Application of persulfate to remediate petroleum hydrocarbon-contaminated soil: feasibility and comparison with common oxidants

Activation of persulfate by a layered double oxide supported sulfidated nano zero-valent iron for efficient degradation of 2,2',4,4'-tetrabromodiphenyl ether in soil

The nano zero-valent iron (nZVI) activated persulfate (PS) is recognized as a promising approach to degrade 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), which is ubiquitous in the soil at electronic waste sites. However, all the reported studies were performed in liquids, gaps in the real behaviour and microbial contribution to the degradation of BDE-47 in soil media need to be urgently filled. The removal efficiency of BDE-47 is low using traditional nZVI as activator because of its aggregation and corrosion. Herein, we designed a novel layered double oxide supported sulfidated nano zero-valent iron (S-nZVI@LDO) composite and explored the performance of S-nZVI@LDO/PS to remediate BDE-47 contaminated soil. The results showed that S-nZVI@LDO has excellent stability and superior reduction capability. It could couple PS to achieve a rapid and efficient degradation of BDE-47, and the removal efficiency reached 92.31 % (5 mg/kg) within 6 h, which was much higher than that of n-ZVI/PS (53.38 %) or S-nZVI/PS (75.69 %). The kinetic constant of BDE-47 degradation by S-nZVI@LDO/PS was 23.6 and 3.7 times higher than that by single S-nZVI@LDO and nZVI/PS, respectively. It is attributable to the efficient production of SO4•-, •OH, O2•-, and 1O2 in the system, in which SO4•- and •OH dominated. The bioinformatic analysis demonstrate that soil remediation by S-nZVI@LDO/PS significantly enriched aromatic compounds-degrading bacteria and increased the abundance of hydrocarbon degradation functions. Microbial degradation may play important roles in the BDE-47 degradation and soil quality recovery. The identification of degradation pathways suggests that BDE-47 was degraded to very low-toxic products based on GHS toxicity prediction through a series process of debromination, hydroxylation, cleavage central oxygen, and ring opening, or even completely mineralized. The findings may provide significant implications for the in-situ clean-up of brominated flame retardants in contaminated soil using S-nZVI@LDO/PS Fenton-like system.

Selective generation of hydroxyl and sulfate radicals under electric field regulation for micropollutants degradation: Mechanism and structure-activity relationship

Peroxymonosulfate (PMS) activation generates potent reactive oxygen species (ROS) such as sulfate radical (SO4·-) and hydroxyl radical (·OH), which play a key role in organic pollutant degradation. However, controlling the generation of these free radicals remains challenging. In this study, various metal (Co, Ni, and Cu)-doped nitrogen carbon compounds (NCs) were synthesized, and their performance in PMS activation under electric field regulation was explored to modulate ROS production for selective pollutant degradation. Bisphenol A (BPA), a readily degradable compound, and ibuprofen (IBU), a recalcitrant pollutant, were chosen as model pollutants to assess degradation efficiency. All catalysts achieved over 95 % BPA removal without the electric field, but the application of an electric field significantly accelerated BPA degradation, achieving complete removal within 3 min. In contrast, IBU degradation showed significant variation depending on the catalyst used and the electric field intensity, with Cu-NC demonstrating the highest performance, enhancing the degradation rate by 3.78-fold. Mechanistic studies revealed that the electric field altered the electron density on the catalyst surface, shifting ROS production from SO4·- to·OH in Co-NC systems. The findings could provide valuable insights into PMS activation under electric field regulation, offering a novel strategy for enhancing micropollutant removal through controlled ROS generation.

Innovative strategy for the treatment of oily wastewater by in-situ synthesis of nitrogen-doped biochar supported FeS for activation of peroxymonosulfate

Disposing of oily wastewater poses a significant challenge in treating oilfield-produced wastewater treatment. This study developed a FeSNC-9/PMS system for the effective degradation of total petroleum hydrocarbons (TPHs) in oily wastewater, while increasing the value of excess sludge, thus achieving the dual purpose of waste treatment. This work involved the in-situ preparation of a porous nitrogen-doped biochar-supported iron sulphide catalyst material using surplus sludge from SBR. Compared to undoped FeS (NC-9), FeSNC-9 exhibited excellent pore structure and abundant functional groups. Fe-Nx served as an effective connecting site between FeS species and the graphite network of biochar. The FeSNC-9/PMS system significantly degraded 74.21% of TPHs within 300 min. The FeSNC-9/PMS system demonstrated remarkable TPHs degradation efficiency across a wide temperature range and under both weak acidity and near-neutral conditions The dominant reactive oxygen species were identified as SO4•- and •OH, with O2•- and 1O2 also confirmed as active species. Gas chromatography semi-quantitative analysis showed that the long-chain alkanes of C20-C30 in total petroleum hydrocarbons were significantly degraded into short-chain alkanes or completely mineralized. This work provides new insights for the low-cost and high-efficiency treatment of TPHs in oilfield-produced water, and delves into the activation mechanism of PMS and the degradation pathways of TPHs.

Sulfur-containing iron carbon nanocomposites activate persulfate for combined chemical oxidation and microbial remediation of petroleum-polluted soil

In this study, sulfur-containing iron carbon nanocomposites (S@Fe-CN) were synthesized by calcining iron-loaded biomass and utilized to activate persulfate (PS) for the combined chemical oxidation and microbial remediation of petroleum-polluted soil. The highest removal efficiency of total petroleum hydrocarbons (TPHs) was achieved at 0.2% of activator, 1% of PS and 1:1 soil-water ratio. The EPR and quenching experiments demonstrated that the degradation of TPHs was caused by the combination of 1O2,·OH, SO4·-, and O2·-. In the S@Fe-CN activated PS (S@Fe-CN/PS) system, the degradation of TPHs underwent two phases: chemical oxidation (days 0 to 3) and microbial degradation (days 3 to 28), with kinetic constants consistent with the pseudo-first-order kinetics of chemical and microbial remediation, respectively. In the S@Fe-CN/PS system, soil enzyme activities decreased and then increased, indicating that microbial activities were restored after chemical oxidation under the protection of the activators. The microbial community analysis showed that the S@Fe-CN/PS group affected the abundance and structure of microorganisms, with the relative abundance of TPH-degrading bacteria increased after 28 days. Moreover, S@Fe-CN/PS enhanced the microbial interactions and mitigated microbial competition, thereby improving the ability of indigenous microorganisms to degrade TPHs.

Biochar-based materials as remediation strategy in petroleum hydrocarbon-contaminated soil and water: Performances, mechanisms, and environmental impact

Petroleum contamination is considered as a major risk to the health of humans and environment. Biochars as low-cost and eco-friendly carbon materials, have been widely used for the removal of petroleum hydrocarbon in the environment. The purpose of this paper is to review the performance, mechanisms, and potential environmental toxicity of biochar, modified biochar and its integration use with other materials in petroleum contaminated soil and water. Specifically, the use of biochar in oil-contaminated water and soil as well as the factors that could influence the removal ability of biochar were systematically evaluated. In addition, the modification and integrated use of biochar for improving the removal efficiency were summarized from the aspects of sorption, biodegradation, chemical degradation, and reusability. Moreover, the functional impacts and associated ecotoxicity of pristine and modified biochars in various environments were demonstrated. Finally, some shortcoming of current approaches, and future research needs were provided for the future direction and challenges of modified biochar research. Overall, this paper gain insight into biochar application in petroleum remediation from the perspectives of performance enhancement and environmental sustainability.

