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Energies 2013, 6(6), 2966-2981; doi:10.3390/en6062966

The Effect of Effluent Recirculation in a Semi-Continuous Two-Stage Anaerobic Digestion System

School of Engineering, University of Borås, Borås 501 90, Sweden
Department of Biotechnology, Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan 81746-73441, Iran
Author to whom correspondence should be addressed.
Received: 5 May 2013 / Revised: 5 June 2013 / Accepted: 9 June 2013 / Published: 17 June 2013
(This article belongs to the Special Issue Biomass and Biofuels 2013)
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The effect of recirculation in increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) in a semi-continuous two-stage anaerobic digestion system using stirred tank reactor (CSTR) and an upflow anaerobic sludge bed (UASB) was evaluated. Two-parallel processes were in operation for 100 days, one with recirculation (closed system) and the other without recirculation (open system). For this purpose, two structurally different carbohydrate-based substrates were used; starch and cotton. The digestion of starch and cotton in the closed system resulted in production of 91% and 80% of the theoretical methane yield during the first 60 days. In contrast, in the open system the methane yield was decreased to 82% and 56% of the theoretical value, for starch and cotton, respectively. The OLR could successfully be increased to 4 gVS/L/day for cotton and 10 gVS/L/day for starch. It is concluded that the recirculation supports the microorganisms for effective hydrolysis of polyhydrocarbons in CSTR and to preserve the nutrients in the system at higher OLRs, thereby improving the overall performance and stability of the process. View Full-Text
Keywords: two-stage anaerobic digestion; recirculation effect; UASB; CSTR; cotton; starch two-stage anaerobic digestion; recirculation effect; UASB; CSTR; cotton; starch

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This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Aslanzadeh, S.; Rajendran, K.; Jeihanipour, A.; Taherzadeh, M.J. The Effect of Effluent Recirculation in a Semi-Continuous Two-Stage Anaerobic Digestion System. Energies 2013, 6, 2966-2981.

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