Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.755265
Title: Enhancing growth using carbon dioxide, and improving efficiency of sedimentation using chitosan, of Chlorella vulgaris in a photobioreactor
Author: Sophonthammaphat, Supatchalee
ISNI:       0000 0004 7428 2637
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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Abstract:
Two of the major problems facing mankind are the energy crisis and environmental changes. The burning of fossil fuels to produce energy impacts on the effects of "greenhouse gasses" and global warming. This study looks at how carbon utilisation by using enhanced levels of CO2 in the air provided to grow algae in a photobioreactor may be one a method of reducing the levels of CO2 entering the atmosphere. In addition the microalgal biomass can produce various forms of energy, thus encouraging the concept of converting waste to energy and the production of "green" energy. The study also looks at how the efficiency of flocculation and sedimentation (as part of harvesting the algae) can be improved by using biopolymers (chitosans) instead of metallic salts. A strain of Chlorella vulgaris (C.vulgaris TISTR 8580) isolated in Thailand, and thus likely to be most suitable for industrial scale growth in that country, was used as the main microalgae to study. Following a series of initial experiments to establish the culture parameters, this algae was grown in a purpose designed photobioreactor system. In this photobioreactor growth rates and yields were measured for cultures with the addition of 0, 6, 12, 24 and 50% CO2 (v/v in air). Growth was measured by turbidity, optical density (OD680), cell count and visual inspection and these measurement techniques were compared and contrasted. The study found that algae grown in 6-12% CO2 (v/v) give the highest yield at 0.98-1.25 gL-1 d-1 with the highest specific growth rate of 1.04- 2.21 d-1 on Day 2. However, the results are more complex when time to harvest is taken into account as higher CO2 levels (12 %) give better results when harvested at a shorter time scale. At 6% CO2, the cumulative turbidity is 2,145.69 NTU. for 4 harvests over 28 days. OD680 and cell number is 41.97 and 2.15 x107 cell/mL respectively. The cumulative dry weight is 18.20 g/L. At 12% CO2 and harvesting every 4 days over the same 28 day period, measurements of biomass by cumulative turbidity, optical density and cell count are 1,852.34 NTU, 41.82, and 2.80 x107 cell/mL respectively. In contrast, growing algae in air alone, and in high CO2 concentrations of 24% and 50% (v/v), results in fluctuating or low growth which, in the case of 24% added CO2 may appear better, but show problems that would limit biomass production on an industrial scale. Bicarbonate additions of 0.1, 0.01, and 0.001 M were investigated to see if there was any growth enhancement from this "solid" form of CO2. The study found that 0.001 M is the maximum amount that could be added because higher levels (0.1, 0.01 M) lead to pH change, which causes growth inhibition. Even at the 0.001 M. level there is no evidence of growth enhancement. Harvesting is a major challenge to the industrial exploitation of microalgae. A major part of this harvesting is separating the algae from the liquid media, particularly without damaging or contaminating them. There are many methods and aids to the separation/concentration of algae and chemical flocculants are one of the most widely used. However, adding chemicals may compromise the quality of the product and may even create a hazardous waste. In this study a comparison was made between some well known flocculating chemicals and natural biopolymer alternatives; chitosans and crab-shell (the latter as a low cost, unprocessed form of chitosan). The study found that metallic salts added at 0.6-1.0 g/L have the ability to flocculate and sediment algae with a removal efficiency of more than 90% in 1 to 12 hr. Crab shell and medium molecular weight chitosan were able to achieve 95% removal in 24 hr. Surprisingly, adding high molecular weight chitosan gave no advantage to the settling process. Although metallic salts have a high efficiency of removal in a shorter time compared to biopolymers, the advantages of their inert nature, non toxicity and, in the case of crab-shell, low cost, may be of considerable advantage in an industrial harvesting process. The thesis reports studies that show that this particular strain of Chlorella vulgaris is likely to be a good candidate for commercial exploitation in Thailand. The study estimates that 5.04 x106 L yr-1 algae (C.vulgaris) volume in 1 ha would be used 4-6% CO2 (v/v) around 6.58 x105 tyr-1 - 9.87x105 t yr-1 . The biomass productivity is around 1,000 t.yr-1 . Total algal oil is about 300 t yr-1 . Biodiesel product from algae should be around 150 tyr-1 . Crab shell and chitosan would be applied in the harvesting process.
Supervisor: Edyvean, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.755265  DOI: Not available
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