Unraveling the mechanisms behind sodium persulphate-induced changes in petroleum-contaminated aquifers' biogeochemical parameters and microbial communities

Sodium persulphate (PS) is a highly effective oxidising agent widely used in groundwater remediation and wastewater treatment. Although numerous studies have examined the impact of PS with respect to the removal efficiency of organic pollutants, the residual effects of PS exposure on the biogeochemical parameters and microbial ecosystems of contaminated aquifers are not well understood. This study investigates the effects of exposure to different concentrations of PS on the biogeochemical parameters of petroleum-contaminated aquifers using microcosm batch experiments. The results demonstrate that PS exposure increases the oxidation-reduction potential (ORP) and electrical conductivity (EC), while decreasing total organic carbon (TOC), dehydrogenase (DE), and polyphenol oxidase (PO) in the aquifer. Three-dimensional excitation-emission matrix (3D-EEM) analysis indicates PS is effective at reducing fulvic acid-like and humic acid-like substances and promoting microbial metabolic activity. In addition, PS exposure reduces the abundance of bacterial community species and the diversity index of evolutionary distance, with a more pronounced effect at high PS concentrations (31.25 mmol/L). Long-term (90 d) PS exposure results in an increase in the abundance of microorganisms with environmental resistance, organic matter degradation, and the ability to promote functional genes related to biological processes such as basal metabolism, transmission of genetic information, and cell motility of microorganisms. Structural equation modeling (SEM) further confirms that ORP and TOC are important drivers of change in the abundance of dominant phyla and functional genes. These results suggest exposure to different concentrations of PS has both direct and indirect effects on the dominant phyla and functional genes by influencing the geochemical parameters and enzymatic activity of the aquifer. This study provides a valuable reference for the application of PS in ecological engineering.

Bioremediation of contaminated soil and groundwater by in situ biostimulation

Bioremediation by in situ biostimulation is an attractive alternative to excavation of contaminated soil. Many in situ remediation methods have been tested with some success; however, due to highly variable results in realistic field conditions, they have not been implemented as widely as they might deserve. To ensure success, methods should be validated under site-analogous conditions before full scale use, which requires expertise and local knowledge by the implementers. The focus here is on indigenous microbial degraders and evaluation of their performance. Identifying and removing biodegradation bottlenecks for degradation of organic pollutants is essential. Limiting factors commonly include: lack of oxygen or alternative electron acceptors, low temperature, and lack of essential nutrients. Additional factors: the bioavailability of the contaminating compound, pH, distribution of the contaminant, and soil structure and moisture, and in some cases, lack of degradation potential which may be amended with bioaugmentation. Methods to remove these bottlenecks are discussed. Implementers should also be prepared to combine methods or use them in sequence. Chemical/physical means may be used to enhance biostimulation. The review also suggests tools for assessing sustainability, life cycle assessment, and risk assessment. To help entrepreneurs, decision makers, and methods developers in the future, we suggest founding a database for otherwise seldom reported unsuccessful interventions, as well as the potential for artificial intelligence (AI) to assist in site evaluation and decision-making.

Sulfate Radical in (Photo)electrochemical Advanced Oxidation Processes for Water Treatment: A Versatile Approach

The search for a simple and clean approach toward the production of sulfate radicals for water treatment gave rise to electrochemical and photoelectrochemical activation techniques. The photoelectrochemical activation method does not just distinguish itself as a promising activation method, it is also used as an efficient water treatment method with the ability to treat a myriad of pollutants due to the complementary effects of highly reactive oxidizing species. This perspective highlights some merits that distinguish sulfate monoanion radicals from hydroxyl radicals. It highlights the electrochemical, photoelectrochemical, and in situ photoelectrochemical routes of generating sulfate radicals for advanced oxidation process approach to water treatment. We provide a detailed account of the few known applications of sulfate radical enhanced photoelectrochemical treatments of water laden with organics. Finally, we placed this area of research in perspective by providing outlooks and conclusive remarks.

Aniline degradation and As (III) oxidation and immobilization by thermally activated persulfate

In the Pearl River Delta of China, many sites are likely contaminated with aniline in the soil and arsenic (As) in the groundwater because of a high As background level and the prevailing printing and dyeing industry. This study is to explore the remediation performance of thermally activated persulfate oxidation for the sites with these two contaminants, aniline and As. The As influence on the aniline degradation and vice versa are also systematically investigated. When the molar ratio of aniline to persulfate is 1: 4.65, over 85% of aniline can be degraded at 40 °C in 24 h, and 100 μg L-1 As(III) in solution can be completely adsorbed by the soil. A higher pH favored the aniline degradation but disfavored the As(III) oxidation. Due to the strong buffer capacity of the soil, aniline in the soil could be more quickly degraded than those in the solution. The As(III), however, seem more easily oxidized in the absence of soil. The coexisting Fe2+ can substantially improve As(III) oxidation and immobilization, although the dilute Fe2+ solution may suppress the aniline degradation. The presence of aniline severely inhibited the As(III) oxidation and adsorption, likely due to the competition for the generated free radicals and the adsorption sites on the soils. In contrast, the existing As(III) has a slight effect on aniline degradation. These findings are believed to provide the theoretical basis for the remediation of aniline-arsenic contaminated sites.

Silica enhanced activation and stability of Fe/Mn decorated sludge biochar composite for tetracycline degradation

In this study, SiO₂-composited biochar decorated with Fe/Mn was prepared by co-pyrolysis method. The degradation performance of the catalyst was evaluated by activating persulfate (PS) to degrade tetracycline (TC). The effects of pH, initial TC concentration, PS concentration, catalyst dosage and coexisting anions on degradation efficiency and kinetics of TC were investigated. Under optimal conditions (TC = 40 mg L^-1, pH = 6.2, PS = 3.0 mM, catalyst = 0.1 g L^-1), the kinetic reaction rate constant could reach 0.0264 min^-1 in Fe₂Mn₁@BC-0.3SiO₂/PS system, which was 12 times higher than that in the BC/PS system (0.00201 min^-1). The electrochemical, X-ray diffractometer (XRD), Fourier transform infrared spectrum (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis showed that both metal oxides and oxygen-containing functional groups provide more active sites to activate PS. The redox cycle between Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) accelerated the electron transfer and sustained the catalytic activation of PS. Radical quenching experiments and electron spin resonance (ESR) measurements confirmed that surface sulfate radical (SO₄^•-) play a key role in TC degradation. Three possible degradation pathways of TC were proposed based on high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis, the toxicity of TC and its intermediates was analyzed by bioluminescence inhibition test. In addition to the enhanced catalytic performance, the presence of silica also improved the stability of the catalyst, as confirmed by cyclic experiment and metal ion leaching analysis. The Fe₂Mn₁@BC-0.3SiO₂ catalyst, derived from low-cost metals and bio-waste materials, offer an environmentally friendly option to design and implement heterogenous catalyst system for pollutant removal in water.

