Scholarly article on topic 'Analysis of the Environmental Benefits of Introducing Municipal Organic Waste Recovery in Hanoi City, Vietnam'

Analysis of the Environmental Benefits of Introducing Municipal Organic Waste Recovery in Hanoi City, Vietnam Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Hoang Trung Thanh, Helmut Yabar, Yoshiro Higano

Abstract Hanoi, the capital of Vietnam, is home to approximately 7 million people. In 2011, the city generated about 2,372,500 tons of municipal solid waste (MSW) (accounting for 11% of national generation) and the collection rate reached 85%, of which 84% was sent directly to landfills (without landfill gas capture systems). This conventional practice has caused not only adverse environmental impacts but also increased greenhouse gas (GHG) emissions and loss of recyclable resources. Since most of the waste generated in the city is organic waste (it accounts for 71% of municipal solid waste), there is high potential for organic waste recovery of MSW in Hanoi. This paper analyzes the potential for environmental benefits of introducing composting of municipal organic waste by proposing five alternative scenarios that range from current situation to composting of both commercial and household organic waste. In order to evaluate the environmental performance of the scenarios, we used three indicators: organic fertilizer production, landfill life extension, and GHG emission reduction. The results show that composting could produce a huge amount of organic fertilizer (i.e. from 6,424to 218,650 tons/year) depending on the scenarios. Diversion of organic waste to composting could reduce the amount of waste disposed in landfills resulting in extending landfill life significantly. Therefore, landfill lifecould be extended from 0.5 to 8.7 years compared to the current situation. Current MSW management practices contributed the highest amount of GHG emission accounting for 1,322,928 tonsCO2-eq/year, whereas the proposed scenarios decrease emissions in accordance with increasing the amount of organic waste used for composting. The estimated emission reduction from the proposed scenarios ranges from 15% to 98% compared to the current situation. The results suggest that composting could bring significant environmental benefits and is a key solution toward sustainable solid waste management for Hanoi city. In addition, composting highlights the potential of climate protection in the waste management sector.

Academic research paper on topic "Analysis of the Environmental Benefits of Introducing Municipal Organic Waste Recovery in Hanoi City, Vietnam"

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Procedía Environmental Sciences 28 (2015) 185 - 194

The 5th Sustainable Future for Human Security (SustaiN 2014)

Analysis of the environmental benefits of introducing municipal organic waste recovery in Hanoi city, Vietnam

Hoang Trung Thanha,b*, Helmut Yabara, Yoshiro Higanoa

a Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577 Japan b Vietnam Institute of Meteorology, Hydrology and Climate Change, 23/62 Nguyen Chi Thanh Street, Hanoi city, Vietnam

Abstract

Hanoi, the capital of Vietnam, is home to approximately 7 million people. In 2011, the city generated about 2,372,500 tons of municipal solid waste (MSW) (accounting for 11% of national generation) and the collection rate reached 85%, of which 84% was sent directly to landfills (without landfill gas capture systems). This conventional practice has caused not only adverse environmental impacts but also increased greenhouse gas (GHG) emissions and loss of recyclable resources. Since most of the waste generated in the city is organic waste (it accounts for 71% of municipal solid waste), there is high potential for organic waste recovery of MSW in Hanoi. This paper analyzes the potential for environmental benefits of introducing composting of municipal organic waste by proposing five alternative scenarios that range from current situation to composting of both commercial and household organic waste. In order to evaluate the environmental performance of the scenarios, we used three indicators: organic fertilizer production, landfill life extension, and GHG emission reduction. The results show that composting could produce a huge amount of organic fertilizer (i.e. from 6,424to 218,650 tons/year) depending on the scenarios. Diversion of organic waste to composting could reduce the amount of waste disposed in landfills resulting in extending landfill life significantly. Therefore, landfill life could be extended from 0.5 to 8.7 years compared to the current situation. Current MSW management practices contributed the highest amount of GHG emission accounting for 1,322,928 tonsCO2-eq/year, whereas the proposed scenarios decrease emissions in accordance with increasing the amount of organic waste used for composting. The estimated emission reduction from the proposed scenarios ranges from 15% to 98% compared to the current situation. The results suggest that composting could bring significant environmental benefits and is a key solution toward sustainable solid waste management for Hanoi city. In addition, composting highlights the potential of climate protection in the waste management sector.

