Browsing by Author "Beyl, Talíta"
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- ItemSynechococcus PCC 7002 growth in anaerobic digestion effluent and off-gas(Stellenbosch : Stellenbosch University, 2018-12) Beyl, Talíta; Pott, Robert William M.; Louw, Tobias M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Anaerobic digestion (AD) effluent is a low-cost and nutrient-rich medium produced at significant volumes, on which algae can be grown. The biogas that is produced by AD is commonly burnt, for heating or electricity generation. The off-gas from this process can be used to enrich the gas fed to an algal cultivation system, to enhance inorganic carbon supply to the growing photoautotrophic species. Therefore, a significant opportunity exists for the integration of the wastes from AD (the nutrient rich effluent, and the carbon dioxide (CO₂) rich off-gas) with the production of microalgae. The potential of using photosynthetic microalgae to produce valuable products is of interest currently. Not only does increasing dependence on non-renewable energy sources jeopardize sustainable supply but increasing CO2 emissions also promote climate change. In addition, rising global energy demands of developing nations threaten the availability of sustainable energy for future generations. Since genetically modified strains on microalgae are available, integrating their growth with AD, which will produce nutrients and inorganic carbon, could support the cause for commercial sustainable chemical production. In this study, AD effluent was treated with a cyanobacterial species, Synechococcus PCC 7002, to reduce turbidity and high concentrations of nutrients present. It was illustrated that by lowering the pH, increasing the total dissolved salts and adding a specific macro-nutrient necessary for growth to the AD effluent, the addition of valuable resources (such as water for effluent dilution and CO2 enriched gas for enhanced growth) can be avoided. This ultimately increases the feasibility of AD-microalgae integrated systems. The study organism was grown in 150 mL batch reactors in modified AD effluent at moderate light conditions to biomass concentrations of up to 1550 mg/L within 310 hours – nearly 3 times faster than in synthetic growing media. By enriching the headspace gas with carbon dioxide to simulate conditions of burnt biogas generated from anaerobic digestion, this biomass concentration was increased to 2230 mg/L within 282 hours. The experiment was repeated, comparing the growth in synthetic media and the optimised AD media in an eight-litre air-lift reactor. Keeping conditions conservative by performing the experiments in low light conditions with air bubbling instead of carbon dioxide enriched air (at a gas hold up of 10% of the total volume of the reactor), the experiment illustrated what growth could be expected at large scale production with minimal costly enhancements. Although both experiments were nutrient limited, higher biomass yields were observed for cyanobacteria grown in AD media (μmax = 0.018 hr-1). For batch experiments in 85% AD effluent enriched with inorganic carbon, total nitrogen was reduced by 90% and in the airlift reactor with atmospheric air bubbling, by 60% within 10 days.