Denitrification and biofilm growth in a pilot-scale biofilter packed with suspended carriers for biological nitrogen removal from secondary effluent

Tertiary denitrification is an effective method for nitrogen removal from wastewater. A pilot-scale biofilter packed with suspended carriers was operated for tertiary denitrification with ethanol as the organic carbon source. Long-term performance, biokinetics of denitrification and biofilm growth were evaluated under filtration velocities of 6, 10 and 14 m/hr. The pilot-scale biofilter removed nitrate from the secondary effluent effectively, and the nitrate nitrogen (NO₃-N) removal percentage was 82%, 78% and 55% at the filtration velocities of 6, 10 and 14 m/hr, respectively. At the filtration velocities of 6 and 10 m/hr, the nitrate removal loading rate increased with increasing influent nitrate loading rates, while at the filtration velocity of 14 m/hr, the removal loading rate and the influent loading rate were uncorrelated. During denitrification, the ratio of consumed chemical oxygen demand to removed NO₃-N was 3.99–4.52 mg/mg. Under the filtration velocities of 6, 10 and 14 m/hr, the maximum denitrification rate was 3.12, 4.86 and 4.42 g N/(m²·day), the half-saturation constant was 2.61, 1.05 and 1.17 mg/L, and the half-order coefficient was 0.22, 0.32 and 0.24 (mg/L)^1/2/min, respectively. The biofilm biomass increased with increasing filtration velocity and was 2845, 5124 and 7324 mg VSS/m² at filtration velocities of 6, 10 and 14 m/hr, respectively. The highest biofilm density was 44 mg/cm³ at the filtration velocity of 14 m/hr. Due to the low influent loading rate, biofilm biomass and thickness were lowest at the filtration velocity of 6 m/hr.     

Greenhouse gas emissions from oilfield-produced water in Shengli Oilfield, Eastern China

Greenhouse gas(GHG) emissions from oil and gas systems are an important component of the GHG emission inventory. To assess the carbon emissions from oilfield-produced water under atmospheric conditions correctly, in situ detection and simulation experiments were developed to study the natural release of GHG into the atmosphere in the Shengli Oilfield,the second largest oilfield in China. The results showed that methane(CH4) and carbon dioxide(CO2) were the primary gases released naturally from the oilfield-produced water.The atmospheric temperature and release time played important roles in determining the CH4 and CO2emissions under atmospheric conditions. Higher temperatures enhanced the carbon emissions. The emissions of both CH4 and CO2from oilfield-produced water were highest at 27°C and lowest at 3°C. The bulk of CH4 and CO2was released from the oilfield-produced water during the first release period, 0–2 hr, for each temperature, with a maximum average emission rate of 0.415 g CH4/(m3·hr) and 3.934 g CO2/(m3·hr), respectively. Then the carbon emissions at other time periods gradually decreased with the extension of time. The higher solubility of CO2 in water than CH4 results in a higher emission rate of CH4 than CO2over the same release duration. The simulation proved that oilfield-produced water is one of the potential emission sources that should be given great attention in oil and gas systems.     

Methane and nitrous oxide emissions from a subtropical coastal embayment (Moreton Bay,Australia)

Surface water methane (CH₄) and nitrous oxide (N₂O) concentrations and fluxes were investigated in two subtropical coastal embayments (Bramble Bay and Deception Bay, which are part of the greater Moreton Bay, Australia). Measurements were done at 23 stations in seven campaigns covering different seasons during 2010–2012. Water–air fluxes were estimated using the Thin Boundary Layer approach with a combination of wind and currents-based models for the estimation of the gas transfer velocities. The two bays were strong sources of both CH₄ and N₂O with no significant differences in the degree of saturation of both gases between them during all measurement campaigns. Both CH₄ and N₂O concentrations had strong temporal but minimal spatial variability in both bays. During the seven seasons, CH₄ varied between 500% and 4000% saturation while N₂O varied between 128 and 255% in the two bays. Average seasonal CH₄ fluxes for the two bays varied between 0.5 ± 0.2 and 6.0 ± 1.5 mg CH₄/(m²·day) while N₂O varied between 0.4 ± 0.1 and 1.6 ± 0.6 mg N₂O/(m²·day). Weighted emissions (t CO₂-e) were 63%–90% N₂O dominated implying that a reduction in N₂O inputs and/or nitrogen availability in the bays may significantly reduce the bays' greenhouse gas (GHG) budget. Emissions data for tropical and subtropical systems is still scarce. This work found subtropical bays to be significant aquatic sources of both CH₄ and N₂O and puts the estimated fluxes into the global context with measurements done from other climatic regions.     