* Corresponding author.

E-mail address: hoangtrungthanh188@gmail.com

1878-0296 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Sustain Society

doi: 10.1016/j.proenv.2015.07.025

© 2015 The Authors. Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-reviewunderresponsibilityof Sustain Society

Keywords:Hanoi;composting, municipal organic waste;landfill life;greenhouse gas emissions

1. Introduction

Waste generation is an unavoidable product of human activities throughout the world. It has very close links to population growth, urbanization, life-style, and affluence\Municipal solid waste management is a major challenge for developing cities because of rapid urbanization and economic growth. As a result, the most common and cheapest solid waste management option is landfill2. This option has many disadvantages including air and water emissions, land occupation, and dumping of valuable materials3. As global environment and climate change are challenges the world faces today, there is an increasing need to evaluate the impact of waste management on environmental quality and greenhouse gasemissions4. There are several treatment options that can be applied towards sustainable MSW management, in which composting is a priority for organic waste recovery.

Composing has been applied worldwide, bringing many advantages for the environment. In African countries, composting is used to stabilize waste and provides a soil improver by applying passively aerated open windrow plants5.In Germany, 950 composting plants treat around 10 million tons of biodegradable waste playing a key role in the treatment and utilization of organic waste6. The organic household composting applied in six different units in Denmark performed better results than other treatments in several of the environmental impact categories7. Singh et al. (2014) undertook research in Kathmandu Metropolitan city, Nepal on integrated municipal solid waste management8. This research emphasizes the importance of organic recovery along with recycling and sanitary landfill improvement in a fast growing city.

Hanoi, the second largest city in Vietnam, generated about 2,372,500 tons of MSW in 2011, of which 84.4% of collected waste was disposed in landfill. The composting only accounted for 2% of total collected waste9. These data represent the improper waste management practice currently applied in Hanoi city. This study considers the possible diversion of composting of organic waste to meet the government obligation on solid waste management strategy towards 2025 and vision to 205010.

The importance of composting has gained increasing attention thanks to the simplicity of the technology, low cost, and the environmental and economic advantages. However, measuring the benefits of composting against other organic waste treatment options like landfill, bio-gasification or waste-to-energy is a complex process. Therefore, this study analyses the significant environmental benefits of composting municipal organic waste instead of landfilling by using major indicators including the amount of organic fertilizer, landfill life extension, and greenhouse gas emission reduction.

2. Materials and methodologies

2.1. Materials

This study was conducted in Hanoi, the fastest growing municipal economy in the country11.The study used the

data provided by government organizations responsible for MSW management as well as official reports from reliable institutions.

Hanoi, the capital of Vietnam, is located in the north part of the country and occupies 3,324.92 square km. It lies

in a typical tropical monsoon climate characterized by high temperature (annual average 26.60C) and rainfall (annual

average 1800 mm). The city had a population of 6,725,500 persons in 2011 and the population growth rate is about 1.1% per year12.

According to Hanoi URENCO's report, MSW generation in Hanoi city was 6,500 tons/day in 2011 (about

2,372,500 tons/year), 85% of MSW derived from households and 15% from commercial sources9. This amount

accounted for about 11% of total MSW generation for the whole country. The amount of MSW is predicted to

increase by 15% annually13. The waste collection rate was estimated to be 95% in the inner city and 60% in suburban areas. Overall, collection of MSW was 85% for the whole city utilizing a kerbside collection system. The

city currently does not apply source separation, however, it is assumed that MSW was separated by organic and

inorganic categories for composting later. To evaluate the benefits of composting among scenarios studied, waste composition is considered for both household and commercial sources as shown in Fig. 1a and 1b.

Organic waste

Textile

Plastic

Others

Organic waste

Textile

Plastic

Others

(Source: [14]) (Source: [14])

Fig. 1a. Composition of household waste in Hanoi (%) Fig. 1b. Composition of commercial waste in Hanoi (%)

Waste treatment in Vietnam is limited to landfill without a CH4 gas capture system. Landfill received more than 80% of collected MSW in Hanoi city. Composting represented allows amount of 2%. Table 1 indicates waste treatment practice in Hanoi in 2011.

