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Review

Decarbonization of the Waste Industry in the U.S.A. and the European Union

by
Evan K. Paleologos
1,*,
Abdel-Mohsen O. Mohamed
2,
Dina Mohamed
3,
Moza T. Al Nahyan
4,
Sherine Farouk
4 and
Devendra N. Singh
5
1
College of Engineering, Abu Dhabi University, Abu Dhabi P.O. Box 59911, United Arab Emirates
2
Uberbinder Limited, Oxford OX4 4GP, UK
3
Educational Research, Lancaster University, Lancaster LA1 4YW, UK
4
College of Business, Abu Dhabi University, Abu Dhabi P.O. Box 59911, United Arab Emirates
5
Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(2), 563; https://doi.org/10.3390/su17020563
Submission received: 9 November 2024 / Revised: 24 December 2024 / Accepted: 7 January 2025 / Published: 13 January 2025
(This article belongs to the Special Issue Sustainable Waste Management Strategies for Circular Economy)
Browse Figures
Versions Notes

Abstract

:
Methane (CH4) emissions from the waste industry in the U.S.A. and the European Union (EU) have decreased by over 38% from 1990 to 2021. The success in CH4 emission reduction in the U.S.A. is attributable to two main reasons. Firstly, the increase in the recycling and composting share to 32% of managed waste, thus removing decomposable material from landfills, and secondly, the implementation of methane capture and utilization programs, which have reduced the CH4 released into the atmosphere from 1990 to 2022 by over 60%. By 2022, the EU had reduced landfilling to 23% of the total waste, with waste-to-energy and composting more than double that of their U.S. counterparts, and recycling alone attaining a share of 30%. The EU’s success has been the result of aggressive European legislation requiring biodegradable MSW going to landfills to be reduced by 2035 to 10% of that in 1995, and 65% of packaging waste to be retrieved and recycled by 2025. In terms of N2O emissions, in the EU there was a decrease from wastewater processes from 1990 to 2021, but an overall increase due to waste-to-energy operations, whereas in the U.S.A., both wastewater treatment and solid waste incineration appear to contribute to N2O emissions.

Graphical Abstract

1. Introduction

Decarbonization of waste management systems is critical in addressing the goal of reducing greenhouse gas (GHG) emissions and combating climate change. These sectors are traditionally energy intensive and contribute significantly to GHG emissions. To facilitate the decarbonization of the waste industry, it is imperative to adopt a holistic approach that encompasses innovative technologies and operations, supportive legislation and policies that balance between sustainability goals and economic feasibility, as well as stakeholder and public engagement and awareness.
USA and China as the two largest economies were responsible for about 41% of the world’s total GHG emissions in 2023, with a 11.3% share from the United States and 30.10% from China [1]. The top countries in GHG emissions (in MMT CO2e/year) and their percentage contribution in the global GHG inventory in 2023 are plotted in Figure 1 [2]. The six countries shown in this figure total 62.73% of the global GHG emissions in 2023.
The data from the European Commission [2] indicate that China had quadrupled by 2023 the GHG that it emitted in 1990, India had tripled them, and Brazil had doubled them during the same period. In contrast, the United States has reduced them by about 4%, Russia’s emissions had declined by 13%, and the EU-27 (European Union-27 member states) had achieved an impressive reduction of about 34% in CO2e emissions from 1990 to 2023.
At the same time, the United States and China are also the largest producers of municipal solid waste (MSW) [3,4,5]. In the U.S.A., the solid and liquid waste industries contribute predominantly in the generation of methane (CH4) and nitrous oxide (N2O) greenhouse gases. Based on the United Nations IPCC (Intergovernmental Panel on Climate Change) Fifth Assessment Report (AR5), CH4 is 28 times, and N2O is 265 times more effective than CO2 in trapping heat in the atmosphere over a 100-year period [6]. In 2022, the U.S. waste activities generated emissions of 166.9 MMT CO2e, which represented 2.6% of the total U.S. GHG emissions [7] (Table 7.1). This quantity does not include emissions from waste-to-energy plants, which were reported by the U.S. EPA (Environmental Protection Agency) [7] under the category of energy emissions and is referred to in the next section of this article. Landfills were the third largest anthropogenic CH4 emission source in the U.S.A., and the top GHG emitter of the waste sector with a 71.8% share in 2022 [7] (Chapter 7. Waste). Wastewater management was third in overall N2O emissions in the U.S.A., behind agricultural and stationary combustion sources, accounting for 5.6% of total N2O emissions in the U.S.A., and perhaps more significantly showing an increase of 48.2% since 1990 [7].
In China, net emissions from landfilling, incineration, composting, and dumping were estimated to have increased from 67  ±  12 million metric tons (MMT) of CO2e in 2000 to 130 ± 25 MMT of CO2e in 2018 [8]. Other sources [9] estimated that China emitted 165 MMT CO2e in 2020 from landfills. The total GHG emissions in China from the wastewater treatment industry were estimated to be 67.07 MMT CO2e in 2017, with approximately 57% from on-site emissions [10].
In India [11], domestic wastewater GHG emissions increased from 43.8 MMT CO2e in 2005 to 63.8 MMT CO2e in 2018 with about 61% of these emissions originating from rural areas and the remaining from urban areas. GHG emissions from industrial wastewater had remained stable during these years at about 37.4 MMT CO2e. Finally, GHG emissions from solid waste disposal had risen from about 7 MMT CO2e in 2005 to 13.3 MMT CO2e in 2018. Total GHG emissions from all waste sector sources were given to be 114.5 MMT CO2e in 2018. It should be noted that these estimates from India [11] were based on the Global Warming Potential (GWP) of gases as these were defined in the IPCC Second Assessment Report (SAR) that gave CH4 as being 21 times, and N2O as being 310 times more effective than CO2 in trapping heat in the atmosphere over a 100-year period [6]. Official data from China and India are not reported in the UNFCC (United Nations Framework Convention on Climate Change) inventory of data from various countries [12] and this does not allow a detailed analysis of the practices in these countries.
Finally, the European Union (EU) decreased total net GHG emissions in 2023 by 37% below 1990 levels [13], whereas the waste sector in the EU reached a 42% decrease in GHG emissions from 1995 to 2017 [14].
The current article aims to analyze the municipal solid waste and wastewater treatment industries’ efforts for decarbonization in the United States and the European Union and, based on existing successful practices, regulatory initiatives, and stakeholder engagement, provide suggestions for improvements toward the goal of reducing GHG emissions from the solid waste and wastewater treatment industries.

