Sewage sludge modified by desulfurization ash and PAM was dewatered and its mechanism studied.The results show that dewatering performance for sludge can be greatly improved by adding desulfurization ash.When desulfurization ash of 3 g稬-1 is mixed with sludge

the biggest volume of sludge sedimentation is 519.5 ml and the decrease of specific resistance(SRF)47.56%

indicating that desulfurization ash makes EPS breaking away and releasing bound water.Better dewatering performance can be obtained by treating sewage sludge with both desulfurization ash with polyacrylamide(PAM).By comparing particle size distribution and scanning electron micrographs(SEM)for original and modified sludge

it is found that the particle size of sludge flocs is obviously smaller for modified sludge than for original one

the frame structure of its small pore has been changed and solider and denser flocs with larger aperture do formed

which makes moisture in sludge removing more easily.PAM plays a role in bridging of particles by adsorption bridge effect and bigger flocs are formed rapidly from unstable sludge flocs

which is more easily for solid-liquid separation to improve sludge dewatering performance.