Remediation of a soil chronically contaminated with hydrocarbons through persulfate oxidation and bioremediation

Remediation of phenanthrene contaminated soil by persulphate coupled with Pseudomonas aeruginosa GZ7 based on oxidation prediction model

Chemical oxidation coupled with microbial remediation has attracted widespread attention for the removal of polycyclic aromatic hydrocarbons (PAHs). Among them, the precise evaluation of the feasible oxidant concentration of PAH-contaminated soil is the key to achieving the goal of soil functional ecological remediation. In this study, phenanthrene (PHE) was used as the target pollutant, and Fe2+-activated persulphate (PS) was used to remediate four types of soils. Linear regression analysis identified the following important factors influencing remediation: PS dosage and soil PHE content for PHE degradation, Fe2+ dosage, hydrolysable nitrogen (HN), and available phosphorus for PS decomposition. A comprehensive model of "soil characteristics-oxidation conditions-remediation effect" with a high predictive accuracy was constructed. Based on model identification, Pseudomonas aeruginosa GZ7, which had high PAHs degrading ability after domestication, was further applied to coupling repair remediation. The results showed that the optimal PS dose was 0.75% (w/w). The response relationship between soil physical, chemical, and biological indicators at the intermediate interface and oxidation conditions was analysed. Coupled remediation effects were clarified using microbial diversity sequencing. The introduction of Pseudomonas aeruginosa GZ7 stimulated the relative abundance of Cohnella, Enterobacter, Paenibacillus, and Bacillus, which can promote material metabolism and energy transformation during remediation.

Uncovering potential mangrove microbial bioindicators to assess urban and agricultural pressures on Martinique island in the eastern Caribbean Sea

Martinique's mangroves, which cover 1.85 ha of the island (<0.1 % of the total area), are considerably vulnerable to local urban, agricultural, and industrial pollutants. Unlike for temperate ecosystems, there are limited indicators that can be used to assess the anthropogenic pressures on mangroves. This study investigated four stations on Martinique Island, with each being subject to varying anthropogenic pressures. An analysis of mangrove sediment cores approximately 18 cm in depth revealed two primary types of pressures on Martinique mangroves: (i) an enrichment in organic matter in the two stations within the highly urbanized bay of Fort-de-France and (ii) agricultural pressure observed in the four studied mangrove stations. This pressure was characterized by contamination, exceeding the regulatory thresholds, with dieldrin, total DDT, and metals (As, Cu and Ni) found in phytosanitary products. The mangroves of Martinique are subjected to varying degrees of anthropogenic pressure, but all are subjected to contamination by organochlorine pesticides. Mangroves within the bay of Fort-de-France experience notably higher pressures compared to those in the island's northern and southern regions. In these contexts, the microbial communities exhibited distinct responses. The microbial biomass and the abundance of bacteria and archaea were higher in the two less-impacted stations, while in the mangrove of Fort-de-France, various phyla typically associated with polluted environments were more prevalent. These differences in the microbiota composition led to the identification of 65 taxa, including Acanthopleuribacteraceae, Spirochaetaceae, and Pirellulaceae, that could potentially serve as indicators of an anthropogenic influence on the mangrove sediments of Martinique Island.

Sequential oxidation-composting-phytoremediation treatment for the management of an oily sludge from petroleum refinery

Oily sludges are generated in large quantities in petroleum refinery wastewater treatment plants. Given their complex composition, they are classified as hazardous waste. Selecting a single treatment technique for their remediation is challenging. This work aims to assess the extent of composting followed by phytoremediation on an oily sludge from an API separator unit, pre-treated by chemical oxidation with alkaline activated persulfate (PS). 18% of total petroleum hydrocarbons (TPH) were determined by IR spectroscopy. The aliphatic hydrocarbon content was 4714 ± 250 ppm by GC-FID, and aromatics were not detectable, suggesting a high amount of non-chromatographable complex hydrocarbons. The density of generalist and hydrocarbon-degrading populations of the oily sludge estimated by quantitative polymerase chain reaction (qPCR) evidenced an autochthonous microbiota with hydrocarbon-degrading capacity. The oxidative treatment with PS removed 31% of the TPH determined by IR after 20 days. The significant reduction of the native bacterial community was counterbalanced by coupling a composting treatment. Co-composting the sludge with goat manure and oat straw produced, after a year, a 96% reduction in TPH content, regardless of the oxidative pretreatment. Organic matter transformation was evidenced by the decrease of dissolved organic carbon (DOC) and the variation in E4/E6 ratio. The matrices obtained of composting were used as substrates for phytoremediation for 4 months. Ryegrass seeds were planted in both PS-treated and untreated sludge substrates. The presence of the plant grown in the pre-oxidised and composted substrate resulted in a higher aerial biomass of ryegrass (67%), an increase in enzymatic activities, and higher concentration of DOC, although without evidence of additional dissipation of TPH. The dynamics of the bacterial communities of the different substrates generated during the biological treatment were analyzed by Illumina NovaSeq DNA sequencing of 16S rRNA amplicons. The findings mirrored a succession compatible with that described in contaminated matrices, but also in other non-contaminated ones. According to these findings, an organic matter transformation process occurred, which included the complex hydrocarbons of the oily sludge, resulting in an active substrate that promoted the retention of nutrients and water and provided the necessary support for plant development.

