Effective degradation of lindane and its isomers by dielectric barrier discharge (DBD) plasma: Synergistic effects of various reactive species.

Lindane is a broad-spectrum organochlorine insecticide which has been included in the persistent organic pollutants (POPs) list together with its two hexachlorocyclohexane (HCH) isomers. Due to its continuous use in the past decades, the environmental impacts of HCHs are still severe now. Therefore, in the present study, dielectric barrier discharge (DBD) plasma was used as an advanced oxidation process for the destruction of HCHs in water. The result indicated that in air-DBD system, over 95.4% of the initial 5 mg L-1 lindane was degraded within 60 min. Moreover, DBD plasma displayed high degradation efficiencies of other HCH isomers including α, ß, and δ-HCH. Electron spin resonance spectra, scavenging experiments and theoretical calculations revealed that the synergistic effects of various reactive species were the main reason for the high efficiency of DBD plasma. For instance, both hydroxyl radicals (•OH) and electrons (e-) could initiate the degradation of HCHs, while other reactive species such as 1O2 and ONOOH played important roles in the decomposition of intermediates. Therefore, the present study not only provided an effective approach for the treatment of HCHs, but also revealed the underlying mechanism based on in-depth experimental investigation and theoretical calculation.

Simultaneous degradation of glucocorticoids and sterilization using bubbling corona discharge plasma based systems: A promising terminal water treatment facility for hospital wastewater.

Glucocorticoids (GCs) have drawn great concern due to their widespread contamination in the environment and application in treating patients with COVID-19. Due to the lack of data about GC removal using advanced treatment processes, a novel Paralleling and bubbling corona discharge reactor (PBCD) combined with iron-loaded activated-carbon fibre (Fe-ACF) was addressed in this study to degrade GCs represented by Hydrocortisone (HC) and Betamethasone (BT). The results showed that the PBCD-based system can degrade GCs effectively and can achieve effective sterilization. The removal rates of GCs were ranked as PBCD/Fe-ACF > PBCD/ACF > PBCD. The concentration of E. coli was reduced from 109 to 102 CFU/mL after 60 min of PBCD-based system treatment. The abundance of bacteria in actual Hospital wastewater (HWW) was significantly reduced. Plasma changed the physical and chemical properties of ACF and Fe-ACF by etching axial grooves and enhancing stretching vibrations of surface functional groups, thus promoting adsorption and catalytic degradation. For GC degradation, the functional reactive species were identified as •OH, 1O2, and •O2 radicals. Possible degradation pathways for HC and BT were proposed, which mainly included defluorination, keto acid decarboxylation, demethylation, intramolecular cyclization, cleavage and ester hydrolysis, indicating a reduction in GC toxicity. Since GCs are widely used in patients with COVID-19 and their wastewater needs to be sterilized simultaneously, the intensive and electrically driven PBCD-based system is promising in GC pollution control and sterilization in terminal water treatment facilities.

Spectroscopic characterization of soil dissolved organic matter during dielectric barrier discharge (DBD) plasma treatment: Effects of discharge power, atmosphere and soil moisture content.

Non-thermal plasma (NTP) technology is an emerging advanced oxidation process, which has shown excellent performances in soil organic pollution remediation. Dissolved organic matter (DOM) is one of the most important components in soil, however, investigations on the structural and compositional changes of DOM during NTP process are lacking. Therefore, in the present study, we systematically investigated the soil DOM changes under different discharge voltages, atmospheres or soils with different moisture contents. The results indicated that after NTP treatment, substantial soil organic matters were released and dissolved in water. For instance, the DOC value of DOM increased dramatically from 21.1 to 197.3 mg L-1 after being discharged for 120 min under the discharge voltage of 80 V. The UV-Vis characterization results indicated the significant increase of hydrophilicity, and decreases of aromaticity and molecular weight for soil DOM during the initial discharge period. However, long time discharge resulted in slight recovery of aromaticity and hydrophobicity, possibly due to the dehydration and re-condensation of small molecules. EEM-FRI results indicated that the total fluorescence intensity of DOM decreased obviously, indicating the destruction of fluorescent dissolved organic matter (FDOM). While the proportions of humic-like and microbial byproduct-like substances increased, indicating that those substances were more recalcitrant under NTP treatment compared with fulvic acid-like and aromatic protein-like substances. Four fluorescence components were identified by PARAFAC, and microbial and terrestrial humic-like substances were more difficult to degrade compared to other humic-like substances and fulvic acid-like substances. Additionally, discharge voltage and atmosphere had great influences on DOM changes, while the impact of soil moisture content was not significant. Overall, this study provided insights into the DOM changes during NTP process, which is valuable for more comprehensive evaluation of the NTP technique application in practical soil remediation.

