Scholarly article on topic 'Reduction of CO2 Emission Using Bioreactor Technology for Waste Management in China'

Reduction of CO2 Emission Using Bioreactor Technology for Waste Management in China Academic research paper on "Earth and related environmental sciences"

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Energy Procedia
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{"Waste management" / "Bioreactor landfill" / "Landfill gas collection" / "CO2 emission reduction"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — XU Qiyong, GE Jiaoju

Abstract Landfill gas emission associated with waste management is becoming significant environmental and energy issues in China. Currently, China is the world's largest municipal solid waste generator and approximate 80% of the generated waste is disposed in landfills. Landfill gas is a byproduct of anaerobic decomposition of organic waste and is typically comprised of methane and carbon dioxide. Due to the high heat value of methane, landfill gas has emerged as an easily available energy source. However, landfill gas collection is not common in most conventional landfills in China. Bioreactor technology provides an environmentally friendly way to increase landfill gas generation in a shorter period of time, which makes landfill gas collection more efficiently and economically. Model simulations were conducted to compare landfill gas generation in both conventional and bioreactor landfills and to estimate CO2 emission reduction under various conditions in this study. The results indicate that bioreactor technology can provide a promising approach for waste management in China.

Academic research paper on topic "Reduction of CO2 Emission Using Bioreactor Technology for Waste Management in China"

Energy

Procedía

IACEED2010

Reduction of CO2 Emission Using Bioreactor Technology for

Waste Management in China

XU Qiyonga, GE Jiaojub*

aSchool of Environment and Energy, Shenzhen Graduate School of Peking University, Shenzhen 518055, China bDepartment of Urban Planning, Economics and Management, Harbin Institute of Technology Shenzhen Graduate School,

Shenzhen 518055 China

Abstract

Landfill gas emission associated with waste management is becoming significant environmental and energy issues in China. Currently, China is the world's largest municipal solid waste generator and approximate 80% of the generated waste is disposed in landfills. Landfill gas is a byproduct of anaerobic decomposition of organic waste and is typically comprised of methane and carbon dioxide. Due to the high heat value of methane, landfill gas has emerged as an easily available energy source. However, landfill gas collection is not common in most conventional landfills in China. Bioreactor technology provides an environmentally friendly way to increase landfill gas generation in a shorter period of time, which makes landfill gas collection more efficiently and economically. Model simulations were conducted to compare landfill gas generation in both conventional and bioreactor landfills and to estimate CO2 emission reduction under various conditions in this study. The results indicate that bioreactor technology can provide a p romis ing ap p roach for waste management in China.

© 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of RIUDS Keywords: Waste management; Bioreactor landfill; Landfill gas collection; CO2 emission reduction

1. Introduction

With the increasing concern of global warming, the emission of greenhouses gases has obtained more and more attention worldwide in recent years. According to U.S. EPA, landfills are the third largest anthropogenic greenhouse gas emission source, accounting for nearly 750 million metric tons of CO2

* Corresponding author. Tel.: +86-755-26033494; fax: +86-755-26033494. E-mail address: jiaoge@hitsz.edu.cn.

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedia 5 (2011) 1026-1031

1876-6102 © 2011 Published by Elsevier Ltd. doi:10.1016/j.egypro.2011.03.181

equivalent (tCO2e) in 2005 [1]. Landfill gas is the byproduct of a series of complex reactions involves in the anaerobic decomposition of organic waste occurring in landfills. Landfill gas generation mainly depends on several factors, such as temperature, moisture content, waste composition etc. Typically, landfill gas comprises approximately 50-60 percent methane (QH0, 40-45 percent CO2, and traces of odorous compounds, such as hydrogen sulfide (H2S). Methane is the second largest contributor to global warming among anthropogenic greenhouse gases after CO2 and it has a global warming potential 21 times greater than CO2, accounts for 16% of all greenhouse gas emissions resulting from human activities [2]. Because the major gas components (CH4 and CO2) of landfill gas are both greenhouse gases, the emission of landfill gas to atmosphere is becoming a big environmental issue.

