Study On Optimization Models For Municipal Solid Waste Collection And Transportation System

With the rapid growth of economy, population and urbanization progresses, the generation of municipal waste is increasing rapidly by 3-10% each year, which made a great problem to the environmental sanitation department. Improper removal causes prominent phenomenon of the waste siege and pollution, which also leads to the increase of the cost of collection, transportation and transshipment. In the integrated management of the municipal solid waste, collection and transportation is an important link, which charges the most amount of the process (60%-80%). The operation is also complicated. Therefore, based on literature review and field investigation, and on account of the municipal solid waste collection and transportation system status and development direction, this study used the methods of theory study, model establishing, algorithm design, example analysis, etc. to establish optimization models for municipal solid waste collection and transportation system. Through the application of the models, it made the collection and transportation system operation economical, high-efficient and stable, with considering the factors of social environment, either. This study provided scientific basis for optimizing the site selection, logistics distribution plan and vehicle routing.As the subsystem of solid waste management system, the collection and transportation system has integrated function and close relationship to the upper system. Therefore, from the standpoint of integrated management of the municipal solid waste, and considering the economic, environmental and social effects of the collection and transportation system, this study established a multiobjective dynamic programming model. The model application could not only reduce the cost of integrated management from 184.2 yuan/t (2011) by mixed collection to 58.4 yuan/t (2020) in Chengdu. At the same time, Incineration increased, and the ratio to landfill increased from 1:3 to 6:1. This treatment change accorded with the solid waste programme requirement in Chengdu and the purpose of "resource-efficient society" construction.To satisfy the requirement of the municipal solid waste separate collection development of future Chengdu, integrating the status of the municipal solid waste recycling and treatment, and in view of the characteristic of high kitchen waste without special bio-treatment facilities, this study established a municipal solid waste separate collection and transportation system, which suggested separate collecting kitchen waste from the source and transporting it to the Dewatering compression transfer station, and then after dewatering, transporting it to waste incineration or landfill plant. This system also used the multiobjective dynamic programming model to optimize the site selection of the dewatering compression transfer station and logistics distribution plan for different waste. The results showed that separate collection and transportation system could not only reduce the cost of integrated management by 23.1%, and also reduce the amount of the waste by 7.7%.Based on the application of system plan model, and account on the two transfer modes (with and without Interim place) in China, we brought forward a vehicle routing node problem model and vehicle routing arc problem model respectively and designed an ant colony algorithm with clustering algorithm strategy to develop the theoretical optimization study of the collection and transportation route. Combining the results and full considering the real road and traffic limit, this study established a solution model to develop the example study in GIS. For example of Shuangnan region in Chengdu, in view of the problems of secondary pollution near the waste stacking place and repetitive work, this study optimized the solid waste collection and transportation route which cancelled temporary stacking place. The result told us under the improved mode, the unit costs were 12.0 yuan/t and 11.8 yuan/t, respectively in the routes without turning limit, which saved 36.51% and 37.57%. The optimization effect was obvious.In addition, in order to avoid the traffic peak and reduce the transportation time, and finally reduce the fuel cost, this study used WCVRPTW model to optimize the domestic waste collection and transportation route in Shuangnan, Chengdu. The study compared with the results of three optimization rules:one without time window, one cost by time and one aimed at the least fuel consumption. The results showed that the optimization aimed at the least fuel consumption, which considered both traffic jam and route length, consumed the least fuel 34400g, which saved 11.73%, comparing to route optimum. This optimization reduced the cost and the negative environmental impact from transportation decreased.The results above indicated that reasonable locating transfer facilities, establishing waste logistics distribution plan and routing plan based on the application of system optimization model would benefit for reducing the cost of integrate management, increasing comprehensive utilization efficiency, and reducing the waste final disposal. It is a good way to gain the maximum social, environmental and economic effect.