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

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 NERCO2
(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.