Arsenic Contamination in Groundwater: Geochemical Basis of Treatment Technologies

Arsenic (As) is abundant in the environment and can be found in both organic (e.g., methylated) and inorganic (e.g., arsenate and arsenite) forms. The source of As in the environment is attributed to both natural reactions and anthropogenic activities. As can also be released naturally to groundwater through As-bearing minerals including arsenopyrites, realgar, and orpiment. Similarly, agricultural and industrial activities have elevated As levels in groundwater. High levels of As in groundwater pose serious health risks and have been regulated in many developed and developing countries. In particular, the presence of inorganic forms of As in drinking water sources gained widespread attention due to their cellular and enzyme disruption activities. The research community has primarily focused on reviewing the natural occurrence and mobilization of As. Yet, As originating from anthropogenic activities, its mobility, and potential treatment techniques have not been covered. This review summarizes the origin, geochemistry, occurrence, mobilization, microbial interaction of natural and anthropogenic-As, and common remediation technologies for As removal from groundwater. In addition, As remediation methods are critically evaluated in terms of practical applicability at drinking water treatment plants, knowledge gaps, and future research needs. Finally, perspectives on As removal technologies and associated implementation limitations in developing countries and small communities are discussed.

Effects of functional group loss on biochar activated persulfate in-situ remediation of phenol pollution in groundwater and its countermeasures

Biochar is considered a good activator for use in advanced oxidation technology. However, dissolved solids (DS) released from biochar cause unstable activation efficiency. Biochar prepared from saccharification residue of barley straw (BC-SR) had less DS than that prepared directly from barley straw (BC-O). Moreover, BC-SR had a higher C content, degree of aromatization, and electrical conductivity than BC-O. Although the effects of BC-O and BC-SR on activation of Persulfate (PS) to remove phenol were similar, the activation effect of DS from BC-O was 73% higher than that of DS from BC-SR. Moreover, the activation effect of DS was shown to originate from its functional groups. Importantly, BC-SR had higher activation stability than BC-O owing to the stable graphitized carbon structure of BC-SR. Identification of reactive oxygen species showed that SO₄•^-, •OH, and ¹O₂ were all effective in degradation by BC-SR/PS and BC-O/PS systems, but their relative contributions differed. Furthermore, BC-SR as an activator showed high anti-interference ability in the complex groundwater matrix, indicating it has practical application value. Overall, this study provides novel insight that can facilitate the design and optimization of a green, economical, stable, and efficient biochar-activated PS for groundwater organic pollution remediation.

Monitoring of in-situ chemical oxidation for remediation of diesel-contaminated soil with electrical resistivity tomography

In-situ chemical oxidation (ISCO) with persulfate, an electrically conductive oxidant, provides a powerful signal for noninvasive geophysical techniques to characterize the remediation process of hydrocarbon contaminants. In this study, remediation with ISCO is conducted in laboratory sandboxes to evaluate the ability of electrical resistivity tomography (ERT) for monitoring the base-activated persulfate remediation process of diesel-contaminated soil. It was found that the resistivity of contaminated sand significantly decreased from 846 Ω·m to below 10 Ω·m after persulfate injection, and all measured chemical parameters showed a noticeable increase. Natural degradation and contamination plume migration were not evident in a reference sandbox without treatment. The area with a resistivity ratio < 0.95 based on imaging before and after injection indicated downward migration of the oxidation plume due to density-driven flow. A comparison between remediation and reference sandboxes showed that the observed resistivity decrease can be due to both contaminant degradation as well as the oxidation plume itself in the contaminated source zone. In contrast, the resistivity decrease in the area with low contamination concentration is attributed to the oxidation plume alone. The derived relationships between resistivity and contaminant indicators further emphasize that the contribution of contaminant consumption to resistivity change in the source area is 25.6%, while it is <16% in the low or non-contaminated area. Although this study showed that resistivity is not solely affected by the chemical transformation of diesel components, it can be combined with sampling data to allow an assessment of the effectiveness of ISCO treatment and to identify target areas for subsequent treatment.

Insight on efficiently oriented oxidation of petroleum hydrocarbons by redistribution of oxidant through inactivation of soil organic matter coupled with passivation of manganese minerals

While extensive works focused on the enhancement of the activity of heterogeneous Fenton catalysts, little was paid attention to the inhibition of soil organic matter (SOM) and Mn minerals in soil remediation. Here, the oxidation of petroleum hydrocarbons in soils (S1: 4.28 % SOM, S2: 6.04 % SOM, S3: 10.33 % SOM) with inactivated SOM and passivated Mn oxides regulating by calcium superphosphate (Ca(H₂PO₄)₂) was carried out. Oily sludge pyrolysis residue was used as precursors to prepare an oleophilic iron-supported solid catalyst (Fe-N @ PR). For regulated systems, under the optimal conditions of 1.8 mmol/g H₂O₂ and 0.05 g/g Fe-N @ PR, 72 ∼ 91 % of total petroleum hydrocarbons (TPHs: 15,616.58 mg/kg) were oxidized, which was 38 ∼ 45 % higher than that of control systems. The mechanism of efficient oxidation was proposed that the passivated Mn minerals stabilized H₂O₂ redistributing more H₂O₂ to sustainably produce •OH, and the inactivated SOM improved the relative reactivity of •OH to TPHs. Additionally, the passivation of Mn oxides was mainly related to the binding of H₂PO₄^-, and the inactivation of SOM was realized by Ca²⁺ combing with -OH and C-O-C to form stable complexes. This study brought us a new perspective on soil remediation through passivating Mn minerals and inactivating SOM.

Remediation of industrial site soil contaminated with PAHs using stage persulfate oxidation activated by Fe2+ chelated with sodium citrate

The remediation for industrial site soil has attracted public concerns because of the hazardous and hydrophobic properties of organic pollutants existed in the soil. The persulfate oxidation activated by Fe²⁺ chelated with sodium citrate (PS/Fe²⁺/SC) was used to remediate different types of industrial site soils in the present study. The maximum removal rates of Σ16 PAHs in the Nanjing site soil (NJS) and Hefei site soil (HFS) were 73.6% and 85.8% after the second-stage oxidation, respectively. The late oxidation stages couldn't enhance the degradation efficiency of PAHs due to the increase of high crystalline Fe mineral phases both in the NJS and HFS, which significantly decreased the Fe²⁺/Fe³⁺ recycle and further inhibited the reactive oxygen species production during the remediation. The remediation using PS/Fe²⁺/SC could change the soil physicochemical properties, such as the functional groups, specific surface area (SSA), total pore volume (TPV) and some UV spectral parameters of soil particles. Additionally, the oxidation of PS/Fe²⁺/SC also altered the composition of soil dissolve organic matters, especially the fulvic acid, which further affected the Fe²⁺ oxidation. The study mainly discloses the mechanism of limitation using persulfate oxidation activated by Fe materials at late oxidation stage.

