ADSORPTION STUDIES AND REMOVAL OF NITRATE FROM BLEACHED KRAFT MILL EFFLUENT BY FLY-ASH AND SEPIOLITE

Abstract

This study aimed to remove nitrate from paper mill industry (4500 m(3) h(-1)) wastewater, which is discharged to sea from a plant located in western Turkey. As adsorbents, fly-ash, raw and heat-activated sepiolite were used. The effect of factors, such as particle size, temperature and pH, on adsorption process was investigated. From kinetic studies, equilibrium time was found as 1h for both adsorbents. The kinetic data support a pseudo-second order model (0.999 >= r(2)) but show very poor fit for a pseudo-first order model. Intra-particle model also shows that there are two separate stages in sorption process, namely, external diffusion and pore diffusion. Adsorption isotherms for fly-ash and activated sepiolite were obtained at three different temperatures. From experiments carried out at different pHs, it was observed that pH plays an important role in the nitrate adsorption process, both ionizing the compounds and modifying sorbent surfaces. It was also observed that heat-activated sepiolite is more effective than raw sepiolite and fly-ash to remove nitrate and, in addition, adsorption of nitrate increases with decreasing particle size. The results of this study suggest that sepiolite and fly-ash, with low-cost and abundant availability, have a potential of being used as sorbent for removal of nitrate from Bleached Kraft Mills Effluent (BKME).