CO2 sequestration utilizing basic-oxygen furnace slag: Controlling factors, reaction mechanisms and V–Cr concerns

Basic-oxygen furnace slag(BOF-slag) contains 35%CaO,a potential component for CO_2sequestration.In this study,slag-water-CO_2 reaction experiments were conducted with the longest reaction duration extending to 96 hr under high CO_2 pressures of 100-300 kg/cm2 to optimize BOF-slag carbonation conditions,to address carbonation mechanisms,and to evaluate the extents of V and Cr release from slag carbonation.The slag carbonation degree generally reached the maximum values after 24 hr slag-water-CO_2 reaction and was controlled by slag particle size and reaction temperature.The maximum carbonation degree of 71%was produced from the experiment using fine slag of0.5 mm under 100℃and a CO_2 pressure of 250 kg/cm~2 with a water/slag ratio of 5.Vanadium release from the slag to water was significantly enhanced(generally 2 orders) by slag carbonation.In contrast,slag carbonation did not promote chromium release until the reaction duration exceeded 24 hr.However,the water chromium content was generally at least an order lower than the vanadium concentration,which decreased when the reaction duration exceeded 24 hr.Therefore,long reaction durations of 48-96 hr are proposed to reduce environmental impacts while keeping high carbonation degrees.Mineral textures and water compositions indicated that Mg-wustite,in addition to CaO-containing minerals,can also be carbonated.Consequently,the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO_2 sequestration capability of the BOF-slag by~20%.Therefore,the BOF-slag is a better CO_2 storage medium than that previously recognized.     

Effect of drainage on CO2, CH4, and N2O fluxes from aquaculture ponds during winter in a subtropical estuary of China

Aquaculture ponds are dominant features of the landscape in the coastal zone of China.Generally,aquaculture ponds are drained during the non-culture period in winter.However,the effects of such drainage on the production and flux of greenhouse gases(GHGs)from aquaculture ponds are largely unknown.In the present study,field-based research was performed to compare the GHG fluxes between one drained pond(DP,with a water depth of 0.05 m)and one undrained pond(UDP,with a water depth of 1.16 m)during one winter in the Min River estuary of southeast China.Over the entire study period,the mean CO_2flux in the DP was(0.75±0.12)mmol/(m~2·hr),which was significantly higher than that in the UDP of(-0.49±0.09)mmol/(m~2·hr)(p0.01).This indicates that drainage drastically transforms aquaculture ponds from a net sink to a net source of CO_2in winter.Mean CH_4and N_2O emissions were significantly higher in the DP compared to those in the UDP(CH_4=(0.66±0.31)vs.(0.07±0.06)mmol/(m~2·hr)and N_2O=(19.54±2.08)vs.(0.01±0.04)μmol/(m~2·hr))(p0.01),suggesting that drainage would also significantly enhance CH_4and N_2O emissions.Changes in environmental variables(including sediment temperature,p H,salinity,redox status,and water depth)contributed significantly to the enhanced GHG emissions following pond drainage.Furthermore,analysis of the sustained-flux global warming and cooling potentials indicated that the combined global warming potentials of the GHG fluxes were significantly higher in the DP than in the UDP(p0.01),with values of739.18 and 26.46 mg CO_2-eq/(m~2·hr),respectively.Our findings suggested that drainage of aquaculture ponds can increase the emissions of potent GHGs from the coastal zone of China to the atmosphere during winter,further aggravating the problem of global warming.     

