Determination of the level of copper and cadmium in drinking water samples from jimma town and their removal using activated carbon prepared from pumpkin seed shells

Abstract

this study was designed for the determination of the level and the removal methods of heavy metal contaminants in drinking water samples from Jimma town, South Western Ethiopia using chemically activated carbon prepared from pumpkin seed shells (Telfairia occidentalis) by H3PO4. The activation was done by heating the mixture in an electrical furnace at 800oC for 3 hrs. Three type of drinking water samples (raw, treated and distribution) had been collected from six different sites having a total of about twenty one samples and they were analyzed using Atomic Absorption Spectrophotometer (AAS). Two heavy metals, copper and cadmium had been studied and their concentration in some of the water samples was found to be (0.3 mg/L for Cu (II) and 0.0072 mg/L for Cd (II)) which is above the maximum permissible levels (MPL) in World Health Organization of the United Nations (WHO) data that was 0.2 mg/L and 0.005 mg/L for copper and cadmium respectively. Adsorption experiments were carried out as a function of pH, contact time, initial Cu (II) and Cd (II) ion concentrations, adsorbent dosage and temperature of the solution for the removal of the ions. The equilibrium data better fitted to the Langmuir isotherm model for studying the adsorption behavior of the ions with correlation coefficient (R2) of > 0.999. Kinetic studies of the data showed that the adsorption follows the pseudo-second order kinetic model. Thermodynamic parameters such as Gibbs free energy change (ΔG0), enthalpy change (ΔH0) and entropy change (ΔS0) were also calculated for the uptake of Cu (II) and Cd (II) ions. This parameter showed that adsorption on the surface of activated carbon prepared pumpkin seed shells was non spontaneous and feasible; and endothermic between temperatures of 25oC and 45oC.