Coordinated production – inventory – distribution - routing problem on closed loop supply chain with recycling option

In this study, a coordinated production, inventory, distribution and routing problem in a closed loop supply chain is considered. The closed loop supply chain tackled in this study is capable of both recycling and disposal activities. The primary aim of this study is to investigate the performance of coordinated decisionmaking for production, inventory, distribution and routing in a closed loop supply chain. The problem is dealt with both the production-inventory trade-off and distribution-routing plans at each period on both forward and backward flows. The problem is formulated as a mixed integer linear programming model and solved optimally. The case study for a fats oil supply chain is conducted and results are given. According to case study results, the proposed coordinated decision-making reduces operational costs of the overall chain by about ten percent. Furthermore, random test instances are generated for evaluating the mathematical programming model. A comprehensive sensitivity analysis of this model is performed to assess the effect of changing the model parameters' values. Problems under different scenarios (such as changes in number of nodes and periods) are also run to investiagte CPU time and optimum cost . A decomposition heuristic based on a simulated annealing algorithm is proposed for solving large scale instances. Furthermore, a software with a graphical user interface is developed to automate all calculations for all problem sizes. An extensive comparative study is conducted to compare the results of the mathematical programming model, proposed heuristic and the two stage approach solving forward and backward flows of CLSC respectively.