Application of Ulva biomass for bioremediation of wastewater
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Date
2024-04-18Embargo Date
2025-01-24
Author
Nelly, Alisha
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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.