Principle and Process of Heavy Metal Removal from Sewage Sludge

Abstract

The sufficient removal of heavy metals from sewage sludge remains to be achieved. Heavy metals that exist on the cell surfaces of the microorganisms in the sludge seem to be dissolved by acid treatments. This study shows that heavy metals in sewage sludge can be removed easily by treating a sludge filter cake with phosphoric acid containing hydrogen peroxide for 1 h at room temperature. Phosphoric acid of 8% concentration with hydrogen peroxide showed good removal rates of heavy metals comparable to those by 1 N hydrochloric acid. Copper is easily removed from the sludge in the presence of hydrogen peroxide. From the results of the investigation of the solubilities of several copper compounds into phosphoric acid with or without hydrogen peroxide, the copper in the sludge does not exist as copper sulfides, but it seems to exist as copper thiolates containing Cu(I) in biopolymers. In this process, the phosphoric acid used for the removal of heavy metals is almost entirely recovered and is reused. Sewage sludge with low content of heavy metals can be recycled as a useful resource.

Leaching of ashes from co-combustion of sewage sludge and wood—Part I: Recovery of phosphorus

“…They found that at room temperature, leaching during 1 hour gave a larger release of trace metals with hydrochloric acid than with sulphuric acid. The most significant difference concerned Pb, were HCl released 100% and H 2 SO 4 just 37% of the available Pb in the sludge [10].…”

“…Hydrochloric acid would add chloride ions to the leachate and these could form soluble complexes with most heavy metals, thus increasing the amount of metals in solution. Yoshizaki and Tomida [10], studied removal of trace metals from sewage sludge by both hydrochloric acid and sulphuric acid in the pH-range 0.8-1.5. They found that at room temperature, leaching during 1 hour gave a larger release of trace metals with hydrochloric acid than with sulphuric acid.…”

Reclamation of Mercury from Used Silver Oxide Watch Batteries

“…Mercury removal from waste sewage sludge is reported [9] employing phosphoric acid as the extractant but this requires an additional step for the elution of mercury from the acid and the purification required for reusing the phosphoric acid. Precipitation method is adopted in [10] for removing lead metal from industrial effluents.…”

Heavy Metal Removal and Phosphorus Retention Using the Fenton Process for Sustainable Recycling of Anaerobically Digested Sewage Sludge

“…Biological acidification of the sludge is a cost-effective process for the elution of heavy metals (Blais et al, 1992;Kitada et al, 2001). Under acidic conditions, utilization of iron-oxidizing bacteria or oxidizing agents such as ferric sulfate (Fe 2 (SO 4 ) 3 ) or hydrogen peroxide (H 2 O 2 ) improved the elution efficiency of heavy metals (Ito et al, 1998;Ito et al, 2000;Yoshizaki and Tomida, 2000). Nowadays, it has been reported that heavy metal elution from the sludge or soil was promoted by the Fenton process using H 2 O 2 and ferrous sulfate (FeSO 4 ) (Dewil et al, 2007;Villa et al, 2008).…”