Dechlorination Research Articles

Isotopic evidence (δ13C, δ37Cl, δ2H) for distinct transformation mechanisms of chloroform: Catalyzed H2-water system vs. zero-valent iron (ZVI)

Catalytic hydrodechlorination is an efficient technology for degrading organochlorinated compounds, such as chloroform (CF), into harmless products. Compound-specific stable isotope analysis (CSIA) of multiple elements is widely used for the investigation of degradation mechanisms. Yet, its application in the study of catalytic hydrodechlorination is still limited. We have applied CSIA to derive chlorine, carbon, and hydrogen isotope enrichment factors (ε) during the degradation of CF over Pd/Al2O3 and over Rh/Al2O3. In addition, the enrichment factors for the same isotopes were derived for the reaction of CF with zero-valent iron (ZVI) for comparison. For the reactions of CF over Pd/Al2O3 and Rh/Al2O3, εC values (−21.9 ± 0.25 ‰ and −23.4 ± 2.3 ‰) and εCl values (−12.1 ± 1.7 ‰ and −10.3 ± 0.6 ‰) were determined, respectively. The corresponding εC and εCl values, for the dechlorination of CF with ZVI were −22.2 ± 2.8 ‰ and −4.7 ± 0.45 ‰, respectively. The apparent kinetic isotope effects (AKIE) of Cl suggest that the transformation mechanism in the catalyzed hydrogen-water system is a non-concerted reaction, unlike the known reductive dechlorination of CF with ZVI. Moreover, dual-isotope slopes (ΛC/Cl) for both catalyzed reactions (ΛPd = 1.8 ± 0.13 and ΛRh = 2.1 ± 0.14) are markedly different than for the ZVI (ΛZVI = 5.8 ± 0.41), reflecting that the reactions proceed in different mechanisms. For hydrogen isotopes, while there was no clear trend for the catalyzed reactions, an inverse secondary hydrogen isotope effect was observed for the reaction of CF with ZVI.

High-molecular-weight by-products of chlorine disinfection

Although drinking water chlorination has reduced the incidence of waterborne disease, the reactions of chlorine with organic matter can lead to the formation of >700 halogenated disinfection by-products (DBPs). Epidemiological studies have linked the consumption of chlorinated drinking water with bladder cancer. With studies indicating that the one- and two-carbon-atom DBPs of current interest account for only ~16% of disinfected water cytotoxicity, there is a need to identify toxicity drivers within the poorly characterized higher-molecular-weight (more than two carbon atoms) DBP fraction. In this Review, we outline the current knowledge regarding this fraction and discuss novel analytical approaches to characterizing the much wider variety of structures that it contains. We detail the products formed from the reactions of chlorine with different categories of precursor, including the characteristics of the elemental formulae of products identified by high-resolution mass spectrometry, the halogenated aromatic DBPs formed from precursors in pristine waters and the products derived from biopolymer-bound monomers in algal- or wastewater-impacted waters. Finally, we discuss the key challenges for research into this important, but until recently, mostly overlooked by-product fraction. Recent toxicological studies have indicated that the poorly characterized high-molecular-weight fraction of disinfection by-products may contribute more to toxicity than the carbon disinfection by-products of current research interest. This Review summarizes what is known about the high-molecular-weight fraction and suggests pathways for future research in this area.

Growth performance and cecal microbiota of broiler chicks as affected by drinking water disinfection and/or herbal extract blend supplementation