Controllable chemical redox reactions to couple microbial degradation for organic contaminated sites remediation: A review

Global environmental concern over organic contaminated sites has been progressively conspicuous during the process of urbanization and industrial restructuring. While traditional physical or chemical remediation technologies may significantly destroy the soil structure and function, coupling moderate chemical degradation with microbial remediation becomes a potential way for the green, economic, and efficient remediation of contaminated sites. Hence, this work systematically elucidates why and how to couple chemical technology with microbial remediation, mainly focused on the controllable redox reactions of organic contaminants. The rational design of materials structure, selective generation of reactive oxygen species, and estimation of degradation pathway are described for chemical oxidation. Meanwhile, current progress on efficient and selective reductions of organic contaminants (i.e., dechlorination, defluorination, -NO2 reduction) is introduced. Combined with the microbial remediation of contaminated sites, several consideration factors of how to couple chemical and microbial remediation are proposed based on both fundamental and practical points of view. This review will advance the understanding and development of chemical-microbial coupled remediation for organic contaminated sites.

Activation of persulfate by g-C3N4/nZVI@SBC for degradation of total petroleum hydrocarbon in groundwater

In this study, we synthesized a high removal efficiency catalyst using biochar-supported nanoscale zero-valent iron and g-C3N4, denoted as g-C3N4/nZVI@SBC, to activate persulfate (PS) for the degradation of total petroleum hydrocarbon (TPH) in groundwater. We characterized the morphology and physiochemical properties of g-C3N4/nZVI@SBC with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), BET surface area analysis, and X-ray photoelectron spectroscopy (XPS). To assess the performance of the g-C3N4/nZVI@SBC catalyst, we investigated various reaction parameters, such as the mass ratio of g-C3N4 to nZVI@SBC, PS concentration, initial pH, initial TPH concentration, and the presence of coexisting ions in the system. The results from batch experiments and repeated use trials indicate that g-C3N4/nZVI@SBC exhibited both excellent catalytic activation capability and impressive durability, making it a promising choice for TPH degradation. Specifically, when the PS concentration reached 1 mM, the catalyst dosage was 0.3 g/L, and the g-C3N4 to nZVI@SBC mass ratio was 2, we achieved a remarkable TPH removal efficiency of 93.8%. Through electron paramagnetic resonance (EPR) testing and quenching experiments, we identified sulfate radicals, hydroxyl radicals, and superoxide radicals as the primary active substance involved in the TPH degradation process. Moreover, the g-C3N4/nZVI@SBC composite proved highly effective for in-situ TPH removal from groundwater and displayed an 86% removal rate, making it a valuable candidate for applications in permeable reactive barriers (PRB) aimed at enhancing environmental remediation. In summary, by skillfully utilizing g-C3N4/nZVI@SBC, this study has made notable advancements in synthesis and characterization, presenting a feasible and innovative approach to addressing TPH pollution in groundwater.

Remediation of crude oil contaminated soil through an integrated biological-chemical-biological strategy

A plausible approach to remediating petroleum contaminated soil is the integration of chemical and biological treatments. Using appropriate chemical oxidation, the integrated remediation can be effectively achieved to stimulate the biodegradation process, consequently bolstering the overall remediation effect. In this study, an integrated biological-chemical-biological strategy was proposed. Both conventional microbial degradation techniques and a modified Fenton method were employed, and the efficacy of this strategy on crude oil contaminated soil, as well as its impact on pollutant composition, soil environment, and soil microorganism, was assessed. The results showed that this integrated remediation realized an overall 68.3 % removal rate, a performance 1.7 times superior to bioremediation alone and 2.1 times more effective than chemical oxidation alone, elucidating that the biodegradation which had become sluggish was invigorated by the judicious application of chemical oxidation. By optimizing the positioning of chemical treatment, the oxidization was allowed to act predominantly on refractory substances like resins, thus effectively enhancing pollutant biodegradability. Concurrently, this oxidating maneuver contributed to a significant increase in concentrations of dissolvable nutrients while maintaining appropriate soil pH levels, thereby generating favorable growth conditions for microorganism. Moreover, attributed to the proliferation and accumulation of degrading bacteria during the initial bioremediation phase, the microbial growth subsequent to oxidation showed rapid resurgence and the relative abundance of typical petroleum-degrading bacteria, particularly Proteobacteria, was substantially increased, which played a significant role in enhancing overall remediation effect. Our research validated the feasibility of biological-chemical-biological strategy and elucidated its correlating mechanisms, presenting a salient reference for the further studies concerning the integrated remediation of petroleum contaminated soil.