Hydrocarbons removal and microbial community succession in petroleum-contaminated soil under hydrogen peroxide treatment

Chemical oxidation as a pretreatment step coupled with bioremediation for petroleum-contaminated soil may pose serious impacts on indigenous microorganisms and the available nutrients. Petroleum-contaminated soil were treated by hydrogen peroxide (H₂O₂) at initial concentrations of 105 mM (HH), 21 mM (HL), and 105 mM in three equal amounts (HT) without adding any external catalyst. The contents of total petroleum hydrocarbons (TPH) and dissolved nutrients (total organic compounds, nitrogen, and phosphate), and the indigenous bacteria community succession (analyzed by high-throughput sequencing of 16S rDNA) were investigated over 50 days. Compared to the control treatment without H₂O₂ addition, H₂O₂ treatments for the petroleum-contaminated soil significantly promoted the TPH removal especially in the first 4 days and impacted the contents of dissolved nutrients. Both of chemical oxidation and nutrients contributed to microbial community structure changes in alpha diversity. Although the soil microbial community structure had undergone significant changes after different chemical oxidation pretreatments, Firmicutes, Proteobacteria, Gemmatimonadetes, and Actinobacteria were the main bacterial phyla. Compared with adding H₂O₂ at one time, H₂O₂ added in stepwise was beneficial to indigenous bacterial diversity recovery and TPH removal. H₂O₂ oxidation treatments showed a great influence on the microbial community structures in the start-up stage, while recovery time rather than the oxidation treatments presented greater effects on the composition of the microbial community structure with the incubation time extended. Therefore, adding H₂O₂ as pretreatment for petroleum-contaminated soil showed little effect on the structure of soil indigenous microbial community from a long-term scale, and was conducive to the continuous removal of TPH by indigenous microorganisms.

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.

A Theoretical Study of the Interactions between Persistent Organic Pollutants and Graphene Oxide

Persistent organic pollutants (POPs) have adverse effects on the human health and ecosystem functioning. Graphene oxide (GO) has been developed to remove trace levels of POPs from wastewater samples. However, many questions involved in these processes are still unresolved (e.g., the role of π-π interaction, the effect of GO on the degradation of POPs, and so on). Revealing the microscopic interactions between GO and POPs is of benefit to resolve these questions. In the present study, a quantum chemical calculation was used to calculate the molecular doping and adsorption energy between eight representative POPs and GO. The influences of GO on the thermodynamic parameters, such as the Gibbs free energy and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, were also reported. We found the molecular doping is dependent on the species of POPs. The adsorption energy of the majority of POPs on GO is between 7 and 8 kJ/mol. Consequently, the GO may make degradation of POPs in wastewater more productive and lead to a change of kinetics of the degradation of POPs.

Petroleum-contaminated soil: environmental occurrence and remediation strategies

Soil is an environmental matrix that carries life for all living things. With the rise of human activities and the acceleration of population, the soil has been exposed in part to pollution by the discharge of various xenobiotics and persistent pollutants into it. The disposal of toxic substances such as polycyclic aromatic hydrocarbons (PAHs) alters soil properties, affects microbial biodiversity, and damages objects. Considering the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and clean-up of PAH-polluted sites represents an important technological and environmental challenge for sustainable growth and development. Though several treatment methods to remediate PAH-polluted soils exist, interesting bacteria, fungi, and their enzymes receive considerable attention. The aim of the present review is to discuss PAHs' impact on soil properties. Also, this review illustrates physicochemical and biological remediation strategies for treating PAH-contaminated soil. The degradation pathways and contributing factors of microbial PAH-degradation are elucidated. This review also assesses the use of conventional microbial remediation compared to the application of genetically engineered microorganisms (GEM) that can provide a cost-effective and eco-friendly PAH-bioremediation strategy.

Overestimate of remediation efficiency due to residual sodium persulfate in PAHs contaminated soil and a solution

Oxidation remediation is a commonly used technology for PAHs contaminated soil presently, but the overestimate of efficiency due to ongoing remediation by residual oxidants during extraction and testing has not been paid enough attention. In this study, persulfate was activated by Fe(II) to investigate the effects of residual oxidants on PAHs removal during detection process and the elimination effects of adding Na₂SO₃ and extending sampling time on residual oxidants. Results verified that the residual oxidants removed PAHs in extraction process, making the results lower than the actual values: the detection recovery rate η of ∑PAHs and 3-6 ring PAHs ranged from 24.3% (25% Na₂S₂O₈ treatment) to 87.4% (5% Na₂S₂O₈+4/4Fe²⁺ treatment), 20.1%-99.0%, 28.9%-87.9%, 20.8%-89.4%, and 18.6%-76.9%, respectively. After adding Na₂SO₃, the accuracy of detection results increased significantly: the η of ∑PAHs and 3-6 ring PAHs increased to 64.1%-96.5%, 58.8%-95.5%, 73.8%-114.4%, 60.6%-95.6%, and 45.4%-77.1%, respectively. After 49 days of adding oxidants, residual oxidants had no considerable effect on the detection of PAHs, indicating it was appropriate to start soil remediation verification sampling49 days after the remediation was completed. The observed results will help scientific evaluation of the remediation effects of chemical oxidation on organic contaminated soil.

Use of an automated respirometer for in situ chemical oxidation (ISCO) activator type and concentration selection

In situ chemical oxidation (ISCO) is a popular remediation technique for hydrocarbon-contaminated soil and groundwater. A range of oxidising agents and activators are available for ISCO; however, selection is usually based on contaminant destruction which is time-consuming and impacted by sample heterogeneity based on 1-10 g sample contaminant analysis. In this paper, we demonstrate the use of an automated respirometer, measuring CO₂ production, as a rapid and reliable approach for activator type and concentration selection. The approach is demonstrated based on tests in matrices of different types (loam soil and sand). In both matrices, CO₂ production was significantly increased following sodium persulphate (SPS) oxidation with iron activation in a concentration-dependant manner. Alkaline activation led to no increased CO₂ production compared to SPS addition without activation. The approach will provide greater confidence in treatability testing and reagent efficiency in ISCO projects.

Optimization and mechanism of oily sludge treatment by a novel combined surfactants with activated-persulfate method

Recently, the extensive discharge of oily sludge, due to excessive use of fossil oil, has become a serious worldwide concern, as it leads to serious environmental pollution and even threat human health. However, the complex properties and compositions of oily sludge make it difficult for the treatment of oily sludge. This study proposed a novel method of combined degradation of oily sludge by surfactants with activated-persulfate, and analyzed the degradation efficiency and degradation pathway. The organics in oil sludge were eluted by surfactant, and the residual oil difficult to be eluted was further oxidized by activated persulfate. The combined method significantly improved the degradation efficiency of oily sludge, and the removal rate reached 94.6 ± 2.8%, and the oil content of the residual oily sludge was 0.57%, which had reached the discharge standard. The mechanism analysis indicated that surfactant could increase the solubility of oil by reducing the surface tension, and the hydroxyl radical and sulfate radical generated by activated persulfate could degrade the complex organic matters into small molecule matters, achieving efficient degradation of oil sludge. This work demonstrated a new avenue for the efficient and cost-effective treatment of oily sludge, opening an environmentally friendly treatment concept.

Foam flushing with soil vapor extraction for enhanced treatment of diesel contaminated soils in a one-dimensional column

A limitation of soil vapor extraction (SVE) remediation for total petroleum hydrocarbons (TPHs) in the unsaturated zone is the inability to remove the less volatile petroleum mixture compounds in diesel fuel. SVE combined with foam flushing may have the potential to enhance dissolution or mobilization of soil sorbed diesel and allow mobilized diesel to move to the SVE extraction well. A nonionic surfactant polyoxyethylene (20) sorbitan monooleate (TW80) was selected for generating foam, and a procedure to incorporate the oxidant sodium persulfate (SPS) in generating TW80/SPS foam to deliver chemical oxidation, was also studied. Both TW80 and TW80/SPS foams exhibited 96-98% quality under 8-32 mM of TW80 and 10-50 mM of SPS. The addition of SPS in TW80 solution resulted in elevated ionic content and degradation of TW80, which may reduce the foam stability and have minor effects on foam quality. Through analysis of interrelationships among column flushing experimental parameters, it was shown that the foam quality was reduced to 42-47% when foam flushed through a diesel contaminated soil column. Moreover, the results of column flushing tests operated for 12 h indicated that the effectiveness of removal of diesel by different foams followed the order of TW80 foam (53%) > TW80/SPS foam (37%) >N₂ gas flow alone (3%). It was shown that foam flushing could be an alternative approach, rather than using N₂ gas flow alone (SVE), in enhancing SVE for reducing diesel contamination in the unsaturated zone.

