title: Modified batch anaerobic digestion assay for testing efficiencies of trace metal additives to enhance methane production of energy crops.
abstract: Batch biochemical methane potential (BMP) assays to evaluate the methane yield of biogas substrates such as energy crops are usually carried out with undiluted inoculum. A BMP assay was performed on two energy crops (green cuttings and grass silage). Anaerobic digestion was performed both with and without supplementation of three commercial additives containing trace metals in liquid, solid or adsorbed form (on clay particles). In order to reveal positive effects of trace metal supplementation on the methane yield, besides undiluted inoculum, 3-fold and 10-fold dilutions of the inoculum were applied for substrate digestion. Diluted inoculum variants were supplemented with both mineral nutrients and pH-buffering substances to prevent a collapse of the digestion process. As expected, commercial additives had no effect on the digestion process performed with undiluted inoculum, while significant increases of methane production through trace element supplementation could be observed on the diluted variants. The effect of inoculum dilution may be twofold: (1) decrease in trace metal supplementation from the inoculum and (2) reduction in the initial number of bacterial cells. Bacteria require higher growth rates for substrate degradation and hence have higher trace element consumption. According to common knowledge of the biogas process, periods with volatile fatty acids accumulation and decreased pH may have occurred in the course ofanaerobic digestion. These effects may have led to inhibition, not only ofmethanogenes and acetogenes involved in the final phases of methane production, but also offibre-degrading bacterial strains involved in polymer hydrolysis. Further research is required to confirm this hypothesis.
authors.affiliation: European Institute for Energy Research (EIFER), Karlsruhe, Germany.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Brulé
authors.affiliation: European Institute for Energy Research (EIFER), Karlsruhe, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Bolduan
authors.affiliation: European Institute for Energy Research (EIFER), Karlsruhe, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Seidelt
authors.affiliation: EnBW Energie Baden-Württemberg AG, Karlsruhe, Germany.
authors.forename: Pascal
authors.initials: P
authors.lastname: Schlagermann
authors.affiliation: Erdgas Südwest GmbH, Ettlingen, Germany.
authors.forename: Armin
authors.initials: A
authors.lastname: Bott
mesh_terms: D000693:Anaerobiosis; D056804:Biofuels; D018533:Biomass; D019149:Bioreactors; D003470:Culture Media; D005232:Fatty Acids, Volatile / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000737:chemistry* / Q000378:metabolism*; D008697:Methane / Q000032:analysis / Q000378:metabolism; D018977:Micronutrients / Q000737:chemistry* / Q000378:metabolism*; D006109:Poaceae / Q000737:chemistry / Q000378:metabolism; D014783:Viscosity
chemical_list: D056804:Biofuels; D003470:Culture Media; D005232:Fatty Acids, Volatile; D008670:Metals; D018977:Micronutrients; D008697:Methane