In addition to the global warming concern, landfill gas emission and migration can also result in odor problems and potential groundwater contamination, posing adverse effects on public health and safety. With a high caloric value of 18,828 ~ 23,012 kJ/Nm3, landfill gas can be used as an environmentally friendly, renewable energy resource [3]. Therefore, instead of allowing landfill gas emission to atmosphere, landfill gas can be collected and used as a renewable energy source.

2. CO2 Emission and Waste Management in China

2.1. CO2 emission in China

According to Energy Information Administration (EIA), China has over passed the U.S. as the biggest CO2 emitting country since 2006 (Fig. 1). In 2007, the total CO2 emissions of China were approximate 6,538 million tons, about 2% higher than the U.S (5,838 million tons), followed by India (1,612 million tons), Russia (1,537 million tons), and Japan (1,254 million tons) [4].

As methane has 21 times more global warming potential than the equivalent amount of CO2, methane from MSW is one of the world's largest contributors of greenhouse gases. Therefore, landfill gas recovery plays an important role in reducing CO2 emission. According to the World Bank, landfill gas collection and recovery is the largest potential source of CO2 emission reductions in China [5].

■*— China o ■■ United States

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Fig. 1 Comparison of TotalCarbon Dioxide Emission between China and the U. S.

2.2. Current situation ofwaste management in China

In 2004, China generated approximate 190,000,000 tons of municipal solid waste (MSW) and surpassed the U.S. as the world's largest waste generation country [5]. Due to rapid increase of urban

population, the total amount of MSW is growing by 8~ 10 percent annually. It was projected that the amount of waste generated in China will reach 480,000,000 tons by 2030 [5]. China is facing great environmental pressure to deal with the increasing quantity of solid waste and over 80 percent of waste generated is landfilled. In 2006, approximate 7.7% MSW waste generated in China was incinerated and about 1.9% MSW was composted, while about 43.2% of the residual MSW was sent to sanitary landfills, and the remainder of the MSW was dumped in landfills that did not meet sanitary landfill status [6].

However, from the aspect of landfill gas recovery, only a few landfills in China have landfill gas collection system and most gas recovery projects are linked with the Clean Development Mechanism (CDM) of the Kyoto Protocol. Under the Clean Development Mechanism, a landfill can receive payments from an interested buyer for landfill gas collection and energy recovery, while the buyer can meet its own obligations to reduce greenhouse gas emission. As of October 2010, there are 24 MSW landfill gas to energy projects registered as CDM projects in United Nations, accounting for over 4 million tons of CO2e annual reduction in China. Table 1 lists the CDM projects associated with landfill gas recovery in China.

T able 1 Summary of CDM Landfill Gas Projects in China

Landfill Reduction (t CO2e/yr) Landfill Reduction (t CO2e/yr)

Nanjing T ianjingwa Landfill 246,107 Fuzhou Hongmiaoling Landfill 143,194

Meizhou Landfill 286,525 Xiamen Dongfu Landfill 71,296

Anding Landfill 75,557 Liaoning Landfill 63,467

Wuxi T aohuashan Landfill 75,343 T aiyuan Xingou Landfill 43,419

Shenzhen Xiaping Landfill 471,619 T aiyuan Shanzhuangt ou Landfill 38,854

Jinan Landfill 112,908 Luoyang Landfill 102,860

Guangzhou Xingfeng Landfill 909,857 Dalian Maoyingzi Landfill 241,053

Jiaozishan Landfill 153,244 Nanchang Mai yuan Landfill 171,663

Nanning Landfill 188,195 Hunan Loudi Miaopu Landfill 10,234

Mianyang Landfill 93,539 Shenyang Daxin Landfill 150,161

Kunming - Wuhua Landfill 143,602 Xiangtan Shuangma Landfill 20,145

Tianjin Shuangkou Landfill 130,444 Hefei Longquanshan Landfill 143,177

2.3. Potential CO2 emission reduction and energy recovery from landfill gas Based on the estimation of World Bank, the total MSW generation in China will reach about 300 million tons in 2015. With the assumption of 80% of the generated MSW being landfilled, approximate

