Comparative life cycle assessment of microalgae-mediated CO2 capture in open raceway pond and airlift photobioreactor system.

Abstract: A comparative life cycle assessment of CO₂ capture potential of microalgae, Scenedesmus dimorphus, during autotrophic cultivation in closed airlift photobioreactor and open raceway pond under Indian conditions has been carried out. The LCA inventory inputs for the both the systems were entirely based on primary experimental data obtained by algal cultivation in 1000-L pilot-scale raceway pond and 5-L airlift photobioreactor, respectively. The primary energy demand, environmental impacts and Net CO₂ capture efficiency of both the systems were evaluated. The results indicated that the primary energy demand and GWP of airlift photobioreactor were 3.7-fold higher than raceway pond. The NER_CO2 (defined as net emission ratio of CO₂ and estimated as ratio of CO₂ sequestered/CO₂ emitted) of raceway pond was fourfold higher as compared to airlift photobioreactor; however, both the cultivation systems were observed to be net negative in terms of CO₂ sequestration. However, the process can become net CO₂ positive, with up to fourfold and 7.5-fold enhancement in biomass productivities (wrt base value) for raceway pond and airlift photobioreactor, respectively. Further, LCA predictions indicated that utilization of energy-efficient motors with lower specific energy consumptions for microalgae cultivation would facilitate algal cultivation systems to achieve net CO₂-positive sequestration. [ABSTRACT FROM AUTHOR]