Optimization of biogas production from Sargassum sp. using a design of experiments to assess the co-digestion with glycerol and waste frying oil

A design of experiments was adopted to assess the optimal conditions for methane production from the macroalgae Sargassum sp. co-digested with glycerol (Gly) and waste frying oil (WFO). Three variables were tested: % total solids of algae (%TSSargassum sp.), co-substrate concentration (gGly/WFO L−1), and co-substrate type (Gly or WFO). The biochemical methane potential (BMP) of Sargassum sp. was 181 ± 1 L CH4 kg−1 COD. The co-digestion with Gly and WFO increased the BMP by 56% and 46%, respectively. The methane production rate (k), showed similar behaviour as the BMP, increasing 38% and 19% with Gly and WFO, respectively. The higher BMP (283 ± 18 L CH4 kg−1 COD) and k (65.9 ± 2.1 L CH4 kg−1 COD d−1) was obtained in the assay with 0.5% TS and 3.0 gGly L−1. Co-digestion with glycerol or WFO is a promising process to enhance the BMP from the macroalgae Sargassum sp.