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•Polypyrrole electrode was prepared by an electro-polymerization method.•Biomass carbon derived from sewage sludge was used as cathode catalyst.•MFC with polypyrrole/sewage sludge ...electrode achieved the maximum power density.•The maximum Cr(VI) reduction rate in MFC could reach 2.16 g·m−3·h−1.•Polypyrrole played an electron shuttling role in reducing Cr(VI).
Microbial fuel cell, a potential bio-electrochemical energy transducer can extract the bio-energy from wastewater by the consumption of the electro-active microorganism adhered the surface of anode, and the MFC performance is greatly inhibited by the cathode catalysts. Herein, polypyrrole/sewage sludge carbon electrode is fabricated by an electro-polymerization loading method and the electrode is employed as the cathode electrode in MFC for the removal of Cr(VI) and bio-energy release at the same time. The electrochemical analysis finds the polypyrrole/sewage sludge carbon electrode exhibits the low charge transfer resistance and Tafel slope, which can demonstrate that the polypyrrole/sewage sludge carbon electrode possesses strong conductivity and excellent electrochemical activity. In addition, Cr(VI) in the cathode chamber of MFC with the polypyrrole/sewage sludge carbon electrode can be totally removed at 30 h. And the maximum output power and Cr(VI) reduction rate of MFCs are 760.7 mW m−2 and 2.16 g·m−3·h−3, which are 2.79 and 1.51 times higher than those of carbon cloth electrode (272.5 mW·m−2 and 1.43 g·m−3·h−3). Moreover, Cr(VI) can be removed and deposited on the electrode in the form of Cr(OH)3. And polypyrrole plays an electron shuttling role in reducing the internal resistance of MFC and enhancing electrochemical activity of the electrode for Cr(VI) reduction. Consequently, the polypyrrole/sewage sludge composite can achieve more stable Cr(VI) removal and power than those of sewage sludge carbon, polypyrrole, and carbon cloth electrodes, demonstrating an effective and low-cost catalyst for accelerating Cr(VI) reduction and strengthening bio-power production.
Organic fertilizer or manure containing antibiotics has been widely used in organic farms, but the distribution and potential impacts of antibiotics to the local environment are not well understood. ...In this study, four quinolone antibiotics in soil samples (n=69) from five organic vegetable farms in a subtropical city, Southern China, were analyzed using high performance liquid chromatography–tandem mass spectrometry. Our results indicated that quinolone compounds were ubiquitous in soil samples (detection frequency>97% for all compounds), and their concentrations ranged from not detectable to 42.0μg/kg. Among the targets, enrofloxacin (ENR) was the dominant compound, followed by ciprofloxacin (CIP) and norfloxacin (NOR). The average total concentrations of four compounds in the soils were affected by vegetable types and species cultivated, decreasing in the order of fruit>rhizome>leaf vegetables. Moreover, the average concentrations of quinolone compounds (except ENR) in open-field soils were higher than those in greenhouse soils. The concentrations of quinolone antibiotics in this study were lower than the ecotoxic effect trigger value (100μg/kg) proposed by the Veterinary Medicine International Coordination commission. Risk assessment based on the calculated risk quotients indicated that NOR, CIP, and ENR posed mainly medium to low risks to bacteria.
•Quinolones in soil of subtropical organic vegetable farms were frequently detected with low concentrations.•Concentrations of quinolones in open-field soil were higher than in greenhouse.•Quinolones in soil of the studied farms posed mainly medium to low ecological risks.
