Impact of groundwater quality and associated byproduct formation during UV/hydrogen peroxide treatment of 1,4-dioxane

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.

Application of electron beam technology to decompose per- and polyfluoroalkyl substances in water

The widespread detection of per- and polyfluoroalkyl substances (PFAS) in environmental compartments across the globe has raised several health concerns. Destructive technologies that aim to transform these recalcitrant PFAS into less toxic, more manageable products, are gaining impetus to address this problem. In this study, a 9 MeV electron beam accelerator was utilized to treat a suite of PFAS (perfluoroalkyl carboxylates: PFCAs, perfluoroalkyl sulfonates, and 6:2 fluorotelomer sulfonate: FTS) at environmentally relevant levels in water under different operating and water quality conditions. Although perfluorooctanoic acid and perfluorooctane sulfonic acid showed >90% degradation at <500 kGy dose at optimized conditions, a fluoride mass balance revealed that complete defluorination occurred only at/or near 1000 kGy. Non-target and suspect screening revealed additional degradation pathways differing from previously reported mechanisms. Treatment of PFAS mixtures in deionized water and groundwater matrices showed that FTS was preferentially degraded (∼90%), followed by partial degradation of long-chain PFAS (∼15-60%) and a simultaneous increase of short-chain PFAS (up to 20%) with increasing doses. The increase was much higher (up to 3.5X) in groundwaters compared to deionized water due to the presence of PFAS precursors as confirmed by total oxidizable precursor (TOP) assay. TOP assay of e-beam treated samples did not show any increase in PFCAs, confirming that e-beam was effective in also degrading precursors. This study provides an improved understanding of the mechanism of PFAS degradation and revealed that short-chain PFAS are more resistant to defluorination and their levels and regulation in the environment will determine the operating conditions of e-beam and other PFAS treatment technologies.

Accelerated Ultraviolet Treatment of Carbamazepine and NDMA in Water under 222 nm Irradiation

Krypton chloride (KrCl*) excimer ultraviolet (UV) light may provide advantages for contaminant degradation compared to conventional low-pressure (LP) UV. Direct and indirect photolysis as well as UV/hydrogen peroxide-driven advanced oxidation (AOP) of two chemical contaminants were investigated in laboratory grade water (LGW) and treated secondary effluent (SE) for LPUV and filtered KrCl* excimer lamps emitting at 254 and 222 nm, respectively. Carbamazepine (CBZ) and N-nitrosodimethylamine (NDMA) were chosen because of their unique molar absorption coefficient profiles, quantum yields (QYs) at 254 nm, and reaction rate constants with hydroxyl radical. Quantum yields and molar absorption coefficients at 222 nm for both CBZ and NDMA were determined, with measured molar absorption coefficients of 26 422 and 8170 M-1 cm-1, respectively, and QYs of 1.95 × 10-2 and 6.68 × 10-1 mol Einstein-1, respectively. The 222 nm irradiation of CBZ in SE improved degradation compared to that in LGW, likely through promotion of in situ radical formation. AOP conditions improved degradation of CBZ in LGW for both UV LP and KrCl* sources but did not improve NDMA decay. In SE, photolysis of CBZ resulted in decay similar to that of AOP, likely due to the in situ generation of radicals. Overall, the KrCl* 222 nm source significantly improves contaminant degradation compared to that of 254 nm LPUV.

Toxicity evolution and control for the UV/H2O2 degradation of nitrogen-containing heterocyclic compounds: SDZ and PMM

