Sustainable heavy metal removal: optimization of adsorption onto oxidized brewery spent grains via response surface methodology

Abstract

Using inexpensive, sustainable adsorbents, including industrial agricultural waste, to remove heavy metals from wastewater treatment is of great interest, as it presents a major environmental problem. The adsorption capacity of brewery-spent grains (BSG) for copper(II) ions (Cu(II)) was examined in this study and was found to increase by oxidation (O@BSG) from 32.51 to 74.48 mg g⁻¹. The adsorption process was optimized using the Box-Behnken design (BBD), and the highest adsorption capacity (30.21 mg g⁻¹) was obtained at pH 5.57, 22.44 mg O@BSG, and 156.98 mg L⁻¹ initial Cu(II) ion concentration. A quadratic mathematical model was formulated to predict the responses. The analysis of variance (ANOVA) demonstrated a significant impact of pH on the adsorption of Cu(II) ions. The models that best describe the adsorption process were pseudo-second-order kinetics and the Langmuir isotherm model. The monolayer adsorption capacity was 69.26 mg g⁻¹. The thermodynamic analysis indicated that the process is spontaneous and endothermic, as well as an increase in disorder at the solid-liquid interface. In conclusion, O@BSG was shown to have significant potential as an economical, efficient, and sustainable adsorbent for Cu(II) removal.