| Abstract |
Fire extinguishers are used to contain the imminent risk posed by fire globally. Suitable disposal and utilization of fire extinguisher powder (FEP) waste have developed into a significant challenge due to high nitrogen and phosphorus content. Harnessing the waste as a secondary resource for integrated waste-to-profit enterprises, such as microalgae cultivation for high-value bio-based products, is considered crucial for sustainable production, resource conservation, and mitigating adverse effects on environments. This paper proposes an algae-based circular economy concept to recycle one of the most difficult to treat wastes globally by applying it as a nutrient resource for microalgae biomass production. Hydrophilizing the waste for nutrient release is critical to this valorization pathway due to its hydrophobicity. Ten solvents were tested, of which five, including ethanol/methanol-sodium hydroxide mixtures, acetate, isopropanol, and polysorbate-20, were effective in hydrophilizing the powder waste, without significant differences (p < 0.05) in nutrients release (80 - 120 mg N-NH4+ gFEP(-1)). Highest biomass productivity (102.7 +/- 3.98 mgL(-1)d(-1)), NH4+-N uptake efficiency (58%), and biomass yield on PO43--P utilized (12.6 g phosphorus g(-1) biomass) were obtained with the most robust microalgal strain (Chlorella sp. MUR269) in isopropanol-based FEP medium under mixotrophic conditions. The inherent low nitrogen to phosphorus ratio (N:P < 1) is prohibitive for bioremediation purposes, creating room to utilize the waste as a phosphorus source. Microalgae performance in culture media in which phosphorus was replaced with FEP was generally similar to the control media (p > 0.05), except for Chaetoceros muelleri, which had 70% more biomass in control than in the waste medium. The protein and carbohydrate contents of Chlorella biomass cultivated in the waste were not significantly different, though significantly higher than carbohydrate (p < 0.001). FEP waste can act as nitrogen and/or phosphorus fertilizers for algal cultivation without significant growth inhibition. The resulting biomass can be valorized to high-value products such as pigments and animal/aquaculture feed due to more than 50% protein content if it meets permissible regulatory levels of contaminants. |