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 ( spirogyra) 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 a 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 charges (pH- pic) 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 a high surface area of 534.414 m 2 /g with a 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.