An Evaluation into the Potential of Biological Processing for the Removal of Metals from Sewage Sludges

Abstract

The use of sewage sludge in agricultural land as a means of sludge disposal and recycling has been shown to be economical and suitable because of the presence of nutrients such as nitrogen and phosphorus. However, municipal sludges often contain high quantities of toxic metals and other compounds that must be removed for its safe use in agricultural soils. The biological leaching of metals from sewage sludges has been shown to be a promising technique for metal detoxifying in such complex matrix. The process efficiency is dependent on several physico-chemical parameters, such as total solids concentration, metal forms, pH-ORP, and temperature. Scale-up of the process has not yet been defined and is still pursuing the correct operational design. Current research involving the bioleaching of metals from sewage sludge and its application to land, which affects soil physical properties, are presented and discussed.

The Effects of Bacterial Leaching on Metal Partitioning in Sewage Sludge

“…Although the original sludge was diluted approximately 50% (from 93 to 46 g l )1 ), its total solid concentration was still high and led to pH buffering effects. As discussed by Lombardi & Garcia (1999), this may be due to the polyelectrolytic nature of the organic material associated with the sludge solid matrix, which hinders redox potential increase (Tyagi et al 1990;Jain & Tyagi 1993;Lombardi et al 2001).…”

Bioleaching of heavy metals from sewage sludge: A review

“…In iron based bioleaching process, the oxidation of reduced iron and sulfur compounds takes place by direct and indirect mechanisms (Tyagi et al, 1988;Lombardi and Garcia, 1999). In direct bacterial leaching, non-ferrous metallic sulfide is directly oxidized by At.…”

“…Previous review on bioleaching of heavy metals from sewage sludge has dealt primarily with the mechanism, the microorganisms involved and the parameters affecting the process (Lombardi and Garcia, 1999). The various methods such as chemical leaching, electro-reclamation, supercritical fluid extraction (SFE) and bioleaching for removal of heavy metals from sewage sludge have been reviewed recently (Babel and Dacera, 2006).…”

Effects of cadmium and nitrogen on lipid composition of Chlorella vulgaris (Trebouxiophyceae, Chlorophyta)

“…However, because sewage sludges are often metal contaminated, such practices increase the content of metal ions in soils (Lombardi & Garcia, 1999), which end up washed into adjacent aquatic ecosystems. In wetlands, where nitrogen and phosphorus are enough to support a diverse biological community, the input of metals can cause severe system disturbances.…”