The effects of arsenic on dechlorination of trichloroethene by consortium DH: Microbial response and resistance

Innovative hollow fiber membranes decorated with cobalt-doped Mn₃O₄: Sustainable solution for effective tetracycline removal from wastewater

Tetracycline (TC) contamination in aquatic environments poses ecological and public health risks due to its persistence and role in antibiotic resistance. Although manganese oxides can oxidatively degrade TC, their instability due to Mn loss limits practical application. In this study, we developed an innovative oxygen-based membrane reactor decorated with cobalt-doped Mn₃O₄ to enhance TC degradation efficiency and material stability. Comprehensive characterization confirmed uniform cobalt doping and structural modifications of Mn₃O₄. Under optimal conditions (pH 7.0 and 0.06 MPa oxygen pressure), the cobalt-doped reactor achieved a TC removal efficiency of 92.9 % at a concentration of 15 mg/L, following pseudo-first-order kinetics (kobs = 0.1962 h⁻¹), outperforming the undoped reactor. Multi-cycle stability tests showed the manganese loss rate of the cobalt-doped system was one-sixth that of the undoped system and retained > 85 % TC degradation efficiency over 10 cycles. Mechanistic studies identified superoxide radicals (•O₂⁻) as the important reactive species, confirmed by electron paramagnetic resonance and quenching experiments. Mass spectrometry analysis further showed that cobalt doping redirects TC degradation pathways, reducing toxicity of transformation products and increasing mineralization to 25 % (vs. 12 % in the control). We propose that cobalt mitigates manganese loss during the reaction, enhancing the stability and reactivity of Mn₃O₄ on hollow fibers. This study offers an effective and sustainable approach for antibiotic degradation from wastewater.

A critical review on ocean acidification driven by disinfection by-products discharge from ships' ballast water management systems: Impacts on carbon chemistry

The world's blue economy is closely tied to maritime trade, but ballast water from ships often carries harmful aquatic organisms and pathogens, which disrupt the marine environment. To address this, the International Maritime Organization (IMO) mandated ballast water treatment to eradicate these invasive species. However, the treatment processes inherently generate numerous Disinfection by-Products (DBPs). The discharge of these DBPs exacerbates ocean acidification through various acid- and CO2-releasing reactions. The IMO's Ballast Water Working Group has listed 41 high-priority DBPs for risk assessment due to their toxicity and prevalence in treated ballast water. This review quantitatively evaluates changes in pH and carbonate ions in seawater using the PyCO2SYS software package. Results reveal that DBPs can reduce ocean pH by ∼0.057 units and carbonate ion concentrations by 24.06 μmol kg-1 during a single discharge of 1 m3 treated water. In addition, this review outlines the challenges and research gaps for marine ecosystems sustainability.

Trichloroethylene detoxification in low-permeability soil via electrokinetic-enhanced bioremediation technology: Long-term feasibility and spatial-temporal patterns

In situ remediation of low-permeability soils contaminated with trichloroethylene (TCE) is challenging due to limited mass transfer and low bioavailability in clay soils. The electrokinetic-enhanced bioremediation (EK-BIO) system offers a promising solution by combining electrokinetics with bioremediation to address these challenges. While previous studies have demonstrated microbial succession and TCE removal, the long-term performance of dechlorination and interactions between electrode reactions and anaerobic dechlorination remain unclear. This study constructed five one-dimensional columns, each operated for a different period (28, 42, 56, 84 and 138 days) to explore spatial and temporal dechlorination patterns. Continuous TCE degradation was achieved, with 46.52 % of TCE recovery. Prolonged electrokinetic operation accelerated the first-step dehalogenation (TCE to DCE). Although Dehalococcoides was widespread at 138 days (2.30-5.74 %), oxygen exposure led to irreversible damage, necessitating secondary inoculation. The presence of aerobic bacteria (Comamonas and Pseudomonas) suggested the formation of aerobic detoxification pathways in electrode chambers. Gene expression analysis (tceA, vcrA and Dhc16S) further confirmed the loss of 2nd and 3rd step dehalogenation (DCE to ethene) over time. These findings demonstrate that secondary inoculation and alternative aerobic pathways can sustain long-term biodegradation in the EK-BIO system. This study highlights the potential of the EK-BIO system for effective remediation of TCE-contaminated low-permeability soils, supporting its field application.

