COMPARATIVE STUDIES ON THE USE OF FLY ASH AND SLUDGE IN THE REMEDIATION OF HEAVY METAL-POLLUTED SOIL

Abstract

Often the remedial measures required to clean-up sites contaminated with heavy metals are so complex that their implementation becomes economically unsustainable. In this work, an investigation has been carried out to assess the potential use of fly ash from coal – fired power stations and sludge from oil palm in immobilizing heavy metals contained in soils from a severely contaminated battery dumpsite in Benin metropolis. Parallel experiments were carried out with soil amended with flyash and sludge at different levels. The amended soil was left for a stabilization period of eight weeks. The parent and the amended soils were analyzed for physicochemical properties using standard methods. The results of the physicochemical properties for parent soil showed the pH, organic carbon and CEC to be 3.0, 4.6% and 9.36meq/100g respectively. The pH, organic carbon and CEC for the fly ash and sludge were respectively 10.5, 0.8%, 4.27meq/100g and 5.2, 45.47%, 15.15 meq/100g. The pseudo metal concentration for the parent soil was 515mg/kg for Fe, 220.3 mg/kg for Zn, 130.15mg/kg for Cu, 48.19 mg/kg for Mn and 52.43 mg/kg for Ni. After amendment, the exchangeable fraction (bioavailable) was reduced to the non-available form. The parent soil was highly contaminated with Fe, Zn, Cu and Ni but was moderately contaminated with Mn. On amendment, fly ash and sludge reduced the level of contamination of metals. From the environmental risk factor, Fe, Zn and Mn posed no potential threat to living organism.