title: The effects of different mixing intensities during anaerobic digestion of the organic fraction of municipal solid waste.
abstract: Mixing inside an anaerobic digester is often continuous and is not actively controlled. The selected mixing regime can however affect both gas production and the energy efficiency of the biogas plant. This study aims to evaluate these effects and compare three different mixing regimes, 150 RPM and 25 RPM continuous mixing and minimally intermittent mixing for both digestion of fresh substrate and post-digestion of the organic fraction of municipal solid waste. The results show that a lower mixing intensity leads to a higher biogas production rate and higher total biogas production in both cases. 25 RPM continuous mixing and minimally intermittent mixing resulted in similar biogas production after process stabilization, while 150 RPM continuous mixing resulted in lower production throughout the experiment. The lower gas production at 150 RPM could not be explained by the inhibition of volatile fatty acids. Cumulative biogas production until day 31 was 295 ± 2.9, 317 ± 1.9 and 304 ± 2.8N ml/g VS added during digestion of fresh feed and 113 ± 1.3, 134 ± 1.1 and 130 ± 2.3N ml/g VS added during post digestion for the 150 RPM, 25 RPM and minimally mixed intensities respectively. As well as increasing gas production, optimal mixing can improve the energy efficiency of the anaerobic digestion process.
authors.affiliation: Mälardalen University, School of Business, Society & Engineering, PO Box 883, SE-721 23 Västerås, Sweden. Electronic address: Johan.lindmark@mdh.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Lindmark
authors.affiliation: Mälardalen University, School of Business, Society & Engineering, PO Box 883, SE-721 23 Västerås, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Eriksson
authors.affiliation: Mälardalen University, School of Business, Society & Engineering, PO Box 883, SE-721 23 Västerås, Sweden. Electronic address: Eva.Thorin@mdh.se.
authors.forename: Eva
authors.initials: E
authors.lastname: Thorin
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D056804:Biofuels; D002947:Cities; D005227:Fatty Acids / Q000737:chemistry; D005232:Fatty Acids, Volatile / Q000737:chemistry; D005740:Gases; D006863:Hydrogen-Ion Concentration; D009930:Organic Chemicals; D012037:Refuse Disposal / Q000379:methods*; D013696:Temperature; D013997:Time Factors; D018505:Waste Management / Q000379:methods*
chemical_list: D056804:Biofuels; D005227:Fatty Acids; D005232:Fatty Acids, Volatile; D005740:Gases; D009930:Organic Chemicals
keywords: Anaerobic digestion; Continuous mixing; Continuously stirred tank reactor; Intermittent stirring; Mixing intensity; Municipal solid waste