Factorial design analysis for biosorption of Reactive Red-84 dye using fermentation spent waste biomass, biosorbent regeneration and desorbed dye photo-degradation using TiO2 nanoparticles

Abstract

In this work, factorial design analysis based on central composite design of experiments was employed to study the effect of process parameters for biosorption of Reactive Red-84 dye onto bioethanol fermentation spent waste biomass of Saccharomyces cerevisiae. Factorial experiments with five factors: mixing rate rpm, incubation period h, process temperature °C, initial dye concentration mg/L and biosorbent dosage wt% (w/v) at three levels were conducted. A highly statistically significant quadratic model at 95% confidence level (p < 0.0001, R2 0.9120 and Radj2 0.8519) was developed to charcterize the influence of the different considered variables on biosorption efficiency. Response surface methodology was employed to optimize the process, recording maximum biosorption % of ≈62% (51.67 mg/g) at 90 rpm, 13 h, 15°C, 100 mg/L and 0.6%, respectively. Approximately 95% of adsorbed dye was desorbed by elution with NaOH solution of pH 9 and the regenerated biosorbent was employed for four successive cycles. TiO2 nanoparticles 6–15 nm were prepared and used for photo-catalytic degradation of desorbed dye solution. The proposed integrating biosorption and photo-catalytic degradation process results in no secondary pollution in the form of any concentrated wastes, which is an important environmental aspect.