Reusing Fe Water Treatment Residual As a Soil Amendment to Improve Physical Function and Flood Resilience

Soil degradation is a global challenge that is intrinsically linked to climate change and food security. Soil degradation has many causes, but all degraded soils suffer from poor soil structure. The increasing global production of water treatment residual (WTR), an organo-mineral waste product from clean water treatment, means that the sustainable reuse of this waste provides a potential timely opportunity, as research has shown that WTR application to soil can improve soil health. Recycling or reuse of WTR to land is commonplace across the world but is subject to limitations based on the chemical properties of the material. Very little work has focused on the physical impacts of WTR application and its potential to rebuild soil structure, particularly improving its ability to hold water and resist the effects of flooding. This paper presents novel research in which the use of Fe WTR and Fe WTR / compost [1 : 1] co-amendment has shown to be beneficial for a soil's water retention, permeability, volume change, and strength properties, all critical in soil health. Application rates of WTR were 10 %–30 % by dry mass. Compared with the control sandy loam soil, co-amended samples have 5.7 times the hydraulic conductivity (570 % improvement), 54 % higher shear strength, and 25 % greater saturated water content. Single WTR-amended soil had 26 times the saturated hydraulic conductivity (2600 % improvement), 129 % higher shear strength, and 13.7 % greater saturated water content. Data indicate that Fe WTR can be added as a single amendment to significantly improve soil physical characteristics where shear strength and hydraulic conductivity are the most important factors in application. Although the co-application of Fe WTR with compost provides a lesser improvement in shear strength and hydraulic conductivity compared with single WTR amendment, the co-amendment has the best water retention properties and provides supplementary organic content, which is beneficial for environmental applications where the soil health (i.e. ability to sustain ecosystem functions and support plants) is critical.