Role of direct current on thermal activated peroxydisulfate to degrade phenanthrene in soil: Conversion of sulfate radical and hydroxyl radical to singlet oxygen, accelerated degradation rate and reduced efficiency

Enhanced sulfamethoxazole removal in water and wastewater by ferrate(VI)/perborate system via borate buffering

Ferrate(VI) is prone to self-decomposition in water, leading to the loss of active substances Fe(V) and Fe(IV). Therefore, the use of Fe(VI) alone has limited practical applicability in municipal wastewater and industrial wastewater treatment scenarios due to its insufficient pollutant removal efficiency. This study discussed the removal efficiency of the Fe(VI)/perborate system for sulfamethoxazole and other 6 drugs in pure water within 5 minutes, and the removal efficiency of the Fe(VI)/perborate system for sulfamethoxazole in effluent and secondary effluent in a wastewater treatment plant (WWTP) within 5 minutes. Results show that the sulfamethoxazole removal efficiency reached 88.63 % in the influent of Lijiang B WWTP and 79 % in the secondary effluent of Wuhan WWTP. The removal efficiency of sulfamethoxazole in pure water reached 25.8 % in 5 minutes. This finding is explained by the buffering with the borate produced by the hydrolysis of Fe(VI)/perborate, which maintains the pH around 9 and, in turn, inhibits the reduction of active species. Moreover, H2O2, 1O2, and O2•- radicals generated by Fe(VI)/perborate accelerate the activation of Fe(VI), and the Fe2+ produced in the system participates in Fenton reactions with H2O2. This study offers a novel approach for using ferrate in practical water treatment.

Efficient oxidative remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil: A thorough comprehension of Fe-loaded biochar activated persulfate

The porous and defective structure of biochar (BC) can accelerate surface electron transfer, promote the generation of more reactive oxygen species (ROS) by persulfate (PS), and effectively degrade organic pollutants in the soil. Electron transfer is a crucial link in this process, directly determining its oxidative degradation efficiency. In this study, using a novel strategy of enhancing electron transfer on the surface of BC by loading iron, three Fe-loaded BC activators (Fe-FeOx@BC, Fe2O3@BC and Fe3O4@BC) were synthesized to support the oxidative remediation of benzo(a)pyrene (BaP, Model compound of PAHs)-contaminated soil by PS. The results showed that Fe3O4@BC supported PS oxidation and remediation of BaP-contaminated soil had the best effect among the three BC-based activators, and the reuse effect was stable. Under the conditions of Fe3O4@BC addition of 1.00 wt%, PS addition of 0.75 wt%, reaction temperature of 35 °C, and solid-liquid ratio of 1:2.5, the removal rate of BaP in the soil reached the maximum of 93.84% at 120 min, and the soil toxicity was significantly reduced after remediation. The defect structure, conductive magnetic particles, and active functional groups on the surface of Fe3O4@BC were the key factors for activating PS to degrade BaP. With the combined action of the free radical pathway caused by ROS and the non-free radical pathway caused by 1O2, electron transfer, and active functional groups, BaP was degraded to small molecules such as CO2 and H2O, achieving rapid and efficient remediation of organic contaminated soil.

Degradation of tetracycline via peroxymonosulfate activation by highly reusable Titanium dioxide/impregnated Zirconium-chitosan beads

The nano-sized powder photocatalysts are prone to agglomeration and poor reusability, which cause secondary pollution. To avoid the loss of powder photocatalyst, Titanium dioxide/(TiO2)/impregnated Zirconium (Zr)-chitosan beads were prepared using a simple cross-linking reaction for the peroxymonosulfate activation to aid the tetracycline degradation. The beads' structural, morphological and optical properties were studied using different techniques. The prepared catalysts effectively degraded 97% of tetracycline (10 mg/L) in 20 min of visible light illumination. The sulfate radicals, superoxide radicals, holes and singlet oxygen were found to be the predominant reactive groups that boosted the tetracycline degradation. The key intermediates were analyzed, and the degradation pathway of tetracycline was proposed. The reusable microspheres exhibited maximum reusability up to 10 cycles with an 11% loss in degradation efficiency. Overall, the important advantages of photocatalytic 3D beads include higher reusability, minimal catalytic mass loss during recovery process and stronger visible light utilization via band gap alteration, opening a new horizon toward effective wastewater management.

Organic radicals driving polycyclic aromatic hydrocarbon polymerization with peracetic acid activation in soil

The use of peracetic acid (PAA) in advanced oxidation processes has gained significant attention recently, but the knowledge of activating PAA to degrade polycyclic aromatic hydrocarbons (PAHs) is limited due to the variety and selectivity of reactive substances in PAA oxidation system. This paper presented the first systemically study on the degradation of PAHs by PAA activation in soil. It was found that heat-activated peracetic acid (heat/PAA) was capable of degrading phenanthrene (PHE) efficiently with degradation efficiency > 90 % within 30 min. Experimental results demonstrated that a series of reactive oxygen species (ROS) including organic radicals (RO•), hydroxyl radicals (HO•) and singlet oxygen (1O2) were generated, while acetylperoxyl (CH3C(O)OO•) and acetyloxyl (CH3C(O)O•) radicals were primarily responsible for PHE degradation in soil. Further analysis shows that polymerization products such as diphenic acid, 2'-formyl-2-biphenylcarboxylic acid and other macromolecules were dominant products of PHE degradation, suggesting polymerization driving PHE degradation instead of the conventional mineralization process. Toxicity analysis shows that most of the polymerization products had less toxicity than that of PHE. These results indicate that PAA activation was a highly effective remediation method for PAHs contaminated soil, which also provided a novel mechanism for pollutant degradation with the PAA activation process for environmental remediation.