Table 1. MSW flow in Hanoi, 2011

Treatment

Collected -

waste Composting Material recycling Incineration Landfill

(tons/year) (tons/year) % (tons/year) % (tons/year) % (tons/year) %

2,016,625 40,150 2.0 165,363 8.2 108,898 5.4 1,702,032 84.4

(Source: [9])

2.2. Methodologies 2.2.1. Scenario proposals

Currently, MSW in Hanoi is collected without any sorting and sent to landfills directly, however, the present landfills are reaching their capacity. The government policy on MSW management approved to separate organic and inorganic waste at sources for sustainable management in the near future10. We suggest the steady improvement approach for solid waste management system (collection, source separation, organic recovery). Therefore, based on the above information and to assess the environmental benefits of organic waste recovery this study proposed five scenarios as follows:

• S1(current situation): Composting of 2.0% of collected waste

• S2: Composting of all commercial organic waste

• S3: Composting of 50% of household organic waste

• S4: Composting of all household organic waste

• S5(ideal practice): Composting of all organic waste

These scenarios are assumed to use the same amount of waste as 2011.Therefore, the results obtained are comparable among scenarios studied.

2.2.2. Organic fertilizer production

The amount of organic fertilizer is estimated based on the actual composting efficiency of technology that currently exists and is applied in Hanoi city. The calculation is defined in equation 1:

Mcomp=(1 - Mev - Mrecy. res - Mres) xMraw in (1)

where:

Mcomp is the total amount of organic fertilizer production (tons/yr)

Mraw in is the total amount of organic waste composted (tons/yr)

Mev is the water mass evaporated after composting (tons/ton of waste composted)

Mrecy.res is the mass of recyclable residue after composting (tons/ton of waste composted)

Mres is the mass of residue sent to landfill after composting (tons/ton of waste composted)

2.2.3. Landfill life extension

The landfill life extension is calculated based on the designed capacity of existing landfill and volume of annual waste disposed as defined in equation 2 and 3:

L _ Vdesigned (2) V _ ^input (3)

V input ^ '

input Pcompacted

where: L is the landfill life (yr)

Vdesigned is the volume of landfill as designed (m3)

Vinput is the volume of annual waste disposed in landfill (m3/yr)

Minput is the total of annual waste disposed in landfill (tons/yr)

Pcompacted is the density of compacted waste (tons/m3)

2.2.4. Estimation of greenhouse gas emissions

GHG emissions from composting

Composting could emit GHG through fossil fuel utilization for operation activities and organic waste degradation. However, it also presents GHG mitigation potential by avoiding chemical fertilizer production thanks to the use of composted product. Therefore, both potential emission and avoidance from composting are defined in the following equations15:

NetGHGcompost — (^operation + Edegradation - AvoidedGHGcompost ) x Mraw in (4)

where:

NetGHGcompost is the net GHG emission from composting (tons CO2-eq) Emissionoperation is the emission from operational activities (tons CO2/ton of waste composted) Emissiondegradation is the emission from organic waste degradation (tons CO2-eq/ton of waste composted) AvoidedGHGcompost is the avoided GHG from composting (tons CO2-eq/ton of waste composted)

Emissianoperation =—-x Energy(MJ/1) x EF(kgCO2/ MJ) (5)

Fuel (l) Waste(tons)

where:

Emissionoperation is the emission from operational activities (kg CO2 per ton of waste composted) in the composting facility:

Fuel is the total fossil fuel consumption per month (litters)

Waste is the total amount of organic waste composted per month(tons) Energy is the energy content of the fossil fuel (MJ/l); (Diesel: 36.42 MJ/L) EF is the emission factor of the fossil fuel (Diesel: 0.074 kg CO2/MJ)

Emissiondeg radation = ECH4 X GWPCH4 + EN2O X GWPN2O (6)

where:

Emissiondegradation is the emission from organic waste degradation (kg CO2-eq per ton of organic waste composted)

ECH4 is the emission of CH4 during organic waste degradation (kg of CH4 per ton of organic waste composted) default value is 4 kg of CH4emitted per ton of organic waste recommended by IPCC 2006. GWPCH4 is the global warming potential of CH4

EN2O is the emission of N2O during organic waste degradation (kg of N2O per ton of organic waste composted); default value is 0.3kg of N2O emitted per ton of organic waste recommended by IPCC 2006. GWPN2O is the global warming potential of N2O

