ABSTRACT
Modernization of our surrounding has resulted to widespread pollutants being disposed amidst which are heavy metals into the surroundings. Heavy metals are toxic to both human health and the environment even at low concentrations. Biosorption studies is considered as a method for the removal of heavy metals from dye wastewater due to its simple design, specific affinity, low cost, effectiveness, reduced chemical and biological sludge, no further nutrient requirement, revitalization of biosorbent, and potentiality of metal recovery. This research investigated the feasibility of using orange peel (OP) and watermelon peel (WP) and their combination (CP) as biosorbents for the removal of cadmium (Cd), lead (Pb) and mercury (Hg) metal ions from dye wastewater. The analysis was performed to study the effects of time, biosorbent dosage and initial pH of the biosorbents on the removal efficiency of the heavy metals, an ANOVA analysis, adsorption kinetics and isotherm modelling were also used. The materials were obtained and prepared in a laboratory where 2.0g of the adsorbent was equilibrated with 50 ml of the dye. From the study, OP had the highest adsorption efficiency for Hg at 96.9%, Cd at 88.8% and Pb at 93.1% in relation to time; OP had the highest adsorption efficiency for Hg at 93.4% and Cd at 98.9% while WP had the highest adsorption efficiency for Pb at 91.4% in relation to dosage. For pH variations the equilibrium was achieved around wastewater pH levels of 6.8-7.7 for the sorption of all metal ions by using all adsorbents. Ranking the adsorption ability of the measured metal ions, the following series was obtained: for OP, ; for WP, the ranking was , and for the CP it's The research shows that both biosorbents can be used to perform metal ions adsorption successfully, they proved to have high adsorption capacities and appeared to have a universal application for adsorption of the metal ions. The research showed the adsorption of metal ions is dependent on contact time, biosorbent dosage and pH. Using the three adsorbents at respective time duration, Cd adsorption was found to be the most effective, with Fischer (F) and Probability (P) values of 13802.04 and 3.2 x 10-29 respectively. Similarly, at respective weight variation, Cd adsorption was also found to be the most effective, with F and P values of 9262.98 and 5.5 x 10-15 respectively. While, at pH levels, Hg adsorption was found to be the most effective, with F and P values of 201.31 and 1.41 x 10-14 respectively. This research also showed that the adsorption kinetics modelling studies for the biosorbent dosage followed the first order kinetic models. The isotherm equilibrium studies confirmed that Freundlich adsorption isotherms well fitted models and revealed that adsorption of metals ions is multi-layer and heterogenous. The results from the research indicated that the process used to adsorb metal ions from wastewater has a possible application for a proper plant design.