This study aimed to achieve toxicity control of sulfadiazine (SDZ) and pirimiphos-methyl (PMM) via the UV/H2O2 process by optimizing the reaction parameters. The results show that both drugs had a good degradation effect under the following parameters: a H2O2 molar ratio of 1:200, and neutral conditions. SDZ and PMM could be degraded by more than 99% within 3 min, respectively. In the Daphnia magna acute toxicity assay and Vibrio fischeri inhibition assay, both SDZ and PMM exhibited a phenomenon of increasing toxicity. Additionally, through the use of density functional theory (DFT) calculation and HPLC-QTOF-MS, 21 transformation products (TPs) were identified, and the principal degradation pathways were proposed. The toxicity of the TPs was determined by comparing the QSAR prediction results with toxicity test data. As a result, under the higher UV light intensity (2300 μW/cm2) and neutral conditions, SDZ showed highest toxicity, whereas PMM showed lowest toxicity under the lowest UV light intensity (450 μW/cm2) and neutral conditions. Four main toxic TPs were identified, and their yields could be reduced by adjusting the reaction parameters. Therefore, the selection of appropriate reaction parameters could reduce the production of toxic TPs and ensure the safety of water environment.

1,4-Dioxane removal in nitrifying sand filters treating domestic wastewater: Influence of water matrix and microbial inhibitors

1,4-Dioxane is a recalcitrant pollutant in water and is ineffectively removed during conventional water and wastewater treatment processes. In this study, we demonstrate the application of nitrifying sand filters to remove 1,4-dioxane from domestic wastewater without the need for bioaugmentation or biostimulation. The sand columns were able to remove 61 ± 10% of 1,4-dioxane on average (initial concentration: 50 μg/L) from wastewater, outperforming conventional wastewater treatment approaches. Microbial analysis revealed the presence of 1,4-dioxane degrading functional genes (dxmB, phe, mmox, and prmA) to support biodegradation being the dominant degradation pathway. Adding antibiotics (sulfamethoxazole and ciprofloxacin), that temporarily inhibited the nitrification process during the dosing period, showed a minor effect in 1,4-dioxane removal (6-8% decline, p < 0.05), suggesting solid resilience of the 1,4-dioxane-degrading microbial community in the columns. Columns amended with sodium azide significantly (p < 0.05) depressed 1,4-dioxane removal in the early stage of dosing but followed by a gradual increase of the removal over time to >80%, presumably due to a shift in the microbial community toward azide-resistant 1,4-dioxane degrading microbes (e.g., fungi). This study demonstrated for the first time the resilience of the 1,4-dioxane-degrading microorganisms during antibiotic shocks, and the selective enrichment of efficient 1,4-dioxane-degrading microbes after azide poisoning. Our observation could provide insights into designing better 1,4-dioxane remediation strategies in the future.

Characterization of 1,4-dioxane degrading microbial community enriched from uncontaminated soil

1,4-Dioxane is a contaminant of emerging concern that has been commonly detected in groundwater. In this study, a stable and robust 1,4-dioxane degrading enrichment culture was obtained from uncontaminated soil. The enrichment was capable to metabolically degrade 1,4-dioxane at both high (100 mg L^-1) and environmentally relevant concentrations (300 μg L^-1), with a maximum specific 1,4-dioxane degradation rate (q_max) of 0.044 ± 0.001 mg dioxane h^-1 mg protein^-1, and 1,4-dioxane half-velocity constant (K_s) of 25 ± 1.6 mg L^-1. The microbial community structure analysis suggested Pseudonocardia species, which utilize the dioxane monooxygenase for metabolic 1,4-dioxane biodegradation, were the main functional species for 1,4-dioxane degradation. The enrichment culture can adapt to both acidic (pH 5.5) and alkaline (pH 8) conditions and can recover degradation from low temperature (10°C) and anoxic (DO < 0.5 mg L^-1) conditions. 1,4-Dioxane degradation of the enrichment culture was reversibly inhibited by TCE with concentrations higher than 5 mg L^-1 and was completely inhibited by the presence of 1,1-DCE as low as 1 mg L^-1. Collectively, these results demonstrated indigenous stable and robust 1,4-dioxane degrading enrichment culture can be obtained from uncontaminated sources and can be a potential candidate for 1,4-dioxane bioaugmentation at environmentally relevant conditions. KEY POINTS: •1,4-Dioxane degrading enrichment was obtained from uncontaminated soil. • The enrichment culture could degrade 1,4-dioxane to below 10 μg L^-1. •Low K_s and low cell yield of the enrichment benefit its application in bioremediation.

