Identification of potential electrotrophic microbial community in paddy soils by enrichment of microbial electrolysis cell biocathodes

Electrotrophs are microbes that can receive electrons directly from cathode in a microbial electrolysis cell (MEC). They not only participate in organic biosynthesis, but also be crucial in cathode-based bioremediation. However, little is known about the electrotrophic community in paddy soils. Here, the putative electrotrophs were enriched by cathodes of MECs constructed from five paddy soils with various properties using bicarbonate as an electron acceptor, and identified by 16S rRNA-gene based Illumina sequencing. The electrons were gradually consumed on the cathodes, and 25%–45% of which were recovered to reduce bicarbonate to acetic acid during MEC operation. Firmicutes was the dominant bacterial phylum on the cathodes, and Bacillus genus within this phylum was greatly enriched and was the most abundant population among the detected putative electrotrophs for almost all soils. Furthermore, several other members of Firmicutes and Proteobacteria may also participate in electrotrophic process in different soils. Soil pH, amorphous iron and electrical conductivity significantly influenced the putative electrotrophic bacterial community, which explained about 33.5% of the community structural variation. This study provides a basis for understanding the microbial diversity of putative electrotrophs in paddy soils, and highlights the importance of soil properties in shaping the community of putative electrotrophs.     

Effects of calcination temperature on physicochemical property and activity of CuSO4/TiO2 ammonia-selective catalytic reduction catalysts

CuSO_4/TiO_2 catalysts with high catalytic activity and excellent resistant to SO_2 and H_2 O,were thought to be promising catalysts used in Selective catalytic reduction of nitrogen oxides by NH_3.The performance of catalysts is largely affected by calcination temperature.Here,effects of calcination temperature on physicochemical property and catalytic activity of CuSO_4/TiO_2 catalysts were investigated in depth.Catalyst samples calcined at different temperatures were prepared first and then physicochemical properties of the catalyst were characterized by N2 adsorption-desorption,X-ray diffraction,thermogravimetric analysis,Raman spectra,Fourier-transform infrared spectroscopy,X-ray photoelectron spectroscopy,temperature-pro grammed desorption of NH_3,temperature-programmed reduction of H_2 and in situ diffuse reflectance infrared Fourier transform spectroscopy.Results revealed that high calcination temperature had three main effects on the catalyst.First,sintering and anatase transform into rutile with increase of calcination temperature,causing a decrement of specific surface area.Second,decomposition of CuSO_4 under higher calcination temperature,resulting in disappears of Br(?)nsted acid sites(S-OH),which had an adverse effect on surface acidity.Third,CuO from the decomposition of CuSO_4 changed surface reducibility of the catalyst and favored the process of NH_3 oxidation to nitrogen oxides(NO_x).Thus,catalytic activity of the catalyst calcined under high temperatures(≥600℃) decreased largely.     

Morphology-dependent interfacial interactions of Fe2O3 with Ag nanoparticles for determining the catalytic reduction of p-nitrophenol

In this work,we fabricated three kinds of Ag/Fe_2O_3 model catalysts with different morphologies to study the interfacial interactions between Ag and Fe_2O_3,and how they affected the catalytic activity in hydrogenation of p-nitrophenol was explored.The hydrothermal method was used to synthesize the metal oxide supported silver catalyst,with various morphologies including nanoplates(NPs),nanospheres(NSs),and nanocubes(NCs).The crystal structure,morphology and surface elements of the composite were investigated by various measurements,such as X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS).The catalytic activity was also evaluated by the reduction of p-nitrophenol to p-aminophenol.It was found that the activities of the above catalysts varied with the morphology of the support.Among them,Ag/Fe_2O_3 NPs promoted the highest performance,Ag/Fe_2O_3 NSs were slightly inferior,and Ag/Fe_2O_3 NCs were the worst.At last,we ascribed the remarkable activity of Ag/Fe_2O_3 NPs to the strong metal-support interactions between Ag and Fe_2O_3.     