Remediation of benzo[a]pyrene contaminated soils by moderate chemical oxidation coupled with microbial degradation

Chemical oxidation is a promising technology for the remediation of organics-contaminated soils. However, residual oxidants and transformation products have adverse effects on microbial activities. This work aimed at moderate chemical oxidation coupled with microbial degradation (MOMD) for the removal of benzo[a]pyrene (BaP) by optimizing the type and dosage of oxidants. Potassium permanganate (KMnO₄), Fe²⁺ + sodium persulfate (Fe²⁺ + PS), Fenton's reagent (Fe²⁺ + H₂O₂), and hydrogen peroxide (H₂O₂) were compared for BaP removal from loam clay and sandy soils. Overall, the removal efficiency of BaP by a moderate dose of oxidant coupled indigenous microorganism was slightly lower than that by a high dose of relevant oxidant. The contributions of microbial degradation to the total removal of BaP varied for different oxidants and soils. The removal efficiency of BaP from loam clay sandy soil by a moderate dose of KMnO₄ (25 mmol/L) was 94.3 ± 1.1 % and 92.5 ± 1.8 %, respectively, which were both relatively higher than those under other conditions. The indirect carbon footprint yielded by the moderate dose of oxidants was 39.2-72.8 % less than that by the complete oxidation. A moderate dose of oxidants also reduced disturbances to soil pH and OC. The microbial communities after MOMD treatment were dominated by Burkholderiaceae, Enterobacteriaceae, Alicyclobacillaceae, and Oxalobacteraceae. These dominant microorganisms promoted the removal of BaP through the expression of polycyclic aromatic hydrocarbon-ring hydroxylated dioxygenase gene. Compared with complete chemical oxidation, MOMD is also a promising technique with the utilization of indigenous microorganism for remediating BaP-contaminated soils.

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.

Bioremediation of Polycyclic Aromatic Hydrocarbons in Contaminated Soils Using Vermicompost

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils are reported in many literatures. Composting, in addition to bioremediation, can simultaneously increase soil organic matter content and soil fertility and is thus regarded as one of the most cost-effective methods of soil remediation. In this study, biodegradation of phenanthrene (PHE) and pyrene (PYR) is reported by microbial consortia enriched by vermicompost. After soil samples preparation and grinding, the samples were contaminated with 100, 200, and 300 mg/kg of PHE and PYR concentrations and inoculated with three concentrations (2, 4, and 6 wt.%) of vermicompost. PHE and PYR concentrations were analyzed by HPLC during bioremediation. After 70 days, two highly capable microbial consortia were used to remove the pollutants in bioaugmentation conditions. Analysis of their microbial composition revealed that the consortia contain several Proteobacteria phylum bacterial species, and the most common genera were Pseudomonas and Citrobacter. Decontamination rates for PHE and PYR were estimated to be 89% and 83% over 45 days, respectively. Biodegradation kinetics revealed that microbial degradation followed a first-order kinetics. This study provides clear evidence on the biodegradation of PHE and PYR, paving the way for the development of bioremediation technologies for the recovery of polluted ecosystems.

Development and microbial characterization of Bio-RD-PAOP for effective remediation of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) as typical halogenated persistent organic pollutants are widely distributed in natural environments, and can be enriched and magnified in organisms via food webs. It is consequently urgent and necessary to develop techniques to completely remove these persistent organohalides. In this study, we developed a process (Bio-RD-PAOP) by integrating microbial reductive dechlorination (Bio-RD) with subsequent persulfate activation and oxidation process (PAOP) for effective remediation of PCBs. Results showed the synergistic combination of advantages of Bio-RD and PAOP in dechlorination of higher-chlorinated PCBs and of PAOP in degradation/mineralization of lower-chlorinated PCBs, respectively. For the PAOP, both experimental evidences and theoretical calculations suggested that degradation rate and efficiency decreased with the increased PCB chlorine numbers. Relative to the Bio-RD and PAOP, Bio-RD-PAOP had significantly higher PCB removal efficiencies, of which values were PCB congener-specific. For example, removal efficiency of Bio-RD-PAOP in removing PCB88 is 2.50 and 1.86 times of that of Bio-RD and PAOP, respectively. In contrast, the efficiency is 1.66 and 3.35 times of Bio-RD and PAOP, respectively, for PCB180 removal. The PAOP-derived oxidizing species (mainly sulfate free radical) significantly decreased microbial abundance, particularly of the organohalide-respiring Dehalococcoides. Notably, co-existence of other microorganisms alleviated the inhibitive effect of oxidizing species on the Dehalococcoides, possibly due to formation of microbial flocs or biofilm. This study provided a promising strategy for extensive remediation of organohalide-contaminated sites, as well as new insight into impact of PAOP-derived oxidizing species on the organohalide-respiring community.

Spectroscopic characterization of soil dissolved organic matter during dielectric barrier discharge (DBD) plasma treatment: Effects of discharge power, atmosphere and soil moisture content

Non-thermal plasma (NTP) technology is an emerging advanced oxidation process, which has shown excellent performances in soil organic pollution remediation. Dissolved organic matter (DOM) is one of the most important components in soil, however, investigations on the structural and compositional changes of DOM during NTP process are lacking. Therefore, in the present study, we systematically investigated the soil DOM changes under different discharge voltages, atmospheres or soils with different moisture contents. The results indicated that after NTP treatment, substantial soil organic matters were released and dissolved in water. For instance, the DOC value of DOM increased dramatically from 21.1 to 197.3 mg L^-1 after being discharged for 120 min under the discharge voltage of 80 V. The UV-Vis characterization results indicated the significant increase of hydrophilicity, and decreases of aromaticity and molecular weight for soil DOM during the initial discharge period. However, long time discharge resulted in slight recovery of aromaticity and hydrophobicity, possibly due to the dehydration and re-condensation of small molecules. EEM-FRI results indicated that the total fluorescence intensity of DOM decreased obviously, indicating the destruction of fluorescent dissolved organic matter (FDOM). While the proportions of humic-like and microbial byproduct-like substances increased, indicating that those substances were more recalcitrant under NTP treatment compared with fulvic acid-like and aromatic protein-like substances. Four fluorescence components were identified by PARAFAC, and microbial and terrestrial humic-like substances were more difficult to degrade compared to other humic-like substances and fulvic acid-like substances. Additionally, discharge voltage and atmosphere had great influences on DOM changes, while the impact of soil moisture content was not significant. Overall, this study provided insights into the DOM changes during NTP process, which is valuable for more comprehensive evaluation of the NTP technique application in practical soil remediation.

