Energetic and environmental analysis of a wastewater treatment plant through static and dynamic monitoring activities

Abstract

The article describes the results achieved in 5 years of monitoring of a large wastewater treatment plant (700,000 PE) in Southern Italy, which has a conventional activated sludge process scheme and electricity as exclusive energy source. The monitoring involved a preliminary phase ("static" monitoring) for the analysis of historical data on the main process-related variables, using the approach of normalization techniques. In the second monitoring phase ("dynamic" monitoring) the theoretical distribution of the energy load among the electromechanical units of the plant was first studied; then, an energy monitoring system was implemented on the most energy-consuming unit of the plant, a 500 kW turbo-blower, with the aim of analysing in detail its real-time performance and investigating potential correlations with other process parameters (wastewater flow rates and associated pollutant load). Results of the static monitoring suggest good overall performances, both from an energy and environmental point of view, even if the plant works close to the maximum hydraulic capacity due to the massive infiltrations. In particular, focusing on the energy performances, the plant consumes on average 0.17 kWh/m3, 28 kWh/PE/year and 0.66 kWh/kgCODremoved. The results of dynamic monitoring, on the other hand, indicate that the turbo-blower consumes 30% less energy than what initially estimated through the theoretical model, but its functioning does not seem to be influenced by the other process parameters; this latter result reveals an inadequate energy management of the most power-absorbing electromechanical units of the plant and the consequent need to adopt effective strategies for energy optimization.