Introduction

The incorporation of environmental sustainability as a relevant dimension is increasingly becoming an essential practice when addressing the integrated management of municipal waste (MW) as a whole system, in the context of the shift towards a more circular economy (Pires et al. 2011). For instance, the policies promoted by the European Union (EU) on waste management have been orientated to meet this requirement (European Commission 2014; European Parliament and Council 2008). As a consequence, the need for analysing and evaluating the performance of the MW management systems has been gaining significance (Pires et al. 2011). Outside of the EU and other high-income nations, developing countries are facing an even more urgent challenge to assess their waste management practices, due to the fast-growing urbanisation processes taking place in those countries (Karak et al. 2012).

These performance analyses have been typically linked with the use of indicators in order to communicate results (Ferreira et al. 2017). The use of indicators was long ago established in the economic and social fields and was later extended (after the 1992 Rio de Janeiro Conference on Environment and Development) to the environmental studies and, particularly, waste management (Ristić 2005). Several innovative proposals on the use of performance indicators for evaluation of MW management systems have been published. Guimarães et al. (2010) suggested for Portugal an approach based on the Balanced Scorecard methodology, later tested by Mendes et al. (2012, 2013). Armijo et al. (2011) proposed a set of indicators fitting in a DPSIR model (Driving force-Pressure-State-Impact-Response). Greene and Tonjes (2014) and Liu et al. (2017) developed sets of indicators and applied them to the particular contexts of the USA and China, respectively; the former also developed a scoring system to evaluate the quality of the indicators. Wilson et al. (2012) analysed waste management performance and governance in 20 cities around the world, a work further updated to become the “Wasteaware” benchmark indicators (Wilson et al. 2015). More examples are found in a revision on the issue presented by Sanjeevi and Shahabudeen (2015).

Indicators can be understood as the result of “compacting” a large amount of information in order to handle it in a manageable format, which allows to quickly realising whether or not a given objective within a project is being reached as expected, and to which extent. In fact, indicators are often the way to transfer to the general public—regardless of technical background—the results supplied by more complex tools. Several of these tools have been used to study MW management, with a significant prevalence of Life Cycle Assessment (LCA) (Pires et al. 2011), and also Life Cycle Cost (LCC) (Sousa et al. 2018). LCA has currently become a common, well-established approach to assess the performance of waste management, primarily regarding the environmental dimension—a thorough review of applications in this field is given by Laurent et al. (2014a, 2014b). However, it requires a costly process of elaboration and, as pointed out by Blengini et al. (2012), it is not easy to understand for non-experts. Therefore, the diverse group of stakeholders involved in waste management planning is not always fully aware of the potential of this analysing tool. This is especially relevant for administrators responsible for taking decisions, who tend to rely more on financial considerations than on environmental benefits (Blengini et al. 2012).

Without overcoming the importance of more complex analysis such as LCA, the incorporation of an integrated indicator which could act as a simplified preview of conclusions about the sustainability of a given system is regarded as worthy of interest. In recent times, there has been some contributions to such an idea of a simple and comprehensive waste management sustainability indicator, including the methodology based on metabolic perspective developed by Fragkou et al. (2010), the “Zero Waste Index” created by Zaman and Lehmann (2013) and tested by Zaman (2014) and the composite indicator proposed by Rigamonti et al. (2016). However, these valuable approaches still leave some questions open to further discussion, one among those being how to take into account the waste prevention efforts. Environmental sustainability can only be fully achieved if the generation of waste is decoupled from economic activity; the mere existence of the “waste” concept is actually a sign of inefficiency. Also, this kind of global sustainability indicators should consequently pay attention too to the economic considerations and social issues related to MW generation and management, even if they are only addressed in a brief manner. In this work, a simplified sustainability set of indicators combining the three aspects environmental, economic and social is developed, with the aim of assessing the progress towards sustainability of the waste management system in a given municipality. This methodology was then applied to two Portuguese municipalities selected for the study.

