Design of experiments to assess pre-treatment and co-digestion strategies that optimize biogas production from macroalgae Gracilaria vermiculophylla

A design of experiments was applied to evaluate different strategies to enhance the methane yield of macroalgae Gracilaria vermiculophylla. Biochemical Methane Potential (BMP) of G. vermiculophylla after physical pre-treatment (washing and maceration) reached 481 ± 9 L CH4 kg−1 VS, corresponding to a methane yield of 79 ± 2%. No significant effects were achieved in the BMP after thermochemical pre-treatment, although the seaweeds solubilisation increased up to 44%. Co-digestion with glycerol or sewage sludge has proved to be effective for increasing the methane production. Addition of 2% glycerol (w:w) increased the BMP by 18%, achieving almost complete methanation of the substrate (96 ± 3%). Co-digestion of seaweed and secondary sludge (15:85%, TS/TS) increased the BMP by 25% (605 ± 4 L CH4 kg−1 VS) compared to the seaweed individual digestion.