Design of a Microbial Remediation Inoculation Program for Petroleum Hydrocarbon Contaminated Sites Based on Degradation Pathways

This paper analyzed the degradation pathways of petroleum hydrocarbon degradation bacteria, screened the main degradation pathways, and found the petroleum hydrocarbon degradation enzymes corresponding to each step of the degradation pathway. Through the Copeland method, the best inoculation program of petroleum hydrocarbon degradation bacteria in a polluted site was selected as follows: single oxygenation path was dominated by Streptomyces avermitilis, hydroxylation path was dominated by Methylosinus trichosporium OB3b, secondary oxygenation path was dominated by Pseudomonas aeruginosa, secondary hydroxylation path was dominated by Methylococcus capsulatus, double oxygenation path was dominated by Acinetobacter baylyi ADP1, hydrolysis path was dominated by Rhodococcus erythropolis, and CoA path was dominated by Geobacter metallireducens GS-15 to repair petroleum hydrocarbon contaminated sites. The Copeland method score for this solution is 22, which is the highest among the 375 solutions designed in this paper, indicating that it has the best degradation effect. Meanwhile, we verified its effect by the Cdocker method, and the Cdocker energy of this solution is −285.811 kcal/mol, which has the highest absolute value. Among the inoculation programs of the top 13 petroleum hydrocarbon degradation bacteria, the effect of the best inoculation program of petroleum hydrocarbon degradation bacteria was 18% higher than that of the 13th group, verifying that this solution has the best overall degradation effect. The inoculation program of petroleum hydrocarbon degradation bacteria designed in this paper considered the main pathways of petroleum hydrocarbon pollutant degradation, especially highlighting the degradability of petroleum hydrocarbon intermediate degradation products, and enriching the theoretical program of microbial remediation of petroleum hydrocarbon contaminated sites.

Survey and Risk Assessment of Contaminants in Soil from a Nitrogenous Fertilizer Plant Located in North China

China is the world’s largest consumer of fertilizer, with fertilizer plants widely distributed throughout the country. With the removal and closing of fertilizer factories in recent years, pollutant surveys and risk assessments (human health risks) for these sites have become increasingly necessary. However, there has been little research on contaminated fertilizer factory sites. This study aimed to characterize the distribution of pollutants, assess the health risk of the site, and calculate the remediation area and volume in a typical fertilizer plant site in North China. A total of 443 samples were collected in 2019; they indicated that the study site had high concentrations of copper (Cu), ammonia-nitrogen (NH3-N), total petroleum hydrocarbons (TPH), and fluoride at maximum ratios (the ratio of the highest value of all test data for a particular pollutant to the standard value of the pollutant) of 3.30, 2.55, 19.69, and 1.10, respectively. The health risk assessment results suggested that some hazard quotients exceeded the threshold safe level (>1 established by environmental regulations). The risk control values of soil were 2000 mg/g (Cu), 826 mg/g (TPH), and 1549 mg/g (NH3-N), and the total remediation soil volume was 72860.71 m3. The results provided basic information on soil pollution control and environmental management in a contaminated fertilizer plant site.

Persulfate Oxidation Coupled with Biodegradation by Pseudomonas fluorescens Enhances Naphthenic Acid Remediation and Toxicity Reduction

The extraction of bitumen from the Albertan oilsands produces large amounts of oil sands process-affected water (OSPW) that requires remediation. Classical naphthenic acids (NAs), a complex mixture of organic compounds containing O₂^- species, are present in the acid extractable organic fraction of OSPW and are a primary cause of acute toxicity. A potential remediation strategy is combining chemical oxidation and biodegradation. Persulfate as an oxidant is advantageous, as it is powerful, economical, and less harmful towards microorganisms. This is the first study to examine persulfate oxidation coupled to biodegradation for NA remediation. Merichem NAs were reacted with 100, 250, 500, and 1000 mg/L of unactivated persulfate at 21 °C and 500 and 1000 mg/L of activated persulfate at 30 °C, then inoculated with Pseudomonas fluorescens LP6a after 2 months. At 21 °C, the coupled treatment removed 52.8-98.9% of Merichem NAs, while 30 °C saw increased removals of 99.4-99.7%. Coupling persulfate oxidation with biodegradation improved removal of Merichem NAs and chemical oxidation demand by up to 1.8× and 6.7×, respectively, and microbial viability was enhanced up to 4.6×. Acute toxicity towards Vibrio fischeri was negatively impacted by synergistic interactions between the persulfate and Merichem NAs; however, it was ultimately reduced by 74.5-100%. This study supports that persulfate oxidation coupled to biodegradation is an effective and feasible treatment to remove NAs and reduce toxicity.

Systematic evaluation of activated carbon-Fe3O4 composites for removing and degrading emerging organic pollutants

In this study, a comparative activity assessment of several activated carbon (AC) and AC-Fe₃O₄ composites was performed to evaluate their efficiency and versatility as Fenton-like catalysts. Although many studies have demonstrated the advantages of AC-based materials as Fenton-like catalysts, most have been developed using only one oxidant and/or one pollutant. Here, untreated (AC₀) and acid-treated AC (AC_A) iron-oxide composites were synthesized, characterized, and compared in terms of activity to bare AC using several oxidants and pollutants, the activation efficiency of hydrogen peroxide (H₂O₂) and ammonium persulfate ((NH₄)₂S₂O₈), and the subsequent oxidation extent and kinetics of bisphenol-A, atrazine, and carbamazepine by the AC-based materials were studied in depth. The persulfate-based systems showed considerably higher pollutant removal in the presence of the catalysts, despite lower persulfate decomposition rates: atrazine and carbamazepine were partially degraded, mainly through a radical-dependent pathway; the highest removal of atrazine was achieved with the AC_A-iron composite, whereas carbamazepine was best removed by the AC₀-iron composite. In contrast, bisphenol A was completely mineralized, probably via a non-radical pathway, in the presence of all AC-based composites, even at very low persulfate concentrations. Furthermore, bisphenol A removal remained high for several consecutive cycles, with the most efficient removal and stability observed in the presence of AC_A. These findings reveal the high complexity of AC-based systems, with multiple binding sites and degradation pathways unique to each combination of pollutants, catalysts, and oxidants. In general, the composition of the waste stream governs the applicability of these materials. Thus, the structure-function correlations and degradation mechanisms revealed here are crucial for improving sorbent-catalyst design and accelerating the implementation of low-cost remediation and in situ regeneration technologies.

Iodometric spectrophotometric determination of peroxydisulfate in hydroxylamine-involved AOPs: 15 min or 15 s for oxidative coloration?

