title: Thermal pretreatment and bioaugmentation improve methane yield of microalgal mix produced in thermophilic anaerobic digestate.
abstract: Liquid fraction produced in anaerobic digestion (AD) of biodegradable waste can be treated on-site with microalgae, which can be recycled back as substrate to the biogas plant. For this research, a pilot high rate algal pond (HRAP) was set with connections to a full scale biogas plant that enabled the use of waste heat and CO2from a combined heat and power gen-set (CHP). The microalgal mix produced in the thermophilic anaerobic digestate supernatant was tested as a substrate for biogas production in the thermophilic AD (i.e. untreated, bioaugmented with anaerobic bacteria Clostridium thermocellum, and thermally pretreated, respectively). The methane potential of the untreated microalgal mix was low (157.5 ± 18.7 mL CH4/g VS). However, after the thermal pretreatment of the microalgae, methane production increased by 62%, while in the bioaugmentation with C. thermocellum under thermophilic conditions (T = 55 °C) it was elevated by 12%. The outcome of our pilot trial suggests that microalgae produced in the thermophilic biogas digestate represent a prospective alternative AD feedstock. At the same time, microalgae reduce the digestate nitrogen and COD to the level sufficient for the outflow to meet the quality required by the sewage system (ammonia-nitrogen max 200 mg/L, nitrite max 10 mg/L).
authors.affiliation: KOTO Ltd., Agrokombinatska 80, 1000 Ljubljana, Slovenia. Electronic address: lea.lavric@koto.si.
authors.forename: Lea
authors.initials: L
authors.lastname: Lavrič
authors.affiliation: AlgEn Ltd, Brnčičeva 29, 1231 Ljubljana, Slovenia.
authors.forename: Ana
authors.initials: A
authors.lastname: Cerar
authors.affiliation: University of Ljubljana, Biotechnical Faculty, Groblje 3, 1230 Domžale, Slovenia.
authors.forename: Lijana
authors.initials: L
authors.lastname: Fanedl
authors.affiliation: AlgEn Ltd, Brnčičeva 29, 1231 Ljubljana, Slovenia.
authors.forename: Borut
authors.initials: B
authors.lastname: Lazar
authors.affiliation: AlgEn Ltd, Brnčičeva 29, 1231 Ljubljana, Slovenia.
authors.forename: Miha
authors.initials: M
authors.lastname: Žitnik
authors.affiliation: University of Ljubljana, Biotechnical Faculty, Groblje 3, 1230 Domžale, Slovenia. Electronic address: Romana.Marinsek@bf.uni-lj.si.
authors.forename: Romana Marinšek
authors.initials: RM
authors.lastname: Logar
mesh_terms: D000693:Anaerobiosis; D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D056804:Biofuels; D001711:Biotransformation; D005285:Fermentation; D008697:Methane / Q000096:biosynthesis*; D058086:Microalgae / Q000378:metabolism*; D013696:Temperature
chemical_list: D056804:Biofuels; D008697:Methane
keywords: Bioaugmentation; Clostridium thermocellum; Digestate supernatant; Microalgae; Thermal pretreatment; Thermophilic biogas production