Activation of spent coffee grounds for the recovery of phenolic compounds from olive mill wastewater

Olive oil processing generates substantial quantities of olive mill wastewater (OMW). While numerous strategies have been applied for treating OMW, achieving efficient phenol removal remains a challenge. Coffee production also yields large volumes of residues; therefore, this study investigates the prospective application of spent coffee grounds (SCG) as an economical and sustainable biosorbent for OMW treatment. Building on earlier work using untreated SCG, the current study evaluates how physical and chemical (methanol, sodium hydroxide) activation affects its adsorption performance. In addition, a new activation method based on coating with a natural agent, milk proteins, was studied. Findings indicate that SCG activation notably enhances its adsorption capacity. The most pronounced increase in adsorption efficiency was observed following thermal activation of SCG at 250 o C. All chemical activation methods led to improved adsorption performance, achieving adsorption efficiencies of up to 60%. Adsorption enhancement was linked to modifications in the SCG surface structure and functional groups. The research contributes novel insight into eco-friendly biosorbent development, highlighting milk protein-coated SCG as a “green” alternative to conventional activation techniques. The above findings support the design of sustainable and cost-efficient approaches for the treatment of phenol-rich effluents such as OMW. • Spent coffee grounds (SCG) were thermally and chemically activated to be used as sorbent. • The surface modifications of activated SCG were examined. • The alterations in the chemical groups and bonding arrangements within the spectra of both raw and activated SCG were investigated. • The achieved change of adsorption efficiency was correlated with modifications in the physicochemical characteristics of SCG.