Chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane kinetics and equilibrium adsorption studies on selective macrocyclic adsorbents.

Chlorinated volatile organic compounds (CVOCs) are often found in combination with 1,4-dioxane which has been used as a solvent stabilizer. It would be desirable to separate these compounds since biodegradation of 1,4-dioxane follows an aerobic pathway while anaerobic conditions are needed for biodegrading CVOCs. Conventional adsorbents such as activated carbon (AC) and carbonaceous resins have high adsorption capacities for 1,4-dioxane and CVOCs but lack selectivity, limiting their use for separation (Liu et al., 2019). In the current work, two macrocyclic adsorbents, ß-CD-TFN and Res-TFN, were examined for selective adsorption of chlorinated ethenes in the presence of 1,4-dioxane. Both adsorbents exhibited rapid adsorption of the CVOCs and minimal adsorption of 1,4-dioxane. Res-TFN had a higher adsorption capacity for CVOCs than ß-CD-TFN (measured linear partition coefficient, Kd 2140 -9750 L⋅kg-1 versus 192-918 L⋅kg-1 for 1,1, DCE, cis-1,2-DCE and TCE, respectively) and was highly selective for CVOCs(TCE Kd ~117 Kd for 1,4-dioxane). By comparison, TCE and 1,4-dioxane adsorption on AC was approximately equal at 100 µg⋅L-1 and approximately 1/3 of the adsorption of TCE on the Res-TFN. The greater adsorption and selectivity of Res-TFN suggest that it can be used as a selective adsorbent to separate CVOCs from 1,4-dioxane to allow separate biodegradation.

Pretreatment for potable reuse: Enhancing the biological removal of 1,4-dioxane from landfill leachate through cometabolism with tetrahydrofuran.

1,4-Dioxane is a probable human carcinogen and a persistent aquatic contaminant. Cometabolic biodegradation of 1,4-dioxane is a promising low-cost and effective treatment technology; however, further demonstration is needed for treating landfill leachate. This technology was tested in two full-scale moving bed biofilm reactors (MBBRs) treating raw landfill leachate with tetrahydrofuran selected as the cometabolite. The raw leachate contained on average 82 µg/L of 1,4-dioxane and before testing the MBBRs removed an average of 38% and 42% of 1,4-dioxane, respectively. First, tetrahydrofuran was added to MBBR 1, and 1,4-dioxane removal was improved to an average of 73%, with the control MBBR removing an average of 37% of 1,4-dioxane. During this period, an optimal dose of 2 mg/L of tetrahydrofuran was identified. Tetrahydrofuran was then fed to both MBBRs, where the 1,4-dioxane removal was on average 73% and 80%. Cometabolic treatment at the landfill significantly reduced the concentration of 1,4-dioxane received from the landfill at a downstream wastewater treatment and indirect potable reuse facility, reducing the load of 1,4-dioxane from 44% to 24% after the study. PRACTITIONER POINTS: Cometabolic degradation of leachate 1,4-dioxane with THF in MBBRs is a feasible treatment technology and a low-cost technique when retrofitting existing biological treatment facilities. The MBBRs can be operated at a range of temperatures, require no operational changes beyond THF addition, and operate best at a mass ratio of THF to 1,4-dioxane of 24. Source control of 1,4-dioxane significantly reduces the concentration of 1,4-dioxane in downstream wastewater treatment plants and potable reuse facilities.

Dichloramine Hydrolysis in Membrane Desalination Permeate: Mechanistic Insights and Implications for Oxidative Capacity in Potable Reuse Applications.

Dichloramine (NHCl2) naturally exists in reverse osmosis (RO) permeate due to its application as an antifouling chemical in membrane-based potable reuse treatment. This study investigated mechanisms of background NHCl2 hydrolysis associated with the generation of oxidative radical species in RO permeate, established a kinetic model to predict the oxidative capacity, and examined its removal efficiency on trace organic contaminants in potable reuse. Results showed that NHCl2 hydrolysis generated transient peroxynitrite (ONOO-) and subsequently dissociated into hydroxyl radical (HO•). The maximal HO• exposure was observed at an RO permeate pH of 8.4, higher than that from typical ultraviolet (UV)-based advanced oxidation processes. The HO• exposure during NHCl2 hydrolysis also peaked at a NH2Cl-to-NHCl2 molar ratio of 1:1. The oxidative capacity rapidly degraded 1,4-dioxane, carbamazepine, atenolol, and sulfamethoxazole in RO permeate. Furthermore, background elevated carbonate in fresh RO permeate can convert HO• to carbonate radical (CO3•-). Aeration of the RO permeate removed total carbonate, significantly increased HO• exposure, and enhanced the degradation kinetics of trace organic contaminants. The kinetic model of NHCl2 hydrolysis predicted well the degradation of contaminants in RO permeate. This study provides new mechanistic insights into NHCl2 hydrolysis that contributes to the oxidative degradation of trace organic contaminants in potable reuse systems.

