Research On The Stirring Technology And Hydraulic Characteristics Of High Solids Content Sludge In Anaerobic Digestion

Anaerobic digestion (AD) is certainly the best way to solve the sludge stabilization andsludge reduction, it can also realize the comprehensive utilization and effective recovery ofthe bio-energy. However, many anaerobic digesters that have been built in china were notfunctioning properly and even laid aside. In fact, co-digestion and the upgrading of sludgetreatment were applied urgently in China in order to solve the polluted problem of organicwastes and achieve energy saving and emission reduction. Sludge and other organic wasteswill be grouped in the central treatment plant. Therefore, Sludge concentration became highand mass transfer became much important in anaerobic digestion. Normal operatingconditions from traditional AD are not suitable to this situation, such as the improvement ofthe sludge thickening technology and centralized disposal of sludge in Sewage TreatmentPlant.This article was to investigate the optimum mixing conditions of sludge anaerobicdigestion under high concentration.Mass transfer is very important in any biological treatment process, especially for sludgewith high solid content, as its hydraulic characteristics have been changed.Gas mixing andmechanical agitation was applied and the water content of sludge at90%was tested in thisexperiment. Then the best way of mixing which was suitable for high concentrations of sludgeanaerobic digestion will be obtained. Through the experiments can be concluded that theeffect of mechanical agitation was better than the gas mixing. The sludge could be rapidlymixed. The best impeller speed was220r/min at the water ratio of90%and the sludge mixedvery well at30minutes. The bottom sludge wasn’t mixed well when she gas mixing was used.This was because the sludge concentration was so high.Mechanical agitation was applied and the water content of sludge at92%、88%was testedin this experiment. The right stirring intensity which was suitable for different concentrationsof sludge will be obtained. When the water content of sludge was92%, the best impellerspeed was160r/min and the mixing time at25minutes. The best impeller speed was240r/minat the water ratio of88%. The tracer reached to equilibrium concentration at40minutes.Mixing is obviously a high-energy-consumption unit during anaerobic digestion. Then,the best stirring frequency will be discussed for insuring the mixing effect. When the stirringfrequency was2times every day、4times every day、6times every day, the effective areavolume rate of reactor was52.03%、68.7%、76.9%.The range of increasing became narrow.