Theses and dissertations (Applied Sciences)
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Item Evaluation of toxicity and biochemical characterisation of a microalgal diatom(2023-05) Beekrum, Lamees; Amonsou, Eric Oscar; Odhav, Bharti; Lalloo, RajOne ofthe critical challengesthat we face in the 21st century isthe need to feed an ever-increasing human population with increasingly limited natural resources. Microalgae have emerged as a potentialsolution for global food security as a sustainable biological food source for humans due to their nutrient-rich composition, particularly rich protein and bioactive compoundsthat provide potential benefits for human health. By establishing microalgae as a new food platform, we can increase the supply of these essential productsto address global demandsin a more efficient and environmentally sustainable way. These under-exploited organisms have been consumed in the human diet for thousands of years. Microalgae cultivation does not compete with land and resources required for traditional crops and has a superior yield compared to terrestrial crops. Diatoms are a major group of microalgae in the phytoplankton community and have the potential to be engineered into cell factoriesforthe sustainable production of bioactive compoundsin food and nutraceutical industries. This study aimed to characterise a rapidly growing marine diatom in terms of its toxicity and biochemical profile. This was done by evaluating the safety profile and biochemical composition, characterising the soluble protein, and investigating the carbohydrate profile with specific emphasis of β-glucan and its effect of cardioprotective properties on ferric-induced oxidative cardiac injury in a rat model. Based on Basic Local Alignment Search Tool (BLAST) analysis, the strain showed the closest similarity to Amphora sp. (JF834543.1) with 99.5% and istherefore represented as Amphora sp., accession number MW721231. The bacterial reverse mutation assay found no evidence of mutagenicity on the methanolic, aqueous, and hexane extracts of Amphora sp. and was found to exert low levels of cytotoxicity against Peripheral Blood Mononuclear Cells (PBMC). A 28- day acute oral toxicity assessment on male Wistar rats showed an absence of adverse effects and mortality in the rats. The biomass exhibited a low lipid profile, modest protein content, notable amino acid content, and excellent carbohydrate and mineral content. Results of this study for antioxidant assays displayed low to moderate activities. Protein extracted using three-phase partitioning (TPP) treatment showed that the protein concentration and total amino acid content were substantially higher in the protein-enriched biomass extract when compared to the dried biomass. The solubility of the protein-enriched biomass extract increased with the increase in pH within the range of pH 2 to pH 12. The biomass consisted of a simple monosaccharide profile comprising glucose, rhamnose, and mannose, and a β-glucan content of approximately 9%. The cardioprotective properties ofthe β-glucan extract on ferric-induced oxidative cardiac injury did not improve the glutathione (GSH) level significantly, it led to increased superoxide dismutase (SOD) and catalase activities, while depleting malondialdehyde (MDA), NO (nitric oxide), low-density lipoprotein cholesterol levels, and simultaneously elevating triglycerides and high-density lipoprotein (LDL) cholesterol levels. GC-MS analysis revealed a complete depletion of the lipid metabolites. Our results advocate the protective capabilities of the β-glucan extract against ferric-induced oxidative cardiac injury as portrayed by its ability to stall oxidative stress and modulate cardiac lipid metabolism while inhibiting the acetylcholinesterase and lipase activities. These results display that the β-glucan extract could be utilized as an alternative for the development of nutraceuticals for maintaining cardiac health. The diversity of food bioactive molecules obtained from microalgae makes these microorganisms a bioresource with full potential of exploitation in the food industry. The richness of compounds in microalgae can contribute to develop an algal-based food industry, focusing on producing and utilizing microalgae for innovative functional food products. Overall, this study demonstrated the potential utilization of the diatom, Amphora sp. as a potential ingredient and nutraceutical in foods.Item An integrated approach for biofuel and fertilizer production using microalgae grown in wastewater(2022-09) Musetsho, Pfano; Bux, Faizal; Renuka, Nirmala; Guldhe, AbhishekMicroalgae are recognized as potential candidates for resource recovery from wastewater and are projected for biorefinery models. Therefore, this study was undertaken to evaluate the potential of poultry litter and municipal wastewater as nutrient and water sources, for the cultivation of Acutodesmus obliquus for lipids production for biodiesel application. The efficacy of lipid extracted biomass (LEA) as fertilizer for mung bean crops was also assessed in microcosm. A. obliquus cultivation in acid pre-treated poultry litter extract (PPLE) showed maximum biomass production of 1.90 g L-1 , which was 74.67% and 12.61% higher than the raw poultry litter extract (RPPE) and BG11 respectively. Higher NO3-N, NH3-N, and PO4-P removal of 79.51%, 81.82%, and 80.52% respectively were observed in PPLE as compared to RPLE treatment. The highest biomass (140.36 mg L-1 d -1 ), lipids (38.49 mg L-1 d -1 ), and carbohydrates (49.55 mg L-1 d -1 ) productivities were observed in the PPLE medium. The application of LEA as a fertilizer for mung bean crops showed improvement in plant growth and soil microbial activity. A maximum increase in organic carbon (59.5%) and dehydrogenase activity (130.8%) was observed in LEA amended soil which was significantly higher than chemical fertilizer (CF) control in 30 days. Whilst plant fresh weight and leaf chlorophyll in the LEA amended soil was comparable to whole algal biomass (WA) and CF control. The findings of the present study could be a basis for sustainable biorefinery for the valorization of wastewater for the production of microalgae-derived biofuel and byproducts for agricultural applications.Item Optimization of biomass and lipids production from microalgae using wastewater in a pilot scale raceway pond(2021) Rawat, Ismail; Bux, FaizalMicroalgae provide a sustainable renewable solution for the production of commodity products such as liquid biofuels. There are numerous benefits to using algae for the production of biofuels, however, the cost of production is a major hurdle to commercial-scale development. Major factors influencing the production of algae are the cost of nutrients, availability of water, contamination, and grazers. Research into algal biomass for biofuels production at laboratory scale does not translate directly to cultivation at large scale due to the change in cultivation conditions and the constant flux of environmental factors. This study focuses on the upstream processes of cultivation of biomass in a ~ 1146 m2 raceway pond. It demonstrates biomass productivity under different climatic conditions and utilisation of post-chlorinated wastewater as a water and nutrient source. The study further elucidates the population dynamics of the system and provides insight into the challenges faced during the cultivation of algae at large scale. An indigenous Scenedesmus sp. gave biomass productivity of 31.23 g/m2 /d with lipid production of 29.6 % lipid/g DCW in a 10 m2 raceway pond in a greenhouse using BG11. Biomass productivity was reduced to 13.09 g/m2 /d with a lipid content of 22.9 % lipid/g DCW under 3-fold higher irradiance. Biomass productivity of circular 3000L ponds at the large scale site resulted in the highest biomass and acceptable lipid content using 250mg/L NaNO3 although significantly lower than the 10 m2 raceway ponds. Wastewater has shown potential to replace conventional media. Post-chlorinated wastewater was found to have low levels of nitrogen and phosphorus but contained metals that act as micronutrients for algae. Supplemented wastewater proved to be an effective growth. Six individual runs of a covered 1146 m2 raceway pond driven by paddlewheel were conducted over 15 months. The average water temperature ranged from 20.61±0.68°C during mid-winter to 31.03±2.22°C in late summer. Daylight ranges from 10.25 to 14 hours in winter and summer respectively. The highest average light intensity was 359.00±212.71 µmol/m2 /s from Mid-winter to early spring and 645.44±330.58 µmol/m2 /s in late summer. Biomass productivities were low ranging from 2.7 to 7.34 g/m2 /d for most runs of the raceway pond, mainly due to the long periods of cultivation. Average productivity at day 7 for all raceway runs was 7.25 g/m2 /d. Adaptive Neuro-Fuzzy Inference System (ANFIS) modelling of the system elicited that the major factors affecting biomass productivity in the raceway pond were light intensity, pH, and depth for the raceway pond. The model showed that maximum biomass productivity is possible at a depth between 20 and 22 cm at light intensities between 200 and 400 µmol/m2 /s. pH in the range of 9 to 9.5 correlated positively with light intensity ranging from 200 to 1000 µmol/m2 /s with maximum biomass expected in the region of 400 to 500 µmol/m2 /s. The main algal constituents for the raceway ponds were Scenedesmus obliquus, Scenedesmus dimorphus, Chlorella, Keratococcus, and species of unidentified cyanobacteria. Either Scenedesmus or Chlorella was dominant for extended periods. Bacteria in open systems can have a positive or negative effect on the growth of microalgae but is dependent on the strains of microalgae and bacteria as well as prevailing conditions making these systems highly complex. Rhodobacteraceae, Plactomycetaceae, Xanthomonadaceae, Flavobacteriaceae, Phycisphaeraceae, Comamonadaceae, and Cyclobacteriaceae were found to be the major families of bacteria that proliferate at different levels during the cultivation period in the circular ponds and the raceway pond. These families of bacteria have several beneficial traits to algae cultivation however further investigation is required. Modelling the system revealed that pH, depth, and light intensity were factors having a substantial effect on biomass productivity. As the system was carbon limited addition of CO2 (preferably a waste stream) could significantly enhance the overall biomass productivity. A major factor negatively affecting biomass productivity was the size of the pond. Inadequate mixing impacts biomass productivity in terms of access to nutrients and gaseous exchange. Shorter periods of cultivation resulted in higher productivities. For the scale of the system, semi-continuous harvesting would be required to achieve shorter residence time. This must be balanced against the energy utilization and cost of harvesting potentially lower culture densities