2. Research Methodology

This study employs data from public domain sources, such as those reported in databases by UNFCC’s inventory of GHG emission data, the U.S. EPA, the European Environment Agency (EEA), the European Commission (EC), and European countries’ government sources. These data are used to conduct analyses and produce figures and table entries that aim to identify the practices and drivers in the United States and the European Union (EU) to curb GHG emissions from the waste industry.
It should be pointed out that some deficiencies exist in the IPCC 2019 framework [15] on which the sources listed above have calculated the GHG emission data and on which the current study relies, which include simplified assumptions and generalized default emission factors. Refinements in the calculations are conducted periodically in the agencies’ reports utilized in this article as more detailed information becomes available.
The aim of the current study is to use existing published data in order to illustrate best case waste management technologies and practices in the U.S.A. and the EU, together with the drivers that helped these countries attain a reduction in GHG emissions by the waste industry. Thus, it is intended that this article will provide recommendations on measures and actions to countries lagging behind in the reduction in the carbon footprint in the solid waste and liquid waste industries.

3. Decarbonization Advances in the Solid Waste Industry

3.1. Advances in MSW Management in the United States

Section 3.1 and Section 3.2 detail the practices in the United States and the EU, which have accomplished a significant reduction over 35% in CH4 emissions in the solid waste industry from 1970 to 2023. The two countries used a different mixture of solid waste management methods in order to achieve this reduction, and both their management methods and technical aspects for CH4 capture can be used by other countries to reduce their waste emissions.
In the U.S.A., in 2018, the MSW management sector distribution was as follows: approximately 50% of the MSW was deposited in landfills, 11.8% was incinerated by waste-to-energy plants, and 32.1% of the MSW was recycled or composted [16].
Figure 2 (based on data from [16], presented in Table 1) indicates the evolution of MSW management practices in the U.S.A. from 1970 to 2018. Thus, in 1970, 93% of MSW was landfilled, 6.6% was recycled, and about 0.4% was handled by waste-to-energy. In contrast, in 2018, landfilling had dropped to about 50%, recycling had reached 23.63%, waste-to-energy 11.81%, and composting 8.51% (other food management methods comprised the remaining approximately 6% of the waste) [16]. It is evident from these data that despite the increase of about 141% in the total amount of MSW generated from 1970 to 2018, the quantities of waste that ended up in landfills remained relatively stable from 1980 to 2018, recycling had increased by 375% during the same period, and composting and waste-to-energy that constituted only 1.82% of the waste stream in 1980 had reached 20.33% of the MSW management scheme in 2018.
Thus, at first level, the success of the U.S. MSW management system in reducing methane emissions by 34% in the last fifty years is attributable to the control of the quantities of waste ending up in landfills, given that landfills are the major source of CH4 emissions in the solid waste industry. Concurrently, removal from the landfilled stream of paper and cardboard [17,18], yard trimmings, and food scraps, among others, which are now recycled or composted, has modified the composition of landfill waste by reducing the decomposable material that would have contributed to GH4 landfill emissions.
Sustainability 17 00563 g002
Figure 2. MSW management methods in the U.S.A. from 1970 to 2018 (based on data from [16]).
Figure 2. MSW management methods in the U.S.A. from 1970 to 2018 (based on data from [16]).
Sustainability 17 00563 g002
Table 1 shows the quantities of MSW handled by various management practices in the United States from 1970 to 2018, as well as in the European Union (EU) from 1995 to 2022. It should be noted that the European Union did not consist of the same number of member states throughout the period of 1995 to 2022. Thus, in 1995, the EU expanded to include 15 nations; in 2004, it consisted of 28 member states, and on 1 February 2020, the United Kingdom withdrew from the EU, resulting in the EU-27. The population of the EU and the U.S.A. in Table 1 are derived from World Bank data [19]. The table shows data from 1970 to 1990 only for the U.S.A. and from 1995 onward for which Eurostat [20] provided data; both countries’ quantities are tabulated with the EU numbers shown in parentheses. Finally, the U.S. EPA data [16] are reported in U.S. short tons, and they are converted in Table 1 in million metric tons (MMT) (1 metric ton equals 0.90718 U.S. short tons).
Table 1. MSW quantities (in MMT) per management method for the United States, based on data from EPA [16] given from 1970 until 2018, and the European Union (given in parentheses) from 1995 to 2022, based on data from Eurostat [20].
Table 1. MSW quantities (in MMT) per management method for the United States, based on data from EPA [16] given from 1970 until 2018, and the European Union (given in parentheses) from 1995 to 2022, based on data from Eurostat [20].
MSW Management Method (in MMT)USA (EU) Population
(Million)		LandfillRecyclingCompostingCombustion with Energy RecoveryTotal
1970203.4102.17.2800.408109.83
1980226.5121.913.1702.504137.56
1990250.1131.8 26.3 3.8 27 189
1995266.6 (426.2)129 (121)37 (30)9.4 (14)29 (23)205 (198)
2000282.2 (429.3) 127 (112)48 (38)15 (23)31 (36)221 (220)
2005295.5 (435.6) 129 (88)54 (46)19 (26)29 (45)230 (221)
2010309.3 (441.5) 124 (79)59 (55)18 (29)27 (53)228 (222)
2015320.7 (444.6) 125 (57)61 (63)21 (33)30 (57)238 (214)
2017325.1 (446.2) 127 (53)61 (66)25 (38)31 (59)244 (220)
2018326.8 (447)133 (53)63 (67)23 (38)31 (59)265 (221)
2022(449.5)(53)(68)(43)(59)(229)
Some conclusions that can be drawn from this table are as follows. Given the population difference, the per capita MSW generation in the United States is higher than the EU’s. Thus, for the year of 2018, the per capita MSW generation in the EU was on average 494.4 kg (1.35 kg/capita/day), whereas in the United States this was 811.6 kg (2.22 kg/capita/day). Secondly, despite a population increase in the EU of about 4.7% between 2000 and 2022, the total MSW generated in the EU remained relatively stable between 220 and 229 MMT/year. In contrast, during the same period, the population in the U.S.A. increased by 15.8% and MSW increased by 20.1% to about 265 MMT/year. Thirdly, the amount of MSW recycled in the EU and the U.S.A. is approximately the same after 2010, but composting in 2018 is about 65% higher in the EU than in the U.S.A. Interestingly, if one were to add landfilling and incineration, one would find that although the amount of MSW handled by these two methods, for the years of 1995 to 2000, was almost similar in the U.S.A. and the EU; after that, and for 2005 to 2010, at about 20 MMT, and by 2018 a 40–50 MMT difference in the amount of MSW handled by these two methods would distinguish the U.S.A. from the EU.
In terms of emissions from the MSW industry, EPA [7] provides the following numbers that are tabulated in Table 2 (in MMT CO2e).
In order to comprehend the measures taken in the U.S.A. for the control of CH4 emissions at MSW landfills [21], Table 3 provides additional details of the CH4 generated, recovered and oxidized at MSW landfills to arrive at the net values of the MSW landfill methane emissions (presented in the previous table) and to calculate the per capita per year CH4 emissions from landfills.
It is apparent from Table 3 that, apart from limiting the amount of MSW ending up at landfills, and promoting recycling, composting, and waste-to-energy schemes, major technological innovations were implemented at landfill sites to capture and utilize CH4 on and off site. Thus, Table 3 shows that from 1990 to 2022 the amount of CH4 released into the atmosphere dropped significantly. While 80.7% of the CH4 generated in 1990 was released into the atmosphere, in 2022, this amount was reduced to about 30% of the methane generated. The last row of Table 3 indicates that the per capita per year emitted CH4 (in tons CO2e) had been cut by 2022 to one-third of the 1990 value.
The success of the landfill methane reduction in the U.S.A. is the result of the EPA’s Landfill Methane Outreach Program (LMOP) [22]. This is a voluntary program that partners communities, landfill operators, utilities, and waste officials, where landfill gas (LFG) captured by horizontal collectors and vertical wellheads, which are emplaced in a landfill, is collected in a collection system, which removes moisture, adjusts the pressure to extract and convey the gas, and flares the part of it that is not utilized in an enclosed space. Depending on site-specific characteristics and the commercial application in which the gas will be put to use, additional treatment of the LFG may be required to remove excess moisture and impurities and to compress the LFG [22].
Approximately 63% of the LFG projects in the United States generate electricity through reciprocating internal combustion engines or gas turbines [23,24]. About 17% of the LFG is transferred, as medium-Btu, by pipes to nearby customers, where it is used to replace coal, gas, or fuel oil in combustion equipment. Upgrading LFG by increasing its methane content and reducing its CO2, N2, and O2 contents can transform it into renewable natural gas (RNG) that can be used on-site or delivered off-site for thermal applications, electricity generation, or as vehicle fuel. About 20 percent of currently operating LFG energy projects are creating RNG [22].
In the U.S.A., as of September 2024, there exist 542 operational LFG energy projects and an additional 444 landfills are projected to be added to the list of LFG projects. This means that of the 2642 landfills (active or closed) in the U.S.A., approximately 21% of them have already implemented methane reduction practices [22]. A list with information on the status of each landfill in the U.S.A. can be found in the files provided at the EPA’s LMOP Landfill and Project Database site [25]. Figure 3, based on these files [25], shows the number of landfills that had opened, each year in the U.S.A., from 1900 to 2024. Of those, 1347 are already closed, 1263 are still open, and for 32, the status is unknown.

