02/03/2021
Abstract
The energy utilization from waste can be achieved with the application of different thermal technologies which can also result in energy recovery form waste. In this study, a life cycle analysis is carried out for different scenarios of managing municipal solid waste in Hai Duong city by 2030. This analysis predicts overall environmental burdens of municipal solid waste towards minimizing environmental pollution, reducing treatment costs and utilizing raw materials in order to emerge opportunities for circular economy. The results show that, with the socio-economic development of Hai Duong city, the construction of incineration plants combined with the production of high calorific fuel pellets is an appropriate treatment plan to suit the local conditions.
Key words: Life cycle analysis, solid waste, integrated solid waste management, recycling
1. Introduction
It is estimated that cities in Việt Nam generate around 38,000 tons of waste per day whit an 85% collection rate. According to the Department of Waste Management, Vietnam Environmet Administration (Ministry of Natural Resources and Environment), domestic waste treatment is not only a concern of some provinces but also an urgent and complicated issue of the whole country Currently, 70% of the generated waste is sent to landfills. Many of these are unsanitary landfills which cause trouble for adjacent people. In addition, due to the large area of land occupied, many urban areas have faced the lack of space for landfills. The pollution of solid waste from the burial process also causes many conflicts with the people living around the landfill, increasing the number of conflict activities such as preventing garbage trucks from entering the area, etc. Thus, the cost of compensation for damage caused by polluting landfills is increasing. The decomposition of rubbish in landfills also generates large amounts of methane, a potent greenhouse gas. Going along with the direct impacts of climate change on human life and the ecological environment, the generation of large amounts of greenhouse gases also represents significant drawbacks of landfills.
Hải Dương City, Hải Dương Province, is recognized as the economic, technical, educational, scientific, medical and service center of the province. The Government has issued Decree 88 / CP establishing Hải Dương City which is defined as a class-III urban area. By 2009, Hai Duong city was a city meeting class II urban standards in Hải Dương Province, being an industrial - services center in the Northern key economic region. Along with increasing urbanization, waste disposal has become a pressing issues in Hải Dương City for many years. The population increase and the rise in the living standards are the main reasons for exponential increase in the volume of municipal solid waste (MSW) generated. The total amount of daily solid waste generated in Hải Dương Province averages 1300 tons per day. The collected amount is about 880 tons per day, accounting for about 68% [1].
In Hải Dương City, besides Soi Nam landfill operating before 2011, which was overloaded causing environmental pollution, all domestic solid waste in the city are collected by Urban Environment Co., Ltd and daily transported to the organic fertilizer manufacturing company. However, this amount of MSW has just accounted for a small proportion of the collected waste. In order to reach the target of hygienic collection and disposal rates in 2020 up to 95% of solid waste which would be collected and treated hygienically, the amount of treated domestic waste has been estimated at 1,300 tons per day. One of the most important environmental issues is the treatment of domestic solid waste which is both environmentally effective and does not occupy too much land. Hence, the method of treating solid waste by thermal method has been considered to show the potential for the local context by reducing the volume of solid waste to the lowest level, reducing methane emissions, generating less leachate, less land area occupied, etc.
LCA (Life Cycle Assessment) is an analysis technique to assess the environmental impacts associated with a product, process or activity by identifying and quantifying energy, materials used, and waste released into the environment, thus identifying and assessing ways of improving its opportunities (according to Society for Environmental Toxicology and Chemistry). The LCA is also defined as a tool for systematic assessment of the environmental aspects of a product or service system through all stages of its life cycle [3].
A system boundary curve model of the LCA is the interface between the waste management system and the environment or other product systems. The life cycle begins when the material or product becomes waste, i.e., its owner removes it in the waste collection bin. Each collection method requires its own infrastructure, i.e., dedicated bins and collection facilities. Depending on the collection system of each country, solid waste can go directly to treatment plants such as incinerators, composting areas or sorted before treatment.
The LCA evaluates resource use, emissions into air, water, and soil, and useful products. All inputs (resources and energy) and outputs (emissions and products) must be identified and quantified during the LCA's life cycle inventory (LCI) phase. The most important LCI components of each management phase are determined by stages of generation - collection - transportation - sorting and disposal.
For these reasons, the authors would like to outline proposals concerning the evaluation of the solid waste treatment using thermal methods in Hải Dương City. The results obtained from the research will partly serve as a basis for selecting solid waste treatment technology for Hải Dương City. It is interesting to note that at the same time the planning for both design and construction of a desirable management system can be carried out to suit the conditions of the study site.
2. Methods and data used
2.1 Object and scope of research
The objects of the study include municipal solid waste generated from households in Hải Dương. The goal of this study is to analyze the current MSW management system and compare with different MSW management strategies that can be effectively implemented in Hai Duong city from an environmental point of view. According to the recent General Development Plan for Hải Dương City up to 2030 with visions towards 2050 approved by the Provincial People's Committee on July 14, 2017, the initiative expanded to include eight more communes in Hải Dương City. They are including Minh Tân, Đông Lạc (Nam Sách District); Ngọc Sơn Commune (Tứ Kỳ District); Tiên Tiến and Quyết Thắng Communes (Thanh Hà District); Gia Xuyên, Liên Hồng, and Thống Nhất (Gia Lộc District) communes with total area of 13,070.78 ha.