Tackling Challenges of Long-Term Electrode Stability in Electrochemical Treatment of 1,4-Dioxane in Groundwater.

Electrochemical advanced oxidation is an appealing point-of-use groundwater treatment option for removing pollutants such as 1,4-dioxane, which is difficult to remove by using conventional separation-based techniques. This study addresses a critical challenge in employing electrochemical cells in practical groundwater treatment─electrode stability over long-term operation. This study aims to simulate realistic environmental scenarios by significantly extending the experimental time scale, testing a flow-through cell in addition to a batch reactor, and employing an electrolyte with a conductivity equivalent to that of groundwater. We first constructed a robust titanium suboxide nanotube mesh electrode that is utilized as both anode and cathode. We then implemented a pulsed electrolysis strategy in which reactive oxygen species are generated during the anodic cycle, and the electrode is regenerated during the cathodic cycle. Under optimized conditions, single-pass treatment through the cell (effective area: 2 cm2) achieved a remarkable 65-70% removal efficiency for 1,4-dioxane in the synthetic groundwater for over 100 h continuous operation at a low current density of 5 mA cm-2 and a water flux of 6 L m-2 h-1. The electrochemical cell and pulse treatment scheme developed in this study presents a critical advancement toward practical groundwater treatment technology.

New potent muscarinic receptor ligands bearing the 1,4-dioxane nucleus: Investigation on the nature of the substituent in position 2.

A new series of muscarinic acetylcholine receptor (mAChR) ligands obtained by inserting different substituents in position 2 of the potent 6,6-diphenyl-1,4-dioxane antagonists 4 and 5 was designed and synthesized to investigate the influence of steric bulk on the mAChR affinity. Specifically, the insertion of a 2-methyl group, affording compounds 6 and 9, resulted as the most favorable modification in terms of affinity for all muscarinic subtypes. As supported by computational studies performed on the hM1 receptor, this substituent may contribute to stabilize the ligand within the binding site by favoring the formation of stable interactions between the cationic head of the ligand and the residue D105. The increase of steric bulk, obtained by replacing the methyl group with an ethyl (7 and 10) and especially a phenyl substituent (8 and 11), caused a marked decrease of mAChR affinity, demonstrating the crucial role played by the steric bulk of the 2-substituent in the mAChR interaction. The most intriguing result was obtained with the tertiary amine 9, which, surprisingly, showed two different pKi values for all mAChRs, with preferential subpicomolar affinities for the M1, M3, and M4 subtypes. Interestingly, biphasic curves were also observed with both the eutomer (S)-(-)-9 and the distomer (R)-( + )-9.

Synergistic interactions in core microbiome Rhizobiales accelerate 1,4-dioxane biodegradation.

Next-generation sequencing (NGS) has revolutionized taxa identification within contaminant-degrading communities. However, uncovering a core degrading microbiome in diverse polluted environments and understanding its associated microbial interactions remains challenging. In this study, we isolated two distinct microbial consortia, namely MA-S and Cl-G, from separate environmental samples using 1,4-dioxane as a target pollutant. Both consortia exhibited a persistent prevalence of the phylum Proteobacteria, especially within the order Rhizobiales. Extensive analysis confirmed that Rhizobiales as the dominant microbial population (> 90 %) across successive degradation cycles, constituting the core degrading microbiome. Co-occurrence network analysis highlighted synergistic interactions within Rhizobiales, especially within the Shinella and Xanthobacter genera, facilitating efficient 1,4-dioxane degradation. The enrichment of Rhizobiales correlated with an increased abundance of essential genes such as PobA, HpaB, ADH, and ALDH. Shinella yambaruensis emerged as a key degrader in both consortia, identified through whole-genome sequencing and RNA-seq analysis, revealing genes implicated in 1,4-dioxane degradation pathways, such as PobA and HpaB. Direct and indirect co-cultivation experiments confirmed synergistic interaction between Shinella sp. and Xanthobacter sp., enhancing the degradation of 1,4-dioxane within the core microbiome Rhizobiales. Our findings advocate for integrating the core microbiome concept into engineered consortia to optimize 1,4-dioxane bioremediation strategies.

