Biochar accelerates microbial reductive debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in anaerobic mangrove sediments

Unveiling the long-term dynamic effects: Biochar mediates bacterial communities to modulate the petroleum hydrocarbon degradation in oil-contaminated sediments

Sediment, as the destination of marine pollutants, often bears much more serious petroleum pollution than water. Biochar is increasingly utilized for remediating organic pollutant-laden sediments, yet its long-term impacts on oil-contaminated sediment remain poorly understood. In this study, simulation experiments adding 2.5 wt% biochars (corn straw and wood chips biochar at different pyrolysis temperatures) were conducted. The effects on petroleum hydrocarbon attenuation, enzyme activities, and microbial community structure were systematically investigated. Results showed enhanced degradation of long-chain alkanes in certain biochar-treated groups. Biochar species and PAH characteristics together lead to the PAHs' attenuation, with low-temperature corn straw biochar facilitating the degradation of phenanthrene, fluorene, and chrysene. Initially, biochars reduced polyphenol oxidase activity but increased urease and dehydrogenase activities. However, there was a noticeable rise in polyphenol oxidase activity for a long time. Biochars influenced bacterial community succession and abundance, likely due to nutrient release stimulating microbial activity. The structural equations model (SEM) reveals that DON affected the enzyme activity by changing the microbial community and thus regulated the degradation of PAHs. These findings shed light on biochar's role in bacterial communities and petroleum hydrocarbon degradation over extended periods, potentially enhancing biochar-based remediation for petroleum-contaminated sediments.

Underexplored Organohalide-Respiring Bacteria in Sewage Sludge Debrominating Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants prevalent in the environment. Organohalide-respiring bacteria (OHRB) can attenuate PBDEs via reductive debromination, but often producing toxic end-products. Debromination of PBDEs to diphenyl ether remains a rare phenomenon and is so far specifically associated with Dehalococcoides isolated from e-waste polluted sites. The occurrence of PBDE debromination in other ecosystems and underpinning OHRB are underexplored. Here we found that debromination of PBDEs is a common trait of sewage sludge microbiota, and diphenyl ether was produced as the end-product at varying quantities (0.6-52.9% mol of the parent PBDEs) in 76 of 84 cultures established with bioreactor sludge. Diverse debromination pathways converting PBDEs to diphenyl ether, including several new routes, were identified. Although Dehalococcoides contributed to PBDE debromination, Dehalogenimonas, Dehalobacter, and uncultivated Dehalococcoidia likely played more important roles than previously recognized. Multiple reductive dehalogenase genes (including bdeA, pcbA4, pteA, and tceA) were also prevalent and coexisted in bioreactor sludge. Collectively, these findings contribute to enhancing our comprehension of the environmental fate of PBDEs, expanding the diversity of microorganisms catalyzing PBDE debromination, and developing consortia for bioremediation application.

The role of iron materials in the abiotic transformation and biotransformation of polybrominated diphenyl ethers (PBDEs): A review

Polybrominated diphenyl ethers (PBDEs), widely used as flame retardants, easily enter the environment, thus posing environmental and health risks. Iron materials play a key role during the migration and transformation of PBDEs. This article reviews the processes and mechanisms of adsorption, degradation, and biological uptake and transformation of PBDEs affected by iron materials in the environment. Iron materials can effectively adsorb PBDEs through hydrophobic interactions, π-π interactions, hydrogen/halogen bonds, electrostatic interactions, coordination interactions, and pore filling interactions. In addition, they are beneficial for the photodegradation, reduction debromination, and advanced oxidation degradation and debromination of PBDEs. The iron material-microorganism coupling technology affects the uptake and transformation of PBDEs. In addition, iron materials can reduce the uptake of PBDEs in plants, affecting their bioavailability. The species, concentration, and size of iron materials affect plant physiology. Overall, iron materials play a bidirectional role in the biological uptake and transformation of PBDEs. It is necessary to strengthen the positive role of iron materials in reducing the environmental and health risks caused by PBDEs. This article provides innovative ideas for the rational use of iron materials in controlling the migration and transformation of PBDEs in the environment.

Metagenomic 16S rRNA analysis and predictive functional profiling revealed intrinsic organohalides respiration and bioremediation potential in mangrove sediment

BACKGROUND

Mangrove sediment microbes are increasingly attracting scientific attention due to their demonstrated capacity for diverse bioremediation activities, encompassing a wide range of environmental contaminants.

MATERIALS AND METHODS

The microbial communities of five Avicennia marina mangrove sediment samples collected from Al Rayyis White Head, Red Sea (KSA), were characterized using Illumina amplicon sequencing of the 16S rRNA genes.

RESULTS

Our study investigated the microbial composition and potential for organohalide bioremediation in five mangrove sediments from the Red Sea. While Proteobacteria dominated four microbiomes, Bacteroidetes dominated the fifth. Given the environmental concerns surrounding organohalides, their bioremediation is crucial. Encouragingly, we identified phylogenetically diverse organohalide-respiring bacteria (OHRB) across all samples, including Dehalogenimonas, Dehalococcoides, Anaeromyxobacter, Desulfuromonas, Geobacter, Desulfomonile, Desulfovibrio, Shewanella and Desulfitobacterium. These bacteria are known for their ability to dechlorinate organohalides through reductive dehalogenation. PICRUSt analysis further supported this potential, predicting the presence of functional biomarkers for organohalide respiration (OHR), including reductive dehalogenases targeting tetrachloroethene (PCE) and 3-chloro-4-hydroxyphenylacetate in most sediments. Enrichment cultures studies confirmed this prediction, demonstrating PCE dechlorination by the resident microbial community. PICRUSt also revealed a dominance of anaerobic metabolic processes, suggesting the microbiome's adaptation to the oxygen-limited environment of the sediments.

CONCLUSION

This study provided insights into the bacterial community composition of five mangrove sediments from the Red Sea. Notably, diverse OHRB were detected across all samples, which possess the metabolic potential for organohalide bioremediation through reductive dehalogenation pathways. Furthermore, PICRUSt analysis predicted the presence of functional biomarkers for OHR in most sediments, suggesting potential intrinsic OHR activity by the enclosed microbial community.

Deciphering the behavior and potential mechanism of biochar at different pyrolysis temperatures to alleviate membrane biofouling

Biofouling limits applications of membrane technology in wastewater treatment, but dosing additives to membrane tanks is an effective method to alleviate biofouling. In this study, biochar derived from corncob and pyrolyzed at 300, 500, and 700°C was dosed to determine the underlying anti-biofouling mechanism. The effects of the biochar on the membrane properties and foulant behavior were systematically investigated. The results showed that biochar delayed the occurrence of the fouling transition (0.5-3.0 h), and decreased the flux decline rate, thus achieving a higher water flux (3.1-3.7 times of the control group). Biochar altered membrane surface properties, and increased the membrane surface charge, roughness, and hydrophilicity, which all contributed to higher membrane permeability. Moreover, adding biochar reduced the number of foulants in the fouling layer, particularly protein substances. The flux model fit and the XDLVO theory further revealed the mitigating effect of biochar on membrane biofouling. At the initial intermediate-blocking stage, the effect of biochar on membrane fouling was determined by its properties, and adsorption capacity to the foulants, BC500 presented the best mitigation performance. At the later cake-filtration stage, the role of biochar in membrane fouling was strongly associated with protein content in the fouling layer, and the minimum rate of flux decline occurred in BC300. This study promotes the understanding and development of biochar to alleviate membrane biofouling.

Petroleum-contaminated soil bioremediation and microbial community succession induced by application of co-pyrolysis biochar amendment: An investigation of performances and mechanisms

This study aimed to remediate petroleum-contaminated soil using co-pyrolysis biochar derived from rice husk and cellulose. Rice husk and cellulose were mixed in various weight ratios (0:1, 1:0, 1:1, 1:3 and 3:1) and pyrolyzed under 500 °C. These biochar variants were labeled as R0C1, R1C0, R1C1, R1C3 and R3C1, respectively. Notably, the specific surface area and carbon content of the co- pyrolysis biochar increased, potentially promoting the growth and colonization of soil microorganisms. On the 60th day, the microbial control group achieved a 46.69% removal of pollutants, while the addition of R0C1, R1C0, R1C3, R1C1 and R3C1 resulted in removals of 70.56%, 67.01%, 67.62%, 68.74% and 67.30%, respectively. In contrast, the highest efficiency observed in the abiotic treatment group was only 24.12%. This suggested that the removal of petroleum pollutants was an outcome of the collaborative influence of co-pyrolysis biochar and soil microorganisms. Furthermore, the abundance of Proteobacteria, renowned for its petroleum degradation capability, obviously increased in the treatment group with the addition of co-pyrolysis biochar. This demonstrated that co-pyrolysis biochar could notably stimulate the growth of functionally associated microorganisms. This research confirmed the promising application of co-pyrolysis biochar in the remediation of petroleum-contaminated soil.

