alexa Photobioreactor for CO2 Sequestration: Possibilities and Challenges | Open Access Journals
ISSN: 2155-6199
Journal of Bioremediation & Biodegradation
Like us on:
Make the best use of Scientific Research and information from our 700+ peer reviewed, Open Access Journals that operates with the help of 50,000+ Editorial Board Members and esteemed reviewers and 1000+ Scientific associations in Medical, Clinical, Pharmaceutical, Engineering, Technology and Management Fields.
Meet Inspiring Speakers and Experts at our 3000+ Global Conferenceseries Events with over 600+ Conferences, 1200+ Symposiums and 1200+ Workshops on
Medical, Pharma, Engineering, Science, Technology and Business

Photobioreactor for CO2 Sequestration: Possibilities and Challenges

Pushap Chawla1, Anushree Malik1* and Sreekrishnan SR2
1Applied Microbiology Laboratory, Centre for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India
2Waste Treatment Laboratory, Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India
Corresponding Author : Anushree Malik
Applied Microbiology Laboratory
Centre for Rural Development and Technology
Indian Institute of Technology Delhi
Hauz Khas, New Delhi-110016, India
Tel: (+) 91-11-2659-1158
E-mail: [email protected]
Received May 19, 2014; Accepted July 14, 2014; Published July 18, 2014
Citation: Chawla P, Malik A, Sreekrishnan SR (2014) Photobioreactor for CO2 Sequestration: Possibilities and Challenges. J Bioremed Biodeg 5:234. doi:10.4172/2155-6199.1000234
Copyright: © 2014 Chawla P, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Related article at
DownloadPubmed DownloadScholar Google

Visit for more related articles at Journal of Bioremediation & Biodegradation

Abstract

Global warming due to increased CO2 emission has become a major issue today. In this regard, algae offer a plethora of opportunities due to its photosynthetic route of conversion of CO2 to biomass which is manifold higher than that of plants. In this regard, this paper highlights the issues, challenges and opportunities generated through algal sequestration of CO2. The paper talks about various factors that enhance the efficiency of algal consumption as well as accumulation of CO2. The parameters like mode of cultivation, photobioreactors design considerations and harvesting of algal biomass have been given due importance. The perspectives offered will provide a deep insight into development of an integrated technology for making CO2 sequestration commercially viable.

Abstract

Global warming due to increased CO2 emission has become a major issue today. In this regard, algae offer a plethora of opportunities due to its photosynthetic route of conversion of CO2 to biomass which is manifold higher than that of plants. In this regard, this paper highlights the issues, challenges and opportunities generated through algal sequestration of CO2. The paper talks about various factors that enhance the efficiency of algal consumption as well as accumulation of CO2. The parameters like mode of cultivation, photobioreactors design considerations and harvesting of algal biomass have been given due importance. The perspectives offered will provide a deep insight into development of an integrated technology for making CO2 sequestration commercially viable.
 
Keywords

Photobioreactor; Carbon dioxide; Sequestration; Algae; Global warming; Climate change
 
Introduction

Increased energy and water demand has resulted in degradation of the environment. Current energy demands are mostly met by conventional sources often leading to emission of greenhouse gases [1]. Across the globe, from developed economies to developing ones, there is a lot of interest generated in finding sustainable solutions to increased CO2 emissions. Algal mediated wastewater treatment and CO2 sequestration could provide impetus to counter concern for clean water, air and energy, effectively treating even complex contaminants like heavy metals and polycyclic aromatic compounds [2-4]. Moreover, algae that have high rate of CO2 sequestration are now preferred for biodiesel production due to their high rate of lipid/oil accumulation going as high as 58,700 L oil per hectare [5,6].

