Evaluation on the efficiency of ethylenediaminetetraacetic acid (EDTA)-modified rice husk as a low-cost sorbent for various dyes removal under continuous flow condition

The potential of ethylenediaminetetraacetic acid (EDTA)-modified rice husk (ERH) as a sorbent to remove both methylene blue (MB) and reactive orange 16 (RO 16) in single and binary dye solutions was studied. Surface characterization of natural rice husk and ERH was investigated using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). From the FESEM micrographs, due to the absence of pores and cavities, it can be concluded that ERH is a non-porous material. The adsorption behaviour of MB and RO 16 onto column packed with ERH was investigated under continuous flow mode with three different parameters: the effect of influent concentration, the effect of bed depth and the effect of flow rate. Column studies indicated that the breakthrough time is longer for MB at lower influent concentration and flow rate. Unusual breakthrough curves were obtained for RO 16 in both single and binary dye solutions with very rapid initial breakthrough. This implies that the adsorption of RO 16 is a slow process and an effective adsorption only takes place after a sufficient lapse of time. Different mathematical models were used to characterize the fixed-bed performance for the adsorption process involved, namely bed depth service time (BDST) model, Adams–Bohart model and Clark model.