3.2. Advances in MSW Management in the European Union

Figure 4, which is based on the data shown in Table 1, depicts the evolution in the mix of MSW management methods in the EU from 1995 to 2022 that led to the landfilled MSW dropping from 121 MMT in 1995 to 53 MMT in 2022, or a 56% drop during this period. Landfilling that constituted 61% of the MSW disposal methods in 1995 was reduced to about 23% of the total MSW in 2022. Recycling had more than doubled, composting had tripled, and waste-to-energy had increased by 1.5 times during this reference period. Thus, in 2022, the EU MSW management mix was as follows. Landfills accepted 23% of the total waste; about 26% of the MSW was handled by waste-to-energy facilities, 19% by composting, and approximately 30% of the total MSW was recycled. The dominance of recycling, followed by incineration as the preferred MSW management method in the EU becomes apparent in Figure 4, after the year 2015.
The success of the EU in curbing GHG emissions from MSW waste has been the result of aggressive European legislation on waste. Thus, the European Directive 31/1999 [26] “on the landfill of waste” (referred to as the “Landfill Directive”) required that biodegradable MSW going to landfills (with the baseline set to the amount of biodegradable MSW produced in 1995) should be reduced to 75% by July 2006, to 50% by 16 July 2009, to 35% by July 2016, and to 10% until 2035. The European Directive 62/1994 [27] “on packaging and packaging waste” required that 50% of the packaging waste must be retrieved and recycled by 2001, a target that was increased to 60% by the end of 2008, and further increased to 65% by the end of 2025.
Thus, while in the U.S.A., the reduction in GHG emissions from the MSW industry was to a large extent the result of EPA’s Landfill Methane Outreach Program (LMOP), a voluntary program that involved all stakeholders, from waste officials, landfill operators, utilities, to communities, the European Union relied on a top–down approach, where member states had to attain specific targets by certain dates set in European directives. In the U.S.A., the regulations governing non-hazardous solid waste are contained in Title 40 of the CFR (Code of Federal Regulations) parts 239 through 259, with part 258 providing the criteria for MSW landfills [28]. In terms of the generated methane, what applies is paragraph §258.23 on the control of explosive gases and §258.24 on air criteria.
However, although the European Directive 31/1999 [26] calls for the landfill gas to be collected from all landfills and either to be treated and used, or if it cannot be used for energy production, to be flared, the EU has stayed behind in this. According to the European Environment Agency (EEA), 60% of the landfill gas in the EU is released into the atmosphere, a percentage that is almost double that corresponding to U.S. atmospheric CH4 emissions. The number of landfills in Europe is estimated to exceed 500,000 and most of them, over 90%, to be non-sanitary landfills [29]. The EU’s “Strategy to Reduce Methane Emissions” [30] notes that GHG emission reduction has been accomplished through the diversion of waste from MSW landfills, but little progress has been made regarding the utilization of the methane from landfills. This document states that in its 2024 review of the Landfill Directive, actions related to landfill gas management will be included. These actions “may include aeration of landfill mass to inhibit the generation of methane, increasing the use of landfill gas to generate energy, or when neither option is possible, the use of techniques that effectively oxidise the methane such as bio-oxidation or flaring” [30,31]. Some European countries, such as Denmark, have advanced in this by implementing technologies that remove CO2, hydrogen sulfide (H2S), and other trace gases from biogas plants that receive household food waste, agriculture waste, and industrial waste, to produce pure methane. This methane is fed into the natural gas grid system and constitutes about one-third of the grid’s gas, with the remaining being natural gas [32].
The UNFCC (United Nations Framework Convention on Climate Change) provides an inventory of data for GHG emissions from different sources and for each GHG from all reporting countries [12]. Table 4 was created by obtaining data from the above database with entries in the category of solid waste disposal; with entries for gas, methane; as countries for comparison, the U.S.A. and the EU, and as baseline year, that of 1990. The table tabulates the methane emissions for solid waste disposal from 1900 to 2021 (the last reporting year to UNFCC) in the EU and the U.S.A.
Table 4 demonstrates that significant methane emission reductions had been attained in both countries by 2021 relative to the base year of 1990. The percentage reduction in CH4 emissions from managed waste disposal sites is almost the same for the EU and the U.S.A., whereas the slightly higher total percentage reduction in the EU has resulted from better control of the unmanaged and uncategorized waste disposal sites of which the USA had none. Methane emissions in the EU in the whole waste sector, which totaled 101 MMT CO2e in 2021, were about 80% due to solid waste disposal, 4% to the biological treatment of solid waste, and 15% due to domestic and industrial wastewater treatment and discharge [33]. It should be noted that the entries for the U.S.A. for a particular year that are presented in Table 4 correspond to the sum of the values for CH4 given for the same year in the first two rows of Table 2.