Coupling between 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) debromination and methanogenesis in anaerobic soil microcosms

Polybrominated diphenyl ethers (PBDEs) are persistent pollutants that may undergo microbial-mediated debromination in anoxic environments, where diverse anaerobic microbes such as methanogenic archaea co-exist. However, current understanding of the relations between PBDE pollution and methanogenic process is far from complete. To address this knowledge gap, a series of anaerobic soil microcosms were established. BDE-47 (2, 2', 4, 4'-tetrabromodiphenyl ether) was selected as a model pollutant, and electron donors were supplied to stimulate the activity of anaerobes. Debromination and methane production were monitored during the 12 weeks incubation, while obligate organohalide-respiring bacteria (OHRBs), methanogenic, and the total bacterial communities were examined at week 7 and 12. The results demonstrated slow debromination of BDE-47 in all microcosms, with considerable growth of Dehalococcoides and Dehalogenimonas over the incubation observed in most BDE-47 spiked treatments. In addition, the accumulation of intermediate metabolites positively correlated with the abundance of Dehalogenimonas at week 7, suggesting potential role of these OHRBs in debromination. Methanosarcinaceae were identified as the primary methanogenic archaea, and their abundance were correlated with the production of debrominated metabolites at week 7. Furthermore, it was observed for the first time that BDE-47 considerably enhanced methane production and increased the abundance of mcrA genes, highlighting the potential effects of PBDE pollution on climate change. This might be related to the inhibition of reductive N- and S-transforming microbes, as revealed by the quantitative microbial element cycling (QMEC) analysis. Overall, our findings shed light on the intricate interactions between PBDE and methanogenic processes, and contribute to a better understanding of the environmental fate and ecological implication of PBDE under anaerobic settings.

Organophosphate Triesters and Their Transformation Products in Sediments of Mangrove Wetlands in the Beibu Gulf, South China Sea

As emerging pollutants, organophosphate esters (OPEs) have been reported in coastal environments worldwide. Nevertheless, information on the occurrence and ecological risks of OPEs, especially the related transformation products, in mangrove wetlands is scarce. For the first time, the coexistence and distribution of OP triesters and their transformation products in three mangrove wetlands in the Beibu Gulf were investigated using ultrasonication and solid-phase extraction, followed by UHPLC-MS/MS detection. The studied OPEs widely existed in all the sampling sites, with the total concentrations ranging from 6.43 ng/g dry weight (dw) to 39.96 ng/g dw and from 3.33 ng/g dw to 22.50 ng/g dw for the OP triesters and transformation products, respectively. Mangrove wetlands tend to retain more OPEs than the surrounding coastal environment. Pearson correlation analysis revealed that the TOC was not the sole factor in determining the OPEs' distribution, and degradation was not the main source of the transformation products in mangrove sediments in the Beibu Gulf. The ecological risks of selected OPEs for different organisms were also assessed, revealing a medium to high risk posed by OP diesters to organisms. The levels or coexistence of OPEs and their metabolites in mangroves need constant monitoring, and more toxicity data should be further studied to assess the effect on normal aquatic organisms.

20 years of polybrominated diphenyl ethers on toxicity assessments

Polybrominated diphenyl ethers (PBDEs) serve as brominated flame retardants which continue to receive considerable attention because of their persistence, bioaccumulation, and potential toxicity. Although PBDEs have been restricted and phased out, large amounts of commercial products containing PBDEs are still in use and discarded annually. Consequently, PBDEs added to products can be released into our surrounding environments, particularly in aquatic systems, thus posing great risks to human health. Many studies and reviews have described the possible toxic effects of PBDEs, while few studies have comprehensively summarized and analyzed the global trends of their toxicity assessment. Therefore, this study utilizes bibliometrics to evaluate the worldwide scientific output of PBDE toxicity and analyze the hotspots and future trends of this field. Firstly, the basic information including the most contributing countries/institutions, journals, co-citations, influential authors, and keywords involved in PBDE toxicity assessment will be visualized. Subsequently, the potential toxicity of PBDE exposure to diverse systems, such as endocrine, reproductive, neural, and gastrointestinal tract systems, and related toxic mechanisms will be discussed. Finally, we conclude this review by outlining the current challenges and future perspectives in environmentally relevant PBDE exposure, potential carriers for PBDE transport, the fate of PBDEs in the environment and human bodies, advanced stem cell-derived organoid models for toxicity assessment, and promising omics technologies for obtaining toxic mechanisms. This review is expected to offer systematical insights into PBDE toxicity assessments and facilitate the development of PBDE-based research.

Insight into the enhancement effect of humic acid on microbial degradation of triclosan in anaerobic sediments

Humic acid (HA) as one class of macromolecular substances plays important roles in mediating environmental behaviors of pollutants in sediments, but its effect on microbial degradation of triclosan (TCS), a common antibacterial drug, remains unclear. In this study, the effects of HA addition with different dosages (0-5%) on TCS degradation in anaerobic sediment slurries and the underlying microbial mechanisms were investigated. The results showed that HA addition significantly accelerated the TCS removal and the maximum removal percentage (30.2%) was observed in the sediment slurry with 5% HA addition. The iron reduction rate, relative abundances of the genera Comamonas, Pseudomonas and Geobacter, and bacterial network complexity in sediment slurry were significantly enhanced due to HA addition. Based on the partial least squares path modeling analysis, the enhancement effect of HA on TCS degradation was mainly explained by Fe(II):Fe(III) ratio with the highest influence on TCS removal (total effect: 0.723), followed by dominant genera abundances (total effect: 0.391), module relative abundance (total effect: 0.272), and network topological features (total effect: 0.263). This finding enhanced our understanding of the role of HA in TCS biodegradation in contaminated sediments for bioremediation purposes.

Bioremediation of PBDEs and heavy metals co-contaminated soil in e-waste dismantling sites by Pseudomonas plecoglossicida assisted with biochar

Biochar-assisted microbial remediation has been proposed as a promising strategy to eliminate environmental pollutants. However, studies on this strategy used in the remediation of persistent organic pollutants and heavy metals co-contaminated soil are lacking, and the effect of the combined incorporation of biochar and inoculant on the assembly, functions, and microbial interactions of soil microbiomes are unclear. Here, we studied 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) degradation and heavy metal immobilization by and biochar-based bacterial inoculant (BC/PP) in an e-waste contaminated soil, and corresponding microbial regulation mechanisms. Results showed that BC/PP addition was more effective in reducing Cu and Pb availability and degrading BDE-47 than inoculant alone. Notably, BC/PP facilitated bound-residue formation of BDE-47, reducing the ecological risk of residual BDE-47. Meanwhile, microbial carbon metabolism and enzyme activities (related to C-, N-, and P- cycles) were enhanced in soil amended with BC/PP. Importantly, biochar played a crucial role in inoculant colonization, community assembly processes, and microbiome multifunction. In the presence of biochar, positive interactions in co-occurrence networks of the bacterial community were more frequent, and higher network stability and more keystone taxa were observed (including potential degraders). These findings provide a promising strategy for decontaminating complex-polluted environments and recovering soil ecological functions.

Mechanistic characterization of anaerobic microbial degradation of BTBPE in coastal wetland soils: Implication by compound-specific stable isotope analysis

As a novel brominate flame retardants, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) has been extensively used in various consumer products, and frequently detected in various environmental matrices. However, the microbial degradation of BTBPE remains unclear in the environment. This study comprehensively investigated the anaerobic microbial degradation of BTBPE and therein stable carbon isotope effect in the wetland soils. BTBPE degradation followed the pseudo-first-order kinetic, with degradation rate of 0.0085 ± 0.0008 day^-1. Based on identification of degradation products, stepwise reductive debromination was the main transformation pathway of BTBPE, and tended to keep the stable of 2,4,6-tribromophenoxy group during the microbial degradation. The pronounced carbon isotope fractionation was observed for BTBPE microbial degradation, and carbon isotope enrichment factor (ε_C) was determined to be -4.81 ± 0.37‰, indicating cleavage of C-Br bond as the rate-limiting step. Compared to previously reported isotope effects, carbon apparent kinetic isotope effect (AKIE_C = 1.072 ± 0.004) suggested that the nucleophilic substitution (S_N2 reaction) was the potential reaction mechanism for reductive debromination of BTBPE in the anaerobic microbial degradation. These findings demonstrated that BTBPE could be degraded by the anaerobic microbes in wetland soils, and the compound-specific stable isotope analysis was a robust method to discover the underlying reaction mechanisms.