Environmental exposures during early life are important for animals' intestinal microbiota composition and their production performance. This experiment investigated the growth performance, hematology parameters, jejunal morphology, and cecal microbiota of broiler chicks as affected by exogenous factors from the aspects of drinking water quality and dietary manipulation. A total of 480-day-old broiler chicks (Arbor acre; 41.59 ± 0.88 g) were randomly assigned into 4 groups (CON, HWGM, CA, CAHWGM). Each group had 6 replicates with 20 birds per replicate. Broiler chicks in CON group were fed with basal diet and drank normal drinking water; in HWGM group were fed with basal diet supplemented with 1.5g/kg herbal extract blend (hops, grape seed, and wheat germ) and drank normal drinking water; in CA group were fed with basal diet and drank sodium dichlorocyanurate (50 mg/L) treated-drinking water; in CAHWGM group were fed with basal diet supplemented with 1.5 g/kg herbal extract blend and drank chlorinated drinking water. The experimental period was 42 d. We found that broiler chicks drank chlorinated drinking water led to an increase in body weight gain and feed efficiency during d 22 to 42 and 1 to 42, as well as a decrease in cecal Dysgonomonas and Providencia abundance. Dietary supplementation of herbal extract blend increased cecal Lactobacillus and Enterococcus abundance, whereas decreased Dysgonomonas abundance. Moreover, we observed that cecal Dysgonomonas abundance synergistically decreased by treating drinking water with sodium dichlorocyanurate and supplementing herbal extract blend to the diet. Therefore, results obtained in this study indicated that providing chlorinated drinking water is an effective strategy to improve the growth performance of broiler chicks by regulating intestinal microbiota. Additionally, dietary supplementation of herbal extract blend alone or combined with chlorinated drinking water is able to regulate cecal microbiota.

Enhanced electrocatalytic cathodic degradation of 2,4-dichlorophenoxyacetic acid based on a synergistic effect obtained from Co single atoms and Cu nanoclusters

Electrochemical reduction-oxidation is an environmentally-friendly process of degrading 2,4-dichlorophenoxyacetic acid (2,4-D). However, the design of electrocatalysts having reductive dechlorination and oxygen-specific active sites remains challenging. In the present study, catalytic cathodes were made from single Co atoms and Cu nanoclusters on nitrogen-doped carbon to enhance the degradation of 2,4-D through a synergistic mechanism. In this process, 2,4-D was dechlorinated on the Cu nanoclusters and then oxidized by ·OH radicals produced by the conversion of O2 on the Co atoms. The Cu nanoclusters served as both conductive bridges and 2,4-D adsorption sites to improve the electron transfer of the circuit and so accelerate the direct electron transfer associated with dechlorination. The single Co atoms first reduced O2 to H2O2 and then continuously catalyzed the decomposition of this H2O2 to form ·OH. As a result of the synergistic combination of these two effects, complete efficient dechlorination and 93.4% total organic carbon removal were achieved after 2 h. The kinetics constant for this reaction was determined to be 546.4 min−1·gmetal−1, indicating exceptional performance relative to previous reports of organic pollutant degradation. This study demonstrates the rational design of a bifunctional electrocatalyst and elucidates the electron transfer pathway and O2 activation mechanism associated with 2,4-D removal by electrochemical reduction-oxidation. This process is likely to have potential applications in the remediation of polluted water.

Inactivation and removal of Klebsiella michiganensis biofilm attached to the inner surfaces of piping by plasma-activated microbubble water (PMBW)

Plasma-activated microbubble water (PMBW) is an environmentally friendly sanitizer that possesses potent antimicrobial activities and imparts substantial shear stress to food contact surfaces. In this study, PMBW, plasma-activated water (PAW), microbubble water (MBW), and chlorine water (100 mg/L) were used to clean PVC tubing inoculated by Klebsiella michiganensis. The sanitizer flow with microbubble was numerically simulated by COMSOL Multiphysics® and the shear stress imparted to the bacteria was calculated. The presence of microbubbles in the flow increased the shear stress imparted to the bacteria. The number of K. michiganensis on the inner surfaces of the pipes was ∼7.4 log CFU/cm2 before washing. PMBW showed the most potent antimicrobial effect, which reduced the number of bacteria by 3.1 log CFU/cm2 at a flow velocity of 1 m/s. PAW, MBW, and chlorine water reduced a similar number of bacteria (2.4 log CFU/ cm2 to 2.6 log CFU/ cm2) at all the selected flow velocities. DI water only reduced the number of K. michiganensis by 0.7 log CFU/ cm2 at 1 m/s flow velocity. Industrial relevancePMBW can potentially be an environmentally friendly sanitizer, which can be employed by food processors to clean their food processing equipment with minimized usage of chemical sanitizers. The technology developed in this study will benefit the food industry by mitigating potential risks of foodborne pathogens without generating environmental hazards.

