Packed bed column studies on Cr (VI) removal from tannery wastewater by neem sawdust

The removal of Cr (VI) from tannery wastewater by neem sawdust was investigated in a fixed bed column. The experiments were conducted to study the effect of important parameters such as bed depth (5–15 cm) and flow rate (5–15 ml min− 1). The bed depth service time model (BDST) fit well with the experimental data. The adsorption capacity estimated from the BDST model was 33,009.9 mg g− 1. The column was regenerated by eluting chromium (VI) using 2 N NaOH after adsorption studies. The desorption of Cr (VI) failed to reach 100% in each cycle because some amount of adsorbed Cr (VI) got reduced to Cr (III) in the biosorbent surface and released into the aqueous phase. The effect of co-ions on adsorption of Cr (VI) was studied in column mode, where the breakthrough and the exhaustion time of the column decreased in the presence of co-ions. In the three cycles of biosorption, about 3.75 L of tannery effluent were treated to reach the chromium (VI) standard (0.1 mg L-1) established by the Central Pollution Control Board (CPCB). Neem sawdust proved to be the potential biosorbent for the removal of Cr (VI) from tannery effluents.