Validation and Collaborative Studies of Headspace Gas Chromatography-Mass Spectrometry (HS GC-MS) for Determination of 1,4-Dioxane in Cosmetic Samples.

BACKGROUND: 1,4-Dioxane (1,4-D) is a by-product of the synthesis of surfactants, typically found in some cosmetics products such as shampoo, toothpaste, and soap. The presence of 1,4-D in cosmetics products is limited to certain amount since 1,4-D is classified as a probable human carcinogen. OBJECTIVE: This present study was intended to validate static headspace gas chromatography-mass spectrometry (HS GC-MS) for the determination of 1,4-D in cosmetics products. METHODS: The condition of headspace and GC-MS was optimized to get the best condition for analysis of 1,4-D using 1,4-Dioxane-d8 (1,4-D-d8) as internal standard (IS). The developed method was validated by evaluating the key performance characteristics, including specificity, linearity, limit of detection (LoD), limit of quantification (LoQ), accuracy, and precision. RESULTS: The results showed that HS GC-MS was specific since the peaks of the selected ion monitoring (SIM) mode could be separated and confirmed at m/z 88 and m/z 96 for 1,4-D and 1,4-D-d8, respectively. The method was linear over the concentration range of 0.1287-1.2875 µg/mL, with R2 > 0.999 and RSD residuals < 2.0. A collaborative study were conducted on this method, with ten participating laboratories from four countries. The outcome of this study was found to be accurate and precise, as evidenced by the excellent recoveries ranged from 94.6-102.1% and with good reproducibility with RSD values ranged from 0.2-1.1%. The collaborative studies exhibited that all data reported by ten participating laboratories in four countries were inliers without any extreme values observed either in mean or RSD values. CONCLUSION: This HS GC-MS is found to be fit and suitable for the determination of trace level of 1,4-D in cosmetics products. HIGHLIGHTS: HS GC-MS method could be proposed as a standard method for quantitative analysis of 1,4-D in cosmetics products since the collaborative studies indicated that the developed method meet the requirement in "Guidelines for Collaborative Study Procedures to Validate Characteristics of a Method of Analysis".

Fabrication of Curcumin-Based Electrochemical Nanosensors for the Detection of Environmental Pollutants: 1,4-Dioxane and Hydrazine.

This work reports the development of novel curcuminoid-based electrochemical sensors for the detection of environmental pollutants from water. In this study, the first set of electrochemical experiments was carried out using curcumin-conjugated multi-walled carbon nanotubes (MWCNT-CM) for 1,4-dioxane detection. The MWCNT-CM/GCE showed good sensitivity (103.25 nA nM-1 cm-2 in the linear range 1 nM to 1 µM), with LOD of 35.71 pM and LOQ of 108.21 pM. The second set of electrochemical experiments was carried out with bisdemethoxy curcumin analog quantum dots (BDMCAQD) for hydrazine detection. The BDMCAQD/GCE exhibited good sensitivity (74.96 nA nM-1 cm-2 in the linear range 100 nM to 1 µM), with LOD of 10 nM and LOQ of 44.93 nM. Thus, this work will serve as a reference for the fabrication of metal-free electrochemical sensors using curcuminoids as the redox mediator for the enhanced detection of environmental pollutants.

Isolation and characterization of pure cultures for metabolizing 1,4-dioxane in oligotrophic environments.