Control of dissolved H2 concentration enhances electron generation, transport and TCE reduction by indigenous microbial community

Electrokinetic enhanced bioremediation (EK-Bio) is practical for trichloroethene (TCE) dechlorination because the cathode can produce a wide range of dissolved H2 (DH) concentrations of 1.3-0 mg/L from the electrode to the aquifer. In this study, TCE dechlorination was investigated under different DH concentrations. The mechanisms were discussed by analyzing the microbial community structure and abundance of organohalide-respiring bacteria (OHRB) using 16S rRNA, and the gene abundances of key enzymes in the TCE electron transport chain using metagenomic analysis. The results showed that the moderate DH concentration of 0.19-0.53 mg/L exhibited the most pronounced TCE dechlorination, even better than the higher DH concentrations, due to the optimal redox environment, the enrichments of OHRB, reductive dehalogenase (rdhA) genes and key enzyme genes in the electron generation and transport chain. More electrons were obtained from H2 metabolism by Dehalobacter by promoting the formation of [NiFe] hydrogenase (HupS/L/C) or from glycolysis by versatile OHRB by stimulating the formation of formate and enriching formate dehydrogenase (FDH) under moderate DH conditions. In addition, the enhanced amino acid metabolism improved the vitamin K cycle for electron transport and enriched the reductive dechlorinating enzyme (RDase) genes. This study identifies the optimal DH concentration that facilitates bioremediation efficiency, provides insights into microbial community shifts and key enzymatic pathways in EK-Bio remediation.

Enhancing reductive dechlorination of trichloroethylene in bioelectrochemical systems with conductive materials

The incorporation of conductive materials to enhance electron transfer in bioelectrochemical systems (BES) is considered a promising approach. However, the specific effects and mechanisms of these materials on trichloroethylene (TCE) reductive dechlorination in BES remains are not fully understood. This study investigated the use of magnetite nanoparticles (MNP) and biochars (BC) as coatings on biocathodes for TCE reduction. Results demonstrated that the average dechlorination rates of MNP-Biocathode (122.89 μM Cl·d-1) and BC-Biocathode (102.88 μM Cl·d-1) were greatly higher than that of Biocathode (78.17 μM Cl·d-1). Based on MATLAB calculation, the dechlorination rate exhibited a more significantly increase in TCE-to-DCE step than the other dechlorination steps. Microbial community analyses revealed an increase in the relative abundance of electroactive and dechlorinating populations (e.g., Pseudomonas, Geobacter, and Desulfovibrio) in MNP-Biocathode and BC-Biocathode. Functional gene analysis via RT-qPCR showed the expression of dehalogenase (RDase) and direct electron transfer (DET) related genes was upregulated with the addition of MNP and BC. These findings suggest that conductive materials might accelerate reductive dechlorination by enhancing DET. The difference of physicochemical characteristics (e.g. particle size and specific surface area), electron transfer enhancement mechanism between MNP and BC as well as the reduction of Fe(III) by hydrogen may explain the superior dechlorination rate observed with MNP-Biocathode.

Sulfate-driven microbial collaboration for synergistic remediation of chloroethene-heavy metal pollution

The treatment of heavy metal(loid) (HM) composite pollution has long posed a challenge for the bioremediation of organohalide-contaminated sites. Given the prevalent cohabitation of sulfate-reducing bacteria (SRB) with organohalide-respiring bacteria (OHRB), we proposed a sulfate-amendment strategy to achieve synergistic remediation of trichloroethene and diverse HMs [50μM of As(III), Ni(II), Cu(II), Pb(II)]. Correspondingly, 50-75 μM sulfate was introduced to HM inhibitory batches to investigate the enhancement effect of sulfate amendment on bio-dechlorination. Dechlorination kinetics and MATLAB modeling indicated that sulfate amendment comprehensively improved the reductive dechlorination performance in the presence of As(III), Ni(II), Pb(II) and mixed HMs, while no enhancement was observed under Cu(II) exposure. Additionally, sulfate introduction effectively accelerated the detoxification of Ni(II), Pb(II), Cu(II), and As(III), achieving removal efficiencies of 76.87 %, 64.01 %, 86.37 %, and 95.50 % within the first three days, respectively. Meanwhile, propionate dynamics and acetogenesis indicated enhanced carbon source and e-donor supply. 16S rRNA gene sequencing and metagenomic analysis results demonstrated that HM sequestration was accomplished jointly by SRB and HM-resistant bacteria via extracellular precipitation (metal sulfide) and intracellular sequestration, while their contribution depended on the specific coexisting HM species present. This study highlights the critical role of sulfate in the concurrent bioremediation of HM-organohalide composite contamination and provides insights for developing a cost-effective in-situ bioremediation strategy.