AvoidedGHGcompost = AC x PCagnculture X AghG (7)

where:

AvoidedGHGcompost is the avoided GHG from composting because of avoidance of chemical fertilizer

production (kg CO2-eq/ton of organic waste composted)

AC is the amount of compost product (ton of compost/ton of organic waste)

PCagriculture is the percentage of compost used for agriculture

AGHG is the GHG avoidance potential from chemical fertilizer production, which is equivalent to one ton of compost (kg CO2-eq/ton of organic waste composted)

GHG emissions from landfill

Landfill generates mainly carbon dioxide (CO2) and methane (CH4). However, the CO2 component is the result of natural biogenic processes so it is not considered GHG. Therefore, GHG emissions from landfill is calculated by equation 816:

CH4emltted = (MSWinput x MSWf x MCF x DOC x DOCf x F x 16/12 - R) x (1 - OX) (8)

where:

CH4emitted is the total CH4emitted from landfill (tons/yr) MSWinput is the total MSW generated collected (tons/yr) MSWf is the fraction of MSW disposed in landfill MCF is the methane correction factor DOC is the degradable organic carbon

DOCf is the fraction of DOC decomposing under anaerobic conditions F is the fraction of methane in landfill gas R is the methane recovered (tons/yr)

The required factors and default values for application of the IPCC 2006 model are presented in Table 2.

Table 2.The default values used for IPCC application

Factor Derivation Method Default value Applied value

MCF The IPCC recommended that default MCF values for different types of landfill including managed (landfill has cover and liner), unmanaged-deep (> 5m waste), unmanaged-shallow (< 5m waste) and uncategorized are 1.0, 0.8, 0.4, and 0.6, respectively. 0.4 - 1 1

DOC DOCMSw = % of food waste x 0.15 + % of garden waste x 0.43 + % of paper waste x 0.4 + % of textile x 0.24 Not specified 0.145

DOCf IPCC recommended value 0.5 0.5

F IPCC recommended value 0.1 - 1 0.5

R This value will be changed based on methane recovery technology applied in landfill 0 0

OX IPCC recommended value for sanitary landfill with cover is 0.1; and for open dumpsite is 0. 0/0.1 0.1

GWPch4 IPCC recommended value 21 21

GWPn2o IPCC recommended value 310 310

Net GHG emission is the total emissions from composting and landfill estimated as equation9:

NetGHGemission (tons CO2-eq/yr) = NetGHGcompost + (CH4emitted x GWPcm) (9)

3. Results and discussions

3.1. Organic fertilizer production

As a country that relies on agriculture as a main economic activity, Vietnam has high potential demand for organic fertilizer production for sustainable agricultural ecosystems. In the urban and suburban areas, organic waste composting plays an important role for agriculture and gardening because of the limits of compostable biomass.

In general, composting takes six weeks after waste has reached the composting facility, including the first three weeks for fermentation and three weeks for maturing. The compost product quality analysis is entrusted to an external organization twice a year, which mainly check the moisture and C/N ratio. Compost products in Hanoi city are being used at several types of farms including fresh vegetable, flower and orchard farms.

Compost product

(Thousand tons/year)

250 200 150 100 50 0

S1 S2 S3 S4 S5 Scenario

Fig. 2. Compost production from scenarios studied

In the case of Hanoi city, composting technology has been utilized since the 1990's, so the efficiency is very low. By using the material balance analysis, compost product accounted for only 16% of composted organic waste, evaporation (41%), recyclable trash (15%), and residue (28%). The results show that organic fertilizer produced

6,424; 24,201; 97,224; 194,449; and 218,650 tons/year for scenarios S1, S2, S3, S4, and S5, respectively. The capacity of the composting facility is currently underutilized compared to the amount of organic waste. Therefore, it is necessary to improve composting capacity and technology for organic waste recovery. One feasible solution to be applied for improvement of composting capacity in coming years is waste separation of organic and inorganic items from commercial sources such as institutions, schools, hotels, restaurants, and markets.