Systematic characterization of sediment microbial community structure and function associated with anaerobic microbial degradation of PBDEs in coastal wetland

As the widely used flame retardant, polybrominated diphenyl ethers (PBDEs) have been ubiquitously detected in wetland sediments. Microbial degradation is the importantly natural attenuation process for PBDEs in sediments. In this study, the microbial degradation of PBDEs and inherent alternation of microbial communities were explored in anaerobic sediments from coastal wetland, North China. BDE-47 and BDE-153 could be degraded by the indigenous microbes, with biodegradation following pseudo-first-order kinetic. In sediments, the major genera for BDE-47 and BDE-153 degradation were Paeisporosarcina and Gp7, respectively, in single exposure. However, Marinobacter was dominant genera in the combined exposure to BDE-47 and BDE-153, and competition against Marinobacter existed between BDE-47 and BDE-153 degradation. Analysis of bacterial metabolic function indicated that membrane transport, amino acid and carbohydrate metabolism were included in degradation. This study provides the systematic characterization of the sediment microbial community structure and function associated anaerobic microbial degradation of PBDEs in coastal wetland.

The thermal degradation and soil recovery of thermal treatment of field-weathered decabrominated diphenyl ether-contaminated soil

A farm at Taoyuan in Taiwan was highly contaminated with decabrominated diphenyl ether (BDE-209), a widely used commercial brominated flame retardant and persistent in the environment, more than 10 years. Since crops are able to absorb and accumulate BDE-209 from soils in our previous research, posing a hazardous risk for humans, it is essential to develop a practical method of soil treatment. Thermal treatment was studied among different approaches. In our previous study (Ko et al., 2022), we found that heating to 450 °C for 30 min achieved a complete removal of BDE-209 in soil. However, the high temperature significantly decreased the original soil organic matter (SOM) from 2.47% to 0.27%, altering the soil texture, damaging microbial biomass, and thus affecting the revegetation after the thermal treatment. Sugarcane bagasse, a common agricultural residue, served as an amendment to restore soil fertility. Current results indicate that 2.5% bagasse can improve the SOM in soil by up to 2.73% and restore its bacterial composition, making the plant growth conditions similar to those of the untreated contaminated soil. In light of the high removal efficiency provided by the 450°C-thermal treatment and the high recovery efficiency of sugarcane bagasse, the strategy presented in this study serves to be a promising method for sustainable remediation.

Manure- and straw-derived biochars reduce the ecological risk of PBDE and promote nitrogen cycling by shaping microbiomes in PBDE-contaminated soil

Pyrolysis of agricultural waste into biochar for soil remediation is a useful solid waste management strategy. However, it is still unclear how different agricultural feedstocks affect the properties of biochars and their effectiveness in remediation of PBDE-contaminated soil. In this study, we systematically investigated dynamic alterations of soil properties, microbial communities, and PBDE dissipation and bioavailability induced by the application of biochars from manure (MBC) and straw (SBC) to PBDE-contaminated soil. The results showed that soil properties, microbial community structure, and diversity changed differently with the incorporation of the two biochars. MBC had a larger surface area (17.4 m²/g) and a higher nutrient content (45.1% ash content), making it more suitable for use as a soil additive to improve soil quality and nutrient conditions, as well as to stimulate microbial growth. SBC showed higher adsorption capacity for 2,2',4,4'-Tetrabromodiphenyl Ether (BDE-47) (26.73 ± 0.65 mg/g), thus lowering the bioavailability and ecological risk of BDE-47 in soil. BDE-47 was stepwise debrominated into lower brominated PBDE by PBDE-degrading bacteria. MBC accelerated the debromination of BDE-47 (10.1%) by promoting PBDE-degrading microorganisms, while this was inhibited by SBC (3.5%) due to strong adsorption of BDE-47. In addition, we found that both types of biochar favored Nitrospirae bacteria and promoted N cycling. Overall, biochars from manure and straw can positively shape soil microbial communities differently by altering soil properties, soil fertility and nutrient availability, and the fate and the effects of contaminants, which ultimately led to a difference in the potential of biochars for their use in soil remediation.

Functional bacterial consortium responses to biochar and implications for BDE-47 transformation: Performance, metabolism, community assembly and microbial interaction

The influence of biochar on the biodegradation of persistent organic pollutants (POPs) has been extensively studied. However, the underlying mechanisms behind the response of functional microbial consortia to biochar remain poorly understood. Herein, we systematically explored the effect of biochar on 2,2',4,4'-tetrabrominated ether (BDE-47) biodegradation, and investigated the interaction and assembly mechanism of the functional bacterial consortium QY2. The results revealed that the biodegradation efficiency of QY2 for BDE-47 increased from 53.85% to 94.11% after the addition of biochar. Fluorescence excitation-emission matrix and electrochemical analysis showed that biochar-attached biofilms were rich in redox-active extracellular polymeric substances (EPS, 3.03-fold higher than free cell), whose strong interaction with biochar facilitated the electron transfer of the biofilm, thus enhancing the debromination degradation of BDE-47. Meanwhile, the assembly model and molecular ecological networks analysis indicated that bacterial community assembly in biofilms was more driven by deterministic processes (environmental selection >75.00%) upon biochar stimulation and exhibited closer interspecific cooperative interactions, leading to higher biodiversity and broader habitat niche breadth for QY2 in response to BDE-47 disturbance. Potential degraders (Methylobacterium, Sphingomonas, Microbacterium) and electrochemical bacteria (Ochrobactrum) were selectively enriched, whose role as keystone bacteria may be participated in biofilm formation and redox-active EPS secretion (r > 0.5, P < 0.05). These findings deepen the understanding of the mechanisms by which biochar promotes microbial degradation of PBDEs and provided a theoretical basis for better regulation of functional bacterial communities during environmental remediation.

Enhancement effects of decabromodiphenyl ether on microbial sulfate reduction in eutrophic lake sediments: A study on sulfate-reducing bacteria using dsrA and dsrB amplicon sequencing

Although sulfate (SO₄^2-) reduction by sulfate-reducing bacteria (SRB) is an important sulfur cycling processes, little is known about how the persistent organic pollutants affect the SO₄^2- reduction process in the eutrophic lake sediments. Here, we carried out a 120-day microcosm experiment to explore the effects of decabromodiphenyl ether (BDE-209) on SO₄^2- reduction mediated by SRB in sediment collected from Taihu Lake, a typical eutrophic lake in China. The results showed that BDE-209 contamination significantly enhanced the activity of dissimilatory sulfite reductase (DSR) (r = 0.83), which led to an increased concentration of sulfide produced by SO₄^2- reduction. This stimulatory effect of BDE-209 on DSR activity was closely related to variations in the dsrA- and dsrB-type SRB communities. The abundances and diversities of the dsrA- and dsrB-containing SRB increased and their community composition varied in response to BDE-209 contamination. The gene copies (r = 0.72), Chao 1 (r = 0.50), Shannon (r = 0.55), and Simpson (r = 0.70) indices of dsrB-containing SRB was positively correlated with BDE-209 contamination. Co-occurrence network analysis revealed that network complexity, connectivity, and the interspecific cooperative relationship in SRB were strengthened by BDE-209 contamination. The keystone species identified in the SRB community mainly belonged to the genera Candidatus Sulfopaludibacter for the dsrA-containing SRB and Desulfatiglans for the dsrB-containing SRB, and their relative abundances were positively correlated with DSR activity in the sediment. The relative abundance of the keystone species and SRB diversity were important microbial factors directly contributing to the variations in DSR activity based on structural equation modeling analysis. Notably, the results of abundance, community structure, and interspecific relationships showed that the dsrB-containing SRB may be more sensitive to the BDE-209 contamination than the dsrA-containing SRB. These results will help us understand the effects of BDE-209 on microbial sulfate reduction in eutrophic lakes.

Humin and biochar accelerated microbial reductive dechlorination of 2,4,6-trichlorophenol under weak electrical stimulation

The extracellular electron transfer (EET) is regarded as one of the crucial factors that limit the application of the bioelectrochemical system (BES). In this study, two different solid-phase redox mediators (RMs), biochar (1.2 g/L, T-B) and humin (1.2 g/L, T-H) were used for boosting the microorganisms accessing the electrons required for 2,4,6-TCP dechlorination under weak electrical stimulation (-0.278 V vs. Standard hydrogen electrode). BES with dissolved RM anthraquinone-2,6-disulfonate (AQDS 0.5 mmol/L, T-A) was used as a comparison. The results showed that dechlorination of 2,4,6-TCP could be greatly accelerated by biochar (1.78 d^-1) and humin (1.50 d^-1) than AQDS (0.24 d^-1) and no RM control (T-M, 0.27 d^-1). Moreover, phenol became the predominant dechlorination product in T-H (78.5 %) and T-B (63.0 %) instead of 4-CP in T-M (67.1 %) and T-A (89.8 %). Pseudomonas, Sulfurospirillum, Desulfuromonas, Dehalobacter, Anaeromyxobacter, and Dechloromonas belonging to Proteobacteria or Firmicutes rather than Chloroflexi might be responsible for the dechlorination activity. Notably, different RMs tended to stimulate distinct electroactive bacteria. Pseudomonas was the most abundant microorganism in T-M (41.92 %) and T-A (17.24 %), while Rhodobacter was most prevalent in T-H (20.04 %) and Azonexus was predominant in T-B (48.48 %). This study is essential in advancing the understanding of EET in BES for microbial degradation of organohalide contaminants under weak electrical stimulation.

