关键词: 医疗废物回收, 路径优化, 风险基于装载量, 多中转点

Abstract: The safe and efficient collection of medical waste is of great significance for ensuring the smooth operation of medical institutions, preventing the secondary pollution of medical waste, and protecting the health and safety of residents. Medical waste collection requires qualified enterprises to arrange vehicles to collect medical wastes at various medical institutions and transport medical wastes to the special treatment center. Whether the arrangement of the routes of collection vehicles is reasonable or not has an important impact on the medical waste collection. If the arrangement of the routes is not appropriate, it is apt to increase the risk of collection and result in an adverse impact. The large number and great dispersion of medical institutions are the difficulties in the medical waste collection. The amount of medical waste generated by a single medical institution, especially a small one, is relatively small. If the collection and transportation of medical wastes are only carried out between medical institutions and the treatment center, the total cost of collection will be too high and bring great pressure on the transportation capacity of medical waste collection enterprises. In order to alleviate this problem, many cities have begun to build medical waste transit points. During the medical waste collection, the medical wastes collected from medical institutions are sent to the transit points first, and then to the treatment center. Although the transit points of medical waste have improved the efficiency of medical waste collection, they are likely to result in a high-risk adverse situation owing to the potential risks related to collection vehicles. Therefore, it is very important to reasonably arrange the routes of collection vehicles in the collection mode with multiple transit points, and the routing optimization for medical waste collection considering load dependent risk and multiple transit points has also become an important research problem.
This research comprehensively considers the actual situation in which the risk of medical waste collection depends on the loads of vehicles and the collection mode with multiple transit points. The entire collection process is divided into three stages for discussion. First, the total cost and maximum risk of each stage are analyzed in depth. Second, based on the analysis results, a bi-objective routing optimization model for medical waste collection considering load dependent risk and multiple transit points is developed, minimizing the maximum risk and the total cost of collection simultaneously. Third, some properties of the problem are analyzed before the solution algorithm is proposed. Fourth, an approximation algorithm is proposed based on the properties of the problem and the epsilon constraint method, and the time complexity and approximation ratio of the algorithm are analyzed. This approximation algorithm determines the routes for vehicles in three stages and includes multiple prohibited conditions. The analysis results show that the algorithm is a polynomial time algorithm. Finally, through a series of generated test instances based on Solomon's instances, the mathematical model and approximation algorithm proposed in this research are tested, and the results show that the proposed approximate algorithm can effectively solve the routing optimization problem for medical waste collection considering load dependent risk and multiple transit points.
According to the sensitivity analysis of the key parameter affecting the risks, that is, the loading capacity of vehicles, it is found that both the total cost of collection and the maximum risk show downward trends. But in some cases, when vehicles with larger loading capacity for medical waste collection are used, these downward trends are not significant. The possible reason is that the maximum risk is tightened, so the increasing loading capacity of vehicles cannot continue to bring about the downward trends of cost and risk due to the limitation of risk.
The contents worthy of further study include three aspects. First, the work of this research is completed under the condition in which the amounts of medical wastes to be collected in each medical institution are not allowed to be split. Thus, the problem that the amounts of medical wastes to be collected can be split is worth studying. Second, the possible risks of temporary storage of medical wastes at transit points have not been considered in this research, and further work is needed to analyze and control the temporary storage risks at transit points. Third, developing algorithms with better time complexities or approximation ratios is also a future research direction.

Key words: medical waste collection, routing optimization, load dependent risk, multiple transit points