Strengthened dewaterability of coke-oven plant oily sludge by altering extracellular organics using Fe(II)-activated persulfate oxidation

Although oily sludge has tremendous resource recovery value, its high water content has hindered its treatment and reuse. This study systematically explored the technical feasibility of using Fe(II)-activated persulfate oxidation (Fe²⁺/S₂O₈ ²⁻) to enhance the dewaterability of oily sludge. To identify the main factors controlling sludge dewatering, this study measured changes in chemical oxygen demand, ammonia nitrogen (NH₄ ⁺-N) and extracellular polymeric substances (EPS). Results showed that at 0.1 mmol-Fe²⁺/g-VSS and 0.08 mmol-S₂O₈ ²⁻/g-VSS, capillary suction time (s) was reduced by roughly 36.1% within 1 min and dewaterability was strengthened strongly. Sulfate radicals originating from Fe²⁺/S₂O₈ ²⁻ oxidized a large amount of EPS, leading to liberation of EPS-bound water. A similar declining trend in NH₄ ⁺-N was evident as a result of the strong oxidizing ability of sulfate radicals. Further analysis via scanning electron microscopy and thermogravimetric-Fourier transform infrared spectrometry revealed that Fe²⁺/S₂O₈ ²⁻ oxidation destroyed the water-oil-gel-like structure of the oily sludge, thereby accelerating the separation of solids and water while reducing CO₂ emissions during the subsequent pyrolysis. Therefore, oily sludge dewatering was enhanced significantly by the Fe²⁺/S₂O₈ ²⁻ process.