Degradation of pyrene using single-chamber air-cathode microbial fuel cells: Electrochemical parameters and bacterial community changes

Spatial distribution of volatile organic compounds in contaminated soil and distinct microbial effect driven by aerobic and anaerobic conditions

The vertical distribution of 35 volatile organic compounds (VOCs) was investigated in soil columns from two obsolete industrial sites in Eastern China. The total concentrations of ΣVOCs in surface soils (0-20 cm) were 134-1664 ng g-1. Contamination of VOCs in surface soil exhibited remarkable variability, closely related to previous production activities at the sampling sites. Additionally, the concentrations of ΣVOCs varied with increasing soil depth from 0 to 10 m. Soils at depth of 2 m showed ΣVOCs concentrations of 127-47,389 ng g-1. Among the studied VOCs, xylene was the predominant contaminant in subsoils (2 m), with concentrations ranging from n.d. to 45,400 ng g-1. Chlorinated alkanes and olefins demonstrated a greater downward migration ability compared to monoaromatic hydrocarbons, likely due to their lower hydrophobicity. As a result, this vertical distribution of VOCs led to a high ecological risk in both the surface and deep soil. Notably, the risk quotient (RQ) of xylene in subsoil (2 m, RQ up to 319) was much higher than that in surface soil. Furthermore, distinct effects of VOCs on soil microbes were observed under aerobic and anaerobic conditions. Specifically, after the 30-d incubation of xylene-contaminated soil, Ilumatobacter was enriched under aerobic condition, whereas Anaerolineaceae was enriched under anaerobic condition. Moreover, xylene contamination significantly affected methylotrophy and methanol oxidation functions for aerobic soil (t-test, p < 0.05). However, aromatic compound degradation and ammonification were significantly enhanced by xylene in anaerobic soil (t-test, p < 0.05). These findings suggest that specific VOC compound has distinct microbial ecological effects under different oxygen content conditions in soil. Therefore, when conducting soil risk assessments of VOCs, it is crucial to consider their ecological effects at different soil depths.

Integrated system of electro-catalytic oxidation and microbial fuel cells for the treatment of recalcitrant wastewater

The emission of recalcitrant wastewater poses serious threats to the environment. In this study, an integrated approach combining electrocatalytic oxidation (EC) for pretreatment and microbial fuel cells (MFC) for thorough pollutant degradation is proposed to ensure efficient degradation of target substances, with low energy input and enhanced bioavailability of refractory organics. When phenol was used as the pollutant, an initial concentration of 2000 mg/L phenol solution underwent EC treatment under constant current-exponential attenuation power supply mode, resulting in a COD removal rate of 54.53%, and a phenol degradation rate of 99.83%. Intermediate products such as hydroquinone and para-diphenol were detected in the solution. After subsequent MFC treatment, only minor amounts of para-diphenol were left, and the degradation rate of phenol and its intermediate products reached 100%, with an output power density of 110.4 mW m-2. When coal chemical wastewater was used as the pollutant, further examination of the EC-MFC system performance showed a COD removal rate of 49.23% in the EC section, and a 76.21% COD removal rate in the MFC section, with an output power density of 181.5 mW m-2. Microbiological analysis revealed typical electrogenic bacteria (such as Pseudomonas and Geobacter), and specific degrading functional bacteria (such as Stenotrophomonas, Delftia, and Brevundimonas). The dominant microbial communities and their proportions adapted to environmental changes in response to the variation of carbon sources.

Microbes and microbial strategies in carcinogenic polycyclic aromatic hydrocarbons remediation: a systematic review

Degradation, detoxification, or removal of the omnipresent polycyclic aromatic hydrocarbons (PAHs) from the ecosphere as well as their prevention from entering into food chain has never appeared simple. In this context, cost-effective, eco-friendly, and sustainable solutions like microbe-mediated strategies have been adopted worldwide. With this connection, measures have been taken by multifarious modes of microbial remedial strategies, i.e., enzymatic degradation, biofilm and biosurfactant production, application of biochar-immobilized microbes, lactic acid bacteria, rhizospheric-phyllospheric-endophytic microorganisms, genetically engineered microorganisms, and bioelectrochemical techniques like microbial fuel cell. In this review, a nine-way directional approach which is based on the microbial resources reported over the last couple of decades has been described. Fungi were found to be the most dominant taxa among the CPAH-degrading microbial community constituting 52.2%, while bacteria, algae, and yeasts occupied 37.4%, 9.1%, and 1.3%, respectively. In addition to these, category-wise CPAH degrading efficiencies of each microbial taxon, consortium-based applications, CPAH degradation-related molecular tools, and factors affecting CPAH degradation are the other important aspects of this review in light of their appropriate selection and application in the PAH-contaminated environment for better human-health management in order to achieve a sustainable ecosystem.

