Effect of Salinity on the Adsorption Behavior of Methylene Blue onto Comminuted Raw Avocado Residue: CCD-RSM Design

Abstract

Textile effluents contain a series of dyes and salts, and their decolorization is strongly affected by salinity. In this work, the influence of salinity on methylene blue (MB) adsorption by comminuted raw avocado seeds was investigated. The adsorbent was firstly characterized. The optimal conditions for MB adsorption on the avocado seeds were determined by response surface methodology (RSM). Subsequently, the influence of ten salts in MB adsorption was evaluated using kinetic and equilibrium studies. The optimal conditions for MB adsorption on the avocado seeds were pH = 10 and adsorbent dosage = 1 g L−1. General order model was able to describe the kinetic profile, and its parameters showed that the adsorption rate and capacity were affected by the presence of salts. The equilibrium was adequately represented by the Sips model. The maximum adsorption capacity without the presence of salts was 97.97 mg g−1. The maximum adsorption capacity was found in the presence of sodium carbonate, which was 103.13 mg g−1. The presence of sodium citrate reduced the adsorption capacity to 80.42 mg g−1. Therefore, even in the presence of salts, comminuted raw avocado seeds demonstrated great potential to treat colored effluents containing MB dye.