Bio-removal and Detoxification of Congo Red Dye in Aqueous Solutions by Using a Sustainable Biosorbent from Robinia pseudoacacia L.

Synthetic dyes cause serious damage to the environment. If synthetic dyes are discharged without treatment, they become a serious environmental problem in aquatic ecosystems. The present study aimed to bio-remove Congo red (CR) from aqueous solutions using Robinia pseudoacacia L. fruit (RPF) biosorbent from aqueous solutions via a biosorption process. Optimization studies were conducted on the biosorption parameters, including stirring speed, temperature, pH, contact time, initial CR dye concentration, zero charge point (pHpzc), and biosorbent dosage. As a result, it was observed that 80% CR was removed from aqueous solutions using RPF biosorbent under optimum conditions (temperature: 303 K, stirring speed: 150 rpm, pH: 6, biosorbent dose: 1 g, contact time: 30 min, and initial CR dye concentration: 10 mg/L). For kinetic studies, the R2 value (R2 = 0.999) of the pseudo-second-order kinetic model was a better fit than the R2 value (R2 = 0.976) of the pseudo-first-order kinetic model. The R2 value of the Langmuir isotherm was 0.997, and the Langmuir isotherm model best fitted the R2 values of the Freundlich (R2 = 0.976), Elovich (R2 = 0.952), and Temkin (R2 = 0.993) isotherm models. Because ∆G˚ values (-3.41, -4.5, -5.59 and -6.68 kJ/mol) were calculated as negative in thermodynamic studies, the biosorption process occurred spontaneously. Moreover, detoxification studies revealed significant recovery of anatomical and physiological parameters in A. cepa and B. oleracea var. acephala after RPF biosorbent treatment. The germination rate of B. oleracea var. acephala seeds decreased to 40% with increasing CR concentrations. Moreover, significant decreases were observed in the fresh weight (0.46 g), dry weight (0.064 g), root length (1.16 cm), and shoot length (1.36 cm). Consequently, the present study highlights the effective treatment, low-cost, and eco-friendly potential of RPF biosorbents for the removal of CR from aqueous solutions.