Improving Permeability of Sewage Sludge by Conditioning with Lignite
Flocculation of sewage sludge by polyelectrolyte is a widely used method for enhancing sludge dewaterability. However, only a limited amount of water (~60%) is possible to remove when the flocculated sludge is pressed in a mechanical pressing device. In this study, use of lignite particles to improve the permeability of flocculated sludge is investigated. Raw sludge is flocculated with polyelectrolyte and further conditioned by mixing with lignite slurry (particle size range 1 to 1000 µm) before it is compressed in a mechanical pressing cell. By using Darcy's conventional filtration theory, the permeability of the filter cake with lignite and without lignite is determined. Permeability results show that the lignite conditioned flocculated sludge is approximately one hundred times higher than flocculated sludge alone after compression at 500 KPa. The effect of particle size range and pH on dewatering rate is also investigated. It is found that both the particle size range and pH have an effect on dewatering rate. Higher dewatering rate is achieved when the lignite particles size range is less than 90 µm and the pH of the lignite slurry is below 4.