Transient behavior of a packed column of Eichhornia crassipes stem for the removal of hexavalent chromium Original Research Article

Various combinations of adsorbents like ADRB1 with Powdered Activated Carbon (PAC), ADRB2 (PAC in combination with polymer beads) and ADRB3 (water hyacinth stem:PAC = 3:1) were used to remove hexavalent chromium from wastewater. Equilibrium was achieved after approximately 18 h. Three isotherm models, namely Temkin isotherm, Freundlich isotherm and Langmuir isotherm were parameterized. The parameters of three different adsorption isotherms were estimated using nonlinear least square scheme, based on the minimization of SSQ. The maximum equilibrium sorption capacity (qmax) of ADRB2 has been found to be 55.68 mg/g in comparison to 31.46 mg/g for ADRB1 and 32.25 mg/g for ADRB3. The adsorption capacity of ADRB3, though less than that of ADRB2, could be used for applications where large quantity of waste water (eg. Leather complexes) containing hexavalent chromium is disposed into a huge water body where plenty of water hyacinths are grown naturally. The dynamics of fixed bed adsorption columns is studied. Rapid occurrence of breakthrough time is observed for higher flow rate of effluent, lower bed height and high initial concentration of effluent. The maximum breakthrough time of 4 h was observed for a 35 cm bed height and an initial feed concentration of 10 ppm.