Use of statistical expressions to evaluate the performance of two parameter adsorption isotherm models on dyes using natural adsorbents

Abstract

Adsorption is a very important, simple, cost effective and efficient method for removal of dye from wastewater due to the availability of a wide range of natural adsorbents.For the process of adsorption to be successful, it is vital to understand the nature of theinteraction between adsorption and the adsorbent used for theremoval of pollutants and this is described by adsorption isotherms. This study is carried out to evaluate the performance of two parameter isotherms like Freundlich, Langmuir, Temkin, Jovanovic, Halsey, Hurkins-Jura and Dubinin-Radushkevic isotherms on methylene blue and methyl orange dyes using fruit and vegetable peel adsorbentslike Watermelon Peel (WMP), Watermelon Rind (WMR), Mosambi Outer Peel (MOP), Mosambi Inner Peel (MIP), Papaya Peel (PAPP) and Potato Peel (POTP). The goodness of fit criterion (R 2) was computed by linear regression for both the dyes using all adsorbents to determine the best fit isotherm and this was further validated using eight different statistical expressions like Chi-Squared test, Mean Absolute Error, Root Mean Square Error, Coefficient of Residual Mass, Error Norm, Coefficient of Efficiency, Modeling Efficiency and Index-of-Agreement.Best fit isotherms according to R 2 values are all isotherms with almost all adsorbents except a few adsorbent. However the statistical expressions show that the Halsey isotherm is fit with all adsorbents while Freundlich and Langmuir isotherms are fit with methylene blue dye. Freundlich isotherm is fit with all adsorbents except POTP with methyl orange dye, while the Langmuir isotherm deviated a lot with all adsorbents for methyl orange dye.The statistical expressions show very poor Temkin and Jovanovich isotherm model fits for both the dyes and the Hurkins-Jura isotherm does not fit MOP adsorbent with methylene blue dye but fits very well with MOP and lesser extent with MIP and PAPP adsorbents for methyl orange dye. It is seen that the Dubinin-Radushkevich Isotherm is fit for methylene blue dye with only WMP adsorbent and methyl orange dye with only WMR adsorbent.