Insight into mixed chlorine/chloramines conversion and associated water quality variability in drinking water distribution systems

Mixed chlorine/chloramines are common in drinking water distribution systems (DWDSs); however, their transformation and impact on chemical and microbial characteristics are not well understood. We systematically investigated water quality parameters associated with mixed chlorine/chloramine species conversion in 192 samples (including raw, finished, and tap water) collected throughout the year in a city in East China. Various chlorine/chloramine species (free chlorine, monochloramine [NH2Cl], dichloramine [NHCl2], and organic chloramines [OC]) were detected in both chlorinated and chloraminated DWDSs. NHCl2 + OC increased with transport distance along the pipeline network. The maximum proportion of NHCl2 + OC in over total chlorine in tap water reached 66 % and 38 % from chlorinated and chloraminated DWDSs, respectively. Both free chlorine and NH2Cl showed a rapid decay in the water pipe systems, but NHCl2 and OC were more persistent. Correlations between chlorine/chloramine species and physicochemical parameters were established. Models for predicting the sum of chloroform/TCM, bromodichloromethane/BDCM, chlorodibromomethane/CBDM, and bromoform/TBM (THM4) (R2 = 0.56) and haloacetic acids (HAAs) (R2 = 0.65) exhibited greater accuracy based on machine learning tuned with chlorine/chloramine species, particularly NHCl2 + OC. The predominant bacterial communities in mixed chlorine/chloramine systems were those resistant to chlorine or chloramine such as proteobacteria. NH2Cl was the most significant explanatory factor (28.1 %) for the variation in microbial community assemblage in chloraminated DWDSs. Although residual free chlorine and NHCl2 + OC, accounted for a smaller proportion of chlorine species in chloraminated DWDSs, they played an essential role (12.4 % and 9.1 %, respectively) in the microbial community structure.

Photo-aging promotes the inhibitory effect of polystyrene microplastics on microbial reductive dechlorination of a polychlorinated biphenyl mixture (Aroclor 1260)

Polychlorinated biphenyls (PCBs) and microplastics (MPs) commonly co-exist in various environments. MPs inevitably start aging once they enter environment. In this study, the effect of photo-aged polystyrene MPs on microbial PCB dechlorination was investigated. After a UV aging treatment, the proportion of oxygen-containing groups in MPs increased. Photo-aging promoted the inhibitory effect of MPs on microbial reductive dechlorination of PCBs, mainly attributed to the inhibition of meta-chlorine removal. The inhibitory effects on hydrogenase and adenosine triphosphatase activity by MPs increased with increasing aging degree, which may be attributed to electron transfer chain inhibition. PERMANOVA showed significant differences in microbial community structure between culturing systems with and without MPs (p < 0.05). Co-occurrence network showed a simpler structure and higher proportion of negative correlation in the presence of MPs, especially for biofilms, resulting in increased potential for competition among bacteria. MP addition altered microbial community diversity, structure, interactions, and assembly processes, which was more deterministic in biofilms than in suspension cultures, especially regarding the bins of Dehalococcoides. This study sheds light on the microbial reductive dechlorination metabolisms and mechanisms where PCBs and MPs co-exist and provides theoretical guidance for in situ application of PCB bioremediation technology.

Molecular and crystal structure characteristics of 2-phenylaminotetrahydro-1,3-thiazepine hydrochloride and 2-phenyliminohexahydro-1,3-thiazepine

