration, and centri-fugation, as well as chemical conditioning by a cationic polymer, and physical conditioning by freeze-thaw on the moisture distribution, are investigated. It is found that the dewatering procedures studied can only remove part of the free and interstitial moisture; surface and bound moisture are not affected. Part of the free and interstitial moisture also remains with the sludge cake, which can be considered as the inherent inefficiency of the dewatering process. The complete removal of all the free moisture can be considered as the theoretical best performance any mechanical dewatering device can achieve. Polymer addition is found to improve the dewaterability of the sludge by reducing the inherent inefficiency, primarily by reducing the amount of free moisture retained in the cake. Freeze-thaw is found to effect the removal of free, interstitial and surface moisture, bringing about a dramatic increase in dewaterability. The treated sludge cake drains readily and retains no free moisture.

Rheology evolution of sludge through high-solid anaerobic digestion

“…The VS reduction , defined as the degradation or removal level based on VS, was calculated by the formula reported by Koch et al (2009). Moisture distribution in the sludge was measured using the method of drying test (Luo et al, 2013;Tsang and Vesilind, 1990). In this work, a thermogravimetric analyzer (TA Q5000IR, USA) system with carrying gas of pure N 2 was utilized, and the sludge sample of 100 mg was dried slowly at 303.15 K until there was no change in sludge mass.…”

Dewatering characteristics of algae-containing alum sludge

“…Both polymers were purchased from the Taiwan Polymer Company. T-2000, a product of the Taiwan Calgone Corporation, is a nonionic polymer with molecular weight of 1.5× 10 7 . In sludge conditioning, various amount of polymer was added into a one-liter stirring apparatus containing 800 ml sludge and then mixed for 60 s at 100 rpm.…”

“…Tsang and Vesilind [7] have further distributed this moisture into four categories: free water, interstitial water, surface water, and bound water, in which the bound water content is regarded as the theoretical limit of mechanical dewatering. Various methods have been applied in estimating the bound water content in sludge.…”

Enhancing the Energy Efficiency of Domestic Dryer by Drying Process Optimization

“…[25][26][27] Free moisture is moisture retained on fabric, yarn and fiber surfaces and moisture in pores between yarns, between the fibers within the yarns and in pores within the fibers. The binding force of free moisture and fabric is relatively small, so free moisture is migrated from fabric in the early drying process (mainly including warming-up stage and constant drying rate stage).…”

“…While bound moisture (directly absorbed in macromolecular structure and hydrophilic group of fiber) and capillary moisture (within capillary voids inside fibers) is very difficult to remove from fabric due to greater binding force between the two kinds of moisture and the fabric, and since this combination generally involves chemical bond combination and thus removing this kind of moisture requires breaking the chemical bond (hydrophilic groups of cotton fiber and polar groups of the water molecule) between molecules. [26] The two kinds of moisture are generally considered to be difficult to migrate or should not be removed to avoid fabric damage.…”