Characterization of percolate from unplanted FS drying beds (Nepal)

The performance of unplanted faecal sludge drying beds was evaluated in terms of dewatering time, contaminant load removal efficiency of leachate (BOD, COD, TS, VS, TSS, and VSS), moisture content, solids generation, VS in the dried sludge considering the depth of filter and sludge application depth. A septic sludge from septic tank was collected and dewatered using three small scale sludge drying beds with different sand media thicknesses of 10, 20, and 30 cm. Three dewatering cycles were conducted and monitored for each chamber at sludge depth of 10, 20, and 30cm. The dewatering time was between 0.125-3 days for the 100 mm filter, 3.12-3.8 days for the 200 mm filter, and 4.2-5.6 days for the 300 mm filter at sludge depth 10 to 30 cm. There was a significant difference in the removal and recovery efficiency of BOD, COD, TS, VS, TSS and VSS for the percolate contaminant loads, with the 300 mm filter achieving the highest removal efficiency for each parameter. The contaminant load removal efficiency and solids recovery i.e. BOD, COD, TS, VS, TSS and VSS of filter media thickness 10 to 30cm was resulted in the range of 96.8-97.2%, 95.5-96.4%, 96.1-98%, 97.6-98%, 90%-93.6% and 86.7-92.5% respectively at sludge depth 30 cm. The best chance of maximizing contaminant load removal and solids recovery from faecal sludge exists with filtering medium configurations similar to 300 mm.