In this study, iodometric spectrophotometry, the most-used method for detecting peroxydisulfate (PDS), was modified by increasing the concentration of potassium iodide (KI) for realizing the immediate PDS determination and avoiding the interference of hydroxylamine. Kinetic studies showed that the reaction between PDS and I^- to generate the yellow-colored I₃^- followed the kinetic equation as [Formula: see text] . Detection time of the iodometric spectrophotometry was shortened from 15 min to 15 s when KI concentration was increased from 0.6 M to 4.8 M. Different with the previous iodometric spectrophotometry, the modified method using 4.8 M KI as the indicator was well tolerable to the interference of hydroxylamine at acidic pH conditions. The calibration curve of the modified method showed a well linear relationship (R² = 0.999) between the absorbance of I₃^- at 352 nm and PDS concentration in the range of 0-80 μM. The modified method was highly sensitive with the absorptivity of 2.5 × 10⁴ M^-1 cm^-1 and the limit of detection of 0.11 μM. Moreover, the modified method was successfully applied for monitoring the change of PDS concentration during the degradation of diclofenac with four different PDS-based AOPs, the calculated reaction stoichiometric efficiency (RSE(%)=DiclofenacdegradedPDSconsumed×100%) followed the order as heat/PDS system > hydroxylamine/Fe²⁺/PDS system > hydroxylamine/Cu²⁺/PDS system > Fe²⁺/PDS system.

Thermal desorption treatment of petroleum hydrocarbon-contaminated soils of tundra, taiga, and forest steppe landscapes

The results of field, analytical, and experimental research at a number of production facilities reflect the properties of oil-contaminated soils in 3 landscapes: the permafrost treeless Arctic ecosystem, boreal forest, and temperate-climate grassland-woodland ecotone. Laboratory studies have revealed the concentrations of petroleum hydrocarbons in soils, ranging from medium levels of 2000-3000 mg/kg to critical figures over 5000 mg/kg, being 2-25 times higher than the permissible content of oil products in soils. The experimentally applied thermal effects for the oil products desorption from the soil allowed finding an optimal regime: the treatment temperature from 25 to 250 °C reduces the concentrations to an acceptable value. The conditions are environmentally sound, given that the complete combustion point of humates is ca. 450 °C. The outcomes suggest the eco-friendly solution for soil remediation, preserving the soil fertility in fragile cold environments and in more resilient temperate climates, where revitalized brownfields are essential for food production.

Degradation of petroleum hydrocarbons in soil via advanced oxidation process using peroxymonosulfate activated by nanoscale zero-valent iron

Recently, the use of nanoscale zero-valent iron (nZVI) for removal of organic contaminants from aqueous and soil system has increased. In this study, we employ nZVI to activate peroxymonosulfate (PMS) for the degradation of total petroleum hydrocarbons (TPHs) in aged diesel-contaminated soil. Upon PMS activation by nZVI, PMS produces more highly reactive oxygen species (ROS) in both aqueous solution and soil compared to other compounds (PMS/Co(II)), as determined by electron paramagnetic resonance spectroscopy. Thus, nZVI is an effective catalyst for PMS activation, leading to the efficient degradation of diesel oil in soil compared to other catalysts and oxidants. The optimal concentrations of PMS and nZVI were found to be 3 and 0.2%, respectively, showing the best degradation efficiency (61.2% in 2 h). The observed TPH degradation was retarded (up to 19.1-37% efficiency) in the presence of radical scavengers, such as tert-butyl alcohol, nitrobenzene, ethyl alcohol, and isopropyl alcohol. These results also demonstrate that ROS (hydroxyl and sulfate free radicals) are generated via PMS activation by nZVI. Moreover, more than 96% of TPH can be degraded by sequential applications of PMS/nZVI. Factors affecting TPH degradation, namely PMS/nZVI concentration, soil:solution ratio, soil pH, activators, and oxidants, are also analyzed. The results demonstrate that TPH is degraded to below the residential soil quality limit using PMS/nZVI based on the advanced oxidation process (AOP), which is therefore an effective option for chemical remediation of diesel-contaminated soils over a wide range of pH.

Generation mechanisms of active free radicals during ciprofloxacin degradation in the ultrasonic/K2S2O8 system

Ciprofloxacin (CIP) removal efficiency in aqueous solutions in the ultrasonic (US), K₂S₂O₈, and US/K₂S₂O₈ systems was investigated. The free radical generation and action ratio were studied based on variations of K₂S₂O₈ concentration, ultrasonic power, pH, and the addition of isopropanol (ISP) or tert-butyl alcohol (TBA) in the US/K₂S₂O₈ system. The results showed that under conditions of 20 mg·L^-1 CIP concentration, 20 mmol·L^-1 K₂S₂O₈ concentration, an ultrasonic power of 360 W and pH = 7, CIP removal efficiency in the US/K₂S₂O₈ system was 92.20% after 180 min. The reaction in the US/K₂S₂O₈ system was explicitly divided into two stages: free radical generation and pollutants degradation. The ultrasonic and chain reaction facilitated enhanced generation of SO₄^-• and HO^•. The presence of K₂S₂O₈ can promote HO^• generation and K₂S₂O₈ concentration also exerted a significant effect on SO₄^-• generation, however, high concentrations were not beneficial to the reaction. Quenching reactions occurred under high concentrations of HO^• and SO₄^-•. During the initial stage of the reaction, HO^• played a more prominent role than SO₄^-•, however, the role of SO₄^-• gradually increased as the reaction proceeded and eventually surpassed HO^•.

Degradation of anthraquinone dye reactive blue 19 using persulfate activated with Fe/Mn modified biochar: Radical/non-radical mechanisms and fixed-bed reactor study

In this study, a heterogeneous activator was prepared via the Fe/Mn modification of sludge-derived biochar (Fe/MnBC) to achieve high-efficiency activation of persulfate (PS) for reactive blue 19 (RB19) degradation. The morphologies and chemical states of Fe/MnBC were examined by various characterizations. A comprehensive assessment was conducted to reveal the effects of biochar preparation conditions and system reaction conditions. According to the results of scavenger quenching experiments and electron paramagnetic resonance (EPR) testing, the mechanisms of Fe/MnBC combined PS system on RB19 degradation were proposed, including radical and non-radical mechanisms. The formation and involvement of sulfate radical (SO₄^·-), hydroxyl radical (OH^·), and singlet oxygen (¹O₂) were proved in this system, and Fe(IV)/Mn(VII) was also speculated to participate in the non-radical degradation process. These findings give a new insight into the mechanisms of PS activated by metal-biochar composite. Besides, fixed-bed reactor (FBR) experiments indicated that the Fe/MnBC has considerable PS activation potential for dyes removal. The degradation process was further modeled by the central composite design (CCD-RSM) and artificial neural networks (ANN) methods. The statistical metrics and prediction indicated that the prediction results of ANN model were better than CCD-RSM model, and the ANN model could perfectly predict the reaction process of Fe/MnBC FBR for engineering applications.

