Dechlorination Products Research Articles

Highly improved dechlorination of 2,4-dichlorophenol in aqueous solution by Fe/Ni nanoparticles supported by polystyrene resin

2,4-dichlorophenol (2,4-DCP) is a typical chlorophenol that has been widely used in industrial production and caused serious pollution to the environment. In this study, the performance of Fe/Ni bimetallic nanoparticles supported on polystyrene cation exchange resin (Fe/Ni-D072) to remove 2,4-DCP was evaluated. The effects including the doping amount of Ni, the dosage of Fe/Ni-DCP, the initial concentration of 2,4-DCP, and pH value of the solution on the removal efficiency were also investigated. The results showed that when the initial concentration of 2,4-DCP was 20 mg/L and pH = 7.3, 90% of 2,4-DCP could be dechlorinated by Fe/Ni-D072 (Ni% = 30 wt%, dosage: 6.7 g/L) after 12 h reaction. The dechlorination process followed a pseudo-first-order model, and the reaction constant was 0.252 h−1. In addition, the effects of humic acid and common coexisting ions on dechlorination were studied. The results showed that humic acid with a low concentration (5 mg/L) and CO32− restrained the degradation of 2,4-DCP. The dechlorination products of 2,4-DCP were identified by HPLC and the result showed phenol was the main product with a slight amount of 2-CP as the dechlorination intermediate, and 4-CP was barely detected. These results suggest that Fe/Ni-D072 was a promising catalytic material for the removal of chlorophenol and has great application prospects in groundwater remediation.

Reduction of chlorinated hydrocarbons using nano zero-valent iron supported with an electric field. Characterization of electrochemical processes and thermodynamic stability

Electric field assisted remediation using nano iron has shown outstanding results as well as economic benefits during pilot applications (Černíková et al., 2020). This method is based on donating electrons to the zero-valent iron that possess an inherently strong reductive capacity. The reduction of chlorinated hydrocarbons may be characterized by a decrease in contaminants or better still by the evolution of ethene and ethane originating from the reduction of chlorinated ethenes. The evolution of ethene and ethane was observed predominantly in the vicinity of the anode despite reduction processes being expected near the cathode – the electron donor. The reduction near the anode occurred due to dissolved Fe2+ ions, whose presence was suggested by a Pourbaix diagram that combines Eh/pH values to characterize electrochemical stabilities between different species. No products of dechlorination were observed in the area of the cathode due to presence of oxidized Fe in the form of Fe3+ or Fe(OH)4-. The experimental work described in this research provides a deeper view of the processes of electrochemical reductive dechlorination using zero-valent iron and DC. It also showed an increase in the efficiency compared to the method using zero-valent iron only.

Hydrodechlorination of carbon tetrachloride with nanoscale nickeled zero-valent iron @ reduced graphene oxide: kinetics, pathway, and mechanisms.

In recent years, carbon tetrachloride (CT) has been frequently detected in surface water and groundwater around the world; it is necessary to find an effective way to treat wastewater contaminated with it. In this study, Ni/Fe bimetallic nanoparticles were immobilized on reduced graphene oxide (NF@rGO), and used to dechlorinate CT in aqueous solution. Scanning electron microscopy (SEM) demonstrated that the two-dimensional structure of rGO could disperse nanoparticles commendably. The results of batch experiments showed that the 4N4F@rGO (Fe/GO = 4 wt./wt., and Ni/Fe = 4 wt.%) could reach a higher reduction capacity (143.2 mgCT/gcatalyst) compared with Ni/Fe bimetallic nanoparticles (91.7 mgCT/gcatalyst) and Fe0 nanoparticles (49.8 mgCT/gcatalyst) respectively. That benefited from the nickel metal as a co-catalyst, which could reduce the reaction activation energy of 6.59 kJ/mol, and rGO as an electrical conductivity supporting material could further reduce the reaction activation energy of 4.73 kJ/mol as presented in the conceptual model. More complete dechlorination products were generated with the use of 4N4F@rGO. Based on the above results, the reductive pathway of CT and the catalytic reaction mechanism have been discussed.