Building the framework

Overview

The proposed set of indicators was developed taking into account the three essential dimensions of sustainability: environmental, economic and social. Furthermore, instead of more common performance indicators reflecting a static picture of the actual situation of the analysed system—which are more intended to compare different alternative waste treatment options or for benchmarking purposes—the approach followed was more focused on the conceptual view of dynamic progress towards sustainability of a waste management utility. Sustainability should be regarded as an ideal situation to be achieved through continuous improvement in each of the three dimensions. Therefore, the framework is organised into three components of progress: (i) environmental; (ii) economic; and (iii) social. To represent each component, two single indicators were selected, resulting in a set of six indicators to compose the whole framework (Fig. 1). The scores on the individual indicators were later aggregated to obtain a single result of overall progress. The framework is generalisable to any context, but it was designed thinking on low-performing waste management utilities eager to improve. In this context, there will be a higher potential for improvement and the proposed framework will be more useful. For high-performing waste management utilities, the framework will provide little information, unless a significant decline is observed. For low-performing utilities with no effort to improve, the framework will be of little or no use.

Figure 1
figure 1

Scheme for the framework

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The definition of each indicator is based on the same logic of comparison between current and previous states, which is shown, in a general form, by Eq. 1:

$$ \%\mathbf{sustainability}\ \mathbf{progress}=\frac{\left(\mathbf{situatio}{\mathbf{n}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}-\mathbf{situatio}{\mathbf{n}}_{\mathbf{year}\ \boldsymbol{i}}\right)}{\mathbf{situatio}{\mathbf{n}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}}\cdot \mathbf{100} $$
(1)

In the proposed form, and also in the proposed indicators explained in the following sections, the comparison is made between the “current” year—actually, the last year with available data—and the previous one—actually, the previous year with available data, thus measuring progress in time. The development presented herein adopts a yearly time scale, since this is a typical time interval for the organisations within the waste management sector to report results, but the user is free to adapt the indicators to other time periods, provided that the required data are available. As seen in Eq. 1, the sign of the indicator provides a simple test to check if the system is progressing towards sustainability (if positive) or, on the contrary, moving away from it (if negative), along with a relative measure of how great the progress (or regression) has been. The variables for each indicator should be used in the form of per capita values when this is applicable, to exclude the effect of population changes between different years. In mathematical terms, any performance indicator in the form of a ratio fails if the value in the denominator is zero (situationyear i − 1 = 0). If this happens, the indicator needs to be computed by one of the following options: (i) if situationyear i also equals to 0, then there is no progress and the indicator result is 0; or (ii) if situationyear i is not 0, then the indicator should take the value of − 100%. The possibility of this situation will be assessed and discussed for each of the proposed indicators.

The ability of the framework to reflect the actual changes taking place in MW generation and management essentially depends on the variables chosen to constitute the indicators that are part of it. The variables were selected attending to the following: (i) the feasibility of being calculated in the form of comparison proposed in Eq. 1; (ii) the availability of readily accessible data to calculate their correspondent values; and (iii) their representativeness of the effects derived from the implementation of a given waste management policy. In this way, the indicators allow the evaluation of the influence of these policies in altering waste flows or consumer behaviour. The selected variables and the indicators derived from them are described in detail in the following sections, for each of the three components of sustainability—environmental, economic and social.

Environmental component

A significant focus for the waste management utilities has been in enhancing separate collection and source separation of recyclable materials. However, within the field of environmental sustainability, it has been already pointed out that the ability to effectively decrease the amount of waste generated independently of the economic activity and wealth is also necessary to achieve the goal of true sustainability. Reduction of the environmental impacts associated with the production and consumption of goods and services will imply the adoption of more environmentally friendly practices by all the supply chain (manufacturers, distributors, retailers, consumers, waste managers, raw/recycled materials suppliers) as well as the consumers. Strengthening of Extended Responsibility schemes (regarding the use of packaging materials), and change of consumer patterns—for instance, through the application of PAYT (pay-as-you-throw) strategies—may contribute to that change actually happening.

On the other hand, waste management entities have the responsibility of implementing the best available practices in accordance with environmental sustainability. Currently, the main guideline for efficient waste management in Europe is given by the waste management hierarchy. Despite some limitations (Van Ewijk and Stegemann 2016), the waste management hierarchy has been widely accepted as a valid scheme of priorities between waste management options and was officially adopted by the EU through the Waste Frame Directive of 2008 (European Parliament and Council 2008). Based on this hierarchy, which places landfilling as the worst option, in the last decades, authorities have focused in improving their performance through the closure of landfills and the diversion of MW to newly established facilities for recovery and valorisation: sorting facilities for recycling, mechanical-biological treatment (MBT) units or Waste-to-Energy (WtE) plants. This has displaced the waste upwards in the waste hierarchy (EEA 2013). Actually, except for the upper categories of the waste hierarchy referred to prevention and reuse of waste materials, every other waste management option usually involves to some extent landfilling of non-recovered materials, either as direct disposal or as secondary disposal of materials rejected in the previous recovery activities. This indirect relationship of the waste hierarchy with landfilling activities is reflected in Fig. 2.