The effects of biochar and its applications in the microbial remediation of contaminated soil: A review

The amendment of biochar for soil bioremediation can improve soil conditions, influence soil microbial community, and achieve co-application of biochar-microbe to promote the removal of pollutants. This paper summarizes the positive effects of biochar on microorganisms, including acting as a shelter, providing nutrients, and improving soil conditions (soil aggregation, pH, cation exchange capacity (CEC), and enzymatic activity). These effects will cause variations in microbial abundance, activity, and community structure. Biochar can act as an electron mediator to promote electron transfer in the process of microbial degradation. And the application of biochar in soil bioremediation is also introduced. Nevertheless, toxic substances carried by biochar that may threaten microbial community shouldn't be overlooked. With this review, we can better understand biochar's involvement in soil bioremediation, which will help us choose and modify biochar in a targeted manner for the desired purpose in practical applications.

The environmental fate of biomass associated polybrominated diphenyl ethers

The widespread use of polybrominated diphenyl ethers (PBDEs) inevitably leads to their occurrence in the atmosphere, soil, and sediment. Biomass, especially dry branches and fallen leaves, may act a large reservoir for PBDEs through atmospheric deposition or soil bioaccumulation. Thus, clarifying the sunlight-induced transformation behaviors of PBDEs on biomass is highly significant for our understanding on its natural self-purification process. In this work, the degradation kinetics and mechanisms of two common PBDEs congeners, decabromodiphenyl ether (BDE-209) and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), on biomass were systematically studied under natural and simulated sunlight irradiation conditions. The highest photodegradation rate constant of BDE-209 and BDE-47 was observed on sour cherry (SC) and zoysia matrella (ZM), respectively, which was related to their larger light receiving area and poor crystallinity. Due to the higher apparent quantum efficiency, BDE-209 degrades faster than BDE-47 (0.063-0.223 vs 0.006-0.026 h^-1). The sunlight self-purification cycle of BDE-209 and BDE-47 on biomass were 6 and 14 days, respectively, with the corresponding sunlight contribution in the range of 0.12-0.51 ng mW^-1. Products analysis by GC-MS and HPLC-MS/MS revealed that the main reactions involved in the photodegradation of BDE-209 and BDE-47 on biomass were debromination, hydroxylation, cyclization, and C-O bond breaking reaction. Especially, it was firstly proposed that hydroxyl H in lignin from biomass participated in the formation of primary products, which were rationalized by density functional theory (DFT) calculations and control experiments.

Insight into microbial degradation of hexabromocyclododecane (HBCD) in lake sediments under different hydrodynamic conditions

Hexabromocyclododecane (HBCD), an emerging persistent organic pollutant, has been widely detected in aquatic ecosystems with various hydrodynamic conditions, however, the effects of hydrodynamic changes on microbial degradation of HBCD in aquatic sediment remains unclear. Here, we conducted an annular flume experiment to characterize variation in HBCD removal from contaminated sediment under three hydrodynamic conditions with different flow velocities, as well as clarify the underlying microbial mechanisms. We detected significant HBCD removal and bromine ion generation in all contaminated sediments, and microbial reduction debromination was an important process for HBCD removal. At the end of the 49-day experiment, both HBCD removal percentage and the bromine ion concentration were significantly lower under dynamic water condition with higher sediment redox potential, compared with static water conditions. The dynamic water conditions resulted a relatively high sediment redox potential and decreased the iron reduction rate and the abundance of organohalide-respiring bacteria (OHRB) in the genera Geobatcer, Dehalogenimonas, Dehalobacter, and Dehalococcoide, which reduced the microbial degradation of HBCD in contaminated sediments. The community composition of both total bacteria and OHRB also differed significantly among hydrodynamic conditions. Some bacterial groups with HBCD degradation abilities such as Pseudomonas and Sulfuricurvum were less abundant under dynamic water conditions, and the HBCD degradation efficiencies were lower. These findings enhance our understanding of the bioremediation potential of HBCD-contaminated sediments in different hydrodynamic areas.

Efficient and Complete Detoxification of Polybrominated Diphenyl Ethers in Sediments Achieved by Bioaugmentation with Dehalococcoides and Microbial Ecological Insights

Polybrominated diphenyl ethers (PBDEs) are prevalent environmental pollutants, but bioremediation of PBDEs remains to be reported. Here we report accelerated remediation of a penta-BDE mixture in sediments by bioaugmentation with Dehalococcoides mccartyi strains CG1 and TZ50. Bioaugmentation with different amounts of each Dehalococcoides strain enhanced debromination of penta-BDEs compared with the controls. The sediment microcosm spiked with 6.8 × 10⁶ cells/mL strain CG1 showed the highest penta-BDEs removal (89.9 ± 7.3%) to diphenyl ether within 60 days. Interestingly, co-contaminant tetrachloroethene (PCE) improved bioaugmentation performance, resulting in faster and more extensive penta-BDEs debromination using less bioinoculants, which was also completely dechlorinated to ethene by introducing D. mccartyi strain 11a. The better bioaugmentation performance in sediments with PCE could be attributed to the boosted growth of the augmented Dehalococcoides and capability of the PCE-induced reductive dehalogenases to debrominate penta-BDEs. Finally, ecological analyses showed that bioaugmentation resulted in more deterministic microbial communities, where the augmented Dehalococcoides established linkages with indigenous microorganisms but without causing obvious alterations of the overall community diversity and structure. Collectively, this study demonstrates that bioaugmentation with Dehalococcoides is a feasible strategy to completely remove PBDEs in sediments.

One-Step Biodiesel Production from Waste Cooking Oil Using CaO Promoted Activated Carbon Catalyst from Prunus persica Seeds

In recent years, the scope for replacing fossil fuels has been appealing to the world, owing to limited conventional fuels, crude oil price volatility, and greenhouse gas emission concerns. In this regard, this article demonstrates the preparation of a novel solid base catalyst for the transesterification of waste cooking oil. A calcium-loaded activated carbon catalyst was prepared through pyrolysis of peach shell followed by chemical activation with KOH and then calcium loading through the wet impregnation method. The prepared catalyst showed the best performance with 20% calcium loading and 650 °C of calcination temperature. The catalyst’s physicochemical, structural, and textural properties were examined using XRD, FTIR, SEM, EDX, and BET analysis. The catalyst showed a maximum yield of 96% at optimized conditions, i.e., 65 °C temperature, oil to methanol ratio 1:8, 5 wt% catalyst concentration, and a 160 min reaction time. Additionally, it illustrated high recyclability up to 10 cycles with negligible leaching of Ca+2 ions. The high activity of the catalyst was due to the presence of calcium ions on the activated carbon support. Physio–chemical properties and GC-MS analysis of prepared biodiesel determined that all attributes were within the biodiesel standard tolerances set by ASTM D6751 and EN 14214. Therefore, all the innovations mentioned above concluded that catalyst generated from peach shell biochar is a promising candidate for biodiesel production, ultimately resulting in solid and liquid waste management.

Coupled Adsorption and Biodegradation of Trichloroethylene on Biochar from Pine Wood Wastes: A Combined Approach for a Sustainable Bioremediation Strategy

Towards chlorinated solvents, the effectiveness of the remediation strategy can be improved by combining a biological approach (e.g., anaerobic reductive dechlorination) with chemical/physical treatments (e.g., adsorption). A coupled adsorption and biodegradation (CAB) process for trichloroethylene (TCE) removal is proposed in a biofilm-biochar reactor (BBR) to assess whether biochar from pine wood (PWB) can support a dechlorinating biofilm by combining the TCE (100 µM) adsorption. The BBR operated for eight months in parallel with a biofilm reactor (BR)-no PWB (biological process alone), and with an abiotic biochar reactor (ABR)-no dechlorinating biofilm (only an adsorption mechanism). Two flow rates were investigated. Compared to the BR, which resulted in a TCE removal of 86.9 ± 11.9% and 78.73 ± 19.79%, the BBR demonstrated that PWB effectively adsorbs TCE and slows down the release of its intermediates. The elimination of TCE was quantitative, with 99.61 ± 0.79% and 99.87 ± 0.51% TCE removal. Interestingly, the biomarker of the reductive dechlorination process, Dehalococcoides mccartyi, was found in the BRR (9.2 × 10⁵ 16S rRNA gene copies/g), together with the specific genes tceA, bvcA, and vcrA (8.16 × 10⁶, 1.28 × 10⁵, and 8.01 × 10³ gene copies/g, respectively). This study suggests the feasibility of biochar to support the reductive dechlorination of D. mccartyi, opening new frontiers for field-scale applications.

Effect of the Zr promoter on precipitated iron-based catalysts for high-temperature Fischer–Tropsch synthesis of light olefins

FeMnxZr and FeMnxZr2Na catalysts prepared by coprecipitation and impregnation methods were applied to investigate the promoting effects of Zr on iron-based catalysts for high-temperature Fischer–Tropsch synthesis (HTFT).