Bioremediation of typical chlorinated hydrocarbons by microbial reductive dechlorination and its key players: A review

Chlorinated hydrocarbon contamination in soils and groundwater has a severe negative impact on the human health. Microbial reductive dechlorination is a major degradation pathway of chlorinated hydrocarbon in anaerobic subsurface environments, has been extensively studied. Recent progress on the diversity of the reductive dechlorinators and the key enzymes of chlororespiration has been well reviewed. Here, we present a thorough overview of the studies related to bioremediation of chloroethenes and polychlorinated biphenyls based on enhanced in situ reductive dechlorination. The major part of this review is to provide an up-to-date summary of functional microorganisms which are either detected during in situ biostimulation or applied in bioaugmentation strategies. The applied biostimulants and corresponding reductive dechlorination products are also summarized and the future research needs are finally discussed.

Sources of polychlorinated biphenyls to Upper Hudson River sediment post-dredging

The Upper Hudson River (UHR) has been contaminated with polychlorinated biphenyls (PCBs) since the 1940s due to the manufacture of capacitors at two plants near Hudson Falls and Fort Edward, NY by General Electric (GE). Dredging of portions of the UHR was conducted from 2009 to 2015 as a partial remedy for this contamination. In 2017, the New York State Department of Environmental Conservation undertook a comprehensive post-dredging survey of sediment contamination in the UHR. Thousands of samples were collected, and 130 of these were analyzed for PCBs using EPA method 1668A. This data set was analyzed using Positive Matrix Factorization. Six factors were observed. One factor resembled the dominant Aroclors used by GE with little alteration. Three factors represented different pathways and/or extents of microbial dechlorination. One factor resembled a mixture of microbial dechlorination products and a higher molecular weight Aroclor used by GE. The congener patterns of the dechlorination factors suggest that removal of chlorines at the ortho position does occur in the UHR sediment, in agreement with several laboratory studies showing that such ortho dechlorination is possible. This ortho dechlorination could theoretically lead to complete dechlorination of PCBs to biphenyl in UHR sediment. Only one factor was not attributable to GE. It represents inputs of PCBs from tributaries and urban areas and explains 1.7% of the PCB mass in the sediments. The small contribution from the non-GE PCB source suggests that recontamination of the sediment after dredging was minor.

Hydrodechlorination of hexachlorobenzene in a miniaturized nano-Pd(0) reaction system combined with the simultaneous extraction of all dechlorination products

The persistent organic pollutant hexachlorobenzene (HCB) and all 11 further chlorobenzenes were hydrodechlorinated at environmentally relevant concentrations in miniaturized reaction systems, catalyzed by low concentrated Pd(0)-nanoparticles, to examine differences in dechlorination rates and pathways. Using solid-phase microextraction coupled to gas chromatography-mass spectrometry allowed the simultaneous extraction and detection of reactants, intermediate products and fully dechlorinated benzene, regardless of their different physicochemical properties. Dechlorination of HCB with formation of intermediates mainly proceeded via pentachlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,3-trichlorobenzene, 1,2-dichlorobenzene, and monochlorobenzene to benzene. Specific catalytic activities of Pd(0)-nanoparticles (100–3400 L g−1 min−1) differed depending on chlorination degree of chlorobenzenes and position of chlorine atoms. An inductive effect is assumed to favor a removal of the vicinal chlorine atom. The presented method permits the facile determination and comparison of nanomaterials’ specific catalytic activities and allows the elucidation of dehalogenation pathways. It further enables to specifically examine formed intermediates to assess their toxicity and biodegradability.

Screening of zero valent mono/bimetallic catalysts and recommendation of Raney Ni (without reducing agent) for dechlorination of 4-chlorophenol

Chlorophenol (CP) is considered as environmentally hazardous material due to its acute toxicity, persistent nature and strong bioaccumulation. The dechlorination of 4-CP was investigated by using various catalysts such as bimetallic (Fe0/Cu0, Al0/Fe0), Pd/C, Raney Ni and Fe0 at room temperature. Among the catalysts studied, Raney Ni proved to be very economical and efficient catalyst that worked without the use of an external reducing agent. The dechlorination of 4-CP by Raney Ni was therefore further explored. Complete dechlorination of 4-CP (30 mg L−1) was achieved in 6 h at an optimum Raney Ni catalyst loading of 3 g L−1. The effect of triethylamine (TEA) and tripropylamine (TPA) was also investigated and it was observed that 100% dechlorination is possible in presence of 45 mg L−1 of TEA. The kinetics of dechlorination of 4-CP was investigated and found to be first order with a rate constant of 0.017 min−1 at 50 οC, and it enhances to 0.109 min−1 with addition of TEA. In the absence of a reducing agent, acidic to neutral pH favors dechlorination of 4-CP. The final product of dechlorination was estimated to be phenol by performing HPLC, LCMS and NMR analysis. Based on the results, a probable dechlorination mechanism of 4-CP is also proposed. It can be concluded that the catalytic hydrodechlorination is an effective and economical technique for dechlorination of 4-CP and it has a potential for the dechlorination of other toxic derivatives of chlorinated aromatics.