1,4-Dioxane concentration in most contaminated water is much less than 1 mg/L, which cannot sustain the growth of most reported 1,4-dioxane-metabolizing pure cultures. These pure cultures were isolated following enrichment of mixed cultures at high concentrations (20 to 1,000 mg/L). This study is based on a different strategy: 1,4-dioxane-metabolizing mixed cultures were enriched by periodically spiking 1,4-dioxane at low concentrations (≤1 mg/L). Five 1,4-dioxane-metabolizing pure strains LCD6B, LCD6D, WC10G, WCD6H, and WD4H were isolated and characterized. The partial 16S rRNA gene sequencing showed that the five bacterial strains were related to Dokdonella sp. (98.3%), Acinetobacter sp. (99.0%), Afipia sp. (99.2%), Nitrobacter sp. (97.9%), and Pseudonocardia sp. (99.4%), respectively. Nitrobacter sp. WCD6H is the first reported 1,4-dioxane-metabolizing bacterium in the genus of Nitrobacter. The net specific growth rates of these five cultures are consistently higher than those reported in the literature at 1,4-dioxane concentrations <0.5 mg/L. Compared to the literature, our newly discovered strains have lower half-maximum-rate concentrations (1.8 to 8.2 mg-dioxane/L), lower maximum specific 1,4-dioxane utilization rates (0.24 to 0.47 mg-dioxane/(mg-protein ⋅ d)), higher biomass yields (0.29 to 0.38 mg-protein/mg-dioxane), and lower decay coefficients (0.01 to 0.02 d-1). These are characteristics of microorganisms living in oligotrophic environments.

Effect of 1,4-Dioxane Solvent on ß-Glucuronidation Using Methyl 1,2,3,4-Tetra-O-acetyl-ß-D-glucuronate as the Glycosyl Donor.

A facile and selective ß-D-glucuronidation of alcohols, such as (-)-menthol, cholestanol, (+)- and (-)-borneols, and 2-adamantanol, using commercially available methyl 1,2,3,4-tetra-O-acetyl-ß-D-glucuronate as the glycosyl donor and trimethylsilyl bis(trifluoromethanesulfonyl)imide (Tf2NTMS) (0.5 equivalent) as the activator in 1,4-dioxane at 60 °C gave products in moderate yields. The addition of MS4A increased the ß : α ratios of D-glucuronides when cholestanol, (+)-borneol, and 2-adamantanol were used as the acceptor substrate.

Implementation of in situ aerobic cometabolism for groundwater treatment: State of the knowledge and important factors for field operation.

In situ aerobic cometabolism of groundwater contaminants has been demonstrated to be a valuable bioremediation technology to treat many legacy and emerging contaminants in dilute plumes. Several well-designed and documented field studies have shown that this technology can concurrently treat multiple contaminants and reach very low cleanup goals. Fundamentally different from metabolism-based biodegradation of contaminants, microorganisms that cometabolically degrade contaminants do not obtain sufficient carbon and energy from the degradation process to support their growth and require an exogenous growth supporting primary substrate. Successful applications of aerobic cometabolic treatment therefore require special considerations beyond conventional in situ bioremediation, such as competitive inhibition between growth-supporting primary substrate(s) and contaminant non-growth substrates, toxic effects resulting from contaminant degradation, and differences in microbial population dynamics exhibited by biostimulated indigenous consortia versus bioaugmentation cultures. This article first provides a general review of microbiological factors that are likely to affect the rate of aerobic cometabolic biodegradation. We subsequently review fourteen well documented field-scale aerobic cometabolic bioremediation studies and summarize the underlying microbiological factors that may affect the performance observed in these field studies. The combination of microbiological and engineering principles gained from field testing leads to insights and recommendations on planning, design, and operation of an in situ aerobic cometabolic treatment system. With a vision of more aerobic cometabolic treatments being considered to tackle large, dilute plumes, we present several novel topics and future research directions that can potentially enhance technology development and foster success in implementing this technology for environmental restoration.

Targeted isolation, identification, and antioxidant evaluation of aromatic polyketides from a plant-derived fungus Ophiobolus cirsii LZU-1509.