The current research includes the synthesis and crystallographic characterization of 2-phenylaminotetrahydro-1,3-thiazepine hydrochloride (HPAT) and 2-phenyliminohexa- hydro-1,3-thiazepine (PIT) compounds. 2-Phenylaminotetrahydro-1,3-thiazepine hydro-chloride was synthesized by cyclization of 1-(4-hydroxybutyl)-3-phenylthiourea in an acidic condition. The second compound, 2-phenyliminohexahydro-1,3-thiazepine, was obtained by neutralizing 2-phenylaminotetrahydro-1,3-thiazepine hydrochloride with sodium hydrocarbonate. Both compounds were characterized by the single-crystal X-ray diffraction method. Crystal data for C11H17N2OClS (HPAT): orthorhombic, space group P212121 (no. 19), a = 4.97183(14) Å, b = 15.1169(4) Å, c = 17.7376(5) Å, V = 1333.14(6) Å3, Z = 4, μ(CuKα) = 3.859 mm-1, Dcalc = 1.299 g/cm3, 9243 reflections measured (7.684° ≤ 2Θ ≤ 152.042°), 2749 unique (Rint = 0.0314, Rsigma = 0.0255) which were used in all calculations. The final R1 was 0.0351 (I &gt; 2σ(I)) and wR2 was 0.0911 (all data). Crystal data for C11H14N2S (PIT): monoclinic, space group P21/n (no. 14), a = 9.6303(9) Å, b = 9.8938(6) Å, c = 11.5627(9) Å, β = 103.419(8)°, V = 1071.62(14) Å3, Z = 4, μ(CuKα) = 2.357 mm-1, Dcalc = 1.279 g/cm3, 3938 reflections measured (10.798° ≤ 2Θ ≤ 152.328°), 2172 unique (Rint = 0.0288, Rsigma = 0.0330) that were used in all calculations. The final R1 was 0.0431 (I &gt; 2σ(I)) and wR2 was 0.1219 (all data). The asymmetric unit of HPAT contains one protonated amine, one chlorine anion, and one water molecule. Chlorine anion and water molecules play the role of the bridge in chain formation along the a- and b-axis through H-bonds with N-H hydrogen atoms. Furthermore, the Hirshfeld surface analyses are performed to determine the nature of the intermolecular contacts stabilizing the crystal structures of 2-phenylaminotetrahydro-1,3-thiazepine hydrochloride and 2-phenyliminohexahydro-1,3-thiazepine.

Identification and synergetic mechanism of TCE, H2 and O2 metabolic microorganisms in the joint H2/O2 system

The sole H2 and O2 usually promote chlorinated hydrocarbons (CHCs) biotransformation by several mechanisms, including reductive dechlorination and aerobic oxidation. However, the mechanism of the CHCs transformation in joint H2 and O2 system (H2/O2 system) is still unclear. In this study, the degradation kinetics of trichloroethene (TCE) were investigated and DNA stable isotope probing (DNA-SIP) were used to explore the synergistic mechanism of functional microorganisms on TCE degradation under the condition of H2/O2 coexistence. In the H2/O2 microcosm, TCE was significantly removed by 13.00 μM within 40 days, much higher than N2, H2 and O2 microcosms, and 1,1-DCE was detected as an intermediate. DNA-SIP technology identified three anaerobic TCE metabolizers, five aerobic TCE metabolizers, nine hydrogen-oxidizing bacteria (HOB), some TCE metabolizers utilizing limited O2, and some anaerobic dechlorinating bacteria reductively using H2 to dechlorinate TCE. It is also confirmed for the first time that 3 OUTs belonging to Methyloversatilis and SH-PL14 can simultaneously utilize H2 and O2 as energy sources to grow and metabolize TCE or 1,1-DCE. HOB may provide carbon sources or electron acceptors or donors for TCE biotransformation. These findings confirm the coexistence of anaerobic and aerobic TCE metabolizers and degraders, which synergistically promoted the conversion of TCE in the joint H2/O2 system. Our results provide more information about the functional microbe resources and synergetic mechanisms for TCE degradation.

Genotoxicity and endocrine disruption potential of haloacetic acids in human placental and lung cells

