title: The effect of magnesium as activator and inhibitor of anaerobic digestion.
abstract: Anaerobic digestion stands as a key technology in the emerging green energy economy. Mg(2+) has been identified as an important element to improve digesters methane production; however the inhibition risk that high Mg(2+) concentrations can cause to the AD process must also be considered when dosing Mg reagents and wastes containing Mg(2+). Despite its importance, Mg(2+) stimulation and inhibition mechanisms as well as threshold values are scarce in the literature. This research paper investigates the impact (stimulation and inhibition) of Mg(2+) on pig manure anaerobic digestion. Mathematical modelling was used to better understand the interaction between substrate, inoculum and magnesium, where Mg(2+) inhibition was modelled by a n-component non-competitive inhibition function. Modelling was done on absolute curves rather than specific methane productions curves (new approach) to account for the lower background methane production of the inoculum as the Mg(2+) concentration increased. Results showed that no stimulation or inhibition occurred between 40 (native concentration) and 400mgMg(2+)L(-1), while minor and major inhibition were observed at 750 and 1000mgMg(2+)L(-1), and at 2000 and 4000mgMg(2+)L(-1), respectively. Mg(2+) half maximal inhibition concentration was estimated at 2140mgMg(2+)L(-1) with an inhibition order of 2. The latter indicates that Mg(2+) inhibition is a progressive rather than a steep inhibition mechanism.
authors.affiliation: Department of Chemical Engineering, University of Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain; Department of Materials Science and Metallurgical Engineering, University of Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain.
authors.forename: M S
authors.initials: MS
authors.lastname: Romero-Güiza
authors.affiliation: Department of Chemical Engineering, University of Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Mata-Alvarez
authors.affiliation: Department of Materials Science and Metallurgical Engineering, University of Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Chimenos
authors.affiliation: Department of Chemical Engineering, University of Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain; Advanced Water Management Centre, The University of Queensland, St. Lucia, QLD 4072, Australia. Electronic address: s.astals@awmc.uq.edu.au.
authors.forename: S
authors.initials: S
authors.lastname: Astals
mesh_terms: D000693:Anaerobiosis; D056804:Biofuels / Q000032:analysis*; D019149:Bioreactors; D008274:Magnesium / Q000378:metabolism*; D008372:Manure / Q000032:analysis*; D008697:Methane / Q000032:analysis*; D008962:Models, Theoretical
chemical_list: D056804:Biofuels; D008372:Manure; D008274:Magnesium; D008697:Methane
keywords: Activation; Anaerobic digestion; Inhibition; Magnesium; Modelling; Toxicity