There are >350 species of the Ophiobolus genus, which is not yet very well-known and lacks research reports on secondary metabolites. Three new 3,4-benzofuran polyketides 1-3, a new 3,4-benzofuran polyketide racemate 4, two new pairs of polyketide enantiomers (±)-5 and (±)-7, two new acetophenone derivatives 6 and 8, and three novel 1,4-dioxane aromatic polyketides 9-11, were isolated from a fungus Ophiobolus cirsii LZU-1509 derived from an important medicinal and economic crop Anaphalis lactea. The isolation was guided by LC-MS/MS-based GNPS molecular networking analysis. The planar structures and relative configurations were mainly elucidated by NMR and HR-ESI-MS data. Their absolute configurations were determined by using X-ray diffraction analysis and via comparing computational and experimental ECD, NMR, and specific optical rotation data. 9 possesses an unreported 5/6/6/6/5 five-ring framework with a 1,4-dioxane, and 10 and 11 feature unprecedented 6/6/6/5 and 6/6/5/6 four-ring frames containing a 1,4-dioxane. The biosynthetic pathways of 9-11 were proposed. 1-11 were nontoxic in HT-1080 and HepG2 tumor cells at a concentration of 20 µM, whereas 3 and 5 exerted higher antioxidant properties in the hydrogen peroxide-stimulated model in the neuron-like PC12 cells. They could be potential antioxidant agents for neuroprotection.

Adsorption Behavior and Kinetics of 1,4-Dioxane by Carbon Aerogel.

1,4-dioxane is a potential carcinogen in water and is difficult to deal with due to its robust cycloether bond and complete miscibility with water. To remove 1,4-dioxane in an economically viable and environmentally friendly way, a series of carbon aerogels were synthesized as adsorbents for 1,4-dioxane. The experiment results showed that adsorption performances were closely related to the preparation conditions of carbon aerogels, such as the molar ratio, heating rate, pyrolysis temperature and residence time, which were carefully controlled. Scanning electron microscope analysis revealed the presence of a three-dimensional porous network structure in carbon aerogels. Brunauer-Emmett-Teller analysis results demonstrated an increase in specific surface area (673.89 m2/g) and total pore volume after carbonization, with an increase in mesoporous porosity and a decrease in microporosity. When considering each variable individually, the highest specific surface area of prepared carbon aerogels was achieved at a pyrolysis temperature of 800 °C, a holding time of 1 h, and a heating rate of 2 °C/min. Under optimal experimental conditions, the adsorption removal of 1,4-dioxane by carbon aerogels exceeded 95%, following quasi-second-order kinetics and Langmuir isothermal adsorption isotherms, indicating that monolayer adsorption on the surface of carbon aerogels occurred. The maximum adsorption capacity obtained was 67.28 mg/g at a temperature of 318 K, which was attributed to the presence of a large proportion of mesopores and abundant micropores simultaneously in carbon aerogels. Furthermore, with the interference of chlorinated solvents such as trichloroethylene (TCE), the removal efficiency of 1,4-dioxane had no obvious inhibition effect. Regeneration experiments showed that after five continuous cycles, the carbon aerogels still kept a comparable adsorption capacity, which illustrates its potential application in 1,4-dioxane-polluted water purification.

Occurrence of Rhodococcus sp. RR1 prmA and Rhodococcus jostii RHA1 prmA across microbial communities and their enumeration during 1,4-dioxane biodegradation.

1,4-Dioxane, a likely human carcinogen, is a co-contaminant at many chlorinated solvent contaminated sites. Conventional treatment technologies, such as carbon sorption or air stripping, are largely ineffective, and so many researchers have explored bioremediation for site clean-up. An important step towards this involves examining the occurrence of the functional genes associated with 1,4-dioxane biodegradation. The current research explored potential biomarkers for 1,4-dioxane in three mixed microbial communities (wetland sediment, agricultural soil, impacted site sediment) using monooxygenase targeted amplicon sequencing, followed by quantitative PCR (qPCR). A BLAST analysis of the sequencing data detected only two of the genes previously associated with 1,4-dioxane metabolism or co-metabolism, namely propane monooxygenase (prmA) from Rhodococcus jostii RHA1 and Rhodococcus sp. RR1. To investigate this further, qPCR primers and probes were designed, and the assays were used to enumerate prmA gene copies in the three communities. Gene copies of Rhodococcus RR1 prmA were detected in all three, while gene copies of Rhodococcus jostii RHA1 prmA were detected in two of the three sample types (except impacted site sediment). Further, there was a statistically significant increase in RR1 prmA gene copies in the microcosms inoculated with impacted site sediment following 1,4-dioxane biodegradation compared to the control microcosms (no 1,4-dioxane) or to the initial copy numbers before incubation. Overall, the results indicate the importance of Rhodococcus associated prmA, compared to other 1,4-dioxane degrading associated biomarkers, in three different microbial communities. Also, the newly designed qPCR assays provide a platform for others to investigate 1,4-dioxane biodegradation potential in mixed communities and should be of particular interest to those considering bioremediation as a potential 1,4-dioxane remediation approach.