Chlorination of water results in the formation of haloacetic acids (HAAs) as major disinfection byproducts (DBPs). Previous studies have reported some HAAs species to act as cytotoxic, genotoxic, and carcinogenic. This work aimed at further exploring the toxicity potential of the most investigated HAAs (chloroacetic (CAA), bromoacetic (BAA), iodoacetic (IAA) acid) and HAAs species with high content of bromine (tribromoacetic acid (TBAA)), and iodine in their structures (chloroiodoacetic (CIAA) and diiodoacetic acid (DIAA)) to human cells. Novel knowledge was generated regarding cytotoxicity, oxidative stress, endocrine disrupting potential, and genotoxicity of these HAAs by using human placental and lung cells as in vitro models, not previously used for DBP assessment. IAA showed the highest cytotoxicity (EC50: 7.5 μM) and ability to generate ROS (up to 3-fold) in placental cells, followed by BAA (EC50: 20–25 μM and 2.1-fold). TBAA, CAA, DIAA, and CIAA showed no significant cytotoxicity (EC50 > 250 μM). All tested HAAs decreased the expression of the steroidogenic gene hsd17b1 up to 40 % in placental cells, and IAA and BAA (0.01–1 μM) slightly inhibited the aromatase activity. HAAs also induced the formation of micronuclei in A549 lung cells after 48 h of exposure. IAA and BAA showed a non-significant increase in micronuclei formation at low concentrations (1 μM), while BAA, CAA, CIAA and TBAA were genotoxic at exposure concentrations above 10 μM (100 μM in the case of DIAA). These results point to genotoxic and endocrine disruption effects associated with HAA exposure at low concentrations (0.01–1 μM), and the usefulness of the selected bioassays to provide fast and sensitive responses to HAA exposure, particularly in terms of genotoxicity and endocrine disruption effects. Further studies are needed to define thresholds that better protect public health.

Reliable purity assay of highly hygroscopic trichloroacetic acid for the development of high-purity reference material of NMIJ CRM 4074-a

Trichloroacetic acid is known as one of the harmful disinfection byproducts with chlorine of tap water and is regulated according to legally binding standards in Japanese Drinking Water Quality Standards. We developed a high-purity trichloroacetic acid reference material, NMIJ CRM 4074-a, with certified purity as a traceability source of standard solution supplied under the Japan Calibration Service System (JCSS). As trichloroacetic acid is hygroscopic, water could be the main impurity. Although all impurities in the sample can be possibly detected by the freezing point depression method (FPD), it was unclear for trichloroacetic acid whether water was detected by FPD owing to evaporation of water from the sample during fusion. Therefore, we confirmed that water in trichloroacetic acid was detected as an impurity by FPD. The procedure was validated from an increment of purity by FPD due to reduction of water content and an agreement of purity by FPD with those by neutralization titrimetry (NT) and mass balance approach (MBA), both methods were based on different measurement principles from FPD. The certified value was determined to be (0.999 ± 0.003) kg kg-1 from the purity assay by FPD and NT, and uncertainties due to the homogeneity and stability of the CRM were included in the expanded uncertainty. The reliability of the certified value was verified by the agreement of purities by FPD, NT, and MBA.

IoT-Enabled Chlorine Level Assessment and Prediction in Water Monitoring System Using Machine Learning

The significance of user participation in sustaining drinking water quality and assessing other factors, such as cleanliness, sanitary conditions, preservation, and waste treatment, is essential for preserving groundwater quality. Inadequate water quality spreads disease, causes mortality, and hinders socioeconomic growth. In addition, disinfectants such as chlorine and fluoride are used to remove pathogens, or disease-causing compounds, from water. After a substantial amount of chlorine has been added to water, its residue causes an issue. Since the proposed methodology is intended to offer a steady supply of drinkable water, its chlorine concentration must be checked in real-time. The suggested model continually updates the sensor hub regarding chlorine concentration measurements. In addition, these data are transmitted over a communication system for data analysis to analyze chlorine levels within the drinking water and residual chlorine percentage over time using a fuzzy set specifically using a decision tree algorithm. Additionally, a performance investigation of the proposed framework is undertaken to determine the efficiency of the existing model for predicting the quantity of chlorine substance employing metrics such as recall, accuracy, F-score, and ROC. Henceforth, the proposed model has substantially better precision than the existing techniques.

