Mohammad J. Raeesossadati, Hossein Ahmadzadeh, Mark P. McHenry and Navid R. Moheimani

Abstract Various microalgae species have shown a differential ability to biore­mediate atmospheric CO2. This chapter reports biomass concentration, biomass productivity, and CO2 fixation rates of several microalgae and cyanobacteria species under different CO2 concentrations and culture conditions. Research indi­cates that microalgal species of Scenedesmuss obliquss, Duniella tertiolecta, Chlorella vulgaris, Phormidium sp., Amicroscopica negeli, and Chlorococcum littorale are able to bioremediate CO2 more effectively than other species. Fur­thermore, coccolithophorid microalgae such as Chrysotila carterae were also found to effectively bioremediate CO2 into organic biomass and generate inorganic CaCO3 as additional means of removing atmospheric CO2. Important factors to increase the rate of CO2 bioremediation such as initial cell concentration, input CO2 concentration, and aeration rate are reviewed and discussed.

7.1 Introduction

In 2012, 34.5 billion tons of CO2 were emitted through human activities, and in 2013, an unprecedented modern age atmospheric CO2 concentration of more than 400 ppm was measured (Olivier et al. 2013). Carbon capture and sequestration (CCS) offers an effective solution to mitigate environmental impacts and can be

M. J. Raeesossadati • H. Ahmadzadeh (H)

Department of Chemistry, Ferdowsi University of Mashhad, Mashhad

1436-91779, Iran

e-mail: h. ahmadzadeh@um. ac. ir

M. P. McHenry

School of Engineering and Information Technology, Murdoch University, Murdoch, WA 6150, Australia

N. R. Moheimani

Algae R&D Centre, School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, Australia

© Springer International Publishing Switzerland 2015

N. R. Moheimani et al. (eds.), Biomass and Biofuels from Microalgae,

Biofuel and Biorefinery Technologies 2, DOI 10.1007/978-3-319-16640-7_7 considered a long-term remediation policy (Yang et al. 2008). There are a number of CO2 remediation methods that can be classified in three main categories: capture, separation, and fixation.

Power plant CO2 capture can be divided into several scenarios, such as post­combustion process, pre-combustion, and oxy-combustion (Fig. 7.1) (Figueroa et al. 2008; Yang et al. 2008), and being stored in aquifers, porous geologic depleted oil and reservoirs, and deep ocean floors. In post-combustion processes, CO2 is separated from other flue gas constituents. In pre-combustion capture, carbon is removed from the fuel before combustion, and in oxy-combustion, the fuel is burned in an oxygen stream that contains little or no nitrogen (Figueroa et al.

2008) . Furthermore, other chemical approaches, such as amine absorption, ammonium absorption, molecular sieve adsorbent, and adsorption by activated carbon (Bezerra et al. 2011; Thote et al. 2010), are amenable for CO2 separation (Yang et al. 2008). The disadvantages of these methods are the use of large amounts of absorbents and solvents which makes the processes generally expensive (Figueroa et al. 2008), in addition to the processes relatively undeveloped and the possible wider impacts of the use of these chemicals which are not well understood (Wang et al. 2008).

In contrast to traditional methods of carbon capture, biological remediation processes via photosynthesis are major contributors to atmospheric CO2 remedia­tion (approximately 12 billion tons per year) (Bilanovic et al. 2009), with photo­synthetic organisms in the oceans responsible for removing over 40 % of annual

CO2 emissions (Pires et al. 2012). Bioremediation of CO2 can be accomplished through forestation, ocean, fungi, cyanobacteria, and algae (Skjanes et al. 2007) (Fig. 7.1). It is estimated that 1.4 ± 0.7 Gt carbon is captured by terrestrial systems from atmosphere via photosynthesis (Yang et al. 2008). The oceans store more CO2 than terrestrial vegetation (Israelsson et al. 2010), with around 38,000 Gt carbon, and about 1.7 ± 0.5 Gt taken up annually from the atmosphere (Yang et al. 2008). The production of phytoplankton at 50-100 Gt carbon annually is much higher than that of terrestrial vegetation. While part of the carbon is released back into the atmosphere by respiration, a large fraction would descend into the deeper ocean in the form of particulate organic matter either by the death of phytoplankton or after grazing. This sequestration process could be enhanced by ocean fertilization that refers to the practice of increasing limiting nutrients to stimulate the production of phytoplankton (Yang et al. 2008).

Organisms that can convert CO2 into organic molecules are called autotrophs and include plants, algae, some bacteria, and some archaea. Microalgae are the most promising bioremediation alternative for many sources of CO2 emissions. They have the capability of removing 10-50 times more CO2 than terrestrial plants, primarily due to more chlorophyll per unit area (Raeesossadati et al. 2014). Mic­roalgae can also utilize CO2 from different sources, such as atmospheric CO2, industrial exhaust gases, or CO2 in the form of soluble carbonates (e. g., NaHCO3 and Na2CO3) (Kumar et al. 2010). Open ponds and closed photobioreactors (PBRs) are commonly used for culturing microalgae to both consume CO2 and produce useful products (Kumar et al. 2010; Pires et al. 2012). Many microalgal strains can tolerate extreme environments and are able to grow with high production rates in large open ponds (e. g., Dunaliella, Spirulina, and Chlorella sp.), whereas closed PBRs allow better control of cultivation and reduce contamination issues (Eberly and Ely 2012; Pires et al. 2012). Despite many advantages of closed PBRs, large — scale open ponds are usually used for commercial microalgae production due to lower investment and production costs per unit of output (Lee 2001; Posten 2009). The ability of microalgae to bioremediate atmospheric CO2 is commonly thought of as dependent on freshwater and land availability, and the associated concerns of negatively influencing food security (Borines et al. 2011a, b; Clarens et al. 2010; McHenry 2012; Moheimani et al. 2013). However, marine and hypersaline mic­roalgae (eukaryotic or prokaryotic) can fix CO2 with almost no need for freshwater (McHenry 2010, 2013; Moheimani et al. 2012a; Sing et al. 2013). As such, microalgae are now one of the most promising alternatives to bioremediate many sources of CO2 emissions (de Godos et al. 2010). The authors have selected the term “bioremediation” as we are discussing temporary fixation of CO2 in the microalgal biomass. Furthermore, biomass productivity plays a significant role in any microalgae production system, and the production of many target constituents is dependent on primary biomass productivity (including the production of lipids, hydrocarbons, polysaccharides, and other energy storage compounds). The more biomass productivity in any microalgal system is the results of more photosynthetic fixation of CO2. Therefore, to produce industry-scale microalgae biomass, there is a need for cheap carbon source and nutrients.