Enhanced degradation of polycyclic aromatic hydrocarbons by indigenous microbes combined with chemical oxidation

Hybrid peroxymonosulfate/activated carbon fiber-sequencing batch reactor system for efficient treatment of coking wastewater: Establishment and influential factors

Coking wastewater contains high concentrations of toxic and low biodegradable organics, causing long hydraulic retention times for its biological treatment process. This study developed a pretreatment method for coking wastewater by using activated carbon fiber (ACF) activated peroxymonosulfate (PMS) to improve the treatment performance of subsequent biological post-treatment process, sequencing batch reactor (SBR). The results showed that, after optimization of treatment processes, the removal efficiency of chemical oxygen demand (COD), phenol, and chroma in coking wastewater reached to 76, 98, and 98%, respectively, with a significantly improved biodegradability. Compared with the sole SBR system without any pretreatment that could remove 73% of COD, the ACF/PMS+SBR system removed over 97% of COD in coking wastewater. Moreover, this pretreatment method facilitated the growth of functional bacteria for organics biodegradation, indicating its high potential as a highly efficacious pretreatment strategy to improve the overall treatment efficiency of coking wastewater.

An improved process for removal and recovery of heavy petroleum from solids using a ferrate-based hybrid oxidant

Persulfate oxidants are widely used in soil remediation and wastewater treatment but perform poorly in degrading polycyclic aromatic hydrocarbons (PAHs), especially heavy fractions in solids. Herein, we propose the utilization of a green peroxymonosulfate-ferrate-FeS (PFI) oxidant as a promising process aid for remediating soils contaminated with heavy petroleum components, including asphaltenes and resins. The PFI oxidant could degrade heavy petroleum fractions because of dual activation of the peroxymonosulfate and ferrate by FeS at ambient conditions. Nevertheless, when dealing with soil with high oil content (>10%), the degradation efficiency remains limited (<30%) regardless of the quantity of oxidants employed. Surface elemental analysis shows that a coating of secondary products (Fe(OH)3, Fe2O3) on the surface and in pores of the soil-pollutant matrix explains the failure of oxidation and inefficient use of oxidant. To address this issue, a strategy of pre-solvent extraction-oxidation hybrid process with sequent acidic washing is proposed, where dichloromethane serves as the solvent, and PFI acts as the oxidant. In this system over 90% of the oil could be recovered with an oxidation efficiency of 80% by alleviating the problem of iron oxide coating the matrix surface. The oxidant consumption is also reduced to 70 wt% of the sludge. The PFI oxidant is found to exhibit excellent universality in treating oily sludge with low petroleum content (<2%), reducing the petroleum content in the residue to less than 0.3 wt% (meeting the national standards). The degradation of low oil content sludge by the PFI oxidant followed pseudo first-order kinetics. These findings not only elucidate the failure of PFI oxidation for high oil content oily sludge and identify its potential engineering application range, but also offer a practical strategy for processing petroleum-contaminated soil with varying oil contents through wet oxidation.

A systematic review on enhancement strategies in biochar-based remediation of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are pervasive ecological pollutants produced essentially during the inadequate burning of organic materials. PAHs are a group of different organic compounds that are made out of various aromatic rings. PAHs pose a serious risk to humans and aquatic ecosystems because of their mutagenic and carcinogenic properties. In this way, there is a critical prerequisite to utilizing successful remediation strategies and methods to limit the dangerous effect of these pollutants on the ecosystem. Biochar has believed of intriguing properties such as simple manufacturing operations and more affordable and more productive materials. Biochar is a sustainable carbonaceous material that has an enormous surface area with bountiful functional groups and pore structure, which has huge potential for the remediation of toxic pollutants. This review emphasizes the occurrence, development, and fate of toxic PAHs in the environment. In the present review, the properties and role of biochar in the removal of PAHs were illustrated, and the influencing factors and an efficient key mechanism of biochar for the remediation of PAHs were discussed in detail. Various surface modification methods can be utilized to improve the biochar properties with the magnetization process; the advancements of modified biochar are pointed out in this review. Finally, the constraints and prospects for the large-scale application of biochar in the remediation of toxic pollutants are highlighted.

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.

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.

