Greenhouse Gas Emissions in the Process of Landfill Disposal in China

Abstract

Quantitative accounting of greenhouse gas (GHG) emissions has become an important global focus. GHG emissions from the waste sector have high potential in GHG emissions reduction. We analyzed the GHG emissions inventory in the waste sector of the European Union, Germany, the United Kingdom, the United States of America, and Canada from 1990 to 2019. Landfill disposal was the main category of GHGs from the waste sector, with a contribution rate between 69% and 95%. Landfill disposal also played a prominent role in emission reduction, with a contribution rate higher than 86%. GHG emissions from landfill sites in China were calculated using the inventory analysis method recommended by the IPCC and combined with actual situations. The results showed that the highest GHG emissions from landfill disposal in China occurred in 2020, with an estimated 165 million tons of carbon dioxide (CO₂) equivalent. In 2019, the per capita GHG emissions from landfill sites in China was 117 kg CO₂ equivalent/person, which was higher than Germany (87 kg CO₂ equivalent/person) but lower than the European Union (189 kg CO₂ equivalent/person).

1. Introduction

Natural environmental changes and human activities have directly or indirectly altered the composition of the global atmosphere, leading to an unprecedented rate of climate change [1,2]. The excessive use of fossil fuels, such as coal and oil, during industrialization has increased emissions of greenhouse gases (GHGs), such as carbon dioxide (CO₂) [3]. The Sixth Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC) indicates that human activity is the main cause of changes in GHG levels [4]. The main areas of the IPCC’s National Greenhouse Gas Inventory Guidelines include energy activities, industrial processes, agricultural activities, land use, land use change and forestry, and waste [5]. The contribution of the waste sector is ranked fourth following the energy, agricultural, and industrial sectors in the European Union [6]. It is also reported that GHG emissions from the waste sector have high potential in GHG emissions reduction [7]. According to IPCC, the waste sector is divided into four categories according to the treatment methods: 5.A solid waste disposal (landfill disposal), 5.B biological treatment of solid waste, 5.C incineration and open burning of waste, and 5.D wastewater treatment and discharge.

The IPCC provides internationally recognized methodologies that countries can use to estimate greenhouse gas inventories for reporting to the United Nations Framework Convention on Climate Change (UNFCCC). The main GHGs included in the guidelines are CO₂, methane (CH₄), and nitrous oxide (N₂O). A series of assessments published by the IPCC has shown that GHG emissions from the waste sector have become important sources of anthropogenic GHGs. Landfill disposal is the main contributor to GHG emissions in the waste sector, with a contribution rate between 69% and 95%. Meanwhile, landfill disposal plays a prominent role in emission reduction, with a contribution rate higher than 86% [6]. Therefore, reducing GHG emissions from solid waste disposal, especially reducing GHG emissions from landfill sites, is an effective way to achieve national emission reductions.

According to the Statistical Yearbook of the Ministry of Housing and Urban-Rural Development of the People’s Republic of China, from 2006 to 2020 [8], the amount of urban and rural domestic garbage removal in China changed significantly. In 2006, China’s urban and rural domestic garbage removal was 211 million tons, of which 148 million tons came from cities and 63 million tons from counties. In 2020, China’s urban and rural domestic garbage removal was expected to reach 303 million tons, and the urban and county domestic garbage removal was expected to reach 235 million tons and 68 million tons, respectively. In the past ten years, the removal of urban domestic garbage has increased by 59%. On the one hand, due to the acceleration of urbanization in China, the rural population is constantly moving to cities; on the other hand, due to the development and improvement of China’s sanitation system, the removal area has been basically covered. The removal of domestic garbage in the county remained at about 70 million tons. China has submitted a total of five reports to the IPCC, which are used as the municipal solid waste treatment data in the years of 1994 [9], 2005 [10], 2010 [11], 2012 [12], and 2014 [13]. Since China is a developing country, the reports only cover the amount of municipal solid waste treatment and disposal data in urban cities and do not pay attention to the data in rural spaces, which, therefore, does not represent the current situation of greenhouse gas emissions in the field of domestic waste treatment in China, and thus cannot be compared directly with other countries. This study looked at both rural and urban data to represent the national GHG emission situation.