Application of dual carbon-bromine stable isotope analysis to characterize anaerobic micro-degradation mechanisms of PBDEs in wetland bottom-water

Polybrominated diphenyl ethers (PBDEs), one kind of persistent organic pollutants, were widely detected in coastal wetlands. Microbial reductive debromination is one of the most important attenuation processes for PBDEs in anaerobic environment, whereas the underlying reaction mechanisms remain elusive. Dual-element stable isotope analysis was recently recognized to distinguish different reaction mechanism for degradation of organic pollutants. In this study, the dual carbon-bromine isotope effects associated with the anaerobic microbial degradation were first investigated to characterize the reaction mechanisms for BDE-47 and BDE-153. Presence of lower brominated congeners indicated stepwise debromination as the main degradation pathway, with the preferential removal of bromine in para position > meta/ortho position. The pronounced isotope fractionation was observed for both carbon and bromine, with similar carbon (ε_C) and bromine isotope enrichment factor (ε_Br) between BDE-47 (ε_C = -5.98‰, ε_Br = -2.44‰) and BDE-153 (ε_C = -5.57‰, ε_Br = -2.06‰) during the microbial degradation. Compared to ε_C and ε_Br, the correlation of carbon and isotope effects (Λ_C/Br = Δδ⁸¹Br/Δδ¹³C) was almost the same between BDE-47 (0.436) and BDE-153 (0.435), indicating the similar reaction mechanism. The calculated carbon and bromine apparent kinetic isotope effects (AKIE_C and AKIE_Br) were 1.0773 and 1.0098 for BDE-47 and 1.0716 and 1.0125 for BDE-153, within range reported for degradation of halogenated compounds following nucleophilic substitution. Combination analysis of degradation products, Λ_C/Br and AKIE, all the results pointed to that the anaerobic reductive debromination of BDE-47 and BDE-153 followed the nucleophilic aromatic substitution, with the addition of cofactor to the benzene ring concomitant with dissociation of carbon-bromine bond via the inner-sphere electron transfer, and the cleavage of C-Br bond was the rate-determining step. This study contributed to the development of dual carbon-bromine isotope analysis as a robust approach to probe the fate of PBDEs in contaminated sites.

Stimulation of pyrolytic carbon materials as electron shuttles on the anaerobic transformation of recalcitrant organic pollutants: A review

Pyrolytic carbon materials (PCMs) with various surface functionalities are widely used as environmentally friendly and cost-efficient adsorbents for the removal of organic and inorganic pollutants. Recent studies have illustrated that PCMs as electron shuttles (ESs) could also show excellent performances in promoting the anaerobic transformation of recalcitrant organic pollutants (ROPs). Numerous studies have demonstrated the excellent electron-shuttle capability (ESC) of PCMs to stimulate the anaerobic reductive transformation of ROPs. However, there is a lack of consistent understanding of the mechanism of ESC formation in PCMs and the stimulation mechanism for ROPs anaerobic transformation. To gain a more comprehensive understanding of the latest developments in the study of PCMs as ESs for ROPs anaerobic transformation, this review summarizes the formation mechanism, influencing factors, and stimulation mechanisms of ESC. ESC benefits from redox functional groups (quinone and phenol groups), persistent free radicals (PFRs), redox-active metal ions, conductive graphene phase, and porous nature of their surface. The factors influencing ESC include the highest treatment temperature (HTT), feedstocks, modification methods, and environmental conditions, of which, the HTT is the key factor. PCMs promote the reductive transformation of ROPs under anaerobic conditions via abiotic and biotic pathways. Eventually, the prospects for the ROPs anaerobic transformation enhanced by PCMs are proposed.

Anaerobic bacterial responses to carbonaceous materials and implications for contaminant transformation: Cellular, metabolic, and community level findings

Carbonaceous materials (CM) enhance the abundance and activity of bacteria capable of persistent organic (micro)pollutant (POP) degradation. This review synthesizes anaerobic bacterial responses to minimally modified CM in non-fuel cell bioremediation applications at three stages: attachment, metabolism, and biofilm genetic composition. Established relationships between biological behavior and CM surface properties are identified, but temporal relationships are not well understood, making it difficult to connect substratum properties and "pioneer" bacteria with mature microorganism-CM systems. Stark differences in laboratory methodology at each temporal stage results in observational, but not causative, linkages as system complexity increases. This review is the first to critically examine relationships between material and cellular properties with respect to time. The work highlights critical knowledge gaps that must be addressed to accurately predict microorganism-CM behavior and to tailor CM properties for optimized microbial activity, critical frontiers in establishing this approach as an effective bioremediation strategy.

Persistent organic pollutants (POPs) in coastal wetlands: A review of their occurrences, toxic effects, and biogeochemical cycling

Coastal wetlands, such as mangroves, seagrass beds, and salt marshes, are highly threatened by increasing anthropic pressures, including chemical pollution. Persistent organic pollutants (POPs) have attracted attention in these particularly vulnerable ecosystems, due to their bioaccumulative, pervasive, and ecotoxic behavior. This article reviews and summarizes available information regarding current levels, biogeochemical cycling, and effects of POPs on coastal wetlands. Sediment POP levels were compared with international quality guidelines, revealing many areas where compounds could cause damage to biota. Despite this, toxicological studies on some coastal wetland plants and microorganisms showed a high tolerance to those levels. These taxonomic groups are likely to play a key role in the cycling of the POPs, with an active role in their accumulation, immobilization, and degradation. Toxicity and biogeochemical processes varied markedly along three main axes; namely species, environmental conditions, and type of pollutant. While more focused research on newly and unintentionally produced POPs is needed, mainly in salt marshes and seagrass beds, with the information available so far, the environmental behavior, spatial distribution, and toxicity level of the studied POPs showed similar patterns across the three studied ecosystems.

Influence of Tubificidae Limnodrilus and electron acceptors on the environmental fate of BDE-47 in sediments by (14)C-labelling

2,2',4,4'-tetrabromodiphenyl ether (BDE-47) was difficult to degrade in sediments. In this study, the environmental behavior of BDE-47 with/without the effect of benthos (Tubificidae Limnodrilus) and electron acceptors in sediments was investigated using C-14 tracer. Generally, extractable residues of BDE-47 were dominant in sediment and posed high environment risk. The amount of non-extractable residues (NERs) accounted for 39.0% of initial radioactivity in oxic sediments was significantly higher than those in anoxic sediments (17.6%). Most of NERs were localized in the humin fraction and presented as sequestrated forms. Under oxic conditions, the present of Limnodrilus significantly increased the proportion of NERs in sediment. Limnodrilus accumulated 34.2% of initial radioactivity. Under anoxic conditions, the addition of iron (Ⅲ) [Fe(III)], sulfate and nitrate reduced the environmental risk of BDE-47 with the increase of NERs formation, while manganese (IV) [Mn(IV)] addition had no effect on the formation of NERs. The present of Limnodrilus and electron acceptors promoted the production of metabolites. Meanwhile, BDE-47 changed the microbial community structure of sediments. These findings indicated that the environmental behavior and risk of BDE-47 was affected by benthos and electron acceptors, and the high proportion of sequestrated NERs posed high bioactivity and toxic threat to ecological environment.

Identification of Reductive Dehalogenases That Mediate Complete Debromination of Penta- and Tetrabrominated Diphenyl Ethers in Dehalococcoides spp

Polybrominated diphenyl ethers (PBDEs) are persistent, highly toxic, and widely distributed environmental pollutants. The microbial populations and functional reductive dehalogenases (RDases) responsible for PBDE debromination in anoxic systems remain poorly understood, which confounds bioremediation of PBDE-contaminated sites. Here, we report a PBDE-debrominating enrichment culture dominated by a previously undescribed Dehalococcoides mccartyi population. A D. mccartyi strain, designated TZ50, whose genome contains 25 putative RDase-encoding genes, was isolated from the debrominating enrichment culture. Strain TZ50 dehalogenated a mixture of pentabrominated diphenyl ether (penta-BDE) and tetra-BDE congeners (total BDEs, 1.48 μM) to diphenyl ether within 2 weeks (0.58 μM Br^-/day) via ortho- and meta-bromine elimination; strain TZ50 also dechlorinated tetrachloroethene (PCE) to vinyl chloride and ethene (260.2 μM Cl^-/day). Results of native PAGE, proteomic profiling, and in vitro enzymatic activity assays implicated the involvement of three RDases in PBDE and PCE dehalogenation. TZ50_0172 (PteA_TZ50) and TZ50_1083 (TceA_TZ50) were responsible for the debromination of penta- and tetra-BDEs to di-BDE. TZ50_0172 and TZ50_1083 were also implicated in the dechlorination of PCE to trichloroethene (TCE) and of TCE to vinyl chloride/ethene, respectively. The other expressed RDase, TZ50_0090 (designated BdeA), was associated with the debromination of di-BDE to diphenyl ether, but its role in PCE dechlorination was unclear. Comparatively few RDases are known to be involved in PBDE debromination, and the identification of PteA_TZ50, TceA_TZ50, and BdeA provides additional information for evaluating debromination potential at contaminated sites. Moreover, the ability of PteA_TZ50 and TceA_TZ50 to dehalogenate both PBDEs and PCE makes strain TZ50 a suitable candidate for the remediation of cocontaminated sites. IMPORTANCE The ubiquity, toxicity, and persistence of polybrominated diphenyl ethers (PBDEs) in the environment have drawn significant public and scientific interest to the need for the remediation of PBDE-contaminated ecosystems. However, the low bioavailability of PBDEs in environmental compartments typically limits bioremediation of PBDEs and has long impeded the study of anaerobic microbial PBDE removal. In the current study, a novel Dehalococcoides mccartyi strain, dubbed strain TZ50, that expresses RDases that mediate organohalide respiration of both PBDEs and chloroethenes was isolated and characterized. Strain TZ50 could potentially be used to remediate multiple cooccurring organohalides in contaminated systems.