Figure 2
figure 2

Relationship of waste hierarchy with landfilling

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These progress are usually evaluated by means of indicators which measure either the recycling rate or the waste diversion from landfill (Zaman and Lehmann 2013). However, the use of such indicators can lead to some misconceptions. The use of recycling rates has been criticised for not being sensitive to the impacts of other treatment options than recycling (Greene and Tonjes 2014). On the other hand, waste diversion figures are sometimes referred to considering landfilling only as a primary treatment option (i.e. direct disposal without any other treatment). In the case of mainland Portugal, while this direct disposal of MW in landfills has been considerably reduced (from 62% in 2010 to 29% in 2016) (APA 2017a), the global disposal in landfills counting also materials rejected after sorting, MBT or WtE is still high. The entities responsible for MW management in mainland Portugal declared that in 2016, around 51% of waste treated went to landfills as the final destination (APA 2017). This global landfilling rate is the selected variable for the first proposed environmental indicator, since it can represent not only the environmental performance of waste management systems—the more landfilling, the less sustainable—but also, to some extent, the variations in waste generation caused by reduction efforts and change on the behaviour of consumers.

Therefore, making use of the general formulation presented in Eq. 1, an indicator of progress in the reduction of final landfilling (Indicator 1) is presented in Eq. 2:

$$ \%\mathbf{progress}\ \mathbf{in}\ \mathbf{landfilling}\ \mathbf{reduction}=\frac{\left(\mathbf{global}\ \mathbf{MSW}\ \mathbf{landfille}{\mathbf{d}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}-\mathbf{global}\ \mathbf{MSW}\ \mathbf{landfille}{\mathbf{d}}_{\mathbf{year}\ \boldsymbol{i}}\right)}{\mathbf{global}\ \mathbf{MSW}\ \mathbf{landfille}{\mathbf{d}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}}\cdot \mathbf{100} $$
(2)

As explained in “Overview”, a positive value in the indicator would mean less landfilling—and then, more sustainability—while a negative value would indicate the opposite trend. As seen in Eq. 2, a + 100% of progress would be reached only if final landfilling in year i is non-existent (a “zero waste” scenario), while on the other extreme, negative progress of − 100% or even worse might be obtained if landfilling increases dramatically. Since a full circular economy implies the diversion of all waste from landfilling, this indicator may fail in mathematical terms in the future due to a zero denominator. However, this scenario means that there is no possibility for more positive progress and it is only possible to maintain (0 progress) or regress (− 100% progress).

As explained before, the result of Eq. 2 considers the possible decrease of MW landfilled regardless of the reason behind that decrease—either MW generation reduction efforts or MW diverted from landfill towards recycling and valorisation processes. For instance: a system able to reduce MW generation by 50% through reduction efforts without changing anything in treatment processes would obtain the same progress towards environmental sustainability as another system which improves by 50% its performance in waste collection and treatment—e.g. due to higher segregate waste collection ratios, better recovery of recyclables at the treatment plant, etc.—with the same MW generation rates.

Nevertheless, the representativeness of the indicator is limited by the implicit assumption that MW is a homogeneous flow with constant composition—something which obviously does not correspond to reality. Actually, the indicator is more sensitive to changes affecting the flow of mixed or residual MW, since, as already mentioned, the most usual treatment options applied to this flow always involve to some extent landfilling, either as direct disposal or in indirect form. On the other hand, recyclable materials (which are separated at source, separately collected and directed to recycling processes) are not landfilled except for a small, refused fraction. For instance, in Portugal, this refused fraction, made of non-recyclable materials, is estimated as roughly 5–10% of the MW in separate collection flows. In this case, the indicator will detect variations only to a limited extent. Take for instance a reduction of 100 t in the amount of mixed waste, which would result in a reduction of 51 t of the amount landfilled considering the present performance of the MW treatment plants in Portugal. A reduction of the same 100 t in the recyclable fractions represents a reduction in landfilling of only 5–10 t. In other words: the proposed indicator is able to detect transfers of waste between the lower categories of the waste hierarchy—those more related to treatment of mixed MW—and the upper categories, but it is less sensitive to transfers between reduction of MW generation and the other high categories in the hierarchy—those related to reutilisation and recycling. Notwithstanding this, and taking into account that landfilling is still the predominant waste disposal method (Karak et al. 2012), the proposed indicator has still a remarkable potential to provide information about the evolution of MW management in countries with poor separation rates.

