Abstract
Excess sludge produced from biological wastewater treatment plant in petroleum industry is a kind of hazardous solid waste. Converting the sludge into biochar catalysts may help to reduce its environmental risk, recover resources and increase economic efficiency. However, the role of the sludge biochar in persulfate activation remains unclear, limiting its application in removing organic pollutants from water body. In this study, metal-rich petrochemical sludge was used to produce activated sludge biochar (ASC) via a two-step method of pyrolytic carbonization (400 °C–800 °C) and subsequent KOH activation (abbreviated as ASC 400–800). The physio-chemical properties of ASC 400–800 were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and Raman. The chloramphenicol (CAP) removal performances of ASC 400-800/peroxymonosulfate (PMS) systems were evaluated. Results showed that porous sludge biochar was successfully prepared by the two-step method. At 800 °C, the specific surface area of ASC reached the highest value of 202.92 m2 g−1. At 600–800 °C, Fe3O4, Fe0, and graphitized carbon were formed in ASC. Among ASC 400–800, ASC 800 exhibited the best CAP removal performance in ASC 800/PMS system by adsorption combined with catalytic degradation. The optimal conditions identified for 0.31 mM CAP removal were ASC 800 2.0 g L−1, PMS 6.2 mM, and pH 2.0. SO4•-, •OH, and 1O2 may contribute to CAP degradation. The degradation pathways of CAP were proposed based on the identified degradation intermediates. Overall, this study confirmed that porous biochar derived from petrochemical sludge was an effective adsorbent or PMS catalyst to remove organic pollutants from wastewater.
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•Petrochemical sludge was treated by sequential pyrolysis and KOH activation.•At 600–800 °C, Fe3O4, Fe0, and graphitized carbon formed in sludge biochar (ASC).•Adsorption combined with PMS activation by ASC 800 facilitated CAP removal.•CAP removal performance was positively related to specific surface area of ASC.•SO4.•-, •OH, and 1O2 from PMS activation by ≡Co, ≡Fe or C–O may degrade CAP.