A mathematical model for municipal solid waste management – A case study in Hong Kong
Introduction
Waste is described as the inescapable remainder of the processes of modernization (Scanlan, 2007). Hong Kong, which is regarded as one of the most modern cities in the world, has faced an increasing amount of waste since its rapid urbanization in the 1990s (Chan, 1998). Hong Kong has been actively promoting recycling activities. In 2013, 37% of municipal solid waste was recycled before delivering to landfills. However, around 9500 tonnes of municipal solid waste every day is sent to the landfills, approximately 67% of which is domestic waste. Municipal solid waste occupied nearly 70% of the total average daily quantity of waste from 2009 to 2013 (Environmental Protection Department (EPD), 2015a). These recent statistics reflect that Hong Kong needs a speedy and effective solution before the saturation of the landfills (Yau, 2012).
Shekdar (2009) indicated a typical framework for solid waste management for Asian countries. It includes sources of waste, collection systems, transportation, processing systems and landfilling. This study conducted a review of waste management practices in Asia as shown in Table 1. In summary, the waste management practices in some Asian countries are well developed while some of them are still in their infancy. Owing to the increasing concerns in achieving specific targets in waste management, both countries require municipal solid waste solutions and appropriate suggestions that suit their needs.
Recent research has concentrated on investigating different approaches, systems and mathematical models regarding waste management (Beigl et al., 2008, Yau, 2010). There are various waste management policies such as Pay-As-You-Throw (PAYT) and the deposit refund system (Reichenbach, 2008). These approaches can encourage people to produce less waste but provide limited information to support future waste management. Research on use Web-GIS based system was conducted in Italy for optimizing municipal solid waste selective collection (Rada et al., 2013) and the proposed approach has been extended and applied in Malaysia and China, which shows the feasibility of Web-GIS oriented tools in countries with transient economies. Although actual data can be collected during implementation, existing waste management systems provide restricted insights to support waste management plans. Mathematical models can further leverage the actual data to generate useful information for future waste management.
Bing et al. (2016) summarised the contemporary waste management practices and operations in Europe. The authors pointed out that one of the current problems is overcapacity in waste management infrastructure. Researchers should consider municipal solid waste management in a holistic view so as to take the whole municipal solid waste management process into account.
This project pertains to the design and development of a mathematical model for municipal solid waste management. Although there are many existing waste management systems around the world, most of them consider implementing different policies to handle waste problems. Scenario analysis or mathematical modelling for waste management have not yet been widely adopted, especially in Hong Kong. Hence, a mathematical model is developed based on the typical framework for solid waste management in Asian countries. Beyond considering the whole municipal solid waste management process, this model also attempts to utilize the capacity of incinerator outside Hong Kong to improve the waste problems.
Section snippets
Mathematical models for municipal solid waste management
Operation research techniques provide guidance for decision-makers to select best strategies or choices among a set of options (Ghiani et al., 2014). As a result, various mathematical programming models were established to facilitate waste management and planning (Dai et al., 2001). For example, the incineration process (Yang et al., 2002), amount of waste from residents (Benítez et al., 2008), formation of perched leachate zone in landfills (Di Bella et al., 2012) and greenhouse gas emissions (
Mathematical model formulation
This section presents a mathematical model for municipal solid waste management which is developed based on the model of Nganda (2007). The model acts as a tool to provide appropriate information for decision-makers to plan how to utilize waste management infrastructures to minimise waste management cost. The basic principles of Nganda’s work are shown as follow: Formulate waste flows between waste collection points, incinerators, replacement truck warehouse and landfills. Use integer linear
Case study and discussion
The waste problem in Hong Kong has become alarming due to the shortage of landfills. A case study was conducted in Hong Kong to realize the proposed mathematical model for municipal solid waste management. The general waste handling practices in Hong Kong are recycling, landfill and exportation. Around 40% of the collected recyclables were recovered for recycling in 2013 (EPD, 2015a). Currently, Hong Kong has three landfills, which are West New Territories (WENT) Landfill, South East New
Conclusion
There is an urgent need of developing a mathematical model to support decision-making regarding municipal solid waste management. A mathematical model with integer linear programming and mixed integer programming is developed. The model determined the optimal number of waste management infrastructures or facilities and suggested utilising the capacity of incinerator outside Hong Kong to improve the waste problem.
The reason for adopting two programming approaches in a model is to consider
Acknowledgements
The authors would also like to express their sincere thanks to the Research Committee of the Hong Kong Polytechnic University for providing the financial support for this research work (Project Code: G-UC83).
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