4. Decarbonization in the Municipal Wastewater Treatment Industry

Table 5 tabulates the methane and nitrous oxide emissions from wastewater treatment in the U.S.A. from 1990 to 2022. In terms of domestic treatment and effluent, CH4 emissions were reduced by about 17.6%, while industrial treatment and effluent increased by 16.1%, resulting in total waste treatment reduction of about 8% during this time period. N2O emissions from domestic treatment and effluent increased by 48.6%, while industrial treatment and effluent, although a very small component of the total wastewater treatment’s N2O emissions, also increased by 25%. Clearly, N2O emissions from domestic treatment and effluent have not been adequately addressed in the U.S.A.
UNFCC provides an inventory of the data on GHG emissions from all reporting countries based on source and gas [12]. Figure 5 was created by obtaining data from the above database with an entry in the category of wastewater treatment and discharge (WTD); as gas, N2O; as countries for comparison, U.S.A. and the EU, and as baseline year that of 1990. The table tabulates the N2O emissions from wastewater treatment and discharge in the EU and the U.S.A from 1990 to 2021 (the last reporting year to UNFCC). One should note that the UNFCC database of the total N2O emissions from WTD has included emissions from domestic wastewater, industrial wastewater, and other wastewater sources. Figure 5 plots for both countries and for each year the total NO2 emissions, as well as those from domestic wastewater only.
One should note that there exist slight differences in the data entries for the U.S.A., from 2019 onward, between the N2O emission data reported by UNFCC [12], plotted in Figure 5, and the EPA’s data [2], given in Table 5. These have resulted by minor adjustments in the calculations and by considering different sources in the two databases. The N2O emissions that are shown in Table 5 and are related to domestic treatment include the following sources: septic systems; centralized treatment aerobic systems, including aerobic systems; centralized anaerobic systems; and centralized wastewater treatment effluent. Thus, for example, for the year 2022, from the 17 MMT CO2e in N2O emissions attributed to domestic treatment, 0.8 MMT CO2e were the result of septic systems, and the remaining about 16.2 MMT CO2e were coming from centrally treated aerobic systems, except constructed wetlands [2] (Table 7-27).
Figure 5 indicates that N2O emissions from domestic wastewater treatment plants in the EU, which were less than half of those in the U.S.A. in 1990 kept on declining over the reported 21-year period, reaching about 29.5% of the equivalent U.S. N2O emissions by 2021. In contrast, in the U.S.A., N2O emissions increased over the years, reaching an almost 42% increase in 2021 relative to 1990.
Figure 5 also shows that N2O emissions in the EU from all sources of wastewater treatment and discharge declined by 15.4% between 1990 and 2021, from 7.38 MT CO2e to 6.24 MT CO2e [12]. Given that the data from the European Commission [2] show an increase in N2O emissions in the EU, from both solid and liquid waste, of approximate 37% between 1990 and 2021, from 8.4 MT CO2e to 11.54 MT CO2e, the difference in N2O emissions from these two sources must be the result of the incineration and biological treatment of solid waste [15,34]. Thus, in the EU, it appears that the increase in N2O emissions is attributable to the expansion of waste-to-energy operations to treat solid waste, whereas in the United States both wastewater treatment and solid waste incineration contribute to N2O emissions.
In the European Union, wastewater is regulated by the European Directive 91/271/EEC on urban waste-water treatment [35] and Directive 86/278/EEC on the use of sewage sludge in agriculture [36]. The former is concerned with the release of treated wastewater in water bodies without making reference to GHG emissions from wastewater treatment plants, and the latter with the soil’s protection from sludge used in agriculture. Both directives are currently being reviewed, and a draft proposal was finalized after public consultation and feedback to the European Commission by March 2023 [37]. Article 11 of the draft proposal sets the obligation to Member States to achieve energy neutrality by 31 December 2040 at the national level in all wastewater treatment facilities, by ensuring “that the total annual renewable energy produced at national level by all urban wastewater treatment plants is equivalent to the total annual energy used by all such urban wastewater treatment plants”. The same article sets the requirement for energy audits of urban wastewater treatment plants “with particular focus to identify and utilize the potential for biogas production, while reducing methane emissions” [37].
In the U.S.A., wastewater treatment and discharge is regulated under the Clean Water Act (CWA). In 2009, the EPA issued rule 74 FR 56260 for the mandatory reporting of greenhouse gases from all economic sectors. This rule “does not require control of greenhouse gases, rather it requires only that sources above certain threshold levels monitor and report emissions” [38]. The 74 FR 56260 rule set the threshold of 25,000 metric tons of CO2e per calendar year for monitoring and mandatory reporting. Preamble-Section II-Part E of this rule, which explains the above threshold, is referred to by the EPA to public questions and comments by operators of centralized municipal wastewater treatment plants [39]. In the U.S.A., there exist more than 16,000 centralized wastewater treatment plants [40]. In terms of wastewater GHG emissions, the EPA considers primarily industrial wastewater facilities, and in terms of wastewater treatment (that includes both municipal and industrial facilities), it has communicated that 118 facilities reported emissions above the threshold in 2023 [41].
