Residual waste sorting as an emerging resource recovery opportunity

Residual waste has traditionally been regarded as the final stream: the material left over after separate collection, destined mainly for landfill or energy recovery. However, STADLER Anlagenbau GmbH is working hard to change this misconception. 

Growing pressure on landfill capacity, rising disposal costs, stricter environmental regulations, and increasing demand for secondary raw materials are encouraging municipalities and waste management companies to look more closely at the value that can still be recovered from this complex stream.

According to the United Nations Environment Programme's Global Waste Management Outlook 2024, municipal solid waste generation is expected to grow from 2.1 billion tonnes in 2023 to 3.8 billion tonnes by 2050. This outlook underlines the need for both environmental and economic solutions.

For STADLER, production and assembly of turnkey recycling and sorting plants for residual waste represents an important opportunity to recover materials that still end up outside dedicated recycling streams. Unlocking this value requires integrated plant design, engineering, process flexibility, and operational safety, supported by a stable regulatory and market environment that gives operators the confidence to invest in advanced sorting infrastructure.

The evolution of a misunderstood resource 

Waste has evolved from being seen mainly as a public health, safety, and disposal issue to being recognized as a resource stream with significant recovery potential.

The benefits are both environmental and economic. Recovering materials from residual waste reduces the need for virgin raw materials, whose extraction and processing can have a significant environmental impact.

Aluminum is a clear example: bauxite mining can affect forests, habitats, soil, and water resources, while recycling aluminum from waste streams can reduce emissions by up to 90-95 percent compared with primary production. At the same time, recovered recyclables can generate revenue and reduce landfill or incineration costs, helping sustainability and profitability go hand in hand, where regulation, disposal costs, and material values support the business case.

Advances in optical sorting, sensor resolution, automation, and AI-based detection are accelerating this transition, expanding the range of fractions that can be recovered as valuable secondary raw materials.

"The material is no longer simply a problem to be solved, but a potential that should be unlocked," explains Sabine Schlögl, technical sales engineer at STADLER. "This shift has also reshaped the relationship between waste management and manufacturing sectors, bringing greater focus to design for recycling, collection systems, and the required quality of secondary raw materials."

"This change is also influencing the role of waste-to-energy. Removing metals, inert materials, and, increasingly, recyclable plastics before incineration reduces the volume of material sent for energy recovery. It can also improve plant performance, enable valuable resources to be recovered, and lower the amount of bottom ash that ultimately requires landfill capacity," adds Schlögl.

Specialized processing systems 

Residual waste is one of the most demanding streams to process, combining high variability, contamination risk, unpredictable material behaviour, and changing recovery targets. For STADLER, performance depends not only on the individual technologies installed, but on how the whole process is engineered — from material reception and dosing through screening, sorting, transfer points, storage, safety, and maintenance access.

Flexibility and safety are central to residual waste sorting. STADLER's adaptable layouts, movable conveyors, and digital control systems allow operators to respond to changing waste streams and market demands, while battery detection, fire protection measures, and multi-level plant designs enhance operational safety and resilience.

Customized sorting solution from STADLER

STADLER's approach is already being applied in advanced residual waste projects. One example is found in Sweden, where STADLER designed and built the Resursutvinning Stockholm municipal solid waste sorting plant for Stockholm Vatten och Avfall (SVOA), Sweden's largest water and waste utility. Processing up to 50 tonnes of waste per hour across two independent sorting lines, the facility recovers organic waste collected in green bags, as well as plastics and ferrous and non-ferrous metals accidentally mixed into the residual material. 

Combining advanced sorting technologies with a highly automated control system, the plant maximizes resource recovery while ensuring operational flexibility.

The project also demonstrates the value of continuous optimization, with SVOA highlighting the positive experience with STADLER, as stated by William Frieberg, project manager at SVOA: "I appreciate STADLER's professionalism, responsiveness, and commitment to continuous improvement. Their support and expertise have helped optimize the plant's performance while maintaining high standards of health, safety, quality, and environmental management."