Reuse of Algal Biomass Waste as Fertilizer for Algae Cultivation

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A recent French study explores ways to maximise the potential of using microalgae to produce biofuels. This includes issues surrounding management of the algal biomass waste, the reuse of the nitrogen and phosphorus inputs as fertilisers in cultivated production and recovery of methane as an additional source of energy from the algal waste.

Using microalgae as a source of biofuels require large quantities of fertilisers (nutrients) for cultivation of algae. While microalgae are estimated to be capable of producing 10-20 times more biodiesel than rapeseed, they need 55 to 111 times more nitrogen fertiliser: 8-16 tonnes per hectare per year. Such quantities of nitrogen and phosphorus could damage the environment. Additionally, it could limit the economic viability of using microalgae. Nitrogen and phosphorus found in algal waste, after the oils have been extracted, must therefore be recycled. The research suggests that 'anaerobic digestion' could accomplish this goal.

Anaerobic digestion of the algal waste produces carbon dioxide, methane and ammonia. Left-over nitrogen and phosphorus compounds can be reused as fertiliser to the algal process. Using the methane as an energy source can further enhance energy recovery from the process.

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