Different waste management treatment practices were investigated and specific alternative proposed MSW management systems using thermal treatment methods were compared. More specifically, three alternative scenarios have been introduced and compared regarding the management of the MSW generated in Hải Dương City.
2.2 Integrated waste management IWM2 software
To achieve foremost the research objective proposed in 2.1, the assessment was carried out using the “Integrated Waste Management” (IWM-2). The model was utilized as a decision supporting tool which takes into account all the environmental loads such as waste streams, collecting, treating and disposing of waste, in order to achieve environmental benefits, economic optimization and social acceptance, etc. This will lead to a practical waste management system for any particular area [4].
IWM-2 is a software created to accurately predict the environmental and economic burden of a specific waste management system. This software is used by diverse groups of individuals including policy makers, waste managers, researchers, environmental groups or students who want to research and evaluate totally both the environmental impact and the economic cost of the waste management system. Models using this software will provide an optimization scenario to compare with other waste management scenarios.
This model does not require a large amount of data thanks to a default data set to provide to the user. However, the more data provided by the users, the more accurate the results of the research waste management system are. To run the model, it is necessary to have data on the number of people and households in the study area, the amount of waste generated per capita in a year, the discharge characteristics of the study area. Data on energy demand, operating costs and performance are also required to describe each waste management process from collection through sorting, biological treatment, heat treatment and burying. One of the most important data to run the model is the electricity grid description. Different options for using the electric network will produce different results for the environment. Therefore, it is necessary to accurately describe the domestic grid of the study area to ensure the most accurate model calculation [4].
WM-2 is used in the LCI phase to assess the life cycle of a specific waste management system. The stages assessed by this model include the emission phase, waste collection, sorting, biological treatment, heat treatment, landfill and generated energy. Secondary impacts (issues related to construction, decommissioning of facilities and waste management facilities) are not included in the model.
In the IWM-2 model, inputs and outputs of each unit process (waste collection, central sorting, biological treatment, heat treatment and landfill) are all carried out on a volume basis, except heat treatment is carried out on mass and measurement basis. Emissions and leachate are distributed on the basis of each component (i.e., based on the composition of the material being buried); This approach takes into account the basic physical relationships between waste and gas and leachate as recommended by ISO 14041 [4].
2.3 Model input data
The input data under examination included in the study are: (i) total population derived from census data and forecasted data to 2030, (ii) total amount of household waste generation, (iii) waste composition, and (iv) the current waste treatment methods.
In the inventory analysis, most of the data used to model the different waste treatment scenarios were obtained from the current state of solid waste treatment in the city, following the National Strategy on Integrated Management of Solid Waste to 2025, with a vision to 2050 and the Decision 26/2020/QD-UBND of the Provincial People's Committee of Hai Duong province. In the cases, recycling is prioritized and performed as energy and useful materials recovery practices for waste that nevertheless arise in order to reduce the volume of waste sent to landfills and the environmental impacts.
The population projection data of 2030 data was taken into account according to the Hải Dương City Master Plan to 2030 with a vision to 2050. Specifically, the amount of solid waste generated in 2030 is 1,678 tons per day and night [2].
The composition of solid waste used in the study is shown in Figure 1.
Figure 1: Solid waste composition analysis at landfills
3. Results and discussion
3.1 Proposed scenarios
- Scenario 1 is considered as the scenario used for reference, therefore, using the current technology, collection rate of solid waste reaches 80%. Households carry out the classification and sorting of waste such as plastic lumps, metal, plastic bottles to sell to bottles buyers. According to some previous studies, the rate of collection of recyclables in households is assumed to be 70% of the generated recyclable waste. After being collected, the waste is transported to Việt Hồng Solid Waste Treatment Facility (Thanh Hà District, Hải Dương). Based on the data taken from the transportation process of solid waste to the factory, 45% of the waste is treated by microbiological method while as the rest is burned. However, by 2030, due to the estimated amount of solid waste generated according to the planning data, up to 612,470 tons per year will exceed the plant's capacity (64,000 tons per year). The remaining amount of waste is assumed to be taken away for burying.
- Scenario 2: The amount of waste collected and transported to the treatment area is similar to the scenario 1, but it is assumed that all collected solid waste will be burned. This scenario was designed taking into account the state of Việt Hồng Solid Waste Treatment Plant, in which the produced compost cannot be sold, so the combustion technology has received more attention from managers.
Figure 2: Simplified flow scheme of incinerator
- Scenario 3: The amount collected and transported to the treatment area is similar to the scenario 1, assuming that the treatment technology consists of the waste-to-energy system in Việt Hồng Solid Waste Treatment Plant with improvement and investment in the fuel pellet processing system, namely RDF.
