AC/SC – Back in black: Spent Coffee Grounds for the Removal of Critical Emerging Contaminants from Water

The new Urban Wastewater Treatment Directive (UWWTD) was published by the European Union in December 2024. It increases the importance of activated carbon (AC) significantly, as it is one method of implementing a fourth treatment step in wastewater treatment plants. Commercially available AC is typically produced using peat or lignite, coconut shells, wood or fruit stones.
AC precursors that are less influenced by natural availability, production processes using other biomasses become increasingly necessary. Spent coffee grounds is an abundant waste material due to the heavy global coffee consumption. In 2022/2023 about 11 million kilotons of spent coffee grounds (SC) worldwide.
Typically, AC production involves physical or chemical activation prior, during or after heat treatment. While the first method usually uses steam or CO₂ atmospheres during heat treatment, the latter one uses harsh chemicals like ZnCl₂ or KOH to open up the porous structures of the precursors.
We present a way of combining both physical and chemical activation in a one-step synthesis using carbonate salts as activating reagents. The resulting ACs show different types of porosities depending on the carbonate salt being used.
In pilot projects the adsorption properties of the generated ACs were tested on the CECs methylene blue (cationic) and methyl orange (anionic) which are applied both in textile and pharmaceutical industries. Additionally, tetracycline as a broadband antibiotic, diclofenac as a popular pain medication and the endocrinic disruptor bisphenol-A, commonly used in polymer industries, were used as model CECs.
Depending on the carbonate salts used, each material shows different adsorption behavior in single-contaminant adsorption experiments, as well as in mixtures of all five CECs. Overall, the adsorption properties were acceptable and comparable to those of conventionally activated spent coffee grounds.