Biotransformation Mechanism of Pesticides by Cytochrome P450: A DFT Study on Dieldrin.

Pesticide biotransformation, especially by cytochrome P450 enzymes (CYPs), may produce metabolites with substantially altered toxicological and physicochemical profiles, which has drawn great attention as a basis for environmental risk assessment. CYPs are active in the metabolism of various reactions of pesticides, and there are potentially different short-lived oxidant species in CYPs (Compound I vs Compound 0), which make elucidating their biotransformation mechanism challenging. To facilitate this task, we performed density functional theory (DFT) calculations to explore the puzzling bifurcation pathways of dieldrin by CYPs. The results show that the two-oxidant mechanism does not work, while the bifurcation pathways are within the mechanistic framework of a two-state reactivity of Compound I. Specifically, 9-hydroxy-dieldrin as a hydroxylation product is formed via H-abstraction and essentially barrierless C-9 alkyl radical rebound in the doublet state; while 3-ketone-dieldrin as a dechlorination product is formed via H-abstraction, C-9 alkyl radical cyclization, and C-3 cyclized radical rebound in the quartet state followed by HCl elimination, originating from a significant barrier for C-9 alkyl radical rebound in the quartet state to provide this radical sufficient lifetime for cyclization. Thus, the ratio [dechlorination]/[hydroxylation] can be estimated as 1:35, consistent with the experimental findings. We envision that application of computational chemistry has a great potential in revealing the complex biotransformation mechanisms of pesticides.

Радиационные и фотохимические методы дехлорирования полихлорбифенилов (Обзор)

В обзоре анализируются результаты исследований и разработок, посвященных применению радиационно-химических и фотохимических методов для дехлорирования опасных химических соединений - полихлорированных бифенилов (ПХБ). ПХБ широко выпускались ранее для применения в качестве диэлектрических жидкостей в трансформаторах и конденсаторах или в качестве присадок к трансформаторным маслам, которые до сих пор продолжают использоваться. В настоящее время ПХБ признаны стойкими органическими загрязнителями и, согласно Стокгольмской конвенции, должны быть обезврежены, а их запасы подлежат утилизации. В обзоре обобщена информация об исследованиях, в которых с помощью радиации и фотохимического воздействия выполняется очистка от ПХБ трансформаторных масел, гидравлических масел и некоторых видов жидких отходов. Рассмотрено воздействие на полихлорбифенилы различных видов ионизирующего излучения и ультрафиолетового излучения, в том числе в присутствии растворителей, щелочи и различных окисляющих добавок. Приведены энергетические выходы разложения, рассмотрены механизмы и скорости реакций деградации, степени разложения, продукты реакций. Сделанные выводы могут быть использованы в качестве практических рекомендаций по обезвреживанию систем, содержащих ПХБ, указанными методами. The review examines research and development progress referring to application of radiation-chemical and photochemical methods for dechlorination of hazardous chemical compounds - polychlorinated biphenyls (PCBs). PCBs have been widely produced previously as dielectric fluids used in transformers and condensers, or as additives for transformer oils, which are still being in use. Currently, PCBs have been recognized as persistent organic pollutants and, according to the Stockholm Convention on POPs, are required detoxification and disposal of their stockpiles. The review summarizes studies applying radiation and photochemical procedures for degradation of PCBs which are contained in transformer oils, hydraulic oils, and some types of liquid wastes. An effect of ionizing radiation and ultraviolet radiation on polychlorinated biphenyls is considered, including degradation protocols involving the presence of solvents, alkali and various kinds of oxidizing agents. The values of degradation energy yields, supposed mechanisms, calculated rates of degradation reactions, degrees of decomposition, and dechlorination products are considered. The conclusions drawn can be used as practical recommendations for disposal of PCB-based systems with the help of the methods indicated above.

