A THESIS SUBMITTED TO THE DEPARTMENT OF ENVIRONMENTAL AND OCCUPATIONAL HEALTH AND SAFETY, INSTITUTE OF PUBLIC HEALTH COLLEGE OF MEDICINE AND HEALTH SCIENCES, UNIVERSITY OF GONDAR IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE IN ENVIRONMENTAL HEALTH.

Abstract

Abstract Introduction: Cadmium as environmental pollutant is highly toxic to humans, plants and animals because it is non-degradable and persistent. It is a major cause of cancer and cardiovascular disease. It can also affects neurological system, lungs, kidneys, liver, and reproductive organs in humans and mammals. The wastewater from the textile and garment sector in Ethiopia is possibly the largest source of Cadmium pollution due to the use of cadmium for the production of colour pigments of textile dyes. Treatments of heavy-metal contamination have shown adsorption as the most effective way to remove Cd (II) from aqueous solution. However, due to the high cost of commercial adsorbents, it is better to develop and utilize a low-cost, accessible, and environmental friendly agrowaste based activated carbon for the treatment of cadmium (II) containing wastewater. Objectives: The aim of the present study is to determine and optimize Cd (II) removal efficiency of Khat stem activated carbon from synthetic aqueous solution. Method: A laboratory based experimental study was conducted from April 15, 2022 to June 30, 2022. A total of 74 samples were included in the study. Proximate and FT-IR analysis was conducted to characterize the KSAC. The effect of initial cadmium concentration, adsorbent dose, pH, contact time and agitation speed on cadmium removal efficiency of Khat stem activated carbon were evaluated. Furthermore the adsorption mechanism was evaluated using adsorption isotherm and kinetics models. Finally Response surface methodology through Face centred central composite design of design expert software version 13.0 was used to identify the optimal condition of process parameters for maximum Cd (II) removal efficiency. Result: The proximate analysis indicated that the KSAC is of good quality with high surface area (615 m2/g).The Fourier transformed infrared spectroscopy result indicated that the presence of O-H, C-H, C=O, and C-O functional groups on the surface of Khat stem activated carbon. The Langmuir isotherm model (R2=0.9945) and the pseudo second order kinetic model (R2=0.9914) were better fitted the experimental data. The highest removal efficiency of cadmium (93.28%) was obtained at optimal value of process parameters; initial cadmium concentration; (30 mg/L), adsorbent dose: (2g/L), pH; (5.13), contact time; (64.5 minutes), and agitation speed; (79.27 RPM). Moreover the Khat stem activated carbon removed 85% and 83% of cadmium (II) from textile and paint wastewater respectively at optimized condition of process parameters. Conclusion: The results obtained in this research demonstrate that the KSAC has high adsorption efficiency for removal of Cadmium (II), from both synthetic and real wastewater. Key words: Cadmium (II) ion, Adsorption, Activated carbon, Optimization, Khat stem activated carbon.