Effects of combined remediation of pre-ozonation and bioaugmentation on degradation of benzo[a]pyrene and microbial community structure in soils

The combination technique of pre-ozonation and bioaugmentation is promising for remediating benzo[a]pyrene (BaP)-contaminated soil. However, little is known about the effect of coupling remediation on the soil biotoxicity, soil respiration, enzyme activity, microbial community structure, and microbial in the process of remediation. This study developed two coupling remediation strategies (pre-ozonation coupled with bioaugmentation by addition of polycyclic aromatic hydrocarbons (PAHs) specific degrading bacteria or activated sludge), compared with sole ozonation and sole bioaugmentation, to improve degradation of BaP and recovery of soil microbial activity and community structure. Results showed that the higher removal efficiency of BaP (92.69-93.19%) was found in coupling remediation, compared with sole bioaugmentation (17.71-23.28%). Meanwhile, coupling remediation significantly reduced the soil biological toxicity, promoted the rebound of microbial counts and activity, and recovered the species numbers and microbial community diversity, compared with sole ozonation and sole bioaugmentation. Besides, it was feasible to replace microbial screening with activated sludge, and coupling remediation by addition of activated sludge was more conducive to the recovery of soil microbial communities and diversity. This work provides a strategy of pre-ozonation coupled with bioaugmentation to further degrade BaP in soil by promoting the rebound of microbial counts and activity, as well as the recovery of species numbers and microbial community diversity.

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.

Insights into the effects of Fenton oxidation on PAH removal and indigenous bacteria in aged subsurface soil

Combined chemical oxidation and bioremediation is a promising method of treating polycyclic aromatic hydrocarbon (PAH) contaminated soil, wherein indigenous soil bacteria play a critical role in the subsequent biodegradation of PAHs after the depletion of the oxidant. In this study, different Fenton conditions were applied by varying either the oxidation mode (conventional Fenton (CF), Fenton-like (LF), modified Fenton (MF), and graded modified Fenton (GMF)) or the H₂O₂ dosage (0%, 3%, 6%, and 10% (v/v)) to treat PAH contaminated soil. The results revealed that when equal dosages of H₂O₂ are applied, PAHs are significantly removed following oxidation treatment, and the removal percentages obeyed the following sequence: CF > GMF > MF > LF. In addition, higher dosages of H₂O₂ improved the PAH removal from soil treated with the same oxidation mode. The ranges of total PAHs removal efficiencies in the soil added 3%, 6%, and 10% of H₂O₂ (v/v) were 18.04%∼59.48%, 31.88%∼71.83%, and 47.56%∼78.16%, respectively. The PAH removal efficiency decreased with increasing ring numbers for the same oxidation treatment. However, the negative influences on soil bacterial abundance, community composition, and function were observed after Fenton treatment. After Fenton oxidation, the bacterial abundance in the soil received 3%, 6%, and 10% of H₂O₂ (v/v) decreased 1.96-2.69, 2.44-3.22, and 3.09-3.42 orders of magnitude compared to the untreated soil. The soil bacterial abundance tended to be impacted by the oxidation mode and H₂O₂ dosage simultaneously. While the main factor influencing the soil bacterial community composition was the H₂O₂ dosages. The results of this study showed that different oxidation mode and H₂O₂ dosage exhibited different effects on PAHs removal and soil bacteria (including abundance, community composition, and function), and there was a trade-off between the removal of PAHs and the adverse impact on soil bacteria.

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.

Effect of Fe3O4 nanoparticles exposure on the treatment efficiency of phenol wastewater and community shifts in SBR system