FOOT-OF-THE-WAVE ANALYSIS OF THE ELECTROCATALYTIC DECHLORINATION OF HEXACHLOROETHANE USING COBALOXIMES

In this work the electrochemical degradation of polychlorinated compounds using Co(dmgH)2Cl(py), Co(dpgH)2Cl(py), Co(chgH)2Cl(py) and Co(dbegH)2Cl(py) (where dmgH is dimethylglyoximato, dpgH is diphenylglyoximato, chgH is 1,2-cyclohexanedionedioximato and dbegH is di(4-methylbenzoate)glyoximato) is described. The degradation was studied using cyclic voltammetry by monitoring current changes in the zone near to the Co(II/I) half wave potential as the concentration of the organochloride in the electrochemical cell is increased. Hexachloroethane (HCA) was used as organohalide substrate, while gamma-hexachlorocyclohexane (lindane), 1,2-dichloroethane, and 1,1,1-trichloroethane were used for comparative studies. The major dechlorination product of HCA, detected through head space GC-MS experiments after bulk electrolysis, was tetrachlorethylene. The rate constants of the dechlorination processes were estimated using the foot-of-the-wave analysis (FOWA), the values obtained were 1.10×105, 2.59×104, 4.91×104 and 1.83×104 for Co(dmgH)2Cl(py), Co(dpgH)2Cl(py), Co(chgH)2Cl(py) and Co(dpegH)2Cl(py) respectively.

Metabolomics reveals that tris(1,3-dichloro-2-propyl)phosphate (TDCPP) causes disruption of membrane lipids in microalga Scenedesmus obliquus

Tris(1,3-dichloro-2-propyl)phosphate (TDCPP) is one of the most widely used organophosphate ester flame retardants. The presence of TDCPP in surface waters and aquatic organisms have been reported worldwide, yet the ecological risk of TDCPP on microalgae is rarely studied. We investigated the biotransformation of TDCPP and its toxicity on the microalga Scenedesmus obliquus using an untargeted metabolomics approach. Exposure to TDCPP resulted in a dose-response decrease of micoalgal biomass. In the presence of microalgae, TDCPP concentration in the media decreased by 25.3–40.6% after 5 days. TDCPP metabolites were identified in the media including hydrolysis and hydroxyl-substituted dechlorination products. A dose-response separation of metabolic profiles of microalgae was observed, with effect seen at the lowest concentration of 10 µg/L tested, which is slightly higher than environmentally relevant concentrations. Differentiated metabolites identified include 52 lipids and 6 polar metabolites. Analysis of altered lipid pathways suggests that microalgal cells reinforce thylakoid membranes (function to protect photosynthesis) by compromising the integrity of plasma membrane (function to protect cellular substances) and extraplastidial cellular membranes. Changes in the polar metabolites might indicate osmotic stress and improved NO signaling after TDCPP exposure. Consistent with perturbation of membrane lipids, further experiment confirmed that exposure to 10 mg/L TDCPP resulted in significant (p < 0.01) plasma membrane damage. This study indicates biotransformation and the membrane damage toxicity mechanism of TDCPP on S. obliquus, demonstrating the usefulness of metabolomics for the toxicity mechanism elucidation of emerging pollutants.

Transformation of 1,1,1,3,8,10,10,10-octachlorodecane in air phase increased by phytogenic volatile organic compounds of pumpkin seedlings

Short chain chlorinated paraffins (SCCPs) are widely distributed persistent organic pollutants (POPs). Airborne chlorodecanes were hypothesized to be transformed by reactive phytogenic volatile organic compounds (PVOCs) in our previous work. To test this hypothesis, PVOCs of pumpkin (Cucurbita maxima x C. moschata) were collected and reacted with 1,1,1,3,8,10,10,10-octachlorodecane in the air phase of a sealed glass bottle under illumination for 10 days (reaction system I, simulating atmospheric reaction conditions with PVOCs). The reaction control group (reaction system II) was set at the same conditions but only had chlorodecane (without PVOCs) inside the bottle. Transformation of SCCPs in the air phase of reaction control group was unexpectedly found. Results showed that 1,1,1,3,8,10,10,10-octachlorodecane was transformed to a great extent to C10Cl5-8, C9Cl6-8, and C8Cl7-8 in the air phase after 10-d illumination in both with and without the presence of PVOCs, which is explained by carbon chain decomposition, dechlorination and chlorine rearrangement products of the parent SCCP. Those transformation processes were increased to some extent by the PVOCs from pumpkin seedlings. This study provides the first experimental data on atmospheric transformation of SCCPs and also the first evidence that plant emissions (PVOCs) can increase the transformation of SCCPs in air under light and experimental conditions. It provides new insight into the potential transformation and fate of CPs in the environment.

