FLUIDIZED-BED BOTTOM-ASH EFFECTS ON INFILTRATION AND EROSION OF SWELLING SOILS

Fluidized bed combustion (FBC) bottom ash, rather than being used as f ill at dumping sites, can be utilized to amend certain soils for erosi on control. Because FBC bottom ash is a source of both electrolytes an d alkalinity, its effectiveness in controlling runoff and erosion shou ld be greater on soils with a predominance of permanent charges. Five soils, with and without addition of 5 Mg ha(-1) surface-applied FBC bo ttom 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,) for the control we re very low, ranging from 1.8 to 5.8 mm h(-1). These rates were increa sed 3.6- to 5.0-fold with the application of FBC bottom ash, with a le sser increase for the highly smectitic and illitic soils. For the cont rol, total soil loss ranged from 220 to 1998 g m(-2), and total water loss from 78 to 112 mn, with the greatest losses for soils with a larg e cation-exchange capacity/clay ratio. The FBC bottom ash reduced tota l water loss by 1.1- to 2.0-fold and total soil loss by 1.5- to 3.9-fo ld. The CFC of the soil was correlated with I,, while aggregate stabil ity was correlated with erosion and total runoff. The FBC bottom ash e ffectiveness in increasing infiltration and controlling erosion on the se soils is attributed to an increase in electrolytes in the runoff, t hus decreasing soil swelling and the dispersion of clay platelets and preventing surface sealing.