Enhanced trichloroethylene biodegradation: The mechanism and influencing factors of combining microorganism and carbon‑iron materials

Anaerobic and aerobic sequential process, a promising strategy for breaking the stagnate of biological reductive dechlorination-TCE bioremediation in the field application

Trichloroethylene (TCE) is a common chlorinated hydrocarbon contaminant in soil and groundwater, and reductive dechlorination is a biological remediation. However, the TCE reductive dechlorination often stagnates in the stage of cis-1,2-dichloroethylene (cDCE) and chloroethylene (VC). Anaerobic/aerobic sequential degradation provides a new approach for the complete detoxification of TCE, while there has been no systematic summary of bacteria, enzymes, and pathways in the synergistic process. Herein, the objectives of this review are (1) to discuss the reasons why it is difficult to completely reduce dechlorination; (2) to analyze the advantages and pathways of TCE complete detoxification through anaerobic/aerobic sequential degradation process; (3) to summarize the major bacteria and catalytic enzymes of the cDCE and VC oxidation process. This review will highlight the anaerobic/aerobic process in TCE biodegradation and increase understanding of the complete detoxification of chlorinated hydrocarbons.

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.

Laccase immobilized on amino modified magnetic biochar as a recyclable biocatalyst for efficient degradation of trichloroethylene

Bioremediation of trichloroethylene (TCE) contaminated groundwater has recently attracted considerable attention. In this study, laccase was immobilized on amino modified magnetic pine biochar (MBC-NH2) by adsorption-crosslinking-covalent binding method, and its application in the degradation of TCE was evaluated. MBC-NH2 was obtained from pine sawdust by calcination, magnetic modification and amino modification. MBC-NH2 had high specific surface area (71.3 m2/g), rich surface functional groups and good magnetism. Under the conditions of 25 °C, pH = 4, glutaraldehyde (GA) concentration of 7 %, crosslinking time of 1 h, laccase concentration of 0.75 mg/mL, and immobilization time of 7 h, the loading capacity of laccase on MBC-NH2 carrier was as high as 782 mg/g. Compared with free laccase, immobilized laccase showed higher pH stability and thermal stability, and its activity remained 48.5 % after being reused for 10 times, and 80.8 % after being stored at 4 °C for 30 days. The immobilized laccase exhibited a good degradation effect on TCE. At 25 °C, pH = 4, immobilized laccase concentration of 0.35 g/L, and initial TCE concentration of 10 mg/L, the degradation efficiency of TCE by immobilized laccase was as high as 92.1 % within 48 h. In addition, the degradation products of TCE were analyzed, and the results showed that immobilized laccase could degrade TCE into non-toxic products through epoxidation, hydroxylation, and dechlorination. The immobilized laccase biocatalyst prepared in this study can achieve efficient degradation of TCE, which provides a feasible solution for chlorinated pollution of water resources. These research results are of great significance for the synthesis of biocatalysts for the efficient degradation of chlorinated hydrocarbons.

Sustainable Abiotic-Biotic Dechlorination of Perchloroethene with Sulfidated Nanoscale Zero-Valent Iron as Electron Donor Source

Combining organohalide-respiring bacteria with nanoscale zero-valent iron (nZVI) represents a promising approach for remediating chloroethene-contaminated aquifers. However, limited information is available regarding their synergistic dechlorinating ability for chloroethenes when nZVI is sulfidated (S-nZVI) under the organic electron donor-limited conditions typically found in deep aquifers. Herein, we developed a combined system utilizing a mixed culture containing Dehalococcoides (Dhc) and S-nZVI particles, which achieved sustainable dechlorination with repeated rounds of spiking with 110 μM perchloroethene (PCE). The relative abundance of Dhc considerably increased from 5.2 to 91.5% after five rounds of spiking with PCE, as evidenced by 16S rRNA gene amplicon sequencing. S-nZVI corrosion generated hydrogen as an electron donor for Dhc and other volatile fatty acid (VFA)-producing bacteria. Electron balance analysis indicated that 68.1% of electrons from Fe0 consumed in S-nZVI were involved in dechlorination, and 6.2, 1.1, and 3.2% were stored in formate, acetate, and other VFAs, respectively. The produced acetate possibly served as a carbon source for Dhc. Metagenomic analysis revealed that Desulfovibrio, Syntrophomonas, Clostridium, and Mesotoga were likely involved in VFA production. These findings provide valuable insights into the synergistic mechanisms of biotic and abiotic dechlorination, with important implications for sustainable remediation of electron donor-limited aquifers contaminated by chloroethenes.