Synergistic effects of Cu species and acidity of Cu-ZSM-5 on catalytic performance for selective catalytic oxidation of n-butylamine

In this work, a series of Cu-ZSM-5 catalysts with different SiO₂/Al₂O₃ ratios (25, 50, 100 and 200) were synthesized and investigated in n-butylamine catalytic degradation. The n-butylamine can be completely catalytic degradation at 350°C over all Cu-ZSM-5 catalysts. Moreover, Cu-ZSM-5 (25) exhibited the highest selectivity to N₂, exceeding 90% at 350°C. These samples were investigated in detail by several characterizations to illuminate the dependence of the catalytic performance on redox properties, Cu species, and acidity. The characterization results proved that the redox properties and chemisorption oxygen primarily affect n-butylamine conversion. N₂ selectivity was impacted by the Brønsted acidity and the isolated Cu²⁺ species. Meanwhile, the surface acid sites over Cu-ZSM-5 catalysts could influence the formation of Cu species. Furthermore, in situ diffuse reflectance infrared Fourier transform spectra was adopted to explore the reaction mechanism. The Cu-ZSM-5 catalysts are the most prospective catalysts for nitrogen-containing volatile organic compounds removal, and the results in this study could provide new insights into catalysts design for VOC catalytic oxidation.     

UV/H2O2 oxidation of tri(2-chloroethyl) phosphate: Intermediate products, degradation pathway and toxicity evaluation

Tri(2-chloroethyl) phosphate (TCEP) with the initial concentration of 5 mg/L was degraded by UV/H₂O₂ oxidation process. The removal rate of TCEP in the UV/H₂O₂ system was 89.1% with the production of Cl^? and PO₄^3? of 0.23 and 0.64 mg/L. The removal rate of total organic carbon of the reaction was 48.8% and the pH reached 3.3 after the reaction. The oxidative degradation process of TCEP in the UV/H₂O₂ system obeyed the first order kinetic reaction with the apparent rate constant of 0.0025 min^?1 (R²=0.9788). The intermediate products were isolated and identified by gas chromatography-mass spectrometer. The addition reaction of HO? and H₂O and the oxidation reaction with H₂O₂ were found during the degradation pathway of 5 mg/L TCEP in the UV/H₂O₂ system. For the first time, environment risk was estimated via the “ecological structure activity relationships” program and acute and chronic toxicity changes of intermediate products were pointed out. The luminescence inhibition rate of photobacterium was used to evaluate the acute toxicity of intermediate products. The results showed that the toxicity of the intermediate products increased with the increase of reaction time, which may be due to the production of chlorine compounds. Some measures should be introduced to the UV/H₂O₂ system to remove the highly toxic Cl-containing compounds, such as a nanofiltration or reverse osmosis unit.     

Responses of nitrification performance, triclosan resistome and diversity of microbes to continuous triclosan stress in activated sludge system

Triclosan(TCS) is commonly found in wastewater treatment plants,which often affects biological treatment processes.The responses of nitrification,antibiotic resistome and microbial community under different TCS concentrations in activated sludge system were evaluated in this study.The experiment was conducted in a sequencing batch reactor(SBR)for 240 days.Quantitative PCR results demonstrated that the abundance of ammonium oxidizing bacteria could be temporarily inhibited by 1 mg/L TCS and then gradually recovered.And the abundances of nitrite oxidizing bacteria(NOB) under 2.5 and 4 mg/L TCS were three orders of magnitude lower than that of seed sludge,which accounted for partial nitrification.When the addition of TCS was stopped,the abundance of NOB increased.The mass balance experiments of TCS demonstrated that the primary removal pathway of TCS changed from adsorption to biodegradation as TCS was continuously added into the SBR system.Moreover,TCS increased the abundance of mexB,indicating the efflux pump might be the main TCS-resistance mechanism.As a response to TCS,bacteria could secrete more protein(PN) than polysaccharide.Three-dimensional excitation-emission matrix revealed that tryptophan PN-like substances might be the main component in PN to resist TCS.High-throughput sequencing found that the relative abundances of Paracoccus,Pseudoxanthomonas and Thauera increased,which could secrete extracellular polymeric substances(EPS).And Sphingopyxis might be the main TCS-degrading bacteria.Overall,TCS could cause partial nitrification and increase the relative abundances of EPS-secreting bacteria and TCS-degrading bacteria.     