In order to improve the ability to reflect changes between the upper categories of the waste hierarchy, a second environmental indicator (indicator 2) was proposed as simply the progress in waste reduction based on the variation of the amounts of MW generated, defined in analogous manner as Eq. 2 and presented in Eq. 3:

$$ \%\mathbf{progress}\ \mathbf{in}\ \mathbf{waste}\ \mathbf{reduction}=\frac{\left(\mathbf{MW}\ \mathbf{generate}{\mathbf{d}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}-\mathbf{MW}\ \mathbf{generate}{\mathbf{d}}_{\mathbf{year}\ \boldsymbol{i}}\right)}{\mathbf{MW}\ \mathbf{generate}{\mathbf{d}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}}\cdot \mathbf{100} $$
(3)

A positive value in the indicator would mean less waste generated, while a negative value would indicate the opposite trend. If the waste generated would become 0, there would be no need for waste management, so it is not logic for this indicator to fail in mathematical terms.

This second indicator complements the previous for assessing the overall goal of waste prevention, providing an indication of the waste efficiency of production, services and consumption. However, this indicator alone fails to capture a full circular economy—if a waste stream is fully recycled and forms a closed loop of production-consumption-recycling, the amount of waste generated will be constant.

The two indicators proposed herein allow addressing separately progress in MW reduction, which divert waste from all other categories towards the top of the hierarchy, and improvements in waste treatment, which simply divert waste from the lower towards the upper categories. Their combination provides a robust evaluation if progress in the environmental dimension of sustainability is being achieved.

Economic component

The question of the financial sustainability of MW management has been worthy of special attention in recent years. The current trend regarding this issue, encouraged by the EU waste policy, is that financing of MW management should rely on the “Polluter-Pays-Principle” (European Parliament and Council 2008), thus assuring equity among citizens. In the case of Portugal, the practical consequence of this policy is that a regulatory board enforces municipalities to equilibrate all expenses and revenues related to the waste management service, making it self-sufficient in financial terms while excluding the possibility of obtaining an economic benefit from waste tariff fees (MAOTE 2014). Even though this situation is still far from being accomplished, there has been a noticeable improvement from the situation reported in 2007, when Portuguese municipalities could only recover on average 30% of expenses on waste management (Simão Pires 2013), to the situation in 2017, when the revenues accounted for 83% of the total costs (ERSAR 2017). It should be noticed that there are large differences between municipalities: in 2017 only 25 municipalities (out of 278 in mainland Portugal) attested to have attained the required financial balance (ERSAR 2017). In the cases where a deficit exists, the remaining costs are subtracted from the municipal budget.

The same situation exists in countries where the cost of MW management is still not recovered by charges. Nevertheless, and despite divergences in different national and local regulations, it can be stated in a general manner that the main driver in MSW financing should be to achieve this full balance between expenses and revenues; hence, both deficit and profit situations are not desired. Therefore, it seems adequate to define the first indicator for assessing the economic component of sustainability (indicator 3) as the evolution of MW management financial balance, as presented in Eq. 4:

$$ \%\mathbf{progress}\ \mathbf{in}\ \mathbf{financial}\ \mathbf{balance}=\frac{{\left|\mathbf{revenue}-\mathbf{expenses}\right|}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}-{\left|\mathbf{revenue}-\mathbf{expenses}\right|}_{\mathbf{year}\ \boldsymbol{i}}}{{\left|\mathbf{revenue}-\mathbf{expenses}\right|}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}}\cdot \mathbf{100} $$
(4)

This equation gives a value different from zero if revenues and expenses are not equal. Therefore, by making use of absolute values, both deficit and profit situations are penalised and the indicator measures the progress towards the financial balance. Since the financial balance is possible and desirable to achieve, this indicator will most probably fail in mathematical terms due to a zero denominator, so the solutions presented in “Overview” need to be used to compute it.

