Fluidized Bed Bottom‐Ash Effects on Infiltration and Erosion of Swelling Soils

Fluidized bed combustion (FBC) bottom ash, rather than being used as fill at dumping sites, can be utilized to amend certain soils for erosion control. Because FBC bottom ash is a source of both electrolytes and alkalinity, its effectiveness in controlling runoff and erosion should be greater on soils with a predominance of permanent charges. Five soils, with and without addition of 5 Mg ha −1 surface‐applied FBC bottom ash, were prewetted and subjected to 110 mm h −1 rain for 90 min. The critical flocculation concentration (CFC) varied from 0.5 mmol c L −1 for the smectitic‐kaolinitic soil to 3.5 mmol c L −1 for the illitic soil. Steady‐state infiltration rates ( I s ) for the control were very low, ranging from 1.8 to 5.8 mm h −1 . These rates were increased 3.6‐ to 5.0‐fold with the application of FBC bottom ash, with a lesser increase for the highly smectitic and illitic soils. For the control, total soil loss ranged from 220 to 1998 g m −2 , and total water loss from 78 to 112 mm, with the greatest losses for soils with a large cation‐exchange capacity/clay ratio. The FBC bottom ash reduced total water loss by 1.1‐ to 2.0‐fold and total soil loss by 1.5‐ to 3.9‐fold. The CFC of the soil was correlated with I s , while aggregate stability was correlated with erosion and total runoff. The FBC bottom ash effectiveness in increasing infiltration and controlling erosion on these soils is attributed to an increase in electrolytes in the runoff, thus decreasing soil swelling and the dispersion of clay platelets and preventing surface sealing.