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

Electrokinetic (EK) delivery followed by thermal activated peroxydisulfate (PS) has turned out to be a potential in situ chemical oxidation technology for soil remediation, but the activation behavior of PS in an electrical coupled thermal environment and the effect of direct current (DC) intervention on PS in heating soil has not been explored. In this paper, a DC coupled thermal activated PS (DC-heat/PS) system was constructed to degrade Phenanthrene (Phe) in soil. The results indicated that DC could force PS to migrate in soil, changing the degradation rate-limiting step in heat/PS system from PS diffusion to PS decomposition, which greatly accelerated the degradation rate. In DC/PS system, ¹O₂ was the only reactive species directly detected at platinum (Pt)-anode, confirming that S₂O₈^2- could not directly obtain electrons at the Pt-cathode to decompose into SO₄^•-. By comparing DC/PS and DC-heat/PS system, it was found that DC could significantly promote the conversion of SO₄^•- and •OH generated by thermal activation of PS to ¹O₂, which was attributed to the hydrogen evolution caused by DC that destroys the reaction balance in system. It was also the fundamental reason that DC leaded to the reduction of oxidation capacity of DC-heat/PS system. Finally, the possible degradation pathways of phenanthrene were proposed on the basis of seven detected intermediates.

An Overview on the Treatment of Oil Pollutants in Soil Using Synthetic and Biological Surfactant Foam and Nanoparticles

Oil-contaminated soil is one of the most concerning problems due to its potential damage to human, animals, and the environment. Nanoparticles have effectively been used to degrade oil pollution in soil in the lab and in the field for a long time. In recent years, surfactant foam and nanoparticles have shown high removal of oil pollutants from contaminated soil. This review provides an overview on the remediation of oil pollutants in soil using nanoparticles, surfactant foams, and nanoparticle-stabilized surfactant foams. In particular, the fate and transport of oil compounds in the soil, the interaction of nanoparticles and surfactant foam, the removal mechanisms of nanoparticles and various surfactant foams, the effect of some factors (e.g., soil characteristics and amount, nanoparticle properties, surfactant concentration) on remediation efficiency, and some advantages and disadvantages of these methods are evaluated. Different nanoparticles and surfactant foam can be effectively utilized for treating oil compounds in contaminated soil. The treatment efficiency is dependent on many factors. Thus, optimizing these factors in each scenario is required to achieve a high remediation rate while not causing negative effects on humans, animals, and the environment. In the future, more research on the soil types, operating cost, posttreatment process, and recycling and reuse of surfactants and nanoparticles need to be conducted.

Chemical safety assessment of transformation products of landfill leachate formed during the Fenton process

Organic chemicals identified in raw landfill leachate (LL) and their transformation products (TPs), formed during Fenton treatment, were analyzed for chemical safety following REACH guidelines. The raw LL was located in the metropolitan region of Campina Grande, in northeast Brazil. We elucidated 197 unique chemical structures, including 154 compounds that were present in raw LL and 82 compounds that were detected in the treated LL, totaling 39 persistent compounds and 43 TPs. In silico models were developed to identify and prioritize the potential level of hazard/risk these compounds pose to the environment and society. The models revealed that the Fenton process improved the biodegradability of TPs. Still, a slight increase in ecotoxicological effects was observed among the compounds in treated LL compared with those present in raw LL. No differences were observed for aryl hydrocarbon receptor (AhR) and antioxidant response element (ARE) mutagenicity. Similar behavior among both raw and treated LL samples was observed for biodegradability; Tetrahymena pyriformis, Daphnia magna, Pimephales promelas and ARE, AhR, and Ames mutagenicity. Overall, our results suggest that raw and treated LL samples have similar activity profiles for all endpoints other than biodegradability.

Effect of nanomaterials on remediation of polycyclic aromatic hydrocarbons-contaminated soils: A review

The remediation of toxic polycyclic aromatic hydrocarbons (PAHs) in the soil is always an important topic since exposure to contaminated soil with carcinogenic, mutagenic, and teratogenic potential can result in serious health effects. With respect to the remediation of PAHs contaminated soil, nanomaterials (NMs) have recently received a great deal of attention due to the special characteristics arising from their nanoscale sizes. However, the usefulness and potency of these NMs depend on their adaption to specific site conditions and soil properties. Since there is no comprehensive review of the applications of NMs, it is of great importance to analyze, discuss, and interpret the latest progress in the application of NMs for the remediation of contaminated soils containing PAHs. This overview essentially captures the novel advances made in nano zero valent-iron (nZVI), metal oxides, carbon-based NMs, and polymer-based materials. Each characteristic of NMs that contributes to the enhancement of the process is highlighted. Moreover, operational conditions in which the best-obtained results are achieved qualitatively summarize. This review is also given special attention to the type of soil and pollutant, which are major influential factors to affect the performance of the process. Furthermore, the potential implication of NMs and PAHs on soil properties is reviewed in terms of the changes in migration behavior of pollutants, plant phytotoxicity, and soil microbial community composition. Discussion on future perspectives is presented on the use and prospects for the application of NMs in contaminated soils.

