3.1. Analysis of Scenario 1 with IPCC 2007 100y
shows the results obtained with IPCC 2007 100y in terms of the environmental impacts of each considered material for the treatment phase, collection phase and external transport to the treatment and disposal facilities. It also contains the percentage contribution (in absolute terms) that each material provides to the total value for the different phases.
Negative values represent an advantage in environmental terms because impacts are avoided. If a process provides negative impacts, it means that, after its adoption, the avoided impacts are greater than the produced impacts.
As shown in Table 5
, the impact values related to the treatment and disposal of the collected materials produce an overall negative impact (with positive and negative values for the single phases). On the other hand, the collection and external transport phases produce only positive impacts. It is worth noting that with IPCC 2007 100y, the overall environmental impacts of the waste management system of Baronissi municipality was positive. In fact, in terms of carbon footprint, the environmental burdens of the transport phases overcame the environmental benefits of the recycling and recovery phases.
In terms of total impact, for eight materials (i.e., aluminium, steel, glass, paper and cardboard, HDPE and PET from the separate collection; aluminium from the residual waste) out of sixteen (namely the 50%), the values of the impacts correspond to avoided impacts. The other eight materials gave positive impacts, with the organic fraction from the separated collection being the most impacting.
Regarding the source-separated organic fraction, the major contributors to the total impact were the collection and external transport. This depended on two factors: the large amounts collected and long distances to reach the composting plants outside the region.
Only four materials provided a percentage contribution greater than 10%: the source-separated aluminium (10.8%), the residual organic fraction (11.8%), the source-separated PET (11.5%), and the PET in the residue (14.5%).
The results obtained for the source-separated aluminium confirm the importance of the aluminium recycling in terms of global warming saving as already reported in other studies [2
It is worth noting that the source-separated PET contributed to the total global warming burden as avoided impact, whilst the residual PET generated positive impacts. In fact, on the one hand, recycling is the treatment for the source-separated plastic materials, while, on the other, incineration is the disposal method for the residual plastic materials. The obtained results emphasize the importance of the separate collection. In particular, the source separation of the plastic materials avoids the consumption of fossil fuels, on the one hand, and avoids the generation of hazardous pollutants due to the incineration processes, on the other [28
As shown in Table 5
, the organic fraction provided the greatest percentage contribution to the total impact for both the internal collection and external transportation. The high quantity of material produced as well as the long distances to reach the treatment plants were the main reasons for such an occurrence.
The phase of internal collection of source-separated paper and cardboard gave another important contribution for the total impact due to the large quantities produced. Finally, the external transportation of glass phase gave a significant contribution due to the long distances to reach the treatment plants.
3.2. Analysis of Scenario 1 with Ecological Footprint and ReCiPe 2008 H
shows the single point environmental impacts generated from the treatment phase, internal collection and external transport to facilities for each considered material calculated with Ecological Footprint and ReCiPe 2008 H. Analogously to IPPC 2007, for both the methods, the processing materials phase overall generated a negative impact, while the collection and external transport phases generated positive impacts.
However, for both the methods, contrary to what happened with IPCC 2007, the overall environmental impacts of the waste management system were negative, because the total avoided impacts of the treatment and disposal phases overcame the environmental loads produced by the collection and external transport phases.
The IPCC method, that only considers the impact category of the global warming, tends to overestimate the environmental burden of the transport phase compared with the avoided impacts of the treatment and disposal phases. Thus, the carbon footprint is not able to take into account the different advantages obtainable with a good level of separate collection and consequent recovery of materials. In fact, only considering the obtained results from a global warming perspective, it had to be concluded that it would not be convenient to push for an increase of the separate collection level.
Analysing the results for each single MW fraction, with Ecological Footprint and ReCiPe 2008 H, ten materials out of sixteen gave total avoided impacts. They were the same eight of the IPPC plus the source-separated organic fraction and the source-separated plastic mix.
