Ozone/percarbonate-Fe3+ conditioning enhanced pressurized electro-osmotic dewatering (PEOD) of waste activated sludge: Feasibility and mechanisms

Pressurized electro-osmotic dewatering (PEOD) process is an emerging technology for high-efficiency solid-liquid separation of sludge and has garnered extensive interest. This study proposed a novel sequential conditioning process based on ozone (O3)/percarbonate (SPC) treatment followed by Fe3+ coagulation, namely O3/SPC-Fe3+ conditioning, to improve the performance of PEOD. The optimal operating conditions and the related dewatering performance of O3/SPC-Fe3+ conditioning-PEOD process were investigated to verify the feasibility. The mechanisms of the O3/SPC-Fe3+ conditioning on improving PEOD process were also discussed from the enhancement of the water/filtrate flow in pores. The results showed that 53.44% water content and 0.95 g/g dry solid (DS) of bound water in dewatered sludge cake were attained in the O3/SPC-Fe3+ conditioning-PEOD process with optimal O3 aeration time of 12 min, SPC dosage of 0.0610 g/g DS and Fe3+ dosage of 0.0310 g/g DS for sludge conditioning then 346 kPa mechanical pressure and 40 V voltage for dewatering. During the O3/SPC-Fe3+ conditioning-PEOD process, the extracellular polymeric substance (EPS) matrix was disintegrated, and the inner EPS migrated to the outside along with water. The values of alpha-helix/(beta-sheet + random coil) adjusted by O3/SPCFe3+ conditioning process decreased to 7.38 and 5.12 in slime and LB-EPS, respectively, and these changes transformed to expose more hydrophobic sites. After conditioning, the proportion of protein-N decreased drastically from 81.67% to 62.34%, while the proportion of inorganic-N increased significantly from 18.33% to 37.66%, indicating that partial protein-N in EPS altered to inorganic-N. The enhancement of PEOD by the O3/ SPC-Fe3+ process can be attributed to the EPS hydrophobicity transformation and the degradation/mineralization of EPS by oxidation of generated & sdot;OH. The former triggered the reduction of water/filtrate viscosity within the interfacial region of pores. The latter provoked the decrease of bulk viscosity of water/filtrate within the pores. These two effects relieved the viscous resistance to water/filtrate flow within pores and promoted dewatering.