Comments on 'Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable'.

A recent review paper considers the potential of algal biomass as a source of liquid and gaseous biofuels, but there are a number of issues concerning the results and conclusions presented. These include the biomass energy values, which in some cases are unusually high; and the apparent production of more energy from processed biomass than is present in the original material. The main causes for these discrepancies include the choice of empirical formula for protein; confusion between values calculated on a total or volatile solids basis; and the lack of a mass balance approach. The choice of protein formula also affects predicted concentrations of ammonia in the digester. These and other minor errors contribute to some potentially misleading conclusions which could affect subsequent interpretations of the overall process feasibility.