Enhanced dewaterability of waste activated sludge via peroxymonosulfate activation process initiated by magnetic biochar derived from iron-rich sludge

The reduction of water content (WC) in waste activated sludge (WAS) is crucial for the recycling and environmentally-friendly treatment sludge in wastewater treatment plants. A new process of combined conditioning of iron-rich sludge biochar (Fe-BC) and peroxymonosulfate (PMS) was proposed and verified to enhance the dewaterability of WAS. The WC of sludge cake decreased significantly from 85.76% to 76.29% after Fe-BC/PMS treatment. For sludge extracellular polymeric substances (EPS) in sludge, the content of protein and polysaccharide in both TB-EPS and LB-EPS exhibited a decrease after Fe-BC/PMS treatment, whereas the S-EPS demonstrated an increase. Three-dimensional fluorescence (3D-EEM) showed that the fluorescence regions of protein-like and soluble microorganisms in both LB-EPS and TB-EPS were weakened. Through the experiment of free radical quenching, it has been demonstrated that the SO4•− and •OH as the primary oxidant in the Fe-BC/PMS system, effectively degrade proteinaceous components and humic substances present in sludge. The variation of particle size showed that the damaged EPS appeared reflocculation and achieved deep dehydration with Fe-BC as the skeleton. Consequently, a four-step mechanism was proposed for Fe-BC/PMS process, namely, oxidation cracking-sludge biochar flocculation-skeleton support – Fe2+ and Fe3+ reflocculation, which demonstrated the combined process with superior sludge dewatering effect and application potential.