Emergy required for the complete treatment of municipal wastewater

The continuous increase of human pressure on the environment and the concomitant pollution threat call for more complete and efficient environmental protection systems. Wastewater treatment plants are a technological response to the accumulation of pollution that occurs during the human-dominated phases of water cycle. In recent years, thanks to significant improvements in sewage treatment methodology, a number of upgrades have been assessed to improve the efficiency and functionality of treatment systems. Nonetheless, this activity requires large material and energy consumptions that have to be carefully accounted for when evaluating the efficiency of the process. In this work we present an emergy approach to the evaluation of a wastewater treatment plant located along the Ligurian coast (NW Mediterranean Sea). Besides the evaluation of the water treatment plant system, a preliminary assessment of the environmental costs in terms of natural fluxes required for the treatment process was performed. In fact, at the end of the treatment discharged water is still loaded with substances that have to be adsorbed by the receiving natural system. The work done by nature assimilating this load is generally considered as free while it is counted as a further cost in the total emergy budget of the water purification process.