A Review of Challenges and Opportunities for Microbially Removing 1,4-Dioxane to Meet Drinking-Water and Groundwater Guidelines

1,4-Dioxane is an emerging contaminant in drinking-water sources and contaminated sites. Microbial removal of 1,4-dioxane has attracted a lot of attention, but faces a challenge: being not able to continuously metabolize 1,4-dioxane to below most drinking-water and groundwater guidelines. The 1,4-dioxane concentrations in most drinking-water sources and contaminated sites are too low to sustain biomass growth. This minireview discusses strategies that may potentially address the challenge. The strategies include: 1) finding oligotrophs for which the minimum 1,4-dioxane concentrations to sustain biomass are low, 2) determining conditions that maximize 1,4-dioxane co-metabolism or co-oxidation, 3) creating novel materials as biomass carriers and contaminant concentrators, and 4) lowering the life-cycle costs of technologies that combine biodegradation with (electro)chemical oxidation or phytoremediation.

Electron beam treatment for the removal of 1,4-dioxane in water and wastewater

Electron beam (e-beam) treatment uses accelerated electrons to form oxidizing and reducing radicals when applied to water without the use of external chemicals. In this study, electron beam treatment was used to degrade 1,4-dioxane in several water matrices. Removal improved in the progressively cleaner water matrices and removals as high as 94% to 99% were observed at a dose of 2.3 kGy in secondary effluent. 1,4-dioxane removal was confirmed to be primarily through hydroxyl radical oxidation. The calculated electrical energy per order was found to be 0.53, 0.26, and 0.08 kWh/m³/order for secondary effluent (Avg. total organic carbon (TOC) 9.25 mg/L), granular activated carbon effluent (TOC 3.46 mg/L), and ultrapure water, respectively, with a 70% generation and transfer efficiency applied.

Hydroxyl-radical based advanced oxidation processes can increase perfluoroalkyl substances beyond drinking water standards: Results from a pilot study

Advanced oxidation processes (AOPs) are popular technologies employed across the U.S. for wastewater reclamation and drinking water treatment of recalcitrant chemicals. Although there is consensus about the ineffectiveness of AOPs to treat perfluoroalkyl substances (PFASs; not polyfluoro compounds by definition here), there is a lack of field data demonstrating their impact on the transformation of unknown PFAS precursors during groundwater treatment. In this study, the fate of PFASs in seven pilot-scale AOPs, including four different technologies (UV/H₂O₂, UV/Cl₂, UV/TiO₂, and O₃/H₂O₂), was assessed at four drinking water systems across New York State (NYS), USA. Seven of 18 PFASs were detected in the influent at concentrations ranging from below method detection to 64 ng/L. Across all systems, all detected PFASs showed an increase in concentration after treatment presumably due to unknown precursor transformation with specific increases for perfluorobutane sulfonate (PFBS), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorononanoic acid (PFNA) averaging 405 (range: 0 - 1220) %, 1.0 (-7 - 9) %, 3.8 (0 - 9.5) %, 3.3 (-11 - 13) %, 14 (0 - 48) %, 13 (3 - 25) %, and 2 (0 - 5.2) %, respectively. The increase in PFAS concentration was dependent on UV and oxidant dose, further confirming that transformation reactions were occurring due to AOPs similar to a total oxidizable precursor assay. At one of the sites, PFOA levels exceeded the current NYS drinking water standard of 10 ng/L after, but not before treatment, highlighting the importance of considering the potential impact of AOP on treated water quality when designing treatment systems for regulatory compliance. The increase in PFAS concentration in the AOP systems positively correlated (r = 0.91) with nitrate levels in groundwater, suggesting that onsite septic discharges may be an important source of PFAS contamination in these unsewered study areas. Results from this pilot-scale demonstration reveal that hydroxyl radical-based AOPs, although ineffective in treating PFASs, can help to reveal the true extent of PFAS contamination in source waters.

