Use of brewery spent grains as a biosorbent for reactive blue 5G dye removal: batch and continuous flow studies

Abstract

The biosorption of the Reactive Blue 5 G dye (RB5G) in batch and continuous flow systems was investigated using brewery spent grains (BSG) as a biosorbent. The biosorbent was characterized by the point of zero charge, scanning electron microscopy, Fourier transforms infrared, and N₂ adsorption/desorption. A rotational central composite design was used in the batch biosorption studies. This design generated a model with a determination coefficient of 0.98. The design results showed that the removal of the dye was favored by the increase in temperature and the pH and mean particle diameter reduction. Equilibrium was reached after 24 h, achieving a dye removal of approximately 94.5%. Batch biosorption data fitted better to the pseudo-second-order kinetics and Langmuir isothermal model, indicating the prevalence of chemical biosorption. The maximum biosorption capacity achieved was 83.42 mg g⁻¹. Considering the continuous flow system, a better biosorption column performance was found for the flow rate of 2 mL min⁻¹ associated with 4 g of biosorbent mass. The equilibrium data for the fixed bed column showed a good fit for both Langmuir and Freundlich models, which may suggest the coexistence of chemical and physical biosorption. The maximum removal capacity was 74.10 mg g⁻¹. The column performance was maintained for both low and high fed dye concentrations. In general, the BSG achieved good results for the biosorption of the RB5G, representing an alternative to remove this dye from textile effluents and also for the destination of this abundant biomass.

Keywords:

• Biosorption isotherm and kinetic
• brewery spent grains
• fixed-bed column biosorption
• reactive blue 5G dye
• response surface

Acknowledgments

The authors would like to acknowledge the financial support of the Higher Education Personnel Improvement Coordination (CAPES) and the National Council for Scientific and Technological Development (CNPq). Support was of fundamental importance for the development of this work.