On the other hand, it seems clear that every reduction of costs can be understood as a positive contribution towards the economic sustainability of waste management. In an analogous manner to the role of landfilling in the environmental indicator introduced by Eq. 1, the improvements in operational efficiency can be tracked through the evolution of associated costs. This gives way to the second economic indicator (indicator 4), presented in Eq. 5:

$$ \%\mathrm{progress}\ \mathrm{in}\ \mathrm{costs}\ \mathrm{reduction}=\frac{\mathrm{expense}{\mathrm{s}}_{\mathrm{year}\ i-1}-\mathrm{expense}{\mathrm{s}}_{\mathrm{year}\ i}}{\mathrm{expense}{\mathrm{s}}_{\mathrm{year}\ i-1}}\cdot 100 $$
(5)

In a circular economy context, it is not impossible to assume that the waste management service may have no costs to the waste producers in the future, but there will always be expenses to provide the service, so the indicator does not fail in mathematical terms due to a zero denominator.

This definition presents the advantage of being sensitive to changes in pricing policy, as well as to other measures intended to improve savings or reduce costs, thus directly altering monetary flows, but it also takes into account the economic effect produced by changes on the MW amount, i.e. a decrease in waste generation would lead to a reduction of the variable costs, e.g. in collection. In this context, Eq. 4 measures the operational efficiency improvement in the waste management service and Eq. 5 the operational efficiency improvement in the link between the waste management sector and the industry reusing waste. Moreover, in the approach suggested in Eq. 5, a lower financial burden on MW for municipalities could be interpreted as indicative of improved efficiency in its management. This would be due either to a lower generation of waste or to a higher recovery of costs through sales of valuable materials or energy produced from waste. In fact, if waste materials are just considered as rejects with no economic value—a consequence of inefficient processes, as stated in “Introduction”, then the existence of an economic charge in the form of a waste tariff is justified by the inevitable need for proper management and disposal of this waste. But if, on the contrary, waste is regarded as a source of valuable resources, suitable to be recovered and reused, then the cost of its management would be compensated by its economic value. So, instead of being subject to a charge, waste materials would be handled as goods with a market price. This already happens in the case of recyclable materials which are separated at the source by consumers and sorted to be later sold to the entities responsible for the recycling. Actually, in 2011, it was estimated that the recycling industry accounts for roughly 1% of the EU Gross Domestic Product (GDP) (European Commission 2011). In an ideal situation of zero waste and circular economy, the existence of waste tariffs would thus be unnecessary.

Social component

Social implications of waste management are probably the most difficult to clearly assess and, as such, still not widely researched (Yıldız-Geyhan et al. 2017). Municipal waste management is typically a complex system which involves different stakeholders and, not rarely, with opposite views between them (Blengini et al. 2012). Therefore, the link between processes and impacts is not straightforward—which, actually, is the usual situation in social impact assessments (Dreyer et al. 2006). Nevertheless, in the case of recycling, there exists an agreement in considering that an increased recycling level is socially beneficial (Bio Intelligence Service 2011, 2015, CE Delft 2013). These social benefits derived from recycling activities are mainly focused on the development of the recycling industry with subsequent creation of jobs and contribution to the economy. This focus on employment opportunities is a common approach to characterise social benefit (European Commission 2018; Ferrão et al. 2014). However, reliable data on the number of real employments created by waste management policies are not always available. In fact, depending on where the recycling facilities are located, these new jobs may be created in geographical areas far from the waste is being generated and, as such, may be out of the scope of the study (e.g. transfers of waste from Europe to East and South Asia, or to other developing countries). Moreover, jobs creation is just only one of the variables of concern when assessing social performance. Other less quantifiable dimensions, such as satisfaction of the population with the waste management system or engagement of people with more environmentally friendly attitudes and practices, play a key role for the success of a given waste management policy (Dunne et al. 2008; Jones et al. 2010; Triguero et al. 2016).

In view of this complicated situation, it is necessary to establish priorities among the many existent social perspectives and variables. According to the UNEP & SETAC guidelines for social life cycle assessment, this prioritising is a necessary step when assessing social impacts (UNEP/SETAC Life Cycle Initiative 2009). As already mentioned, the involvement of the local community is essential for tackling the waste problem, thus assuming it as a collective issue rather than a “problem of no one”. Therefore, the preference in this work was to focus on the perspective of the population—the users of the system. These users interact with the waste management system mainly through their access to the waste collection service in order to dispose of the waste they produce. Hence, the indicators selected herein to represent the social component of sustainability refer to this interaction. Aiming at facilitating the data collection and enabling the practical use of the proposed indicators, it was decided to make use of information which, in Portugal as in other European countries, is readily available either through the environmental authority reports or directly from municipalities.