240 million tons of MSW will be annually disposed in landfills. The methane generation potential was estimated to range from 28 to 70 m3 CH4 per ton of solid waste [7]. The landfilled MSW can generate 6.5 to 15.8 billion m3 of methane annually. If landfill gas collection efficiency is 50%, the reduction of equivalent CO2 emission from landfill gas will be 42~ 110 million tons. After removing of the trace organic compounds, landfill gas can be used in internal combustion engines and gas turbines for generation of heat and electricity. Other energy recovery options include alternative vehicle fuel, pipeline-quality gas, and chemical energy storage [8].

Fig. 2 shows the change of total energy production and net energy as a function of time in China. Currently, China is the world's second largest energy consumer behind the United States and the energy consumption has been greater than the energy production since 1998. For example, the energy shortage

was over 6 e xajoule (x10 J) in 2008 (Fig. 2). According to EIA, the shortage of nature gas in China was over 1 billion m3 in 2008. With 50% landfill gas collection efficiency, the annual methane generation from landfilled MSW will range from 3.3 to 8.9 billion m3 in 2015. To some extent, energy recovery from landfill gas can alleviate the increasing energy demand in China and benefits the environment by reducing pollution and greenhouse gas emissions.

2000 Year

Fig. 2 The Change of Net Energy and T otal Energy Production over T ime in China

However, as mentioned above, most landfills in China do not have landfill gas collection system. One of the main reasons is the slow waste biodegradation in conventional landfills which are primarily designed to minimize water contact with landfilled waste. As a result, the degradation of waste occurs slowly and thus landfill gas generation rate is low, which in turn increases the operation costs of landfill gas collection and energy recovery. Bioreactor technology, however, can accelerate waste biodegradation and increase landfill gas generation rate, which makes gas collection more economical feasible.

3. 3 Bioreactor Landfill

3.1. 3.1 Comparison of traditional landfill and bioreactor landfill

A bioreactor landfill is a controlled landfill where liquid and gas conditions are actively managed in order to accelerate or enhance biostabilization of the waste. In contrast to conventional landfills, bioreactor landfills rely on maintaining optimal moisture content by recirculating leachate to enhance microorganism activity. Operating a landfill as a bioreactor provides several advantages over a conventional landfill, including accelerated waste decomposition, increasing landfill gas generation rate, reducing leachate management and post-closure costs etc. [9-10].

Due to high moisture content, waste decomposition in a bioreactor landfill can occur in a much shorter time frame than in a conventional landfill. A simulation model was conducted to compare the landfill gas generation rates in a conventional and a bioreactor landfill (Fig. 3). Landfill gas generation from a given mass or batch of waste can be modeled as follows:

G(t) = 2LokMoe-kt (1)

where G(t) = landfill gas production (m3 yr-1) at time t (yr), Lo = methane generation potential (m3 CH4 ton-1 solid waste), k = methane generation rate constant (yr-1), and Mo = mass of solid waste (ton). The landfill is assumed to operate for 10 years with an average annual waste accepting rate of 100,000 tons.

The methane generation potential, L0, is assumed as 50 m3 ton-1. The maximum gas generation rate of the bioreactor landfill (11 million m3/year) is much higher than that that in the conventional landfill, 3.3 m3/year. In addition, the time frame of major gas generation in the bioreactor is about15 years, while it is over 50 years in the conventional landfill. The results indicate that a bioreactor can generate landfill gas at a higher rate over a shorter period of time than the conventional landfill.