Several models have indicated the techno-economic feasibility of integrated algal use by utilizing nutrients from wastewater, carbon from waste gases and subsequent production of biofuel [7]. The key problem associated with the current research is that the investigations are mostly confined to laboratory experiments where often the conditions are controlled which deviate a lot from the real ones. On a larger scale, the applicability of lab findings itself become a challenge. In some cases, the size has been increased to a mere pilot scale of 1000 L but owing to difficulties in scale up of the given design, less breakthroughs have been achieved in design of bioreactor where scale up is taken to industrial level in case of simultaneous CO2 sequestration and waste water treatment [8].
 
Strain selection and mode of cultivation

There are multiple parameters to be taken care of for algal mediated CO2 sequestration. The very basic and primary step is strain selection. Certain desirable qualities include tolerance to high CO2 concentration, high biomass productivity, tolerance to variations in temperature and most importantly high CO2 fixation rates. Most commonly used algal species are depicted in Table 1.

Strain selection is directly linked with mode of cultivation. The conditions of cultivation of algae have a peculiar effect on end result. The photoautotrophic cultivation mode utilizes light for energy requirement and inorganic carbon as carbon source. In this mode, there are large variations in lipid content which can be tilted towards user’s advantage by increasing the lipid accumulation through nitrogen limiting condition [5,9]. Totally opposite mode of cultivation is heterotrophic condition where algae utilize organics for both energy as well as nutrient requirement. Since it does not require light, hence it is under the dark conditions [10,11]. Another mode of cultivation is the mixotrophic growth where light is used an energy source and depending upon the availability, both organics as well as inorganics are used as nutrient source. This is particularly required in cases where algal cultures are cultivated in wastewater with CO2 injection. In such cases, algae utilizes light for energy, CO2 as carbon source while simultaneously utilizing organics for treatment of wastewater hereby making the process more economically viable [7,12,13].
 
Photobioreactor design considerations

Once the strain selection is made, well designed photobioreactor becomes need of the hour. Cultivation could be done in open as well as closed system. Open systems, like unstirred ponds, circular ponds, raceways and modified raceways offer ease of operation and are more economical than closed system [22]. Major constraints offered by open systems include poor light utilization efficiency, huge evaporative losses and biological contamination. For high rate of CO2 sequestration, open system are not viable as gas mixing becomes a challenge due to low depth of ponds [23]. When the efficacy of algal mediated CO2 sequestration was tested in outdoor open photobioreactor, the results indicated that flue gas decarbonisation decreased with increasing flue gas injection rate into culture [17].

For high rate of CO2 sequestration, mainly closed type photobioreactors are employed. The various design parameters for closed type photobioreactors include type of reactors, height to diameter ratio, mode of delivery, minimizations in temperature variations, optimum intensity of light, maximum utilization of light, proper mixing, optimum light - dark cycles, minimization of CO2 losses. As depicted in Table 1, multiple designs of photobioreactors present multiple opportunities and challenges. These include mainly tubular type photobioreactors (horizontal and vertical), stirred tank photobioreactors and flat panel photobioreactors. Tubular photobioreactors are fairly easy to operate with decent biomass productivities due to high illumination surface area [22]. This system incorporates gas sparging as a means to provide overall mixing and high gas transfer efficiency [24]. Other variants include bubble column photobioreactor and airlift photobioreactor [25]. In a three stage tubular reactor, though the CO2 fixation rate was high yet the problems associated with flocculating Spirulina sp. highlighted the importance of strain selection [14]. In the study concerning vertical tank reactors, it was noted that the algal sequestration of CO2 could be increased by multiplicity of reactors hereby presenting an insight with regard to scale up [16]. In case of membrane photobioreactor, gas (CO2) exchange efficiency improved from the introduction of membrane module hereby resulting in minimization of losses [15]. While in membrane carbonation photobioreactor the bubble less gas transfer through membranes allows precise control of CO2 delivery hereby minimizing the loss of CO2 to atmosphere [18]. There is also need to highlight the maximized fixation of CO2 by optimizing the light intensity for minimization of CO2 losses [20].