Dichlorination in a circulating fluidized-bed incinerator for municipal solid waste incineration system

Cl is one of the main pollutants emitted from domestic waste incineration systems. In this study, we focused on the process of Ca dechlorination in the furnace of a circulating fluidized-bed waste incineration system. We analyzed the stability of CaCl2 and Ca in the furnace, the dechlorination process, and distribution of Cl in the incineration system. The results show that the optimal Ca/Cl molar ratio for Ca dechlorination in the circulating fluidized-bed waste incinerator is 2:1; moreover, the dechlorination product CaCl2 was found to decompose at high temperatures (> 850 °C). At temperatures > 700 °C, we measured CaCl2 decomposition rates up to 80%. Ca was added in the furnace, mainly to provide a dechlorination Ca source for the decomposition of limestone into tail flue gas. The amount of Ca2+ in the flue decreased gradually, parallelly to the temperature of the flue gas. Stable CaCl2 was formed after HCl was captured, and relatively small solid particles appeared in the ash collecting bag.

Efficiently complete degradation of 2,4-DCP using sustainable photoelectrochemical reduction and sequential oxidation method

Halogenated organic compounds (HOCs) like chlorophenols (CPs) are one of persistent organic pollutants in environment, and it is an urgent issue to remove HOCs efficiently because they are detrimental to aquatic organisms and human beings. Electrocatalytic hydrodechlorination (ECH) technique has been widely studied to deal with chlorophenols. However, litter attention has been paid to the further treatment of the dechlorination product phenol. Meanwhile, photoelectrocatalysis is regarded as a promising method for contaminants elimination and water splitting using inexhaustible solar energy. Therefore, this study proposed a photoelectrochemical reductive hydrodechlorination and sequential oxidation method for thorough degradation of 2,4-dichlorophenol (2,4-DCP) using WO3/Mo-doped BiVO4 as photoanode and Pd/Ni foam as cathode. Several factors such as Pd-loading amount, initial pH, overpotential, and Cl− that would influence the efficiency of 2,4-DCP hydrodechlorination and phenol oxidation have been investigated in detail. The 2,4-DCP could be completely hydrodechlorinated to phenol, and removal efficiency of the obtained phenol reached ~45% for 4 h reaction under optimized conditions. Additionally, there was no secondary chlorinated pollutant generated during the oxidation process even though the existence of Cl−. Lastly, the possible mechanism and degradation pathway were also explored based on LC-MS. This study proposed an efficient and environmental-friendly technique for complete degradation of chlorophenols, which might be also suitable for other HOCs and would be industrialized with the help of further studies.

Accelerated microbial reductive dechlorination of 2,4,6-trichlorophenol by weak electrical stimulation

Microbial reductive dechlorination of chlorinated aromatics frequently suffers from the long dechlorination period and the generation of toxic metabolites. Biocathode bioelectrochemical systems were verified to be effective in the degradation of various refractory pollutants. However, the electrochemical and microbial related working mechanisms for bio-dechlorination by electro-stimulation remain poorly understood. In this study, we reported the significantly improved 2,4,6-trichlorophenol dechlorination activity through the weak electro-stimulation (cathode potential of −0.36 V vs. SHE), as evidenced by the 3.1 times higher dechlorination rate and the complete dechlorination ability with phenol as the end dechlorination product. The high reductive dechlorination rate (20.8 μM/d) could be maintained by utilizing electrode as an effective electron donor (coulombic efficiency of 82.3 ± 4.8%). Cyclic voltammetry analysis of the cathodic biofilm gave the direct evidences of the cathodic respiration with the improved and positive-shifted reduction peaks of 2,4,6-TCP, 2,4-DCP and 4-CP. The optimal 2,4,6-TCP reductive dechlorination rate (24.2 μM/d) was obtained when a small amount of lactate (2 mM) was added, and the generation of H2 and CH4 were accompanied due to the biological fermentation and methanogenesis. The electrical stimulation significantly altered the cathodic biofilm structure and composition with some potential dechlorinators (like Acetobacterium) predominated. The microbial interactions in the ecological network of cathodic biofilm were more simplified than the planktonic community. However, some potential dechlorinators (Acetobacterium, Desulfovibrio, etc.) shared more positive interactions. The co-existence and possible cooperative relationships between potential dechlorinators and fermenters (Sedimentibacter, etc.) were revealed. Meanwhile, the competitive interrelations between potential dechlorinators and methanogens (Methanomassiliicoccus) were found. In the network of plankton, the fermenters and methanogens possessed the more positive interrelations. Electro-stimulation at the cathodic potential of −0.36 V selectively enhanced the dechlorination function, while it showed little influence on either fermentation or methanogenesis process. The study gave suggestions for the enhanced bioremediation of chlorinated aromatics, in views of the electro-stimulation capacity, efficiency and microbial interrelations related microbial mechanism.