Firstly, as indicated by Wilson et al. (2015), the existence of the MW collection service is mainly justified to prevent public health problems derived from waste presence. Thus, in order to be really effective in meeting this target, the service must reach all citizens. The waste collection coverage, defined as the percentage of households which are adequately served by the waste collection service, is a common social performance indicator of MW management systems (Wilson et al. 2015). For instance, in Portugal, it is regularly reported by every municipality. According to Portuguese environmental authorities, to be “adequately served by the waste collection service” means in practice that the waste bins must be placed at a distance of not more than 100 m from every household in urban locations, or 200 m in rural ones. In 2017, the average level of coverage in mainland Portugal was 87% for the mixed MW collection service, but only 58% for separate collection schemes (ERSAR 2017). Considering the room for improvement which is still needed to fulfil the 100% target, particularly in terms of expanding access to separate collection service, the progress of this coverage is selected as the first social single indicator (indicator 5; Eq. 6):

$$ \%\mathbf{progress}\ \mathbf{in}\ \mathbf{accessibility}\ \mathbf{to}\ \mathbf{separate}\ \mathbf{collection}=\frac{\left(\mathbf{coverag}{\mathbf{e}}_{\mathbf{year}\ \boldsymbol{i}}-\mathbf{coverag}{\mathbf{e}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}\right)}{\mathbf{coverag}{\mathbf{e}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}}\cdot \mathbf{100} $$
(6)

It is noteworthy to remark that in this case, the order of operands in the numerator of Eq. 6 was reversed relative to the other indicators, in order to keep the same criterion for signs: positive for improvements, negative for decline. Moreover: by definition, if there is a waste management service, its coverage should not be zero. Therefore, this indicator does not fail in mathematical terms due to a zero denominator.

Aiming at a possible generalisation of this framework to other geographical contexts, it is likely that the accessibility to the collection service might be evaluated in a different manner for every place: in the worst case, the question would be to which extent a regular MW collection service exists. Therefore, the precise definition of accessibility, and thus the way of calculating the indicator, should be adapted to each particular situation.

Secondly, in line with the previous explanations, it was deemed convenient to somehow evaluate the satisfaction of users with the MW collection service. In Portugal, this information is currently not directly available, since no regular surveys are performed and a satisfaction indicator as such is not part of the published performance reports. However, municipalities keep records of all complaints and suggestions posed by citizens. Hence, the number of complaints related to MW collection was thought to be a reasonable general proxy indicator of the satisfaction with the system, so that a lower number of complaints would imply a higher level of satisfaction. In this way, the second social single indicator (indicator 6) is defined in Eq. 7 as the progress in reduction of the number of registered complaints:

$$ \%\mathbf{progress}\ \mathbf{in}\ \mathbf{complaints}\ \mathbf{reduction}=\frac{\left(\mathbf{complaint}{\mathbf{s}}_{\mathbf{year}\ \boldsymbol{i}}-\mathbf{complaint}{\mathbf{s}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}\right)}{\mathbf{complaint}{\mathbf{s}}_{\mathbf{year}\ \boldsymbol{i}-\mathbf{1}}}\cdot \mathbf{100} $$
(7)

Considering that the goal of any organisation is to have zero complaints, this indicator is highly prone to fail in mathematical terms due to a zero denominator. Again, the solutions presented in “Overview” need to be used to compute it.

With these two indicators, it becomes possible to assess the progress towards social sustainability for the local waste management system through the two evaluated aspects: if the waste management service is advancing on the accomplishment of its primary social function of preserving public health and safety, and if it is doing so in a satisfactory manner.

Practical application

Case of study

Two Portuguese municipalities—purposely named A and B—of different size and characteristics were selected as a case of studies for demonstrating the application of the proposed framework for evaluating sustainability progress. Municipality A is located on the Atlantic coast and is a significant industrial, trade, academic and touristic hub. It can be considered a medium-size city. Municipality B is a rural town in the inland, part of a bigger urban agglomeration. This municipality is mainly set on a rural environment, while the town itself acts as a local centre of services and possesses also some small industries. Both municipalities are currently interested in establishing PAYT systems, hence their interest in evaluating the sustainability of their MW management situation.

