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.