Increasing magnetic Fe₃O₄ nanoparticles (Fe₃O₄ NPs) application has aroused concern about its potential environmental toxicity. During acute and chronic exposure, key enzymes involved in phenol biodegradation were promoted at 0-600 mg/L Fe₃O₄ NPs, while were inhibited at 800 mg/L Fe₃O₄ NPs, correspondingly affected phenol degradation efficiency. Lactic dehydrogenase (LDH) increased when Fe₃O₄ NPs exceeded 600 mg/L, indicated the more severe cell rupture at high Fe₃O₄ NPs concentration. At the same Fe₃O₄ NPs concentration, the removal of EPS further inhibited key enzymes, decreased phenol degradation, and increased LDH, indicating that the existence of EPS relieved the adverse effects on microorganisms. Spectroscopic analysis showed that protein and polysaccharide associated bonds in EPS decreased at 0-600 mg/L Fe₃O₄ NPs, while increased when Fe₃O₄ NPs exceeded 600 mg/L, which was in accordance with EPS content. Biopolymer-degrading and phenol-degrading genera increased at 0-600 mg/L Fe₃O₄ NPs, while decreased at Fe₃O₄ NPs exceeded 600 mg/L, which conformed to EPS content and phenol degradation efficiency.

Shifts in a Phenanthrene-Degrading Microbial Community are Driven by Carbohydrate Metabolism Selection in a Ryegrass Rhizosphere

Plants usually promote pollutant bioremediation by several mechanisms including modifying the diversity of functional microbial species. However, conflicting results are reported that root exudates have no effects or negative effects on organic pollutant degradation. In this study, we investigated the roles of ryegrass in phenanthrene degradation in soils using DNA stable isotope probing (SIP) and metagenomics to reveal a potential explanation for conflicting results among phytoremediation studies. Phenanthrene biodegradation efficiency was improved by 8% after 14 days of cultivation. Twelve and ten operational taxonomic units (OTUs) were identified as active phenanthrene degraders in non-rhizosphere and rhizosphere soils, respectively. The active phenanthrene degraders exhibited higher average phylogenetic distances in rhizosphere soils (0.33) than non-rhizosphere soils (0.26). The K_a/K_s values (the ratio of nonsynonymous to synonymous substitutions) were about 10.37% higher in the rhizosphere treatment among >90% of all key carbohydrate metabolism-related genes, implying that ryegrass may be an important driver of microbial community variation in the rhizosphere by relieving the carbohydrate metabolism pressure and improving the survival ability of r-strategy microbes. Most K_a/K_s values of root-exudate-related metabolism genes exhibited little change, except for fumarate hydratase that increased 13-fold in the rhizosphere compared to that in the non-rhizosphere treatment. The K_a/K_s values of less than 50% phenanthrene-degradation-related genes were affected, 30% of which increased and 70% behaved oppositely. Genes with altered K_a/K_s values had a low percentage and followed an inconsistent changing tendency, indicating that phenanthrene and its metabolites are not major factors influencing the active degraders. These results suggested the importance of carbohydrate metabolism, especially fumaric acid, in rhizosphere community shift, and hinted at a new hypothesis that the rhizosphere effect on phenanthrene degradation efficiency depends on the existence of active degraders that have competitive advantages in carbohydrate and fumaric acid metabolism.

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.

FerrateVI oxidation of polycyclic aromatic compounds (PAHs and polar PACs) on DNAPL-spiked sand: degradation efficiency and oxygenated by-product formation compared to conventional oxidants

In situ chemical oxidations are known to remediate PAH contaminations in groundwater and soils. In this study, batch-scale oxidations aim to compare the PAC (polycyclic aromatic compound) degradation of three oxidation processes traditionally applied for soil treatment: permanganate, heat-activated persulfate (60 °C) and Fenton-like activated by magnetite, to results obtained with ferrates (Fe^VI). Widely studied for water treatments, ferrates are efficient on a wide range of pollutants with the advantage of producing nontoxic ferric sludge after reaction. However, fewer works focus on their action on soil, especially on semi-industrial grade ferrates (compatible with field application). Oxidations were carried out on sand spiked with dense non-aqueous phase liquid (DNAPL) sampled in the groundwater of a former coking plant. Conventional 16 US-EPA PAHs and polar PACs were monitored, especially potential oxygenated by-products that can be more harmful than parent-PAHs. After seven reaction days, only the Fenton-like showed limited degradation. Highest efficiencies were obtained for heat-activated persulfate with no O-PAC ketones formed. Permanganate gave important degradation, but ketones were generated in large amount. The tested ferrates not only gave slightly lower yields due to their auto-decomposition but also induced O-PAC ketone production, suggesting a reactional pathway dominated by oxidoreductive electron transfer, rather than a radical one.