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Highlights: [•] Successful thermophilic anaerobic co-digestion between pig manure and glycerol. [•] Glycerol limiting concentration was 3%, on wet-basis. [•] Glycerol provided easy biodegradable matter which led to high biogas flow rates. [•] Larger residence time was required to use co-digestion digestate as soil fertiliser. [Copyright &y& Elsevier]

Crude glycerol derived from biodiesel production is characterized by its high concentration of organic carbon and its solubility in water; properties that make it a suitable co-substrate to improve the efficiency of a manure digester. An increase of about 400% in biogas production was obtained under mesophilic conditions when pig manure was co-digested with 4% of glycerol, on a wet-basis, compared to mono-digestion. The increase in biogas production was mainly a consequence of the increase in organic loading rate. However, the differences could also be related to the synergy between both substrates and the carbon-to-nitrogen ratio. Moreover, the analysis of the macro-compounds, protein, lipids, carbohydrates and fibers, showed lower removal efficiencies in the co-digester as the microorganisms obtained nutrients from the soluble carbohydrates provided by the glycerol. The digestate stability, evaluated through a respirometric assay, showed that co-substrate addition does not exert a negative impact on digestate quality. [ABSTRACT FROM AUTHOR]