Intensification of methane production from waste frying oil in a biogas-lift bioreactor

"Available online 31 December 2020"Biogas upgrading from anaerobic digestion of waste frying oils (WFO) was accessed in this study. For that, two bioreactors (Rb-biogas-lift bioreactor with gas and liquid recirculation, Rc-control reactor with liquid recirculation) were fed three times per week, with a mixture of WFO, glycerol and volatile fatty acids (VFA). Rb produced 1.4 times more biogas with higher methane content (79%) than Rc (67%). Higher relative abundance of hydrogenotrophic methanogens (34%-39%) was observed in Rb, when compared to Rc (16%-21%). The relative abundance of Sprochaetia class, which includes some homoacetogens/syntrophic acetate oxidizing genera, was also higher in Rb. This work shows that biogas recirculation applied in the biogas-lift bioreactor facilitated WFO degradation, most probably due to the selective enrichment of hydrogenotrophic methanogens. Recirculation of CO2 present in the biogas and reverse homoacetogenesis (i.e. syntrophic acetate oxidation) seem to be the main factors involved in the stimulation of hydrogenotrophic methanogenesis.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte.info:eu-repo/semantics/publishedVersio

Biochemical conditions for anaerobic digestion of agricultural feedstocks: A full-scale study linking elements concentration and residual methane potential

4 Figuras.-- 2 TablasAgricultural biogas plants should operate at the highest biological efficiency, with a fast anaerobic conversion of organic feedstocks leading to a low Residual Methane Potential (RMP). Optimal biochemical conditions boost the metabolic activity of microorganisms, providing better process performances. In this study, RMP of 16 full scale agricultural biogas plants operating with different agri-based feedstock categories was used as indicator of biological efficiency and linked to their operational parameters such as Organic Loading Rate (OLR), Hydraulic Retention Time (HRT) and to chemical elements concentration in the digestate. RMP ranged between 1% and 26% of the total biomethane produced revealing a clear relation with HRT. The Principal Component Analysis (PCA) showed how specific trace elements supplementation, in the order Se > Mo > Co, and their concentration ratios (Ni/Co and Ni/Se) lead to RMP reduction in full-scale agricultural biogas plants with low HRT (3.61 kgVS m−3 day−1) mainly fed with manure and agro-industrial by-products.Peer reviewe

Mechanical pretreatments of different agri-based feedstock in full-scale biogas plants under real operational conditions

5 Figuras.-- 4 TablasMechanical pretreatments are commonly used devices at full-scale to reduce the size of feedstock and to increase methane production, improving mixing, heat, and mass transfer into the anaerobic digesters of biogas plants. Nevertheless, physical pretreatments require considerable energy. This work aimed to investigate how the energy consumption in different mechanical pretreatments that effectively run under real operational conditions at full-scale level affects physical modifications and anaerobic degradability of agri-based feedstock. Four mechanical pretreatment were investigated: knife milling, hammer milling, extrusion, shredding + hydrodynamic cavitation. After pretreatments, the specific methane yield increased in the range from 1% to 13% and the maximum methane production rate increased in the range from 4% to 48%. Each pretreatment leads to a positive energy balance (0.14–27 kJ kJ−1 used). The increasing of energy consumption indicates a more intense pretreatment with an incremental reduction of particles with diameter bigger than 5 mm. On the basis of the calculated regression analysis, a specific combination of additional specific surface area and additional energy in the day of maximum methane production should be expected with mechanical pretreatment that run effectively at full-scale level.This research was carried out within the research project AGROENER (D.D. n. 26329 del 1 Aprile 2016), which was financially supported by Italian Ministry of Agriculture (MiPAAF).Peer reviewe