Treatment of excess sludge containing heavy metal by chemical ways

The concentration of heavy metals in excess sludge from municipal wastewater treatment plants has restricted its convertion to soil fertilizer, so it is necessary to remove the heavy metals from sludge. In this article, the effects of heavy metal removal by some mineral acids such as HCl, H2SO4, H3PO4, HNO3 were analysed, when treating excess sludge from a second sediment tank in municipal wastewater treatment plants. To improve the treatment, a combination of H2O2 and acid was also investigated. Consequently, the difference of heavy metal removal among those acids was showed. Its removal of Hg by HNO3 was better than by other acids. Lower pH enhanced the dissolving of heavy metal, yet the removal of Cr was insensitive to the pH. Aided by H2O2, the removal by the acid was enhanced. The suitable dosage of H2O2 was specially related to the solid content of sludge, pH and the acid kind.