Life cycle assessment of dewatering routes for algae-derived biodiesel processes

Biodiesel derived from algae is considered a sustainable fuel, but proper downstream processing is necessary to minimize the environmental footprint of this process. Algae is grown in dilute liquid cultures, and achieving the low water contents required for extraction represents one of the greatest challenges for the production of algae derived biodiesel. An analysis of the life cycle emissions associated with harvesting, dewatering, extraction, reaction, and product purification stages for algae biodiesel was performed. This base case found 10,500 kg of total emissions per t BD with 96% of those attributed to the spray dryer used for dewatering. Alternative cases were evaluated for various sequences of mechanical and thermal dewatering techniques. The best case, consisted of a disc stack centrifuge, followed by the chamber filter press, and a heat integrated dryer. This resulted in 875 kg emissions /t BD, a 91% reduction from the base case. A model indicated the optimal case of the disc stack centrifuge, spiral plate centrifuge, heat assisted rotary filter press, and then drying, resulting in equivalent reductions. Significant reductions in life cycle emissions were achieved compared to the base case, but further improvements using these existing technologies were limited. Additional improvements will require the development of new techniques for water removal or wet extractions