title: Influence of temperature and pretreatments on the anaerobic digestion of wastewater grown microalgae in a laboratory-scale accumulating-volume reactor.
abstract: This laboratory-scale study investigated the performance of a low-cost anaerobic digester for microalgae. Low (∼2%) solids content wastewater-grown microalgal biomass (MB) was digested in an unmixed, accumulating-volume reactor (AVR) with solid and liquid separation that enabled a long solids retention time. AVRs (2 or 20 L) were operated at 20 °C, 37 °C or ambient temperature (8-21 °C), and the influence of two pretreatments - low-temperature thermal (50-57 °C) and freeze-thaw - on algal digestion were studied. The highest methane yield from untreated MB was in the 37 °C AVR with 225 L CH4 kg volatile solids (VS)(-1), compared with 180 L CH4 kg VS(-1)added in a conventional, 37 °C completely stirred tank reactor (CSTR), and 101 L CH4 kg VS(-1)added in the 20 °C AVR. Freeze-thaw and low-temperature thermal pretreatments promoted protein hydrolysis and increased methane yields by 32-50% at 20 °C, compared with untreated MB. Pretreatments also increased the mineralisation of nitrogen (41-57%) and phosphorus (76-84%) during digestion. MB digestion at ambient temperature was comparable with digestion at 20 °C, until temperature dropped below 16 °C.
authors.affiliation: National Institute of Water and Atmospheric Research (NIWA), P.O. Box 11-115, Gate 10, Silverdale Road, Hamilton, New Zealand; Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 541, 33101 Tampere, Finland. Electronic address: viljami.kinnunen@tut.fi.
authors.forename: Viljami
authors.initials: V
authors.lastname: Kinnunen
authors.affiliation: National Institute of Water and Atmospheric Research (NIWA), P.O. Box 11-115, Gate 10, Silverdale Road, Hamilton, New Zealand. Electronic address: r.craggs@niwa.co.nz.
authors.forename: Rupert
authors.initials: R
authors.lastname: Craggs
authors.affiliation: Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 541, 33101 Tampere, Finland. Electronic address: jukka.rintala@tut.fi.
authors.forename: Jukka
authors.initials: J
authors.lastname: Rintala
mesh_terms: D000693:Anaerobiosis; D017756:Aquaculture / Q000191:economics / Q000295:instrumentation / Q000379:methods*; D056804:Biofuels / Q000032:analysis; D019149:Bioreactors; D003080:Cold Temperature; D008697:Methane / Q000378:metabolism; D058086:Microalgae / Q000254:growth & development* / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D010865:Pilot Projects; D062065:Wastewater / Q000032:analysis*
chemical_list: D056804:Biofuels; D008697:Methane; D009584:Nitrogen; D010758:Phosphorus; D062065:Wastewater
keywords: Biogas production; Freeze-thaw pretreatment; Low-temperature thermal pretreatment; Methane production