Anaerobic co-digestion of pig manure and algae: Impact of intracellular algal products recovery on co-digestion performance

• Pig manure was anaerobically co-digested with raw and processed algae.
• Processing increased algae biodegradability but not its degradation rate.
• Synergy between raw algae and pig manure increased methane yield of the mixture.
• There was no significant synergy between processed algae and pig manure.
• Concept was presented for a combined biorefinery processing pig manure and algae.

This paper investigates anaerobic co-digestion of pig manure and algae (Scenedesmus sp.) with and without extraction of intracellular algal co-products, with views towards the development of a biorefinery concept for lipid, protein and/or biogas production. Protein and/or lipids were extracted from Scenedesmus sp. using free nitrous acid pre-treatments and solvent-based Soxhlet extraction, respectively. Processing increased algae methane yield between 29% and 37% compared to raw algae (VS basis), but reduced the amount of algae available for digestion. Co-digestion experiments showed a synergy between pig manure and raw algae that increased raw algae methane yield from 0.163 to 0.245 m3 CH4 kg−1 VS. No such synergy was observed when algal residues were co-digested with pig manure. Finally, experimental results were used to develop a high-level concept for an integrated biorefinery processing pig manure and onsite cultivated algae, evaluating methane production and co-product recovery per mass of pig manure entering the refinery.

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