Microbial electrochemical system: an emerging technology for remediation of polycyclic aromatic hydrocarbons from soil and sediments

Worldwide industrialization and other human activities have led to a frightening stage of release of hazardous, highly persistent, toxic, insoluble, strongly adsorbed to the soil and high molecular weight ubiquitous polycyclic aromatic hydrocarbons (PAHs) in soils and sediments. The various conventional remediation methods are being used to remediate PAHs with certain drawbacks. Time taking process, high expenditure, excessive quantities of sludge generation, and various chemical requirements do not only make these methods outdated but produce yet much resistant and toxic intermediate metabolites. These disadvantages may be overcome by using a microbial electrochemical system (MES), a booming technology in the field of bioremediation. MES is a green remediation approach that is regulated by electrochemically active microorganisms at the electrode in the system. The key advantage of the system over the conventional methods is it does not involve any additional chemicals, takes less time, and generates minimal sludge or waste during the remediation of PAHs in soils. However, a comprehensive review of the MES towards bioremediation of PAHs adsorbed in soil and sediment is still lacking. Therefore, the present review intended to summarize the recent information on PAHs bioremediation, application, risks, benefits, and challenges based on sediment microbial fuel cell and microbial fuel cell to remediate mount-up industrial sludge, soil, and sediment rich in PAHs. Additionally, bio-electrochemically active microbes, mechanisms, and future perspectives of MES have been discussed.

Recent trends in polycyclic aromatic hydrocarbons pollution distribution and counteracting bio-remediation strategies

Polycyclic aromatic hydrocarbons (PAHs) are distributed worldwide due to long-term anthropogenic pollution sources. PAHs are recalcitrant and highly persistent in the environment due to their inherent properties, such as heterocyclic aromatic ring structures, thermostability, and hydrophobicity. They are highly toxic, carcinogenic, immunotoxic, teratogenic, and mutagenic to various life systems. This review focuses on the unique data of PAH sources, exposure routes, detection techniques, and harmful effects on the environment and human health. This review provides a comprehensive and systematic compilation of eco-friendly biological treatment solutions for PAH remediation, such as microbial remediation approaches utilizing microbial cultures. In situ and Ex situ bioremediation of PAH methods, including composting land farming, biopiles, bioreactors bioaugmentation, and phytoremediation processes, are discussed in detail, as is a summary of the factors affecting and limiting PAH bioremediation. This review provides an overview of emerging technologies that use multi-process combinatorial treatment approaches and answers to generating value-added by-products during PAH remediation.

Bioelectrochemical stability improvement by Ce-N modified carbon-based cathode in high-salt stress and mechanism research

Although microbial fuel cells (MFCs) have potential for high-salt wastewater treatment, their application is limited by poor salt tolerance, deactivation and unstable catalytic performance. This study designed Ce-C, N-C, and Ce-N modified activated carbon (Ce-N-C) based on the catalytic mechanism and salt tolerance performance of Ce and N elements to address these limitations. With activated carbon (AC) as the control, this study analyzed the stability of the four cathodes under different salinity environments using norfloxacin (NOR) as a probe to assess the effect of cathodes and salinity on MFC degradation performance. After three months, comparing with other three cathodes, the Ce-N-C cathode demonstrated superior and stable electrochemical and power generation performance. In particular, the advantages of Ce-N-C in high-salt (600 mM NaCl) environment is more significant than no-salt or low-salt. The potential of Ce-N-C-End at current density of 0 was 14.0% higher than AC-End, and the power density of the MFC with Ce-N-C cathode was 105.7 mW/m², which was 3.1 times higher than AC. Also, the stability of NOR removal under the function of Ce-N-C improved with the increase of NaCl concentration or operation time. The CeO₂(111) crystal form, N-Ce-O bond and pyridine N might be the key factors in improving the catalytic performance and salt tolerance of the Ce-N modified carbon-based cathode using XPS and XRD analysis.

