Long-term anaerobic digestion of microalgae grown in HRAP for wastewater treatment. Effect of microwave pretreatment

This paper describes the anaerobic digestion of microalgal biomass from high rate ponds in continuous anaerobic reactors for biogas production. With hydraulic retention times (HRT) of 15 and 20 days, the volatile solids (VS) removal did not exceed 30%, and the methane production rate ranged between...

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Bibliographic Details
Published in:Water research (Oxford) 2014-02, Vol.49, p.351-359
Main Authors: PASSOS, Fabiana, HERNANDEZ-MARINE, Mariona, GARCIA, Joan, FERRER, Ivet
Format: Article
Language:English
Subjects:
Anaerobic digestion
Anaerobiosis
Applied sciences
Biodegradation, Environmental
Biogas
Biological and medical sciences
Biological treatment of waters
Biomass
Biotechnology
Cell Wall - ultrastructure
Energy
Energy consumption
Environment and pollution
Exact sciences and technology
Fundamental and applied biological sciences. Psychology
General purification processes
Industrial applications and implications. Economical aspects
Irradiation
Methane
Methane - metabolism
Microalgae - cytology
Microalgae - growth & development
Microalgae - ultrastructure
Microwaves
Natural energy
Pollution
Ponds
Pretreatment
Temperature
Thermodynamics
Time Factors
Waste Water - microbiology
Wastewaters
Water Purification - methods
Water treatment and pollution
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Summary:This paper describes the anaerobic digestion of microalgal biomass from high rate ponds in continuous anaerobic reactors for biogas production. With hydraulic retention times (HRT) of 15 and 20 days, the volatile solids (VS) removal did not exceed 30%, and the methane production rate ranged between 0.12 and 0.14 L CH4/L day. To improve process performance, microwave irradiation at 900 W for 3 min (specific energy ∼70,000 kJ/kg VS) was applied as a pretreatment step. The VS removal increased to 40 and 45% at 15 and 20 days HRT, respectively. Consequently, the methane production rate increased to 0.16 and 0.20 L CH4/L day at 15 and 20 days HRT, respectively. Microscopic analysis confirmed cell wall damage, although generally without lysis, after irradiating microalgal biomass. However, the energy consumption was much higher than the extra energy production of the process. Indeed, microalgal biomass should not only be thickened but also dewatered if microwave irradiation was to be applied as a pretreatment to anaerobic digestion for biogas production.
ISSN:0043-1354
1879-2448
DOI:10.1016/j.watres.2013.10.013