The potential of Nannochloropsis sp. in a waste-to-resource system: bioremediation of contaminants of emerging concern and biomass valorisation

Contaminants of emerging concern (CECs) are chemicals or biological agents of increasing awareness due to their potential risks to the environment and human health. Paracetamol (PAR), Methylparaben (MP), Imidacloprid (IMID), Bisphenol A (BPA), Triclosan (TCS) and Ibuprofen (IBU) are part of that group and require effective removal strategies to reduce their concentration in wastewater. Nannochloropsis sp., a marine microalgae, have demonstrated bioremediation ability. In addition, its biomass is rich in valuable biomolecules and can accumulate valuable polymers such as cellulose and polyhydroxibutirate with biotechnological interest. In this context, the potential of Nannochloropsis sp. to be a part of a waste-to-resource system was studied. First, a RP-HPLC method was successfully developed and validated to quantify the six CECs in the context of microalgae bioremediation. The bioremediation studies demonstrated the viability of the Nannochloropsis sp. culture system to effectively remove the mixture of contaminants at an initial concentration of 10 μg mL-1, with removals of 22.05 ± 5.61, 72.62 ± 12.06, 14.01 ± 4.31, 84.51 ± 5.98 and 45.72 ± 13.28% for PAR, MP, IMID, BPA and IBU, respectively. Results were inconclusive for TCS. Removal strategies were assessed. Abiotic factors had a major role in the removal of MP, IMID, BPA and IBU, and microalgae bioremediation was mostly relevant for removing PAR. The culture medium enhanced photodegradation through the formation of reactive species. The growth of Nannochloropsis sp. was inhibited in the presence of the mixture at higher concentrations, even with high inoculum density. Individual experiments demonstrated that IBU was the most toxic pollutant to the microalgae. The biomass valorization was assessed by exploring the extraction of the under- researched biopolymers from microalgae: cellulose and polyhydroxibutirate (PHB). Cellulose was extracted using a biorefinery approach. Fourier-transmission infrared (FTIR) analysis suggested the presence of the cellulose polymer. The extraction of PHB was successfully performed for the first time from Nannochloropsis sp., as far as known, as suggested by the analytic methods. In this dissertation, the microalgae Nannochloropsis sp. demonstrated the potential to integrate a waste-to-resource system, through its efficiency in removing CECs from wastewater, and additionally, through its ability to produce biopolymers for future utilization as biomaterials, with biotechnological interest.