Effect of Sludge Water Distribution on the Liquid–Solid Separation of a Biological Sludge

Abstract

Water distribution in sludge is worthy of investigation due to its importance in the liquid-solid separation of sludge. Biological sludge contains different physical states of water, including free water, interstitial water, vicinal water, and water of hydration, associated with sludge solids. Conventional dewatering processes can remove only the free water and a part of the interstitial water. Release of interstitial water held inside the cell structure requires the disruption of sludge cells. This study investigates the effect of water distribution on the liquid-solid separation of a biological sludge. Sludge cells were disrupted by alkali treatment, NaCl treatment, heat treatment, and sonication. Water distribution in sludge was determined by differential scanning calorimetry (DSC) and centrifugation. The results of this study indicated that the sludge cell disruption changed the water distribution in sludge and improved its compactibility (as a measure for liquid solid separation). It released a considerable amount of interstitial water trapped inside the cells. Cell disruption created extra surfaces for water binding and increased the unfreezable water content (mostly vicinal water, water of hydration, and a fraction of interstitial water). Compactibility (liquid-solid separation property) of the sludge in terms of cake solids content was improved to about 2-7.5 folds depending on the disruption method used.

A review on sludge dewatering indices

“…-Centrifugal settling test: in this test, sludge is centrifuged at very high rotational speeds of 3500 -4000 rpm and the water content of sludge sediment is reported as bound water content. -Differential thermal analysis (DTA) and Differential scanning calorimetry (DSC): both techniques assume that bound water does not freeze below the given threshold temperature such as -20 o C. DTA and DSC, respectively, measure the temperature difference and the flow heat difference between sample and a thermally inert material (reference material) (Erdincler & Vesilind 2003;Lee & Lee 2004;Deng et al2011). These two methods can be considered as fast and valuable tools for bound water determination (Katsiris & Kouzeli-Katsiri 1987), however, Lee & Hsu (1995) pointed out that they are not practical for measuring the water distribution of activated sludge due to the sludge's non-uniformity.…”

Biosolids and Sludge Management

“…Floc structure was found to be an important determinant of dewaterability for the low suctions employed in the CST apparatus. Erdincler and Vesilind (2003) investigated the effect of water distribution on the dewaterability of biomass by initially treating samples with alkali, NaCl, heat and sonication and then measuring the water distribution and dewaterability of the samples. Disruption of the cells by these techniques released interstitial water and resulted in enhanced dewaterability and compactability of the biomass.…”

Non-isothermal drying kinetics of human feces

“…Only the free water and a part of the interstitial water are removed by conventional dewatering processes. [8] Establishing the drying stages of fecal solids is thus important for predicting drying profiles.…”