Since the 1950s, China’s warming rate has been significantly higher than the global average for the same period, and the region is a sensitive and significant area of global climate change. The UNFCCC for 1992 required countries around the world to assume considerable responsibilities and obligations in accordance with their level of economic development to achieve carbon dioxide reduction. To date, 54 countries have reached their peak carbon dioxide emissions [14]. The “Carbon Peak, Carbon Neutral” target was included in the Report on the Work of the Government and the Outline of Vision Goals for the Fourteenth Five-year Plan for National Economic and Social Development of China. At present, China’s carbon emissions are large and still growing; they have not yet reached their peak. Therefore, more effort should be put into reaching the carbon peak and achieving carbon neutrality targets. A clear understanding of China’s key areas of current carbon emissions is fundamental to developing scientific and reasonable emission reduction measures and pathways. However, the GHG emissions inventory is not clear in China, and further research is urgently needed.

2. Materials and Methods

2.1. Data Sources

This study focuses on the amount of solid waste landfill in China (including urban and rural) from 2010 to 2019. Statistical data for China, including the population and quantity of landfill disposal, were used [15]. The urban and rural solid waste treatment and disposal options for China are shown in

Table 1. Urban and rural solid waste treatment and disposal options in China.

		2010	2011	2012	2013	2014	2015	2016	2017	2018	2019
Collection amount (104 t)		22,121	23,138	23,919	23,744	24,518	25,797	27,028	28,268	29,461	31,078
Harmless treatment (104 t)
	Sanitary landfill	11,135	12,518	13,791	14,398	15,006	16,171	16,780	17,125	16,700	16,093
	Incineration	2432	2802	3876	4931	5674	6577	7957	9322	11,226	13,492
	others	218	494	513	363	480	525	618	728	837	1029
Non-harmless treatment (104 t)		8071	7320	5739	4052	3357	2524	1673	1094	684	455
Harmless ratio (%)		64	68	76	83	86	90	94	96	98	99
Quantity of landfill disposal (104 t)		19,206	19,838	19,530	18,450	18,363	18,695	18,453	18,219	17,384	16,548
Ratio for landfill disposal (%)		86.82	85.74	81.65	77.7	74.9	72.47	68.28	64.45	59.01	53.25

.

2.2. Physical Component of Solid Waste

Generally, the proportion of carbon in solid waste is about 15% and fossil carbon in household waste accounts for approximately one third to one half. In our study, one ton of solid waste contained 100 kg of biomass carbon and 50 kg of fossil carbon [16]. The fossil source of carbon dioxide had a greenhouse effect and the biological source of carbon dioxide did not have a greenhouse effect [17].

2.3. Landfill Gas Production

Since this study was a large-scale national study, which went on for decades, the seasonal, as well as regional, changes of the typical yield of landfill gas per mass unit of waste were ignored. During landfill, biomass carbon is converted to CH₄ and CO₂ with a volume proportion of 50% for each. Based on the results from the LandGEM Gas Emission Model (v3.02) [18] and empirical data on landfill gas generation from Chinese landfills, the landfill gas production potential was set as 150 m³/t waste during the whole process. Landfill gas releases continue for decades, but the rate of landfill gas production decreases after overlaying. Empirical measurements showed the period of landfill gas production was about 10 years and peak gas production was measured in the third or fourth year [19]. For convenient calculation, the landfill gas production from 1 ton of solid waste over 10 years (150 m³) was distributed to each year, as shown in Figure 1.

2.4. Emission Factors for GHG Inventory Calculation

The most commonly used and simplest methodology recommended by the IPCC combines information on the extent to which activities occur (known as “activity data” or “AD”), with a factor for quantifying emissions or removals per unit of activity. These coefficients are called “emission factors” (EFs). The basic equation is shown as Equation (1) [5]:

Emissions = AD × EF

(1)

The GHG emissions inventory factors for the waste sector are shown in

Table 2. Greenhouse gas emission factors for the waste sector.

Emission	Source	Disposal	Atmosphere Concentration Trend	Global Warming Potential (100 Years)
CO2 (from Fossil C)	Burning of plastic	Incineration treatment	Increase	+1
CO2 (from Biogenic C)	Biomass burns Biological breathing	Incineration Landfill Composting Anaerobic digestion	Stable	0
CH4	Biomass under anaerobic conditions Break down methane	Anaerobic digestion	Increase	+25
N2O	Released from the soil, fertilizer is produced	Fertilizer applications	Increase	+298

. In general, methane emissions from landfill are the largest source of GHG emissions in the waste sector. In addition, carbon dioxide from waste incineration from fossil carbon (e.g., plastics), methane from composting and anaerobic digestion, and nitrogen oxides are major sources of greenhouse gases that need to be estimated and reported statistically. However, in the IPCC, GHG emissions from waste materials directly used as fuel or converted into fuel are reported in the energy sector [5].

