Rainfall erosion resistance and stability of various composts

Compost use in landscaping and erosion control applications has become widespread. Various types of composts have been utilized on highway embankments for soil conservation and runoff reduction. Different compost materials could have different erosion control effects. The objective of this study is to investigate the erosion resistance of three commonly used composts and their effects on slope stability. Bench-scale experiments were conducted to test the erosion of three natural base soils (sand, silt, and clayey sand). Rainfall simulators were constructed to simulate a rainfall intensity of 3.1 in h–1 (7.9 cm hr–1). Soil boxes were designed and built to simulate an inclined embankment. The soils were tested under one hour of rainfall. Significant soil solid losses—over 100 g (0.22 lb) on a 0.91 × 0.30 m (35.8 × 11.8 in) plot area—were observed in all base soil erosion tests, and the silt slope slid during the test. Repeated rainfall erosion tests were performed on the three base soils, respectively, with three types of compost covers (green compost, manure compost, and co-compost made of biosolid and green compost). Both manure compost and co-compost retained slope stability and reduced soil erosion. Green compost reduced solids loss of the silt and sand slopes, but it induced more solids loss of the clayey sand slope, which was stable without a compost cover. Mechanisms of the soil erosion of the three composts on the three base soils were investigated. It is concluded that different composts, when possessing different properties such as density, particle size distribution, and organic matter content, may vary significantly in erosion control resistance. An erodible compost cover can trigger the slope failure (sliding) of an embankment that is stable without a compost cover. Metal concentrations, biochemical oxygen demand, and coliform bacteria in the runoff were analyzed, and it was found that composts reduced the concentrations of some heavy metals in the runoff.