In order to counteract man-made climate change and to comply with the recycling rates defined by the European Commission, innovative solution concepts are researched in the field of waste management. The Chair of Waste Processing Technology and Waste Management (AVAW) at the Montanuniversitaet Leoben is also conducting research on a "waste management plant system of the future". The varying composition of mixed municipal waste and the occurrence of interfering substances complicate the treatment process of waste and the extraction of secondary raw materials and substitute fuels. Therefore, the interfering substances in waste treatment plants and the different effects that result from them are building one field of focus. By conducting a survey among Austrian and German operators of treatment plants for solid, non-hazardous waste from households and industry, it was possible to analyse the issue of contaminants in more detail. The frequency with which different contaminants occur, the aggregates at which they cause problems and the effects resulting from them, have been investigated. The data from all the participants, 54 company operators, including mechanical-biological treatment plants, splitting plants and substitute fuel producers, provide information on the current state of the art regarding the occurrence and handling of interfering substances in waste treatment. Following the evaluation, three different groups of contaminants were identified: Product, emission and process contaminants. The different contaminants were classified into these groups according to the type of problems they cause. The survey showed that especially metals, large, bulky parts and tapes, nets and strings frequently cause negative effects. The most frequently affected aggregates are shredding units and sieves, followed by conveyor belts and deflection rollers. The effects on the waste treatment process can be quite different. In the expert interviews, impacts from increased wear of the aggregates, lower throughput and reduced product quality of the secondary raw material or substitute fuel, to endangering employees through fires and explosions were mentioned. The numerous, often serious problems, underline the urgency of research and development in the sector of innovative waste treatment.