The Mechanism Research Of Sludge Ultrasonic Pretreatment

Sludge anaerobic digestion is the most popular method which is used for sludge stabilization. However, sludge hydrolysis reaction is the rate-limiting step of sludge anaerobic digestion. It is necessary to pretreat sludge for destroying the floc structure and breaking down the cell walls so as to improve the biodegradability of sludge. Ultrasonication have been put into engineering application as an effective and environmentally-friendly sludge pretreatment method.In this study, based on the mechanism of ultrasonication, we simulate the motion equation of cavitation bubbles for analyzing the impact of ultrasonic conditions on the cavitation intensity. Furthermore, we study the influence of different conditions on sludge ultrasonication effect, and explore the main path of sludge ultrasonication and measures of increasing efficiency. Results are as follows:(1) Simulation results shows the better range of control conditions: low ultrasonic frequency (20KHz), a range of acoustic pressure amplitude(5.065×105Pa～20.26×105Pa), cavitation bubbles with a range of initial radius(1μm～50μum), and an appropriate concentration of sludge (optimal concentration range:5.7g/L～22.9g/L, corresponding sludge viscosity:1.0×10-3Pa·s～5.0×10-3Pa·s).(2) The thermal effect to sludge ultrasonication can be neglected. Besides, on the condition of0.215W/mL at30min, the power consumption of ultrasonic thermal effect is41.34%of ultrasound output power. Temperature controlling is bad for ultrasonic effect. It can be helpful to save energy and improve ultrasonication effect if taking appropriate measures to reduce energy dissipation of thermal effect, such as using thermal insulation envelope structure, SCOD value of sludge can be improved by18.4%. (3) On the condition of0.215W/mL, the contribution of hydraulic shear forces and free radical oxidation effect to the sludge ultrasonication account for82.91%、17.08%respectively. And the main path of ultrasonic sludge disintegration is the hydraulic shear forces generated by cavitation.(4) Compared to ultraonication without aeration, the SCOD and SCOD dissolution rate values are basically unchanged after ultrasonication with aeration on aeration intensity of11.7-35L/min for5min.