Phthalic acid esters (PAEs) is a class of prevalent pollutants in agricultural soil, threating food safety through crop uptake and accumulation of PAEs. Accumulation of PAEs varies largely among crop ...species and cultivars. Nevertheless, how root exudates affect PAE bioavailability, dissipation, uptake and accumulation is still not well understood. In the present study, desorption and pot experiments were designed to investigate how root exudates from high-(Peizataifeng) and low-(Fengyousimiao) PAE accumulating rice cultivars affect soil PAE bioavailability, dissipation, and accumulation variation. Rice root exudates including low molecular weight organic acids (LMWOAs) of Peizataifeng and Fengyousimiao could enhance desorption of two typical PAE compounds, di-n-butyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), from aged soil to their available fractions by increasing soil dissolved organic carbon (DOC), thus improving their bioavailability in soil. Peizataifeng produced twice higher amounts of oxalic acid, critic acid and malonic acid in root exudates, and exhibited stronger effects on enhancing desorption and bioavailability of DBP and DEHP than Fengyousimiao. Higher (by about 50%) total organic carbon contents of root exudates from Peizataifeng led to higher (by 10–30%) soil microbial biomass carbon and nitrogen than Fengyousimiao, and thus promoted more PAE dissipation from soil than Fengyousimiao. Nevertheless, higher (by 20–50%) soil DOC and significantly higher PAE bioavailability in the soils planted Peizataifeng resulted in greater (by 53–93%) PAE accumulation in roots and shoots of Peizataifeng than Fengyousimiao, confirming by higher (by 1.82–3.48 folds) shoot and root bioconcentration factors of Peizataifeng than Fengyousimiao. This study reveals that the difference in root exudate extent and LMWOAs between Peizataifeng and Fengyousimiao differentiates PAE accumulation.
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•Rice root exudates enhanced PAE desorption from aged soil by increasing DOC.•Rice root exudates improved soil PAE bioavailability and dissipation.•Peizataifeng with more root exudates showed stronger promotion of PAE bioavailability than Fengyousimiao.•Root exudates played an important role in cultivar variation of PAE accumulation.
•PFOS degradation can keep a high level by electrochemical oxidation.•Electrochemical oxidation was effective to multiple organic contaminants.•DFT calculations confirmed electron can be transferred ...from PFOS to PMS.•Ti4O7 could serve as the conductive bridge to promote the electron transfer.•The ultrasonic treatment can effectively active electrode for PFOS degradation.
Polyfluoroalkyl and perfluoroalkyl chemicals (PFCs) widely used in lubricants, surfactant, textiles, paper coatings, cosmetics, and fire-fighting foams can release a large deal of organics contaminants into wastewater and pose great risks to the health of humans and eco-environments. Although advanced oxidation processes can effectively deconstruct various organic contaminants via reactive radicals, the stable structure of PFCs makes it difficult to be degraded. Here, we confirm that electrochemical oxidation process coupled with peroxymonosulfate (PMS) reaction can efficiently destroy stable structure of PFCs via electron transfer and meanwhile completely degrade PFCs via generated active radicals. We further studies via capturing and scavenging radicals, and DFT calculations find that electron hydroxyl radials play a dominant role in degrading PFCs. Based on the calculations of adsorption energy and molecular orbital energy we further demonstrate that many active sites on the surface of Ti4O7 (1 0 4) plane can rapidly take part in electrochemical reaction for generating radials and removing organic contaminants. These results give a promising insight towards high-effective and deep degradation of PFCs via electrochemical reaction coupled with advanced oxidation processes, as well as providing guidance and technical support for the remove of multiple organic contaminants.
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Aims
Arbuscular mycorrhizal fungi (AMF) can enhance cadmium (Cd) tolerance and decrease Cd uptake of rice plant. However, in these processes, the essential role of reactive oxygen species ...(ROS)-antioxidants interactions is so far not investigated.
Methods
We inoculated AMF,
Funneliformis mosseae
(Fm) and
Rhizophagus intraradices
(Ri), to upland rice subjected to 0, 2 or 10 mg Cd kg
−1
in soil. ROS, antioxidants, chlorophyll, mesophyll cell ultrastructure, Cd concentration and Cd transporters were measured.
Results
Results showed that the levels of ROS (i.e., superoxide, hydrogen peroxide and lipid peroxidation) were mitigated in +AMF + Cd treatments, especially in +Ri + Cd, compared with −AMF + Cd. For antioxidants, lower levels of catalase, peroxidase and superoxide dismutase, whereas higher levels of glutathione and glutathione peroxidase were observed in +AMF + Cd compared with −AMF + Cd. Chlorophyll content and mesophyll cell ultrastructure were improved by AMF. Cd concentrations in plants were significantly decreased in +AMF + Cd (10 mg Cd kg
−1
) treatments.
