title: Thermophilic co-digestion of pig manure and crude glycerol: process performance and digestate stability.
abstract: Anaerobic co-digestion has been widely used to enhance biogas production of digesters and, therefore, to improve the anaerobic plants economic feasibility. In the present study, glycerol, a by-product of the biodiesel industry, was used as a co-substrate for pig manure. The results showed that the thermophilic anaerobic co-digestion of pig manure supplemented with 3% of glycerol, on weight basis, was satisfactory. The specific biogas production of the co-digester was 180% higher than the one obtained by the reference digester, which was only fed with pig manure. The improvement was related to the double of the organic loading rate, the high biodegradability of the crude glycerol, the slight reduction of the free ammonia concentration and the optimisation of the carbon-to-nitrogen ratio. Moreover, the analysis of the organic matter (protein, lipids, carbohydrates and fibers) of the influent and the effluent of both digesters together with their biogas flow rates indicated that the microorganisms in the co-digester obtained large amounts of nutrients from the glycerol, whereas the microorganisms of the reference digester mainly produced biogas from the particulate matter. However, the digestate obtained from the co-digester cannot be directly applied as soil fertiliser or conditioner due to the presence of high levels of biodegradable matter, which may exert negative impacts on the plant-soil system. Thus, a longer hydraulic retention time, a reduction of the glycerol concentration and/or a post-treatment is required if the digestate is to be used as soil fertiliser or conditioner. In contrast, pig manure digestate can be directly applied on land.
authors.affiliation: Department of Chemical Engineering, University of Barcelona, C/ Martí i Franquès, no. 1, 6th floor, 08028, Barcelona, Spain. sastals@ub.edu
authors.forename: S
authors.initials: S
authors.lastname: Astals
authors.forename: V
authors.initials: V
authors.lastname: Nolla-Ardèvol
authors.forename: J
authors.initials: J
authors.lastname: Mata-Alvarez
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D001673:Biodegradation, Environmental; D056804:Biofuels; D005308:Fertilizers; D005990:Glycerol; D008372:Manure / Q000032:analysis; D013552:Swine; D013696:Temperature
chemical_list: D056804:Biofuels; D005308:Fertilizers; D008372:Manure; D005990:Glycerol