Microalgae-based Bioenergy with Carbon Capture and Storage quantified as a Negative Emissions Technology

Abstract

In this paper, microalgae are considered to produce bioenergy through firing. Emitted CO2 would then be captured and stored. This “negative emissions” process, called Microalgae-based Bioenergy with Carbon Capture and Storage (MBECCS), is quantified for the first time, and compared to “classical” Bioenergy with Carbon Capture and Storage (BECCS) using plants. Our goal is to remove 10 Gt per year of CO2 from the atmosphere using MBECCS only. The needed area for cultivation is 4 times less than with BECCS. Because of the high water consumption, marine microalgae should be used. On the other hand, nutrients taken from world wastewater are insufficient, and remain an issue. Planktonic and biofilm microalgae are considered: the latter offer a better areal productivity and require less energy since they are in a concentrated form.For both planktonic and biofilm microalgae, the process produces net heat. Concerning electrical efficiency, we show that it is better for biofilms, as expected. Moreover, for low productivities, MBECCS consumes electricity, comparably to Direct Air Capture, another energy-consuming negative emissions process. Finally, for higher productivities, we show that MBECCS produces net electricity, comparably to other renewable sources such as wind turbines and to BECCS.