Dealing with a cluster of large centralized municipal wastewater treatment plants: A case study

The article deals with a cluster of large centralized municipal wastewater treatment plants (LCMWWTPs) assessing the main economic, energy, environmental and management aspects. With reference to the case study of the Regi Lagni system (Southern Italy), composed of five WWTPs for an overall effective population of 2,235,800 inhabitants the study focused first on the multi-disciplinary characterization of the system investigated and then on potential future upgrading options, identifying the best suitable solution. For the scope, several indicators such as running costs, energy consumptions, Greenhouse Gas Emissions (GHG), waste for landfilling and two scenarios were defined. The first scenario focused on the role of anaerobic digestion while the dewatered sludge was sent to landfill. The second scenario implemented the same operations of the previous one although the construction of a thermal treatment plant for the dewatered sludge was also planned. Results showed how LCMWWTPs could be characterised by low resilience; the upgrading of plants to comply with the increasingly stringent legal limits was difficult, especially where works were carried out to ensure continuity of operation. Multi-criteria analysis allowed the cluster system based on anaerobic digestion to be the best solution from an economic, energy and environmental point of view.