Improvement of the sludge flocculation dewatering efficient by electromagnetic wave loading: research based on removal of bound water.

Excess sludge was loaded by 2450 MHz electromagnetic wave in this study. The mechanism of electromagnetic wave loading on the releasing of bound water before sludge flocculation dewatering was investigated through observing the changes of extracellular polymeric substances (EPS) composition, surface charge, and particle size distribution. The results showed that the 8.55 g/g total suspended solids (TSS) of bound water was reduced with 160 J/mL electromagnetic wave, and the moisture content of sludge decreased by 3.02%. The EPS structure in the sludge floc matrix was destroyed and the LB-EPS content reduced. Simultaneously, infrared spectrum analysis indicated that bound water content was correlated both to the changes of hydrophilic and hydrophobic functional groups. Moreover, protein secondary structure analysis found that looser protein structure facilitated the exposure of internal hydrophobic groups and further promoted the sludge hydrophobic properties. Additionally, electromagnetic wave disintegrated colloidal stability through dipole motion. The zeta potential increased from - 25.57 to - 14.32 mV; the medium particle size (d) decreased from 119.99 to 80.41 μm. More small molecules created in the supernatant were helpful to release bound water, which could further improve flocculation dewaterability of sludge with electromagnetic wave loading.