The source-separated organic fraction goes to the composting process for the production of an agriculture soil conditioner (i.e., the compost) with a proper fertilising capacity [29
]. The use of compost avoids the production of mineral fertilizers. Due to their multiple-issues approach, Ecological Footprint and ReCiPe 2008 are able to take into consideration the avoided impacts due to the avoided production of mineral fertilizers. On the other hand, due to its single-issue approach, IPCC 2007 is not able to consider all the advantages and drawbacks of the recovery of materials and energy obtainable with the source-separated collection.
The recycling process of the source-separated plastics mix provides recycled plastic as a final product to use as street furniture components (benches, fences, planters); this would avoid using wood for the construction of such components [24
]. Analysing the contributions of each damage category of Ecological Footprint (see Table 7
), it is evident that Land occupation predominates largely over the others and provides a contribution in terms of avoided impact, while the category that takes into account the CO2
production contributes with a positive impact. This is in line with the results obtained with the IPCC method that, in fact, assigns a positive impact to the treatment source-separated plastic mix.
The Land occupation category of Ecological Footprint takes into account the avoided wood, replaced by recycled heterogeneous plastic. In fact, this category expresses the direct use of soil that is the quantity of biologically productive land needed to produce the resources consumed [25
] and therefore, in this specific case, it expresses the avoided utilization of land required in the production of wood.
The climate change impact category itself will not be able to evaluate properly all the aspects related to the recycling processes.
Similarly, ReCiPe 2008 takes into account the benefit of the avoided use of wood through one of its endpoints categories: damage to ecosystems. In fact, this category is the one that most influences the total impact and contributes in terms of avoided impact (see Table 7
Even for Ecological Footprint and ReCiPe 2008 H, it is interesting to analyse the obtained results in terms of percentage contributions that the impact of each single phase gave to the total impact, at the endpoint level (at the midpoint level this is obviously not possible due to the different impact category indicators). Table 8
shows only the percentage contributions relating to the treatment phase of materials because for the phases of internal collection and external transport, the percentage contributions are very similar to those obtained with IPCC (see Table 5
Regarding the results obtained with the Ecological Footprint, only the treatment of two materials provided a percentage contribution greater than 10%: the source-separated paper and cardboard (42.4%), and the source-separated PET (10%). While, in terms of ReCiPe 2008 H, three fractions gave a contribution greater than 10%: the source-separated paper and cardboard (27.5%), the source-separated PET (16.2%), and the source-separated steel (11.9%).
The source-separated paper and cardboard, especially in terms of Ecological Footprint but also for ReCiPe 2008 H, gave a predominant percentage incidence compared with the other materials. On the contrary, with IPCC, the contribution to the total provided by the source-separated paper and cardboard was only 5.8%.
To understand why the recycling process of source-separated paper and cardboard had such a significant influence on the total impacts calculated with Ecological Footprint and ReCiPe 2008 H, it is necessary to go into the details of the impact/damage categories of these two methods (see Table 7
Even in this case, as for the recycling process of source-separated plastics mix, the categories that most influenced the total impact giving a contribution in terms of avoided impacts were Land occupation for Ecological Footprint and Ecosystem for ReCiPe 2008. The use of recycled paper avoids the production of virgin paper for the same use: Ecological Footprint and ReCiPe 2008 H are able to take better into account the positive effects of the avoided production of virgin paper while regarding the problem of the deforestation.
It is interesting to carry out a focus on the results obtained with ReCiPe 2008 in order to evaluate what were the impact categories that contributed the most to the total impact of the waste management system (Scenario 1).
Among the categories that contributed for more than one percent, only Climate change provided a positive impact, thus representing an environmental burden.