Potassium peroxoborate: A sustained-released reactive oxygen carrier with enhanced PAHs contaminated soil remediation performance

Seeking for a safe, efficient, inexpensive, and eco-friendly oxidizer is always a big challenge for in-situ chemical oxidation (ISCO) technology. This study adopted the potassium peroxoborate (PPB), a novel peroxide, for soil remediation for the first time. PPB based chemical oxidation system (PPB-CO) could efficiently degrade polycyclic aromatic hydrocarbons (PAHs) without other reagents added, reaching 72.1 %, 64.2 %, and 50.0 % removal rates for naphthalene, phenanthrene, and pyrene after 24 h reaction, respectively. The superior total PAHs removal efficiency (60.6 %) was 3.6-4.7 times higher than that of other commercial peroxides (2Na2CO3•3H2O, CaO2, and H2O2). Mechanism analysis revealed that varieties of reactive oxygen species (ROS) can be generated by PPB through Fenton-like or non-Fenton routines, including H2O2, perborates species, O2•-, •OH, and 1O2. The sustainable generation of H2O2 reduced the disproportionation effect of H2O2 by 86 %, significantly improving the utilization rate. Moreover, sandbox experiments and actual contaminated soil remediation experiments verified the feasibility of PPB-CO in a real polluted site. This work provides a novel strategy for effectively soil remediation, highlighting the selection and application of new oxidants.

Lab-scale transport and activation of peroxydisulfate for phenanthrene degradation in soil: A comprehensive assessment of the remediation process, soil environment and microbial diversity

Electrokinetic transport followed by electrical resistance heating activation of peroxydisulfate is a novel in situ soil remediation method. However, the strategy of electrokinetic transport coupled with electrical resistance heating and the comprehensive evaluation of restored soil need to be further explored. In this study, a lab-scale simulation device for in situ electrokinetic transport coupled with electrical resistance heating activation of peroxydisulfate was constructed to monitor the transport and transfer of peroxydisulfate, target pollutants, and process parameters, and the physicochemical properties and bacterial community of treated soil were evaluated. The results showed that adding 10 wt% peroxydisulfate to both the anode and cathode resulted in the optimized transfer rate and cumulative concentration of peroxydisulfate under electrokinetics. After 8 h, the cumulative concentration of peroxydisulfate reached 66.15- 166.29 mmol L-1, which was attributed to the migration of a large amount of S2O82- from the cathode to the soil under electromigration. Additionally, the anodic interfacial electric potential was improved, which was more conducive to electroosmotic transport of peroxydisulfate from the anode chamber. By alternating electrokinetic transport and electrical resistance heating activation of peroxydisulfate for two cycles, the phenanthrene degradation efficiency in four evenly distributed wells between electrodes reached 75.4 %, 87.6 %, 92.3 %, and 94.4 %. With slight variations in soil morphology and structure, the electrokinetic transport coupled with electrical resistance heating activation of peroxydisulfate elevated the soil fertility index. The abundance and diversity of bacterial communities in treated soil recovered to above the original soil level after 15 days. Our findings may support the application of electrokinetic transport coupled with electrical resistance heating activation of peroxydisulfate as a promising green ecological technology for the in situ remediation of organic-contaminated soil.

Enhanced ferrate(VI) oxidation of organic pollutants through direct electron transfer

Fe(VI) is a versatile agent for water purification, and various strategies have been developed to improve its pollutant removal efficiency. Herein, it was found that in addition to intermediate iron species [Fe(IV)/Fe(V)], direct electron transfer (DET) played a significant role in the abatement of organic pollutants in Fe(VI)/carbon quantum dots (CQDs) system. Around 86, 83, 73, 64, 52, 45 and 17% of BPA, DCF, SMX, 4-CP, phenol, p-HBA, and IBP (6 μM) could be oxidized by 30 μM of Fe(VI), whereas with the addition of CQDs (4 mg/L), the oxidation ratio of these pollutants increased to 98, 99, 80, 88, 87, 66 and 57%, respectively. The negative impact induced by solution pH and background constituents on Fe(VI) abatement of pollutants could be alleviated by CQDs, and CQDs acted as catalysts for mediating DET from organic pollutants to Fe(VI). Theoretical calculation revealed that iron species [Fe(VI)/Fe(V)/Fe(IV)] was responsible for the oxidation of 36% of phenol, while DET contributed to the oxidation of 64% of phenol in the Fe(VI)/CQDs system. Compared with iron species oxidation, the CQDs mediated DET from pollutants to Fe(VI) was more efficient for utilizing the oxidation capacity of Fe(VI). The DET mechanism presented in the study provides a prospective strategy for improving the pollution control potential of Fe(VI).