Sludge deep dewatering enhanced by zero-valent iron/peroxymonosulfate/walnut shell powder

To enhance sludge dewatering performance, Zero-valent iron/peroxymonosulfate/walnut shell powder was used to condition sludge at 55 oC and pH=3 (ZVI/PMS/WSP-T/pH), and the dewatering mechanism was also analyzed. The results showed that the capillary suction time (CST) and water content of sludge cake (Wc) were reduced to 6.8 s and 62.1%, respectively, and net sludge yield (YN) increased to 58.74 kg/(m2 center dot h) after being treated by ZVI/PMS/ WSP-T/pH. The thermal and acid conditions could promote the corrosion of Fe2+ from ZVI and enhance PMS to produce more SO4. and center dot OH. The radicals combined with acid and thermal hydrolysis could efficiently reduce extracellular polymeric substances (EPS), especially tightly bound EPS (TB-EPS), destroy sludge floc and release bound water. The stripping off of EPS and neutralization of Fe3+, Fe2+ and H+ caused the zeta potential to increase to. 0.91mV. The flocculation of cations and adsorption of WSP further increased the fractal dimension to 1.71. Moreover, the rigid and porosity structure of WSP increased sludge incompressibility and formed channels for water. Under the combined oxidation, acid/thermal hydrolysis, re-aggregation and skeleton builder functions, the sludge dewatering performance was greatly improved.