Nitrous oxide, apart from being a potent GHG, is also predicted to be the most harmful ozone-depleting gas in the coming years [42]. Nitrogen in wastewater primarily exists in the form of complex amino sugars, sugar molecules where a hydroxyl group has been replaced by an amine group with the general formula R-NH2. The latter are functional groups and compounds containing a nitrogen atom and a lone pair. Important amines are the amino acids, of which the α-amino acids with the generic formula H2NCHRCOOH are protein-building. These organic nitrogen compounds are degraded to ammonia (NH4) by microbes in the sewerage system and the bioreactor. NH4 is converted to NO2− and NO3− by microbial nitrification in zones or compartments of the bioreactor where aerobic conditions are established. The nitrite (NO2−) and the nitrate (NO3−) ions are reduced to N2 during denitrification, which takes place under anoxic conditions in other zones of the bioreactor. Nitrous oxide can be generated in both these processes. During denitrification, NO2− is reduced to NO, N2, and N2O by autotrophic ammonia-oxidizing bacteria (AOB). Heterotrophic denitrification can also produce N2O as an intermediate step of the NO3− reduction to N2 [43]. Several laboratory studies have shown that AOB also contribute to the generation of N2O under aerobic conditions and this outcome is pH-dependent [44] or is influenced by the transition to aerobic conditions after a period of anoxia [45].
Proposed mitigation strategies to reduce N2O emissions from wastewater treatment plants, which have been tested at the laboratory scale, include the following: avoidance of transient pH changes during aerobic conditions by slow feeding rather than pulse feeding [44]; applying solids’ retention times greater than 5 days, and a dissolved oxygen (DO) content higher than 0.5 mg O2 L−1 in order to increase AOB biomass concentration [46,47]; and sequential aeration in a membrane-aerated biofilm reactor [48].
At the full-scale wastewater treatment plant level, Foley et al. [49] reported that plants that were designed and operated with high recycling rates, large bioreactor volumes, long solids’ retention time, with balanced influent flow, achieved both low effluent total nitrogen and low N2O emissions. Duan et al. [50], in a mitigation strategy implemented at a full scale WWTP, found that reducing dissolved oxygen (DO) levels resulted in a 35% reduction in N2O emissions, potentially due to reduction in the N2O generated via the NH2OH oxidation pathway as a result of lowering DO level. This mitigation strategy also reduced energy requirements for aeration by 20%. Song et al. [51] analyzed the published results from monitoring campaigns at about two hundred water resource recovery facilities (WRRFs) and concluded that “…some technologies such as sequencing batch reactor (SBR) and membrane bioreactor (MBR) have 2–4 times more emissions compared with other processes such as anaerobic/anoxic/oxic (A2O) and modified Ludzack–Ettinger (MLE)”. Factors that have been assessed to contribute to high N2O emissions in membrane bioreactors include a decrease in the carbon-to-nitrogen (C/N) ratio, which by increasing pH and free ammonia has been seen to cause stress on the growth of nitrifying species and increase N2O emissions in both gaseous and dissolved phases. The highest N2O concentration in the dissolved phase of membrane bioreactors was found in the permeate [52]. MBR’s oxic tanks were found to be the major source of N2O nitrous oxide emissions in a study by Mannina [53]. Variations in influent carbon and nitrogen load were seen to significantly influence both removal efficiency and N2O emissions in SBR systems [54].
It should be noted that de Haas and Andrews [55] and Song et al. [51] found that the linear regression, used to derive an “average” (default) emission factor (EF) for N2O from full-scale WWTPs, included literature citation errors resulting in an over-estimation of the default EF in the IPCC (2019) Guidelines [56]. The correction implemented by these authors suggested an EF value of 1.1% of WWTP influent total nitrogen (TN) load emitted as N2O, instead of the IPCC EF value of 1.6%. This revised default EF value was supported by datapoints from newer (2018–2021) references and was in closer agreement with the weighted average N2O emission factors published by the Danish Environmental Protection Agency in 2020 [55].
At the same time, several authors warned that traditional N2O measurement techniques used in wastewater treatment plants may be under- or over-estimating N2O emissions [43]. Song et al. [51] proposed a tool to recalibrate wastewater N2O emission estimates, based on a much larger database than those relying on the uniform emission factor (EF) proposed by the IPCC [57]. Based on their method, these authors estimated that wastewater N2O emissions in the U.S.A. were “11.6 MMT CO2e, about 75% of the N2O emissions of 15.4 (8.7–41.1) MMT CO2e from wastewater treatment plants reported by EPA in 2021”.
It appears, therefore, that until now both the EU and the United States have not put in place specific regulations for GHG emissions from municipal wastewater treatment facilities, despite the fact that improvements could be accomplished with relatively moderate technical and operational enhancements.

