Mechanical treatment of large volumes of soil infested by Japanese knotweed rhizomes: sifting-crushing technique

Abstract

In the context of the numerous operations to restore aquatic environments that it carries out, the Compagnie Nationale du Rhône (CNR) has been confronted with the lack of treatment channels for invasive introduced plants, particularly concerning large volumes of land colonized by Japanese knotweed rhizomes. Since 2011, the CNR has therefore decided to develop internally various treatment methods with the aim of immediately devitalizing the plant rhizomes in earth excavation. After two years of tests and three years of in-house application of the tested methods, the results are very satisfactory and a particularly effective technique has been proposed and deployed on large-scale restoration operations monitored by the CNR. The method in question consists of two key steps: a first sifting step to separate the fine elements from the coarse elements present in the alluvial materials, the second to devitalize the rhizomes present in the coarse fraction by fine crushing. The treated materials can thus be returned to the watercourse, valorized as planting substrate or evacuated in an inert waste storage facility (ex "class 3 landfill").