Mechanistic insights into ball milling enhanced montmorillonite modification with tetramethylammonium for adsorption of gaseous toluene

Montmorillonite is widely used for pollutants adsorption due to its porous structure and low price. However, the low specific surface area and small porosity limit its application in gas adsorption field. In this study, montmorillonite was organically modified using a facile dry ball milling method by tetramethylammonium bromide. The adsorption behaviour of toluene as a model VOC compound on organic montmorillonite was systematically investigated through adsorption breakthrough curves, adsorption kinetics and isotherms. After modification by ball milling, the specific surface area of ball milling with tetramethylammonium bromide for montmorillonite modification (BMTMt) was increased from 20.6 m²/g to 186.4 m²/g, and the microporosity proportion was up to 47%. Dynamic adsorption experiments showed that the best performance of BMTMt for toluene (55.9 mg/g) was 6 times higher than that of original montmorillonite (8.8 mg/g). Compared with the water bath preparation method, ball milling method promoted the intercalation of tetramethylammonium bromide into the layers of montmorillonite, resulting in a higher proportion of micropores. Density functional theory calculations indicated that the interaction between tetramethylammonium bromide and montmorillonite was mainly electrostatic forces, and the enhanced adsorption performance for toluene was mainly through microporous filling. BMTMt was proved to be a promising adsorbent for VOCs removal.

A novel chitosan-urea encapsulated material for persulfate slow-release to degrade organic pollutants

A novel eco-friendly material (CS-U@PS) for persulfate slow-release to effectively degrade organic pollutants (methyl orange and pyrene) was synthesized using chitosan and urea as the encapsulated framework materials via an emulsion cross-linking method for the first time. The obtained CS-U@PS exhibits spherical shapes with a uniform size of approximately 2-3 µm according to the particle-size distribution and SEM image results. The slow-release mechanism was proposed through a kinetics model study and the Ritger-Peppas model fit well (r² = 0.9699) to indicate that the slow-release process is non-Fickian diffusion. The influences of urea and PS dosages and oxidative conditions on methyl orange degradation were studied, and all the results suggested that urea played an important role in PS slow-release and can also catalyze the activation of PS by iron to further produce radicals and improve the removal efficiency of pollutants. A pyrene removal rate of 90.53% was achieved in aqueous solutions and an above 80% removal rate was obtained in weakly acidic or neutral soil environments by CS-U@PS activated by Fe²⁺ with citric acid as the chelating agent. Therefore, the fabricated slow-release oxidation materials exhibit application potential for the remediation of organic polluted groundwater and soil.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Degradation of organic contaminants in marine sediments by peroxymonosulfate over LaFeO3 nanoparticles supported on water caltrop shell-derived biochar and the associated microbial community responses

Sediment is an important final repository of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Herein, a novel catalyst of LaFeO₃ nanoparticles supported on biochar was synthesized from water caltrop shell by chemical precipitation. The composite (LFBC) was used as peroxymonosulfate (PMS) activator to oxidize PAHs in real marine sediments. Systematic surface characterization confirmed the immobilization of well crystalline nano LaFeO₃ particles onto the biochar surface. Under optimal conditions, i.e., [PMS] = 3 × 10^-4 M, [LFBC] = 0.75 g/L, pH 6.0, and seawater, the total PAH degradation efficiency was 90%, while that of 2-, 3-, 4-, 5-, and 6-ring PAHs was 52%, 61%, 66%, 56%, and 29%, respectively, in 24 h. The Langmuir-Hinshelwood equation better predicted the PAHs degradation kinetics over LFBC by PMS. Interactions between surface oxygen species at LaFeO₃ defective sites and the graphitized biochar network facilitated the PAHs degradation. Furthermore, changes in the bacterial community during the LFBC/PMS treatment were highlighted to assess the sustainable development of the sediment ecosystem. The LFBC/PMS process enhanced the biological richness and diversity of sediment eco-systems. The major phylum was Proteobacteria initially, while Hyphomonas was the genera after LFBC/PMS treatment of the sediment.

