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+/S2O82-) 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-S2O82-/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+/S2O82- oxidized a large amount of EPS, leading to liberation of EPS-bound water. A similar dedining 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+/S(2)O(8)(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+/S2O82- process. (C) 2019 Elsevier B.V. All rights reserved.