Modified design model for the adsorption of dye onto peat

For over 20 years, peat has been recognized as a potential biosorbent for the treatment of wastewaters. Several studies have been reported in the literature including its use in cleaning oil spills¹, the removal of heavy metals from wastewaters², the removal of herbicides³, the treatment of slaughterhouse wastewaters, septic tank effluents and dairy wastes⁴. The ability of peat to remove several dyes from aqueous effluent was reported some time ago⁵. Further studies on single component adsorption of basic and acid dyes were carried out to study equilibrium isotherms⁶, diffusion based mass transport processes for batch and fixed bed systems⁷. Carbon has been used for acid dyes in fixed beds⁸. However, in these previous studies, conventional simplified design methods - namely, bed depth service time (BDST) and empty bed residence time (EBRT) models - were applied to the experimental breakthrough curve data but failed to correlate these data due to the non-linearity of the BDST versus bed height data obtained. In the present paper new modifications have been developed based on an expression, N_t/N₀ = 1 - exp(-a*sqrt(t)), where N_t, N₀, a, t represent the bed capacity at service time t, the saturated bed capacity found in isotherm experiments, a rate constant and the service time of the bed respectively. The expression correlates the residence time in the adsorption bed with the time dependent fraction degree of saturation of the bed. It enables modified BDST and EBRT models to be applied and correlate the experimental data very accurately. This model is particularly suited to predicting the performance of fixed bed adsorbers, when the system requires a long time to reach equilibrium or when several fixed bed adsorbers are used in series.