Algae are a prolific source of biochemicals with economic importance, including nutraceuticals, biofuels, animal feed, etc. The general aim of this study was to establish how the hydrodynamic conditions generated within specific types or designs of photobioreactors determine their respective algae growth. The specific objectives of this study were: (1) To determine and compare key hydrodynamic parameters in the Air Accordion photobioreactor and the conventional bubble column, including Residence Time, Vessel Dispersion Number, Bodenstein Number, Mixing Time and oxygen liquid mass transfer coefficient (kla); and, (2) To test how differences in the hydrodynamic conditions would result in significant difference in growths of the green alga Scenedesmus obliquuus between the photobioreactors. The results of the study showed that: (1) The Residence Time of 566 s for the Air Accordion significantly exceeded by 28% that of 444 s for the bubble column, signifying greater liquid mixing in the Air Accordion; (2) The Vessel Dispersion Number for the Air Accordion of 0.168 significantly exceeded that for the bubble column of 0.166, indicating greater degree of mixing in the Air Accordion than in the bubble column; (3) The Mixing Time in both the Air Accordion and the bubble column declined as the air flow rate increased, indicating that the tracer ions in both photobioreactors mixed more quickly. For each of the flow rates tested, however, the mixing time for the bubble column significantly exceeded that for the Air Accordion, indicating that liquid mixing in the Air Accordion occured significantly quicker than in the bubble column. At 1.0 LPM, the bubble column's Mixing Time of 10 s exceeded by 25% that of the Air Accordion of 8 s; (4) The oxygen liquid mass transfer coefficients in both photobioreactors increased as the air flow rate increased, indicating that the transfer of oxygen from the air bubbles into the liquid within the photobioreactors gained efficiency. For each of the air flow rates tested, however, the oxygen liquid mass transfer coefficient for the Air Accordion significantly exceeded that for the bubble column, indicating a significantly more efficient oxygenation of the liquid in the Air Accordion occurring than in the bubble column. At 1.0 LPM, the Air Accordion's oxygen liquid mass transfer coefficient of 0.00138 s⁻¹ exceeded by 48% that of the bubble column of 0.000931 s⁻¹; and (5) The growth of Scenedesmus obliquus in the Air Accordion significantly exceeded that in the bubble column for both 0.1 LPM and 1.0 LPM. The final algae density of 0.25 g DW/L in the Air Accordion significantly exceeded by 31% that of 0.18 g DW/L in the bubble column at 0.1 LPM. Similarly, the final algae density of 0.37 g DW/L in the Air Accordion significantly exceeded by 19% that of 0.31 g DW/L in the bubble column at 1.0 LPM. Thus, the growth of Scenedesmus obliquus in the Air Accordion photobioreactor -- with significanlty more favorable hydrodynamic characteristics in terms of Residence Time, Vessel Dispersion Number, Mixing Time and oxygen liquid mass transfer coefficient -- significantly exceeded algae growth in the bubble column of the same volume and under the same environmetal conditons.

The tidal stream industry has seen large growth in recent years, and the number of pre-commercial scale devices currently being tested reflects this development. However, commercialising this technology whilst showing that their environmental impacts is minimal remains a challenge. The impact on benthic communities is not considered to be a key strategic consenting issue, yet it is anticipated that the benthic habitat will change as a result of the presence of tidal turbines. To date, only single tidal turbine devices have been installed to demonstrate the application of tidal stream technology but despite successful tests there are still uncertainties surrounding the quantitative impacts these turbines have on local benthic communities. Unlike the wind industry, where physical effects of wind turbines have been catalogued through deployment of thousands of turbines, the tidal stream industry lacks these array scale quantitative data. Local impacts are known, but understanding the scale of the impacts and their relative significance of large arrays remains unknown. Tidal turbines (both single and arrays) interact with the hydrodynamics by decreasing the near field current flow directly in its wake through energy extraction and the drag caused by the physical structure. However, turbines may also affect the far field hydrodynamics, altering bed characteristics, sediment transport regimes and suspended sediment concentrations. As benthic habitats are closely linked to the physical seabed composition and the hydrodynamic conditions, the benthic environment is affected by to changes in the current flow. This thesis presents a series of studies investigating the interaction between tidal turbines and the benthic environment. Based on the hydrodynamic modelling software, TELEMAC2D, a numerical model has been developed to investigate the hydrodynamic impact of a single tidal array at Ramsey Sound, Pembrokeshire as well as the cumulative impact of multiple tidal developments in the Irish Sea. Based on the results of the models, the hydrodynamic outputs were used as inputs to drive a species distribution model, based on the software MaxEnt, to investigate how the distribution of benthic species altered in the presence of a 10MW tidal array at Ramsey Sound. Results of the study showed the development would have a minimal negative impact on the benthic environment.