Ozone pollution characteristics and sensitivity analysis using an observation-based model in Nanjing, Yangtze River Delta Region of China

Ground-level ozone (O₃) has become a critical pollutant impeding air quality improvement in Yangtze River Delta region of China. In this study, we present O₃ pollution characteristics based on one-year online measurements during 2016 at an urban site in Nanjing, Jiangsu Province. Then, the sensitivity of O₃ to its precursors during 2 O₃ pollution episodes in August was analyzed using a box model based on observation (OBM). The relative incremental reactivity (RIR) of hydrocarbons was larger than other precursors, suggesting that hydrocarbons played the dominant role in O₃ formation. The RIR values for NO_X ranged from –0.41%/% to 0.19%/%. The O₃ sensitivity was also analyzed based on relationship of simulated O₃ production rates with reductions of VOC and NO_X derived from scenario analyses. Simulation results illustrate that O₃ formation was between VOCs-limited and transition regime. Xylenes and light alkenes were found to be key species in O₃ formation according to RIR values, and their sources were determined using the Positive Matrix Factorization (PMF) model. Paints and solvent use was the largest contributor to xylenes (54%), while petrochemical industry was the most important source to propene (82%). Discussions on VOCs and NO_X reduction schemes suggest that the 5% O₃ control goal can be achieved by reducing VOCs by 20%. To obtain 10% O₃ control goal, VOCs need to be reduced by 30% with VOCs/NO_X larger than 3:1.     

精神活性物质在北京市某污水处理厂中的污染特征与生态风险

为了解污水处理厂对精神活性物质的去除特征及总出水对受纳水体的生态风险,采用固相萃取-高效液相色谱-串联质谱法调查了北京市某污水处理厂中13种精神活性物质的浓度水平与负荷量变化,并运用RQ（risk quotient,风险熵）对总出水中精神活性物质进行风险评估.结果表明:①13种精神活性物质在总进水与总出水中均能检出,总质量浓度平均值分别为2 395.10和63.59 ng/L,其中ρ（EPH）（EPH表示麻黄碱）占比分别为93.9%和67.9%,其次为COD（可待因）与METH（甲基苯丙胺）.污水处理厂上游地表水中ρ（EPH）、ρ（METH）与ρ（KET）（KET为氯胺酮）均高于总出水及其下游地表水,说明上游沿河可能有新的污染源输入.②污水处理厂对NK（去甲氯胺酮）、BE（苯甲酰爱康宁）和MTD（美沙酮）均呈负去除,其他精神活性物质的去除主要发生在二级生物处理与三级处理（超滤膜与UV消毒）阶段.③污水处理厂服务区域内精神活性物质的周内负荷量存在一定波动,AMP（苯丙胺）、METH、MDA（3,4-亚甲二氧基苯丙胺）、MDMA（3,4-亚甲二氧基甲基苯丙胺）、KET与HER（海洛因）的负荷量均在周末升高.④污水处理厂总出水中精神活性物质的生态风险均较低（RQ < 0.10）.研究显示,污水处理厂不能完全去除污水中的精神活性物质,总出水中残留精神活性物质对受纳河流生态系统产生的长期混合效应不容忽视.      

On-going nitrification in chloraminated drinking water distribution system (DWDS) is conditioned by hydraulics and disinfection strategies

Within the drinking water distribution system (DWDS) using chloramine as disinfectant, nitrification caused by nitrifying bacteria is increasingly becoming a concern as it poses a great challenge for maintaining water quality. To investigate efficient control strategies, operational conditions including hydraulic regimes and disinfectant scenarios were controlled within a flow cell experimental facility. Two test phases were conducted to investigate the effects on the extent of nitrification of three flow rates (Q = 2, 6, and 10 L/min) and four disinfection scenarios (total Cl₂=1 mg/L, Cl₂/NH₃-N=3:1; total Cl₂=1 mg/L, Cl₂/NH₃-N=5:1; total Cl₂=5 mg/L, Cl₂/NH₃-N=3:1; and total Cl₂=5 mg/L, Cl₂/NH₃-N=5:1). Physico-chemical parameters and nitrification indicators were monitored during the tests. The characteristics of biofilm extracellular polymetric substance (EPS) were evaluated after the experiment. The main results from the study indicate that nitrification is affected by hydraulic conditions and the process tends to be severe when the fluid flow transforms from laminar to turbulent (2300<Re<4000). Increasing disinfectant concentration and optimizing Cl₂/NH₃-N mass ratio were found to inhibit nitrification to some extend when the system was running at turbulent condition (Q = 10 L/min, Re = 5535). EPS extracted from biofilm that was established at the flow rate of 6 L/min had greater carbohydrate/protein ratio. Furthermore, several nitrification indicators were evaluated for their prediction efficiency and the results suggest that the change of nitrite, together with total organic carbon (TOC) and turbidity can indicate nitrification potential efficiently.