Effect of SRT and digester staging on the anaerobic digestion of municipal sludge
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ORIGINAL PAPER
Effect of SRT and digester staging on the anaerobic digestion of municipal sludge Jesus A. Cacho Rivero1 · Makram T. Suidan2 Received: 2 September 2020 / Accepted: 29 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The effect of solids retention time (SRT) on the mesophilic anaerobic digestion of a mixture of primary and waste activate sludge (WAS) was investigated. Twelve laboratory-scale (8 L) digesters were operated in triplicate at four different SRTs (5, 10, 20 and 40 days). The performance of the digesters was evaluated through measuring gas production and composition, total and volatile suspended solids (TSS & VSS) and other effluent quality parameters. VSS removal ranged between 37.6 and 53.6%. The rate of solids disintegration was modeled as a first-order decay reaction taking place in a plug-flow reactor with recycle. The calculated biodegradable fraction of the VSS and the first-order reaction rate constant were 55.3% and 0.38 d−1, respectively. During the second phase of the study, a comparison between multistage digesters in series versus a single-stage digester of equivalent total SRT was performed. Staging was found to always affect greater VSS destruction than single-stage operation. A mathematical model describing VSS destruction in a multistage reactor was developed. Graphic abstract QO Xob Xonb
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Keywords Anaerobic digestion · Excess municipal sludge · VSS destruction · Single-stage · Multistage · Mathematical model
Introduction The generation of excess municipal sludge is on the rise since new wastewater treatment plants are now designed for increased levels of contaminant removal (Hall 1999). Treatment and disposal of sludge generated during * Makram T. Suidan [email protected] 1
Veolia Research and Innovation, 291 Av. Dreyfous Ducas, 78520 Limay, France
Rafik Hariri University, Mechref, Lebanon
2
wastewater treatment can represent up to 60% of operating costs of municipal sewage treatment plants (Canales et al. 1994). Therefore, sludge disposal is an economic consideration in addition to its environmental impact. Traditional disposal solutions such as landfilling and incineration are restricted with new regulations. Anaerobic digestion is a promising technology that may complement these solutions and also enhance the possibility of land application. It stabilizes and reduces the biodegradable fraction of sludge produced, thus decreasing both the environmental and economic impacts of excess sludge handling. It also reduces or eliminates some of the contaminants in
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the sludge in order to meet required standards. Moreover, anaerobic digestion provides for complete air pollution control due to the fact that it takes place in a closed system. The lack of complete understanding of the anaerobic process can easily lead to improper operation. This is why despite all the positive aspects mentioned earlier anaerobic digestion has not been often used. The an
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