Co-pyrolysis of spent coffee grounds with carbonates towards activated biochars for wastewater treatment

The ongoing climate change is leading to an increase in extreme weather events such as droughts and floods, significantly affecting water availability and quality worldwide. According to UNESCO, approximately 80% of global wastewater is currently discharged into the environment without prior treatment, posing a growing threat to human health and ecosystems. Even in regions with advanced water treatment infrastructure, such as Europe, concentrations of pollutants are rising in surface and groundwater. In Germany, about 70% of drinking water is sourced from groundwater, which is increasingly contaminated with residues of pharmaceuticals, pesticides, and other pollutants. Activated carbon (AC) has proven to be an efficient material in water treatment removing such contaminants. Due to its large surface areas and possible surface functionalities it can be used as an adsorbent filtering out pollutants of all kinds. Common industrial sources of AC at this point are coconut shells, peat and coal or wood wastes. With the increasing demand of materials for water treatment, other raw materials for AC production are gaining interest, especially raw materials aiming at more ecological and economical sustainable AC synthesis routes. As of 2025, most syntheses of AC out of biowaste materials include harsh chemical pretreatments prior to heat treatment, the so called pyrolysis, to achieve large surface areas and good adsorption properties. To explore more sustainable and eco-friendly synthesis routes, this study investigates the use of spent coffee grounds (SCG) as a precursor for AC production. While coffee is grown in only a few regions world-wide, it is consumed in large amounts all over the world, producing tremendous amounts of spent coffee grounds along the way. Hence, SCG are locally available and abundant. For activating reagents different types of carbonate salts have been selected. Industrial calcium carbonate (CaCO3), but also from biogenic resources of egg and mussel shells, as well as magnesium carbonate (MgCO3) and zinc carbonate (ZnCO3) influence the material properties in different ways each. In total five different materials are introduced. They are thoroughly characterized via N2-sorption, powder-X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), infrared (IR) and Raman spectroscopy and point of zero charge (PZC) measurements. The adsorption performance of the materials is evaluated using five representative water pollutants: The organic dyes methylene blue (MB) and methyl orange (MO), the pharmaceuticals diclofenac (DCF) and tetracycline (TET), and the plasticizer bisphenol-A (BPA). All of them present a hazard when left untreated and increasing in concentrations not only towards the environment but towards humans as well. This thesis examines their adsorption behaviors at different solution-pH as well as their kinetics. Additionally, competitive adsorption behaviors in mixed solutions of all contaminants are studied in deionized (d.i.) water and laboratory tap water (LW). Single-solute systems are analyzed via ultraviolet/visible light (UV/Vis) spectroscopy. High-performance liquid chromatography (HPLC) coupled with UV/VIs spectroscopy and mass spectrometry is applied on mixed solutions with multiple pollutants. The results demonstrate that SCG-derived activated carbons activated with carbonate salts offer promising potential for sustainable water purification applications. The materials show adsorption performances comparable to classically activated materials.