The effect of light intensity and mixing on the efficacy of a novel photobioreactor

Abstract

Over the last two decades, there has been increased attempts to reduce reliance on dirty energy sources derived from fossil fuels, and more support for research into, and the development of, alternative energy sources derived from sustainable and reliable energy-rich oils. Photosynthetic algae cultivated in Photobioreactors (PBR) is a viable energy source, which when produced in large enough amounts can provide an alternative to fossil-derived fuels. Harnessing photosynthetic algae’s inherent ability to convert light, carbon dioxide, and available nutrients into the water, sugars, oxygen, and energy-rich biomass combined with the treatment of municipal wastewater to an acceptable quality provides an alternative to fossil fuels. This research project aimed to; use a computer model to predict, and then conduct laboratory experiments to test, the extent to which a novel PBR efficiency is improved through enhancing the lighting conditions. For standard lighting conditions, both for the model and experiments, the only source of light to the PBR was overhead lights. The light conditions in the second PBR was enhanced through the use of reflective mirrors that were placed on either side of the growth compartments. Results from the model were compared to data obtained from three sets of laboratory experiments. The test culture used in laboratory studies was Chlorella Vulgarus, and each experimental run was carried over seven days with water samples being collected on days zero, one, three, five, and seven. All samples were assayed for pH, total nitrogen, ammonia, nitrate, phosphates, and chlorophyll-a. Total nitrogen, ammonia, nitrate, and phosphate were measured using commercial test kits as per standard methods: 108:14763 (total nitrogen), 54:14752 (ammonia), 139:09713 (nitrate), and 1.10428.0001 (phosphate). Chlorophyll-a was measured using a modified ESS Method 150.1 test. The pH was measured using calibrated pH-meter. On average algal growth, as measured by Chlorophyll-a production, in the novel PBR was substantially lower than the baseline PBR, which was used as a control. This set of results contradicted the prediction of the models. However, between experimental days, the light enhanced PBR’s growth rates were significantly higher compared to the control PBR