3.3. Landfill life extension

Hanoi city has three designed sanitary landfills. These landfills received 1,701,630tons/year, which accounted for84.4% of the total collected MSW. Nam Son is the biggest landfill covering an area of 236 ha and received more than 4,400 tons of MSW/day. Kieu Ky landfill received 150 tons of MSW/day and is expected to be closed within the next few years because of overload. Xuan Son landfill received 100 tons of MSW/day9. The space for creating MSW landfill is becoming scarce because of urbanization and economic development17. Therefore, it is clear that the need to reduce the amount of waste sent to landfills through reducing, reusing, and recycling is urgent. Therefore, composting is one economical and environmental solution for sustainable MSW management practice.

Organic waste is the major component disposed of in landfills in Hanoi. Therefore, landfill life will be short depending on the amount (volume) of organic waste deposited. In this study, the information of volume of two small landfills (Kieu Ky and Xuan Son) was not available, therefore the authors assumed that the largest site (Nam Son) with a designed capacity of 12,544,100 m3 after expansion in 2011, received all MSW for Hanoi city9. The mixed waste was compacted before disposing into landfill cells. To calculate landfill life, density of compacted waste was used. For MSW in Hanoi, the density of compacted waste was 0.85 ton/m9.

Scenario S5

S4 S3 S2 S1

0 2 4 6 8 10 12 14 16 Year

Fig. 3. Landfill life extension of scenarios

Composting could reduce significantly the amount of waste sent to landfill. Therefore, landfill life could be extended as shown in Fig. 2. If the current management model still applies, the landfill life will be 6.2 years. When organic waste is composted, landfill life could be extended to 6.7, 8.4, 12.9, and 14.9 years for proposed scenarios S2, S3, S4, and S5, respectively. Although S2 represents a short extension of landfill life (6-month extension), it brings economic benefits through compost products and other environmental concerns. The results of S3 and S4 indicate that household organic waste has an important influence on landfill life extension. Landfill life could be doubled if all household organic waste was diverted to composting. The ideal practice(S5) shows the longest extension of landfill life, however, this practice seems infeasible because of the low quality of municipal organic waste and source separation limits in Hanoi city.

3.4. GHG emission reduction

For GHG emissions concern, this study considers three main gases including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) and two emission sources including composting sites and landfills. The term of carbon dioxide equivalent (CO2-eq) and Global Warming Potential (GWP) were used to make scenarios comparable.

3.4.1. GHG emissions from composting

Composting could emit GHGs through combustion of fossil fuel for on-site activities and from organic waste degradation.

The CO2 emitted from fossil fuel combustion is considered in the GHG inventory; however, CO2 emitted from biodegradation would not be calculated as GHG because of its biogenic origin. The CO2 emission factor of diesel is 0.074 kg/MJ and the energy content of diesel is 36.42 MJ/L15. Consumption of diesel on-site was 5.43 L/ton of organic composted waste14.

For biodegradation, CH4 is generated under anaerobic digestion in the deep layers of composting piles and it is also oxidised in the aerobic layers of waste piles. The amount of CH4 emitted depends heavily on the anaerobic condition of waste piles. Moreover, N2O can be formed by a limited amount of bacterial activity. According to the IPCC, there are 4kg of CH4 and 0.3 kg of N2O emitted per ton of wet organic waste composted.

Composting presents high potential for GHG reduction through avoiding chemical fertilizer production since the compost product is used as agricultural fertilizer to replace the chemical alternative. One ton of compost product can supply soil nutrients of 7.1 kg of nitrogen, 4.1 kg of phosphorus, and 5.4 kg of potassium18. In Hanoi city, all compost products were used for agricultural and gardening purposes.

The amount of GHG emissions from composting is shown in Fig.3. The results show the negative emission values, indicate the potential GHG saving and climate protection through composting. Potential of GHG savings are 6,097; 22,968; 92,272; 184,544; and 207,512 for scenarios S1, S2, S3, S4, and S5, respectively. The amount of GHG savings increases in accordance with the amount of waste sent to composting.

3.4.2. GHG emissions from landfill

Landfill is the third biggest contributor of CH4 emission from anthropogenic sources [19]. The anaerobic digestion of organic waste generates landfill gas containing approximately 40% of CO2 and 60% of CH4, whereby only CH4 is considered as GHG [20]. CO2 emitted from landfill is not considered GHG because of its biogenic origin. The amount of CH4 generated depends on several physical and biochemical factors, climatic conditions, and physical characteristics of landfill. The managed sanitary landfills produce a higher CH4 yield than that from unmanaged and open dumping sites because of different anaerobic conditions. In addition, the deeper disposal sites generate greater CH4 than shallow ones. This study used GWP recommended by the IPCC to finalise the amount of GHG emissions in terms of carbon dioxide equivalent for scenarios studied. The GWP of CH4 and N2O are 21 and 310 time greater compared to CO2.

