Bioremoval of the azo dye Congo Red by the microalga Chlorella vulgaris

Discharge of dye-containing wastewater by the textile industry can adversely affect aquatic ecosystems and human health. Bioremoval is an alternative to industrial processes for detoxifying water contaminated with dyes. In this work, active and inactive biomass of the microalga Chlorella vulgaris was assayed for the ability to remove Congo Red (CR) dye from aqueous solutions. Through biosorption and biodegradation processes, Chlorella vulgaris was able to remove 83 and 58% of dye at concentrations of 5 and 25 mg L⁻¹, respectively. The maximum adsorption capacity at equilibrium was 200 mg g⁻¹. The Langmuir model best described the experimental equilibrium data. The acute toxicity test (48 h) with two species of cladocerans indicated that the toxicity of the dye in the effluent was significantly decreased compared to the initial concentrations in the influent. Daphnia magna was the species less sensitive to dye (EC₅₀= 17.0 mg L⁻¹), followed by Ceriodaphnia dubia (EC₅₀= 3.32 mg L⁻¹). These results show that Chlorella vulgaris significantly reduced the dye concentration and toxicity. Therefore, this method may be a viable option for the treatment of this type of effluent.