Waste Management & Research: The Journal for a Sustainable Circular Economy

Anthropogenic sources of greenhouse gas emissions are known to contribute to global increases in greenhouse gas concentrations and are widely believed to contribute to climate change. A reference carbon dioxide concentration of 383 ppm for 2007 is projected to increase to a nominal 500 ppm in less than 50 years according to business as usual models. This concentration change is equivalent to an increase of 7 billion tonnes of carbon per year (7 Gt C year^—1). The concept of a stabilization wedge was introduced by Pacala and Socolow (Science, 305, 968—972, 2004) to break the 7 Gt C year^{— 1} into more manageable 1 Gt C year^{— 1} reductions that would be achievable with current technology. A total of fifteen possible ‘wedges’ were identified; however, an integrated municipal solid waste (MSW) management system based on the European Union’s waste management hierarchy was not evaluated as a wedge. This analysis demonstrates that if the tonnage of MSW is allocated to recycling, waste to energy and landfilling in descending order in lieu of existing ‘business-as-usual’ practices with each option using modern technology and best practices, the system would reduce greenhouse gas emissions by more than 1 Gt C year ^—1. This integrated waste management system reduces CO₂ by displacing fossil electrical generation and avoiding manufacturing energy consumption and methane emissions from landfills.

The global warming factor (GWF; CO₂-eq. tonne^—1 waste) performance of municipal waste management has been investigated for six representative European Member States: Denmark, France, Germany, Greece, Poland and the United Kingdom. The study integrated European waste statistical data for 2007 in a life-cycle assessment modelling perspective. It is shown that significant GWF benefit was achieved due to the high level of energy and material recovery substituting fossil energy and raw materials production, especially in Denmark and Germany. The study showed that, despite strong regulation of waste management at European level, there are major differences in GWF performance among the member states, due to the relative differences of waste composition, type of waste management technologies available nationally, and the average performance of these technologies. It has been demonstrated through a number of sensitivity analyses that, within the national framework, key waste management technology parameters can influence drastically the national GWF performance of waste management.

Historical data on organic waste and wastewater treatment during the period of 1970—2020 were used to assess the impact of treatment on energy and greenhouse gas (GHG) balances. The assessment included the waste fractions: Sewage sludge, food waste, yard waste and other organic waste (paper, plastic, etc.). Data were collected from Aalborg, a municipality located in Northern Denmark. During the period from 1970—2005, Aalborg Municipality has changed its waste treatment strategy from landfilling of all wastes toward composting of yard waste and incineration with combined heat and power production from the remaining organic municipal waste. Wastewater treatment has changed from direct discharge of untreated wastewater to full organic matter and nutrient (N, P) removal combined with anaerobic digestion of the sludge for biogas production with power and heat generation. These changes in treatment technology have resulted in the waste and wastewater treatment systems in Aalborg progressing from being net consumers of energy and net emitters of GHG, to becoming net producers of energy and net savers of GHG emissions (due to substitution of fossil fuels elsewhere). If it is assumed that the organic waste quantity and composition is the same in 1970 and 2005, the technology change over this time period has resulted in a progression from a net annual GHG emission of 200 kg CO ₂-eq. capita^—1 in 1970 to a net saving of 170 kg CO₂-eq. capita^—1 in 2005 for management of urban organic wastes.

Global warming factors (kg CO₂-eq.-tonne^—1 of waste) have been modelled for 40 different municipal waste management scenarios involving a variety of recycling systems (paper, glass, plastic and organics) and residual waste management by landfilling, incineration or mechanical—biological waste treatment. For average European waste composition most waste management scenarios provided negative global warming factors and hence overall savings in greenhouse gas emissions: Scenarios with landfilling saved 0—400, scenarios with incineration saved 200—700, and scenarios with mechanical-biological treatment saved 200— 750 kg CO₂-eq. tonne^{— 1} municipal waste depending on recycling scheme and energy recovery. Key parameters were the amount of paper recycled (it was assumed that wood made excessive by paper recycling substituted for fossil fuel), the crediting of the waste management system for the amount of energy recovered (hard-coal-based energy was substituted), and binding of biogenic carbon in landfills. Most other processes were of less importance. Rational waste management can provide significant savings in society’s emission of greenhouse gas depending on waste composition and efficient utilization of the energy recovered.

In an effort to obtain the most accurate climate change impact assessment, greenhouse gas (GHG) accounting is evolving to include life-cycle thinking. This study (1) identifies similarities and key differences between GHG accounting and life-cycle assessment (LCA), (2) compares them on a consistent basis through a case study on a waste management business unit. First, GHG accounting is performed. According to the GHG Protocol, annual emissions are categorized into three scopes: direct GHG emissions (scope 1), indirect emissions related to electricity, heat and steam production (scope 2) and other indirect emissions (scope 3). The LCA is then structured into a comparable framework: each LCA process is disaggregated into these three scopes, the annual operating activities are assessed, and the environmental impacts are determined using the IMPACT2002+ method. By comparing these two approaches it is concluded that both LCA and GHG accounting provide similar climate change impact results as the same major GHG contributors are determined for scope 1 emissions. The emissions from scope 2 appear negligible whereas emissions from scope 3 cannot be neglected since they contribute to around 10% of the climate change impact of the waste management business unit. This statement is strengthened by the fact that scope 3 generates 75% of the resource use damage and 30% of the ecosystem quality damage categories. The study also shows that LCA can help in setting up the framework for a annual GHG accounting by determining the major climate change contributors.