Selective removal of phenanthrene for the recovery of sodium dodecyl sulfate by UV-C and UV-C/PDS processes: Performance, mechanism and soil washing recycling

Soil washing is commonly used to remediate PAHs contaminated sites. However, the effluent after washing containing PAHs and surfactant may cause secondary pollution and remediation cost is still high, unless PAHs are selectively removed from the effluent and the surfactant is recovered and recycled. Herein, ultraviolet irradiation (254 nm, UV-C) and its combination with peroxydisulfate (UV-C/PDS) were applied to selectively degrade PHE in the synthetic soil washing effluent. At natural pH of 8.6, 98.2 % of PHE was removed within 30 min under 6 W UV-C irradiation. After adding 2 mM PDS, the time was shortened to 8 min but still achieving 98.7 % PHE removal and less toxic treated effluent than UV-C alone. The ¹O₂ was the main oxidizing species in UV-C alone system, while ¹O₂ as well OH and SO₄^- were responsible for PHE removal in the UV-C/PDS system. The possible intermediates of PHE degradation were recognized using liquid chromatography-mass spectrometry technique and the degradation pathways in both systems were proposed. Soil washing recycling experiments verified the recovered SDS could be reused directly without surfactant supplement and the soil washing efficiency changed insignificantly during three cycles. It indicates UV-C/PDS coupled with soil washing is a promising remediation technology.

Tailored photocatalysts and revealed reaction pathways for photodegradation of polycyclic aromatic hydrocarbons (PAHs) in water, soil and other sources

Polycyclic aromatic hydrocarbons (PAHs), which are in the class of persistent organic pollutants, are considered as hazardous pollutants. To date, these compounds were detected globally in soil, sludge, water, and other contamination sources. A variety of treatment methods have been used in recent years to degrade PAHs in the environment. Photocatalysis, among advanced techniques, is proposed as the most effective method for the treatment of PAHs. In this context, we introduce the classification of PAHs, summarize, and highlight the recent studies on photodegradation of various types of PAHs. A series of efficient photocatalysts, including TiO₂-, Ag₃PO₄-, ZnO-, MHCFs-based, and others, have been reported with the potential result for photodegradation of PAHs. Focus is also placed on revealing several possible reaction pathways for different types of PAHs that have been proposed in the literature. Particular attention to current status, challenges, and prospects in the future for enhanced photodegradation of PAHs are also discussed.

Adsorption of phenanthrene from aqueous solutions by biochar derived from an ammoniation-hydrothermal method

An innovative ammoniation-hydrothermal method of biochar production was developed for the adsorption of phenanthrene (PHE) from aqueous solutions in this paper. Phragmites australis (PA) was used to produce biochar in a hydrothermal kettle at 280 °C in muffle furnace using urea as an ammoniation reagent. Characterizations were executed by scanning electron microscope (SEM), N₂ adsorption/desorption isotherms, X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) to explore its morphological, physical, and chemical properties. Batch experiments of PHE adsorption were carried out to study the adsorption isotherms and kinetics. Quantum chemistry computational simulations were employed based on density functional theory (DFT) to establish and optimize adsorption configurations and analyze the biochar's structural effects on adsorption performance. Results showed that the ammoniation-hydrothermal method produced biochar with a higher surface area and a maximum equilibrium adsorption capacity of 1.97 mg/g. The adsorption fitted well with Freundlich isotherm model (R² > 0.96) and Pseudo-second-order kinetic model (R² > 0.82). Adsorption energy calculation revealed that the N functionalities, especially pyridine N in the N-doped biochar structure, exhibited stronger binding ability with PHE, which contributed most to the favorable adsorption ability of the ammoniation-hydrothermal biochar.

Photocatalytic removal of phenanthrene and algae by a novel Ca-Ag3PO4 composite under visible light: Reactivity and coexisting effect

In this study, the feasibility of a novel Ca-Ag₃PO₄ composite with visible light irradiation for the phenanthrene (PHE) degradation and algae inactivation in artificial seawater was firstly investigated. The experimental findings revealed that Ag₃PO₄ phase was sucessfully formed on the Ca-based material, and the presence of Ca-based material could effectively keep Ag₃PO₄ particles stable. An excellent performance on PHE degradation or algae inactivation was observed from Ca-Ag₃PO₄ composite under visible light irradiation. The degradation of PHE or inactivation of algae not only could be efficiently achieved in the single mode, but also could be successfully achieved in the coexisting mode. Above 96% of PHE and algae were simultaneously removed within 12 h in the Ca-Ag₃PO₄/visible light system. It was further observed that the degradation of PHE and/or inactivation of algae increased with the increase of Ca-Ag₃PO₄ dosage. HO was the primary radical responsible for PHE degradation, whereas HO and Ag⁺ released from Ca-Ag₃PO₄ mainly contributed to the algae inactivation. A possible mechanism involving the catalytic removal of PHE and algae by Ca-Ag₃PO₄ under visible light irradiation was proposed. This study provides helpful guide for the simultaneous removal of various pollutants in real seawater.