Consecutive adsorption and ozonation treatment of real coffee processing wastewater with coffee husk adsorbent—a circular approach

Coffee processing waste is a significant source of environmental pollution, as coffee is one of the most merchandised commodities worldwide. Coffee processing generates substantial volumes of solid and liquid waste, and its management is complex. Various physical, chemical, and biological methods were explored for treating coffee processing wastewater (CPWW), but most have failed to achieve optimal performance. This study provides new insights into an integrated approach for treating real CPWW by combining batch adsorption with ozonation. This study utilises a circular approach, in which CPWW is treated using coffee husk (CH) waste produced from the same industry as an adsorbent. The design of experiments was carried out using the response surface methodology tool, central composite design, with the operational parameters being contact time and adsorbent dosage. Maximum efficiency was obtained at 120 min and an adsorbent dosage of 5 g, with 54.9% COD and 66.6% color removal. Furthermore, the pseudo-first-order, pseudo-second-order, Weber-Morris intraparticle diffusion, Elovich model and Bangham’s pore diffusion kinetic models were applied to fit the experimental results among which pseudo-second order kinetics was obtained as the best-fitted model. Ozonation experiments were performed after adsorption, for 120 min at an ozone dosage of 15 g/h. The degradation of pollutants by ozonation proceeded through direct molecular ozone and indirect hydroxyl radical oxidation, achieving 82.3% COD and 93.7% color removal. Based on the results, coupling these processes achieves significantly higher removal efficiencies for COD and color. The environmental implications of the study were examined, providing a sustainable solution for CPWW treatment.