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives

Chlorinated organic pollutants constitute a significant category of persistent organic pollutants due to their widespread presence in the environment, which is primarily attributed to the expansion of agricultural and industrial activities. These pollutants are characterized by their persistence, potent toxicity, and capability for long-range dispersion, emphasizing the importance of their eradication to mitigate environmental pollution. While conventional methods for removing chlorinated organic pollutants encompass advanced oxidation, catalytic oxidation, and bioremediation, the utilization of biochar has emerged as a prominent green and efficacious method in recent years. Here we review biochar's role in remediating typical chlorinated organics, including polychlorinated biphenyls (PCBs), triclosan (TCS), trichloroethene (TCE), tetrachloroethylene (PCE), organochlorine pesticides (OCPs), and chlorobenzenes (CBs). We focus on the impact of biochar material properties on the adsorption mechanisms of chlorinated organics. This review highlights the use of biochar as a sustainable and eco-friendly method for removing chlorinated organic pollutants, especially when combined with biological or chemical strategies. Biochar facilitates electron transfer efficiency between microorganisms, promoting the growth of dechlorinating bacteria and mitigating the toxicity of chlorinated organics through adsorption. Furthermore, biochar can activate processes such as advanced oxidation or nano zero-valent iron, generating free radicals to decompose chlorinated organic compounds. We observe a broader application of biochar and bioprocesses for treating chlorinated organic pollutants in soil, reducing environmental impacts. Conversely, for water-based pollutants, integrating biochar with chemical methods proved more effective, leading to superior purification results. This review contributes to the theoretical and practical application of biochar for removing environmental chlorinated organic pollutants.

Biochar, microbes, and biochar-microbe synergistic treatment of chlorinated hydrocarbons in groundwater: a review

Dehalogenating bacteria are still deficient when targeted to deal with chlorinated hydrocarbons (CHCs) contamination: e.g., slow metabolic rates, limited substrate range, formation of toxic intermediates. To enhance its dechlorination capacity, biochar and its composites with appropriate surface activity and biocompatibility are selected for coupled dechlorination. Because of its special surface physical and chemical properties, it promotes biofilm formation by dehalogenating bacteria on its surface and improves the living environment for dehalogenating bacteria. Next, biochar and its composites provide active sites for the removal of CHCs through adsorption, activation and catalysis. These sites can be specific metal centers, functional groups or structural defects. Under microbial mediation, these sites can undergo activation and catalytic cycles, thereby increasing dechlorination efficiency. However, there is a lack of systematic understanding of the mechanisms of dechlorination in biogenic and abiogenic systems based on biochar. Therefore, this article comprehensively summarizes the recent research progress of biochar and its composites as a "Taiwan balm" for the degradation of CHCs in terms of adsorption, catalysis, improvement of microbial community structure and promotion of degradation and metabolism of CHCs. The removal efficiency, influencing factors and reaction mechanism of the degraded CHCs were also discussed. The following conclusions were drawn, in the pure biochar system, the CHCs are fixed to its surface by adsorption through chemical bonds on its surface; the biochar composite material relies on persistent free radicals and electron shuttle mechanisms to react with CHCs, disrupting their molecular structure and reducing them; biochar-coupled microorganisms reduce CHCs primarily by forming an "electron shuttle bridge" between biological and non-biological organisms. Finally, the experimental directions to be carried out in the future are suggested to explore the optimal solution to improve the treatment efficiency of CHCs in water.