Effect of coupled chloride salt erosion and Freeze-thaw on the dynamic mechanical properties of EPS cement soils

EPS cement soil is a type of material widely used in engineering, but it is often in a complex engineering environment. Freeze-thaw cycles and chloride salt erosion have a large impact on the strength of cement soils in engineering, and it is a very important subject to investigate the strength trends of cement soils under severe conditions of salt erosion and freeze–thaw environments. In this study, the apparent characteristics and dynamic mechanical property characteristics of the EPS cement soil after different numbers (0, 3, 6, 9, 12, 15) of freeze–thaw cycles in different concentrations of NaCl (0 g/L, 4.5 g/L, 18 g/L, 30 g/L) solutions were investigated by chlorine salt erosion and freeze–thaw cycle coupling test and SHPB test. The changes of appearance morphology, dynamic stress–strain curve, dynamic compressive strength and energy dissipation after impact were analyzed, and the mechanism of strength change of the cement soil was explained from the microscopic perspective. The results of the tests show that the cement soil mainly undergoes elastic deformation, plastic yielding and damage stages during the impact damage process; with the increase of chlorine salt concentration and the increase of the number of freeze–thaw cycles, the dynamic compressive strength of the cement soil specimens decreases continuously, and the rate of strength loss gradually slows down first, and when the number of freeze–thaw cycles is more than 9, the rate of strength loss begins to increase. In the 30 g / L chloride erosion environment, after 3,6,9,12, and 15 freeze–thaw cycles, the dynamic compressive strength decreased by 16.48 %, 22.35 %, 28.77 %, 34.36 %, and 55.87 %, respectively. Under the immersion environment of clear water and low concentration (4.5 g / L) chlorine salt, when the number of freeze–thaw cycles exceeds 12 times, the absorption energy and energy absorption efficiency of the sample decrease sharply. Under the immersion of high concentration (18 g / L and 30 g / L) chlorine salt, the absorption energy and energy absorption efficiency decrease rapidly after more than 9 freeze–thaw cycles.

Sustained detoxification of 1,2-dichloroethane to ethylene by a symbiotic consortium containing Dehalococcoides species

1,2-Dichloroethane (1,2-DCA) is a ubiquitous volatile halogenated organic pollutant in groundwater and soil, which poses a serious threat to the ecosystem and human health. Microbial reductive dechlorination has been recognized as an environmentally-friendly strategy for the remediation of sites contaminated with 1,2-DCA. In this study, we obtained an anaerobic microbiota derived from 1,2-DCA contaminated groundwater, which was able to sustainably convert 1,2-DCA into non-toxic ethylene with an average dechlorination rate of 30.70 ± 11.06 μM d−1 (N = 6). The microbial community profile demonstrated that the relative abundance of Dehalococcoides species increased from 0.53 ± 0.08% to 44.68 ± 3.61% in parallel with the dechlorination of 1,2-DCA. Quantitative PCR results showed that the Dehalococcoides species 16S rRNA gene increased from 2.40 ± 1.71 × 108 copies∙mL−1 culture to 4.07 ± 2.45 × 108 copies∙mL−1 culture after dechlorinating 110.69 ± 30.61 μmol of 1,2-DCA with a growth yield of 1.55 ± 0.93 × 108 cells per μmol Cl− released (N = 6), suggesting that Dehalococcoides species used 1,2-DCA for organohalide respiration to maintain cell growth. Notably, the relative abundances of Methanobacterium sp. (p = 0.0618) and Desulfovibrio sp. (p = 0.0001995) also increased significantly during the dechlorination of 1,2-DCA and were clustered in the same module with Dehalococcoides species in the co-occurrence network. These results hinted that Dehalococcoides species, the obligate organohalide-respiring bacterium, exhibited potential symbiotic relationships with Methanobacterium and Desulfovibrio species. This study illustrates the importance of microbial interactions within functional microbiota and provides a promising microbial resource for in situ bioremediation in sites contaminated with 1,2-DCA.

Substrate Electronics Dominate the Rate of Reductive Dehalogenation Promoted by the Flavin-Dependent Iodotyrosine Deiodinase.

