Author: Maria McShane, Bachelor of Engineering in Chemical & Biopharmaceutical Engineering – Level 8, Department of Process, Energy and Transport Engineering, Cork Institute of Technology (supervisor: Ian O’Sullivan BEng, MEngSc, lecturer) The dependency on petroleum-sourced fuels has sparked a global campaign from the scientific community to develop green alternative sources of power (1). The production of biodiesel from microalgae is one such option. Microalgae have high intracellular lipid concentrations that can vary between 1% and 70% by dry weight (2). Microalgae are micro-organisms that only require sunlight, carbon dioxide and some other nutrients to grow. Microalgae can grow in water that may be unsuitable for other uses and they typically double their biomass every 24 hours (3). These characteristics make the production of biodiesel from microalgae a very attractive option. [caption id="attachment_13164" align="alignright" width="571"] Fig. 1: Microalgae production process (5) (click to enlarge)[/caption] However, there is a lack of a general consensus as to how best to cultivate algae – and cultivation typically costs 77% of the total cost of production. Therefore, the development of an effective cultivation process is the key to the advancement of biodiesel production from algae (4). OBJECTIVE The Institution of Chemical Engineers has identified, in a recent review of its technical strategy entitled ‘Chemical Engineering Matters’, four key challenging areas that are in dire need of solutions from the chemical engineering world. The report focuses on: securing sustainable energy supplies; food and nutrition; access to clean water; and health and wellbeing (see Fig. 2). These are areas where chemical engineers can make a positive impact. [caption id="attachment_13166" align="alignright" width="1708"] Table 1: Comparison of some sources of biodiesel (3)[/caption] The main objective of carrying out this project is: to design a cultivation system for the production of biodiesel from microalgae that incorporates the four key issues facing the world today.

  • Aquaponics
Aquaponic food production combines soil-less vegetable growing (hydroponics) and fish farming (aquaculture) within a closed recirculating system. This system is dependent on a symbiotic relationship between three organisms and revolves around the Nitrogen Cycle. There are numerous advantages of aquaponics: it uses between 90-99% less water than traditional methods (8); it yields four to ten times greater crop production (8); and it is organic, using no fertilisers/pesticides (8). With regard to the disadvantages of traditional crop/fish farming, irrigation claims 70% of the water that we use (9) and fish farms create huge amounts of waste - a typical 200,000-salmon fish farm produces nitrogen equivalent to 20,000 humans (10). Hypothesis testing: bench-scale design [caption id="attachment_13168" align="alignright" width="878"] Fig. 2: Four key global issues as identified by the IChemE (6)[/caption] The hypothesis was that cultivation of the microalgae Chlorella Vulgaris could be done so as part of an aquaponics system. All organisms are co-dependent and all are expected to show healthy signs of growth. On a large-scale application, the system would provide solutions to the four key challenges:
  • Providing renewable green biodiesel;
  • Water conservation: using less water than traditional farming methods (fish/crops) and acting as a wastewater treatment process;
  • Providing a sustainable food supply of fish and crops; and
  • Carbon sequestration: using flue gases as the carbon supply for microalgae.
[caption id="attachment_13173" align="alignright" width="4320"] Fig. 3: Bench scale algae-aquaponics system[/caption] With regard to strain selection, Chlorella Vulgaris is readily available (Culture Collection of Algaie and Protozoa UK). It is robust and easy to cultivate, has a fast growth-rate and medium-to-high lipid yields between 5% to 58% (11). CONCLUDING RESULTS The bench-scale algae-aquaponics system provided invaluable insight into how all of the organisms interacted with each other. All four organisms (C. Vulgaris, Goldfish, Vietnamese Coriander and nitrifying bacteria Nitrosomonas Sp. and Nitrobacter Sp.) thrived in the system and proved accurate the hypothesis that they would strike up an ecological balance and symbiotic relationship. Quantitative data was not obtained for the system (i.e. growth rates, uptake rates, biochemical conversion rates etc.), as time and resources were restricted. [caption id="attachment_13175" align="alignright" width="925"] Fig. 4: Restructured design of algae-aquaponics system[/caption] This practical application, in conjunction with intensive review of papers, journals, books and reports, has led to a complete restructuring of the cultivation process design. It is highly recommended that this work be commenced next year to implement the following design. New components of algae-aquaponics system:
  • Bacteria nursery
  • Nitrate-rich water split
  • Hybrid photobioreactor and open-tank system
Photobioreactor + Growbed Effluent  Algae Cultivation Tank (High Biomass)    + (Low Nitrogen)     → (High Lipid Yield) References
  1. Veillette M, Chamoumi M, Nikiema J, Fauxcheux N, Heitz M (2012). ‘Production of Biodiesel from Microalgae.’ Advances in Chemical Engineering. Dr Zeeshan Nawaz (Ed.) ISBN: 978-953-51- 0392-9, InTech
  2. Li Y, Horsman M, Wu N, Lan CQ, Dubois-Calero N (2008) ‘Biofuels from microalgae.’ Biotechnology Progress, 24(4):815–20
  3. Chisti, Y (2007). ‘Biodiesel from microalgae.’ Biotechnology Advances 25, 294–306
  4. Beal CM, Hebner RE, Webber ME, Ruoff RS, Seibert AF, King CW (2012). ‘Comprehensive evaluation of algae production: experimental and target results.’ Energies:5:1943–81
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  12. Greenfish (2013) Greenfish Aquaponic Hobbyist Manual
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