Rapid thermal conditioning of sewage sludge.
Item
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Title
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Rapid thermal conditioning of sewage sludge.
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Identifier
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AAI9720160
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identifier
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9720160
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Creator
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Zheng, Jianhong.
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Contributor
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Adviser: Robert A. Graff
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Date
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1997
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Sanitary and Municipal | Engineering, Chemical | Engineering, Environmental | Energy
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Abstract
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Rapid thermal conditioning (RTC) is a developing technology recently applied to sewage sludge treatment. Sludge is heated rapidly to a reaction temperature (up to about 220{dollar}\sp\circ{dollar}C) under sufficient pressure to maintain the liquid phase. Reaction is quenched after 10 to 30 seconds when the mixture of sludge and steam pass through a pressure let-down valve. This process reduces the amount of sludge requiring land disposal, eliminates the need for polymer coagulant, improves dewaterability, increases methane production, and further reduces the concentration of pathogens. The odor problem associated with traditional thermal conditioning processes is largely minimized. Ammonia removal is readily integrated with the process.;For this research, a pilot unit was constructed capable of processing 90 liters of sludge per hour. Over 22 runs were made with this unit using sludge from New York City Water Pollution Control Plants (WPCP). Sludges processed in this equipment were tested to determine the effect of RTC operating conditions on sludge dewaterability, biodegradability, and other factors affecting the incorporation of RTC into wastewater treatment plants.;Dewaterability of thermally conditioned sludge was assessed for cetrifugeability and filterability. Bench scale centrifugation was used for evaluating centrifugeability, pressure filtration and capillary suction time (CST) for filterability. A mathematical model developed for centrifuge dewatering was used to predict the effect of RTC on full scale centrifuge performance. Particle size distribution and solids density of raw and treated PDS were also analyzed. An observed increase in sludge solids density at least partially explains its improved centrifugeability.;An investigation of thermally conditioned amino acids showed that the L-isomer is highly biodegradable while the D-isomers are generally less so. Glucose is highly biodegradable, but rapidly becomes refractory as thermal conditioning time is lengthened. This shows the fundamental importance of rapid processing.;Rapid thermal conditioning may be incorporated into a wastewater treatment plant where biological treatment is used. For purposes of a concrete example, flow-sheets for the incorporation of the RTC process into the New York City Wards Island WPCP were prepared, and experimental data from the laboratory scale RTC test facility were used to set design parameters. A design incorporating nitrogen removal into the RTC flow sheet was also examined. ASPEN software was used to design the proposed processes and perform economic analyses. Cost estimates for these alternatives show a substantial advantage to implement RTC in comparison to present plant operation. About one third of the current sludge processing cost can be saved by incorporation of RTC into the Wards Island Plant. With nitrogen removal, the economics are even more attractive.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
