1. Introduction
Italy generated around 29.6 million tons of municipal solid waste (MSW) in 2017 [
1]. As for the management systems adopted, very pronounced differences may be noted depending on the geographic area considered, and in general between northern and central or southern regions, both in terms of collection methods and treatment strategies applied. As for collection, increasing targets for the separate collection of specific waste streams to achieve by set timeframes were established [
2]. Specifically, by 2012, the separate collection rate was set to reach 65%. The current national waste report states that, in 2017, 16.4 million tons of MSW was intercepted by separate collection, which means that an overall collection rate of just over 55.5% was attained countrywide [
1], still below the 2012 target. However, northeast regions such as Veneto, Lombardy, and Trentino Alto Adige reached, and in some areas even greatly exceeded, this target [
3,
4]. High separate collection rates should lead to higher material recycling and, hence, lower overall environmental impacts of the waste management system (e.g., References [
5,
6]). Material recycling and recovery in fact divert waste from landfills and thermal treatment, thus leading to a reduction in impacts, including leachate production (in the case of landfilling) and greenhouse gas emissions [
7]. Furthermore, recycled materials replace (at least partially) virgin raw materials and, therefore, lead to resource savings (e.g., energy, materials, and water), as well as avoiding emissions to the environment, related to extraction and processing. In a long-term perspective, recycling should lead to a decrease in the requirement of raw materials needed for production and, thus, postpone the exhaustion of scarce resources; however, in addition to the recycling rate, product lifetime and the production growth rate are important factors [
8].
The European Union (EU) waste policy, hence, placed increasing emphasis on material recycling and set, within its recent circular economy package legislation, targets on recycling and preparation for reuse of MSW (e.g., 55% by 2025) and for the recycling of packaging materials [
9,
10]. Specifically, EU member states will be expected to achieve the following recycling rates by 2025: all packaging waste 65%, plastics 50%, wood 25%, ferrous metals 70%, aluminum 50%, glass 70%, and paper and cardboard 75% [
10]. In addition, by 2035, MSW landfilling should be reduced to 10% or less of the total amount of generated municipal waste [
11]. This means that, in the next few years, EU countries will need to develop and implement integrated waste management strategies (e.g., Reference [
12]) that allow to reach high yields not only in terms of separate collection, but also of actual recycling and reuse of selected fractions.
In this study, we chose to focus on one of the most advanced waste management systems applied at a sub-regional level currently in Italy, the Sinistra Piave Basin, made up by 44 small- to medium-size municipalities of the province of Treviso (Veneto region). In 2015, the consortium that runs the waste management service in this area, serving a total population of around 300,000 inhabitants, was awarded first place as a waste recycling consortium in Italy by the environmental association Legambiente, since it achieved an 80% separate collection rate on average for its whole territory. The attainment of this result was made possible by the adoption of multiple measures, both technical and managerial, such as an efficient door-to-door collection service for the main waste fractions and the presence of 38 eco-centers located close to the main towns (average availability of one center per 3500 households) for the collection of the remaining fractions. In addition, the consortium developed communication strategies targeted both at citizens (also in foreign languages) and educational campaigns for children and students at schools, discouraging incorrect practices via regular controls, remote monitoring, and fines.
The main objective of this study was to quantitatively analyze the whole integrated management system applied in the Sinistra Piave Basin—from collection to recycling of specific MSW fractions and treatment of the residual ones—to evaluate the effects of the applied strategies and in particular of the separate collection yields achieved. Specifically, we decided to assess, for two different years for which different separate collection yields were achieved, the potential environmental impacts associated with the consortium-based management system.
