Abstract
Sludges are byproducts of sewage treatment process. Land application of sewage sludge is one of the final steps of waste water treatment, but solubilization of toxic metals restricts this method of sludge disposal. In our paper cobalt, zinc, cadmium and cesium sorption by suspension of non-treated activated sewage sludge (14 g/dm3, dry wt.) from waste water spiked with 60CoCl2, 65ZnCl2, 109CdCl2 or 137CsCl were determined in laboratory experiments at 20°C. Activated sludge supplied by the municipal sewage treatment plant in Zeleneč (Trnava region, Slovakia) showed high efficiency to sorb Co2+, Zn2+, Cd2+ and Cs+ ions from waste water pH 6-7. The process can be characterized by the concentration equilibrium (Csolid/Cliquid) typical for sorption processes. Efficiency of the sorption increased in the order Cs < Co < Zn < Cd. Metal sorption process was not inhibited by pretreatment of the sludge with 0.2% formaldehyde or thermal inactivation at 60°C, what confirms that the process was not dependent on metabolic activity of the sludge. Cobalt, zinc, cadmium and cesium were easily removable from the
 sludge by washing with diluted HCl, EDTA or water solutions of the corresponding metal ions, but with low efficiency by deionized water.
Highlights
Several physico-chemical methods were used for removal of heavy metals from industrial liquid wastes, such as ion-exchange, chemical precipitation, chemical reduction and adsorption
The non-treated activated sludge from aerobic phase of municipal waste water treatment plant contains the whole spectrum of metals
The sorption capacity of the sludge is much higher than actual concentration of heavy metals in treated waste waters
Summary
Several physico-chemical methods were used for removal of heavy metals from industrial liquid wastes, such as ion-exchange, chemical precipitation, chemical reduction and adsorption. There are still some problems associated with these methods since these are cost-expensive and they themselves can produce other wastes, which will limit their industrial applications. Among the available treatment processes, the application of biological sorbents is the most promising due to the following reasons: requirement of chemicals for the treatment process is reduced, low operation costs, eco-friendly and cost-effective alternative of conventional techniques and high efficiency at low levels of contaminations. Sludge of municipal waste water treatment plants are produced in huge amounts and generally represent one of the main problems of European countries (FYTILI and ZABANIOTOU, 2008). The activated sludge can be considered as a biosorbent capable to bind toxic metals from liquid wastes of industrial origin
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