Application of Ulva biomass for bioremediation of wastewater
Nelly, Alisha
Nelly, Alisha
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Publication Date
2024-04-18
Type
Thesis
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Abstract
The remarkable growth rate and environmental adaptability of Ulva species have attracted considerable interest for their potential applications in aquaculture and bioremediation. Ulva's capacity to absorb nutrients from various wastewaters, including those originating from the dairy industry, positions it as a promising solution for addressing soluble contaminants. To identify Ulva strains with enhanced tolerance to low salinity to support applications with typical terrestrial wastewater streams, a series of laboratory and pilot scale experiments were performed. These experiments involved the co-cultivation of multiple strains from three distinct Ulva species(Ulva lacinulata, Ulva gigantea and Ulva compressa) under different conditions, encompassing varying salinity levels (17.5 PPT and 35 PPT salinity) and diverse wastewater sources. Waters tested included Final Effluent (FEF) water (treated water ready for release downstream), reverse osmosis reject (RO) water (by-product of reverse osmosis process containing concentrated impurities (high nitrate levels) which of often used for treatment of fats), river water (water from River Deel running parallel to factory), balance water (raw sewage which has undergone pH alteration and fat removal) and filtered balance water (balance water filtered to reduce turbidity). The findings from these experiments revealed that filtered balance water supported superior growth rates compared to unfiltered balance water. The co-cultivation studies highlights the strain-specific nature of Ulva's tolerance to low salinity, with certain strains exhibiting higher growth and survival rates under specific conditions. The investigation unveiled fluctuations in the characteristics of FEF water as growth media over a seven-day period. The presence of precipitate (identified as aragonite, a crystal form of CaCO3) on Ulva biomass cultivated in FEF and ASW (Artificial Seawater) dilution was associated with diminished growth and nutrient uptake, emphasizing the intricate relationship between environmental factors and Ulva's growth dynamics. Additionally, the study demonstrated that while FEF water alone did not sustain Ulva growth, the supplementation of F/2 nutrients to FEF water resulted in enhanced growth rates compared to F/2 + ASW alone, which also facilitated a prolonged selection process, allowing for the coexistence of multiple Ulva species. The final aspect of the project focused on the outdoor cultivation trials of the best performing Ulva species (Ulva lacinulata), coupled with detailed biochemical analyses, to elucidate the impact of growth conditions on biomass quality. The results indicated that a density of 2 g/L was excessive for outdoor Ulva cultivation, leading to self-shading and reduced growth rates. Reducing the density to 1 g/L resulted in improved growth performance, suggesting its suitability for outdoor cultivation under optimal conditions. The addition of river water failed to mitigate the formation of precipitate on Ulva biomass when combined with FEF or RO water. Metabolite analysis revealed variations in ash and ulvan content in Ulva cultivated in RO + FEF + river water. Ulva grown in river water exhibits higher ulvan and lower protein content, consistent with the low nitrate levels in river water. Although river water alone did not support Ulva growth due to its low nitrate content, continuous water flow was identified as a potential factor that could enhance Ulva cultivation in such conditions. To conclude, this project shows that wastewater type, time of collection, salinity and strain of Ulva all play important roles in the use of Ulva for bioremediation. Indicating the potential of Ulva spp. in bioremediation of dairy factory effluent. Moreover, conducting additional trials has potential to develop a reliable treatment protocol, capable of not only remedying polluted waters but also generating valuable compounds for diverse downstream applications.
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NUI Galway