Biological sludge contains various fractions of water associated with sludge solids which are mostly microorganisms. These water fractions affect the liquid-solid separation of sludge. A considerable amount of sludge water is trapped either inside the sludge microorganisms or within the floc structure and this is labeled interstitial water. Release of interstitial water held inside the cell structure involves disruption of sludge cells and this does not occur during conventional dewatering. In this study, sludge cell disruption is introduced as a new method to improve the compactibility of sludge. Biological sludge cells are disrupted by different methods including alkali treatment, NaCl treatment, heat treatment, and sonication. The effect of cell disruption on compactibility of biological sludge is investigated. The results of the study indicate that the disruption of the sludge cells changes the water distribution in sludge and improves the compactibility of sludge. Disruption apparently releases from 60% to 80% of interstitial water, depending on the disruption method used. On the other hand, it causes creation of extra surfaces for water binding and leads to an increase in the unfreezable water content (vicinal water, water of hydration and a fraction of interstitial water) of sludge. The cell disruption increases the solid content of compacted sludge up to 87% depending on the cell disruption method used.

There are many factors affecting the biological sludge dewaterability such as particle size distribution, floc structure, extracellular polymeric substances (EPS), etc. In this research, the role of the protein and carbohydrate parts of EPS (EPS(carbohydrate), and EPS(protein)) on the dewaterability of biological sludges was investigated. The sludge EPS composition was altered by feeding the sludges of same origin, in different reactors, with synthetic media having carbon to nitrogen (C/N) ratios of 8, 19 and 30 (in terms of COD/NH3-N), respectively. EPS in sludge samples were extracted by a cation exchange resin (CER). The characteristics of EPS were investigated by analytical methods and by using FT-IR spectroscopy. The dewaterability of the sludges was determined in terms of filterability and compactibility. Filterability, as filterability constant (X), and compactibility, as cake solids concentration, of sludges were determined by using the capillary suction time (CST) test and the centrifugation, respectively. The floc structure of sludge samples was also observed microscopically. Filterability and compactibility of the sludge samples were improved considerably with the increasing carbohydrate part and the decreasing protein part of the sludge EPS. EPS(protein) was inversely related to the cake solids concentration, which might be explained by the water holding capacity of EPS(protein). Filterability and compactibility of sludges improved by the increase of the size and strength of the flocs.

No 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.

This study investigates the effect of ultrasonication and microwave sludge disintegration/pre-treatment techniques on the anaerobic co-digestion efficiency of wastewater sludges with olive and grape pomaces. The effects of both co-digestion and sludge pre-treatment techniques were evaluated in terms of the organic removal efficiency and the biogas production. The "co-digestion" of wastewater sludge with both types of pomaces was revealed to be a much more efficient way for the biogas production compared to the single (mono) sludge digestion. The ultrasonication and microwave pre-treatments applied to the sludge samples caused to a further increase in biogas and methane yields. Based on applied specific energies, ultrasonication pre-treatment was found much more effective than microwave irradiation. The specific energy applied in microwave pre-treatment (87,000kj/kgTS) was almost 9 times higher than that of used in ultrasonication (10,000kj/kgTS), resulting only 10-15% increases in biogas/methane yield. Co-digestion of winery and olive industry residues with pre-treated wastewater sludges appears to be a suitable technique for waste management and energy production.