Phytoremediation of pyrene-contaminated soils: A critical review of the key factors affecting the fate of pyrene

Soil contamination by pyrene has increased over the years due to human-related activities, urgently demanding for remediation approaches to ensure human and environment safety. Within this frame, phytoremediation has been successfully applied over the years due to its green and cost-effectiveness features. The scope of this review includes the main phytoremediation mechanisms correlated with the removal of pyrene from contaminated soils and sediments to highlight the impact of different parameters and the supplement of additives on the efficiency of the treatment. Soil organic matter (SOM), plant species, aging time, environmental parameters (pH, soil oxygenation, and temperature) and bioavailability are among the main parameters affecting pyrene removal through phytoremediation. Phytoextraction only accounts for a small part of the entire phytoremediation process, but the addition of surfactants and chelating agents in planted soils could increase pyrene accumulation in plant tissues by 20% as a consequence of the increased pyrene bioavailability. Rhizodegradation is the main phytoremediation mechanism involved due to the activity of bacteria capable of degrading pyrene in the root area. Inoculated-planted soil treatments have the potential to decrease pyrene accumulation in shoots and roots by approximately 30 and 40%, respectively, further stimulating the proliferation of pyrene-degrading bacteria in the rhizosphere. Plant-fungi symbiotic association results in an enhanced accumulation of pyrene in shoots and roots of plants as well as a higher biodegradation. Finally, pyrene removal from soil can be improved in the presence of amendments, such as natural non-ionic surfactants, biochar, and bacterial mixtures.

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.

Effects of organic matter addition on chronically hydrocarbon-contaminated soil

Soil is the recipient of organic pollutants as a consequence of anthropogenic activities. Hydrocarbons are contaminants that pose a risk to human and environmental health. Bioremediation of aging contaminated soils is a challenge due to the low biodegradability of contaminants as a result of their interaction with the soil matrix. The aim of this work was to evaluate the effect of both composting and the addition of mature compost on a soil chronically contaminated with hydrocarbons, focusing mainly on the recovery of soil functions and transformations of the soil matrix as well as microbial community shifts. The initial pollution level was 214 ppm of polycyclic aromatic hydrocarbons (PAHs) and 2500 ppm of aliphatic hydrocarbons (AHs). Composting and compost addition produced changes on soil matrix that promoted the release of PAHs (5.7 and 15 % respectively) but not the net PAH elimination. Interestingly, composting stimulated AHs elimination (about 24 %). The lack of PAHs elimination could be attributed to the insufficient PAHs content to stimulate the microbial degrading capacity, and the preferential consumption of easily absorbed C sources by the bacterial community. Despite the low PAH catabolic potential of the aging soil, metabolic shift was driven by the addition of organic matter, which could be monitored by the ratio of Proteobacteria to Actinobacteria combined with E₄/E₆ ratio. Regarding the quality of the soil, the nutrients provided by the exogenous organic matter contributed to the recovery of the global functions and species diversity of the soil along with the reduction of phytotoxicity.

Iron-based persulfate activation process for environmental decontamination in water and soil

Sulfate radical based advanced oxidation processes have been extensively studied for the degradation of environmental contaminants. Iron-based materials such as ferrous, ferric, ZVI, iron oxides, sulfides etc., and various natural iron minerals have been explored for activating persulfate to generate sulfate radicals. In this review, an overview of different iron activated persulfate systems and their application in the removal of organic pollutants and metals in water and soil are summarised. The chemistry behind the activation of persulfate by homogenous and heterogeneous iron-based materials with/without the assistance of electrochemical techniques are also discussed. Besides, the soil decontamination by iron persulfate system and a brief discussion on the ability of the persulfate system to reduce metals presence in wastewater are also summarised. Finally, future research prospects, believed to be useful for all researchers in this field, based on up to date research progress is also given.

Remediation of PBDEs-metal co-contaminated soil by the combination of metal stabilization, persulfate oxidation and bioremediation

Laboratory experiments were performed to investigate the efficiency of a simultaneous metal stabilization, persulfate oxidation and bioremediation for decontaminating polybrominated diphenyl ethers (PBDEs) and toxic metals from an actual soil polluted by the recycling activity of electronic waste. Biochar and bentonite were applied to the soil for immobilizing heavy metals (Cu, Pb, Zn and Ni). It was found that the toxicity level declined most significantly in the case of 20 g/kg biochar +20 g/kg bentonite. A low dose of persulfate (20 mmol/kg soil) was found to be suitable for oxidizing soil PBDEs and enhancing the bioavailability of PBDEs residue. Persulfate oxidation reduced the soil organic matter content, and caused dramatic decrease of bacterial density. Nevertheless, microbial activity and number recovered on the whole during 90 days of bioremediation. Finally, a degradation efficiency of 94.6% and a mineralization efficiency of 60.3% were obtained by the hybrid treatment scheme. The pyrosequencing analysis indicates that soil bacterial community changed obviously during the treatments, and there was an enrichment of PBDE-degrading populations during bioremediation relative to that of oxidized soil.