Degradation of 3-chlorocarbazole in water by sulfidated zero-valent iron/peroxymonosulfate system: Kinetics, influential factors, degradation products and pathways.

As an emerging class of organic contaminants, polyhalogenated carbazoles (PHCZs) have been increasingly detected all over the world since 1980s. Due to the environmental persistence, bioaccumulation, and dioxin-like toxicity, PHCZs have aroused widespread concerns in recent years. However, efficient approach for the degradation of PHCZs is quite limited so far. Therefore, in this study, an advanced oxidation process (AOP), sulfidated zero-valent iron/peroxymonosulfate (S-ZVI/PMS) system was used to degrade 3-chlorocarbazole (3-CCZ), which is one of the mostly detected PHCZs congeners. The degradation of 3-CCZ was systematically studied under different conditions by varying the molar ratio of S/Fe, the dosage of S-ZVI or PMS, pH and temperature. The results indicated that S-ZVI/PMS was an effective strategy for PHCZs treatment. The 20-min degradation efficiency of 3-CZZ was up to 96.6% with the pseudo-first-order rate constant of 0.168 min-1 under the conditions of 5 mg/L 3-CZZ, 0.3 g/L S-ZVI (S/Fe = 0.2), 1.0 mM PMS, pH 5.8 and 25 °C. HCO3-, Cl- and humic acid (HA) showed inhibitory effects to different degrees. Results of the electron paramagnetic resonance (EPR) and scavenging experiments clarified the dominant role of •OH, followed by 1O2 and SO4•─. The product analysis and DFT calculation revealed three degradation pathways of 3-CCZ, namely hydroxylation, dechlorination and C-N bond cleavage, which largely alleviated the toxicity of the parent compound. This study showed the effectiveness of S-ZVI/PMS system in PHCZs treatment and provided a comprehensive investigation on the degradation behaviors of PHCZs in AOPs.

Reactive Nitrogen Species Generated by Gas-Liquid Dielectric Barrier Discharge for Efficient Degradation of Perfluorooctanoic Acid from Water.

Perfluorooctanoic acid (PFOA) poses a serious threat to the ecological environment and biological health because of its ubiquitous distribution, extreme persistence, and high toxicity. In this study, we designed a novel gas-liquid dielectric barrier discharge (GLDBD) reactor which could efficiently destruct PFOA. PFOA removal efficiencies can be obtained in various water matrices, which were higher than 98.0% within 50 min, with energy yields higher than 114.5 mg·kWh-1. It was confirmed that the reactive species including e-, ONOOH, •NO2, and hydroxyl radicals (•OH) were responsible for PFOA removal. Especially, this study first revealed the crucial role of reactive nitrogen species (RNS) for PFOA degradation in the plasma system. Due to the generation of a large amount of RNS, the designed GLDBD reactor proved to be less sensitive to various water matrices, which meant a broader promising practical application. Moreover, influential factors including high concentration of various ions and humic acid (HA), were investigated. The possible PFOA degradation pathways were proposed based on liquid chromatograph-mass spectrometer (LC-MS) results and density functional theory (DFT) calculation, which further confirmed the feasibility of PFOA removal with RNS. This research, therefore, provides an effective and versatile alternative for PFOA removal from various water matrices.

Enhancing Interface Reactions by Introducing Microbubbles into a Plasma Treatment Process for Efficient Decomposition of PFOA.

Efficient destruction of perfluoroalkyl compounds in contaminated waters remains a challenge because of highly stable C-F bonds. In this study, mineralization of perfluorooctanoic acid (PFOA) with high concentration (∼30 mg/L) was realized in a needle-plate pulsed discharge reactor integrated with a water jet (NPDW) to which microbubbles (MBs) with different carrier gases (air, N2, and Ar) were introduced to enhance interfacial reactions. MBs effectively enrich dispersed PFOA from a bulk solution to a liquid surface to allow enhancing contact with reactive species and also expanding the plasma discharge area and channels. The PFOA removal efficiency in air and Ar discharge reached 81.5 and 95.3% in 2 h, respectively, with a defluorination ratio of no less than 50%. Energy requirements (EE/O) ranged from 216.49 to 331.95 kWh/m3. Aside from fluoride, PFOA was degraded to a range of short-chain perfluoroalkyl acids and, to a minor extent, at least 20 other fluorinated transformation products. PFOA degradation mechanisms were proposed, including decarboxylation, hydroxylation, hydrogenation reduction, and defluorination reactions. Real water matrices (groundwater, tap water, wastewater effluent, and surface water) showed moderate impact on treatment outcomes, demonstrating the robustness of the treatment process. The study demonstrated an environmentally friendly nonthermal plasma technology for effective PFOA degradation.