Peroxymonosulfate activation by oxygen vacancies-enriched MXene nano-Co3O4 co-catalyst for efficient degradation of refractory organic matter: Efficiency, mechanism, and stability

Cobalt-based catalysts have been widely explored in the degradation of organic pollutants based on peroxymonosulfate (PMS) activation. Herein, we report an MXene nano-Co₃O₄ co-catalyst enriched with oxygen vacancies (O_v) and steadily fixed in nickel foam (NF) plates, which is used as an efficient and stable PMS activator for the removal of 1,4-dioxane (1,4-D). Ti originating from MXene was doped into the Co₃O₄ crystal, generating large amounts of O_v, which could provide more active sites to enhance PMS activation and facilitate the transformation of Co²⁺ and Co³⁺, causing a high stability. As a result, the 1,4-D removal efficiency of the NF/MXene-Co₃O₄/PMS system (k_app: 2.41 min^-1) was about four times higher than that of the NF/Co₃O₄/PMS system (k_app: 0.62 min^-1). In addition, singlet oxygen was the predominant reactive oxygen species. Notably, the 1,4-D removal of the NF/MXene-Co₃O₄/PMS system was over 95% after 20 h operation in the single-pass filtration mode with only 3.72% accumulative Co leaching, showing excellent stability and reusability of NF/MXene-Co₃O₄. This work provides a defect engineering strategy to design a robust and stable catalytic system for water treatment, which expands the application of MXene in the field of environmental remediation.

Interface engineering strategy of a Ti4O7 ceramic membrane via graphene oxide nanoparticles toward efficient electrooxidation of 1,4-dioxane

Although Ti₄O₇ ceramic membrane has been recognized as one of the most promising anode materials for electrochemical advanced oxidation process (EAOP), it suffers from relatively low hydroxyl radical (^•OH) production rate and high charge-transfer resistance that restricted its oxidation performance of organic pollutants. Herein, we reported an effective interface engineering strategy to develop a Ti₄O₇ reactive electrochemical membrane (REM) doped by graphene oxide nanoparticles (GONs), GONs@Ti₄O₇ REM, via strong GONs-O-Ti bonds. Results showed that 1% (wt%) GON doping on Ti₄O₇ REM significantly reduced the charge-transfer resistance from 73.87 to 8.42 Ω compared with the pristine Ti₄O₇ REM, and yielded ^•OH at 2.5-2.8 times higher rate. The 1,4-dioxane (1,4-D) oxidation rate in batch experiments by 1%GONs@Ti₄O₇ REM was 1.49×10^-2 min^-1, 2 times higher than that of the pristine Ti₄O₇ REM (7.51×10^-3 min^-1) and similar to that of BDD (1.79×10^-2 min^-1). The 1%GONs@Ti₄O₇ REM exhibited high stability after a polarization test of 90 h at 80 mA/cm², and within 15 consecutive cycles, its oxidation performance was stable (95.1-99.2%) with about 1% of GONs lost on the REM. In addition, REM process can efficiently degrade refractory organic matters in the groundwater and landfill leachate, the total organic carbon was removed by 54.5% with a single-pass REM. A normalized electric energy consumption per log removal of 1,4-D (EE/O) was observed at only 0.2-0.6 kWh/m³. Our results suggested that chemical-bonded interface engineering strategy using GONs can facilitate the EAOP performance of Ti₄O₇ ceramic membrane with outstanding reactivity and stability.

Oxidative degradation of commingled trichloroethylene and 1,4-dioxane by hydroxyl radicals produced upon oxygenation of a reduced clay mineral

