Integrating Anaerobic Digestion of Pig Slurry and Thermal Valorisation of Biomass
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The feasibility of coupling the anaerobic digestion of pig manure and co-pyrolysis of its digestate with milk thistle as lignocellulosic biomass was studied. Kinetic analysis was performed along with an evaluation of energy recovery attained from a combined approach
Pig slurry was digested under mesophilic semi-continuous conditions. Digestate was dried and submitted to thermogravimetric analysis under inert atmosphere along with milk thistle samples. Kinetic evaluation was carried out using non-isothermal methods. Assessment of the energy obtained from the combined digestion and pyrolysis process was performed.
Digestion resulted in a yield of 308.5 ± 18.2 mL CH4/g VS. The evaluation of co-pyrolysis of mixtures at different contents of milk thistle showed no interactions between the two materials during pyrolysis. The energy need associated with thermal drying of digestate was 476 MJ/m3 of pig slurry.
Co-pyrolysis of lignocellulosic biomass and digestate [25% content of digestate (w/w)] resulted in a lower char production, associated with the lower ash content of the former. The extra supply of energy needed for thermal drying of the digestate might be obtained from co-pyrolysis with biomass. This approach presented an energy recovery of about 29.4%
KeywordsAnaerobic digestion Pyrolysis Energy recovery Pig slurry Kinetic analysis
The authors thank the Spanish Ministry of Economy and Competition (Refs.: CTM2013-48697-C2-1-R and CTQ2015-68925-R) for financial support. J. González-Arias would like to thank the Junta de Castilla y León (Consejería de Educación) fellowship, Orden EDU/1100/2017, co-financed by the European Social Fund.
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