Efficient degradation of tetracycline by RGO@black titanium dioxide nanofluid via enhanced catalysis and photothermal conversion.

The applications of photocatalytic pollutant degradation have remained limited due to the low efficiency of solar energy utilization. In this study, a photothermal catalyst consisting of reduced graphene oxide @ black TiO2 (RGO@BT) nanofluid with effective full-spectrum (from ultraviolet to infrared light) absorption was synthesized by a typical two-step method of high temperature calcination and hydrothermal method. Moreover, the photothermal catalytic performance of the RGO@BT nanofluid on tetracycline was verified. Compared with individual processes (i.e, photocatalysis and thermocatalysis), the photothermal catalytic process significantly enhanced tetracycline degradation under simulated global standard spectrum sunlight (AM 1.5G, 1000 W m-2). The maximum photothermal conversion efficiency reached 91.8%, which resulted in 94.7% tetracycline degradation (40 mg L-1) after 120 min of treatment with 200 mg L-1 RGO@BT nanofluid. Holes, OH, and O2- were found to be the main active species during the photothermal catalytic process. Moreover, heat was spontaneously converted from light energy without the use of any external energy source. The elevated system temperature facilitated the tetracycline degradation based on the Arrhenius behavior. These findings provide insights into the improvement of photocatalytic efficiency in organic contaminant degradation via solar energy-efficient photothermal conversion materials.

Remediation of perfluorooctanoic acid (PFOA) polluted soil using pulsed corona discharge plasma.

Perfluorooctanoic acid (PFOA) from contaminated soil accumulates in higher organisms, and causes health risks to humans. In this research, 71 % of the PFOA was degraded, of which 51 % was decomposed into short chain by-products, 19 % mineralized, and 1 % volatilized with 30 kV of voltage, 50 Hz of discharge frequency, 1 % of soil moisture, 300 ppm of PFOA concentration and 6.3 of soil pH using pulsed positive discharge plasma. From a series of experiments, electrons were identified as the dominant active means of PFOA degradation. The decomposition by-products were analyzed by LC-MS. The results indicated that PFOA was decomposed into small by-products including perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), perfluorobutyric acid (PFBA), pentafluoropropionic acid (PFPrA) and trifluoroacetic acid (TFA). Moreover, in plasma treated soil, the concentration of ammonia nitrogen increased from less than 10 ppm-462 ppm, and the average dry weight of lettuce was 1.6 mg higher than that in natural soil. Additionally, Planctomycetes and Nitrospirae increased after treatment, indicating that plasma technology promotes the process of nitrogen cycle. Thus, PFOA polluted soil could be remediated using this pulse corona plasma technology, and simultaneously improve the fertility of soil without chemical injections.

Effect of Dielectric Barrier Discharge Cold Plasma on Pea Seed Growth.

Traditional seed pretreatment methods cause secondary pollution for the application of various chemicals. This study investigated the effect of dielectric barrier discharge (DBD) cold plasma on seedling growth. Effects of plasma-activated tap water (PATW) and plasma-activated seeds (PAS) were compared for germination rates, seedling height, dry weight, and chlorophyll content. Results show that compared with controls these growth parameters were all increased by more than 50%. The yields and contributions of hydrogen peroxide, nitrate, nitrite, and ammonium were quantified. Hydrogen peroxide and nitrate have an important role in seedling growth. By etching, the seed epidermis free radicals can reduce the apparent contact angle and increase the water absorption of the seeds. In addition to the low cost of PATW and PAS compared with commercial fertilizers, DBD does not involve any chemical addition. Thus, both PATW and PAS can be an alternative for improvement of agricultural production.

UV/Nitrilotriacetic Acid Process as a Novel Strategy for Efficient Photoreductive Degradation of Perfluorooctanesulfonate.

Perfluorooctanesulfonate (PFOS) is a toxic, bioaccumulative, and highly persistent anthropogenic chemical. Hydrated electrons ( eaq-) are potent nucleophiles that can effectively decompose PFOS. In previous studies, eaq- are mainly produced by photoionization of aqueous anions or aromatic compounds. In this study, we proposed a new photolytic strategy to generate eaq- and in turn decompose PFOS, which utilizes nitrilotriacetic acid (NTA) as a photosensitizer to induce water photodissociation and photoionization, and subsequently as a scavenger of hydroxyl radical (•OH) to minimize the geminate recombination between •OH and eaq-. The net effect is to increase the amount of eaq- available for PFOS degradation. The UV/NTA process achieved a high PFOS degradation ratio of 85.4% and a defluorination ratio of 46.8% within 10 h. A pseudo-first-order rate constant ( k) of 0.27 h-1 was obtained. The laser flash photolysis study indicates that eaq- is the dominant reactive species responsible for PFOS decomposition. The generation of eaq- is greatly enhanced and its half-life is significantly prolonged in the presence of NTA. The electron spin resonance (ESR) measurement verified the photodissociation of water by detecting •OH. The model compound study indicates that the acetate and amine groups are the primary reactive sites.