3. Results

3.1. Amount of Solid Waste Landfill in China

In 2010, 221 million tons of solid waste in urban and rural areas were collected, while in 2019, there were 311 million tons. In the past 10 years, the amount of harmless disposal (such as sanitary landfill, incineration, and others) increased from 138 million tons to 306 million tons, while the ratio of harmless treatment increased from 64% to 99%.

As the level of harmless treatment continued to rise, non-harmless disposal, such as open dumping or unsanitary landfill showed a decreasing trend year by year. The volume of non-harmless waste decreased from 81 million tons in 2010 to 5 million tons in 2019.

The quantity of sanitary landfill grew from 111 million tons in 2010 to 171 million tons in 2017, and then fell to 161 million tons in 2019. The quantity of incineration continued to grow, from 24 million tons in 2010 to 135 million tons in 2019. Other disposal technology processing increased from 2 million tons in 2010 to 10 million tons in 2019 but accounted for less than 5% of total waste disposal.

Under the guidance of China’s policies, such as zero-waste cities construction, zero landfill, increasing the disposal capacity of incineration, and other policies, since 2010, the total quantity of landfill disposal has shown a continuous downward trend, but landfill disposal is still the main choice for waste disposal in urban and rural areas of China, accounting for more than 50%.

3.2. GHG Emissions from Landfill Sites in China

Even though the harmless treatment rate of solid waste is relatively high, some of the waste still cannot be treated harmlessly or called simple landfill. According to IPCC, the methane production rate of simple landfill is only 0.4 times that of regular anaerobic landfill because it is in the aerobic environment; we also assumed that all of the landfill gases were released in one year.

The landfill methane recovery rate in the European Union was relatively low. In 1990, only 4% of methane was collected and only 2.6% was used for energy recovery. Methane collection increased to 35% in 2019 and the amount used for energy recovery increased to 31.6% [6]. Based on empirical data in China, the level of 25% of methane used for energy recovery was applied in the current study.

According to the quantity of landfill from 2010 to 2019, and the landfill gas production regulation over the years, it was calculated that the maximum gas production occurred in 2020 (Figure 2). Under a collection ratio of 25% of sanitary landfill, most of the CH₄ was released into the atmosphere, while in simple landfills, all of the CH₄ was released. With an emission factor of 25 between CH₄ and CO₂, this was equivalent to 165 million tons of CO₂ equivalent.

The amount of GHG emissions from landfill following the year 2020 was estimated, and according to the degree of harmless treatment is getting higher and higher; most of them are sanitary landfills, and according to the landfill gas emissions displayed in Figure 1, some of the GHG emissions after the year 2020 are generated by the waste that was landfilled in previous years, and the rest is generated by new landfilled waste. Therefore, as the number of landfills become lower and lower and most of them are harmless landfill disposals, there is a year-on-year decline in Figure 2 after 2020, and the total emissions are consistent with GHG emissions from sanitary landfill.

3.3. Per Capita Quantity of Landfill

In the past 30 years, the changes to the structure of municipal solid waste treatment and disposal is the main reason for the decrease in per capita quantity of landfill in the EU [6].

The per capita quantity of landfill generally showed a downward trend except for the United States (Figure 3). Germany and the United Kingdom had the largest declines, followed by the European Union.

In the past few years, the per capita quantity of landfill in the European Union decreased from 302 kg/person to 113 kg/person (a reduction of 62%). There was a high reduction rate in Germany from 267 kg/person to 5 kg/person. In the United Kingdom, the per capita quantity decreased from 414 kg/person to 70 kg/person (a reduction of 83%). In the United States, there was little change in the per capita amount of landfill, with values in the range of 420 kg/person to 500 kg/person. In Canada, there was a decrease from 806 kg/person to 586 kg/person, however, the per capita quantity of landfill was still the highest value in the current study. In China, the per capita quantity of landfill has decreased from 178 kg/person to 117 kg/person over the past ten years. There are many policies that have been created in recent years, such as zero-waste city construction, zero landfilled of organic waste, etc.; China are aiming to reduce the amount of waste into landfill, so the amount of per capita landfill has decreased, and the amount of incineration or biomass treatment has increased.

