Single and combined treatment processes for rhodamine B removal by coagulation–flocculation and adsorption

In this paper, two physico-chemical methods were adopted for the removal of rhodamine B from aqueous solutions. The first one is the adsorption process using biochar derived from olive stones (OSB). Results demonstrated that the removal efficiency reached 97.79% within an equilibrium time of one hour. It was observed that the pH had no significant effect on the degradation of rhodamine B by OSB. The adsorption process was characterized by the endothermic nature, spontaneity, favorability, and disorder at the solid-liquid interface. Langmuir isotherm analysis revealed a maximum adsorption capacity of 11.82 mg g^-1, and the prepared biochar could be reused for up to four cycles. For the second method, coagulation-flocculation using FeCl₃ as a coagulant was investigated. The findings displayed that an increase in the dosage of FeCl₃ enhanced the degradation process, with the best performance registered at a dose of 2000 mg L^-1 of FeCl₃. The optimum pH for this process was found to be 2. A combination approach by these two methods, starting with coagulation-flocculation and followed by adsorption, was also investigated. The results showed that the combined approach improved the removal performance compared to each process alone, with minimal doses of both coagulant and adsorbent. Thus, the combination of these two physico-chemical processes allows benefits from the advantages and reduces the disadvantages of each individual method.