Continuous Fixed-Bed Adsorption of Heavy Metals Using Biodegradable Adsorbent: Modeling and Experimental Study

In this study, a continuous fixed-bed column was investigated for heavy metal removal using modified wheat bran as adsorbent. Clay and chitosan were used as binders with the adsorbent to prepare adsorbent pellets in a $1:1:3$ ($\mathrm{clay}:\mathrm{chitosan}:\mathrm{adsorbent}$) ratio by weight. Clay and chitosan provide adhesiveness and mechanical strength to the pellet. The scanning electron microscopy analysis–energy dispersive X-ray spectroscopy (SEM-EDS) analysis confirms the adsorption of copper, chromium, and cadmium in the adsorbent pellet. The fixed bed was operated at a pH of 6 and temperature of 35°C for heavy metal removal. A mathematical model was prepared for continuous column and then experiments were carried out with various parameters such as bed height (0.15–0.45 m), initial concentration ($100–500\mathrm{mg}/\mathrm{L}$), and flow rate ($5–15\mathrm{mL}/\min$). The removal order for heavy metals follows $\mathrm{Cr}>\mathrm{Cu}>\mathrm{Cd}$. The optimum conditions obtained were a flow rate $5\mathrm{mL}/\min$, bed height of 0.45 m, and initial concentration of $100\mathrm{mg}/\mathrm{L}$. The breakthrough curve obtained from experimental data was compared with the curve obtained from the model. It was found that the prepared adsorbent pellets were efficient at removing heavy metals. The developed mathematical model could predict column behavior with desirable accuracy. Further, high $R^2$, low chi-squared, and mean absolute percentage error (MAPE) values of up to 0.999, 0.025%, and 0.378%, respectively, indicate that model and experimental data were well fitted.