Light intensity can also be increased by better designs (internally illuminated) where light utilization rate is significantly higher as compared to bubble column and airlift reactors [21]. Studies have exhibited equal importance of dark cycles for algal growth. The dark cycle allows for re-oxidation of electron transporters of photosynthetic apparatus for sustained productivities [26]. Even the importance of optimum concentration where one has to remove the excess biomass continuously in order to provide maximum spread area to volume ratios, can’t be ignored [27].
 
Harvesting of algal biomass post CO2 sequestration

Keeping in mind the process economics, significant economical addition to the entire process can be done through harvesting of algal biomass and then use of algal biomass for bioenergy generation [7]. Depending upon the scale, size and density of algal culture, various harvesting techniques like centrifugation, flocculation, gravity sedimentation, filtration, electrophoresis etc. can be employed. Centrifugation can result in high harvesting efficiency but the process is costly and energy intensive [28]. Flocculation is a process where particles form heavy aggregates which make their settling easily [29]. This could be done via increase in pH (autoflocculation) through base (NaOH) addition or through chemical flocculants like ferric chloride (FeCl3) or aluminium sulphate Al2(SO4)3 [24]. Success of gravity sedimentation highly depends upon size and density of algal cultures [30]. Efficiency of gravity sedimentation can be increased using flocculation [29]. Filtration involves passing of culture through screen of particular pore size. Major associated problem with filtration is high concentration of algal biomass often results in blocking of filtering material [31]. Other techniques include electrophoresis where electric current induced electrostatic field forces the movement of charged algal cells out of solution [32].
 
Recent large scale developments in the field of CO2 sequestration

The ENN group from China has developed a technology where a microalga is used to fix CO2 released from coal production and subsequently biofuel is produced. The pilot plant consists of equipment required for microalgae cultivation with CO2 absorption, oil extraction and bio-diesel production. This pilot system can absorb 110 tonnes of CO2 and produce 20 and 5 tonnes of bio-diesel and proteins per year, respectively. Based on this pilot plant, a demonstration project has been initiated by ENN group in Dalate (Mongolia) in 2010 where microalgae will be utilized to absorb CO2 emitted from flue gas of coal-derived methanol and coal derived dimethylether production equipment and will produce biodiesel and feed.

Another group from Sweden, has set up a pilot plant in eastern Germany where algae is used to absorb greenhouse gas emissions from a coal-fired power plant. The gas emitted from the brown-coal-fired plant is pumped through a broth into the plastic tanks where algae is cultivated. The resultant algal biomass is used to produce biodiesel, to feed biogas power plants and as a nutrient supplement for fishes.
 
Conclusion

There is a need for informed and effective design of photobioreactor which could replicate the real conditions and could provide an alternative solution. In this cost driven world, this idea of algal use is bound by importance of light as a parameter in algal growth. Across the world, there are places with abundance of sunlight available almost throughout the year. This advantage is still underutilized mainly because of lack of bioreactors which maximizes algal productivity and CO2 sequestration. While the CO2 sequestration offers huge environmental benefit, one has to make effort in the direction to make it economically viable. This can be made possible by integration of CO2 sequestration with wastewater treatment and biofuel generation.
 
Acknowledgement

Authors are grateful to Ministry of New and renewable Energy, Government of India for financial support.
 
References

































Tables and Figures at a glance

Table icon
Table 1
Select your language of interest to view the total content in your interested language
Post your comment

Share This Article

Relevant Topics

Recommended Conferences

Article Usage

  • Total views: 11639
  • [From(publication date):
    September-2014 - Jun 27, 2017]
  • Breakdown by view type
  • HTML page views : 7860
  • PDF downloads :3779
 

Post your comment

captcha   Reload  Can't read the image? click here to refresh

Peer Reviewed Journals
 
Make the best use of Scientific Research and information from our 700 + peer reviewed, Open Access Journals
International Conferences 2017-18
 
Meet Inspiring Speakers and Experts at our 3000+ Global Annual Meetings

Contact Us

 
© 2008-2017 OMICS International - Open Access Publisher. Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version
adwords