Conclusions
AMF not only decreased Cd accumulation in rice but also regulated the ROS scavenging activities. The variations of ROS and antioxidants were restrained to smaller ranges by AMF. AMF may assist in Cd restriction and thus helping the host to release glutathione for ROS scavenging.
Microbial degradation is considered the most promising method for removing phthalate acid esters (PAEs) from polluted environments; however, a comprehensive genomic understanding of the entire PAE ...catabolic process is still lacking. In this study, the repertoire of PAE catabolism genes in the metabolically versatile bacterium Rhodococcus sp. 2G was examined using genomic, metabolic, and bioinformatic analyses. A total of 4930 coding genes were identified from the 5.6 Mb genome of the 2G strain, including 337 esterase/hydrolase genes and 48 transferase and decarboxylase genes that were involved in hydrolysing PAEs into phthalate acid (PA) and decarboxylating PA into benzoic acid (BA). One gene cluster (xyl) responsible for transforming BA into catechol and two catechol-catabolism gene clusters controlling the ortho (cat) and meta (xyl &mhp) cleavage pathways were also identified. The proposed PAE catabolism pathway and some key degradation genes were validated by intermediate-utilising tests and real-time quantitative polymerase chain reaction. Our results provide novel insight into the mechanisms of PAE biodegradation at the molecular level and useful information on gene resources for future studies.
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•The strain 2G could efficiently degrade a wide range of PAEs.•A repertoire of the whole PAEs-catabolism process was obtained.•An array of genes involved in PAEs catabolic pathway in the 2G genome were excavated.•Strain 2G has two gene clusters of ring cleavage pathways in catechol degradation.
Selecting and cultivating low-accumulating crop varieties (LACVs) is the most effective strategy for the safe utilization of di-(2-ethylhexyl) phthalate (DEHP)-contaminated soils, promoting cleaner ...agricultural production. However, the adsorption-absorption-translocation mechanisms of DEHP along the root-shoot axis remains a formidable challenge to be solved, especially for the research and application of LACV, which are rarely reported. Here, systematic analyses of the root surface ad/desorption, root apexes longitudinal allocation, uptake and translocation pathway of DEHP in LACV were investigated compared with those in a high-accumulating crop variety (HACV) in terms of the root-shoot axis. Results indicated that DEHP adsorption was enhanced in HACV by root properties, elemental composition and functional groups, but the desorption of DEHP was greater in LACV than HACV. The migration of DEHP across the root surface was controlled by the longitudinal partitioning process mediated by root tips, where more DEHP accumulated in the root cap and meristem of LACV due to greater cell proliferation. Furthermore, the longitudinal translocation of DEHP in LACV was reduced, as evidenced by an increased proportion of DEHP in the root apoplast. The symplastic uptake and xylem translocation of DEHP were suppressed more effectively in LACV than HACV, because DEHP translocation in LACV required more energy, binding sites and transpiration. These results revealed the multifaceted regulation of DEHP accumulation in different choysum (Brassica parachinensis L.) varieties and quantified the pivotal regulatory processes integral to LACV formation.
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•Root traits determined the DEHP adsorption capacity on root surfaces.•DEHP showed high affinity for the root cap and meristem of root apexes.•The low-accumulating crop variety (LACV) had a greater root retention capacity for DEHP.•DEHP translocation in the LACV depends more on energy, binding sites and transpiration.•The fate of DEHP on the root-shoot axis caused variation formation.
Microbial fuel cell (MFC), a promising bio-electrochemical reactor could decompose organics in wastewater by redox processes of electro-active microorganism in anode and produce bio-energy, and the ...total MFC performance could mainly rely on electrochemical performance anode. Here, biomass carbon derived from municipal sludge was employed as low-cost and high-performance bio-anode for enhancing bioelectricity generation and wastewater treatment in MFC simultaneously. The electrochemical tests demonstrated that the large electrochemical active surface area, strong conductivity, and good biocompatibility in sludge carbon (SC) electrode resulted in higher power density (615.2 mW m−2) and lower power loss (5.4%) than those of none carbon (NC) electrode in long term operation. After 30-cycle of continuous running, the low loss of chemical oxygen demand (COD) removal was achieved up to 5.2%, which was smaller than that of NC electrode (14.1%), indicating that the MFC with SC anode could effectively treat wastewater and keep stable redox processes in anode electrode. After the formation of biofilm, the charge transfer resistance of SC electrode (16.38 Ω) was 72.4% lower than that of NC electrode (59.35 Ω). High-throughput analysis of biofilm exhibit Proteobacteria was the dominant electro-active bacteria, and the modification of SC could slightly change the bacterial community. Therefore, resource utilization of natural wastes provided the novel concept of anode catalyst fabrication for MFC in enhancing electron transfer, power output and wastewater decomposition.