Figure 3: Cross-section of typical RDF system [5]
The material circulation flows according to the above scenarios are shown in Figure 4 (a, b, c).
a. Scenario 1
b. Scenario 2
c. Scenario 3
Figure 4: Solid waste circulating stream by three scenarios
(Note: Unit in circulating stream is ton per day and night)
3.2 Evaluation of environmental effectiveness of options
IWM-2 software was used to calculate and compare the scenarios according to the following parameters:
- Exhaust gases: CO2, CH4, NOx, HCl, SO2
- Leachate: COD in water
- The remaining solid waste is put into landfill
Calculation results are shown in Table 1 and Figure 3.
Table 1: Assessment results calculated by IWM2 of three scenarios
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
|
|
CO2 (kg/year) |
302,786 |
1,243,299 |
-18,713 |
|
CH4 (kg/year) |
122,614 |
5,925 |
66,313 |
|
NOx (kg/year) |
1 |
-79 |
-264 |
|
HCl (kg/year) |
21 |
13 |
15 |
|
SO2 (kg/year) |
6 |
26 |
-457 |
|
COD (kg/year) |
592 |
32 |
324 |
|
Final solid waste (kg/year) |
1,620 |
235 |
736 |
Figure 5: Comparison of scenarios based on environmental parameters
After using IWM-2 model in three scenarios developed in case of Hải Dương City, the results are presented as follows:
- Scenario 1: When the current treatment facilities are taken into account, Hải Dương’s government needs to invest in building a new waste landfill site with a capacity of 1620 tons per day. Such a large amount of solid waste is put into landfills, which also increases the pollutants in leachate and exhaut gases. Moreover, the burial of solid waste occupies a large area of land and can easily cause more conflicts with households living in the vicinity of the landfill site.
- Scenario 2: By putting all domestic solid waste into incineration, this method generates the waste residual, mainly ash, accounting for the smallest amount of the three scenarios. However, the amount of CO2 released into the environment is still the largest, which is a prodominent disadvantage when we need to consider the treatment plan in terms of reducing environmental pollution. To implement this scenario, Hải Dương City needs to invest in building 9 more incinerators with the same capacity as the current incinerator, which is also a major drawback of this scenario.
- Scenario 3: In this scenario, the remaining solid waste is three times higher than the scenario 2 but only accounts for 45% compared to the scenario 1. In the scenario 3, the local government should invest in additional technologies, including compression, cutting and forming processes to produce fuel pellets. The numbers of incinerators that need additional investment is three. They can directly use fuel pellets to burn power generation (results calculated by the software are 683,617kWh of electricity) and reduce the moisture content of waste. In addition, this scenario also reduces the amount of NOx and SOx acids due to the change of not burning waste directly but indirectly burning through fuel pellets. If the amount of unused energy due to the reduction of solid waste put into the incinerators is calculated, the amount of energy savings in this scenario would reach 1,267,234 kWh (Figure 6).
Figure 6: The amount of energy savings due to the reduction of solid waste put into the incinerators
Conclusion
Through the development of solid waste treatment scenarios for Hải Dương City, the optimal urban solid waste treatment scenario for Hải Dương City is proposed as follows:. After being collected, the waste is transported to a waste treatment plant. The amount of 612,470 tons of solid waste per year is treated at the facility using the method of processing pellets of fuel (RDF) and burning on site to generate electricity. According to this scenario, the local government needs to invest more in the fuel pellet production system with 4 incinerators designed with the same capacity to the current capacity. The estimated amount of electricity generated is 683,617kWh which is capable of serving the plant itself or joining the national grid. This is also a source of funding to offset the cost of solid waste treatment. Simultaneously, the 3rd scenario shows that it is technically possible to reduce the amount of energy needed for the treatment process, the operating costs, adapting the urgent need to make the scenario more economically feasible.
Nguyễn Thu Huyền, Lương Thanh Tâm
Hanoi University of Natural Resources and Environment
References
1. Thông Chi, “The notorious waste treatment plant in Hải Dương dumps ash and ash into the environment”, Lao Dong Newspaper, May 20, 2020.
2. Bùi Mai Phương, Master's thesis in 2020 on “Research and evaluate the effectiveness of solid waste treatment by thermal methods in Hải Dương City”.
3. Forbes R McDougall, Peter R White, Marina Franke, Peter Hindle, “Integrated solid waste management: A Life Cycle Inventory”, 2nd edition, 2003.
4. Lương Mai Hương, PhD thesis on "Application of Life Cycle Research (LCA) to reduce the amount of landfill solid waste activities in Hanoi"
5.Marc J. Rogoff, Francois Screve, “Waste-to-Energy Technologies and Project Implementation”, (Second Edition), 2012
6. WHO, 1999, “Safe Management of Wastes from Health Care Activities”, 1999