Insights into interactions between vanadium (V) bio-reduction and pentachlorophenol dechlorination in synthetic groundwater

Aquifer co-contamination by vanadium (V) and pentachlorophenol (PCP) involves complicated biogeochemical processes that remain poorly understood, particularly from the perspective of microbial metabolism. Batch experiment results demonstrated that V(V) and PCP could be competitively bio-reduced, with 96.0 ± 1.8% of V(V) and 43.4 ± 4.6% of PCP removed during 7 d operation. V(V) was bio-transformed to vanadium (IV), which could precipitate naturally under circumneutral conditions, facilitating the removal of up to 78.2 ± 3.1% dissolved total V. The PCP reductive dechlorination products were mainly 2,4,6-trichlorophenol and 4-monochlorophenol with lower toxicity. High-throughput 16S rRNA gene sequencing indicated that Pseudomonas, Soehngenia, and Anaerolinea might be responsible for the two bio-transformations, with detected functional genes of nirS and cprA. Extracellular reduction by cytochrome c and intracellular conversion by nicotinamide adenine dinucleotide (NADH) occurred for both V(V) and PCP. Extracellular proteins in microbial-secreted extracellular polymeric substances (EPS) might also be involved in these enzymatic bioprocesses. EPS could protect microbial cells through V(V) binding by the chemically reactive carboxyl (COO−), and hydroxyl (–OH) groups. These findings elucidate the metabolic processes during anaerobic V(V) and PCP biotransformation, advance understanding of their biogeochemical fates, and provide a foundation on which to develop novel strategies for remediation of co-contaminated aquifers.

Multifunctional Pd/Fe-biochar composites for the complete removal of trichlorobenzene and its degradation products

To elucidate the effect of structure and property of biochar on the structure-activity relationship among the composites of biochar supported Pd/Fe and 1,2,4-trichlorobenzene (1,2,4-TCB) and its dechlorination products, biochar supported Pd/Fe nanoparticles with different mass ratios were investigated for the enhanced removal of 1,2,4-TCB (52 μmol/L) and its dechlorination products. 1,2,4-TCB was removed through the electrochemical dechlorination by Pd/Fe and adsorption by biochar simultaneously. As the mass ratio of CS700 to Pd/Fe was 0.1:1, biochar within the Pd/Fe-CS7000.1 system played a significant role in the adsorption of 1,2,4-TCB. However, there is little adsorption to biochar for dechlorination products due to strong competition by 1,2,4-TCB. As the mass ratio of CS700 to Pd/Fe was increased to 5:1, 1,2,4-TCB was completely removed from the solution by the composites within 0.5 h. The dechlorination products (1,2-DCB, MCB, benzene and trace 1,3-DCB) were completely sequestered on solid phase but absent in aqueous solution. However, the excessive biochar increased the inaccessibility of 1,2,4-TCB or decreased the reactive sites of Pd/Fe leading to the less dechlorination of 1,2,4-TCB. The alkaline biochar did not influence the chemical reactivity of Pd/Fe in the composites and buffered the acid and alkaline solutions with pH being maintained at neutral conditions under initial pH ranging from 3.07 to 10.03. The highly hydrophobicity of biochar could maintain the affinity of the composite for the chlorinated compounds even if the concentration of 1,2,4-TCB was up to 80.9% of its aqueous solubility. This study provides efficient synergistic removal support for the treatment of TCB affected groundwater.

