Environmental impact assessment of municipal solid waste management incorporating mechanical treatment of waste and incineration in Hangzhou, China
Introduction
Municipal solid waste (MSW) management is an important issue for the urbanizing world, especially in developing countries, where economic development and expansion have significantly increased the generation of MSW. The vast amount of MSW generated in growing cities around the world requires sustainable management. The majority of waste is currently disposed of in landfills from where it emits landfill gas (LFG) that contains methane, a substance that makes a significant contribution to global warming. Waste and waste water together account for 3% of the global greenhouse gas (GHG) emissions, with landfill gas methane being the largest source (IPCC, 2014).
The amount of MSW in China has increased rapidly in recent years, and China is now the world's largest producer of MSW. In 2004, China generated 155 million tons (120 kg per capita) of MSW (National Bureau of Statistic of China (2005)) and by 2013 this figure had reached 172 million tons (126 kg per capita) (National Bureau of Statistic of China (2014)). These statistics do not include the waste collected by pickers, which is estimated to represent 8–10% of the total MSW generated (Chen et al., 2010).
The MSW that is generated in China is predominantly treated via landfilling and incineration. For example, in 2010, 79% of MSW was landfilled, 19% was incinerated, and 2% was composted (Dong et al., 2014a). Between 2002 and 2010, the proportion of incineration steadily increased from 3.7% to 19%. Modern landfill sites in China employ LFG collection equipment and modern leachate treatment systems to satisfy national pollution standard requirements. To be considered environmentally sound, cities in China should have safe disposal rates, which include landfilling, incineration, and composting, of between 85% and 90% (Chen et al., 2010).
In 2010, the share of mixed MSW disposed of in landfills in Hangzhou, which is one of the most developed areas in China, was 51%, while the rest was sent to incineration (Chi et al., 2014). The first MSW landfill (Tianziling Solid Waste Landfill) was constructed in Hangzhou in 1991, and it utilizes cement curtain technology to prevent leachate from polluting groundwater (Zhang et al., 2010).
Life cycle assessment (LCA) is used to deduce the impacts that different activities, including waste management systems, have on the environment with the intention of comparing how different configurations of the given systems vary (Cleary, 2009, Coventry et al., 2016, Ekvall et al., 2007, Fernández-Nava et al., 2014, Finnveden, 1999, Laurent et al., 2014, Turner et al., 2016; W. Zhao et al., 2009a).
Many researchers have conducted LCAs of waste management systems. Dong et al. (2013) examined the effect that source separation had on MSW management in Hangzhou and found that 23% of GHG emissions could be reduced in comparison to the base scenario. Chi et al. (2014) calculated that it was possible to achieve a 30% reduction in GHG in Hangzhou through improving source separation. More recently, Dong et al. (2014b) compared the disposal of MSW into landfills with and without LFG recovery and incineration and concluded that incineration is the most viable option for waste management in Hangzhou. Zhao et al. (2009b) used a LCA approach to estimate emissions from Hangzhou's MSW management system and found that landfills made the biggest contribution to the emissions that cause global warming, while incineration contributed the most to acidification. Zhao et al. (2011) examined MSW management in Tianjin using LCA and life cycle costing (LCC) and concluded that the operation of current and new landfills in combination with LFG recovery would represent a promising approach to waste management in Tianjin.
To date, the LCA studies that have assessed Chinese MSW management systems have focused on the incineration of mixed MSW with coal and improving source separation or improving landfill disposal practices. These studies have ignored the potential of refuse-derived fuel (RDF) production through the mechanical treatment and utilization of RDF in waste incineration. The production of RDF from mixed MSW could potentially be used to improve the fuel qualities of mixed MSW, thus removing the need to use coal as an auxiliary fuel in waste incineration plants in China. This mechanical treatment could also enable the recovery of recyclable waste from the MSW. In addition to RDF, there is also a significant organic reject fraction coming from mechanical treatment that requires treatment. To that end, the current study had two main objectives. The first of these objectives was to assess the change in the environmental impacts that transitioning from mixed MSW co-combustion with coal to the mechanical treatment of mixed MSW in combination with the incineration of RDF would have. The second objective was to determine the most environmentally sound method by which the organic reject from the mechanical treatment of mixed MSW could be processed.
Section snippets
Materials and methods
A environmental impact assessment was conducted in accordance with ISO standards 14040 and 14044 using life cycle assessment (LCA) tool GaBi 6 (ISO 14040, 2006, ISO 14044, 2006). The four major phases in the environmental impact assessment include goal and scope definition, inventory analysis, impact assessment, and the interpretation of results. Environmental impact assessment is a relative approach that requires a functional unit that defines what is being studied. All subsequent analyses are
Results and discussion
The results of the life cycle assessment of the study scenarios are presented as total values of GWP (Fig. 4), AP (Fig. 5), and EP (Fig. 6). The figures also include the results of the uncertainty calculation, which are represented by the error bars. The order of scenarios remained unchanged during the uncertainty analysis. According to the uncertainty calculation, the highest uncertainty was related to the EP values with the changes related to the default value being, on average, between −322%
Conclusions
The life cycle assessment study presented in this paper demonstrated that the environmental situation in Hangzhou could be improved by changing the MSW management system that is currently employed in the area. The highest improvement potential arises from producing RDF that is of a higher quality than the original MSW for energy recovery. However, the benefits gained may be easily diminished if the organic reject from RDF production is landfilled. To prevent this, the organic reject from RDF
Acknowledgments
This study was conducted as part of the Material value chains (ARVI) program (2014–2016). Funding for the program was provided by Tekes (the Finnish Funding Agency for Innovation), industry representatives, and research institutes.
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