Photodegradation of methylmercury in Jialing River of Chongqing,China

Photodegradation (PD) of methylmercury (MMHg) is a key process of mercury (Hg) cycling in water systems, maintaining MMHg at a low level in water systems. However, we possess little knowledge of this important process in the Jialing River of Chongqing, China. In situ incubation experiments were thus performed to measure temporal patterns and influencing factors of MMHg PD in this river. The results showed that MMHg underwent a net demethylation process under solar radiation in the water column, which predominantly occurred in surface waters. For surface water, the highest PD rate constants were observed in spring (12 × 10^− 3 ± 1.5 × 10^− 3 m²/E), followed by summer (9.0 × 10^− 3 ± 1.2 × 10^− 3 m²/E), autumn (1.4 × 10^− 3 ± 0.12 × 10^− 3 m²/E), and winter (0.78 × 10^− 3 ± 0.11 × 10^− 3 m²/E). UV-A radiation (320–400 nm), UV-B radiation (280–320 nm), and photosynthetically active radiation (PAR, 400–700 nm) accounted for 43%–64%, 14%–31%, and 16%–45% of MMHg PD, respectively. PD rate constants varied substantially with the treatments that filtered the river water and amended it with chemicals (i.e., Cl⁻, NO₃⁻, dissolved organic matter (DOM), Fe(III)), which reveals that suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelength range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%–46%, 6.2%–12%, and 42%–65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/(m²·year) in the study site. Our results are very important to understand the cycling characteristics of MMHg in the Jialing River of Chongqing, China.     

Characteristics of change in water quality along reclaimed water intake area of the Chaobai River in Beijing, China

To reveal the basic characteristics and controlling factors of water quality change in the project Wenyu to Chaobai reclaimed water diversion, the water quality in the study area was monitored for one year at seven monitoring sites. Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the hydrochemistry characteristics of reclaimed water and the factors. The monitoring results indicated that nitrogen and phosphorus contents were significantly reduced along the river mainly caused by seasonal and location variation. The pH ranged from 7.44 to 9.81. Photosynthesis of algae and denitrification in anaerobic microenvironment ultimately led to a sudden p H increase after the Jian River and the Chaobai River confluence. Mg~(2+)and SO_4~(2-) levels dropped obviously in the summer and increased in winter seasons after intersection. Na+and Cl-are relatively stable, and marked drop in the concentration only after the two rivers meet. And there is a decrease of Ca~(2+) and HCO~(3-) and increase in CO_3~(2-) during monitoring period. As a whole, the primary ions and nutrient components, including nitrogen and phosphorus, had high levels in winter. Algae's photosynthesis and respiration were observed to have an impact on the river water quality; there was precipitation–dissolution of minerals and denitrification from upstream to downstream. Inverse geochemical PHREEQC modeling confirmed that there was precipitation of aragonite or calcite, and gypsum or anhydrite in summer, and dissolution in winter; as well as precipitation of dolomite in winter, and cationic exchange and denitrification along the river.     

A hydroxyl radical detection system using gas expansion and fast gating laser-induced fluorescence techniques

An OH radical measurement instrument based on Fluorescence Assay by Gas Expansion(FAGE)has been developed in our laboratory.Ambient air is introduced into a low-pressure fluorescence cell through a pinhole aperture and irradiated by a dye laser at a high repetition rate of 8.5 k Hz.The OH radical is both excited and detected at 308 nm using A-X(0,0)band.To satisfy the high efficiency needs of fluorescence collection and detection,a 4-lens optical system and a self-designed gated photomultiplier(PMT)is used,and gating is actualized by switching the voltage applied on the PMT dynodes.A micro channel photomultiplier(MCP)is also prepared for fluorescence detection.Then the weak signal is accumulated by a photon counter in a specific timing.The OH radical excitation spectrum range in the wavelength of 307.82–308.2 nm is detected and the excited line for OH detection is determined to be Q_1(2)line.The calibration of the FAGE system is researched by using simultaneous photolysis of H_2O and O_2.The minimum detection limit of the instrument using gated PMT is determined to be 9.4×10~5molecules/cm~3,and the sensitivity is 9.5×10~(-7)cps/(OH·cm~(-3)),with a signal-to-noise ratio of 2 and an integration time of 60 sec,while OH detection limit and the detection sensitivity using MCP is calculated to be 1.6×10~5molecules/cm~3and 2.3×10~(-6)cps/(OH·cm~(-3)).The laboratory OH radical measurement is carried out and results show that the proposed system can be used for atmospheric OH radical measurement.     

