Multi-objective dynamic recycling-routing-inventory for different pharmaceutical items with considering discount in a closed-loop supply chain

In this paper, a closed-loop supply chain for pharmaceutical items consists of a pharmacy, a distribution center, a recycling center and several pharmacy sites is considered in which two types of routing are performed. The first involves the routing of vehicles between the distribution center and the pharmacies, and the second involves the routing of vehicles to the recycling center and all nodes. Two types of pharmaceutical items are considered for this purpose, and their demand varies for different periods. The distribution center can offer discounts depending on the pharmacy orders. In addition, the distribution center can increase its capacity by renting more warehouses. Also, we have two objective functions: minimizing costs and environmental pollutants caused by carbon dioxide emissions. This problem is solved in the small-sized problem by the Epsilon constraint method and in the large cases by two hybrid algorithms based on the Fordyce-Webster algorithms and NSGAII-FW and MOSA and evaluated by different criteria. The computational results show that the NSGAII-FW algorithm is more efficient than the MOSA algorithm.