Degradation of different wastewater by a biological sponge iron system: microbial growth and influencing factors

The bio-ZVI process has undergone widespread development in wastewater treatment in recent years. However, there has been limited examination of the growth and degradation characteristics of functional microorganisms within the system. In the present research, strains were isolated and identified from the bio-ZVI system constructed by sponge iron (encoded as SFe-M). The consistency of operating conditions in treating different wastewater was explored. Three SFe-acclimated microorganisms exhibiting characteristics of degrading organic pollutants and participating in the nitrogen removal process were isolated. The adaptation time of these microorganisms prolonged as the substrate toxicity increased, while the pollutant degradation was related to their metabolic rate in the logarithmic phase. All these functional bacteria exhibited the ability to treat wastewater in a wide pH range (5-8). However, the improper temperature (such as 10 °C and 40 °C) significantly inhibited their growth, and the optimal working temperature was identified as 30 °C. The iron dosage had a significant impact on these function bacteria, ranging from 1 g L-1 to 150 g L-1. It was inferred that the SFe-acclimated microorganisms are capable of resisting the poison of excessive iron, that is, they all have strong adaptability. The results provide compelling evidence for further understanding of the degradation mechanism involved in the bio-ZVI process.

An innovative permeable reactive bio-barrier to remediate trichloroethene-contaminated groundwater: A field study

Permeable reactive bio-barrier (PRBB), an innovative technology, could treat many contaminants via the natural gradient flow of groundwater based on immobilization or transformation of pollutants into less toxic and harmful forms. In this field study, we developed an innovative PRBB system comprising immobilized Dehalococcoides mccartyi (Dhc) and Clostridium butyricum embedded into the silica gel for long-term treatment of trichloroethene (TCE) polluted groundwater. Four injection wells and two monitoring wells were installed at the downstream of the TCE plume. Without PRBB, results showed that the TCE (6.23 ± 0.43 μmole/L) was converted to cis-dichloroethene (0.52 ± 0.63 μmole/L), and ethene was not detected, whereas TCE was completely converted to ethene (3.31 μmole/L) with PRBB treatment, indicating that PRBB could promote complete dechlorination of TCE. Noticeably, PRBB showed the long-term capability to maintain a high dechlorinating efficiency for TCE removal during the 300-day operational period. Furthermore, with qPCR analysis, the PRBB application could stably maintain the populations of Dhc and functional genes (bvcA, tceA, and vcrA) at >108 copies/L within the remediation course and change the bacterial communities in the contaminated groundwater. We concluded that our PRBB was first set up for cleaning up TCE-contaminated groundwater in a field trial.

Simultaneous removal of calcium, cadmium and tetracycline from reverse osmosis wastewater by sycamore deciduous biochar, shell powder and polyurethane sponge combined with biofilm reactor

The treatment of reverse osmosis concentrate generated from urban industrial sewage for resource recovery has been hot. In this research, a biofilm reactor was constructed by combining sycamore deciduous biochar, shell powder, and polyurethane sponge loaded with Zobellella denitrificans sp. LX16. For ammonia nitrogen (NH4+-N), calcium (Ca2+), chemical oxygen demand (COD), cadmium (Cd2+), and tetracycline (TC), the removal efficiencies were 98.69 %, 83.95 %, 97.26 %, 98.34 %, and 69.12 % at a hydraulic retention time (HRT) of 4 h, pH of 7.0, and influent salinity, Ca2+, and TC concentrations of 1.0, 180.0, and 3.0 mg/L, respectively. The biofilm reactor packing has a three-dimensional structure to ensure good loading of microorganisms while promoting electron transfer and metabolic activity of microorganisms and increasing the pollutant tolerance and removal efficiency. The reactor provides a practical reference for the sedimentation of reverse osmosis concentrate to remove Cd2+ and TC by microbial induced calcium precipitation (MICP).

Controlled-Release Materials for Remediation of Trichloroethylene Contamination in Groundwater

Groundwater contamination by trichloroethylene (TCE) presents a pressing environmental challenge with far-reaching consequences. Traditional remediation methods have shown limitations in effectively addressing TCE contamination. This study reviews the limitations of conventional remediation techniques and investigates the application of oxidant-based controlled-release materials, including encapsulated, loaded, and gel-based potassium permanganate since the year 2000. Additionally, it examines reductant controlled-release materials and electron donor-release materials such as tetrabutyl orthosilicate (TBOS) and polyhydroxybutyrate (PHB). The findings suggest that controlled-release materials offer a promising avenue for enhancing TCE degradation and promoting groundwater restoration. This study concludes by highlighting the future research directions and the potential of controlled-release materials in addressing TCE contamination challenges.