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•Municipal sludge was used to synthesize biomass carbon.•Sludge carbon possessed outstanding electrochemical properties.•Sludge carbon was utilized as highly-effective anode material in MFC.•MFC with sludge carbon anode could produce high energy output.•The total cost for preparing sludge carbon was 21 US$ kg−1.
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•A reliable technique to prepare titanium-based composites.•RGO/TiO2-1 was used as air-cathode catalysts of MFC.•Cathode catalyst loading played a key role in MFC.•RGO/TiO2-1 ...exhibited higher catalytic activity than other composites.
A kind of reduced graphene oxide decorated with titanium-based (RGO/TiO2) composites are successfully synthesized and employed in this current study as a novel nonprecious metal catalyst for enhancing bioelectricity generation and cathodic oxygen reduction reaction (ORR) in single chamber microbial fuel cells (MFCs). Compared with commercial Pt/C, RGO/TiO2 shows obviously enhanced oxygen reduction reaction activity due to the appropriately-permeated, large electrochemical active area, enough exposure of electrocatalytic active sites of RGO/TiO2. The air-cathode MFC with RGO/TiO2-1 cathode achieves 1786.7 mW m−3 of power density, 86.7% ± 1.2% of COD removal and 31.6% ± 1.1% of CE, which are higher than commercial Pt/C. Moreover, RGO/TiO2-1 cathode exhibits high-effective electrocatalytic activity, and the power density of RGO/TiO2-1 can keep a stable level and only has a minor decline (5.35%) during 30-cycles operation. These results indicate that RGO/TiO2-1 is a potential cathode catalyst, markedly enhancing cathode ORR, wastewater treatment efficiency, and bioelectricity generation of MFC.
The growing incidence of microcystins (MCs) in the environment has become an issue of global concern for the high ecological and human health risks. Herein, a comparative adsorption of three MCs ...(MC-LR, MC-YR and MC-RR) by spent mushroom substrate (SMS)-derived biochars from contrasting pyrolytic conditions (temperature: 600/300 °C; and gas steam: CO2/N2) was surveyed to better understand the mechanisms and factors affecting the adsorption performance. For biochar preparation, 600 °C and CO2 led to greater levels of aromaticity, ash, SBET, and porosity, while 300 °C and N2 created more surface functional groups. The adsorption of MCs by biochars was a pH-dependent and endothermic physisorption process, following the pseudo-second-order kinetics (R2 = 0.99) and linear isotherm model (R2 > 0.88). The distribution coefficients Kd (0.98–19.2 L/kg) varied greatly among MCs (MC-YR > MC-RR > MC-LR) and biochars (BC600 > BN600 > BC300 > BN300), which depends on the combined effects of hydrophobicity, electrostatic attraction, H-bonding, cation bridging, and the amounts of adsorption sites on biochars. Higher ash, SBET, and total pore volume of BC600 facilitated the adsorption capacity for MCs relative to other biochars. Furthermore, the co-adsorption efficacy for MCs (Kd = 1.09–8.86 L/kg) was far below those for the single adsorption, indicating strong conflicts among competing MCs. This study sheds light on the roles of pyrolytic temperature and gas steam in biochar properties, and elucidates the mechanisms and factors affecting the adsorption performance of different MCs, which lays a foundation for MCs removal from water.
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•Higher peak temperature (PT) and CO2 better form biochar structure than did lower PT and N2.•Microcystin adsorption by biochars is a pH-dependent and endothermic physisorption.•MC-YR shows the highest affinity to biochars, followed by MC-RR and MC-LR.•SBET and pore volume are more vital for microcystin adsorption than surface function groups.
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