Spatial and seasonal variability of CO2 flux at the air-water interface of the Three Gorges Reservoir

Difusive carbon dioxide(CO2) emissions from the water surface of the Three Gorges Reservoir, currently the largest hydroelectric reservoir in the world, were measured using floating static chambers over the course of a yearlong survey. The results showed that the average annual CO2 flux was(163.3 ± 117.4) mg CO2/(m2·hr) at the reservoir surface, which was larger than the CO2 flux in most boreal and temperate reservoirs but lower than that in tropical reservoirs. Significant spatial variations in CO2 flux were observed at four measured sites, with the largest flux measured at Wushan(221.9 mg CO2/(m2·hr)) and the smallest flux measured at Zigui(88.6 mg CO2/(m2·hr)); these diferences were probably related to the average water velocities at diferent sites. Seasonal variations in CO2 flux were also observed at four sites, starting to increase in January, continuously rising until peaking in the summer(June-August) and gradually decreasing thereafter. Seasonal variations in CO2 flux could reflect seasonal dynamics in pH, water velocity,and temperature. Since the spatial and temporal variations in CO2 flux were significant and dependent on multiple physical, chemical,and hydrological factors, it is suggested that long-term measurements should be made on a large spatial scale to assess the climatic influence of hydropower in China, as well as the rest of the world.     

Phosphate recovery from anaerobic digester effluents using CaMg(OH)4

Dolomite lime(DL)(CaMg(OH)_4) was used as an economical source of Mg~(2+)for the removal and recovery of phosphate from an anaerobic digester effluent of a municipal wastewater treatment plant(MWWTP) wastewater. Batch precipitation results determined that phosphate was effectively reduced from 87 to less than 4 mg-P/L when the effluent water was mixed with 0.3 g/L of DL. The competitive precipitation mechanisms of different solids in the treatment system consisting of Ca~(2+)–Mg~(2+)–NH_4~+–PO_4~(3-)CO_3~(2-)were determined by comparing model predictions with experimental results. Thermodynamic model calculations indicated that hydroxyapatite(Ca_(10)(PO_4)_6(OH)_2), Ca_4H(PO_4)_3?3H_2O, Ca_3(PO_4)_2(beta), and Ca_3(PO_4)_2(am2)were more stable than struvite(MgNH_4PO_3?6H_2O) and calcite(CaCO_3). However, X-ray diffraction(XRD) analysis determined the formation of struvite and calcite minerals in the treated effluent. Kinetic experimental results showed that most of the phosphate was removed from synthetic effluent containing NH_4~+within 2 hr, while only 20% of the PO_4~(3-)was removed in the absence of NH_4~+after 24 hr of treatment. The formation of struvite in the DL-treated effluent was due to the rapid precipitation rate of the mineral. The final pH of the DL-treated effluent significantly influenced the mass ratio of struvite to calcite in the precipitates. Because more calcite was formed when the p H increased from 8.4 to 9.6, a p H range of 8.0–8.5 should be used to produce solid with high PO_4~(3-)content. This study demonstrated that DL could be used for effective removal of phosphate from the effluent and that resultant precipitates contained high content of phosphate and ammonium.     

Continuous desulfurization and bacterial community structure of an integrated bioreactor developed to treat SO2 from a gas stream

Sulfide dioxide(SO2) is often released during the combustion processes of fossil fuels. An integrated bioreactor with two sections, namely, a suspended zone(SZ) and immobilized zone(IZ), was applied to treat SO2 for 6 months. Sampling ports were set in both sections to investigate the performance and microbial characteristics of the integrated bioreactor. SO2 was effectively removed by the synergistic effect of the SZ and IZ, and more than 85%removal efficiency was achieved at steady state. The average elimination capacity of SO2 in the bioreactor was 2.80 g/(m3·hr) for the SZ and 1.50 g/(m3· hr) for the IZ. Most SO2 was eliminated in the SZ. The liquid level of the SZ and the water content ratio of the packing material in the IZ affected SO2 removal efficiency. The SZ served a key function not only in SO2 elimination, but also in moisture maintenance for the IZ. The desired water content in IZ could be feasibly maintained without any additional pre-humidification facilities. Clone libraries of 16 S r DNA directly amplified from the DNA of each sample were constructed and sequenced to analyze the community composition and diversity in the individual zones.The desulfurization bacteria dominated both zones. Paenibacillus sp. was present in both zones, whereas Ralstonia sp. existed only in the SZ. The transfer of SO2 to the SZ involved dissolution in the nutrient solution and biodegradation by the sulfur-oxidizing bacteria.This work presents a potential biological treatment method for waste gases containing hydrophilic compounds.     

