A biorefinery approach to cultivating diatom thalassiosira Pseudonana on palm oil mill effluent-based media for multiproduct recovery / Karthick Murugan Palanisamy

Faculty of Industrial Sciences and Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang - 2026

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Microalgal biorefineries integrated with wastewater treatment provide a sustainable method for producing valuable products and cleaning up the environment. Conversely, traditional singleproduct extraction from diatom biomass destroys biomass and underutilizes important components. In this study, the indigenous marine diatom Thalassiosira pseudonana was isolated from Kuantan coastal waters and evaluated for biomass production using palm oil mill effluent (POME)-based media and following multi-product recovery from biomass by the cascade extraction method. Key cultivation parameters were optimized to improve productivity. The strain demonstrated strong adaptability to POME-based media, and the combination of 20% POME supplemented with F/2 medium produced the highest dry biomass production (0.74±0.07 g/L) among the investigated media formulations through response surface methodology. Growth profile analysis confirmed improved specific growth rate (0.317±0.0158 μ/day), biomass productivity (0.047±0.004 g/L/d), and doubling time (3.221±1.46), indicating efficient metabolic performance in effluent-based media. A sequential cascade extraction approach was developed to maximize biomass valorisation through stepwise recovery of pigments (0.14±0.015 g/g), lipids (30%), and biosilica frustules (13%). The optimized pigment extraction process achieved a recovery yield of up to 14%, with HPLC analysis confirming the presence of chlorophyll-a (747.85 μg/ml), chlorophyll-c (143.97 μg/ml), and fucoxanthin (284.94μg/ml). The post-pigment extracted biomass was further processed for lipid recovery. Solvent optimization (30.9±3.5%) and ultrasonication (30.3±1.5%) significantly enhanced cell disruption efficiency, improving lipid recovery. GC-MS confirmed the presence of key fatty acids, including palmitic acid (215.52±10.9 μg/μL), eicosapentaenoic acid (62.45±1.65 μg/μL), and docosahexaenoic acid (10.67±2.16 μg/μL). Whereas LC-QTOF quantifies the predominant C20:0 (10.61μg/mg), palmitoleic acid (12.25 μg/mg), and eicosapentaenoic acid (5.99μg/mg). Following lipid extraction, the residual biomass was processed for biosilica recovery to ensure the silica composition and a few organic residues. FTIR revealed a strong Si-O stretch was observed at a wavelength of 1089.04 cm-1 with a strong and sharp peak because silica is the dominant component in the cleaned frustules. XRD confirms the purity of silica in frustule by high intensity with sharp peaks found at 2θ ≈ 26.63°. The FESEM EDX confirms the presence of silicon (45.50%) and oxygen (34.67%), and the primary elements. Thus, cascade biorefineries increase recovery efficiency over traditional techniques by allowing full biomass usage and minimizing waste production. Overall, the cascade biorefinery approach enhanced recovery efficiency by maximizing biomass utilization and minimizing waste. Additionally, cultivation in POME-based media enabled simultaneous biomass production and wastewater nutrient removal, supporting environmental sustainability and circular bioeconomy development.