Effect of hydraulic loading frequency on performance of planted drying beds for the treatment of faecal sludge

This study was conducted to evaluate the effect of loading frequency on treatment performance of faecal sludge (FS) with drying beds planted with Echinochloa pyramidalis. Beds were loaded at a constant total solids (TS) loading rate of 200 kg TS/m(2)* year, at a frequency of 1X, 2X or 3X per week. The FS was highly variable, with a range of 2,600-21,492 mg/L TS, which resulted in variable hydraulic loadings. Weekly monitoring was conducted 23 times over a period of nine months. Increased loading frequency resulted in increased plant growth with 211, 265 and 268 plants/m(2), respectively, for the 1X, 2X and 3X, and the 2X and 3X loadings had 12-13% more liquid lost due to evapotranspiration versus percolation. Even with high removals that were resistant to variable hydraulic loadings, leachate had 883-5,228 mg/L TS, 49-727 mg/L total suspended solids and 92-1,853 mg/L chemical oxygen demand due to the high initial concentrations. Increased loading frequency resulted in greater nitrification, with 7-28, 18-43 and 28-51 mg/L NO3- for 1X, 2X and 3X, respectively. FS requires a longer storage time than three months for stabilization and pathogen reduction. These results provide valuable information for FS planted drying bed operation.