Anaerobic digestion of marine microalgae in different salinity levels

• Boost the anaerobic conversion into CH4 of saline microalgae organic residues.
• Three different anaerobic microbial consortia were tested in high saline condition.
• Most promising CH4 production for halophilic methanogens at 35 g L−1 of salinity.
• Hydrolytic, acidogenic and acetogenic activities at 150 g L−1 of salinity.

In the context of biofuel production from marine microalgae, anaerobic digestion has the potential to make the process more sustainable and to increase energy efficiency. However, the use of salt-containing microalgae organic residues entails the presence of salts which inhibits methanogenesis. The search for suitable anaerobic microbial consortium adapted to saline conditions can boost the anaerobic conversion into methane. The anaerobic digestion performance of three different anaerobic microbial consortia was assessed in batch tests at different salinities between 15 and 150 g L−1 and for three successive substrate additions. After an acclimation period, the methane (CH4) yield of the halophilic methanogens at 35 g L−1 of salinity was close to the reference value without salt addition. Above 75 g L−1 of salinity, methanogenesis was considerably slowed down. The results underline that methane production from halophilic sediment can be envisaged and promoted for practical application at a seawater concentration.