Optimizing Reverse Logistics for Waste Materials: A Multi-Stage Processing and Transportation Model

Companies currently face substantial challenges in adopting recycling technologies
and establishing facilities due to their high costs (Iakovou et al., 2024).
Nevertheless, European regulations targeting the plastics strategy, which seek to
transform the design, production, usage, and recycling of plastic products within
the EU, emphasize the critical need to improve efforts in the plastic recycling
sector (European Commission, 2023). Advancing this sector will require the development
of efficient supply chains optimized to manage reverse waste flows,
focusing on minimizing both costs and environmental impacts. In fact, transport
costs, sorting and recycling logistics can account for a substantial share of
the economic and environmental cost of recovered material. The study focuses on
polyvinyl chloride (PVC), extensively used in construction and building for products
like window frames, pipes, cables, and flooring. However, challenges persist,
as conventional mechanical recycling cannot process all PVC waste. Advanced
recycling offers a promising solution by purifying PVC and removing harmful
additives.
We formulate a bi-objective, multi-stage material processing and transportation
model to support the reverse logistics of PVC materials derived from the
construction, renovation and demolition sectors. The objectives are twofold: minimizing
the costs related to transport, processes, and inventories, as well as the
negative environmental impacts by incorporating Life Cycle Assessment (LCA)
throughout the whole reverse supply chain. This case-specific model has several
unique features. First, the production setup involves two plants, each with
distinct operations. The model includes two types of inventory: one before processing
and one post-processing at each plant. With regard to distribution, only
a single type of transport mode is considered in this research phase. Transportation
costs account for travel time, loading, and unloading, based on estimates
from the transportation partner. Batch sizes are also customized for this project,
allowing containers of 10m³, 20m³, or 40m³ depending on the quantity collected
at each source.
A critical challenge in reverse logistics is managing uncertainties in supply site
locations, yield capacities, and operational durations. To address this, the current
deterministic model establishes a robust baseline for project-specific conditions.
Future enhancements will introduce stochastic elements and expand scalability
to an industrial level, broadening applicability to diverse environments and industries.
This initiative is expected to produce several significant results. The project
aims to develop bi-objective optimization models for the collection, sorting and
recovery of PVC waste specifically from the construction, renovation and demolition
sectors. The resulting findings will support industry managers in making
strategic and tactical decisions by identifying optimal production lot sizes and
determining the quantities of materials to transport between multiple processing
sites over a defined planning horizon. In addition, waste traceability will be
improved, allowing data collection to monitor the progress and effectiveness of
recycling activities. This approach aims to make recycling competitive with the
low costs of incineration and disposal techniques.