A comprehensive study on simultaneous enhancement of sludge dewaterability and elimination of polycyclic aromatic hydrocarbons by Fe2+ catalyzing O3 process

Simultaneous removal of polycyclic aromatic hydrocarbons (PAHs) in the process of enhancement of sludge dewaterability via oxidation of hydroxyl radicals (center dot OH) and flocculation of Fe3+ by Fe2+-catalyzing O-3 were investigated as a novel research focus. The results showed that capillary suction time (CST) and water content of dewatered sludge cake (Wc) were reduced from 57.9 s and 85.1% to 13.6 s and 69.65% under the optimum usage of 60 mg/g dry solids (DS) O-3 and 80 mg/g DS FeSO4, respectively. The relevant dewatering mechanism of Fe2+-catalyzing O-3 treatment was elucidated. It was found that extracellular polymeric substances-bound (EPS-bound) and intracellular water was dramatically released through destroying sludge cells and EPS gel-like structure by produced center dot OH. In addition, the results of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and C-13 NMR spectroscopy revealed that center dot OH oxidized and mineralized hydrophilic organic matters intensifying hydrophobicity of sludge surface. Moreover, Fe3+ generated by oxidation of Fe2+ agglomerated fragmented fine particles into large aggregates and decreased exposure of hydrophilic sites by neutralizing negative charge, which promoted water-solids separation. Meanwhile, sludge surface roughness was decreased which was determined by material type upright confocal laser microscope (CLM). As a consequence, center dot OH and Fe3+ were mainly responsible for enhancement of sludge dewaterability. Moreover, more than 40% of removal rate of PAHs was accomplished by Fe2+-catalyzed O-3 treatment mitigating the environmental risks of PAHs spread.

Automated summary

Simultaneous removal of polycyclic aromatic hydrocarbons (PAHs) and enhancement of sludge dewaterability were achieved through oxidation of hydroxyl radicals (center dot OH) and flocculation of Fe3+ by Fe2+-catalyzing O-3 treatment. This treatment effectively released water from sludge cells and extracellular polymeric substances-bound (EPS-bound), and intensified the hydrophobicity of sludge surface. Additionally, Fe3+ generated by oxidation of Fe2+ promoted water-solids separation by agglomerating fragmented particles and neutralizing negative charge. The treatment also reduced the roughness of sludge surface. Furthermore, Fe2+-catalyzed O-3 treatment resulted in over 40% removal rate of PAHs, mitigating the environmental risks associated with PAHs.