Life cycle analyses of CO2, energy, and cost for four different routes of microalgal bioenergy conversion

•Analyzed four major routes of microalgal bioenergy system.•Assessment was carried using data obtained from respectable references.•Conducted extensive assessment of the energy production, CO2 removal and economic feasibility.•Included CO2 mitigation and market feasibility of the microalgal bioenergy systems.•Covered a complete scheme of microalgae propagation, bioenergy conversion, and waste disposal.

With a target production of 1000 ton of dry algae/yr, lipid content of 30 wt.%, and productivity of 30 g/m2-d in a 340-day annual operation, four common scenarios of microalgae bioenergy routes were assessed in terms of cost, energy, and CO2 inputs and outputs. Scenario 1 (biodiesel production), Scenario 2 (Scenario 1 with integrated anaerobic digestion system), Scenario 3 (biogas production), and Scenario 4 (supercritical gasification) were evaluated. Scenario 4 outperformed other scenarios in terms of net energy production (1282.42 kWh/ton algae) and CO2 removal (1.32 ton CO2/ton algae) while Scenario 2 surpassed the other three scenarios in terms of net cost. Scenario 1 produced the lowest energy while Scenario 3 was the most expensive bioenergy system. This study evaluated critical parameters that could direct the proper design of the microalgae bioenergy system with an efficient energy production, CO2 removal, and economic feasibility.