The European Union indicates Circular Economy (CE) as the sustainable development model for the future. The concept of Circular Economy is to keep the value of products as much as possible within the economic sphere, increasing resource efficiency and decreasing environmental load. Thus, current linear business models should move to circular business models and open economic flows should become closed, as far as possible. Great attention has to be paid on the last stages of the economic processes, namely the treatment of waste. In CE the waste of one system should become the input of another. Therefore, two or more systems compose the new circular model and the quantification of the advantages could be complex. Life cycle assessment (LCA) can be useful for the evaluation of the effects of CE, since it is a scientifically based tool for measuring the environmental impacts of products, services and business models. On the basis of the LCA results, it is possible to understand the effectiveness of a circular solution, in terms of reduction of negative environmental effects. The LCA is carried out following the ISO 14040:2006 and 14044:2006 standards. In this study the LCA methodology was used to evaluate the environmental sustainability of the application of CE principles to the urban wastewater treatment plants in Milan. Treated wastewater is discharged in canals and used for irrigation of agricultural lands in Milan south area. Moreover, sludge, that represents the main waste flow leaving the plant, is recovered. This waste contains a high concentration of nutrients (N and P), which represent a valuable alternative to chemical fertilizers. This is the reason why, after a proper treatment to ensure protection of human health, more than 80% of sludge is recovered through agricultural application. To make those two solutions possible, the urban water system operator has to carry out tertiary treatments (sand filtration, disinfection) to adapt the system outputs to subsequent reuse or recovery. Limiting the study to the wastewater treatment plant, the treated wastewater and the sludge deriving from the system cause negative environmental impacts; moreover, high impacts are determined by the tertiary treatments applied. However, expanding system boundaries, i.e. including treated wastewater reuse for irrigation and agricultural sludge application, the environmental impact of the system is reduced, thanks to: (1) the reduction of the amount of wastes exiting the system, (2) the reduction of eutrophication impact of nutrients discharge into freshwater, (3) the reduction of resource consumption for agricultural soil fertilization, (4) the reduction of water withdrawal for irrigation. In this case study the wastes of the wastewater treatment plant represent a resource for agriculture, hence this CE model impacts positively on two systems. These findings confirm the appropriateness of system boundaries expansion approach for the correct evaluation of CE models.
LCA - Wastewater treatment plant - Water reuse - Nutrients recovery - Environmental sustainability
5c. Circular economy, zero waste & innovation