Response of gaseous carbon emissions to low-level salinity increase in tidal marsh ecosystem of the Min River estuary, southeastern China

Although estuarine tidal marshes are important contributors to the emission of greenhouse gases into the atmosphere, the relationship between carbon dioxide(CO_2), methane(CH_4)emission, and environmental factors, with respect to estuarine marshes, has not been clarified thoroughly. This study investigated the crucial factors controlling the emission of CO_2 and CH_4from a freshwater marsh and a brackish marsh located in a subtropical estuary in southeastern China, as well as their magnitude. The duration of the study period was November 2013 to October 2014. Relevant to both the field and incubation experiments, the CO_2 and CH_4emissions from the two marshes showed pronounced seasonal variations. The CO_2 and CH_4emissions from both marshes demonstrated significant positive correlations with the air/soil temperature(p 0.01), but negative correlations with the soil electrical conductivity and the pore water/tide water Cl-and SO_4~(2-)(p 0.01). The results indicate no significant difference in the CO_2 emissions between the freshwater and brackish marshes in the subtropical estuary, whereas there was a difference in the CH_4 emissions between the two sites(p 0.01). Although future sea-level rise and saltwater intrusion could reduce the CH_4 emissions from the estuarine freshwater marshes, these factors had little effect on the CO_2 emissions with respect to an increase in salinity of less than 5‰. The findings of this study could have important implications for estimating the global warming contributions of estuarine marshes along differing salinity gradients.     

Kinetic and products study of the gas-phase reaction of Lewisite with ozone under atmospheric conditions

The rate constant for the gas-phase reaction of O_3 and Lewisite was studied in air using the smog chamber technique. The experiments were carried out under pseudo-first-order reaction conditions with [O_3] [Lewisite]. The observed rate constant of O_3 with Lewisite was(7.83 ± 0.38) × 10~(-19)cm~3/(molecule·sec) at 298 ± 2 K. Lewisite was discussed in terms of reactivity with O_3 and its relationship with the ionization potential. Our results show that the rate constant for the gas-phase reaction of O_3 with Lewisite is in line with the trend of the rate constants of O_3 with haloalkenes.     

Denitrification on Andosols in an intensive dairy farming region of central Japan

Evaluation of denitrification capacities is necessary to develop a sustainable manure management system in order to reduce NO₃⁻ leaching and N₂O emissions from agricultural soils. Denitrification rates were measured using the acetylene inhibition technique on intact soil cores from eight Andosols under three different cropping systems in an intensive livestock catchment of central Japan. The N application rates ranged from 200 to 800 kg N ha⁻¹ yr⁻¹. The denitrification rates were highly variable across fields, and were influenced significantly by land uses and manure forms. Compared with upland fields, paddy rice fields had a greater denitrification rate up to 1380 and 85 mg N m⁻² day⁻¹ in the top 30-cm soil layer during flooding and non-flooding periods, respectively. In upland fields, the maximum value for the top 30-cm soils was 44 mg N m⁻² day⁻¹ and most of the rates were less than 10 mg N m⁻² day⁻¹. The greater denitrification rates were often associated with slurry application rather than composted dry manure. Overall, denitrification from Andosols in this study displayed a lower capacity than that of non-Andosols.     

Optimization of CO2 adsorption capacity and cyclical adsorption/desorption on tetraethylenepentamine-supported surface-modified hydrotalcite

