Rapid thermal conditioning of sewage sludges to improve digestibility, methane production, and metals solubilization.
Item
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Title
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Rapid thermal conditioning of sewage sludges to improve digestibility, methane production, and metals solubilization.
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Identifier
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AAI9510703
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identifier
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9510703
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Creator
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Pierides, Kyriacos Michael.
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Contributor
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Adviser: John Fillos
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Date
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1994
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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, Civil | Engineering, Sanitary and Municipal | Engineering, Chemical
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Abstract
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Sludge was conditioned in a continuous-flow Rapid Thermal Conditioning Reactor (RTCR) by mixing sludge with steam. Operating temperatures were varied between 25{dollar}\sp\circ{dollar}C and 220{dollar}\sp\circ{dollar}C, the hydraulic retention times (HRT) between 10 and 180 seconds, and pH values between 1 and 12.;Most experiments were done on digested sludge, referred to in this study as partially digested sludge (PDS). Optimum conditions were achieved at an RTCR temperature of 220{dollar}\sp\circ{dollar}C. At unmodified pH, 220{dollar}\sp\circ{dollar}C, and 10 seconds, the COD solubilization increased from 3.4% (25{dollar}\sp\circ{dollar}C) to 13% (220{dollar}\sp\circ{dollar}C) and the volatile solids (VS) solubilization increased from 8.1% (25{dollar}\sp\circ{dollar}C) to 60% (220{dollar}\sp\circ{dollar}C).;Batch anaerobic digestion experiments showed improvement in the kinetic biodegradation rates and in the ultimate biodegradation. At 220{dollar}\sp\circ{dollar}C, ultimate biodegradation improved by 50% at an RTC retention time of 10 seconds, and by 100% at 60 seconds. No additional improvement was obtained at 120 seconds and 180 seconds.;PDS conditioning at various pH levels resulted in the same biodegradation improvement as the pH-unmodified PDS but at lower temperatures. For example, the PDS improvement at pH4 and 100{dollar}\sp\circ{dollar}C was the same as at unmodified pH and 220{dollar}\sp\circ{dollar}C.;Waste activated sludge (WAS) solids and COD solubilization reached 50% and 40%, respectively, which may be caused by the high RTC temperatures lysing the bacteria. The anaerobic biodegradation of WAS (220{dollar}\sp\circ{dollar}C, 10 seconds) increased by 80% but there was no improvement in the biodegradation of primary sludge.;The RTC biodegradation results (220{dollar}\sp\circ{dollar}C, 10 seconds) were confirmed in a continuous flow stirred tank reactor, where methane production improved by more than 200% at a 15-day HRT. Biodegradation at a 3-day HRT was equivalent to the biodegradation of unconditioned PDS but at a 15-day HRT, resulting from an improvement in kinetic removal rates.;Thermal conditioning of sludge alone was sufficient to solubilize metals, with equivalent results reached when the pH was lowered to 1.5. Cu and Mo were solubilized by more than 50% in pH-unmodified RTC sludge; Zn and Pb were solubilized by 90% and 70%, respectively, in acidified RTC sludge; and Se, Cd, and Mo were solubilized by 75%, 55%, and 55%, respectively, in alkaline RTC sludge. The choice of pretreatment conditions to solubilize metals depends on the nature of the metal in the sludge and the type of sludge. The concentration of metals remaining in sludge cake after dewatering depends on the solubilization of solids because the metals can only be removed when their solubility exceeds that of solids.
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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.
