Olive stones have been widely used as a renewable energy biowaste source. As they are rich in elemental carbon (40–45 wt%), much research focussed on effectively converting olive stones, as precursors, into activated carbon adsorbents. However, only a few studies have concentrated on summarising the various techniques used to produce activated carbon from olive stone. This article reviews the research undertaken on the production and application of activated carbon as an adsorbent from olive stones for wastewater treatment. Various physical, chemical and physico-chemical treatments to remove heavy metals, organics and dyes are discussed, and the resultant adsorption capacities are reported. In several cases, very high adsorption capacities are recorded. Finally, the future prospects of these materials as adsorbents are discussed, and after further development work, olive stone-derived activated carbons have great potential especially in the area of organic polluted wastewaters. Activation process of olive stone Graphical abstract

This study investigates the production of high-performance activated carbon (AC) from coconut shells (CS) through acid and base activation processes, along with pre- and post-functionalization of the biochar, aiming to effectively remove dyes from aqueous solutions. The resulting AC exhibited outstanding adsorption capabilities, with the Langmuir model providing a good fit to the experimental data. Maximum adsorption capacities were observed at different temperatures: 805 mg g⁻¹ at 298 K, 904 mg g⁻¹ at 318 K, and 1000 mg g⁻¹ at 338 K for NaOH-activated AC, and 252 mg g⁻¹ at 298 K, 295 mg g⁻¹ at 318 K, and 305 mg g⁻¹ at 338 K for H₂SO₄-activated AC. The presence of active sites and functional groups on the surface of AC facilitated dye adsorption. The influence of various parameters, including adsorbent dosage, dye concentration, pH, and temperature, on the adsorption process were also examined, identifying the ideal conditions for dye removal. Thermodynamic analysis confirmed the endothermic nature of the adsorption process, with higher temperatures leading to increased adsorption capacities. Overall, the research highlights the potential of various activation routes for the production of high-value AC as a sustainable and effective adsorbent for dye removal from wastewater.

The study provides a review of various applications of biomass-derived biochars, waste-derived biochars, and modified biochars as adsorbent materials for removing dyestuff from process effluents. Processing significant amounts of dye effluent discharges into receiving waters can supply major benefits to countries which are affected by the water crisis and anticipated future stress in many areas in the world. When compared to most conventional adsorbents, biochars can provide an economically attractive solution. In comparison to many other textile effluent treatment processes, adsorption technology provides an economic, easily managed, and highly effective treatment option. Several tabulated data values are provided that summarize the main characteristics of various biochar adsorbents according to their ability to remove dyestuffs from wastewaters.