Fe-ZSM-5 zeolite catalyst for heterogeneous Fenton oxidation of 1,4-dioxane: effect of Si/Al ratios and contributions of reactive oxygen species.

Heterogeneous Fenton oxidation using traditional catalysts with H2O2 for the degradation of 1,4-dioxane (1,4-DX) still presents challenge. In this study, we explored the potential of Fe-ZSM-5 zeolites (Fe-zeolite) with three Si/Al ratios (25, 100, 300) as heterogeneous Fenton catalysts for the removal of 1,4-DX from aqueous solution. Fe2O3 or ZSM-5 alone provided ineffective in degrading 1,4-DX when combined with H2O2. However, the efficient removal of 1,4-DX using H2O2 was observed when Fe2O3 was loaded on ZSM-5. Notably, the Brønsted acid sites of Fe-zeolite played a crucial role during the degradation of 1,4-DX. Fe-zeolites, in combination with H2O2, effectively removed 1,4-DX via a combination of adsorption and oxidation. Initially, Fe-zeolites demonstrated excellent affinity for 1,4-DX, achieving adsorption equilibrium rapidly in about 10 min, followed by effective catalytic oxidative degradation. Among the Fe-ZSM-5 catalysts, Fe-ZSM-5 (25) exhibited the highest catalytic activity and degraded 1,4-DX the fastest. We identified hydroxyl radicals (·OH) and singlet oxygen (1O2) as the primary reactive oxygen species (ROS) responsible for 1,4-DX degradation, with superoxide anions (HO2·/O2·-) mainly converting into 1O2 and ·OH. The degradation primarily occurred at the Fe-zeolite interface, with the degradation rate constants proportional to the amount of Brønsted acid sites on the Fe-zeolite. Fe-zeolites were effective over a wide working pH range, with alkaline pH conditions favoring 1,4-DX degradation. Overall, our study provides valuable insights into the selection of suitable catalysts for effective removal of 1,4-DX using a heterogeneous Fenton technology.

Dual phytoremediation and biochar production by Eichhornia crassipes in hydroponic system receiving different 1,4-dioxane dosages.

This study focuses on applying phytoremediation as a low-effective and simple process to treat wastewater laden with 1,4 dioxane (DIOX). A floating macrophyte (Eichhornia crassipes) was cultivated under hydroponic conditions (relative humidity 50-67%, photoperiod cycle 18:6 h light/dark, and 28-33 °C) and subjected to different DIOX loads between 0.0 (control) and 11.5 mg/g fresh mass (FM). The aquatic plant achieved DIOX and chemical oxygen demand (COD) removal efficiencies of 76-96% and 67-94%, respectively, within 15 days. E. crassipes could tolerate elevated DIOX-associated stresses until a dose of 8.2 mg DIOX/g, which highly influenced the oxidative defense system. Malondialdehyde (MDA) content, hydrogen peroxide (H2O2), and total phenolic compounds (TPC) increased by 7.3, 8.4, and 4.5-times, respectively, in response to operating the phytoremediation unit at a DIOX load of 11.5 mg/g. The associated succulent value, proteins, chlorophyll-a, chlorophyll-b, and pigments dropped by 39.6%, 45.8%, 51.5%, 80.8%, and 55.5%, respectively. The suggested removal mechanism of DIOX by E. crassipes could be uptake followed by phytovolatilization, whereas direct photodegradation from sunlight contributed to about 19.36% of the total DIOX removal efficiencies. Recycling the exhausted E. crassipes for biochar production was a cost-efficient strategy, making the payback period of the phytoremediation project equals to 6.96 yr.

Eichhornia crassipes could be used in phytoremediation of 1,4 dioxane (DIOX)-laden water at DIOX load< 8.2 mg/g FM. E. crassipes removed 77­97% DIOX via uptake and phytovolatilization. Recycling exhausted-plant to produce biochar was cost-efficient with 7 yr-payback period.

Complete genome sequence of Moraxella sp. strain DOX410, a bacterium potentially degrading 1,4-dioxane isolated from river sediment.