Enhancement effect of nanoscale zero-valent iron addition on microbial degradation of BDE-209 in contaminated mangrove sediment

Chemical and biological methods have been employed to remedy polybrominated diphenyl ether contamination, but the removal of decabromodiphenyl ether (BDE-209) by either method still has limitations. The present study aims to evaluate the combined effect of nanoscale zero-valent iron (nZVI) (from 0.1 to 10%) reduction and microbial debromination on BDE-209 removal in mangrove sediments under an anaerobic condition. During the 12-months incubation, nZVI significantly enhanced BDE-209 removal, with 17.03% to 41.99% reduction in sterilized sediments. The reduction was even higher in non-sterilized sediments with living indigenous microorganisms, achieving 15.80%, 33.50%, 55.83% and 66.95% removal of BDE-209 at 0 (control without nZVI), 0.1%, 1% and 10% nZVI, respectively. In control sterilized sediments, no debromination was found, and debromination occurred according to spiked levels of nZVI, with BDE-153 being the dominant congener. The concentrations of debrominated congeners in non-sterilized sediments also increased with nZVI levels, but were significantly higher than the respective sterilized sediment. The relative proportions of different debrominated congeners in non-sterilized sediments depended on nZVI levels, with BDE-99 being the dominant congener in low nZVI amended sediments but shifted to BDE-153 under high nZVI. Higher concentrations of ferrous iron (Fe²⁺) were detected in both sterilized and non-sterilized sediments spiked with more nZVI, and their concentrations significantly correlated with BDE-209 removal. Growth of total bacteria in sediments with 1% and 10% nZVI was inhibited within first two months, but their numbers resumed to that in the control at the end of 12 months. The present study demonstrates the synergy between chemical and microbiological methods, and a combination of nZVI and indigenous microorganisms could be an efficient and feasible mean to remedy BDE-209 in contaminated sediments.

Competitive microbial degradation among PBDE congeners in anaerobic wetland sediments: Implication by multiple-line evidences including compound-specific stable isotope analysis

Polybrominated diphenyl ethers (PBDEs) are widespread contaminants in the environment. Microbial reductive debromination is one of the important attenuation processes for PBDEs in the anaerobic sediments. This study first investigated the interaction between BDE-47 and BDE-153 during the microbial degradation in wetland sediments by the multiple-line approaches including biodegradation kinetics, microbial community structures and stable isotope composition. BDE-47 and BDE-153 biodegradation fitted pseudo-zero-order kinetics, with the higher degradation rates in single than combined exposure, indicating the mutual inhibition in co-exposure condition. BDE-47 and BDE-153 shared the common dehalogenators (genus Dehalococcoides and Acinetobacter) with enrichment in combined exposure, indicating the potential competition in dehalogenating bacteria during biodegradation. Microbial degradation could lead to the isotopic fractionation of BDE-47 and BDE-153, with the smaller changes in δ¹³C in combined than single exposure. The apparent kinetic isotope effect of carbon (AKIE_C) was different between BDE-47 and BDE-153 in single exposure, whilst identical in combined exposure, indicating the similar degradation mechanism for BDE-47 and BDE-153 in co-exposure condition. These results revealed that the competition on microbial degradation occurred among PBDEs in co-exposure condition, which was important for the comprehensive risk assessment of simultaneous exposure to multiple PBDE congeners in the environment.

Adsorption of microcystin contaminants by biochars derived from contrasting pyrolytic conditions: Characteristics, affecting factors, and mechanisms

The growing incidence of microcystins (MCs) in the environment has become an issue of global concern for the high ecological and human health risks. Herein, a comparative adsorption of three MCs (MC-LR, MC-YR and MC-RR) by spent mushroom substrate (SMS)-derived biochars from contrasting pyrolytic conditions (temperature: 600/300 °C; and gas steam: CO2/N2) was surveyed to better understand the mechanisms and factors affecting the adsorption performance. For biochar preparation, 600 °C and CO₂ led to greater levels of aromaticity, ash, S_BET, and porosity, while 300 °C and N₂ created more surface functional groups. The adsorption of MCs by biochars was a pH-dependent and endothermic physisorption process, following the pseudo-second-order kinetics (R² = 0.99) and linear isotherm model (R² > 0.88). The distribution coefficients K_d (0.98-19.2 L/kg) varied greatly among MCs (MC-YR > MC-RR > MC-LR) and biochars (BC600 > BN600 > BC300 > BN300), which depends on the combined effects of hydrophobicity, electrostatic attraction, H-bonding, cation bridging, and the amounts of adsorption sites on biochars. Higher ash, S_BET, and total pore volume of BC600 facilitated the adsorption capacity for MCs relative to other biochars. Furthermore, the co-adsorption efficacy for MCs (K_d = 1.09-8.86 L/kg) was far below those for the single adsorption, indicating strong conflicts among competing MCs. This study sheds light on the roles of pyrolytic temperature and gas steam in biochar properties, and elucidates the mechanisms and factors affecting the adsorption performance of different MCs, which lays a foundation for MCs removal from water.

Microbial and enzymatic degradation of PCBs from e-waste-contaminated sites: a review

Electronic waste is termed as e-waste and on recycling it produces environmental pollution. Among these e-waste pollutants, polychlorinated biphenyls (PCBs) are significantly important due to ubiquitous, organic in nature and serious health and environmental hazards. PCBs are used in different electrical equipment such as in transformers and capacitors for the purposes of exchange of heat and hydraulic fluids. Bioremediation is a reassuring technology for the elimination of the PCBs from the environment. In spite of their chemical stability, there are several microbes which can bio-transform or mineralize the PCBs aerobically or anaerobically. In this review paper, our objective was to summarize the information regarding PCB-degrading enzymes and microbes. The review suggested that the most proficient PCB degraders during anaerobic condition are Dehalobacter, Dehalococcoides, and Desulfitobacterium and in aerobic condition are Burkholderia, Achromobacter, Comamonas, Ralstonia, Pseudomonas, Bacillus, and Alcaligenes etc., showing the broadest substrate among bacterial strains. Enzymes found in soil such as dehydrogenases and fluorescein diacetate (FDA) esterases have the capability to breakdown PCBs. Biphenyl upper pathway involves four enzymes: dehydrogenase (bphB), multicomponent dioxygenase (bphA, E, F, and G), second dioxygenase (bphC), hydrolase, and (bphD). Biphenyl dioxygenase is considered as the foremost enzyme used for aerobic degradation of PCBs in metabolic pathway. It has been proved that several micro-organisms are responsible for the PCB metabolization. The review provides novel strategies for e-waste-contaminated soil management.

Application of biochar for the remediation of polluted sediments

Polluted sediments pose potential threats to environmental and human health and challenges to water management. Biochar is a carbon-rich material produced through pyrolysis of biomass waste, which performs well in soil amendment, climate improvement, and water treatment. Unlike soil and aqueous solutions, sediments are both the sink and source of water pollutants. Regarding in-situ sediment remediation, biochar also shows unique advantages in removing or immobilizing inorganic and organic pollutants (OPs). This paper provides a comprehensive review of the current methods of in-situ biochar amendments specific to polluted sediments. Physicochemical properties (pore structure, surface functional groups, pH and surface charge, mineral components) were influenced by the pyrolysis conditions, feedstock types, and modification of biochar. Furthermore, the remediation mechanisms and efficiency of pollutants (heavy metals [HMs] and OPs) vary with the biochar properties. Biochar influences microbial compositions and benthic organisms in sediments. Depending on the location or flow rate of polluted sediments, potential utilization methods of biochar alone or coupled with other materials are discussed. Finally, future practical challenges of biochar as a sediment amendment are addressed. This review provides an overview and outlook for sediment remediation using biochar, which will be valuable for further scientific research and engineering applications.

