Removal of Cr3+ From Tannery Wastewater Using Unmodified And Acid-Modified Arabica Coffee Husk Adsorbent

Abstract

Tannery effluent containing chromium is a major problem in leather industry. In Kenya, tannery effluent is discharged directly into the main domestic sewage system, making wastewater treatment plants more difficult to operate. Chromium has long been employed in tanning because of the outstanding characteristics it provides to the leather as well as its ease of use. Only 60% of the entire chromium salt reacts with the hides, though. In other words, around 40% of the chromium remains in the solid and liquid wastes. Subsequently, the removal and reuse of the chromium content of these wastewaters is vital for environmental protection and economic reasons. This study explored the potential for removal and recovery of chromium from tannery effluent using unmodified (UCH) and modified (MCH) coffee husk biomass adsorbents. The raw coffee husk was subjected to sulphuric acid treatment, followed by characterization using FTIR and SEM analysis. The effects of initial metal ion concentration, agitation time, dosage, and pH were investigated in batch experiments. Effluent was obtained from Dogbones tannery in Dandora, Nairobi and was subjected to adsorption process at optimum conditions. Batch adsorption tests on these coffee husks revealed that as the initial metal ion concentration increased, the adsorption of metal ions increased as well. At pH = 4.5, the highest metal uptake was recorded. Maximum percentage removal was 47.52 % and 69.3 % for the UCH and MCH, respectively. For the UCH and MCH, the adsorption equilibrium was attained after 25 minutes and 15 minutes, respectively. Optimum dose of 3 g was realized for the two adsorbents. The presence of hydroxyl, carboxylic, and carbonyl functional groups was detected using FTIR. The surface texture and morphology of the biosorbent were revealed by scanning electron microscopy. The findings imply that coffee husk, in both modified and unmodified forms, is a low-cost, ecologically acceptable biosorbent that can be used to remove chromium ions from tannery effluent and other industrial effluents.