5. Stakeholder Engagement in Waste Policy Development in the U.S.A. and the EU

Recycling of waste material has been the central pillar in the efforts of the U.S.A. and the EU to reduce the amounts of waste ending up in landfills and incineration facilities, conserve resources, and reduce GHG emissions, not only from the waste industry, but also from the mining and processing operations of new raw material [58]. In 2001, the EPA established the U.S. Recycling Economic Information (REI) project with the collaboration of several states and regions. The 2020 REI report found that recycling had resulted in 526 MMT of recycled goods, had generated 681,000 jobs, USD 37.8 billion in wages, and USD 5.5 billion in tax revenues [59].
In the U.S.A., a number of initiatives and national strategies have been announced as part of the country’s “Circular Economy Strategy”. These include the “National Recycling Strategy” [60], and The White House’s “National Strategy for Reducing Food Loss and Waste and Recycling Organics” [61].
These documents reflect the active engagement of every stakeholder in the development of national strategies and legislation in the MSW and wastewater treatment industries that characterizes policy development in the United States. Thus, the list includes input from: federal offices, among others, the U.S. Department of Energy (DOE), the U.S. Department of Commerce (DOC), the U.S. Department of Defense (DOD), the U.S. Department of State (DOS), the U.S. Department of Agriculture (USDA); agencies, such as the National Science Foundation (NSF), the National Oceanic and Atmospheric Administration (NOAA), and the National Institute of Standards and Technology (NIST); tribal and state entities, such as the U.S. Conference of Mayors, the National Tribal Caucus, the Environmental Council of the States (ECOS), and other; recycling professional and industry associations and private companies, such as the Institute of Scrap Recycling Industries (ISRI), the National Waste and Recycling Association (NWRA), the Solid Waste Association of North America (SWANA), and Waste Management (WM); non-profit organizations, such as the GreenBlue Institute, Keep America Beautiful (KAB), the National Recycling Coalition, etc.; and private citizens, state, tribal and local governments, academia, non-governmental organizations, industry associations, and private companies [60].
Similarly, in the European Union, legislation, such as, for example, regarding the EU rules on urban wastewater treatment [37], was preceded by a one-and-a-half month initial feedback, in 2020, where input was received by several European countries’ authorities (for example, the national association of Dutch water companies, and Dutch Water Authorities; EurEau (representing nearly all wastewater operators in Europe); Aqua Publica Europea (the European Association of Public Water Operators); the Chamber of Commerce of Austria; the Danish Water and Wastewater Association; the Spanish Steel Association, UNESID; BIBM, the Federation of the European Precast Concrete Industry, etc. Subsequently, from April to July 2021, public consultation was sought via questionnaires related to the proposed legislation EU Member States’ public authorities at national, regional and local level, “…industrial/economic actors, such as associations and companies (including small and medium sized enterprises), water associations at European, national and regional level, international organizations, NGOs, consumer organizations, academia, research and innovation organizations and institutes...” Finally, the EU Commission adoption feedback period was conducted from the end of October 2022 to the middle of March, 2023, when the final feedback for the proposed directive was received [37].
Thus, both the United States and the European Union are characterized by extensive consultation and inclusion of all stakeholders’ concerns and inputs in the process of developing legislation on waste.

