High pressure thermal hydrolysis as pre-treatment to increase the methane yield during anaerobic digestion of microalgae

Anaerobic digestion of algal biomass will be an essential component of algal biofuel production systems, yet the methane yield from digestion of algae is typically much lower than the theoretical potential. In this work, high pressure thermal hydrolysis (HPTH) is shown to enhance methane yield during algae digestion. HPTH pre-treatment was applied to both raw algae and algal residue resulting from lipid extraction. HPTH and even the lipid extraction process itself increased methane yield, by 81% and 33% respectively; in combination they increased yield by 110% over that of the raw algae (18 L CH4 g VS−1 substrate). HPTH had little effect on the rate of anaerobic digestion, however lipid extraction enhanced it by 33% over that for raw algae (0.21 day−1). Digestion resulted in solubilisation of nitrogen (and phosphorous to a lesser degree) in all cases, showing that there is potential for nutrient recycling for algal growth.