PROJECT DESCRIPTION
BACKGROUND
The implementation of the Urban Waste Water Treatment Directive is increasing the amount of sewage sludge for disposal and the number of small- to medium-size plants. It also requires Member States to provide collecting systems for all agglomerations with populations of more than 2 000.
Wastewater from households and industry is a significant pressure on the water environment because of the loads of organic matter and nutrients as well as hazardous substances. Given that a large percentage of the population of EEA member countries lives in urban areas, a significant amount of wastewater is collected by sewers connected to public wastewater treatment plants. In the EU, about 10 million tonnes of sewage sludge are produced after water treatment every year. A low percentage of this sewage sludge, however, is recycled in agriculture. Incineration and landfilling are the most common disposal methods, both causing significant environmental, economic and social impacts. This scenario cannot be considered a sustainable approach to sludge management in the long term.
OBJECTIVES
The main objective of the ELECTRO-SLUDGE project ws to design, develop and demonstrate an innovative electro-osmotic dewatering system that is able to dewater urban sludge from wastewater treatment plants and thus obtain a dry solid content (DS) equal to, or greater than, 30%.
The project would reduce both the volume and weight of urban sludge (drying process) and the concentration of some heavy metals in the dewatered sludge (osmotic process), leading to an increase in the amount of sludge that meets regulations for its safe use in agriculture. Consequently, the project would:
- Reduce the amount of waste directed to incineration and landfilling (which has to be phased out gradually according to EU Directive 99/31); and
- Drastically reduce sludge volumes to final disposal, limiting CO2 emissions due to transport.
RESULTS
The ELECTRO-SLUDGE project did not achieve any of the foreseen objectives. Partial results have however been achieved with the identification of four wastewater treatment plants as well as sites where to install in rotation the demonstration plant and a preliminary design of the electro-osmotic dewatering prototype. The project also developed the procedure for the urban sludge classification and characterised sludge coming from the selected wastewater treatment plants.
The technology for sludge electro de-watering was only tested at lab scale, proving that the proposed technology (rotating anode) improves electro de-watering if compared with other existing technologies. The ELECTRO-SLUDGE technology could not implemented at pilot scale, hence the project's null demonstration value.