Evaluation of a packed bed tri-medium system for the removal of iron and manganese from groundwater

Abstract

Clean water access is drastically deteriorating globally due to stresses posed by an increase in industrial development, population growth, and expanding economic activities. Industry development escalates water pollution, which has societal impacts on human lively hoods by causing diseases such as diarrhoea, malnutrition and cancer, Africa being one of the continents suffering from this predicament. The expansion of population and economic activities doubles the demand for clean water globally every twenty-one years. This lessens the supply and availability of clean drinking water since the earth comprises 97% saline water; only 3% is deemed freshwater for human consumption. Out of this percentage, a low 0.06% is accessible, while the rest are ice, groundwater, and wastewater. Groundwater has become the natural alternative source of water that is substantially reliable. However, it consists of heavy metals that significantly impact nature and human health. The contamination of groundwater is a global challenge as this puts pressure on the necessity for filtration before any use. Iron and manganese are abundant elements found in the earth's crust and are primarily found in pollutants in the surface and groundwater; even though they are aesthetic, higher concentrations of these elements have adverse health effects and can damage equipment. This study takes the treatment of groundwater to remove iron and manganese. These metals are abundantly found in the earth's crust, if not treated, might damage equipment such as pipes and geysers and have health effects on humans if consumed in high concentrations. The previous studies determined that it was complex to remove iron and manganese simultaneously. This study aimed to assess the effect of flow rates, contact time and pH for removing these metals in one system with variously packed media (tri-medium). The experiment was performed in a laboratory-scale treatment process in a packed bed integrated tri-medium (three media system consists of glass, polystyrene beads and ion exchange)for the treatment of iron (Fe) and manganese (Mn) from ground water in line with the City of Cape Town and South African National Standards 241 (SANS241) standards for potable application. This research followed an experimental quantitative approach. The study comprises of two parts, which entail the application of chemical oxidation r and the evaluation of a tri-medium system. The three medium used in this experiment was characterized using Fourier Transform Infrared Spectroscopy (FTIR) to determine their surface chemical functional group. Design Expert 10 was used to generate a predictive model using the Box-Behnken Design (BBD) approach to describe the effect of operating conditions on Fe and Mn removal. Isotherms models (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich) were used to assess the system adsorption performance and kinetic models (Pseudo-First Order (PFO), Pseudo-Second Order (PSO), Intra-Particle Diffusion (IP) and Elovich) to investigate the rate of mass transfer mechanism on the experimental data collected. Mathematical (Thomas Model, Adams & Bohart and Yoon-Nelson) models were utilized to determine the efficiency and capabilities of the fixed bed column. The highest average removal percentage of Fe and Mn were found to be 71% and 89%, respectively, after 60 minutes of running time. The best percentage removal after adsorption was 93% at operating conditions of pH: 8.5, flow rate: 0.174l/min and dosage: 1.67ml/min for Fe and pH: 6.5, flow rate: 2.52l/min and dosage: 0.262ml/min for Mn. This was deemed the best operation condition for removing Fe and Mn for the experiment. These results indicate that the treated effluent aligns with national standards for safe disposal or reuse since the concentration of Fe and Mn was found to be 0.15mg/l and 0.2mg/l, respectively. The FTIR revealed the “media” contained bonds that are advantageous for the adsorption of Fe & Mn. The adsorption kinetic data for Fe was shown to follow pseudo-second-order reaction kinetics the best with linear regression R2=1 and follow the Freundlich adsorption isotherms the closest with R2 0.99. The adsorption kinetic data for Mn was directed to follow pseudo-second-order reaction kinetics with high R2=0.99 compared to other models and follow the Freundlich adsorption isotherms the closest with R2=0.99. It was observed that the predictive model successfully described the optimal operating conditions for removing Fe and Mn within the design space of the model. Mathematical models were investigated to determine this fixed bed column's appraisal efficiency and capabilities. Adams & Bohart's Model illustrated high adsorption capacities compared to Yoon Nelson and Thomas's model. According to the results determined from this study, the tri-medium packed bed system indicated a positive outcome for the simultaneous removal of iron and manganese.