Impact of humic acid on the photoreductive degradation of perfluorooctane sulfonate (PFOS) by UV/Iodide process.

Iodide photolysis under UV illumination affords an effective method to produce hydrated electrons (eaq-) in aqueous solution. Therefore, UV/Iodide photolysis can be utilized for the reductive degradation of many recalcitrant pollutants. However, the effect of naturally occurring organic matter (NOM) such as humic and fulvic acids (HA/FA), which may impact the efficiency of UV/Iodide photoreduction, is poorly understood. In this study, the UV photoreductive degradation of perfluorooctane sulfonate (PFOS) in the presence of I- and HA is studied. PFOS undergoes a relatively slow direct photoreduction in pure water, a moderate level of degradation via UV/Iodide, but a rapid degradation via UV/Iodide/HA photolysis. After 1.5 h of photolysis, 86.0% of the initial [PFOS] was degraded in the presence of both I- and HA with a corresponding defluorination ratio of 55.6%, whereas only 51.7% of PFOS was degraded with a defluorination ratio of 4.4% via UV/Iodide illumination in the absence of HA. The relative enhancement in the presence of HA in the photodegradation of PFOS can be attributed to several factors: a) HA enhances the effective generation of eaq- due to the reduction of I2, HOI, IO3- and I3- back to I-; b) certain functional groups of HA (i.e., quinones) enhance the electron transfer efficiency as electron shuttles; c) a weakly-bonded association of I- and PFOS with HA increases the reaction probability; and d) absorption of UV photons by HA itself produces eaq-. The degradation and defluorination efficiency of PFOS by UV/Iodide/HA process is dependent on pH and HA concentration. As pH increases from 7.0 to 10.0, the enhancement effect of HA improves significantly. The optimal HA concentration for the degradation of 0.03 mM PFOS is 1.0 mg L-1.

Efficient photoreductive decomposition of N-nitrosodimethylamine by UV/iodide process.

N-nitrosodimethylamine (NDMA) has aroused extensive concern as a disinfection byproduct due to its high toxicity and elevated concentration levels in water sources. This study investigates the photoreductive decomposition of NDMA by UV/iodide process. The results showed that this process is an effective strategy for the treatment of NDMA with 99.2% NDMA removed within 10min. The depletion of NDMA by UV/iodide process obeyed pseudo-first-order kinetics with a rate constant (k1) of 0.60±0.03min-1. Hydrated electrons (eaq-) generated by the UV irradiation of iodide were proven to play a critical role. Dimethylamine (DMA) and nitrite (NO2-) were formed as the main intermediate products, which completely converted to formate (HCOO-), ammonium (NH4+) and nitrogen (N2). Therefore, not only the high efficiencies in NDMA destruction, but the elimination of toxic intermediates make UV/iodide process advantageous. A photoreduction mechanism was proposed: NDMA initially absorbed photons to a photoexcited state, and underwent a cleavage of NNO bond under the attack of eaq-. The solution pH had little impact on NDMA removal. However, alkaline conditions were more favorable for the elimination of DMA and NO2-, thus effectively reducing the secondary pollution.

Spatiotemporal distribution and potential sources of perfluoroalkyl acids in Huangpu River, Shanghai, China.

Perfluoroalkyl acids (PFAAs) have been found to be ubiquitously disseminated in the environment due to their widespread use in recent decades. In this study, the occurrence and spatiotemporal distribution of PFAAs in the surface water of Huangpu River, Shanghai, China were investigated from 2012 to 2014. The total concentration of 14 PFAAs (ΣPFAAs) ranged from 39.8 to 596.2 ng L-1, with a mean value of 226.3 ng L-1. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were dominant, with their mean concentrations of 139.6 and 46.5 ng L-1, respectively. The concentration of ΣPFAAs increased greatly downstream especially in the lower reach of an industrial and urbanized area. Samples collected in different seasons were used to analyze the seasonal variation. The results showed that higher concentration of ΣPFAAs occurred in the wet season, especially downstream. Therefore, industrial discharges, municipal wastewater and surface runoff were identified as major potential sources. The annual discharge load of ΣPFAAs from Huangpu River to Yangtze River was estimated to be 2263.4 kg yr-1. The hazard assessment suggested that the contamination of PFAAs in Huangpu River could pose risks to the aquatic environment and drinking water safety, which should draw more attention.