Valorization of residual ashes from boiler combustion process into activated carbon for adsorption of food industry wastewater

This study investigated the production of renewable activated carbon derived from residual ashes generated during the boiler combustion process for the treatment of food industry wastewater. The chemical modification of ashes into activated carbon was optimized using potassium hydroxide, phosphoric acid, and nitric acid. The results indicated that the adsorbent synthesized with phosphoric acid exhibited the best performance in removing indigo carmine dye, achieving 98% removal rate when using the adsorbent at a concentration of 0.5 g L⁻¹, with an average particle diameter of 0.088 mm. The surface area increased from 120.3 to 605.1 m² g⁻¹ with phosphoric acid activation, resulting in a high-quality adsorbent with a capacity for reuse up to four times. The Redlich–Peterson isotherm model provided the best fit for experimental data on indigo carmine dye adsorption, with a maximum adsorption capacity of approximately 100 mg g⁻¹ according to the Langmuir model. In the treatment of food industry wastewater (cheese whey), the adsorbent reduced the lactose content (32.45%), turbidity (62.92%), BOD₅ (90.48%), and COD (93.07%). The removal of these adsorbates from cheese whey effluent reduced the organic load of cheese whey, enabling the water reuse within the food industry. In conclusion, activated carbon produced from residual ashes can be considered as a sustainable alternative for treating food industry effluents, advocating water reuse.