Bengal gram seed husk as an adsorbent for the removal of dyes from aqueous solutions – Column studies

Abstract

A continuous fixed bed (column) study was carried out by using seed husk of Bengal gram (Cicer arietinum) (SHBG) as a biosorbent for the removal of direct dye, Congo red (CR) from aqueous solutions. The effects of important factors, such as the value of initial pH, the flow rate, the influent concentration of CR, bed depth, particle size of SHBG, foreign ions and regeneration of CR were studied. The effect of similar type of direct dyes like direct turquoise blue 86 (DTB) and direct black 38 (DB) on the adsorption of CR in column containing SHBG is also studied by keeping other parameters constant. The studies confirmed that the breakthrough curves were dependent on flow rate, initial dye concentration, size of SHBG, initial pH of solution of CR and bed depth. The bed depth service time analysis (BDST) model was applied at different bed depths to predict the breakthrough curves. The model is found suitable for describing the biosorption process of the dynamic behaviour of the SHBG column and the data were in good agreement with BDST model. When the flow rate was 0.67 mL/min and the influent concentration of CR was mg L−1, the column capacity was 6.572 mg g−1. The removal capacity of SHBG was more in case of CR (6.572 mg g−1) compared to other similar direct dyes of DTB (1.984 mg g−1) and DB (1.612 mg g−1). The removal of CR was enhanced in the presence of foreign ion potassium (8.308 mg g−1) and decreased in the presence of calcium (5.58 mg g−1). 120 ml of acetone is required for the completion of regeneration of the column and the total amount of CR recovered in this case. All the results suggested SHBG as a potential adsorbent for removal of CR from aqueous solution so that the rate of bio-sorption process is rapid. Keywords: Column, Bengal gram seed husk, Congo red, Bed depth service time analysis