title: Extremely fast increase in the organic loading rate during the co-digestion of rapeseed oil and sewage sludge in a CSTR--characterization of granules formed due to CaO addition to maintain process stability.
abstract: In a co-digestion system running with rapeseed oil and sewage sludge, an extremely fast increase in the organic loading rate was studied to develop a procedure to allow for flexible and demand-driven energy production. The over-acidification of the digestate was successfully prevented by calcium oxide dosage, which resulted in granule formation. Mineralogical analyses revealed that the granules were composed of insoluble salts of long chain fatty acids and calcium and had a porous structure. Long chain fatty acids and calcium formed the outer cover of granules and offered interfaces on the inside thereby enhancing the growth of biofilms. With granule size and age, the pore size increased and indicated degradation of granular interfaces. A stable biogas production up to the organic loading rate of 10.4 kg volatile solids m(-3) d(-1) was achieved although the hydrogen concentration was not favorable for propionic acid degradation. However, at higher organic loading rates, unbalanced granule formation and degradation were observed. Obviously, the adaption time for biofilm growth was too short to maintain the balance, thereby resulting in a low methane yield.
authors.affiliation: German Research Centre for Geosciences GFZ, Section 4.5 Geomicrobiology, Potsdam 14473, Germany E-mail: wuerdemann@gfz-potsdam.de; Institute of Geological Sciences, Jagiellonian University, Krakow 30-063, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Kasina
authors.affiliation: German Research Centre for Geosciences GFZ, Section 4.5 Geomicrobiology, Potsdam 14473, Germany E-mail: wuerdemann@gfz-potsdam.de.
authors.forename: A
authors.initials: A
authors.lastname: Kleyböcker
authors.affiliation: Institute of Geological Sciences, Jagiellonian University, Krakow 30-063, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Michalik
authors.affiliation: German Research Centre for Geosciences GFZ, Section 4.5 Geomicrobiology, Potsdam 14473, Germany E-mail: wuerdemann@gfz-potsdam.de; University of Applied Science Merseburg, Department of Engineering and Natural Sciences, 06217 Merseburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Würdemann
mesh_terms: D018441:Biofilms / Q000187:drug effects; D056804:Biofuels; D019149:Bioreactors; D017610:Calcium Compounds / Q000494:pharmacology; D005229:Fatty Acids, Monounsaturated; D008697:Methane / Q000378:metabolism*; D010087:Oxides / Q000494:pharmacology; D010938:Plant Oils / Q000378:metabolism*; D000074262:Rapeseed Oil; D012722:Sewage; D013997:Time Factors
chemical_list: D056804:Biofuels; D017610:Calcium Compounds; D005229:Fatty Acids, Monounsaturated; D010087:Oxides; D010938:Plant Oils; D000074262:Rapeseed Oil; D012722:Sewage; C016538:lime; D008697:Methane