Use of biochar/persulfate for accelerating the stabilization process and improving nitrogen stability of animal waste digestate

In China, the growing amount of digestate from anaerobic digestion produced by animal husbandry is an emerging challenge. A common treatment used to eliminate this digestate is long-term stabilization ponds. However, this process can lead to a shortage of digestate storage space and loss of nitrogen nutrients within the digestate. To alleviate those shortcomings, this study developed an efficient stabilization pond using biochar and persulfate (BC/PS treatment). Using this treatment, the germination index (GI) of the digestate increased from 56% to 85% and the stabilization efficiency increased nearly 2.7 times. In addition, the dehydrogenase activity (DHA) in the BC/PS treatment remained between 0.47 and 0.91 μg/(g·h) across the 40 days, which indicated that BC/PS had a positive effect on microbial inactivation. In the traditional stabilization process (CK treatment), dissolved organic nitrogen (DON) decreased from 47.77 mg/L to 0.81 mg/L and ammonium nitrogen almost disappeared. The BC/PS treatment led to the promotion of nitrogen nutrient composition. Particulate total nitrogen (21.49% of total nitrogen) decomposed into dissolved total nitrogen and the DON increased from 47.77 to 58.89 mg/L. The BC/PS treatment showed a faster stabilization time, good microbial inactivation, lower toxicity, and stable nitrogen nutrient composition of the digestate compared to traditional methods.

An electrochemiluminescence sensor for 17β-estradiol detection based on resonance energy transfer in α-FeOOH@CdS/Ag NCs

An electrochemiluminescence (ECL) resonance energy transfer system is constructed for 17β-estradiol (E2) detection using α-FeOOH@CdS nanospheres as the ECL-active substrates and Ag NCs as an efficient quencher. CdS QDs loaded onto three-dimensional (3D) urchin-like α-FeOOH nanospheres (α-FeOOH@CdS nanospheres) exhibited excellent ECL responses, which is attributed to dual-amplification of α-FeOOH frameworks. The 3D hierarchical structure of the α-FeOOH nanospheres provided abundant sites for loading ECL-active species, thus significantly improving the ECL performance of substrates; While Fe³⁺ presented on surface of α-FeOOH nanospheres could be reduced to Fe²⁺ in negative potentials, after which might activate persulfate in a Fenton-like process, resulting in more sulfate free radicals for more effective ECL responses via electron transfer reactions. Additionally, Ag nanoclusters (Ag NCs) stabilized by single stranded oligonucleotide were introduced as quenching probes for CdS QDs owing to the well-matched donor-acceptor spectrum for efficient energy transfer, which makes them appropriate for detection of E2. The proposed strategy displayed a desirable dynamic range from 0.01 to 10 pg mL^-1 with a limit of detection of 0.003 pg mL^-1. The proposed strategy based on the ECL-RET strategy offered an ideal way for E2 detection, and also revealed an alternative platform for detection of other small molecules.

Enhanced degradation of total petroleum hydrocarbons in real soil by dual-frequency ultrasound-activated persulfate

Ultrasound (US) can be employed to activate persulfate (PS) for degrading total petroleum hydrocarbons (TPH). In this study, to improve the degradation efficiency, PS is combined with dual-frequency US (DFUS) towards synergistic degradation of TPH in real soil. After 180 min, the degradation percentages for DFUS/PS, DFUS, high-frequency US and high-frequency US/PS are around 88.9%, 38.7%, 7.3% and 54.2%, respectively. Additionally, the influence of US power, PS content, slurry pH and temperature, and TPH components on the degradation percentage in the DFUS/PS process are explored. Scanning electron microscopy (SEM) images and the results of specific surface area verify that the DFUS can break the soil aggregates more effectively than the single-frequency US, and thus enhance the TPH desorption and accelerate the oxidant diffusion. Moreover, the investigation of the mechanism is further evaluated through quenching and electron spinning resonance spectrum (ESR) tests. The results indicate that the generation of SO₄^- and OH in DFUS/PS is ~1.6 times and ~2.5 times as much, respectively, as in high frequency US/PS. The relative contributions to the synergistic TPH degradation in the DFUS/PS system are: SO₄^- (PS activation via the heat induced by US) > pyrolysis inside the bubbles (hydrophobicity of TPH) > SO₄^- (PS activation via US cavitation) >OH. Finally, the hypothesis is confirmed via the evaluation of the degradation kinetics, which shows that the combined process of DFUS/PS is not a simple addition of the US and PS, but provides a highly effective process of synergistic degradation.

Current status of soil and groundwater remediation technologies in Taiwan

The purpose of this review is the analysis of the soil and groundwater remediation technologies referred as in situ chemical oxidation and phytoremediation, and to discuss the successes that have been made. The technology of phytoremediation has yet to be commercially accepted but shows emerging capabilities. In situ chemical oxidation (ISCO) is a frequently used technology in Taiwan for the remediation of organic compounds. Several studies have been conducted in Taiwan so show their feasibility and potential. This article reviews studies concerning these two remediation technologies. Other processes such as monitored natural attenuation, flushing, thermal treatment, or soil washing are not covered within this article.

Application of biochar in advanced oxidation processes: supportive, adsorptive, and catalytic role

The advanced oxidation processes (AOPs), especially sulphate radical (SO₄^•-)-based AOPs (SR-AOPs), have been considered more effective, selective, and prominent technologies for the removal of highly toxic emerging contaminants (ECs) due to wide operational pH range and relatively higher oxidation potential (2.5-3.1 V). Recently, biochar (BC)-based composite materials have been introduced in AOPs due to the dual benefits of adsorption and catalytic degradation, but the scientific review of BC-based catalysts for the generation of reactive oxygen species (ROSs) through radical- and non-radical-oriented routes for EC removal was rarely reported. The chemical treatments, such as acid/base treatment, chemical oxidation, surfactant incorporation, and coating and impregnation of minerals, were applied to make BC suitable as supporting materials (SMs) for the loading of Fenton catalysts to boost up peroxymonosulphate/persulphate/H₂O₂ activation to get ROSs including ^•OH, SO₄^•-, ¹O₂, and O₂^•- for targeted pollutant degradation. In this review, all the possible merits of BC-based catalysts including supportive, adsorptive, and catalytic role are summarised along with the possible route for the development prospects of BC properties. The limitations of SR-AOPs especially on production of non-desired oxyanions, as well as disinfection intermediates and their potential solutions, have been identified. Lastly, the knowledge gap and future-oriented research needs are highlighted.

Degradation of trichloroethylene by photoelectrochemically activated persulfate

Chlorine-containing organic compounds were discharged informally as a result of untreated industrial wastewater, which caused groundwater pollution. In this study, titanium dioxide nanotube arrays (TNAs) were modified with copper oxide to photoelectrochemical (PEC) active persulfate to degrade trichloroethylene (TCE). The SEM results show copper nano-particles with a cubic shape were successfully deposited on the surface of TNAs. The results of UV-vis analysis indicate the absorption wavelengths red-shift to 550-600 nm for better light utilization. CuO/TNAs were dominated by the anatase phase after sintering at 450 °C with significant visible light response. The chemical contents for the surface of CuO/TNAs are 23.7, 53.4, 18.4 and 4.4% for C, O, Ti and Cu, respectively. The photocurrent of CuO/TNAs is 1.89 times higher than that of TNAs_{-93 cm^2-1hr} under 100 W Hg-lamp illuminations. This demonstrates the efficiency of light utilization of TNAs was improved by the modification with copper nanoparticles. The degradation rate of TCE in the anodic chamber is more effective than that in the cathodic chamber because of the synergistic effect of hydroxyl and sulfate radicals. The mechanism of TCE degradation via persulfate in the PEC system was proposed and discussed in detail.