The environmental performance of an integrated waste management system is typically evaluated by life-cycle assessment (LCA), a decision support tool that can be used in policy and decision-making to identify the system with the best performance through a comparative analysis of different scenarios that refer to a specific district or region (see Reference [
13] and references within). For example, LCA was employed to compare 12 management scenarios, 10 of which differed only in the separate collection yields of specific fractions, in order to identify the system leading to the lowest environmental impacts for Avellino province in southern Italy; the results showed that the best performance could be achieved for the highest separate collection yield, with regard to paper and cardboard recycling in particular [
5]. In another study, LCA was employed to analyze the environmental impacts of different integrated waste management strategies for two provinces in northern Italy (Piedmont region); separate collection and downstream recycling resulted in both cases as the most effective tools to improve energy efficiency and to lower environmental impacts [
14]. Another LCA carried out for different provinces of Lombardy region in northern Italy analyzed both the environmental impacts related to the actual integrated waste management scenarios at the time of the analysis and those resulting from future modifications; an increase in the separate collection of recyclable fractions (and consequent decrease in residual waste for disposal) again yielded an overall great improvement and benefits at both the environmental and energy level [
15].
LCA was employed also in this study to analyze the potential environmental impacts associated with an integrated system adopted to manage, in this case, the waste generated in the Sinistra Piave Basin. However, here, the two analyzed scenarios are not different options or future scenarios based on specific assumptions, but two past scenarios referring to two specific years characterized mainly by differences with regard to the type of waste collection system adopted and consequent separate collection yield achieved, as well as other differences concerning the location of treatment plants and the treatments adopted for residual fractions. Specifically, the analysis regarded the evaluation of the impacts related to the management of the following fractions: paper and cardboard, glass, multi-material (plastics and metals), food waste, garden waste, and the dry residual fraction. In the year 2015 (scenario 1), the collection of the abovementioned materials was carried out almost exclusively (98%) by a door-to-door system, whereas, in the year 2004 (scenario 2), a mixed collection method, leading to a lower separate collection yield, was adopted. The aim of this study was to quantify the environmental benefits resulting from the system for which the higher separate collection yields were achieved and to identify the system modifications that lead to the greatest savings in terms of impacts, in order to propose strategies that may yield further potential improvements. The results of the study can be of interest both for MSW management stakeholders and for citizens to motivate their contribution in increasing separate collection yields.
4. Conclusions
This LCA study was aimed at evaluating the environmental impacts of a consortium-based waste management system with regard to six MSW fractions and two different years. The aim was to investigate the effect of the increase in separate collection rates achieved in over 10 years on potential environmental impacts, and to identify the sub-processes that are more critical in terms of impacts for one or more categories, thereby identifying potential further improvements that could be implemented. Overall, the results of the study indicated that an efficient separate collection system, coupled with plants employing technologies that allow obtaining material and energy recovery, may lead to great benefits in terms of the reduction of environmental impacts.
The overall recycling efficiencies achieved appear to already be in line with the EU targets for 2025. An exception may be plastics and metals that were collected together as a multi-material fraction and for which it was not possible to separately evaluate the recycling yields achieved. In order to be able to better monitor the amounts collected, treated, and prepared for recycling for each of these types of materials, dedicated separate collection strategies could be implemented also for specific types of plastics presenting the highest recycling potential (e.g. PET). In this study, a rough estimate was made with regard to the composition of the recovered plastics; therefore, it would be important in the future to analyze the average composition of the collected plastics and the actual recycling rates achieved for each type.
The collection and transport stages were shown to exert a lower contribution to impacts (the former in particular) compared to treatment. However, in addition to the optimization of the geographic location of the treatment plants, another improvement that may reduce the impacts of these phases is the change in type of collection/transport vehicles employed. To this regard, the consortium started substituting its vehicles with biomethane-fueled ones, since the anaerobic digestion plant treating the organic waste fraction was recently equipped with a biogas upgrading unit.
As for the treatment stage, material recycling, which was significantly promoted by the change in type of collection method, was shown to be a key contributor for reducing impacts. As for the treatment/disposal of residues, although there was an almost four-fold decrease in landfilling, ecotoxicity impacts were still positive. Therefore, in order to allow reducing impacts even more, further waste diversion from landfills, if feasible, should be pursued. With regard to the better performance found for eutrophication for the 2004 scenario compared to the 2015 one, it should be considered that the wastewater treatment model process that was used to estimate the emissions is less advanced with respect to the one implemented in the plant receiving the consortium’s organic waste; therefore, the impacts may have been overestimated. Also, in this case, a more accurate modeling of the process based on plant data could be performed.