Battershill, ChristopherCraggs, RupertGavin, ChanelleGauss, ChristianJayasooriya, Nethmie2025-01-072025-01-072024-07-17https://hdl.handle.net/10289/17108Upgrading and maintaining large-scale wastewater treatment plants (WWTPs) is notably expensive, particularly in rural areas of New Zealand. Freshwater macroalgae ponds may offer a cost-effective alternative for wastewater treatment in these areas. These ponds produce significant amounts of residual macroalgae biomass as a by-product of the bioremediation process, which is nutrient-rich and contains valuable biopolymers like cellulose. Utilizing this residual biomass as a substrate for high-value cellulose production is yet to be demonstrated. Therefore, this thesis investigated the potential of utilizing this residual freshwater macroalgae biomass to develop bioproducts (cellulose and biostimulants) aligning with the principles of a circular economy and waste recovery. The first chapter investigated the dual extraction process of biostimulants and high-purity cellulose from Oedogonium calcareum grown in primary effluent. It introduces an economical and effective extraction method utilizing a hot alkali, which also provides disinfection, ensuring that the biomass is free from pathogens, making it safe for further use. The biostimulant extract was found to be comprised of several plant-promoting substances. Subsequently, the residual biomass was used to extract cellulose, and the quality of this Oedogonium-derived cellulose was assessed to determine its characteristics for potential future use in biocomposites. In the second chapter, a comparative analysis was conducted on cellulose extracted from four macroalgae species, namely Rhizoclonium sp., Zygnema sp., Oedogonium sp., and Stigeoclonium sp. This research filled a significant gap by providing a detailed characterization of cellulose derived from freshwater macroalgae, which has been less studied compared to cellulose from marine macroalgae. This chapter makes a significant contribution by fully characterizing the physicochemical properties of freshwater macroalgae cellulose, which as a by-product of wastewater treatment, provides an alternative and sustainable source of cellulose with potential future applications in biocomposites. The final chapter details the development of biocomposite films using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) reinforced with cellulose nanofibers derived from a naturally co-existing mixed algae culture of Cladophora sp. and Rhizoclonium sp. The production and characterization of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-oxidized Cellulose NanoFibre (CNF) from these macroalgae was accessed. Additionally, PHBV polymer biocomposite films incorporating either commercially available plant-derived CNF, unmodified algae cellulose, or TEMPO-oxidized CNF were compared. The films were comprehensively characterized, with a focus on their mechanical and thermal properties. The results demonstrated the potential of these biocomposite films for use in applications such as packaging materials, highlighting their environmental and functional benefits. Overall, this thesis demonstrates significant advancements in the utilization of algae grown in wastewater for the successful extraction of bioproducts. It investigated the efficient recovery and application of macroalgae-derived cellulose and also highlighted the potential of these bio-based materials in enhancing the properties of the PHBV polymer, thus contributing to the development of sustainable biocomposite materials.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.cellulosenanocellulosemacroalgaebioproductsthermoplastic polymersThesis