Physical Properties of Water Treatment Residue and Their Effects on Plant Growth as a Substitute Soil

Technology that can reuse a larger amount of water treatment residue (WTR) is required. In this study, the physical properties of the WTR, and the WTR medium to which organic materials (OM) were added, were measured, and the effects of the properties on plant growth were studied to reuse the medium as a substitute soil. Relative gas diffusivity (D/D0), saturated hydraulic conductivity (Ks) and water retention ability of the fine WTR (particle size <3 mm), the coarse WTR (particle size 3-8 mm) and WTR media all displayed high ability for reuse. However, available water capacities (RAW, PAW) of the WTR and WTR media were lower than those of typical soil. The RAW and PAW of the fine WTR were higher than the coarse WTR because capillary porosity of the fine WTR which was composed of relatively small particles retained more water. The RAW and PAW of the fine media were significantly higher than those of coarse media. The plant growth with the fine medium was greater than the coarse medium in the WTR medium with an OM content of 10%. The RAW and PAW may affect plant growth as a limiting factor more than the D/D0, Ks and water retention ability in the WTR medium with less available water capacity. When making a WTR medium for the substitute soil, a particle size of less than 3 mm of WTR is recommended.