###### Abstract  
The management of swine wastewater (SW) presents significant environmental challenges, requiring solutions that combine effective treatment with resource recovery. This study highlights the dual role of microalgae in wastewater remediation and bioenergy production. _H. rubescens_ KNUA214 was cultivated in media containing varying concentrations of diluted swine wastewater (DSW; 0%, 25%, 50%, and 100%). Cultivating with Blue Green-11 (BG-11) medium + 50% DSW maximized biomass growth, the chlorophyll content, and carotenoid production. Nutrient removal efficiency in 100% DSW over 8 days demonstrated reductions of 59.3% in total nitrogen, 67.7% in ammonia nitrogen, and 40.7% in total phosphorus, confirming the species' capacity for effective wastewater treatment. The carotenoid analysis using HPLC revealed that astaxanthin, lutein, canthaxanthin, and beta-carotene exhibited the highest levels in BG-11 + 50% DSW. Furthermore, the biomass analyses confirmed its potential for bioenergy applications, with high calorific values and significant polyunsaturated fatty acid concentrations, enhancing its utility for bioenergy and biolubricant production. These findings position _H. rubescens_ KNUA214 as an effective resource for integrating SW management with the sustainable production of high-value biochemicals, offering environmental and economic benefits. microalgae; swine wastewater; bioenergy; biolubricant; carotenoids +
Footnote †: journal: Applied sciences  
0000-0001-9313-3313  
and ability to thrive in diverse aquatic environments make them a sustainable alternative to terrestrial bioenergy crops; and they require less land and water resources, avoiding competition with food production [6; 7; 8; 9]. Furthermore, microalgae can be harnessed for bioremediation--removing pollutants from wastewater and converting them into valuable biomass, which can then be used for producing biofuels, high-value biochemicals, and nutraceuticals, demonstrating their multifaceted utility in sustainable industrial applications [10; 11; 12; 13]. Efforts to utilize microalgae in wastewater treatment have demonstrated their potential, not only for purifying water, but also for producing valuable biomass. Researchers have used microalgae to treat municipal, agricultural, and industrial wastewater [14; 15]. Microalgae utilize nutrients such as nitrogen (N) and phosphorus (P) from wastewater to grow, simultaneously reducing the pollutant load and recovering resources [16; 17; 18]. This dual functionality underscores the role of microalgae as a cornerstone in the sustainable management of water resources. Furthermore, the biomass generated from these systems has diverse applications, thereby increasing its utility and effectiveness across various sectors [19; 20; 21; 22] Microalgal biomass, which is rich in proteins, lipids, and carbohydrates, not only provides energy, but also serves as a valuable source for animal feed, dietary supplements, and the production of high-value compounds such as antioxidants, pigments, and essential fatty acids [23; 24; 25; 26]. Each application not only represents a step toward more sustainable production processes, but also aligns with the principles of a circular economy by turning waste into wealth. The diversity among microalgal species necessitates the continuous discovery and study of species-specific strains to match specific environmental or industrial needs. While some strains may be effective in nutrient removal or biomass production in lab-scale experiments using standard media, transitioning to real-world applications such as wastewater treatment introduces variables that can impact efficacy [27; 28]. Factors such as fluctuating nutrient concentrations and the presence of toxins in actual wastewater challenge the reproducibility observed in controlled environments [29]. This highlights the need for rigorous pilot and field testing to optimize algal strains, not just in laboratories, but also under practical conditions.