POTENTIAL REMOVAL OF CHROMIUM (VI) IONS BY MACADAMIA NUTSHELL FROM STEEL INDUSTRY WASTEWATER

Steel industries generate wastewater laden with toxic metals such as Chromium VI(Cr 6+ ) which are classified as carcinogenic and toxic to aquatic life.There is need to meet standards for effluent discharge in order to comply with local and international standards.Chemical precipitation is a commonly applied low-cost technology, but has proven to be unsustainable due to sludge disposal that creates secondary pollution.Devki steel factory located in Ruiru municipality, Kiambu County is a factory that process steel products.Chemical precipitation is applied in Cr 6+ treatment at effluent discharged at the factory which exceed international and local effluent discharge standard limits.There is thus need to develop innovative yet affordable technologies for Cr 6+ .The potential of carbonized macadamia nutshell (CMN) in Cr 6+ adsorption as an alternative and eco-friendly technology was evaluated.Carbonization process modified the adsorbent surface properties by increasing the surface area, pore size, carbon content, and Cr 6+ removal rate from 40.21-380.64m 2 /g, 1.63-8.78Å, 47.01-57.2%and 71-97% respectively.Maximum Cr 6+ adsorption was obtained at a metal concentration 50mg/L, pH 4, contact time of 2 hours, 0.2g dose, and at 30℃.The equilibrium data were well depicted by Langmuir and Freundlich isotherm.Experimental data were well fitted with Pseudo second-order kinetics.Maximum adsorption capacity of 24.3 mg/g and removal efficiency at 97.2% was attained by CMN compared to raw macadamia nutshell (RMN) 17.95 mg/g and 71.6% respectively.The desorption results revealed that the spent adsorbent could be reused for three adsorption cycles, which makes the process eco-friendly.