Challenges and opportunities for microalgae‐mediated CO₂ capture and biorefinery

Abstract

Aquacultures of microalgae are frontrunners for photosynthetic capture of CO2 from flue gases. Expedient implementation mandates coupling of microalgal CO2 capture with synthesis of fuels and organic products, so as to derive value from biomass. An integrated biorefinery complex houses a biomass growth and harvesting area and a refining zone for conversion to product(s) and separation to desired purity levels. As growth and downstream options require energy and incur loss of carbon, put together, the loop must be energy positive, carbon negative, or add substantial value. Feasibility studies can, thus, aid the choice from among the rapidly evolving technological options, many of which are still in the early phases of development. We summarize basic engineering calculations for the key steps of a biorefining loop where flue gases from a thermal power station are captured using microalgal biomass along with subsequent options for conversion to fuel or value added products. An assimilation of findings from recent laboratory and pilot-scale experiments and life cycle analysis (LCA) studies is presented as carbon and energy yields for growth and harvesting of microalgal biomass and downstream options. Of the biorefining options, conversion to the widely studied biofuel, ethanol, and manufacture of the platform chemical, succinic acid are presented. Both processes yield specific products and do not demand high-energy input but entail 60-70% carbon loss through fermentative respiration. Thermochemical conversions, on the other hand, have smaller carbon and energy losses but yield a mixture of products.

Elevated carbon dioxide levels lead to proteome-wide alterations for optimal growth of a fast-growing cyanobacterium, Synechococcus elongatus PCC 11801

“…Cyanobacteria are gram-negative, oxygenic photoautotrophs that harness sunlight to fix inorganic carbon into biomass. With a rise in carbon dioxide levels and its predicted atmospheric concentration reaching approximately 1072 ppmv (parts per million by volume) by the year 2100 1 , the concept of CO 2 uptake and mitigation by photosynthetic microorganisms has gained immense impetus 2 . Furthermore, to circumvent environmental concerns like diminishing fossil fuel reserves, their increasing costs and mounting CO 2 emissions, the focus has recently shifted towards the development of alternative sustainable fuels with abated greenhouse release 2,3 .…”

Chlorella vulgaris (SAG 211-12) biofilm formation capacity and proposal of a rotating flat plate photobioreactor for more sustainable biomass production

“…The potential of the strain C. vulgaris SAG 211-12 for enhanced lipid production was characterized at pilot plant using flat panel airlift technology (Münkel et al 2013). The possibility of cultivating this strain attached to a substrate in biofilm reactors, to the best of our knowledge, has not yet been referred in the literature and could be important in the context of the production system optimization for future integration in a biorefinery system (Seth and Wangikar 2015). Moreover, the utilization of a simple methodology to assess the effectiveness of the adhesion and biofilm development process, similarly to what is used in bacterial biofilm studies (An and Friedman 1997), is of practical interest.…”

An informatics-based analysis of developments to date and prospects for the application of microalgae in the biological sequestration of industrial flue gas

“…The current level of understanding of microalgal biofuel production is not sufficiently deep. Currently, like the status of algal biodiesel (Chisti 2013), the application of microalgae for industrial flue gas biosequestration is not industrially produced anywhere in the world, and even a widespread availability on a large scale is certainly not likely in the near term (Seth and Wangikar 2015).…”

“…Although many techniques and mechanism researches of the application of microalgae in the biological sequestration of industrial flue gas, including microalgae species selection (Ho et al 2011;Seth and Wangikar 2015), gas capture (Rahaman et al 2011), cultivation and influencing factors (Cheah et al 2015;Pires et al 2012), bioreactor technology (Kumar et al 2010;Niu and Leung 2010), biomass applications (e.g., lipid production) and residual biomass utilization (e.g., anaerobic digestion) (Farrelly et al 2013;Pires et al 2012;Seth and Wangikar 2015;Sialve et al 2009), and synergistic combination of other biological techniques (e.g., wastewater treatment) (Acien Fernandez et al 2012;Wang et al 2008), have been extensively studied and reviewed during the past few years, most of the studies have only focused on CO 2 fixation and utilization by algal biomass. In addition, studies on biological DeNOx (bio-DeNOx) of NOx by using microalgae were limited, although capture of NOx from the flue gases for microalgal cultivation has received increasing interest.…”