Sustained-release nitrate combined with microbial fuel cell: A novel strategy for PAHs and odor removal from sediment

Nitrate addition is a biostimulation technique that can improve both the oxidation of acid volatile sulfide (AVS) through autotrophic denitrification and the biodegradation of polycyclic aromatic hydrocarbons (PAHs) via heterotrophic denitrification. However, during the remediation, parts of the dissolved nitrate in the sediment migrates from the sediment to the overlying water, leading to the loss of effective electron acceptor. To overcome this limitation, a combined approached was proposed, which involved nitrocellulose addition and a microbial fuel cell (MFC). Results indicated the nitrate could be slowly released and maintained at a higher concentration over long term. In the combined system, the removal efficiencies of PAHs and AVS were 71.56% and 89.76%, respectively. Furthermore, the voltage attained for the MFC-nitrocellulose treatment was maintained at 146.1 mV on Day 70, which was 5.37 times higher than that of the MFC-calcium nitrate treatment. Sediments with nitrocellulose resulted in lower levels of nitrate and ammonium in the overlying water. Metagenomic results revealed that the combined technology improved the expression of nitrogen-cycling genes. The introduction of MFC inhibited sulfide regeneration during incubation by suppressing the enzyme activity like EC4.4.1.2. The enhanced biostimulation provided potential for in-situ bioremediation utilizing MFC coupled with slow-released nitrate (i.e., nitrocellulose) treatment.

Biomonitoring of polycyclic aromatic hydrocarbons, heavy metals, and plasticizers residues: role of bees and honey as bioindicators of environmental contamination

Polycyclic aromatic hydrocarbons (PAHs), heavy metals, and plasticizer residues are continuously released into the environment. The use of living organisms, such as Apis mellifera L. and honey, is advantageous as bioindicator of the environmental health status, instead of traditional monitoring methods, showing the ability to record spatial and temporal pollutant variations. The PAHs and heavy metal presence were determined in two sampling years (2017 and 2018) in five different locations in the Molise region (Italy), characterized by different pollution levels. During 2017, most PAHs in all samples were lower than limit of detection (LOD), while in 2018, their mean concentration in bee and honey samples was of 3 μg kg^-1 and 35 μg kg^-1, respectively. For heavy metals, lower values were detected in 2017 (Be, Cd, and V below LOD), while in 2018, the mean concentrations were higher, 138 μg kg^-1 and 69 μg kg^-1, in bees and honey, respectively. Honey has been used as indicator of the presence of phthalate esters and bisphenol A in the environment. The satisfactory results confirmed that both bees and honey are an important tool for environmental monitoring. The chemometric analysis highlighted the differences in terms of pollutant concentration and variability in the different areas, validating the suitability of these matrices as bioindicators.

Mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX mixed contaminants in soil by native microbial consortium

Despite the co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) in the field, to date, knowledge on the bioremediation of benzene and benzo[a]pyrene (BaP) mixed contaminants is limited. In this study, the mechanisms underlying the biodegradation of benzene and BaP under individual and co-contaminated conditions followed by the enhanced biodegradation using methanol, ethanol, and vegetable oil as biostimulants were investigated. The results demonstrated that the benzene biodegradation was highly reduced under the co-contaminated condition compared to the individual benzene contamination, whereas the BaP biodegradation was slightly enhanced with the co-contamination of benzene. Moreover, biostimulation significantly improved the biodegradation of both contaminants under co-contaminated conditions. A trend of significant reduction in the bioavailable BaP contents was observed in all biostimulant-enhanced groups, implying that the bioavailable BaP was the preferred biodegradable BaP fraction. Furthermore, the enzymatic activity analysis revealed a significant increase in lipase and dehydrogenase (DHA) activities, as well as a reduction in the catalase and polyphenol oxidase, suggesting that the increased hydrolysis of fats and proton transfer, as well as the reduced oxidative stress, contributed to the enhanced benzene and BaP biodegradation in the vegetable oil treatment. In addition, the microbial composition analysis results demonstrated that the enriched functional genera contributed to the increased biodegradation efficiency, and the functional genera in the microbial consortium responded differently to different biostimulants, and competitive growth was observed in the biostimulant-enhanced treatments. In addition, the enrichment of Pseudomonas and Rhodococcus species was noticed during the biostimulation of benzene and BaP co-contamination soil, and was positively correlated with the DHA enzyme activities, indicating that these species encode DHA genes which contributed to the higher biodegradation. In conclusion, multiple lines of evidence were provided to shed light on the mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX co-contamination with native microbial consortiums.

Deciphering the fate of antibiotic resistance genes in norfloxacin wastewater treated by a bio-electro-Fenton system

The misuse of antibiotics has increased the prevalence of antibiotic resistance genes (ARGs), considered a class of critical environmental contaminants due to their ubiquitous and persistent nature. Previous studies reported the potentiality of bio-electro-Fenton processes for antibiotic removal and ARGs control. However, the production and fate of ARGs in bio-electro-Fenton processes triggered by microbial fuel cells are rare. In this study, the norfloxacin (NFLX) average residual concentrations within two days were 2.02, 6.07 and 14.84 mg/L, and the average removal efficiency of NFLX was 79.8 %, 69.6 % and 62.9 % at the initial antibiotic concentrations of 10, 20 and 40 mg/L, respectively. The most prevalent resistance gene type in all processes was the fluoroquinolone antibiotic gene. Furthermore, Proteobacteria was the dominant ARG-carrying bacteria. Overall, this study can provide theoretical support for the efficient treatment of high antibiotics-contained wastewater by bio-electro-Fenton systems to better control ARGs from the perspective of ecological security.