Moraxella sp. strain DOX410 was isolated from a systematic enrichment culture to investigate strains with 1,4-dioxane degradation potential. The genome of strain DOX410 consists of five complete contigs and contained genes related to degradation of the aromatic ring structure of 1,4-dioxane.

Simultaneous biodegradation kinetics of 1,4-dioxane and ethane.

Biodegradation of 1,4-Dioxane at environmentally relevant concentrations usually requires the addition of a primary electron-donor substrate to sustain biomass growth. Ethane is a promising substrate, since it is available as a degradation product of 1,4-Dioxane's common co-contaminants. This study reports kinetic parameters for ethane biodegradation and co-oxidations of ethane and 1,4-Dioxane. Based on experiments combined with mathematical modeling, we found that ethane promoted 1,4-Dioxane biodegradation when the initial mass ratio of ethane:1,4-Dioxane was < 9:1 mg COD/mg COD, while it inhibited 1,4-Dioxane degradation when the ratio was > 9:1. A model-independent estimator was used for kinetic-parameter estimation, and all parameter values for 1,4-Dioxane were consistent with literature-reported ranges. Estimated parameters support competitive inhibition between ethane as the primary substrate and 1,4-Dioxane as the secondary substrate. The results also support that bacteria that co-oxidize ethane and 1,4-Dioxane had a competitive advantage over bacteria that can use only one of the two substrates. The minimum concentration of ethane to sustain ethane-oxidizing bacteria and ethane and 1,4-Dioxane-co-oxidizing bacteria was 0.09 mg COD/L, which is approximately 20-fold lower than the minimum concentration reported for propane, another common substrate used to promote 1,4-Dioxane biodegradation. The minimum 1,4-Dioxane concentration required to sustain steady-state biomass with 1,4-Dioxane as the sole primary substrate was 1.3 mg COD/L. As 1,4-Dioxane concentrations at most groundwater sites are less than 0.18 mg COD/L, providing ethane as a primary substrate is vital to support biomass growth and consequently enable 1,4-Dioxane bioremediation.

Effect of ferric salt addition on UV/electro-chlorine advanced oxidation process.

This study discussed the effect of ferric salt addition on UV/electro-chlorine advanced oxidation process using a train of electrolytic and UV flow cells with an ozone-free low-pressure mercury vapour lamp (total irradiance:0.60 W at 254 nm). Ferric salt addition enhanced 1,4-dioxane degradation at an electrolytic current of 0.100 A. By contrast, an inhibitory effect of ferric salt addition was observed at a current of 0.500 A. The enhanced accumulation of free chlorine at a current of 0.500 A directly decreased the 1,4-dioxane degradation rate by scavenging reactive radicals like HO˙ and Cl˙. However, at an electrolytic current of 0.100 A, UV irradiance was relatively excessive for electrochemical chlorine production. The excess UV energy enhanced the photoreduction of FeOH2+, followed by the Fenton-type reaction of Fe2+ and HOCl, which produced HO˙ and consumed free chlorine. As a result, the free chlorine concentration decreased, and the reaction efficiency between the reactive radicals and 1,4-dioxane improved. Thus, the addition of ferric salt to a UV/electro-chlorine system is recommended when the UV irradiance in the system is excessive compared to the electrochemical chlorine supply.

Self-assembling a 1,4-dioxane-degrading consortium and identifying the key role of Shinella sp. through dilution-to-extinction and reculturing.

IMPORTANCE: Assembling a functional microbial consortium and identifying key degraders involved in the degradation of 1,4-dioxane are crucial for the design of synergistic consortia used in enhancing the bioremediation of 1,4-dioxane-contaminated sites. However, due to the vast diversity of microbes, assembling a functional consortium and identifying novel degraders through a simple method remain a challenge. In this study, we reassembled 1,4-dioxane-degrading microbial consortia using a simple and easy-to-operate method by combining dilution-to-extinction and reculture techniques. We combined differential analysis of community structure and metabolic function and confirmed that Shinella species have a stronger 1,4-dioxane degradation ability than Xanthobacter species in the enriched consortium. In addition, a new dioxane-degrading bacterium was isolated, Shinella yambaruensis, which verified our findings. These results demonstrate that DTE and reculture techniques can be used beyond diversity reduction to assemble functional microbial communities, particularly to identify key degraders in contaminant-degrading consortia.