3.4. Per Capita GHG Emissions from Landfill Sites

The per capita GHG gas emissions from landfill disposal are shown in Figure 4. There is a noticeable downward trend. Germany and the United Kingdom had the largest declines, followed by the European Union and the United States.

Over the past 30 years, the per capita GHG emissions from landfill disposal in the European Union decreased by 52% from 394 kg CO₂ equivalent/person to 189 kg CO₂ equivalent/person. Emissions in Germany decreased from 546 kg CO₂ equivalent/person to 87 kg CO₂ equivalent/person. The United Kingdom has the biggest reduction in per capita GHG emissions, from 1057 kg CO₂ equivalent/person to 215 kg CO₂ equivalent/person. A decrease of 52% was recorded in the United States, with a decrease from 707 kg CO₂ equivalent/person to 343 kg CO₂ equivalent/person. The decline in Canada was not significant, decreasing 23% from 897 kg CO₂ equivalent/person to 691 kg CO₂ equivalent/person.

At present, Canada has the highest per capita GHG emissions from landfill sites, followed by the United States and Germany. In 2019, China’s per capita GHG emissions from landfill sites were 117 kg CO₂ equivalent/person, higher than Germany (87 kg CO₂ equivalent/person) but lower than the European Union (189 kg CO₂ equivalent/person). The per capita GHG emissions from landfill sites in Canada are six times those of China.

The main reasons for the reduction in European Union countries [6] is that they have enacted decrees to limit the total amount of landfill, reduce the number of unmanaged landfill sites, and increase the collection and utilization of landfill gases. Improvements in methane recovery rates is another major reason for the reduction. Only 2.6% of methane in the European Union was recovered in 1990, while 31.6% of methane was collected for energy recovery in 2019. Nevertheless, there is still much room for improvement.

The main measure for Germany [20] to reduce emissions in the waste sector was domestic waste incineration instead of landfill, which reduced methane emissions, while in the United Kingdom, it was mainly due to the implementation of landfill gas recovery systems in landfills and reduced landfill capacity [21].

3.5. Implied Emission Factor of CH₄ from Landfill

The greenhouse gas emission from landfill is calculated based on actual experiences in this paper, which is different from the method recommended by IPCC. The significance of discussing the implied emission factor of CH₄ with other countries is to verify the new method’s reliability. The results show that the implied emission factor of CH₄ calculated by the new method is similar with the data of other countries (except for Germany).

Data concerning the implied emission factor of CH₄ are submitted to the IPCC by each country to represent the CH₄ emission factor per ton of landfilled waste for the current year. The implied emission factor of CH₄ from landfill sites is shown in Figure 5. There is a relatively stable trend except for Germany. With the improvement of the harmless treatment level, almost all landfill sites are managed. Although the implied emission factors are categorized as managed waste disposal sites, unmanaged waste disposal sites, and uncategorized waste disposal sites, we only selected the implied emission factor for managed waste disposal sites for analysis.

The Chinese implied emission factor of CH₄ from landfill sites was calculated among 0.02 to 0.04 in the current study, which is consistent with international levels. In 2019, Germany had the highest value, 0.55, while the other countries in our study ranged from 0.01 to 0.05. There are two reasons for the high German values since 2005. Germany implemented a strict law following the year 2005, which meant zero primary waste could go to landfill; however, because of the waste previously landfilled, the waste was still releasing greenhouse gases, and this value was large. The trend in other countries is relatively stable and more comparable to that of our country. However, if countries were to tighten their grip on landfills, their trends would converge with Germany’s.

In the national greenhouse gas emission inventory reports submitted to the IPCC, many countries have conducted qualitative analysis of changes in the nearly 30 years from 1990 to 2019, and from the EU’s national greenhouse gas emission inventory report, we read the endogenous reasons for the reduction in carbon emissions in the field of solid waste treatment and disposal.

The changes in the per capita amount of landfill, the per capita GHG emissions from landfill sites, and the implied emission factor are mainly affected by changes in the choice of solid waste disposal. Methane production is also closely tied to the composition of waste landfill.

