On the Impact of Land Application of Secondary Sludge

Sewage sludge from the extended aeration municipal wastewater treatment plant of Kalamata (Greece), dewatered and dried was tested for potential land application. Experiments were carried out simulating rainfall, one low-rate high-duration at 20 mm/d, and one high-rate low-duration at 6.6 mm/d. Leachate was collected and analyzed as a function of accumulated rainfall. The sludge was found suitable for agricultural uses on the basis of the relevant EEC Directive. Leachates contained P and heavy metals well above the allowable limits for discharge, implying that transport through the soil can be decisive on the likelihood of groundwater contamination. High-rate low-duration rain events give higher contaminant concentrations in the accumulated leachates.