Microalgae dewatering for biofuels: A comparative techno-economic assessment using single and two-stage technologies

Microalgae-based biofuels have the potential to replace fossil fuels and contribute towards carbon sequestration. However, the growth of this industry is challenged by the financial viability of scale-up at various production stages. Dewatering is a critical stage which accounts for 20-30% of biofuels' production costs, therefore a techno-economic assessment of two dewatering cases was conducted. The first case was a conventional clarifier-centrifuge dewatering system (Case 1), while the second case investigated a single stage dewatering approach, using the wet-end of a paper machine (Fourdrinier former; Case 2). Mass and energy balances were modelled at a process scale of 175 t/d to produce biomass with 25% dry substance content, from which the associated costs were calculated. The minimum selling price (MSP) to achieve a return of 12% at a corporate tax rate of 30% over a 20-year plant life, was AU$354.28/t and AU$59.68/t for Case 1 and Case 2 respectively. Electricity cost was 90% of operational expenditure for two-stage dewatering and 38% for single stage. Case 2 made a better investment case with an annual profit after tax of AU$131,020 and net present value (NPV) of AU$164 million, as against that of Case 1 with an annual profit after tax of AU$112,610 and NPV of AU$71 million. The single stage dewatering deserves further investigation to fully explore the cost reduction potentials. The adoption of low cost technologies with reduced energy use implies lower embedded GHG emissions and process costs when compared to conventional technologies. This is desired for the near-term actualization of sustainable and clean production pathways for microalgae based biofuels. (C) 2019 Elsevier Ltd. All rights reserved.