The choice of solid waste disposal in the European Union has changed between 1995 and 2019. In 1995, the majority (65%) of solid waste disposal was landfill. By 2019, the share of landfill disposal had decreased to 24%. However, there are significant differences in the selection of landfill as the main technology for solid waste disposal among European Union countries. In Bulgaria, Greece, Croatia, and Iceland, for example, landfill is the main method for solid waste disposal, generally more than 60%. In contrast, in countries, such as Germany, Denmark, Belgium, and the United Kingdom, landfill disposal accounts for less than 20%.

Since 1990, the German government has formulated and promulgated a series of laws and regulations and adopted many household waste collection and disposal control measures to reduce the amount of household waste in German cities. In 2004, there were about 330 landfill sites in Germany. Under the strict laws and regulations at the time, all landfills had to be equipped with landfill gas recovery and treatment equipment, which significantly reduced methane emissions from landfills. In 2005, Germany closed more than half its landfills. As a result, only about 150 household landfills are still in operation. In addition, since 2005, Germany has banned the dumping of organic waste directly, and organic waste must be pretreated by mechanical, biological, or thermal processes, limiting the formation of large amounts of methane from landfill sources. With the reduction in the quantity of methane emitted from old landfills, total emissions from landfills will be significantly reduced and will remain low in the long term. The experience of the German government has shown that reducing the amount of organic waste in landfills is more significant than recycling and using landfill gases.

In the United Kingdom, landfill disposal only consists of managed landfill sites; unmanaged landfill sites were closed by 1980 when the solid landfill legislation reform came into force. This category of GHG mainly refers to methane produced by landfill anaerobic decomposition. Carbon dioxide emitted from landfills is a biocarbon source and is not included in the statistics. Non-methane volatile organic compounds (NMVOCs) released from landfills are estimated to have an emission factor of 0.0036 kg NMOVC/ton of waste and are included in the statistics. Methane emissions from landfills depend largely on the carbon content of biodegradable waste and the ability to efficiently capture and recover fugitive methane gas. In both areas, the United Kingdom has developed a range of legal and regulatory measures for both source prevention and end-of-life governance. The most important measure is the Landfill Directive 1999, which calls for a reduction in biodegradable waste and improvements in the design, operation, and management of landfills. Since 1990, methane emissions from landfills have decreased significantly because of increased landfill gas recovery, reduced biodegradable material in landfills, and increased recovery and composting rates. In recent years, the landfill gas recovery rate has stabilized, which has led to a stabilization in GHG emissions.

Since landfills in the United States [22] are effectively managed, 5.A only includes methane emissions from managed landfills, ignoring emissions, such as trace amounts of nitrous oxide. According to statistical data in 2019, the United States operated 1700 to 2000 landfills and landfill methane emissions that were about 114 million tons of CO₂ equivalent. Of these, urban household waste landfill emissions accounted for 87%, while industrial landfill emissions accounted for 13%.

In Canada [23], with the increasing population, more waste is being generated. Most of the solid waste is disposed of in landfill sites, and landfill gas collection and landfill covers are common requirements. In addition, there are bans on organic waste landfill, which contributes to a large increase on organic waste. To reduce the amount of waste, there is also a reduction target on per capita waste generation.

4. Conclusions

To clarify the GHG inventory of Chinese landfill sites, this paper conducted a systematic analysis of GHG emissions inventories from the waste sector in the European Union, Germany, the United Kingdom, the United States, and Canada. Results showed that landfill disposal was a key component of GHG emissions (69% to 95%) from the waste sector and was also a major source of emission reduction contributions (>86%). Using data on China’s solid waste landfill disposal and the IPCC inventory analysis method, the current study found that GHG emissions from landfill sites were estimated to have reached a peak of 165 million tons CO₂ equivalent in 2020. The per capita quantity of landfill in China in 2019 was 117 kg/person, consistent with the European Union (113 kg/person). Since landfill is still the main choice for solid waste disposal (>52%), China has a large GHG emission reduction space. The following specific emission reduction pathways are recommended:

(1)

Strengthen the source reduction measures to reduce the amount of solid waste generation;

(2)

Increase the recycling and utilization of landfill gas;

(3)

Avoid the entry of the organic fraction of waste into landfill;

(4)

Screen the excavation of old landfills to avoid the continued release of methane gas;

(5)

Increase the proportion of incineration in the solid waste treatment system.