Design of Carbon Beds to Remove Humic Substances

Abstract

The homogeneous surface diffusion model (HSDM) was found capable of simulating effluent concentration history profiles for a commercial humic acid, a peat fulvic acid (PFA), and a coagulated PFA. The model successfully simulated column data for four granular activated carbons (GAC), several empty bed contact times (EBCTs), two GAC mesh sizes, several infuent concentrations, and several hydraulic loadings. Accordingly, the HSDM was used to evaluate the impact of process design variables on cost and adsorber performance for the removal of these humic substances. Model calculations were carried out to evaluate the impact of EBCT and influent concentration on adsorber performance. It was found that for each doubling of EBCT in the range of 3.77–75.4 minutes the bed life of the carbon was more than doubled. For 50% reductions in influenct concentration, the bed life was about doubled for influent TOC concentrations ranging from 1–20 mg/L. By estimating the cost of treatment for various EBCTs, the most economical EBCT was determined for a single adsorber, for two adsorbers in-series, for two adsorbers in-parallel, and for three adsorbers in-parallel. Two adsorbers operated in-parallel were found to be more economical than a single adsorber, or two adsorbers operated in-series. The lowest cost operation was for three adsorbers operated in-parallel. Treatment costs for two adsorbers in-parallel were found to decrease with increasing treatment plant size, decreasing influent concentration, and decreasing GAC particle size.