Biological pretreatments and co-digestion with bovine manure for improving the anaerobic digestion of sargassum

The arrival of Sargassum natans and Sargassum fluitans on the Caribbean coast has serious environmental and economic impacts in the region. Several processes have been proposed to deal with the massive algal biomass harvested, including methane and energy recovery. A drawback of this option is the hydrolysis reaction, which is the limiting step to produce methane from sargassum biomass, due to the complex structure of its constituents. In this work, biological pretreatments and co-digestion with manure were applied to improve the hydrolysis of sargassum, using Biochemical Methane Potential (BMP) tests to determine their effectiveness. Results show that the sargassum pretreated with the enzyme Cellic CTec2 increased BMP by 69 %, compared to raw sargassum, confirming that hydrolysis of cellulose is key for methane production. However, the alginate lyase used in this work had no hydrolytic effect on sargassum. The microbial pretreatment applied did not affect the BMP since the microorganisms in the consortia consumed the products of hydrolysis as they were produced. Bovine manure proved to have hydrolytic activity in sargassum, increasing net BMP by 37 %, compared with the control test. Co-digesting sargassum and bovine manure in a 5:1 proportion increased 57 % the gross BMP vs. the control test, showing this is a promising option to increase methane yield at a full-scale level. • Methane from sargassum is an option for managing its massive presence in the coast. • BMP was applied to assess methane yield increase after bio-pretreatments of sargassum. • CellicCTec2 increased sargassum BMP by 69 %, with no effect of the alginate lyase used. • Co-digesting manure and sargassum increased BMP in 37 % due to its hydrolytic activity. • Storing sargassum 6 months at 6 °C increased 30 % BMP due to its indigenous consortia.