Iodotyrosine deiodinase (IYD) is unusual in its reliance on flavin to promote reductive dehalogenation of halotyrosines under aerobic conditions. Applications of this activity can be envisioned for bioremediation, but expansion of its specificity requires an understanding of the mechanistic steps that limit the rate of turnover. Key processes capable of controlling steady-state turnover have now been evaluated and described in this study. While proton transfer is necessary for converting the electron-rich substrate into an electrophilic intermediate suitable for reduction, kinetic solvent deuterium isotope effects suggest that this process does not contribute to the overall efficiency of catalysis under neutral conditions. Similarly, reconstituting IYD with flavin analogues demonstrates that a change in reduction potential by as much as 132 mV affects kcat by less than 3-fold. Furthermore, kcat/Km does not correlate with reduction potential and indicates that electron transfer is also not rate determining. Catalytic efficiency is most sensitive to the electronic nature of its substrates. Electron-donating substituents on the ortho position of iodotyrosine stimulate catalysis and conversely electron-withdrawing substituents suppress catalysis. Effects on kcat and kcat/Km range from 22- to 100-fold and fit a linear free-energy correlation with a ρ ranging from -2.1 to -2.8 for human and bacterial IYD. These values are consistent with a rate-determining process of stabilizing the electrophilic and nonaromatic intermediate poised for reduction. Future engineering can now focus on efforts to stabilize this electrophilic intermediate over a broad series of phenolic substrates that are targeted for removal from our environment.

Compost-derived humic acid impacts on the biodechlorination of pentachlorophenol in high organic matter paddy soil

The long-term accumulation of pentachlorophenol (PCP) has adversely affected the paddy soil ecosystem. PCP reductive dechlorination under anaerobic conditions is an efficient pathway for PCP degradation. This process is affected by the content of organic matter and the iron mineral composition of the soil. Our previous study analyzed the effects of compost-derived Humic acids (HAs) on reductive dechlorination of PCP in a paddy soil system under Fe-reducing conditions. The effects and mechanisms of high organic matter and compost-derived HAs in promoting PCP dechlorination need further investigation. This study examined paddy soils with high organic matter content in Heilongjiang Province. PCP reductive dechlorination in this system was studied using HAs from three stages of municipal solid waste compost as soil supplements. The results showed that natural HA and microorganisms could promote the dechlorination and transformation of PCP in the paddy soil system. After removing humic acid, the detected concentrations of PCP in paddy soil and solid-liquid interface were 1.84 and 9.67 times of those in the original soil experiment, respectively. The concentration of low chlorine products decreased significantly in the sterilized group. Compost-derived HAs from different stage were also presented various effect on PCP reductive dichlorination. Furthermore, the synergistic effect between natural HA and compost-derived HAs would limit the electron donating capacity of compost-derived HAs in the paddy soil with high organic matter. Organic matter in soil has an important influence on pollutant fate. Late-stage HA were more effective in promoting PCP degradation than early-and middle-stage HAs. The research provided a comprehensive and meticulous analyses of the effects of compost-derived HAs on PCP bio-dechlorination in paddy soil with high organic matter.

Decoupling Fe0 Application and Bioaugmentation in Space and Time Enables Microbial Reductive Dechlorination of Trichloroethene to Ethene: Evidence from Soil Columns.

Fe0 is a powerful chemical reductant with applications for remediation of chlorinated solvents, including tetrachloroethene and trichloroethene. Its utilization efficiency at contaminated sites is limited because most of the electrons from Fe0 are channeled to the reduction of water to H2 rather than to the reduction of the contaminants. Coupling Fe0 with H2-utilizing organohalide-respiring bacteria (i.e., Dehalococcoides mccartyi) could enhance trichloroethene conversion to ethene while maximizing Fe0 utilization efficiency. Columns packed with aquifer materials have been used to assess the efficacy of a treatment combining in space and time Fe0 and aD. mccartyi-containing culture (bioaugmentation). To date, most column studies documented only partial conversion of the solvents to chlorinated byproducts, calling into question the feasibility of Fe0 to promote complete microbial reductive dechlorination. In this study, we decoupled the application of Fe0 in space and time from the addition of organic substrates andD. mccartyi-containing cultures. We used a column containing soil and Fe0 (at 15 g L-1 in porewater) and fed it with groundwater as a proxy for an upstream Fe0 injection zone dominated by abiotic reactions and biostimulated/bioaugmented soil columns (Bio-columns) as proxies for downstream microbiological zones. Results showed that Bio-columns receiving reduced groundwater from the Fe0-column supported microbial reductive dechlorination, yielding up to 98% trichloroethene conversion to ethene. The microbial community in the Bio-columns established with Fe0-reduced groundwater also sustained trichloroethene reduction to ethene (up to 100%) when challenged with aerobic groundwater. This study supports a conceptual model where decoupling the application of Fe0 and biostimulation/bioaugmentation in space and/or time could augment microbial trichloroethene reductive dechlorination, particularly under oxic conditions.

