Enhancement of perchloroethene dechlorination by a mixed dechlorinating culture via magnetic nanoparticle-mediated isolation method

Enhanced dechlorination and degradation of Aroclor 1260 by resuscitation-promoting factor under alternating anaerobic-aerobic conditions: Superior performance and associated microbial populations

The combined processes of dechlorination and degradation are essential for the effective bioremediation of environments contaminated with complex polychlorinated biphenyl (PCB) mixtures. Although resuscitation-promoting factor (Rpf) has been reported to enhance anaerobic dechlorination and aerobic degradation of PCBs by microorganisms, its impact on microbial populations during alternating anaerobic-aerobic treatments remains unexplored. This study investigated the dechlorination and degradation of Aroclor 1260 under anaerobic (AN), aerobic (AE), and alternating anaerobic-aerobic (AA) conditions, both with and without Rpf supplementation. The results demonstrated that Rpf significantly promoted Aroclor 1260 dechlorination under AN conditions, enhanced degradation under AE conditions, and markedly improved both processes under AA conditions, achieving nearly twice the degradation efficiency compared to AE alone. Furthermore, Rpf supplementation significantly increased the abundance of dechlorination-associated microbial taxa, including members of Firmicutes, Chloroflexi, Bacteroidota, and Desulfobacterota under AN conditions, as well as degradation-associated genera such as Pseudomonas and Sphingomonas under AE and AA conditions. Rpf also strengthened microbial interactions by enhancing positive correlations among functional populations and increasing network complexity. These findings establish Rpf as a powerful enhancer of PCB dechlorination and degradation, which provide valuable insights into its superior efficiency in PCB removal under AA conditions.

Enhanced microbial dechlorination of PCBs by anaerobic digested sludge and enrichment of low-abundance PCB dechlorinators

The slow rate of anaerobic microbial dechlorination in natural environments limits the application of polychlorinated biphenyl (PCB) bioremediation. Anaerobic digested sludge (ADS), abundant in nutrients and microorganisms, could be an effective additive to improve microbial dechlorination. This research investigates the influence of ADS on Aroclor 1260 dechlorination performance, microbial community composition, and the abundance of functional genes. Moreover, further enrichment of organohalide-respiring bacteria (OHRB) was examined using tetrachloroethene (PCE) as the electron acceptor, followed by the serial dilution-to-extinction method in conjunction with resuscitation promoting factor (Rpf) supplementation. The results demonstrated that the addition of 5 g/L ADS achieved more extensive and efficient dechlorination of PCBs. ADS enhanced the removal of meta- and para-chlorine without significantly changing the dechlorination pathways. The abundances of dechlorinators, including Dehalobium and Dehalobacter within the Chloroflexi and Firmicutes phyla, as well as non-dechlorinators from the Desulfobacterota, Euryarchaeota, and Bacteroidetes phyla, were significantly increased with ADS amendment. Similarly, an increased abundance of bacteria, OHRB, reductive dehalogenase (RDase) genes, and archaeal 16S rRNA genes was observed. Additionally, obligate OHRB, such as Dehalobacter and Dehalobium, were further enriched. These findings indicate that ADS effectively enhances microbial reductive dechlorination and highlight the potential for enriching and isolating OHRB with Rpf.

Controlled electrocatalysis of the dechlorination and detoxification of chlorinated ethylenes to avoid production of highly toxic intermediates

In this study, electrochemical dechlorination and detoxification of a mixture of chlorinated ethylenes was investigated under various conditions using a double monoatomic synergistic metal catalytic cathode. Electrocatalytic degradation of mixed chlorinated with stepwise voltage and alternating current exhibited excellent dechlorination efficiency. The removal ratios of 1,2-dichloroethylene (1,2-DCE), trichloroethylene (TCE), and tetrachloroethylene (PCE) reached 78.79 %, 79.27 %, and 93.44 % in 10 min, and 98.14 %, 97.56 %, and 98.70 % in 30 min, respectively. The toxicity was evaluated using a quantitative structure-activity relationship model. The cumulative toxicity was reduced to 8.00 % of the initial cumulative toxicity in 30 min. An electrochemical dechlorination strategy for selective degradation and detoxification of mixtures of chlorinated pollutants is proposed. Controlled dechlorination and detoxification under low-voltage control avoided the accumulation of toxic intermediates. Cumulative toxicity was reduced by strategies of selective dechlorination, and segmented and alternating current decreased the energy consumption. The strategy provides a basis for alternating current electrocatalytic dechlorination associated with mixed chlorinated pollutants treatment.

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.