Improper disposal of chlorinated solvents such as trichloroethylene (TCE) and its stabilizer 1,4-dioxane has resulted in extensive contamination in soils and groundwater. Oxidative degradation of these contaminants by strong oxidants has been proposed recently as a remediation strategy, but specific mechanisms and degradation efficiencies are still poorly understood, especially in commingled systems. In this study, a reduced iron-bearing clay (RIC), nontronite (rNAu-2), was oxygenated to produce hydroxyl radicals (•OH) for degradation of TCE and 1,4-dioxane under circumneutral and dark conditions. Results showed that TCE and 1,4-dioxane could be effectively degraded during oxygenation of rNAu-2 in both single and commingled systems. Compared with the single compound system, the degradation rates and efficiencies of TCE and 1,4-dioxane decreased in the commingled system. The negative effect was more significant for TCE than 1,4-dioxane. The commingled TCE and 1,4-dioxane impacted the degradation pattern of each other, due to their difference in •OH scavenging efficiency, surface affinity to rNAu-2 and solubility. Moreover, solution pH, buffer type, rNAu-2 dosage, and dissolved organic matter all affected •OH production and contaminant degradation efficiency. Our findings provide new insights for investigating the natural attenuation of commingled chlorinated solvents and 1,4-dioxane by RIC in redox-fluctuating environments and offer guidance for developing possible in-situ remediation strategies.

Degradation of 1,4-dioxane by biochar activating peroxymonosulfate under continuous flow conditions

1,4-Dioxane degradation under both batch-scale and column experiments has been investigated within the biochar activated peroxymonosulfate (PMS) system for in-situ remediation of 1,4-dioxane contaminated groundwater. In case of the batch experiments, the 1,4-dioxane degradation efficiencies were significantly increased with the increased biochar pyrolysis temperatures. The optimized 1,4-dioxane degradation efficiency at 89.2% was achieved with 1.0 g L^-1 of biochar (E800) and 8.0 mM PMS. In the absence of PMS, the breakthrough rates of 1,4-dioxane in biochar packed column experiments under the dynamic flow conditions were relatively slow compared with those in sand packed columns. Simultaneously, based on the integrated areas (IA) from the 1,4-dioxane breakthrough curves, the degradation efficiency at 70.2% was estimated in biochar packed column (W_E800:W_Sand = 1:9) under continuous injections of 16.0 mM PMS. Electron paramagnetic resonance (EPR) indicated that hydroxyl, sulfate and superoxide radicals were generated within the biochar/PMS systems and alcohol quenching experiments suggested that the dominated hydroxyl and sulfate radicals were responsible for 1,4-dioxane degradation. The findings of this study suggested that the biochar activated PMS system is a promising and cost-effective strategy for the remediation of 1,4-dioxane contaminated groundwater.

Electro-activation of peroxymonosulfate by a graphene oxide/iron oxide nanoparticle-doped Ti4O7 ceramic membrane: mechanism of singlet oxygen generation in the removal of 1,4-dioxane

Electro-activation of peroxymonosulfate (PMS) has been widely investigated for the degradation of organic pollutants. Herein, we employ graphene oxide (GO)/Fe₃O₄ nanoparticles (NPs) doped into a Ti₄O₇ reactive electrochemical membrane through strong chemical bonding as the cathode to activate PMS for the degradation of 1,4-dioxane (1,4-D). The strong chemical interaction between GO, Fe₃O₄-NPs, and Ti₄O₇ via Fe-O---GO---O-Ti bonds enhances the electron-transfer efficiency and provides catalytically active sites that boost the electro-activation of PMS. As a result, the 1,4-D oxidation rate of the GO/Fe₃O₄-NPs@Ti₄O₇ REM cathode is ~3 times higher (7.21 × 10^-3 min^-1) than those of other Ti₄O₇ ceramic membranes, and ¹O₂ plays a key role (59.9%) in the degradation of 1,4-D. The ¹O₂ generation mechanism in the electro-activation process of PMS was systematically investigated, and we claimed that ¹O₂ is mainly generated from the precursors H₂O₂ and O₂^•-/HO₂^• rather than by O₂ or ^•OH, as has been reported in previous studies. A flow-through mode test in the PMS electro-activation system is firstly reported, and the 1,4-D decay efficiency is 7.1 times higher than that obtained by a flow-by mode, showing that an improved PMS mass transfer efficiency enhances the conversion to reactive oxygen species.