Treatment of wastewater from petroleum industry: current practices and perspectives

Petroleum industry is one of the fastest growing industries, and it significantly contributes to economic growth in developing countries like India. The wastewater from a petroleum industry consist a wide variety of pollutants like petroleum hydrocarbons, mercaptans, oil and grease, phenol, ammonia, sulfide, and other organic compounds. All these compounds are present as very complex form in discharged water of petroleum industry, which are harmful for environment directly or indirectly. Some of the techniques used to treat oily waste/wastewater are membrane technology, photocatalytic degradation, advanced oxidation process, electrochemical catalysis, etc. In this review paper, we aim to discuss past and present scenario of using various treatment technologies for treatment of petroleum industry waste/wastewater. The treatment of petroleum industry wastewater involves physical, chemical, and biological processes. This review also provides scientific literature on knowledge gaps and future research directions to evaluate the effect(s) of various treatment technologies available.

Oxidation of nine petroleum hydrocarbon compounds by combined hydrogen peroxide/sodium persulfate catalyzed by siderite

A system consisting of hydrogen peroxide/persulfate (H₂O₂/S₂O₈^2-) catalyzed by siderite was attempted to oxidize nine representative petroleum hydrocarbon compounds [benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, 1,2,4-trimethylbenzene, methyl-tert-butyl ether, and naphthalene] that tend to persist in the environment. Oxidation under different siderite dosages, H₂O₂:S₂O₈^2- ratios, and pH conditions were investigated. Results indicated that oxidation rates increased from 1.21-4.62 to 1.77-8.94 d^-1 as siderite increased from 0.16 to 0.48 g/40 mL (H₂O₂:Na₂S₂O₈ = 5:1, initial pH = 3.0), except for naphthalene (decreased from 0.58 to 0.45 d^-1 with increased siderite dosage). When the H₂O₂:S₂O₈^2- ratio was increased from 1:1 to 5:1 (siderite = 0.16 g, initial pH = 3.0), the oxidation rates increased from 0.02-0.73 to 0.33-2.19 d^-1. However, as pH increased to > 5.5 (siderite = 0.16 g, H₂O₂:Na₂S₂O₈ = 2.5:1), the oxidation rates of petroleum hydrocarbons decreased to 0.003-0.09 d^-1, which was approximately 90% less than that at pH = 3.0. The partial correlations and principal component analysis of the experimental data were conducted. Overall, both siderite dosage and H₂O₂:S₂O₈^2- ratio correlated positively with oxidation efficiency. The oxidation potential by H₂O₂/S₂O₈^2- mixtures towards the target petroleum hydrocarbon compounds seemed to be more sensitive to pH conditions than to siderite dosages or H₂O₂:S₂O₈^2- ratios.

Degradation of petroleum hydrocarbons in unsaturated soil and effects on subsequent biodegradation by potassium permanganate

To date, the oxidation of petroleum hydrocarbons using permanganate has been investigated rarely. Only a few studies on the remediation of unsaturated soil using permanganate can be found in the literature. This is, to the best of our knowledge, the first study conducted using permanganate pretreatment to degrade petroleum hydrocarbons in unsaturated soil in combination with subsequent bioaugmentation. The pretreatment of diesel-contaminated unsaturated soil with 0.5-pore-volume (5%) potassium permanganate (PP) by solution pouring and foam spraying (with a surfactant) achieved the total petroleum hydrocarbon (TPH) removal efficiencies of 37% and 72.1%, respectively. The PP foam, when coupled with bioaugmentation foam, further degraded the TPH to a final concentration of 438 mg/kg (92.1% total reduction). The experiment was conducted without soil mixing or disturbance. The relatively high TPH removal efficiency achieved by the PP-bioaugmentation serial foam application may be attributed to an increase in soil pH caused by the PP and effective infiltration of the remediation agent by foaming. The applied PP foam increased the pH of the acidic soil, thus enhancing microbial activity. The first-order biodegradation rate after PP oxidation was calculated to be 0.068 d^-1. Furthermore, 94% of the group of relatively persistent hydrocarbons (C₁₈-C₂₂) was removed by PP-bioaugmentation, as verified by chromatogram peaks. Some physicochemical parameters related to contaminant removal efficiency were also evaluated. The results reveal that PP can degrade soil TPH and significantly enhance the biodegradation rate in unsaturated diesel-contaminated soil when combined with bioaugmentation foam.

Effects of the structures and micropores of sedimentary organic matter on the oxidative degradation of benzo(a)pyrene by Na2S2O8

In this study, we investigated how the desorption and degradation processes of radiolabeled benzo[a]pyrene (BaP) that was aged in various marine sediments were influenced by sedimentary organic matter properties. The stable OC fraction (STOC) and the demineralized fraction (DM) were isolated and characterized via advanced solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR) and a CO₂ gas adsorption technique, respectively. Sodium persulfate preferentially removed the unstable OC fractions (USOC) and the aromatic C groups, and the residual STOC fractions were enriched with aliphatic C groups. The aliphatic C showed stronger resistance to degradation by persulfate than that of the aromatic C. A first-order kinetic model described the degradation process by sodium persulfate solutions very well (R² > 0.997). The desorption percentages, degradation percentages and rates k (h^-1) of BaP gradually decreased from the estuarine sediments to the offshore marine sediments and were highly significantly and negatively correlated with STOC-bulk, F_aliph-bulk, and V_o-bulk (R²>0.903, p < 0.01). It was demonstrated that sodium persulfate degraded not only desorbed BaP but also a portion of the bound BaP fraction that was difficult to desorb. The BaP fractions that sorbed on USOC were degraded initially; then, the fractions of BaP that were released from STOC were degraded. This study demonstrated the important roles of STOC, aliphatic moieties, and micropores in the degradation process of BaP during the Na₂S₂O₈ treatment of the sediments.

Thermally activated persulfate for the chemical oxidation of chlorinated organic compounds in groundwater

Chlorinated pesticides were extensively produced in the XX century, generating high amounts of toxic wastes often dumped in the surroundings of the production sites, resulting in hot points of soil and groundwater pollution worldwide. This is the case of Bailín landfill, located in Sabiñánigo (Spain), where groundwater is highly polluted with chlorobenzenes (mono, di, tri and tetra) and hexachlorocyclohexanes. This study addresses the abatement of chlorinated organic compounds (COCs) present in the groundwater coming from the Bailín landfill by thermally activated persulfate, PS (TAP). The influence of temperature (30-50 °C) and oxidant concentration (2-40 g L^-1) on the efficiency of COCs (initial concentration of COCs = 57.53 mg L^-1, determined by the solubility of the pollutants in water) degradation has been investigated. Raising the reaction temperature and PS concentration the degradation of COCs significantly accelerates, as a result of higher production of sulfate radicals. The thermal activation of PS implies side reactions, involving the unproductive decomposition of this oxidant. The activation energy calculated for this reaction (128.48 kJ mol^-1) reveals that is slightly more favored by temperature than the oxidation of COCs by sulfate radicals (102.4-115.72 kJ mol^-1). At the selected operating conditions (PS = 10 g L^-1, 40 °C), the almost complete conversion of COCs and a dechlorination and mineralization degree above 80% were obtained at 168 h reaction time. A kinetic model, able to adequately predict the experimental concentration of COCs when operating at different temperatures and initial concentration of PS has been proposed.