Global warming is a focus of political interest and life-cycle assessment of waste management systems reveals that energy recovery from municipal solid waste is a key issue. This paper demonstrates how the greenhouse gas effects of waste treatment processes can be described in a simplified manner by considering energy efficiency indicators. For evaluation to be consistent, it is necessary to use reasonable system boundaries and to take the generation of electricity and the use of heat into account. The new European R1 efficiency criterion will lead to the development and implementation of optimized processes/systems with increased energy efficiency which, in turn, will exert an influence on the greenhouse gas effects of waste management in Europe. Promising technologies are: the increase of steam parameters, reduction of in-plant energy consumption, and the combined use of heat and power. Plants in Brescia and Amsterdam are current examples of good performance with highly efficient electricity generation. Other examples of particularly high heat recovery rates are the energy-from-waste (EfW) plants in Malmö and Gothenburg. To achieve the full potential of greenhouse gas reduction in waste management, it is necessary to avoid landfilling combustible wastes, for example, by means of landfill taxes and by putting incentives in place for increasing the efficiency of EfW systems.

At Vienna University of Technology, the so-called balance method (BM) was developed to determine fossil and biogenic CO₂ emissions from waste-to-energy (WTE) plants. Meanwhile, the BM has been routinely applied to several WTE plants for some years, providing a large set of data. The average site-specific emission factors for fossil CO₂ were found to be in the range of 260— 780 kg CO₂ t^—1 waste, and 30—67 kg CO₂ GJ^—1 energy of the waste incinerated. These values are significantly different from the values that are found in the literature. Our results show that there is no such typical emission factor for WTE which could be applied to national CO₂ measurements or accurate emission trading. This study reveals that instead of generic emission factors the BM can be used as a standard for WTE plants, since its application requires either no or only a few additional installations.

A major challenge for modern waste management lies in a smart integration of waste-to-energy installations in local energy systems in such a way that the energy efficiency of the waste-to-energy plant is optimized and that the energy contained in the waste is, therefore, optimally utilized. The extent of integration of thermal waste treatment processes into regular energy supply systems plays a major role with regard to climate control. In this research, the specific waste management situation looked at scenarios aiming at maximizing the energy recovery from waste (i.e. actual scenario and waste-to-energy process with 75% energy efficiency [22.5% electricity, 52.5% heat]) yield greenhouse gas emission savings due to the fact that more greenhouse gas emissions are avoided in the energy sector than caused by the various waste treatment processes. Comparing dedicated waste-to-energy-systems based on the combined heat and power (CHP) process with concepts based on sole electricity production, the energy efficiency proves to be crucial with regard to climate control. This underlines the importance of choosing appropriate sites for waste-to-energy-plants. This research was looking at the effect with regard to the climate impact of various waste management scenarios that could be applied alternatively by a private waste management company in Austria. The research is, therefore, based on a specific set of data for the waste streams looked at (waste characteristics, logistics needed, etc.). Furthermore, the investigated scenarios have been defined based on the actual available alternatives with regard to the usage of treatment plants for this specific company. The standard scenarios for identifying climate impact implications due to energy recovery from waste are based on the respective marginal energy data for the power and heat generation facilities/industrial processes in Austria.

Greenhouse gas (GHG) emission reductions and utilization of landfill gas (LFG) were researched by comparing LFG displacing the use of natural gas (scenario 2) with electricity generation using LFG (scenario 3) at three different LFG collecting efficiencies; 35, 50 and 65%. The results show that the utilization of LFG in scenario 2 is 1.4 times that in scenario 3. GHG emission reductions generated by scenario 2 are slightly less than that of scenario 3. The GHG emission reductions and utilization of LFG are restricted by LFG collecting efficiencies. It will be helpful to improve the management level of landfill and the GHG emissions reduction by introducing the CDM. However, the utilization of LFG will be still short of financial attractiveness if the LFG collection efficiency is less than 50%.

Disposal of municipal solid waste in sanitary landfills is still the main waste management method in the Attica region, as in most regions of Greece. Nevertheless, diversion from landfilling is being promoted by regional plans, in which the perspectives of new waste treatment technologies are being evaluated. The present study aimed to assess the greenhouse gas (GHG) emissions impact of different municipal solid waste treatment technologies currently under assessment in the new regional plan for Attica. These technologies are mechanical—biological treatment, mass-burn incineration and mechanical treatment and have been assessed in the context of different scenarios. The present study utilized existing methodologies and emission factors for the quantification of GHG emissions from the waste management process and found that all technologies under assessment could provide GHG emission savings. However, the performance and ranking of these technologies is strongly dependent on the existence of end markets for the waste-derived fuels produced by the mechanical—biological treatment processes. In the absence of these markets the disposal of these fuels would be necessary and thus significant GHG savings would be lost.