PHOSPHORUS REMOVAL IN FILTERS FILLED WITH LWA MADE OF FLY ASHES

The effectiveness of phosphorus removal in vertical-flow filters with double-layer filling composed of light weight aggregate made of fly ashes from sewage sludge thermal treatment (FASSTT LWA) and gravel was determined. Synthetic wastewaters containing 7.36 mg/L of phosphorus were fed into filter columns filled with gravel and FASSTT LWA (gravel was the bed's lower layer, whereas the top layer of the FASSTT LWA constituted 0, 12, 25, 50, and 100% of the depth of the column) at hydraulic loads from 0.003, to 0.007 m/d. The study demonstrated that the efficiency of phosphorus removal depends on the ratio between the gravel and FASSTT LWA. Phosphorus removal is mainly due to adsorption on the surface of the filter filling. The highest phosphorus removal rate was achieved in the filter column with 50% FASSTT LWA and 50% gravel content, irrespective of the hydraulic load applied. The study confirmed the possibility of using FASSTT LWA to produce granular filling and application as the filling of filter columns used for the treatment of wastewaters containing significant concentration of phosphorus.