Unravelling the processes involved in biodegradation of chlorinated organic pollutant: From microbial community to isolated organohalide degraders

Hundreds of studies have demonstrated the bioremediation of chlorinated organic pollutants (COPs) in flooded environments. However, the role of specific functional strains in degrading COPs under complex media such as wetlands is still unclear. Here, we focused on the microbial characteristics of COP-polluted sediments, identified the bacteria responsible for degradation and conducted a genomic analysis of these bacteria. Four strains were obtained and identified as Petrimonas sulfuriphila PET, Robertmurraya sp. CYTO, Hungatella sp. CloS1 and Enterococcus avium PseS3, respectively. They were capable of degrading a typical COP, γ-hexachlorocyclohexane (γ-HCH). The residual γ-HCH concentrations were 58.8 % (PET), 45.6 % (CYTO), 60.2 % (CloS1), and 69.3 % (PseS3) of its initial value, respectively. Strain PET, CYTO and CloS1 could degrade γ-HCH to its dehalogenation product chlorobenzene. Each strain harbors genes annotated to the pathway of halogenated organic matter degradation (e.g. 2-haloacid dehalogenase) and cobalamin biosynthesis, which are involved in the degradation of COPs. Comparative genomic analysis of the four strains and other classical organohalide-respiring bacteria (e.g. Dehalococcoides mccartyi and Sulfurospirillum multivorans DSM 12446) showed that they share orthologous clusters related to the cobalamin biosynthetic process (GO:0009236). VB12 was also detected in the culture systems of the four strains, further highlighting the importance of cobalamin in COPs degradation. In the genome of the four strains, some genes were annotated to the halogenated organic matter degradation and cobalamin biosynthesis pathway within horizontal gene transfer (HGT) regions. This further indicated that microorganisms carrying these genes can adapt faster to pollution stress through HGT. Together, these findings revealed the co-evolution mechanism of functional strains and may provide novel insights into improved bioremediation strategies for COP-polluted complex media based on generalist organochlorine-degrading bacteria.

Magnetic nanoparticle-mediated enrichment technology combined with microfluidic single cell separation technology: A technology for efficient separation and degradation of functional bacteria in single cell liquid phase

Although there are many microorganisms in nature, the limitations of isolation and cultivation conditions have restricted the development of artificial enhanced remediation technology using functional microbial communities. In this study, an integrated technology of Magnetic Nanoparticle-mediated Enrichment (MME) and Microfluidic Single Cell separation (MSC) that breaks through the bottleneck of traditional separation and cultivation techniques and can efficiently obtain more in situ functional microorganisms from the environment was developed. MME technology was first used to enrich rapidly growing active bacteria in the environment. Subsequently, MSC technology was applied to isolate and incubate functional bacterial communities in situ and validate the degradation ability of individual bacteria. As a result, this study has changed the order of traditional pure culture methods, which are first selected and then cultured, and provided a new method for obtaining non-culturable functional microorganisms.

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.

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

Inorganic arsenic and organochlorines are frequently co-occurring contaminants in anoxic groundwater environments, and the bioremediation of their composite pollution has long been a rigorous predicament. Currently, the dechlorination behaviors and stress responses of microbial dechlorination consortia to arsenic are not yet fully understood. This study assessed the reductive dechlorination performance of a Dehalococcoides-bearing microcosm DH under gradient concentrations of arsenate [As(V)] or arsenite [As(III)] and investigated the response patterns of different functional microorganisms. Our results demonstrated that although the dechlorination rates declined with increasing arsenic concentrations in both As(III/V) scenarios, the inhibitory impact was more pronounced in As(III)-amended groups compared to As(V)-amended groups. Moreover, the vinyl chloride (VC)-to-ethene step was more susceptible to arsenic exposure compared to the trichloroethene (TCE)-to-dichloroethane (DCE) step, while high levels of arsenic exposure [e.g. As(III) > 75 μM] can induce significant accumulation of VC. Functional gene variations and microbial community analyses revealed that As(III/V) affected reductive dechlorination by directly inhibiting organohalide-respiring bacteria (OHRB) and indirectly inhibiting synergistic populations such as acetogens. Metagenomic results indicated that arsenic metabolic and efflux mechanisms were identical among different Dhc strains, and variations in arsenic uptake pathways were possibly responsible for their differential responses to arsenic exposures. By comparison, fermentative bacteria showed high potential for arsenic resistance due to their inherent advantages in arsenic detoxification and efflux mechanisms. Collectively, our findings expanded the understanding of the response patterns of different functional populations to arsenic stress in the dechlorinating consortium and provided insights into modifying bioremediation strategies at co-contaminated sites for furtherance.

