Sustainable carotenoid production and agro-industrial wastewater remediation by Rhodotorula sp. through nutrient supplementation

Cassava wastewater (CW), a byproduct of cassava starch processing, contains substantial amounts of organic matter, nitrogen, phosphorus and various essential minerals, making it a promising low-cost substrate for microbial cultivation. Rhodotorula species, classified as red yeasts, are recognised for biosynthesising carotenoids with significant biological functions, including provitamin A activity, antioxidant properties and potential anticancer effects. These compounds have wide-ranging applications in food, pharmaceutical and cosmetic industries. This study tested the hypothesis that nutrient supplementation enhances carotenoid production in Rhodotorula sp . TISTR 5089 was cultivated in CW. Batch cultivation was conducted under controlled conditions (initial pH 5.0, 150 rpm, 30°C) for 168 h. The effects of various nitrogen sources, including ammonium sulphate, yeast extract and urea, at concentrations ranging from 1.13 to 4.55 g/L, selected based on preliminary optimization experiments, were systematically evaluated in combination with macro- and microelement supplementation. The highest biomass production (11.22±0.11 g/L) and carotenoid yield (1,262.03±10.48 μ g/L) were obtained when the medium was supplemented with 2.27 g/L urea and microelements. High-performance liquid chromatography analysis revealed that the predominant carotenoids produced were β -carotene, γ -carotene, torulene, torularhodin and lycopene. Additionally, the cultivation process achieved a 62.92% reduction in chemical oxygen demand, indicating effective organic pollutant removal. These findings demonstrate the dual advantage of this bioprocess: sustainable production of high-value carotenoids and simultaneous bioremediation of agro-industrial wastewater. The use of CW as a fermentation medium offers a viable, eco-friendly approach for circular bioeconomy applications, particularly in regions with abundant cassava starch processing industries. • Cassava wastewater was valorized as a low-cost medium for Rhodotorula sp. cultivation. • Urea at 2.27 g/L with microelements enhanced carotenoid yield to 1,262.03 μ g/L. • Rhodotorula sp. produced β -carotene, γ -carotene, torulene, torularhodin, and lycopene. • Carotenoid production reduced COD in cassava wastewater by 62.92%. • This process integrates wastewater treatment with carotenoid bioproduction sustainably supporting the circular bioeconomy and advancing SDGs.