Optimization of fixed bed column process for removal of Fe (II) and Pb (II) ions from thermal power plant effluent using NaOH-rice husk ash and spirogyra.

Abstract

This study was carried out to investigate and optimize the potentials of green algae ( spir- ogyra) supported with treated NaOH- rice husk ash in a fixed bed column for the removal of Fe(II) and Pb(II) ions from a thermal power plant effluent. The optimization was done with central composite design using the Design Expert 10.0.0 software. The effluent was characterised using atomic absorption spectrophotometer with initial concentration values of 17.9 and 4.95 mg/l for Fe(II) and for Pb(II) ions respectively. The developed rice husk- spirogyra adsorbent was characterized using proximate analysis, SEM, BET, FTIR and TGA. The results from the proximate analysis gave a moisture content of 13%, bulk density of 0.347 g/cm 3 , loss of mass ignition of 2.2 g, pH of 6.97 and pH point of zero charge (pH- pzc) of 4.94. The SEM images revealed an adsorbent with numerous pores, cavities and an irregular rough surface. The FTIR showed the O –H, C = O and C –O functional groups as being responsible for the adsorption of the heavy metal ions. The BET analysis revealed high surface area of 534.414 m 2 /g with pore volume of 0.3219 cm 3 /g and pore size of 2.810 nm which reduced drastically to a surface area of 375 m 2 /g after adsorption. For the column sorption study, the effects of bed height, (5, 10 and 20 cm), at flow rate, (3, 6, and 9 ml/min), and initial concentrations of Fe(II) (17.9, 10.23, and 5.53 mg/L) and Pb(II) (1.65, 3.1, and 4.95 mg/L) established that an increase in bed heights, reduced flow rates and in- let concentrations gave over 48.3 and 58.30% removal of the Fe(II) and Pb (II) ions which had a significant effect on the breakthrough and exhaustion time. The data were subjected to kinetics isotherms with the Clark model given the best fit with R 2 values of 0.9643 for Fe(II) and 0.9594 for Pb(II) ions.