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Dissolved organic matter (DOM) in soluble microbial products (SMP), loosely bound (LBEPS) and tightly bound extracellular polymeric substances (TBEPS) were extracted from wastewater sludge, fractionated by size exclusion chromatography and characterized by ultraviolet absorbance at 230, 254 and 280 nm, the dissolved organic carbon (DOC) content and excitation-emission-matrix (EEM) spectra. The DOM of molecular weight (MW) > 20000 Da accounted for 33% of SMP, including proteins of high aromaticity, and 22% of both LBEPS and TBEPS, which were composed of organic acid-like substances and proteins, respectively. Polyaluminum chloride (PACl) coagulation effectively removed this DOM fraction. Conversely, the DOM of MW < 1000 Da were mostly non-aromatic organic acids (and possibly polysaccharides) of low aromaticity for SMP and both EPS, and removal by PAC1 coagulation was minimal. The findings indicated that the chemical characteristics of DOM in SMP and LBEPS were similar but not identical. The TBEPS and LBEPS exhibited significantly different DOM based on DOC distribution or EEM fingerprint. [ABSTRACT FROM AUTHOR]

Distributions of six priority controlled Phthalic acid esters (PAEs), including di-methyl phthalate (DMP), di-ethyl phthalate (DEP), di-butyl phthalate (DBP), benzyl butyl phthalate (BBP), di-(2-ethylhexyl) phthalate (DEHP), di-octyl phthalate (DOP) were studied based on soluble and insoluble fractions of sludge samples collected at four wastewater treatment plants in Shanghai, China. Three sludge samples comprised hydrophilic colloidal particles of high protein contents and low aromaticity. Meanwhile, these sludges contained DBP of 4.2∼5.7 mg kg-1 dried solids (ds) and DEHP of 21.1∼55.6 mg kg-1 ds, respectively. Another sludge sample comprised mainly hydrophobic colloidal particles of humic substances and high aromaticity. It contained DBP of 1.18 mg kg-1 ds and DEHP of 2.89 mg kg-1 ds, respectively. The most abundant components noted amongst the six studied PAEs were DBP and DEHP, which mostly associated with the insoluble fraction of sludge. Specifically, the DBP and DEHP in insoluble fraction (the solid residual phase) accounted for 89.8∼98.2% and 88.6∼99.6% of those in the whole sludge. The partition coefficients of DBP and DEHP for the soluble and insoluble fractions of sludge correlated with the suspension SUVA254, suggesting that interaction between π-electrons of DBP or DEHP and those of organic particulates in suspension contributes most of the sorption processes. [ABSTRACT FROM AUTHOR]

The rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The shear creep compliance experiments and the dynamic viscosity measurements were conducted. The shear creep compliance experiments indicate the addition of polymer coagulants to the sludge samples will form more rigid structures. The elastic solid-like behaviors were always observed in the samples with polymers. The Voigt model was successfully employed in modeling the viscoelastic retardation behavior of sludge samples in the shear creep compliance tests. Moreover, the dynamic viscosity curves of the sludge samples with/without polymer could be described by the power law model of Ostwald and de Waele at the medium shear rates, ca. 100–300 s -1 . Consequently, addition of polymer to the sludge tends to extend the applicable ranges of the shear rates for the power law model as well as to decrease the power law index. [ABSTRACT FROM AUTHOR]

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated. [ABSTRACT FROM AUTHOR]

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50–60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed. [ABSTRACT FROM AUTHOR]

The Hsinchu Science-based Industrial Park (HSIP) is the main manufacturing base of "high-tech" commodities of Taiwan. The treatment of wastewater of HSIP produces hard-to-dewater sludge, at a rate of 80 Mg/day, which is resistant to chemical conditioning, whose disposal is costly. The use of chemical flocculation and physical conditioning, including heating and freezing and thawing, on the dewaterability of HSIP sludge was examined in this Note. The dewaterability of the original sludge was poor, and neither chemical flocculation nor thermal heating enhanced its dewatering. However, the freezing and thawing could release up to 83% of moisture from the sludge body; in line with this occurence, the settleability and filterability of the sludge were considerably enhanced. The ice front developed during freezing, which could destroy the floc network, release the interstitial water, and might correspond to the successful conditioning using freezing and thawing. [ABSTRACT FROM AUTHOR]

The disposal of sludge from wastewater treatment presents highly complex problems to any municipality. Most of the sludge disposal methods have varying degrees of environmental impact. Hence, it is necessary to explore potential areas of reuse in order to alleviate sludge disposal problems and to conserve natural resources. Industrial sludge and marine clay are two forms of high-volume wastes. Using these wastes as a resource of raw materials to produce construction aggregates would enable large-scale sludge reuse. The aggregates were produced at various sludge-clay combinations containing 0, 20, 50, 80 and 100% clay contents, respectively. The pelletized aggregates displayed lower particle densities ranged between 1.48 and 2.25 g/cm³, compared to the density of granite at 2.56 g/cm³. Good 28-day concrete compressive strength of 38.5 N/mm² achieved by the 100% sludge aggregate was comparable to the value of 38.0 N/mm² achieved of the granite control specimens. The leachate contamination levels from the aggregates after 150 days were found acceptable when used in concrete, indicating insignificant environmental contamination. The heat flow study showed increases in heat flow at the temperatures of 480°C and between 660°C and 900°C, indicating a need for the extension of heating time around these temperatures. [ABSTRACT FROM AUTHOR]

We examined in this work the drying characteristics of wastewater sludge. The drying flux of the constant-rate period for sludge cake could be up to 40% higher than that from a sand bed. Owing to the considerable volume shrinkage of cake, cracks would form and develop on the crack surface, which yielded three-dimensional but rather than the one-dimensional cake structure assumed in conventional drying theories. The crack length was fully developed in the first 30 min of drying, while the width of crack increased linearly with time. Using these data the drying flux from the cracks was estimated. Enhanced drying flux was noticeable which depended on the crack shape and the crossflow velocity. [ABSTRACT FROM AUTHOR]

We examined in this study the use of a "high-speed" freezing technique, with the assistance of liquid nitrogen freezing, to condition an activated sludge and an alum sludge. The freezing speed reached up to 200 μm/s (0.72m/h), which is much faster than that adopted in most literature works on sludge freezing. After 3-min liquid nitrogen freezing the alum sludge could achieve finite improvement of dewaterability. Such an improvement is not noticeable for activated sludge. Curing has no effect on both sludges after liquid nitrogen freezing. However, curing does have profound influence on the slowfreezing activated sludge. The underlying mechanisms and the feasibility of using high-speed freezing to condition sludge are proposed and commented. [ABSTRACT FROM AUTHOR]