AOPs-based remediation of petroleum hydrocarbons-contaminated soils: Efficiency, influencing factors and environmental impacts

Petroleum hydrocarbons are a class of anthropogenic compounds including alkanes, aromatic hydrocarbons, resins, asphaltenes and other organic matters, and soil pollution caused by petroleum hydrocarbons has drawn increasing interest in recent years. Multiple advanced oxidation processes (AOPs) are emerging to remediate petroleum hydrocarbons-contaminated soils, while very few studies have focused on the features of AOPs applied in soils. This review aims to provide an updated overview of the state of the science about the efficiency, influencing factors and environmental implications of AOPs. The key findings from this review include: 1) cyclodextrin and its derivatives can be used to synthesize targeting reagents; 2) soil organic matter (SOM), glucose and cement can activate persulfate; 3) SOM affects redox circumstance in soil and could be further developed for enhancing the catalysis effect of transition metals; 4) non-thermal plasma and wet oxidation are promising methods of AOPs to remove petroleum hydrocarbons from soil; 5) the occurrence, fate, and transformation of intermediates during the degradation of petroleum hydrocarbons in soil should be considered more. Overall, this review reveals an urgent need to develop the cost-effective remedial strategies for petroleum hydrocarbons contaminated soils, and to advance our knowledge on the generation, transport and propagation of radicals in soils.

Co-treatment of an oily sludge and aged contaminated soil: permanganate oxidation followed by bioremediation

The bioremediation of an oily sludge (321 ± 30 mg of polycyclic aromatic hydrocarbons/kg_{DRY SLUDGE} and 13420 ± 1300 mg of aliphatic hydrocarbons/kg_{DRY SLUDGE}) by mixture with contaminated soil (23 ± 2 mg of polycyclic aromatic hydrocarbons/kg_{DRY SOIL} and 98 ± 10 mg of aliphatic hydrocarbons/kg_{DRY SOIL}) was studied. Furthermore, the effect of oxidative pretreatments (persulfate and permanganate) on the performance of the global process was examined. The treatments reached contamination levels lower than the original residues, indicating the presence of synergic processes between a highly contaminated sludge and soil with a selected hydrocarbon-degrading community. Pretreatment with permanganate significantly improved biodegradation, possibly due to the increase in bioavailability and biodegradability of petroleum hydrocarbons. Two months of incubation was enough to reach the complete elimination of polycyclic aromatic hydrocarbons and 92% elimination of aliphatic hydrocarbons. Monitoring using five parameters (concentration of total petroleum hydrocarbons, total cultivable heterotrophic bacteria count, lipase and dehydrogenase activities, and polycyclic aromatic hydrocarbon-degrading bacteria count) as an approach for a preliminary scanning of the effectiveness of a treatment is proposed based on principal components analysis.

Monitoring, assessment, and prediction of microbial shifts in coupled catalysis and biodegradation of 1,4-dioxane and co-contaminants

Microbial community dynamics were characterized following combined catalysis and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Although a few specific bacterial taxa are capable of removing 1,4-dioxane and individual CVOCs, many microorganisms are inhibited when these contaminants are present in mixtures. Chemical catalysis by tungstated zirconia (WO_x/ZrO₂) and hydrogen peroxide (H₂O₂) as a non-selective treatment was designed to achieve nearly 20% 1,4-dioxane and over 60% trichloroethene and 50% dichloroethene removals. Post-catalysis, bioaugmentation with 1,4-dioxane metabolizing bacterial strain,Pseudonocardia dioxanivorans CB1190, removed the remaining 1,4-dioxane. The evolution of the microbial community under different conditions was time-dependent but relatively independent of the concentrations of contaminants. The compositions of microbiomes tended to be similar regardless of complex contaminant mixtures during the biodegradation phase, indicating a r-K strategy transition attributed to the shock experienced during catalysis and the subsequent incubation. The originally dominant genera Pseudomonas and Ralstonia were sensitive to catalytic oxidation, and were overwhelmed by Sphingomonas, Rhodococcus, and other catalyst-tolerant microbes, but microbes capable of biodegradation of organics thrived during the incubation. Methane metabolism, chloroalkane-, and chloroalkene degradation pathways appeared to be responsible for CVOC degradation, based on the identifications of haloacetate dehalogenases, 2-haloacid dehalogenases, and cytochrome P450 family. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase that were in line with shifting predominant genera, confirming the deterministic processes guiding the microbial assembly. Collectively, this study demonstrated that catalysis followed by bioaugmentation is an effective treatment for 1,4-dioxane in the presence of high CVOC concentrations, and it enhanced our understanding of microbial ecological impacts resulting from abiotic-biological treatment trains. These results will be valuable for predicting treatment synergies that lead to cost savings and improve remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

Removal of polycyclic aromatic hydrocarbons (PAHs) and the response of indigenous bacteria in highly contaminated aged soil after persulfate oxidation

Integrated chemical-biological treatment is a promising alternative to remove PAHs from contaminated soil, wherein indigenous bacteria is the key factor for the biodegradation of residual PAHs after the application of chemical oxidation. However, systematical study on the impact of persulfate (PS) oxidation on indigenous bacteria as well as PAHs removal is still scarce. In this study, the influences of different PS dosages (1%, 3%, 6%, and 10% [w/w]), as well as various activation methods (native iron, H₂O₂, alkaline, ferrous iron, and heat) on PAHs removal and indigenous bacteria in highly contaminated aged soil were investigated. Apparent degradation of PAHs in the soil treated with PS oxidation was observed, and the removal efficiency of total PAHs in the soil ranged from 38.28% to 79.97%. The removal efficiency of total PAHs in the soil increased with increasing consumption of PS. However, the bacterial abundance in soil was negatively affected following oxidation for all of the treatments added with PS, with bacterial abundance in the soil decreased by 0.89-2.93 orders of magnitude compared to the untreated soil. Moreover, the number of total bacteria in the soil decreased as PS consumption increased. Different PS activation methods and PS dosages exhibited different influences on the bacterial community composition. Bacteria capable of degrading PAHs under anoxic conditions were composed predominantly by Proteobacteria and Firmicutes. The total amount of Proteobacteria and Firmicutes also decreased with increasing consumption of PS. The results of this study provide important insight for the design of PAHs contaminated soil remediation projects.

