Chloride Removal from Tannery Soaking Wastewater by Adsorption onto Activated Alumina

Abstract

Tannery soaking waste water is characterized by very high chloride content that is responsible for severe environmental problems such as damage to human health, microbial population and aquatic lives. This study was aimed by the preparation and characterization of activated alumina along with its application for chloride adsorption from tannery soaking waste liquor. Activated alumina was prepared through sol-gel technique using aluminum nitrate as precursor with the pHpzc of 8.1. The XRD analysis revealed the both crystalline and fine amorphous nature of the alumina with average particle size of 5.04nm.  Chlorides adsorption experiments onto activated alumina was conducted by both batch and column adsorption method to explore the optimal adsorption condition and to investigate the practical usability of the adsorbent. The batch study revealed that pH of 6 and temperature of 40 ⁰C was the optimal operational conditions for chloride adsorption onto activated alumina. In the column study, higher chloride removal was observed at lower flow rates, with a reduction in efficiency from 93.27% to 86.94% as the flow rate increased from 2 to 4 mL/min. Breakthrough curve analysis at different flow rates revealed that a comparatively higher break point of 270 minutes and 240 minutes was observed for lower flow rates, 2 and 4 mL/min, respectively, whereas at higher flow rates, 8 mL/min breakpoint was noticed at 150 minutes. Breakthrough curve modeling demonstrated that the column adsorption process followed the Thomas model of adsorption kinetics. Better regeneration of the alumina up to two wash cycles was achieved for alkali wash. The adsorption efficacy of activated alumina for chlorides, BOD and COD as 93.24%, 69.18%, 75.68% from raw soaking liquor and 43.19%, 32.23% and 38.69% from diluted soaking wastewater signifies its potentiality to adsorb not only chlorides but also organic pollutants from tannery effluent.