Chromium Removal from Electroplating Wastewater Using Activated Coffee Husk Carbon

Abstract

Chromium (Cr) is a heavy metal that has a serious environmental pollution problem. Electroplating wastewater contains high level of Cr that surpassed the acceptable environmental discharge standard limit in surface water bodies and causes aquatic ecosystem risks. Various studies have been conducted in Ethiopia on the removal of Cr from various types of wastewater; however, factual studies on the adaptability of cost-effective activated coffee husk carbon for the removal of Cr from electroplating wastewater are lacking. Thus, this study was conducted to evaluate the Cr adsorption efficiency of activated coffee husk carbon from electroplating wastewater at laboratory scale. The activated coffee husk carbon’s pH, electrical conductivity (EC), ash content, moisture content, bulk density, particle size, pore volume, porosity, volatile organic matter, carbon yield, and carbon:nitrogen ratio were determined following standard methods. In the adsorption experiment, adsorbent dosage, agitation speed, contact time, pH, and initial concentration were optimized. Models were used to examine the adsorption isotherms and kinetics. The ability of activated coffee husk carbon to desorb Cr was investigated. The adsorbent functional groups and surface morphology were examined using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM), respectively. Analysis of the physicochemical characteristics of the adsorbent showed that the activated coffee husk carbon has good quality, and thus, playing an important role in metal adsorption. Furthermore, FTIR analysis also confirmed the presence of hydroxyl, carboxyl, and other important functional groups, which promote heavy metal adsorption. The adsorption process optimization revealed 99.65% maximum Cr adsorption efficiency at 120 min contact time, 40 mgL-1 initial concentration, 150 rpm agitation speed, pH 7.0, and 20 gL-1 adsorbent dosages. From the adsorption model studies, Freundlich sorption isotherm and pseudosecond-order models were well fitted with respective $R^2$ values of 0.987 and 0.999. A 60% Cr was removed according to desorption studies. In general, due to the ease with which coffee husk can be obtained from coffee processing facilities, its use as an absorbent will be cost-effective and considered as an alternative option in removing Cr metal from wastewaters.