Potential of Bioremediation and PGP Traits in Streptomyces as Strategies for Bio-Reclamation of Salt-Affected Soils for Agriculture

Environmental limitations influence food production and distribution, adding up to global problems like world hunger. Conditions caused by climate change require global efforts to be improved, but others like soil degradation demand local management. For many years, saline soils were not a problem; indeed, natural salinity shaped different biomes around the world. However, overall saline soils present adverse conditions for plant growth, which then translate into limitations for agriculture. Shortage on the surface of productive land, either due to depletion of arable land or to soil degradation, represents a threat to the growing worldwide population. Hence, the need to use degraded land leads scientists to think of recovery alternatives. In the case of salt-affected soils (naturally occurring or human-made), which are traditionally washed or amended with calcium salts, bio-reclamation via microbiome presents itself as an innovative and environmentally friendly option. Due to their low pathogenicity, endurance to adverse environmental conditions, and production of a wide variety of secondary metabolic compounds, members of the genus Streptomyces are good candidates for bio-reclamation of salt-affected soils. Thus, plant growth promotion and soil bioremediation strategies combine to overcome biotic and abiotic stressors, providing green management options for agriculture in the near future.

Hazardous waste treatment technologies

This is a review of the literature published in 2018 on topics related to hazardous waste management in water, soils, sediments, and air. The review covers treatment technologies applying physical, chemical, and biological principles for contaminated water, soils, sediments, and air. PRACTITIONER POINTS: The management of waters, wastewaters, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) was reviewed according to the technology applied, namely, physical, chemical and biological methods. Physical methods for the management of hazardous wastes including adsorption, coagulation (conventional and electrochemical), sand filtration, electrosorption (or CDI), electrodialysis, electrokinetics, membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, persulfate-based, Fenton and Fenton-like, and potassium permanganate processes for the management of hazardous were reviewed. Biological methods such as aerobic, anaerobic, bioreactor, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed.

Effect of various chemical oxidation reagents on soil indigenous microbial diversity in remediation of soil contaminated by PAHs

Chemical oxidation is a promising pretreatment step coupled with bioremediation for removal of polycyclic aromatic hydrocarbons (PAHs). The effectiveness of Fenton, modified Fenton, potassium permanganate and activated persulfate oxidation treatments on the real contaminated soils collected from a coal gas plant (263.6 ± 73.3 mg kg^-1 of the Σ16 PAHs) and a coking plant (385.2 ± 39.6 mg kg^-1 of the Σ16 PAHs) were evaluated. Microbial analyses showed only a slight impact on indigenous microbial diversity by Fenton treatment, but showed the inhibition of microbial diversity and delayed population recovery by potassium permanganate reagent. After potassium permanganate treatment, the microorganism mainly existed in the soil was Pseudomonas or Pseudomonadaceae. The results showed that total organic carbon (TOC) content in soil was significantly increased by adding modified Fenton reagent (1.4%-2.3%), while decreased by adding potassium permanganate (0.2%-1%), owing to the nonspecific and different oxidative properties of chemical oxidant. The results also demonstrated that the removal efficiency of total PAHs was ordered: permanganate (90.0%-92.4%) > activated persulfate (81.5%-86.54%) > modified Fenton (81.5%-85.4%) > Fenton (54.1%-60.0%). Furthermore, the PAHs removal efficiency was slightly increased on the 7th day after Fenton and modified Fenton treatments, about 14.6%, and 14.4% respectively, and the PAHs removal efficiency only enhanced 4.1% and 1.3% respectively from 1st to 15th day after potassium permanganate and activated persulfate treatments. The oxidants greatly affect the growth of soil indigenous microbes, which cause further influence for PAHs degradation by bioremediation.

The relief effects of organic acids on Scirpus triqueter L. under pyrene-lead stress

During phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals, the phytoremediation plants are often stressed by pollutants, which would reduce the efficiency of phytoremediation. The addition of organic acids from root exudates could alleviate the stress. In this study, three organic acids (citric acid, succinic acid, glutaric acid) were added to investigate the effects of organic acids on the stress response of Scirpus triqueter L. at two pyrene-lead concentrations. The activities of reactive oxygen species, malondialdehyde, plasma membrane H⁺-ATPase, and vacuolar H⁺-ATPase and PPase activity, as well as the activities of antioxidant enzymes (SOD, POD, and CAT) in Scirpus triqueter L. were determined. The addition of organic acids could effectively reduce the activities of reactive oxygen species, malondialdehyde, plasma membrane H⁺-ATPase, and vacuolar H⁺-ATPase and PPase activities. Under higher pollution, the damage of plant plasma membrane is more serious, but the addition of citric acid can alleviate this situation and even more effective than the relief under low pollution. The effect of citric acid was more significant than that of succinic acid and glutaric acid. These results demonstrated that organic acids could attenuate the stress of pyrene and lead to Scirpus triqueter L.

