Mechanisms of Sludge Biochar Effects on Thermal Properties of a Loess Soil (Sierozem)

The purpose of this study was to analyze the effects of sludge biochar (BC) application (2, 5, 10, 15% w/w) on the physico-chemical and thermal properties (thermal capacity, thermal conductivity and thermal diffusivity) of loess and the mechanism of action. The results showed that the application of BC changed the soil particle size distribution, reduced the soil bulk density, increased the soil total porosity (1.19-11.51%), organic matter content (10.94-85.02%), saturated water content (1.85-7.15%) and field water capacity (0.09-13.00%), and decreased the soil thermal capacity, thermal conductivity and thermal diffusivity, with an average decreasing amplitude of 2.13, 5.45 and 7.54%, respectively. Soil bulk density and water content (<30%) were positively correlated with soil thermal capacity, thermal diffusivity and thermal conductivity. The mechanisms are mainly that the negative impact of changing soil solid composition and increasing total porosity by biochar with low density and thermal parameter values; and the positive effect of raising water content by improving soil water holding capacity. Sludge biochar shows great potential in soil improvement and can realize sludge sustainable management.