Physical and mechanical properties of washed sediment mixed with organic matter

Soil from cleaning and washing of sugar beet during processing is collected and decanted in tanks each year over a period of several months. Instead of spreading it on agricultural land, another option is to reuse the sediment for crop growth. The physical and mechanical properties of the non-structured washed soil (WS) and the efficiency of added organic matter (peat and green waste compost) were evaluated by comparison with an arable silt loam soil (AS). Water retention data were expressed in a double-exponential function which characterized soil structural and matrix pore space. The effects on saturated hydraulic conductivity and pore space morphology from applying loads of 60 and 200 kPa on two initial volumetric water contents (12 and 25%) were investigated using image analysis. WS was a silt loam with no plasticity, and its void ratio and water retention were higher than the AS before compression. However, WS had a very small amount of structural pore space and despite its higher void ratio, its hydraulic conductivity was always lower than AS after compression. Organic matter improved all the WS properties by increasing structural porosity and vertical stress resistance. Organic matter created elongated and tortuous pores and increased K _s values by changing pore size distribution. During compression large pores with a radius >1500 μm disappeared in WS mixtures but were still observed in AS and were maintained by aggregate stability.