Agricultural land occupation is the impact category that contributed the most (as an environmental saving) to the total impact with 36.3%; at the midpoint level, this impact was equal to −2,133,180 m2/year (corresponding to −126.8 m2/year/inhabitant). Fossil depletion and Metal depletion provided a percentage contribution of 28.4% and 16.2%, respectively; the impacts at midpoint level were equal to −274,099 kg oil eq. (corresponding to −16.3 kg oil eq./inhabitant) and −362,475 kg Fe eq. (corresponding −21.6 kg Fe eq./inhabitant), respectively. The results obtained for such categories highlight the environmental advantages achievable with a good level of source-separate collection that allows to recycle materials and, thus, to avoid the use of virgin raw materials.
The other two categories that contributed for more than one percent even providing a negative impacts were Particulate matter formation (3.0%; −1211.5 kg PM10 eq.) and Human toxicity (2.2%; −329,017 kg DB eq.). As already mentioned, Climate change was the only category, among those with a contribution more than one percent, that provided a positive value of impact (500,940 kg CO2 eq., corresponding to 29.8 kg CO2 eq./inhabitant). Such category at endpoint level is considered for damage caused to human health (Climate change Human Health) as well as for ecosystems damage (Climate change Ecosystems), and together they provided a contribution to the total impact of about 12%. The positive value of the impact is not a surprise and the reasons are the same previously discussed for the results obtained with the IPCC 2007 method.
The results highlight the importance of considering more than one single impact assessment method or, alternatively, more environmental impact categories in order to be able to assess all the different aspects related to the analysed processes. Considering more impact categories, it is important to try to put together the results obtained for the single categories. In fact, it is necessary to remember that LCA is a procedure to support decision makers. From this point of view, it is difficult to take decisions if the midpoint impact categories give conflicting results. In current literature, there are many studies discussing the results of LCA studies for each single impact category (usually global warming, acidification, eutrophication, etc.) without trying to give some suggestions to the decision makers. The damage categories at the endpoint level offer a valuable help in this sense.
3.3. Scenario 1 vs. Scenario 2
The obtained results highlighted the importance of the source-separate organic fraction collection and transportation to the treatment plants. This material contributed for 40% of the total impact of the internal collection and for 67% to the total impact of the external transport, with all the evaluation methods considered. As discussed above, there were two main reasons for this result: the high quantities collected as well as the huge distances to transport these quantities to the treatment plants located out of the region.
In order to highlight, in environmental terms, the importance of the presence on the territory of adequate treatment facilities, a second scenario was modelled in which the presence of a composting plant 10 km from the municipality of Baronissi was hypothesized. Comparing the environmental performances of the two scenarios, it was possible to show how the environmental performance of the common waste management system could improve.
a–c show the comparison between the environmental performances of the two scenarios considered, with the three evaluation methods adopted.
The results obtained for Scenario 2 show that there would be a clear improvement in the environmental profile of the waste management system because of the significant reduction of environmental impacts due to external transport, which are about one-third of the impact obtained for Scenario 1. Therefore, it is necessary to take into consideration the importance of the presence on the territory of appropriate facilities to support and improve the environmental performance of waste management systems based on the source-separate collection [15
The environmental impacts of the transport derive from the combination of travelled distances and transported quantities (of organic fraction in this case). Therefore, in order to reduce these impacts, in addition to shortening the distances, it can be useful to reduce the organic waste amount.
Using an openwork basket for the household collection of the organic waste allows to easily and conveniently reduce the quantity of putrescibles. In fact, the uniform openings around the entire basket (also below), together with a compostable plastic bag or compostable paper bag, facilitate water evaporation. The results are a weight reduction of 20%–30% as well as a complete disappearance of odours due to the reduction of putrescibility. The weight loss produces a consequent reduction of the environmental impacts of the municipal collection as well as the external transport to the composting plants.
d shows that the transport phases (internal collection and external transport) gave the most significant percentage contribution with IPCC 2007 for both the compared scenarios. On the contrary, the treatment and disposal phases (T & D) had a percentage incidence on the total impacts calculated with Ecological Footprint and ReCiPe 2008 H greater than 72%.
Once again, the obtained results show that, considering an assessment method that consider a unique impact category, there is a certain risk of misleading conclusions.