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Molecules 2018, 23(9), 2096; https://doi.org/10.3390/molecules23092096

Strategies to Optimize Microalgae Conversion to Biogas: Co-Digestion, Pretreatment and Hydraulic Retention Time

1
GEMMA—Group of Environmental Engineering and Microbiology, Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya·BarcelonaTech, c/Jordi Girona 1-3, Building D1, E-08034 Barcelona, Spain
2
Department of Evolutionary Biology, Ecology and Environmental Sciences, Faculty of Biology, Universitat de Barcelona, Av. Diagonal 643, 08007 Barcelona, Spain
3
Department of Sanitary and Environmental Engineering, Federal University of Minas Gerais, Antonio Carlos Avenue 6627, 31270-090 Belo Horizonte, Brazil
*
Author to whom correspondence should be addressed.
Received: 13 July 2018 / Revised: 9 August 2018 / Accepted: 16 August 2018 / Published: 21 August 2018
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Abstract

This study aims at optimizing the anaerobic digestion (AD) of biomass in microalgal-based wastewater treatment systems. It comprises the co-digestion of microalgae with primary sludge, the thermal pretreatment (75 °C for 10 h) of microalgae and the role of the hydraulic retention time (HRT) in anaerobic digesters. Initially, a batch test comparing different microalgae (untreated and pretreated) and primary sludge proportions showed how the co-digestion improved the AD kinetics. The highest methane yield was observed by adding 75% of primary sludge to pretreated microalgae (339 mL CH4/g VS). This condition was then investigated in mesophilic lab-scale reactors. The average methane yield was 0.46 L CH4/g VS, which represented a 2.9-fold increase compared to pretreated microalgae mono-digestion. Conversely, microalgae showed a low methane yield despite the thermal pretreatment (0.16 L CH4/g VS). Indeed, microscopic analysis confirmed the presence of microalgae species with resistant cell walls (i.e., Stigioclonium sp. and diatoms). In order to improve their anaerobic biodegradability, the HRT was increased from 20 to 30 days, which led to a 50% methane yield increase. Overall, microalgae AD was substantially improved by the co-digestion with primary sludge, even without pretreatment, and increasing the HRT enhanced the AD of microalgae with resistant cell walls. View Full-Text
Keywords: anaerobic digestion; bioenergy; co-digestion; hydraulic retention time; microalgal biomass; primary sludge; thermal pretreatment anaerobic digestion; bioenergy; co-digestion; hydraulic retention time; microalgal biomass; primary sludge; thermal pretreatment
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Solé-Bundó, M.; Salvadó, H.; Passos, F.; Garfí, M.; Ferrer, I. Strategies to Optimize Microalgae Conversion to Biogas: Co-Digestion, Pretreatment and Hydraulic Retention Time. Molecules 2018, 23, 2096.

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