Current progress in degradation and removal methods of polybrominated diphenyl ethers from water and soil: A review

The widespread of polybrominated diphenyl ethers (PBDEs) in the environment has caused rising concerns, and it is an urgent endeavor to find a proper way for PBDEs remediation. Various techniques such as adsorption, hydrothermal and thermal treatment, photolysis, photocatalytic degradation, reductive debromination, advanced oxidation processes (AOPs) and biological degradation have been developed for PBDEs decontamination. A comprehensive review of different PBDEs remediation techniques is urgently needed. This work focused on the environmental source and occurrence of PBDEs, their removal and degradation methods from water and soil, and prospects for PBDEs remediation techniques. According to the up-to-date literature obtained from Web of Science, it could be concluded that (i) photocatalysis and photocatalytic degradation is the most widely reported method for PBDEs remediation, (ii) BDE-47 and BDE-209 are the most investigated PBDE congeners, (iii) considering the recalcitrance nature of PBDEs and more toxic intermediates could be generated because of incomplete degradation, the combination of different techniques is the most potential solution for PBDEs removal, (iv) further researches about the development of novel and effective PBDEs remediation techniques are still needed. This review provides the latest knowledge on PBDEs remediation techniques, as well as future research needs according to the up-to-date literature.

Degradation of 2, 2', 4, 4'-Tetrabrominated diphenyl ether (BDE-47) via the Fenton reaction driven by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1

A microbially facilitated approach was developed to degrade 2, 2', 4, 4'-tetrabrominated diphenyl ether (BDE-47). This approach consisted of biological production of Fe(II) and H₂O₂ by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 during the repetitive anoxic/oxic cycles and abiotic production of hydroxyl radical (HO^●) with the biologically produced Fe(II) and H₂O₂ via Fenton reaction. Under the condition tested, BDE-47 did not inhibit the growth of S. oneidensis MR-1. Water soluble Fe(III)-citrate and the solid minerals ferrihydrite [Fe(III)₂O₃•0.5H₂O] and goethite [Fe(III)OOH] were tested in this study. Under anoxic condition, the amounts of Fe(II) produced by S. oneidensis MR-1 varied among the Fe(III)s tested, which decreased in the order of Fe(III)-citrate > ferrihydrite > goethite. Under subsequent oxic condition, H₂O₂ was produced via O₂ reduction by S. oneidensis MR-1. The amounts of H₂O₂ detected also varied, which decreased in the order of the reactions with Fe(III)-citrate > goethite > ferrihydrite. S. oneidensis MR-1 maintained its ability to produce Fe(II) and H₂O₂ for up to seven anoxic/oxic cycles. At each end of anoxic/oxic cycle, HO^● was detected. The amount of HO^● produced decreased in the order of the reactions with ferrihydrite > goethite > Fe(III)-citrate, which was opposite to that of H₂O₂ detected. Compared to the controls without HO^●, the amounts of BDE-47 in the reactions with HO^● decreased. The more HO^● in the reaction, the less amount of BDE-47 detected. Furthermore, no BDE-47 degradation was observed when HO^● was scavenged or ferrihydrite was either omitted or replaced by nitrate. Finally, identification of degradation products, such as hydroxylated BDE-47 and trisBDE, dibromophenol and monobromophenol, suggested that OH-addition and Br-substitution by HO^● were the main mechanisms for degrading BDE-47. Collectively, all these results demonstrated for the first time that the Fenton reaction driven by S. oneidensis MR-1 degraded BDE-47 effectively.

P-nitrophenol degradation by pine-wood derived biochar: The role of redox-active moieties and pore structures

Biochar can both adsorb and degrade p-nitrophenol (PNP); however, the PNP degradation mechanism has not been well investigated. We prepared two biochars at pyrolysis temperatures of 500 °C (B500) and 700 °C (B700). Although B500 showed much stronger free radical signals (which are associated with organic degradation, according to previous studies), the apparent PNP degradation was approximately 3 times higher in the B700 system. The degradation increased significantly after the biochars were washed with water. According to a quantitative analysis of the sorption and degradation and two-compartment first-order kinetics modeling of the apparent removal kinetics, sorption occurred mainly in the initial period, whereas degradation continued throughout the removal process. The PNP degradation rate constant depended mainly on the external surface area at a relatively low concentration (200 mg/L) and was controlled by the microporous surface area at a relatively high concentration (800 mg/L). In addition, the apparent degradation did not depend on the biochar particle size. Therefore, PNP degradation may be related to the three-dimensional structure of the biochar in addition to the exposed external surface. The well-developed pore structure, more accessible surface, and larger electron exchange capacity of B700 may promote electron transfer between the biochar and PNP, and thus accelerate PNP degradation. This study demonstrates that various properties of the biochar may contribute to PNP degradation.

Effective passivation of lead by phosphate solubilizing bacteria capsules containing tricalcium phosphate

Phosphate solubilizing bacteria (PSBs) shows high potential to be used for lead passivation in sediments due to the abilities of releasing phosphate and the subsequent formation of insoluble Pb-phosphate compounds. In this research, microbial capsules implemented with sodium alginate and CaCl₂, containing Leclercia adecarboxylata L15 (a lead resistant PSB) and Ca₃(PO₄)₂, were developed and the performance on lead passivation under different conditions was examined. The optimal concentrations of sodium alginate and CaCl₂ for formulating the capsules were determined to be 0.3% and 10%, respectively. The removal efficiency of Pb²⁺ by capsules containing L15 and Ca₃(PO₄)₂ was up to 98% with a capsule dosage of 2%, initial Pb²⁺ concentration of 1mM and pH of 3.0, which was better than that of free L15 (18%) and capsules containing only L15 (34%). Lead was immobilized via the formation of Pb₅(PO₄)₃Cl on the surface and Pb₃(PO₄)₂ in the interior of the capsules. The simulated sediment remediation experiments showed that the acid soluble fraction of lead reduced from 28% to 14% and transformed into more stable fractions after 10 days. The experiment results indicated that PSBs capsules coupled with phosphate materials have a great promise for application in remediation of lead contaminated sediments.

Role of Pyrogenic Carbon in Parallel Microbial Reduction of Nitrobenzene in the Liquid and Sorbed Phases

Surface functional groups and graphitic carbons make up the electroactive components of pyrogenic carbon. The role of pyrogenic carbon with different contents of electroactive components in mediating electron transfer in biochemical reactions has not been systematically studied. Here, we determined the electron exchange capacity (EEC) of pyrogenic carbon to be 0.067-0.120 mmol e^-·(g of pyrogenic carbon)^-1, and the maximum electrical conductivity (EC) was 4.85 S·cm^-1. Nitrobenzene was simultaneously reduced in both the liquid and sorbed phases by Shewanella oneidensis MR-1 in the presence of pyrogenic carbon. Pyrogenic carbon did not affect the aqueous nitrobenzene reduction, and the reduction of sorbed nitrobenzene was much slower than that of the aqueous species. Enhancing contents of oxygenated functional moieties in pyrogenic carbon with HNO₃ oxidation elevated bioreduction rates of the aqueous and sorbed species. Anthraquinone groups were deemed as the most likely oxygenated functional redox compounds on the basis of both voltammetric curve tests and spectroscopic analysis. The reactivity of pyrogenic carbon in mediating the reduction of sorbed nitrobenzene was positively correlated with its EC, which was demonstrated to be related to condensed aromatic structures. This work elucidates the mechanism for pyrogenic carbon-mediated biotransformation of nitrobenzene and helps properly evaluate the role of pyrogenic carbon in biogeochemical redox processes happening in nature.

Fate of lower-brominated diphenyl ethers (LBDEs) in a red soil - Application of 14C-labelling

Lower-brominated diphenyl ethers (LBDEs) occur ubiquitously in soil, however their fate there has not been well evaluated, mainly owing to that the unavailability of commercial radioactively labelled LBDE congeners hampers the investigation on fate of LBDEs in the environment with complex matrixes, such as soil and sediment. Here, we successfully synthesized three congeners of LBDEs, i.e., 4-bromodiphenyl ether (BDE3), 4,4'-dibromodiphenyl ether (BDE15), and 2,2',4,4'-tetrabromodiphenyl ether (BDE47), with ¹⁴C-labelling on one aromatic ring, starting from commercially available ¹⁴C-labelled phenol in two steps with high yields and high radiochemical purities. Using the ¹⁴C-labelled congeners, we studied the fate of LBDEs in a red soil under oxic conditions, where LBDEs have been frequently detected in high levels. The major fate of the LBDE congeners in the soil was formation of NERs, followed by mineralization to CO₂, while no transformation product was detected in the soil after incubation for 105 days. The mineralization strongly decreased with increasing number of the bromine atom on the congener molecule, amounting to 10.4 ± 0.3%, 2.45 ± 0.04%, and 0.51 ± 0.05% for BDE3, BDE15, and BDE47, respectively, at the end of incubation, while mineralization rate constant was independent of the molecular structure, suggesting that solubility of LBDEs is the limit factor for their persistence in soil. The mineralization was positively linearly correlated with the formation of NERs (22.5 ± 1.9%, 11.0 ± 3.6%, and 6.7 ± 2.7% for BDE3, BDE15, and BDE47, respectively), which was mainly located in humin fraction and formed also in sterilized soil, suggesting a binding of transformation intermediates to soil humic substances and a physico-chemical entrapment of LBDEs in soil. The results provide new insights into fate of LBDE congeners in soil, and suggest a need to elucidate nature of the NERs of LBDEs, especially the stability of NERs in the environment.

