The project originates from the residual soil problems in potato processing. Residual soil is soil that still adheres to supplied potatoes and is sieved or washed away at potato processors. As far as possible, it is returned with growers (potato suppliers). Previous studies showed that this residual soil may occasionally contain plant-harmful organisms (in particular plant parasitic nematodes and reproductive forms of the aggressive weed tuber cyperus) and that they are able to spread via the residual soil return system, which leads to new infections among growers every year. An interesting approach is to process residual earth at processors in such a way that the harmful organisms present (with a focus on nematodes and tuber cyperus) are killed.
The recently ended Flanders' FOOD project “Restaarde Circular” showed that thermal treatments based on convection were insufficient for this. During the final phase of the project, industrial microwave heating was explored as an alternative. The preliminary tests (on nematodes) showed that they could be killed quickly via this route. After project completion, fluidized bed heating was also put forward by the companies involved as possibly also suitable technology. At present, residual soil is not heat-treated, let alone microwave-treated or fluidized bed heated. The present follow-up project is aimed at collective research and knowledge dissemination as a step towards their possible industrial implementation for residual earth treatment with a view to safe and high-quality return to agriculture.

The aim is to determine the optimal microwave heating conditions (temperature-time combinations) for killing (cysts) nematodes (quarantine organisms) and tuber cyperus propagules in residual soil, respectively. In addition, those conditions are being sought that can generate this effect in different types of soil and at moisture levels that occur in practice. Subsequently, the aim is to determine whether these heating conditions can best be applied on an industrial scale via microwave technology or via fluidized bed technology. This is done through a comparative deskstop study that takes into account the desired processing capacity, the technical requirements and the different types of costs (energy, investment and operating costs). For fluidized bed heating, this is supplemented with a lab-scale challenge test. The final objective is to put together an industrial pilot process concept for the technology that comes out best (choice of guidance group) to demonstrate industrial implementability and to demonstrate the process (adjustment) possibilities in order to achieve the desired temperature / time relationships in different conditions (eg soil types, moisture contents). Experiments will also be carried out here with which the energy consumption and stability (with continuous use) can be estimated for real industrial process installations with different capacities.
The proposed project was initiated in response to the demand from potato processors, but a sugar beet processing company has now also joined this demand. We can consider these companies as pioneers, because in principle this project is aimed broadly at any company that has an (increasing, significant) residual earth problem (processors of root and tuber crops) or any company that disinfects soil / earth products, for example producers of potting soil.