Statistical Optimization of Dye Adsorption by Bottom Ash Using Response Surface Methodology

Abstract

Coal-based power generation units typically produce more than 20% bottom ash as a by-product. Bottom ash is made up of heterogeneous, multi-layered surfaces, which are available for adsorption, and also it is being used as structural fill, construction, and road base materials. Recently, there has been growing interest in utilizing bottom ash as a sorbent for various pollutants, especially water. The qualities like particle size, inherent large surface area, and high porosity of bottom ash make it a good choice for use as a low-cost adsorbent. The bottom ash sample from Ballari Thermal Power Station, Ballari, Karnataka, was collected to test the adsorption characteristics. This study is undertaken to optimize the percentage adsorption for both acid-washed and unwashed bottom ash samples. The process variables like contact time, dye concentration, and ash quantity were varied, and a regression model is developed for percentage adsorption using a statistical tool (MINITAB V 14). 3D response surface plots are generated for each pair of variables. The results indicate that the adsorption capacity of unwashed bottom ash is 1.4 times higher than the acid-washed bottom ash. The unwashed bottom ash has shown a maximum of 74% adsorption at 3g of ash quantity, 60 min of contact time for 10ppm dye concentration.