Both municipalities share the same MW management structure. The mixed fraction of MW is collected and treated on a mechanical-biological treatment (MBT) facility, where after the recovery of recyclable materials, the remaining organic-rich fraction is first anaerobically digested to produce biogas and then composted. There are also sorting centres for the classification of recyclable materials from a separate collection.

Data provided by the municipalities of MW generation in the last years are shown in Fig. 3, for both mixed MW and separate collected recyclable materials. In the previous years, a significant decrease in the waste generation was observed from 2010 until a slight recovery from 2014 onwards. This trend is the same registered for the whole country and is explained by the 2008 economic crisis and beginning of recovery after 2014. It is also observed that separate collection is at a much lower level than mixed collection, reaching only roughly a 7% of the total amount in both municipalities A and B. This is a poor yield, even if compared with the national average (14.4%, see 2.2). Moreover, this value has remained mostly stagnated over the last years. Both negative figures suggest that the municipalities still have to do more efforts to face this problem.

Figure 3
figure 3

MW generation in tonnes per year (■ mixed MW municipality A; ♦ separate collection municipality A; ● mixed MW municipality B; ▲ separate collection municipality B)

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Results

As previously explained, the values for the six indicators of the framework were determined making use of the available information for the two selected municipalities.

Environmental results

For the indicators in the environmental component, the results are shown in Table 1 for the period 2015–2016 and based on per capita values. The quantities of MW are the ones annually reported by the managing entity; the share of global landfilling is reported only for the entire management system, serving 36 municipalities on the same region. Thus, the percentage of landfilling declared for the whole system was assumed to be the same for each municipality. Regarding the landfilling reduction indicator (Eq. 2), for both municipalities, the amount of MW effectively landfilled increased; hence, the indicator shows negative values. Also, a negative result—moving away from sustainability—is verified for the reduction indicator (Eq. 3), since the total waste generation also increased.

Table 1 Results for environmental sustainability indicators
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According to the objectives set by Portuguese Government (MAOTE 2014), by 2020 the per capita generation of MW should have decreased at least a 10% with respect to 2012. However, this objective is currently far from being met, since per capita municipal waste generation rate has increased by 4.6% between 2012 and 2016 (INE 2016). MW generation has increased again in the last years, accompanying the recent economic growth, thus confirming that waste generation is still directly related to economic activity. A second circumstance might be also the inefficient performance of MBT facilities, which might be partly attributed to the low “quality” of the incoming waste, consequence of the poor degree of source separation and the lack of customers for the sale of refuse-derived fuel (RDF).

If economic recovery continues in the future, this increasing trend of generation will probably follow the same path, therefore moving away from the desired goal of sustainability.

Economic results

In the case of economic sustainability, the results are presented in Table 2. Data for expenses and revenues were retrieved from the Portuguese National Statistics Institute (INE 2016). In both municipalities, the results of the indicators show that costs have been reduced, despite the increase in MW generation. Hence, it can be concluded that economic efficiency has improved in the period considered.

Table 2 Results for economic sustainability
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With regard to financial balance, relevant progress has been achieved: in 2015, both municipalities found themselves in a profit situation where the revenues from waste tariff were higher than the expenses, but in 2016, municipality A has reversed the situation reducing both expenses and revenues up to a point of slight deficit, while municipality B has reached the objective of financial balance. This progress is reflected in the value of the correspondent indicator, which shows a result of 100% progress. According to the definition of Eq. 4, this result means that the gap from the initial situation has been fully overcome, so that sustainability in financial balance has been attained. In this situation, no further progress could be expected in the future, other than preserving the current optimal situation. This corresponds to the particular limit situation explained in “Overview”.

Social results

Finally, for the social dimension, the values for both progress in accessibility to separate collection and number of complaints are shown in Table 3 for municipality A and municipality B. The first one showed clear negative results for both municipalities. The reason behind this trend is the changes applied by the Portuguese regulatory body to the methodology for determining the degree of collection coverage, which aimed at obtaining a more realistic picture of the situation. In general, the revised values widely showed poorer accessibility to the service than previously thought. This lack of accessibility has been pointed out as a relevant reason for the low performance of separate collection in Portugal and other European countries (Struk 2017; Oliveira et al. 2018). This fact opens a room for improvement by the municipalities in the next years.