In Vietnam, landfill, including sanitary and open dumping sites, is the most common treatment applied throughout thecountry9. According to the Vietnam initial and second national communication to the United Nations Framework Convention on Climate Change, the waste sector contributed about 2.4% in 1994 and 5.3% of total GHG emissions, where solid waste accounted for 53% of emission21, 22. In the context of climate change and sea level rise, the Vietnamese government has approved several environmental policies related to GHG reduction from all sources including the waste sector. In case of Hanoi city, all landfills are managed without a CH4 gas capture system. This practice results in more than 90% of GHG emitted from solid waste management by landfills23.

The amount of GHG emissions from landfill is shown in Fig. 3. Current MWS management (S1) contributed the greatest amount of GHG emissions at 1,329,025 tons CO2-eq. This amount indicates the high potential of CDM projects and climate impact from landfills in Hanoi. The amount of GHG emissions decreases significantly in accordance with the decrease in organic waste amount sent to landfill presented in S2, S3, S4, and S5. Emissions are 1,149,120; 723,870; 309,518; and 233,334 tons CO2-eq for S2, S3, S4, and S5, respectively.

3.4.3. Net GHG emission

In order to assess the impact of waste management on climate change and global warming, net GHG emission is used in this study. The net emission is the sum of emission from individual treatments(i.e. composting and landfill). The amount of net emission is shown in Fig.3.

The current MSW management practice contributed the highest amount of net emission at 1,322,928 tons CO2-eq, whereas the scenarios S5 (ideal practice) generated the lowest GHG emissions at 25,822 tons CO2-eq. The proposed

scenarios generated 1,126,152; 631,598; and 124,974 tons CO2-eq for S2, S3, and S4, respectively. These figures present emissions from S2, S3, S4, and S5 accounted for 85%, 48%, 9%, and 2% compared to S1. The net emission demonstrates the potential emission reduction achievable from composting for all scenarios studied. These results also suggest that composting has high potential for climate protection.

Fig.4. GHG emissions from scenarios studied

4. Future study

This study was conducted based on the organic waste recovery option. The results therefore depend heavily on source separation; however, Hanoi city has very few small places that can implement separation pilot projects. Therefore, the first step is to propose an effective source separation program for MSW utilising organic and inorganic categories for composting.

The IPCC's default factors were applied to calculate the GHG emissions. However, almost all influencing factors such as emission and oxidation vary from region to region depending on climatic conditions and other regional factors. Therefore, for accurate calculation, the authors plan to determine the regional factors suitable to tropical monsoon climatic conditions and waste characteristics for Hanoi city as well.

This study focused on three main environmental benefits of composting in comparison with landfilling; however, composting could bring more benefits to the environment. Thus, for future study, an integrated MSW management approach including all treatment options will be undertaken to create an overall evaluation for the city.

5. Conclusion

In this study, we used Hanoi city as a typical case characterized by high organic waste component in developing countries. We proposed five scenarios based on source separation expectation, national policies on solid waste management, and applicable options. The current situation indicates improper MSW management applied in Hanoi as 84.4% of waste was sent to landfill. The results obtained present the key environmental benefits of municipal organic waste composting. This strategy could significantly increase the amount of organic fertilizer production, extend landfill life, and reduce GHG emissions when compared to current practice. With rapid economic growth and urbanization and climate change mitigation concerns, these benefits are considerable for Hanoi city.

For progress towards sustainable MSW management, it is strongly recommended that source separation of waste should be implemented as soon as possible followed by steadily improving the capacity of composting facilities. Therefore, scenario S2 can be applied to fulfil short-term needs and the other scenarios utilized by government to fulfil medium and long-term goals. In addition, future research is necessary to identify and evaluate cost and benefits for each scenario.

Acknowledgements

The authors would like to thank the Japanese Grant Aid for Human Resource Development Scholarship (JDS Scholarship)as well as the University of Tsukuba for funding and support for this research. All comments and discussions by reviewers are greatly appreciated.

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