6. Conclusions

Methane (CH4) emissions from the waste industry in the U.S.A. and the European Union (EU) have decreased by about 34% from 1970 to 2023. This trend has not been followed by the nitrous oxide (N2O) emissions, which are the result, primarily, of wastewater treatment and discharge operations, with the U.S.A. having a 120%, and the EU a 67% increase in N2O emissions, during the same period.
The success in CH4 emission reduction in the U.S.A. can be attributed to two main reasons. The change in the mix of management methods for municipal solid waste (MSW) in the U.S.A., which by 2018 had reached 50% landfilling, 24% recycling, 12% waste-to-energy, and 9% composting. Thus, from 1970 to 2018, landfilling had been reduced from 93% to 50%; recycling had increased from 6.6% to 23.6%; and waste-to-energy and composting had reached by 2018 a combined approximate 21% of the MSW handled, from only 0.4% in 1970. The second major reason was the implementation of methane capture and utilization programs at about 21% of the existing landfills that led net CH4 landfill emissions in 2022 to correspond to about half of those released into the atmosphere in 1990.
In contrast, in the EU, in 2022, recycling held the top place as a MSW management method, receiving 30% of the total MSW, and followed by waste-to-energy with 26%. Landfilling held the third place, handling 23% of the MSW, followed closely by composting with a 19% share in the waste stream, and expected to surpass landfilling, given the targets set in European Directives. The success of the EU has been the result of aggressive European legislation on waste. Two critical European Directives have been the Landfill Directive 31/1999 “on the landfill of waste” and the European Directive 62/1994 “on packaging and packaging waste,” The former required that biodegradable MSW going to landfills should be reduced, incrementally, by 2035 to 10% of that in 1995. The latter required that 65% of packaging waste must be retrieved and recycled by the end of 2025. The intense recycling in both countries, apart from reducing waste quantities from MSW landfill, removes, in particular, biodegradable material, such as paper and paperboard, yard trimmings, and food scraps, which would have contributed significantly to the generation of greenhouse gases.
In terms of N2O emissions from wastewater treatment plants, those from the EU, which were about half of those in the U.S.A. in 1990, reached less than one-third of the equivalent U.S N2O emissions in 2021. Given that N2O emissions in the EU from all sources of wastewater treatment and discharge declined by 15.4% between 1990 and 2021, but those from the overall management of solid and liquid waste had increased by approximately 37% during the same period, this must be the result of the extensive incineration and biological treatment of solid waste taking place in the EU. In the U.S.A., N2O emissions from wastewater increased over the years, reaching an almost 42% increase in 2021 relative to 1990. Thus, in the EU it appears that the increase in N2O emissions is attributable to the expansion of waste-to-energy operations to treat solid waste, whereas in the United States both wastewater treatment and solid waste incineration contribute to N2O emissions.

Author Contributions

Conceptualization, E.K.P. and A.-M.O.M.; methodology, E.K.P.; formal analysis, E.K.P.; investigation, E.K.P. and A.-M.O.M.; resources, E.K.P. and D.M.; data curation, E.K.P. and D.M.; writing—original draft preparation, E.K.P. and A.-M.O.M.; writing—review and editing, A.-M.O.M. and D.N.S.; visualization, E.K.P. and A.-M.O.M.; funding acquisition, E.K.P., M.T.A.N. and S.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Abu Dhabi University’s internal grant 19300866 to E.K.P.

