Life cycle assessment of biomethane produced from microalgae grown in municipal waste water

Microalgae are considered a promising feedstock for the production of sustainable biofuels and biochemicals. Within the EU-funded demonstration project ‘Industrial scale Demonstration of Sustainable Algae Culture for Biofuels Production’ All-Gas (FP7-268208), a comprehensive life cycle assessment (LCA) was carried out. The project aims at demonstrating the feasibility of the sustainable production of biomethane based on low-cost microalgae cultures grown in municipal waste water. The full chain of processes from open algae ponds, downstream processing for biomethane production as well as the demonstration of use in vehicles is being implemented on a 10-ha facility in Chiclana de la Frontera (Spain). In contrast to many other LCA studies on algal biofuels, this LCA study used real pilot-scale data. However, it became clear that there still remains the challenge to acquire data with a high quality in particular for algae cultivation which requires a consistent data acquisition over several years. The results of the LCA show that compared to conventional waste water treatment and to the use of biomethane instead of compressed natural gas as vehicle fuel, the investigated algae biorefinery offers clear benefits with regard to the protection of the climate, protection of fossil resources and ozone depletion. In other impact categories such as particulate matter formation, photochemical oxidant formation, water deprivation or eutrophication, the performance of the investigated algae biorefinery is worse. Although there are still technical and environmental drawbacks associated with the algae biorefinery under investigation, the positive aspects already present at this time make it seem worthwhile to further develop and to further optimise this technological approach.