14000 -

3 12000 -o

10000 -

Ql 8000 -c O

g 6000 -c 0 a

0, 4000 -ro

2000 -

0 10 20 30 40 50

Time (yr)

Fig. 3 Landfill Gas Generation Comparison Between Conventional and Bioreactor Landfill 3.2. Sensitive analysis ofCO2 emission reduction

A problem for landfill gas recovery efforts is the lack of enough data in China, due to different waste composition and landfill operation. Therefore, a sensitive analysis was conducted to evaluate the reduction of CO2 emissions using different waste composition (L0 values) and various gas collection efficiencies. To compare the reduction of CO2 emissions, two model simulations were conducted to represent the conventional and bioreactor landfill condition, respectively. Landfill gas was collected for 15 years (from year 3 to year 17) in both simulations to represent the same amount of operation cost for gas collection. The simulation results are presented in Fig. 4. With methane generation potential of 50 m3 ton-1 and gas collection efficiency of 70%, approximate 3 million tons more CO2e can be reduced if the landfill is operated as a bioreactor.

From the CO2 emission reduction perspective, the bioreactor landfill is more efficient than the conventional landfill (Fig. 4). On the other hand, it also indicates that the bioreactor increases the economic feasibility for energy recovery from landfill gas. Based on a study conducted by the US Department of Energy, if the bioreactor technology were applied to 50% of the landfilled waste, it could generate over 7 billion cubic meters of methane annually. According to a World Bank Report, China will need to develop an additional 1,400 landfills over the next 20 years [5]. The bioreactor technology landfill provides a promising approach for waste management and landfill gas recovery in China.

- Conventional Landfill (k = 0.04 yr"1)

--Bioreactor Landfill (k = 0.3 yr"1)

/ I M0 = 100,000 Ton / yr

/ 1 L0 = 50 m3/ Ton waste

/ 1 / I / \ / \

G(t) = Z2L0kM0e"kti

/ \ / \ 1 \ 1

1 / \ / X \ ^

Fig. 4 Additional CO2 Emission Reduction Using Bioreactor under Various Conditions 4. 4 Summary and Conclusion

MSW landfills are a significant source of greenhouse gas emissions. As a primary constituent of landfill gas, methane is a potent greenhouse gas and can be used as a renewable energy source due to its high heating value. The collection and energy recovery from landfill gas not only reduce greenhouse gas emission and air pollutants, but also reduce the dependence of non-renewable energy, such as petroleum and coal. With its rapid economic development and urbanization, China is facing a big challenge for municipal solid waste management. Currently, China is the world's largest municipal solid waste generator and greenhouse gases emitter. Landfills provide a huge opportunity to reduce CO2 emissions and a potential renewable energy source. Bioreactor landfill can accelerate waste decomposition and increase landfill gas generation rate, which make it economic feasible for landfill gas collection and energy recovery. The bioreactor technology provides a promising approach for waste management and landfill gas recovery in China.

References

[1] U.S. EPA. Landfill Methane Recovery and Use Opportunities. Methane to Markets.2008, p.1~2

[2] U.S. EPA. Methane to Markets Partnership Fact Sheet. www.methanetomarkets.org (accessed Nov. 15, 2010)

[3] Prosser, D. and Wang, W. Promoting Methane Recovery and Utilization from Mixed Municipal Refuse in China. 2005. CPR/96/G31

[4] United Nations Statistics Division, Millennium Development Goals indicators: Carbon dioxide emissions (CO2). 2010

[5] World Bank. Waste Management in China: Issues and Recommendations. 2005

[6] Xu, H. All the Waste in China—the Development of Sanitary Landfilling. Waste Management World. 2008, 4, p.60-67

[7] U.S. EPA. User's Manual of China Landfill Gas Model: Version 1.1. 2009. EP-W-06-022

[8] Bove, R and Lunghi, P. Electric Power Generation from landfill Gas Using Traditional and innovative Technologies. Energy Conversion and Management 2006,47, p. 1391-1401

[9] Townsend, T., Kumar, D., and Ko, J. Bioreactor Landfill Operation: A Guide for Development, Implementation and Monitoring. Prepared for the Hinkley Center for Solid and Hazardous Waste Management, Gainesville, FL. 2009

[10] Reinhart, D. and Townsend, T. Landfill Bioreactor Design & Operation. CRC Press. 1998.

[11] U.S. EPA. Bioreactors. http://www.epa.gov/osw/nonhaz/municipal/landfill/bioreactors.htm (accessed Nov. 10, 2010)