A comprehensive review of coffee waste based adsorbents for the sequestration of different water contaminants

Currently, the presence of different contaminants like heavy metals, dyes, pharmaceutical waste, pesticides, etc. in water is problematic due to their toxic and carcinogenic nature. Among the various remediation processes, the adsorption process is attractive and efficient. Every year, more than 6 million tons of coffee are grown worldwide, and 0.68 tons of coffee waste are produced for every ton of coffee. Coffee waste is remarkable in wastewater treatment because (i) it has a porous surface, (ii) it contains a cellulose, hemicellulose, and lignin structure that can provide abundant functional groups, and (iii) it is recyclable. Reusing it not only reduces processing costs but also supports environmentally sustainable development. This review focuses on the application of coffee waste adsorbents in the removal of pollutants from wastewater. Physical, chemical, and composite modification methods of coffee waste have been discussed. The modified adsorbents have great enhancement in functional groups, surface active sites, pore properties, catalytic degradation ability, easy separation, and excellent capacity to adsorb different contaminants. Important elements influencing the adsorption process are also discussed, including the impact of solution pH, contact time, temperature, and adsorbent dosage.