Optimization Research of Mechanical Dewatering of Sludge with High Pressure

Reducing the sludge water content is the key point of sludge disposal. Based on filter-pressing test by self made constant pressure filtration device, under 2 MPa pressure and 10min filter time can quickly remove the moisture content and decrease to 75.30%. Adding 3% FeCl3can decrease the moisture content to 63.38%, while adding 3% AlCl3can decrease the moisture content to 71.98%. Biomass additives also have good effects, sludge with sawdust/straw at the ratio of 2 ∶1 mixture, filter-pressured sludge moisture content can decrease to 60.22% and 63.75%, with the effect of adding sawdust better than straw. Due to the highly absorbent of biomass, the apparent moisture content of filter-pressured sludge cake is 43.83% and 45.90%. In addition, biomass which improves the heat value of sludge can be used for preparation of sludge-biomass mixture. When chemical additive and biomass additive are synergistic at the optimum conditions, the moisture contents decrease to 55.23% and apparent moisture contents decrease to 39.16%, with quite obvious effect of sludge reduction.