BIODEGRADATION OF RHODAMINE-B TEXTILE DYE USING CYANOBACTERIA UNDER OLIGOTROPHIC CONDITIONS

Abstract

The persistence and resistance of Rhodamine-B and other analogous synthetic dyes in aquatic ecosystems are a cause of serious environmental and public health concern. Their persistence against degradation by conventional wastewater treatment methods urges the pursuit of new, environmentally friendly alternatives. The present study investigated the potential of a filamentous cyanobacterial strain, CB4, isolated from a freshwater body in Sri Lanka, to degrade Rhodamine-B under oligotrophic (nutrient-deprived) conditions. A 10 ppm of Rhodamine-B solution was inoculated with 6 mL of CB4 culture in the exponential phase and incubated at room temperature under light illumination of 2000–3000 lux for 28 days. The medium was not supplemented with any nutrients, simulating indigenous effluent conditions. Decolourization was quantified spectrophotometrically at 563 nm, while growth was measured at 680 nm. Although the dye received a lower decolourization efficiency (6.16%), CB4 exhibited a good adaptability to the dye medium with 89.81% growth efficiency and 10 mg/day biomass accumulation. High-Performance Liquid Chromatography (HPLC) analysis revealed a 10.26% reduction of peak area compared to the control, implicating partial degradation of Rhodamine-B. The phytotoxicity assay using green gram (Vigna radiata) seedlings revealed enhanced mean shoot and root lengths in the CB4-treated sample (9.65 cm and 9.92 cm, respectively), compared to the untreated control. These findings demonstrate that CB4 can tolerate and bring about partial biodegradation of Rhodamine-B under oligotrophic conditions. Despite incomplete decolourization, the reduction of phytotoxicity and detectable dye degradation highlighted CB4 as a promising candidate for low-cost, sustainable bioremediation of dye-contaminated textile wastewater.