Ordered porous nitrogen-doped carbon with atomically dispersed FeN4 for efficient oxygen reduction reaction in microbial fuel cell

It is necessary to develop cost-effective platinum group materials (PGM)-free cathode catalysts for the oxygen reduction reaction (ORR) to replace the state-of-the-art noble metal for the commercialization of microbial fuel cells (MFCs). Fe-N-C catalysts are one of the promising candidates for commercial Pt/C. Herein, a new cost-effective and highly stable Fe-N-C catalyst was designed and successfully prepared via a facile process. The catalyst was prepared through one single thermal conversion from Fe-doped ZIF-8 (zeolitic imidazolate framework), a metal-organic framework (MOF) containing well-defined FeN₄ coordination. The mesopores in the unique structure of MOF promoted efficient mass transfer, while those arising from the pyrolysis of the MOF produced more active sites. Unlike previous preparation methods, post-treatments were avoided here. As a result, the Fe-N-C cathode had a high ORR activity with a half-wave potential (E_1/2) of 0.85 V in a 0.1 M KOH aqueous solution. The classic MFC with this cathodic catalyst provided a maximum power density of up to 1508 mW m^-2.

Bio-electrical stimulation process on degradation of Phenanthrene from aqueous solution using a novel anode modified with carbon cloth: Operational performance, microbial activity and energy

Phenanthrene as the hazardous PAHs-component are extensively detected in industrial wastewater. However, the impacts of bioelectrostimulation process on Phenanthrene degradation in aerobic reactors remained unclear. Here, a novel bioelectrostimulation process equipped with carbon cloth as electrodes was developed to investigate the removal efficiency of Phenanthrene and ATPase enzyme activity in the synthetic wastewater. The results obtained from the present study indicated that a complete Phenanthrene degradation (100%) can be achieved using microbial electrostimulation systems steel mesh coated with carbon cloth (MES-CC) as anode under optimal operational conditions (electrical current: 4 mA, HA concentration: 15 mg L^-1) within 18 h. The conductive carbon cloth provides a biofilm carrier to easily transfer the electrons between electrodes and microbial communities. In addition, the highest ATPase enzyme activity (5176 U) was observed when the aerobic MES-CC reactors were operated with electrical current 4 mA. Furthermore, the COD removal efficiency in MES-CC increased from 49% to 96% when the C: N ratio decreased from 20 to 5. The highest value of V_max in MES-CC for suspended and attached growth were determined to be 2.87 and 0.54 g COD g^-1 biomass. Overall, the results demonstrated that MES equipped with carbon cloth and continuous electrical current mode has good potential for efficient Phenanthrene wastewater treatment.

Remediation of soil polluted with petroleum hydrocarbons and its reuse for agriculture: Recent progress, challenges, and perspectives

Petroleum hydrocarbons (PHs) are used as raw materials in many industries and primary energy sources. However, excessive PHs act as soil pollutants, posing serious threats to living organisms. Various ex-situ or in-situ chemical and biological methods are applied to restore polluted soil. However, most of the chemical treatment methods are expensive, environmentally unfriendly, and sometimes inefficient. That attracts scientists and researchers to develop and select new strategists to remediate polluted soil through risk-based analysis and eco-friendly manner. This review discusses the sources of PHs, properties, distribution, transport, and fate in the environment, internal and external factors affecting the soil remediation and restoration process, and its effective re-utilization for agriculture. Bioremediation is an eco-friendly method for degrading PHs, specifically by using microorganisms. Next-generation sequencing (NGS) technologies are being used to monitor contaminated sites. Currently, these new technologies have caused a paradigm shift by giving new insights into the microbially mediated biodegradation processes by targeting rRNA are discussed concisely. The recent development of risk-based management for soil contamination and its challenges and future perspectives are also discussed. Furthermore, nanotechnology seems very promising for effective soil remediation, but its success depends on its cost-effectiveness. This review paper suggests using bio-electrochemical systems that utilize electro-chemically active microorganisms to remediate and restore polluted soil with PHs that would be eco-friendlier and help tailor-made effective and sustainable remediation technologies.