Achieving Long-Term Stability of Partial Nitrification and Autotrophic Denitrification in an MABR via Sulfide Dosing

While partial nitrification (PN) has the potential to reduce energy for aeration, it has proven to be unstable when treating low-strength wastewater. This study introduces an innovative combined strategy incorporating a low rate of oxygen supply, pH control, and sulfide addition to selectively inhibit nitrite-oxidizing bacteria (NOB). This strategy led to a stable PN in a laboratory-scale membrane aerated biofilm reactor (MABR). Over a period of 260 days, the nitrite accumulation ratio exceeded 60% when treating synthetic sewage containing 50 mg NH4+-N/L. Through in situ activity testing and high-throughput sequencing, the combined strategy led to low levels of nitrite-oxidation activity (<5.5 mg N/m2 h), Nitrospira species (relative abundance <1%), and transcription of nitrite-oxidation genes (undetectable). The addition of sulfide led to simultaneous PN and autotrophic denitrification in the single-stage MABR, resulting in over 60% total inorganic nitrogen removal. Sulfur-based autotrophic denitrification consumed nitrite and inhibited NOB conversion of nitrite to nitrate. The combined strategy has potential to be applied in large-scale sewage treatment and deserves further exploration.

Elucidating the impacts of cobalt (II) ions on extracellular electron transfer and pollutant degradation by anodic biofilms in bioelectrochemical systems during industrial wastewater treatment

Electrogenic biofilms in bioelectrochemical systems (BES) are critical in wastewater treatment. Industrial effluents often contain cobalt (Co2+); however, its impact on biofilms is unknown. This study investigated how increasing Co2+ concentrations (0-30 mg/L) affect BES biofilm community dynamics, extracellular polymeric substances, microbial metabolism, electron transfer gene expression, and electrochemical performance. The research revealed that as Co2+ concentrations increased, power generation progressively declined, from 345.43 ± 4.07 mW/m2 at 0 mg/L to 160.51 ± 0.86 mW/m2 at 30 mg/L Co2+. However, 5 mg/L Co2+ had less effect. The Co2+ removal efficiency in the reactors fed with 5 and 10 mg/L concentrations exceeded 99% and 94%, respectively. However, at 20 and 30 mg/L, the removal efficiency decreased substantially, likely because of reduced biofilm viability. FTIR indicated the participation of biofilm functional groups in Co2+ uptake. XPS revealed Co2+ presence in biofilms as CoO and Co(OH)2, indicating precipitation also aided removal. Cyclic voltammetry and electrochemical impedance spectroscopy tests revealed that 5 mg/L Co2+ had little impact on the electrocatalytic activity, while higher concentrations impaired it. Furthermore, at a concentration of 5 mg/L Co2+, there was an increase in the proportion of the genus Anaeromusa-Anaeroarcus, while the genus Geobacter declined at all tested Co2+ concentrations. Additionally, higher concentrations of Co2+ suppressed the expression of extracellular electron transfer genes but increased the expression of Co2+-resistance genes. Overall, this study establishes how Co2+ impacts electrogenic biofilm composition, function, and treatment efficacy, laying the groundwork for the optimized application of BES in remediating Co2+-contaminated wastewater.

Electrokinetic bioremediation of trichloroethylene and Cr/As co-contaminated soils with elevated sulfate