Response and recovery of microbial communities subjected to oxidative and biological treatments of 1,4-dioxane and co-contaminants

Microbial community dynamics were characterized following combined oxidation and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Bioremediation is generally inhibited by co-contaminate CVOCs; with only a few specific bacterial taxa reported to metabolize or cometabolize 1,4-dioxane being unaffected. Chemical oxidation by hydrogen peroxide (H₂O₂) as a non-selective treatment demonstrated 50-80% 1,4-dioxane removal regardless of the initial CVOC concentrations. Post-oxidation bioaugmentation with 1,4-dioxane metabolizer Pseudonocardia dioxanivorans CB1190 removed the remaining 1,4-dioxane. The intrinsic microbial population, biodiversity, richness, and biomarker gene abundances decreased immediately after the brief oxidation phase, but recovery of cultivable microbiomes and a more diverse community were observed during the subsequent 9-week biodegradation phase. Results generated from the Illumina Miseq sequencing and bioinformatics analyses established that generally oxidative stress tolerant genus Ralstonia was abundant after the oxidation step, and Cupriavidus, Pseudolabrys, Afipia, and Sphingomonas were identified as dominant genera after aerobic incubation. Multidimensional analysis elucidated the separation of microbial populations as a function of time under all conditions, suggesting that temporal succession is a determining factor that is independent of 1,4-dioxane and CVOCs mixtures. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase, in line with the shifts of predominant genera and various developing directions during different steps of the treatment train. Collectively, this study demonstrated that chemical oxidation followed by bioaugmentation is effective for treating 1,4-dioxane, even in the presence of high levels of CVOC mixtures and residual peroxide, a disinfectant, and enhanced our understanding of microbial ecological impacts of the treatment train. These results will be valuable for predicting treatment synergies that lead to cost savings and improved remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

Identification of an intermediate for 1,8-dihydroxynaphthalene-melanin synthesis in a race-2 isolate of Fulvia fulva (syn. Cladosporium fulvum)

Fulvia fulva (syn. Cladosporium fulvum, Mycosphaerellaceae) is a dematiaceous fungus that causes tomato leaf mould. It is characterized by its biotrophic lifestyle and the synthesis of the bianthraquinone secondary metabolite, cladofulvin. The aim of the study was to characterize the dark pigment photochemically synthesized by F. fulva and to elucidate its biochemical pathway. We isolated a black pigment from in vitro cultures of the fungus. We determined the pigment to be 1,8-dihydroxynaphthalene (DHN)-melanin based on its chemical and photochemical characteristics, as well as the presence of flaviolin, when fungal reductases were inhibited by tricyclazole. Furthermore, the pks1 gene involved in pigment synthesis has a KS domain already associated with DHN-melanin. Our findings support the relevance of studying melanization in F. fulva.

Microbial Endophytes that Live within the Seeds of Two Tomato Hybrids Cultivated in Argentina

Tomato (Solanum lycopersicum L.) is probably the most important vegetable consumed around the world, and like other produce is affected by stresses and diseases that reduce the yield and production. The purpose of this work was to study the phytobiome of the tomato seeds of two hybrids in order to understand first of all whether tomato cultivars host similar groups of organisms, as well as their effect on the community structure, particularly of those microbes with the potential to promote growth and/or control plant pathogens. Different cultivars of tomato (genotypes) host significantly different endophytic communities, which is also reflected at the order level. These communities are particularly rich in spore-forming bacteria that have the ability either to promote plant growth or synthetize antimicrobial compounds that deter plant pathogens. We conclude that the seeds of the tomato cultivars Elpida and Silverio are sources of endophytic bacteria capable of synthetizing antifungal substances that could potentially be used for biocontrol against plant-pathogenic fungi.

Simultaneous removal of polycyclic aromatic hydrocarbon and heavy metals from an artificial clayey soil by enhanced electrokinetic method

Contamination of soil by a mixture of organic and non-organic pollutants due to various anthropogenic and natural causes is one of the most important issues in soil pollution. Generating a single layer of soil is a time-consuming process, and soil is a significant part of the environmental cycle; thus, protection and remediation of soil are of paramount importance. In this study, phenanthrene (PHE) as a representative for polycyclic aromatic hydrocarbon and lead (Pb), zinc (Zn), and nickel (Ni) as heavy metal pollutants were used because of their synergistic effects and abundant presence in soil. Soils with three different organic matter levels (OM0, OM1, and OM2) were prepared, spiked with pollutants, placed in electrokinetic cells, and remediated for 15 days. To improve the remediation process and increase the efficacy of pollutant removal, pH control methods and extracting agents were used. Two non-ionic surfactants, Tween 80 and Brij 35, and one chelating agent, EDTA, were utilized for this purpose. A total of nine tests were performed. The soil was divided into five equal sections at the end of each test, and the pH and concentration of pollutants were analyzed. Results indicated that the highest removal percentage of PHE was accomplished by Brij 35 (61%) in OM0. Increasing organic matter resulted in decreasing PHE removal. In this regard, Tween 80 showed enhanced performance. The order of removal of heavy metals was zinc > nickel > lead, and zinc had the highest removal rate of 61%.