Fate of triclosan, triclocarban, and their transformation products in wastewater under nitrifying conditions

The nitrification process was simulated using benchtop bioreactors to gain insight into the fate of the antimicrobials triclosan (TCS) and triclocarban (TCC), as well their transformation products, during wastewater treatment. Currently, little information exists on the impact of nitrification treatment on concentrations of TCC, TCC degradation products, and TCS degradation products. Reactors were run using samples collected from a large municipal wastewater treatment plant at two pH ranges (6.5–7.5 and 8.5–9.5) for 171 h to simulate an extended hydraulic retention time (HRT). TCS was degraded under both pH conditions, with a 28.5% overall reduction in solids samples when the pH range was 6.5–7.5 and an overall reduction of 83.2% in solids samples when the pH ranged 8.5–9.5. Methyltriclosan (MeTCS) was formed in solids samples during both treatment conditions. MeTCS formed the most rapidly during the first 25 h of treatment at pH 8.5–9.5. Levels of 2,4-dichlorophenol, a TCS photolysis product, and TCC did not change over the 171 h treatment period, indicating that nitrification is not an effective treatment for reduction of these compounds. Three TCC dechlorination products and triclosan-O-sulfate were not observed at or above the limit of quantitation in any bioreactor samples.

Investigation of physical and chemical properties for upgraded SAP (SiO2[sbnd]Al2O3[sbnd]P2O5) waste form to immobilize radioactive waste salt

Metal chloride waste generated from pyroprocessing is considered as one of the more problematic wastes in radioactive waste immobilization for the reprocessing of used nuclear fuel. This waste cannot be directly vitrified using the conventional approach using a borosilicate matrix because of the high chloride content in the waste. Thus, an indirect immobilization method using a SAP (SiO2Al2O3P2O5) composite via dechlorination of the salt waste was evaluated as an alternative with a binder glass to aid in the consolidation process. Additionally, U-SAP was developed by adding consolidation promoters such as B and Al to the SAP and then, the glass binder was not needed. In the present contribution, basic properties of U-SAP dechlorination products and U-SAP waste forms were characterized by physical and chemical analysis methods. Structure of U-SAP waste form was investigated with X-ray diffraction, transmission, scanning transmission, and scanning electron microscopies, energy dispersive spectroscopy, secondary ion mass spectrometry, and atom-probe tomography. The results showed that uniform and nano-sized droplets were composed of crystalline Li3PO4 or a mixture of Li3PO4 and amorphous phosphorous-based phases. The droplets were encapsulated by durable silicate glass. Interfacial region composed of SiOAl(B) and Al(B)OP components connected immiscible silicate and phosphorous phases. The Li3PO4, which is not chemically durable, was protected by silicate glass from leaching and very small amount of Li was contained in silicate glass. The good leaching properties of the U-SAP waste form are attributed to this structure.

Electrocatalytic dechlorination of 2,4-dichlorobenzoic acid using different carbon-supported palladium moveable catalysts: Adsorption and dechlorination activity

In the present study, carbon black (CB), multi walled carbon nanotubes (MWCNTs), and granular activated carbon (GAC) were employed to support palladium (Pd) catalyst. The prepared Pd/CB, Pd/MWCNTs and Pd/GAC moveable catalysts were aimed to address the common issues (easy loss of catalyst and poor long-term performance) of normal fixed catalysts. The results of various characterizations (e.g., TEM, XRD, and XPS) clearly show that the Pd nanoparticles were successfully loaded onto the carbon-supports, especially CB and MWCNTs. And more importantly, the morphologies, Pd distribution, and chemical structure of these moveable catalysts were almost not changed after 3 h reaction. The moveable Pd/CB, Pd/MWCNTs, and Pd/GAC catalysts had good reactivity for 2,4-dichlorobenzoic acid (2,4-DCBA) dechlorination, and Pd/CB exhibited the best performance. The Pd/CB also shows the best adsorption capacity of 2,4-DCBA and dechlorination product (benzoic acid, BA), and the adsorption of BA was significantly inhibited in the presence of current due to the repulsion between the both negatively charged compounds and adsorbents. The removal of 2,4-DCBA and the generation rate of BA was improved with a pre-adsorption process, which was a promising strategy with higher dechlorination rate and shortened electrolysis time. Moreover, the loss of Pd catalyst was negligible during the 10 consecutive cycles experiment, and the improved longevity could be expected. These results suggested the good reactivity, stability, and reusability of moveable Pd/CB catalyst.