Shuai Zhu,Zhuoyu Li,Meiqi Yu,Qinghong Wang,Chunmao Chen,Jun Ma
The petroleum wastewater (PWW) contains a diverse range of recalcitrant organic contaminants . Of particular concern is the removal of naphthenic acids (NAs) due to the high toxicity and persistence. Persulfate (PS) based oxidation processes have shown promising in treating refractory wastewater, while the high costs of prepared catalysts limited their widespread implementation. This study aims to develop a cost-effective natural pyrite activated PS system for PWW treatment . The removal of NAs by pyrite/PS system was initially investigated. More than 90% of cyclohexanoic acid (CHA), a model NA, was removed in pyrite/PS system (2.0 g/L pyrite, 4.0 mM PS) at initial pH of 3–11. Scavenging experiments revealed that Fe(II) on pyrite surface was the reactive site for PS activation to generate reactive species, including sulfate radical (SO 4 ·− ), Fe(IV) and hydroxyl radical (·OH) for CHA degradation. Reactions of Fe(III) with S helped restore Fe(II) and enhance PS activation, resulting in the sustained catalytic activity of pyrites over five cycles. Cl − , SO 4 2− and NO 3 − below 10 mM had minimal impact on CHA degradation in pyrite/PS system. However, over 1 mM of HCO 3 − inhibited 80% of CHA removal due to the buffer effect to maintain the high solution pH. Removing HCO 3 − from real PWW restored the removal of CHA and of total organic carbon (TOC) to over 90% and 71.3% in pyrite/PS system, respectively. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results indicated that O 2‒6 species including NAs were primarily eliminated through mineralization and oxygen addition. Besides, O 3 – 5 S, NO 3 – 5 S and N 3 O 2‒4 species were the most susceptible to oxidation in PWW, resulting in the increase of the oxidation level (i.e., O/C wa ) from 0.41 to 0.56 after treatment. This study provides valuable insights into the treatment of NAs in real PWW, and potential application of natural minerals in the treatment of industrial wastewater .
In this study, an electrochemical/peroxymonosulfate/Fe(III) (EC/PMS/Fe(III)) system was established for efficient degradation of four naphthenic acids (NAs) compounds including cyclohexanecarboxylic (CHA), heptanoic (HPA), benzoic (BA) and 2-methylhexanoic acids (2-MHA). The introduction of electric field enhances the redox cycle of Fe(III)/Fe(II) to activate PMS for degredation of NAs. Complete degradation of NAs compounds (5 mg/L) has been achieved within 30 min in the EC/PMS/Fe(III) system. The results of electron paramagnetic resonance (EPR) analysis, scavenging experiment, and chemical probe experiments indicated hydroxyl radical ( • OH), sulfate radical (SO 4 •− ) and singlet oxygen ( 1 O 2 ) are primary reactive oxygen species (ROS) in the EC/PMS/Fe(III) system. NAs compounds with different structures exhibit inconsistent degradation efficiency in current system ( k CHA > k BA > k HPA > k 2-MHA ), depending on the selectivity of the different ROS and stability of respective intermediate organic radicals. Besides, multiple degradation pathways of CHA, mainly including hydroxylation and carbonylation , were proposed by combining the results of mass spectrometry analysis with the calculated Fukui index based on density functional theory (DFT) calculation. In addition, the EC/PMS/Fe(III) system exhibited robust performance with the addition of co-existing ions. This work provides a novel strategy for efficient degradation of NAs for future remediation of petroleum wastewater.
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