Potential of UV-B and UV-C irradiation in disinfecting microorganisms and removing N-nitrosodimethylamine and 1,4-dioxane for potable water reuse: A review

The ultraviolet (UV)-based advanced oxidation process (AOP) is a powerful technology for removing pathogenic microorganisms and contaminants of emerging concern (CECs) from water. AOP in potable water reuse has been predominantly based on traditional low-pressure mercury (LP-Hg) lamps at 254 nm wavelength, supplemented by hydrogen peroxide addition. In this review, we assessed the potential of unconventional UV wavelengths (UV-B, 280-315 nm and UV-C, 100-280 nm) compared to conventional one (254 nm) in achieving the attenuation of pathogens and CECs. At the same UV doses, conventional 254 nm LP-Hg lamps and other sources such as, 222 nm KrCl lamps and 265 nm UV-LEDs, showed similar disinfection capability for viruses, protozoa, and bacteria, and the effect of hydrogen peroxide (H₂O₂) addition on disinfection remained unclear. The attenuation levels of key CECs in potable water reuse (N-nitrosodimethylamine and 1,4-dioxane) by 185 + 254 nm LP-Hg or 222 nm KrCl lamps were generally greater than those by conventional 254 nm LP-Hg and other UV lamps. CEC degradation was generally enhanced by H₂O₂ addition. Overall, our review suggests that 222 nm KrCl or 185 + 254 nm LP-Hg lamps with the addition of H₂O₂ would be the best alternative to conventional 254 nm LP-Hg lamps for achieving target removal levels of both pathogens and CECs in potable water reuse.

Critical factors for enhancing the bioremediation of a toxic pollutant at high concentrations in groundwater: Toxicity evaluation, degrader tolerance, and microbial community

Groundwater near refinery and natural gas plants often contain elevated concentrations of toxic sulfolane. Studies on any concentration of sulfolane are limited. Column experiment was conducted to investigate the effects of adding a low dose of H₂O₂ and nutrient on bioremediation. Vibrio fischeri light inhibition test was used evaluate the toxicity of effluents. The continuous column experiment conditions were sulfolane at 100 mg L^-1, dissolved oxygen at 7 mg L^-1, absence of phosphorus, and very short hydraulic retention time (7.9 h). A low dose of H₂O₂ (5.88 mM) enhanced the sulfolane (27.1%) and COD removal (11.8%) in comparison with the control set. Adding nutrient increased bicinchoninic acid protein assay levels, sulfolane removal (99.6%) and COD removal (80.3%). Addition of both H₂O₂ and nutrient further improved COD removal (90.3%) and COD/sulfolane ratio (0.90) and toxicity removal (Vibrio fischeri light inhibition ratio < 1%). Batch experiment indicated the degraders tolerated sulfolane up to 400 mg L^-1. The DGGE method and dendrogram analysis were utilized to investigate the changes of degrader community structure.

Photocatalytic degradation of 1,4-dioxane using liquid phase plasma on visible light photocatalysts

The compound 1,4-dioxane (DO) irritates the eyes, skin, and mucous membrane and is classified as a carcinogen. In this study, the decomposition of DO by photocatalytic reaction using liquid phase plasma (LPP) with photocatalyst was suggested. Plasma was directly discharged as an aqueous DO solution to enhance photocatalytic decomposition activity. To increase the decomposition efficiency of DO by plasma, bismuth ferrite (BFO) prepared by a sol-gel method was introduced as a visible-light photocatalyst. In the application of LPP and BFO photocatalyst, the decomposition of DO by photocatalytic reaction was evaluated. BFO showed UV-vis diffusion reflectance spectroscopy results of absorption of UV and visible light over 600 nm, with a bandgap of approximately 2.2 eV. BFO showed visible light photochemical reaction characteristics to decompose particulate matter (PM) in the irradiation of 6 W visible light LED lamps. It seems that the narrow bandgap of BFO led to the photocatalytic activity in the visible light. In the decomposition reaction of DO with a photocatalyst and LPP, BFO showed better decomposition efficiency than TiO₂. BFO can cause photocatalytic reactions in both UV and visible light in the case of LPP irradiation, which emits strong ultraviolet and visible light.