Resuscitation-Promoting Factor Accelerates Enrichment of Highly Active Tetrachloroethene/Polychlorinated Biphenyl-Dechlorinating Cultures

The anaerobic bioremediation of polychlorinated biphenyls (PCBs) is largely impeded by difficulties in massively enriching PCB dechlorinators in short periods of time. Tetrachloroethene (PCE) is often utilized as an alternative electron acceptor to preenrich PCB-dechlorinating bacteria. In this study, resuscitation promoting factor (Rpf) was used as an additive to enhance the enrichment of the microbial communities involved in PCE/PCBs dechlorination. The results indicated that Rpf accelerates PCE dechlorination 3.8 to 5.4 times faster than control cultures. In Aroclor 1260-fed cultures, the amendment of Rpf enables significantly more rapid and extensive dechlorination of PCBs. The residual high-chlorinated PCB congeners (≥5 Cl atoms) accounted for 36.7% and 59.8% in the Rpf-amended cultures and in the corresponding controls, respectively. This improvement was mainly attributed to the enhanced activity of the removal of meta-chlorines (47.7 mol % versus 14.7 mol %), which did not appear to affect dechlorination pathways. The dechlorinators, including Dehalococcoides in Chloroflexi and Desulfitobacterium in Firmicutes, were greatly enriched via Rpf amendment. The abundance of nondechlorinating populations, including Methanosarcina, Desulfovibrio, and Bacteroides, was also greatly enhanced via Rpf amendment. These results suggest that Rpf serves as an effective additive for the rapid enrichment of active dechlorinating cultures so as to provide a new approach by which to massively cultivate bioinoculants for accelerated in situ anaerobic bioremediation. IMPORTANCE The resuscitation promoting factor (Rpf) of Micrococcus luteus has been reported to resuscitate and stimulate the growth of functional microorganisms that are involved in the aerobic degradation of polychlorinated biphenyls (PCBs). However, few studies have been conducted to investigate the role of Rpf on anaerobic microbial populations. In this study, the enhancement of Rpf on the anaerobic microbial dechlorination of PCE/PCBs was discovered. Additionally, the Rpf-responsive populations underlying the enhanced dechlorination were uncovered. This report reveals the rapid enrichment of active dechlorinating cultures via Rpf amendment, and this sheds light on massively enriching PCB dechlorinators in short periods of time. The enhanced in situ anaerobic bioremediation of PCBs could be expected by supplementing Rpf.

Aerobic starvation treatment of activated sludge enhances the degradation efficiency of refractory organic compounds

Many refractory organic compounds (ROCs) in wastewater are toxic to human and aquatic organisms. Here, we reported an aerobic starvation approach to improve the degradation efficiencies of ROCs in activated sludge systems. The highest degradation rates of bisphenol AF (BPAF) (11.4 mg/g VSS · h) and gabapentin (GBP) (8.9 mg/g VSS · h) were achieved on the second day of the starvation process. While, the degradation rate of bisphenol A (BPA) on the 43rd day reached the maximum value of 0.8 mg/g VSS ·h, which was significantly higher than that of the seeding sludge (0.01 mg/g VSS · h). To investigate the mechanisms of this finding, we applied magnetic-nanoparticle mediated isolation, 16S rRNA gene sequencing, metagenomic sequencing and metatranscriptomic sequencing to analyze the microbial community structures and functions during the starvation process. The results showed that the increase of the BPA degradation ability was caused by the increase of the relative abundance of BPA degrading bacteria (Sphingomonas, Achromobacter, etc.), while, the enhancement of BPAF and GBP degradation was attributed to the increase of the expression of ROC degrading genes. Overall, these results improve our understanding of the microbial ecology of starved activated sludge and provide useful information for the future development of ROC removal technologies.

Optimization of Dechlorination Experiment Design Using Lightweight Deep Learning Model

This exploration intends to remove chloride ions in production and life, enhance buildings' durability, and protect the natural environment from pollution. The current dechlorination technology is discussed based on the relevant theories, such as the lightweight deep learning (DL) model and chloride ion characteristics. Next, data statistics and comparative analysis methods are used to study the adsorption and desorption performance of dechlorination adsorbents. Finally, the lightweight DL model is introduced into the chloride diffusion prediction experiment of slag powder and fly ash concrete. The results show that in the study of dechlorination adsorption performance, the chloride ion concentration decreases gradually with the extension of adsorption time. However, with the increasing temperature, the chloride ion removal rate is increasing. The removal rate of chloride ions in water can decrease slowly with the increase of adsorbent. Therefore, selecting the 2 mol/L sodium hydroxide as the alkali concentration for adsorbent regeneration is the most appropriate. Besides, the regeneration performance of the adsorbent gradually declines with the increase of sodium chloride concentration in the solution. The lightweight DL model is applied to the chloride diffusion prediction experiment of slag powder and fly ash concrete. It is found that when the curing age is selected at 18 days, 90 days, and 180 days, respectively, the error between the lightweight DL model and the experimental results is about 0.2. It shows that the lightweight DL model is feasible for predicting the diffusion of chloride ions. Therefore, this exploration designs and studies the dechlorination experiment based on the lightweight DL model, which provides a new theoretical basis and optimization direction for removing chloride ions in the future industry.