Optimising waste flows

With 3.3 million citizens served, and more than 4 million tons of waste treated, Herambiente S.p.A is the largest waste operator in Italy and one of the largest in Europe. Waste management is no longer simply source-to-landfill, with waste moving through a network of preliminary treatments before reaching differentiated final destinations. Herambiente routes all kinds of waste through about 90 directly controlled facilities and several hundred facilities owned by third-party companies. This requires complex management, with decisions being taken at different levels of detail, from strategic to operational.

Before the use of Operational Research, each level of decision-making was supported only by general purpose IT tools. The definition of a good, feasible solution was highly labour-intensive, requiring weeks to create the data and elaborate the decisions. The company could only examine an extremely reduced subset of possibilities and the risk of losing profits was tangible.

Herambiente S.p.A’s owner, the Hera Group, began a project with the OR group at the University of Bologna aimed at evaluating the potentials of the use of optimisation in waste collection and treatment. Good results and the increase complexity of the business led to the creation of a complete Decision Support System (DSS) capable of supporting the entire planning process at Herambiente. Prototypes were made available to central planners to start a thorough refinement and revision process, which delivered OptiWasteFlow for roll-out across Herambiente’s operations.

The user can generate and navigate through several scenarios, each giving a complete and independent representation of an alternative configuration of the system. Scenarios can be optimised on a remote server where solutions are produced in just a few minutes. Results are then displayed graphically and can be exported to spreadsheets and as reports.

The optimisation model considers treatment and disposal costs and revenues, logistic costs for transportation of waste, and revenues from selling the sub-products as electric power or recycled materials. Different types of limitations can be imposed, such as upper and lower limits for flow rates across waste subsets. Additional features can be integrated in the model, like temporary storages, digester facilities, delayed flows, logic constraints and economies of scale on waste transportation.

Thanks to OptiWasteFlow, optimal or near-optimal solutions for the highest level Industrial Plan can be obtained within an extremely short computing time, while human resources are dedicated to key activities such as solution evaluation, what-if analysis and consequent strategic decision-making. The system has been continuously improved by the addition of new features and functionalities to exploit new savings and efficiency opportunities.

Results were the subject of deep qualitative and quantitative analysis to assess the validity of the tool. An overall increase of 14% in foreseen incomes was obtained, mostly thanks to a more efficient use of facilities resulting in decreased disposal and treatment costs.

Logistical costs, which are subject to long-term contracts with external carriers, were not included but optimisation reduced logistic flows by more than 40%, which undoubtedly means fewer kilometres travelled by the waste over expensive paths. This will most likely lead to even more savings when carrier contracts are periodically renegotiated.

Besides the excellent revenues that were generated, OptiWasteFlow also fostered the diffusion of OR-supported planning within other branches of the Hera Group such as the waste collection and district heating divisions.

Full article available in Impact Magazine, Autumn 2017: ‘Optimising Waste Flows’ pp15-18