Valorization of different agricultural wastes for yeast based Reactive Black 5 bioaccumulation

The textile industry generates large volumes of dye-laden effluents that pose risks to aquatic ecosystems and human health. This study evaluates the bioaccumulation of Reactive Black 5 (RB5) using Candida boidinii and Kluyveromyces marxianus yeast strains. Key operational parameters including initial pH, incubation time, dye concentration, and microbial growth were systematically investigated. In addition, the effects of low-cost agricultural wastes-carrot pomace (CP), industrial tea waste (ITW), and pumpkin pomace (PP)-as supplementary substrates were compared. Results showed that CP was the most effective substrate, with 100 g/L CP significantly enhancing RB5 removal. At pH 5.0 and 50 mg/L RB5, removal efficiencies reached 96.88% for C. boidinii and 81.76% for K. marxianus with CP, compared to 72.90% and 65.07% with PP. Although removal efficiency decreased at higher dye concentrations, the maximum dye uptake capacity (q_m) increased with initial RB5 concentration, reaching 52.52 mg/g for C. boidinii and 33.23 mg/g for K. marxianus over the tested range (≈50-600 mg/L). To our knowledge, this is the first report demonstrating RB5 removal by these yeasts using CP as a low-cost substrate. Overall, CP significantly improves yeast-based RB5 bioaccumulation and represents a promising, sustainable option for treating dye-contaminated wastewater.