Table 3 Results for social sustainability
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Regarding the evolution in the number of complaints, the results differ between both municipalities: while in municipality A they have decreased, in municipality B there was an augment between 2015 and 2016 and, as seen in the information of Table 3, the relative number of complaints has surpassed that of municipality A. A large part of these complaints are about the placement of MW roadside containers, so this indicator is partially related to the previous one dealing with accessibility to the collection service. The rest of the complaints are mostly about the general quality of the collection service and issues related to the tariff.

Global progress

The calculated values for the six indicators are jointly shown in Fig. 4, which can be understood as a combined representation of the overall progress towards sustainability of waste management in municipalities A and B. From this figure it can be concluded that, while the economic situation of waste management in the municipalities is advancing in the good direction, i.e. achieving a balanced situation and reducing costs, this is not happening in the other two sustainability dimensions. In the environmental side, prevention measures are still not widespread, so that MW generation is still dependent on economic cycles. Moreover, the flows of materials are not moving in closed loops, as would be desirable from a perspective of a circular economy. The low degree of source separation in these municipalities is a major cause for this poor performance. This results in more MW sent to the landfill, with associated environmental impacts. In the social aspects, even though in municipality A complaints from citizens have decreased, new actions and measures are still required to improve the quality of the service. Particularly, the accessibility to the collection of recyclable materials needs to be further extended. This would also be helpful to improve environmental performance by diverting more waste from landfilling.

Figure 4
figure 4

Combined results for progress towards sustainability

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If the results of the six indicators are averaged, an integrated “sustainability progress index” is obtained, as seen in Table 4.

Table 4 Global sustainability progress between 2015 and 2016
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In view of the results in Table 4, it may be concluded that Municipality A has progressed positively during the considered period. It has improved by 10% in the sustainability of MW management, while Municipality B has worsened its situation by 3%. However, it would be necessary to discuss whether it is fair or not to attribute the same importance to every indicator. The result would probably be altered if some kind of weighting were assigned to each of the indicators in the set, in order to “normalise” them. This normalisation step is usually regarded as a sensible matter which requires careful judgement based on experience (Rigamonti et al. 2016; Wilson et al. 2015). Moreover, the relative weight given to each variable is dependent on the context. For instance: as pointed by Greene and Tonjes (2014), preserving public health through the access to the MW collection system might be a more urgent challenge in developing countries than in industrialised ones, where environmental issues are currently a more important concern because accessibility is already mostly assured. For the sake of simplicity, in this analysis, it was decided to give the same weight to each indicator as a first assessment, leaving the question of a more accurate weighing procedure for future studies. Perhaps a transformation of the different impacts into monetary flows could be an appropriate way for normalisation.

Conclusions

The proposed framework for sustainability progress evaluation can be employed as a simple communicating tool to quickly assess the performance of the waste management system in a municipality, making use of publicly and readily available data. The results provide a clear picture of the progress towards sustainability and circular economy, thus helping to evaluate where the efforts should be focused.

The followed approach relies on calculations which, intentionally, are not excessively complicated. An open question (discussed in “Global progress”) remains, when considering how the different results on the environmental, economic and social indicators could be numerically normalised and synthesised in a single “sustainability progress index” by some kind of weighting. This consideration about normalisation leads to another thorny question when addressing waste management assessments: how to ensure comparability between different cases? Besides the problem of comparing different sources of data, the specific features of each case play also a relevant role. The two municipalities chosen as the case of study in this work provide an adequate example: it seems clear that a city or urban area can count with more financial and technical resources to afford measures and policies directed to tackle the waste problem than a rural town. Therefore, the level of demanded performance achievements should be adapted to each situation—contrary to the current practice in Portugal of establishing common rankings of municipalities related to the level of accomplishment of general objectives. Nevertheless, the proposed framework is deemed as useful to inform if improvement efforts in MW management are being done in the right direction, and how fast are they progressing.

Further testing of the framework in new municipalities and in countries other than Portugal could be an interesting source for further improvements. Some other issues, such as the benefits of energy recovery from waste or a more thoroughly evaluation of the social implications may also be included in future updates of the study.

A final comment regarding the framework is that it is not suitable for benchmarking purposes, since the progress is not an indicator of the absolute performance. In fact, worse-performing utilities have a larger margin for improvement and could, therefore, present higher progress than waste management utilities already performing well (in theory, a perfect case scenario has no room for improvement and the progress will be zero). As such, the framework is particularly useful for contexts such as the Portuguese, where significant improvements have to be implemented to achieve sustainability in waste management.