Rod-Like Nanostructured Cu-Co Spinel with Rich Oxygen Vacancies for Efficient Electrocatalytic Dechlorination.

Dichloromethane (CH2Cl2) hydrodechlorination to methane (CH4) is a promising approach to remove the halogenated contaminants and generate clean energy. In this work, rod-like nanostructured CuCo2O4 spinels with rich oxygen vacancies are designed for highly efficient electrochemical reduction dechlorination of dichloromethane. Microscopy characterizations revealed that the special rod-like nanostructure and rich oxygen vacancies can efficiently enhance surface area, electronic/ionic transport, and expose more active sites. The experimental tests demonstrated that CuCo2O4-3 with rod-like nanostructures outperformed other morphology of CuCo2O4 spinel nanostructures in catalytic activity and product selectivity. The highest methane production of 148.84 μmol in 4 h with a Faradaic efficiency of 21.61% at -2.94 V (vs SCE) is shown. Furthermore, the density function theory proved oxygen vacancies significantly decreased the energy barrier to promote the catalyst in the reaction and Ov-Cu was the main active site in dichloromethane hydrodechlorination. This work explores a promising way to synthesize the highly efficient electrocatalysts, which may be an effective catalyst for dichloromethane hydrodechlorination to methane.

Antibiotic Resistance of Heterotrophic Bacteria Isolated from Drinking Water – from the Water Source to the Consumers’ Taps

The aim of this study was to determine the antibiotic resistance (ABR) phenotype of heterotrophic bacteria isolated from a Bulgarian drinking water supply system. The disc diffusion method of Kirby-Bauer was used in the bacterial isolates susceptibility testing toward 13 antibiotics from 7 classes. The ABR phenotype of 233 bacterial strains was determined and the influence of drinking water treatment and its transportation in the water supply network on the ABR prevalence was assessed. Among the isolates, the ABR incidence was low or medium, only tetracycline resistance was very rare, and no gentamicin resistance was detected; 42% of the isolates were resistant to one class of antibiotics, and 11% exhibited multiple resistance. Water chlorination has led to restructuring of the aquatic community and changes of the predominant ABR phenotypes. The ABR phenotype of the isolates differed depending on the drinking water sampling point demonstrating the local influence of the water supply network. Although there is no regulation of the ABR of drinking water, the data demonstrated prevalence of bacterial resistance to different antibiotics and need of a greater concern the microbiological water quality.

Wide distribution of extracellular electron transfer functionality in natural proteinaceous organic materials for microbial reductive dehalogenation.

Extracellular electron transfer materials (EETMs) in the environment, such as humic substances and biochar, are formed from the humification/heating of natural organic materials. However, the distribution of extracellular electron transfer (EET) functionality in fresh natural organic materials has not yet been explored. In the present study, we reveal the wide distribution of EET functionality in proteinaceous materials for the first time using an anaerobic pentachlorophenol dechlorinating consortium, whose activity depends on EETM. Out of 11 natural organic materials and 13 reference compounds, seven proteinaceous organic materials (albumin, beef, milk, pork, soybean, yolk, and bovine serum albumin) functioned as EETMs. Carbohydrates and lipids did not function as EETMs. Comparative spectroscopic analyses suggested that a β-sheet secondary structure was essential for proteins to function as EETMs, regardless of water solubility. A high content of reduced sulfur was potentially involved in EET functionality. Although proteinaceous materials have thus far been considered simply as nutrients, the wide distribution of EET functionality in these materials provides new insights into their impact on biogeochemical cycles. In addition, structural information on EET functionality can provide a scientific basis for the development of eco-friendly EETMs.