title: Semi-continuous anaerobic co-digestion of cow manure and steam-exploded Salix with recirculation of liquid digestate.
abstract: The effects of recirculating the liquid fraction of the digestate during mesophilic anaerobic co-digestion of steam-exploded Salix and cow manure were investigated in laboratory-scale continuously stirred tank reactors. An average organic loading rate of 2.6 g VS L(-1) d(-1) and a hydraulic retention time (HRT) of 30 days were employed. Co-digestion of Salix and manure gave better methane yields than digestion of manure alone. Also, a 16% increase in the methane yield was achieved when digestate was recirculated and used instead of water to dilute the feedstock (1:1 dilution ratio). The reactor in which the larger fraction of digestate was recirculated (1:3 dilution ratio) gave the highest methane yields. Ammonia and volatile fatty acids did not reach inhibitory levels, and some potentially inhibitory compounds released during steam explosion (i.e., furfural and 5-hydroxy methyl furfural) were only detected at trace levels throughout the entire study period. However, accumulation of solids, which was more pronounced in the recycling reactors, led to decreased methane yields in those systems after three HRTs. Refraining from the use of fresh water to dilute biomass with a high-solids content and obtaining a final digestate with increased dry matter content might offer important economic benefits in full-scale processes. To ensure long-term stability in such an approach, it would be necessary to optimize separation of the fraction of digestate to be recirculated and also perform proper monitoring to avoid accumulation of solids.
authors.affiliation: Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway. Electronic address: maria.magdalena.estevez@nmbu.no.
authors.forename: Maria M
authors.initials: MM
authors.lastname: Estevez
authors.affiliation: Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway; Department of Environmental Engineering, Bitlis Eren University, 13000 Bitlis, Turkey.
authors.forename: Zehra
authors.initials: Z
authors.lastname: Sapci
authors.affiliation: Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Frederik A. Dahls vei 20, 1432 Ås, Norway.
authors.forename: Roar
authors.initials: R
authors.lastname: Linjordet
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway; Department of Microbiology, Uppsala BioCenter, Swedish University of Agricultural Sciences, P.O. Box 7025, SE 750 07 Uppsala, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Schnürer
authors.affiliation: Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway.
authors.forename: John
authors.initials: J
authors.lastname: Morken
mesh_terms: D000641:Ammonia / Q000737:chemistry; D000693:Anaerobiosis; D000818:Animals; D001673:Biodegradation, Environmental; D056804:Biofuels / Q000032:analysis; D057919:Biological Oxygen Demand Analysis; D018533:Biomass; D019149:Bioreactors; D002417:Cattle; D005232:Fatty Acids, Volatile / Q000737:chemistry; D005662:Furaldehyde / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008372:Manure; D008697:Methane / Q000737:chemistry; D032108:Salix / Q000737:chemistry*; D013227:Steam; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D056804:Biofuels; D005232:Fatty Acids, Volatile; D008372:Manure; D013227:Steam; D000641:Ammonia; D005662:Furaldehyde; D008697:Methane
keywords: Anaerobic co-digestion; Liquid digestate recirculation; Manure; Salix; Steam explosion