Conflicts of Interest

Author Abdel-Mohsen O. Mohamed was employed by the company Uberbinder Limited. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Top countries in GHG emissions from 1990 to 2023 (based on data from [2]).
Figure 1. Top countries in GHG emissions from 1990 to 2023 (based on data from [2]).
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Figure 3. Number of landfills opened per year in the U.S.A. from 1990 to 2024 (based on data from [25]).
Figure 3. Number of landfills opened per year in the U.S.A. from 1990 to 2024 (based on data from [25]).
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Figure 4. MSW management methods in the European Union from 1995 to 2022 (based on data from the Eurostat [20]).
Figure 4. MSW management methods in the European Union from 1995 to 2022 (based on data from the Eurostat [20]).
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Figure 5. NO2 emissions (in MMT CO2e) from wastewater treatment and discharge (WTD) in EU and U.S.A. (1990–2021) (based on data from UNFCC [12]).
Figure 5. NO2 emissions (in MMT CO2e) from wastewater treatment and discharge (WTD) in EU and U.S.A. (1990–2021) (based on data from UNFCC [12]).
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Table 2. Emissions (in MMT CO2e) from solid waste management methods in USA from 1990 to 2022 based on AR5 CO2 equivalent values [7] (Tables 7.1, 7.3, and 3.1).
Table 2. Emissions (in MMT CO2e) from solid waste management methods in USA from 1990 to 2022 based on AR5 CO2 equivalent values [7] (Tables 7.1, 7.3, and 3.1).
Gas/Year1990200520182019202020212022
CH4
MSW landfill *185.5131.6107.7109.9105.2103.1100.9
Indus. landfill12.216.118.718.818.918.918.9
Composting0.42.12.52.52.62.62.6
Incineration of WasteFor all years emissions do not exceed 0.05 MMT CO2e
N2O
Composting0.31.51.81.81.81.81.8
Incineration of Waste0.40.30.40.40.30.40.3
CO2
Incineration of Waste12.913.3 13.312.912.912.512.4
* The values for CH4 emissions from MSW landfills represent net emissions after recovered and oxidized CH4 has been subtracted.
Table 3. CH4 emissions (in MMT CO2e) from MSW landfills in USA from 1990 to 2022 based on AR5 CO2 equivalent values [7] (Table 7.3).
Table 3. CH4 emissions (in MMT CO2e) from MSW landfills in USA from 1990 to 2022 based on AR5 CO2 equivalent values [7] (Table 7.3).
MSW Landfills1990200520182019202020212022
CH4 generated230.0303.7332.0340.9340.9335.9331.4
CH4 recovered(23.8)(148.4)(195.2)(201.4)(206.3)(203.3)(199.8)
CH4 oxidized(20.6)(23.6)(29.2)(29.6)(29.4)(29.5)(30.7)
Net CH4 emissions185.5131.6107.7109.9105.2103.1100.9
Percent CH4 recovered and oxidized19.3%56.6%67.6%67.8%69.1%69.3%69.55%
Net CH4 per capita/year
(t CO2e)		0.910.440.330.330.320.310.30
Table 4. CH4 emissions (in MT CO2e) from: managed waste disposal sites (MWDS), unmanaged waste disposal sites (UMWDS), and uncategorized waste disposal sites (UWDS) in the EU and the U.S.A. [12].
Table 4. CH4 emissions (in MT CO2e) from: managed waste disposal sites (MWDS), unmanaged waste disposal sites (UMWDS), and uncategorized waste disposal sites (UWDS) in the EU and the U.S.A. [12].
CH4/Year19902000200520102015
MSW disposal methodEUUSAEUUSAEUUSAEUUSAEUUSA
MWDS107.94197.75106.47156.4292.64147.7180.813970.03125.81
UMWDS27.74No27.24No23.34No18.99No13.54No
UWDS1.39No0.89No0.68No0.47No0.35No
Total137.07197.75134.6156.42116.66147.71100.2613983.92125.81
CH4/Year2018201920202021% change from 1990
MSW disposal methodEUUSAEUUSAEUUSAEUUSAEUUSA
MWDS67.48126.6967.2412967.17124.7765.62122.61−39−38
UMWDS11.24No10.68No10.08No9.59No−65No
UWDS0.29No0.27No0.26No0.24No−83No
Total79.01126.6978.1912977.51124.7775.45122.61−45−38
Table 5. Emissions (in MMT CO2e) from wastewater treatment in the U.S.A. from 1990 to 2022 based on AR5 CO2 equivalent values [2] (Table 7.7).
Table 5. Emissions (in MMT CO2e) from wastewater treatment in the U.S.A. from 1990 to 2022 based on AR5 CO2 equivalent values [2] (Table 7.7).
Gas/Year1990200520182019202020212022
CH4
Domestic treatment15.114.612.311.911.711.411.6
Domestic effluent1.41.42.02.02.12.12.0
Industrial treatment5.56.16.56.66.66.76.7
Industrial effluent0.70.60.60.50.50.50.5
Total wastewater
Treatment		22.722.721.421.121.020.720.8
N2O
Domestic treatment10.513.716.216.617.217.117.0
Domestic effluent3.93.94.54.54.64.54.4
Industrial treatment0.30.40.40.40.40.40.4
Industrial effluent0.10.10.10.10.10.10.1
Total wastewater
treatment		14.818.121.221.622.322.121.9
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Paleologos, E.K.; Mohamed, A.-M.O.; Mohamed, D.; Al Nahyan, M.T.; Farouk, S.; Singh, D.N. Decarbonization of the Waste Industry in the U.S.A. and the European Union. Sustainability 2025, 17, 563. https://doi.org/10.3390/su17020563

AMA Style

Paleologos EK, Mohamed A-MO, Mohamed D, Al Nahyan MT, Farouk S, Singh DN. Decarbonization of the Waste Industry in the U.S.A. and the European Union. Sustainability. 2025; 17(2):563. https://doi.org/10.3390/su17020563

Chicago/Turabian Style

Paleologos, Evan K., Abdel-Mohsen O. Mohamed, Dina Mohamed, Moza T. Al Nahyan, Sherine Farouk, and Devendra N. Singh. 2025. "Decarbonization of the Waste Industry in the U.S.A. and the European Union" Sustainability 17, no. 2: 563. https://doi.org/10.3390/su17020563

APA Style

Paleologos, E. K., Mohamed, A.-M. O., Mohamed, D., Al Nahyan, M. T., Farouk, S., & Singh, D. N. (2025). Decarbonization of the Waste Industry in the U.S.A. and the European Union. Sustainability, 17(2), 563. https://doi.org/10.3390/su17020563

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