Assessing microbial degradation degree and bioavailability of BDE-153 in natural wetland soils: Implication by compound-specific stable isotope analysis

Microbial degradation is an important pathway for the attenuation of polybrominated diphenyl ethers (PBDEs) in natural soils. In this study, the compound-specific stable isotope analysis (CSIA) was applied to characterize microbial degradation of BDE-153, one of the prevailing and toxic PBDE congeners, in natural wetland soils. During the 45-day incubation, the residual percentages of BDE-153 decreased to 67.9% and 73.6% in non-sterilized soils spiked with 1.0 and 5.0 μg/g, respectively, which were both much lower than those in sterilized soils (96.0% and 97.2%). This result indicated that microbial degradation could accelerate BDE-153 elimination in wetland soils. Meanwhile, the significant carbon isotope fractionation was observed in non-sterilized soils, with δ¹³C of BDE-153 shifting from -29.4‰ to -26.7‰ for 1.0 μg/g and to -27.2‰ for 5.0 μg/g, respectively, whilst not in sterilized soils. This phenomenon indicated microbial degradation could induce stable carbon isotope fractionation of BDE-153. The carbon isotope enrichment factor (ε_c) for BDE-153 microbial degradation was first determined as -7.58‰, which could be used to assess the microbial degradation and bioavailability of BDE-153 in wetland soils. Based on δ¹³C and ε_c, the new methods were developed to dynamically and quantitatively estimate degradation degree and bioavailability of BDE-153 during degradation process, respectively, which could exclude interference of physical processes. This work revealed that CSIA was a promising method to investigate in situ microbial degradation of PBDEs in field studies.

Pyrolysis-temperature depended electron donating and mediating mechanisms of biochar for Cr(VI) reduction

Biochar could be involved in environmentally relevant redox reactions, and their redox-active moieties may change with pyrolysis temperature. In this study, pyrolysis-temperature depended electron donating and mediating ability of biochar for Cr(VI) reduction were evaluated. All biochar derived from peanut shell at 400-800 °C effectively reduced Cr(VI) into Cr(III), and the reduction capability decreased as the pyrolysis temperature increased (400-600 °C), and then increased (600-800 °C). The electron donating moieties transformed from the -OH functional groups at lower pyrolysis temperature (<600 °C) to the functional groups associated with conjugated structure at higher temperature (>600 °C). Biochar could mediate the reduction of Cr(VI) by lactate, with the reduction rates of Cr(VI) increased up to 16.3 and 345 times that by either biochar or lactate alone, respectively. The redox ability of biochar was the premise, but its conductivity was the dominant factor, for the mediating reduction of Cr(VI). The mediation capability of biochar increased with elevated pyrolysis-temperature due to its increased conductivity related to the growth of conjugated clusters and carbon defects. Our results indicated that pyrolysis-temperature affects the formation of functional groups and conjugated carbon structure of biochars which have a distinguishable influence on the electron donating and mediating ability for Cr(VI) reduction.

Degradation of BDE-47 in mangrove sediments with amendment of extra carbon sources

Polybrominated diphenyl ethers (PBDEs) are widely detected in coastal wetlands but their remediation is still difficult. In this study, different carbon sources, namely formate, acetate, pyruvate, lactate, succinate, methanol and ethanol, were added to mangrove sediments contaminated with BDE-47, a common PBDE congener, to enhance its degradation. After 2-month incubation, all carbon addition significantly enhanced degradation percentages. The residual BDE-47 percentage significantly correlated with the abundance of total bacteria and Dehalococcoides spp. The addition of methanol, acetate and succinate also achieved significantly higher degradation rates and shorter half-lives than sediments without carbon amendment at the end of 5-month incubation, although degradation percentages were comparable between sediments with and without extra carbon. The degradation pathway based on the profiles of degradation products was also similar among treatments. The results indicated the stimulatory effect of extra carbon sources on BDE-47 degradation in contaminated sediments was carbon- and time-specific.

Maize straw biochar addition inhibited pentachlorophenol dechlorination by strengthening the predominant soil reduction processes in flooded soil

Biochar has received increasing attention for its multifunctional applications as a soil amendment. The dual effect of biochar on reductive organic pollutants and soil biogeochemical processes under anaerobic environments in parallel has yet to be fully explored. In this study, anaerobic batch experiments were conducted to examine the effect of biochar on both reductive transformation of pentachlorophenol (PCP) and soil redox processes in flooded soil. Compared to biochar-free controls, the reductive dechlorination of PCP was significantly inhibited following biochar addition, with the inhibition degree increased with increasing amount of biochar. Dissimilatory iron and sulfate reduction, as well as the production of methane, were significantly enhanced following biochar addition. The bacterial and archaeal communities showed a functional selection responded to the addition of biochar and PCP, with the core functional groups at the genus level including Dethiobacter, Clostridium, Geosporobacter, Desulfuromonas, Desulfatitalea, and Methanosarcina. These findings indicated that biochar could affect soil microbial redox processes and may act as an electron mediator altering electron distribution from PCP dechlorination to the predominant soil reduction processes, and increase understanding regarding biochar's comprehensive effects on the remediation of natural flooded soil polluted by chlorinated organic pollutants that can be degraded reductively.

Do pyrene and Kandelia obovata improve removal of BDE-209 in mangrove soils?

Combined pollution caused by polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) in mangrove wetlands is serious, with their remediation to be been paid more and more attention. However, little is known about the combined impact of PAHs and mangrove species on removal of PBDEs in contaminated soils. In this study, BDE-209 and pyrene were selected and a 9 months experiment was conducted to explore how BDE-209 removal in contaminated soil varied with pyrene addition and Kandelia obovata planting, and to clarify corresponding microbial responses. Results showed that BDE-209 removals in soil induced by pyrene addition or K. obovata planting were significant and stable after 6 months, with the lowest levels of BDE-209 in combined pyrene addition with K. obovata planting. Unexpected, root uptake of BDE-209 in K. obovata was limited for BDE-209 removal in soil, which was verified by lower total amount of BDE-209 bioaccumulated in K. obovata's root. In soil without K. obovata planting, BDE-209 removal caused by pyrene addition coexisted with changed bacterial abundance at phylum Planctomycetes and Chloroflexi, class Planctomycetacia, and genus Blastopirellula. K. obovata-induced removal of BDE-209 in soil may be related to bacterial enrichment in phylum Proteobacteria, class Gammaproteobacteria and genus Ilumatobacter, Gaiella. Thus, in BDE-209 contaminated soil, microbial community responses induced by pyrene addition and K. obovata planting were different at phylum, class and genus levels. This is the first study demonstrating that pyrene addition and K. obovata planting could improve BDE-209 removal, and differently affected the corresponding responses of microbial communities.

Interaction with low molecular weight organic acids affects the electron shuttling of biochar for Cr(VI) reduction

Biochar can act as "electron shuttle" in soil redox reactions. It is possible that biochar accepts the electrons from low molecular weight organic acids (LMWOAs) in soil and then transfer them to the acceptors, e.g., Cr(VI). This study evaluated the interaction between seven soil LMWOAs and peanut shell biochar (BC) as well as its effect on the electron shuttling of biochar for Cr(VI) reduction. Both redox reactions and sorption process occurred during the interaction of biochar and LMWOAs, which altered the contents of Cr(VI) reduction-relevant groups (i.e., CO and CO) on the surface of biochar. The redox reactions were more important to the electron transfer between biochar produced at 400℃ (BC400) and LMWOAs due to the repeated cycle of reduction-oxidation of surface functional groups. The reduction rate of Cr(VI) by LMWOAs mediated by BC400 was 1.10-7.09 × 10^-3 h^-1, among which tartaric acid had the best reduction efficiency due to its highest reducing capability. For biochar produced at 700℃ (BC700), the sorption process of LMWOAs was the key factor to the direct electron shuttling process through the conjugated structure of biochar. The reduction rate of Cr(VI) by LMWOAs mediated by BC700 was significantly higher and ranged 7.40-864 × 10^-3 h^-1, with the oxalic acid having the best reduction efficiency due to its highest sorption capacity by BC700. The results obtained from this study can help to establish the linkage between biochar and LMWOAs in soil electron network, which better explains the multifunctional roles of biochar during the redox processes such as Cr(VI) reduction in soil.

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.