Studies of selected heavy metals removal from nakuru industrial wastewater using sugarcane bagasse and valorised bagasse

Abstract

Adsorption of heavy metals is a novel technology for treatment of wastewaters containing different types of heavy metals. This study aimed at using sugarcane bagasse (NSCB) and valorised bagasse (VSCB) adsorbents made out of sugarcane bagasse, a viable and low cost agricultural waste material from Nzoia sugar factory in Westem Kenya, to investigate kinetic and thennodynamic properties for the removal of selected heavy metals (cadmium(II), copper(II), chromium(III), nickel(II) and lead(II)) from industrial wastewater at controlled pH, using Atomic Absorption Spectrophotometer (AAS). Sugarcane bagasse (NSCB) was divided into smaller particle sizes and air-dried at room temperature, dried in a drying oven at 70 °C for 24 h; while Valorised sugarcane bagasse (VSCB) was prepared by slowly heating bagasse at 300 °C for 3 hours. NSCB and VSCB were sieved through standardized sieves of 150-595um. Batch experiments were done to get the optimum conditions of pH, adsorbent dosage, particle size, contact time, concentration and temperature. Eleven (l 1) industrial Wastewater samples were collected randomly from three major locations (A, B, and C), lying between 0° l0’ 0” S and 36°10’ 00” E within Nakuru City in Nakuru County, Kenya. The levels of heavy metals in the untreated wastewater ranged respectively from: 0.02 — 2.02 ppm for lead, 0.02-0.8lppm for copper, 0.02-0.10 ppm for cadmium, 0.024-0.670 ppm for nickel and 0.004-9.94 ppm for chromium. The levels of lead, copper, cadmium and chromium in some of the Wastewater samples were above the limits set by the Kenya Bureau of Standardisation (KEBs). The study showed that the adsorption efficiency of NSCB and VSCB powder was higher in aqueous solution than in Wastewater. The removal kinetics of the metal ions fitted well with the pseudo-second-order model. For NSCB, the adsorption isotherm models of Pb2+ and Ni“ showed better fitting for Freundlich isotherm while Cd”, Cu2+ and Cr“ showed better fit on the Langmuir isothenn model. While Pb”, Ni2+, Cd“, and Cu2+ had a better fit for the Freundlich isotherm as Cr“ has a better fit with the Langmuir isotherm model on VSCB. The negative free energy change (AG) values revealed spontaneous adsorption process of the metal ions onto NSCB and VSCB, respectively. The enthalpy change (AH) and entropy change (AS) ranged from 28.34 - 74.84 k]mol'1 and lll.70-344.23 Jmol'lK’1 for NSCB and VSCB further reflecting higher affinity ofthe metal ions onto NSCB and VSCB. This study addresses sustainable developmental goal 6 (SDG 6) which seeks to improve water quality by reducing pollution and proportions of heavy metals in untreated Wastewater using NSCB and VSCB adsorbents.