Co-digestion strategies to enhance microalgae anaerobic digestion: A review

• Published in: Renewable & sustainable energy reviews 2019-09, Vol.112, p.471-482
• Main Authors: Solé-Bundó, Maria, Passos, Fabiana, Romero-Güiza, Maycoll S., Ferrer, Ivet, Astals, Sergi
• Format: Article
• Language: English
• Subjects: Anaerobic co-digestion; Biogas; Biomass energy; Biorefinery; Biotecnologia; Cyanobacteria; Energia de la biomassa; Energies; Microalgae; Microalgae residues; Microalgal biomass; Microalgues; Àrees temàtiques de la UPC
• ISSN: 1364-0321; 1879-0690
• DOI: 10.1016/j.rser.2019.05.036

Microalgae biorefineries for the production of biofuels and high-value products have captured the attention of academia and industry. Implementing an anaerobic digestion step can enhance resource recovery from microalgae and microalgae residues. Anaerobic co-digestion, the simultaneous digestion of two or more substrates, is an opportunity to overcome the low biodegradability and the risk of ammonia inhibition associated with microalgae and microalgae residues mono-digestion. Besides, microalgae can also be used as co-substrate in biogas plants, with the aim of increasing the organic loading rate while providing alkalinity, macro- and micronutrients. Sewage sludge is the most researched co-substrate for microalgae since microalgae photobioreactors can be used for secondary, tertiary and anaerobic digestion supernatant treatment in wastewater treatment plants. However, microalgae and microalgae residues have been successfully co-digested with a wide variety of wastes, including crops, energy crops, paper waste, animal manure, vinasse, olive mill waste, and fat, oil and grease. Lipid-spent microalgae and glycerol co-digestion has also been largely researched due to the growing interest on microalgal-derived biodiesel. Most studies have assessed the impact of co-digestion on the methane yield and process kinetics through biochemical methane potential (BMP) tests. However, BMP test is not the most suitable method to assess the impact of co-digestion on other important factors such as supernatant nutrient content, digestate dewaterability, biosolids quality, and H2S concentration in the biogas. Overall, more lab-scale and pilot-scale continuous experiments are needed to get a holistic understanding of microalgal anaerobic co-digestion. •Co-digestion overcomes the limitations of microalgae anaerobic mono-digestion.•Ideal co-substrates boost methane production without increasing the nitrogen load.•In WWTPs, sludge can be co-digested with microalgae used for wastewater treatment.•Microalgae as co-substrate also provides alkalinity and macro and micronutrients.•More research is needed to get a holistic understanding of microalgal co-digestion.