## 2 Experimental Section
### Analytical Methods  
Leaching of the volatile organic compounds in sludge: 110 g of sludge was added into a zero-headspace extraction vessel (ZHE, Anyi Co., Ltd., Anhui, China). Then, deionized water was added into the sludge to ensure the liquid-solid ratio (L: Kg) of 10:1. The ZHE was then fixed in an inverted oscillator (AYZ-K, Anyi Co., Ltd., Anhui, China) and shook at 30 r/min for 19 h. After the oscillation, the leachate was collected and stored under cold conditions [33].  
Leaching of the heavy metals and the non-volatile organic compounds in sludge: 180 g of sludge was placed in a Teflon bottle. Then, an acid solution with a pH of 3.2 (configured by a mixture of concentrated sulfuric acid and concentrated nitric acid with a mass ratio of 2:1) was added into the Teflon bottle to maintain the liquid-solid ratio (L:kg) of 10:1. The bottle was then fixed in a flip-type shaker and shaken at a speed of 30 r/min for 19 h. After the oscillation, the leachate was collected and stored under cold conditions.  
High-temperature incineration of sludge: 500 g of dried sludge was placed in a high-temperature muffle furnace (QSX-3-12, Cinite Co., Ltd., Hebei, China) and heated to 850 \({}^{\circ}\)C for 10 min. After incineration, the ash was taken out and cooled to room temperature.  
The volatile organic compounds in the leachate were all determined by a gas chromatography-mass spectrometry (GC-MS) (7890b-5977b, Agilent Co., Ltd., Palo Alto, CA, USA), except for the ethylbenzene which was determined by a gas chromatography (GC) (7890B, Agilent Co., Ltd., Palo Alto, CA, USA). The test conditions were in accordance with Chinese Environmental Protection Industry Standard HJ/299-2007 [34].  
The non-volatile organic compounds in the leachate including dinitrobenzene, phenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, benzopyrene, and dibutyl phthalate were determined by GC-MS; the nitrobenzene was determined by a high-performance liquid chromatography (HPLC) (1260 VWD, Agilent Co., Ltd., Palo Alto, CA, USA); p-nitrchlorobenzene, 2,4-dinitrochlorobenzene, pentachlorophenol, and dioctyl phthalate were determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS) (Agilent 1100 MSD, Agilent Co., Ltd., Palo Alto, CA, USA); the polychlorinated biphenyl was determined by GC. The test conditions were in accordance with Chinese Environmental Protection Industry Standard HJ/299-2007 [34].  
The metal elements in the leachate, sludge and ash were measured by an inductively-coupled plasma mass spectrometer (ICP-MS) (ICP-6300, Thermo Sentific Co., Ltd., Waltham, MA, USA).  
The dioxin contents in the sludge were determined by a high-resolution gas chromatography high-resolution mass spectrometry (HRGC-HRMS) (Agilent 6890 GC/Waters AutoSpec Premier, USA) in accordance with Chinese Environmental Protection Industry Standard HJ/77.3-2008 [35]. The petroleum hydrocarbon contents in the sludge were measured by an infrared spectrometer (Nicolet 6700, Thermo Fisher Scientific Co., Ltd., Massachusetts, USA) in accordance with Chinese National Standard 5085.6-2007 [36]. The contents of C, H, and N were determined in accordance with the method specified in Chinese National Standard GB/T 30733-2014 [37]; the content of O was determined in accordance with the method specified in Chinese National Standard GB/T 476-2001 [38]; the contents of S, Cl, and P were determined in accordance with the methods specified in Chinese National Standard GB/T 214-2007 [39], British Standard--European Norm BS EN 14582-2016 [40], and Chinese Environmental Protection Industry Standard HJ 712-2014 [41], respectively.  
The corrosiveness, flammability, and reactivity of petrochemical excess sludge samples were tested in accordance with Chinese National Standards GB 5085.1-2007 [42], GB 5085.4-2007 [43], and GB 5085.5-2007 [44], respectively.