Co-contaminants and complex subsurface conditions pose great challenges to site remediation. This study demonstrates the potential of electrokinetic bioremediation (EK-BIO) in treating co-contaminants of chlorinated solvents and heavy metals in low-permeability soils with elevated sulfate. EK-BIO columns were filled with field soils, and were fed by the electrolyte containing 20 mg/L trichloroethylene (TCE), 250 μM Cr(VI), 25 μM As(III), 10 mM lactate, and 10 mM sulfate. A dechlorinating consortium containing Dehalococcoides (Dhc) was injected several times during a 199-d treatment at ∼1 V/cm. Sulfate reduction, Cr/As immobilization, and complete TCE biodechlorination were observed sequentially. EK-BIO facilitated the delivery of lactate, Cr(VI)/As(III), and sulfate to the soils, creating favorable reductive conditions for contaminant removal. Supplementary batch experiments and metagenomic/transcriptomic analysis suggested that sulfate promoted the reductive immobilization of Cr(VI) by generating sulfide species, which subsequently enhanced TCE biodechlorination by alleviating Cr(VI) toxicity. The dechlorinating community displayed a high As(III) tolerance. Metagenomic binning analysis revealed the dechlorinating activity of Dhc and the potential synergistic effects from other bacteria in mitigating heavy metal toxicity. This study justified the feasibility of EK-BIO for co-contaminant treatment and provided mechanistic insights into EK-BIO treatment.

Unveiling the inhibitory mechanisms of chromium exposure on microbial reductive dechlorination: Kinetics and microbial responses

Chromium and organochlorine solvents, particularly trichloroethene (TCE), are pervasive co-existing contaminants in subsurface aquifers due to their extensive industrial use and improper disposal practices. In this study, we investigated the microbial dechlorination kinetics under different TCE-Cr(Ⅲ/VI) composite pollution conditions and elucidated microbial response mechanisms based on community shift patterns and metagenomic analysis. Our results revealed that the reductive dechlorinating consortium had high resistance to Cr(III) but extreme sensitivity to Cr(VI) disturbance, resulting in a persistent inhibitory effect on subsequent dechlorination. Interestingly, the vinyl chloride-respiring organohalide-respiring bacteria (OHRB) was notably more susceptible to Cr(III/VI) exposure than the trichloroethene-respiring one, possibly due to inferior competition for growth substrates, such as electron donors. In terms of synergistic non-OHRB populations, Cr(III/VI) exposure had limited impacts on lactate fermentation but significantly interfered with H2-producing acetogenesis, leading to inhibited microbial dechlorination due to electron donor deficiencies. However, this inhibition can be effectively mitigated by the amendment of exogenous H2 supply. Furthermore, being the predominant OHRB, Dehalococcoides have inherent Cr(VI) resistance defects and collaborate with synergistic non-OHRB populations to achieve concurrent bio-detoxication of Cr(VI) and TCE. Our findings expand the understanding of the response patterns of different functional populations towards Cr(III/VI) stress, and provide valuable insights for the development of in situ bioremediation strategies for sites co-contaminated with chloroethene and chromium.

Biomolecular insights into the inhibition of heavy metals on reductive dechlorination of 2,4,6-trichlorophenol in Pseudomonas sp. CP-1

Influences of heavy metal exposure to the organohalide respiration process and the related molecular mechanism remain poorly understood. In this study, a non-obligate organohalide respiring bacterium, Pseudomonas sp. strain CP-1, was isolated and its molecular response to the five types of commonly existed heavy metal ions were thoroughly investigated. All types of heavy metal ions posed inhibitory effects on 2,4,6-trichlorophenol dechlorination activity and cell growth with the varied degree. Exposure to Cu (II) showed the most serious inhibitive effects on dechlorination even at the lowest concentration of 0.05 mg/L, while the inhibition by As (V) was the least with the removal kinetic constant k decreased to 0.05 under 50 mg/L. Further, multi-omics analysis found compared with Cu (II), As (V) exposure led to the insignificant downregulation of a variety of biosynthesis processes, which would be one possible account for the less inhibited activity. More importantly, the inhibited mechanisms on the organohalide respiration catabolism of strain CP-1 were firstly revealed. Cu (II) stress severely downregulated NADH generation during TCA cycle and electron donation of organohalide respiration process, which might decrease the reducing power required for organohalide respiration. While both Cu (II) and As (Ⅴ) inhibited substrate level phosphorylation during TCA cycle, as well as electron transfer and ATP generation during organohalide respiration. Meanwhile, CprA-2 was confirmed as the responsible reductive dehalogenase in charge of 2,4,6-TCP dechlorination, and transcriptional and proteomic studies confirmed the directly inhibited gene transcription and expression of CprA-2. The in-depth reveal of inhibitory effects and mechanism gave theoretical supports for alleviating heavy metal inhibition on organohalide respiration activity in groundwater co-contaminated with organohalides and heavy metals.