The objective of this research was to investigate CO_2adsorption capacity of tetraethylenepentamine-functionalized basic-modified calcined hydrotalcite(TEPA/b-c HT)sorbents at atmospheric pressure formed under varying TEPA loading levels,temperatures,sorbent weight to total gaseous flow rate(W/F)ratios and CO_2concentrations in the influent gas.The TEPA/b-c HT sorbents were characterized by means of X-ray diffraction(XRD),Fourier transform infrared spectrometry(FT–IR),thermal gravimetric analysis(TGA),Brunauer–Emmet–Teller(BET)analysis of nitrogen(N_2)adsorption/desorption and carbon–hydrogen–nitrogen(CHN)elemental analysis.Moreover,a full 2~4factorial design with three central points at a 95%confidence interval was used to screen important factor(s)on the CO_2adsorption capacity.It revealed that85.0%variation in the capacity came from the influence of four main factors and the15.0%one was from their interactions.A face-centered central composite design response surface method(FCCCD–RSM)was then employed to optimize the condition,the maximal capacity of 5.5–6.1 mmol/g was achieved when operating with a TEPA loading level of 39%–49%(W/W),temperature of 76–90°C,W/F ratio of 1.7–2.60(g·sec)/cm~3and CO_2concentration of 27%–41%(V/V).The model fitted sufficiently the experimental data with an error range of±1.5%.From cyclical adsorption/desorption and selectivity at the optimal condition,the 40%TEPA/b-c HT still expressed its effective performance after eight cycles.     

Comparison between UV and VUV photolysis for the pre- and post-treatment of coking wastewater

In this study, ultraviolet (UV) and vacuum ultraviolet (VUV) photolysis were investigated for the pre-treatment and post-treatment of coking wastewater. First, 6-fold diluted raw coking wastewater was irradiated by UV and VUV. It was found that 15.9%–35.4% total organic carbon (TOC) was removed after 24 hr irradiation. The irradiated effluent could be degraded by the acclimated activated sludge. Even though the VUV photolysis removed more chemical oxygen demand (COD) than UV, the UV-irradiated effluent demonstrated better biodegradability. After 4 hr UV irradiation, the biological oxygen demand BOD₅/COD ratio of irradiated coking wastewater increased from 0.163 to 0.224, and its toxicity decreased to the greatest extent. Second, the biologically treated coking wastewater was irradiated by UV and VUV. Both of them were able to remove 37%–47% TOC within 8 hr irradiation. Compared to UV, VUV photolysis could significantly improve the transparency of the bio-treated effluent. VUV also reduced 7% more ammonia nitrogen (NH₄⁺–N), 17% more nitrite nitrogen (NO₂⁻–N), and 18% more total nitrogen (TN) than UV, producing 35% less nitrite nitrogen (NO₃⁻–N) as a result. In conclusion, UV irradiation was better in improving the biodegradability of coking wastewater, while VUV was more effective at photolyzing the residual organic compounds and inorganic N-species in the bio-treated effluent.     

Fluoride removal by Al, Ti, and Fe hydroxides and coexisting ion effect

Batch experiments were conducted to evaluate fluoride removal by Al,Fe,and Ti-based coagulants and adsorbents,as well as the effects of coexisting ions and formation of aluminum–fluoride complexes on fluoride removal by co-precipitation with alum(Al_2(SO_4)_3·18H_2O).Aluminum sulfate was more efficient than the other coagulants for fluoride removal in the pH range between 6 and 8.Nano-crystalline TiO_2 was more effective for fluoride removal than Al and Fe hydroxides in a pH range of 3–5.Coexisting anions in water decreased the removal of fluoride in the order:phosphate(2.5 mg/L) arsenate(0.1 mg/L) bicarbonate(200 mg/L) sulfate(100 mg/L) = nitrate(100 mg/L) silicate(10 mg/L) at a pH of 6.0.The effect of silicate became more significant at pH 7.0.Calcium and magnesium improved the removal of fluoride.Zeta-potential measurements determined that the adsorption of fluoride shifted the PZC of Al(OH)_3 precipitates from 8.9 to 8.4,indicating the chemical adsorption of fluoride at the surface.The presence of fluoride in solution significantly increased the soluble aluminum concentration at pH 6.5.A Visual MINTEQ modeling study indicated that the increased aluminum solubility was caused by the formation of AlF~(2+),AlF~(+2),and AlF_3complexes.The AlF_x complexes decreased the removal of fluoride during co-precipitation with aluminum sulfate.     

A nanofilter composed of carbon nanotube-silver composites for virus removal and antibacterial activity improvement

We have developed a new nanofilter using a carbon nanotube-silver composite material that is capable of efficiently removing waterborne viruses and bacteria.The nanofilter was subjected to plasma surface treatment to enhance its flow rate,which was improved by approximately 62%.Nanoscale pores were obtained by fabricating a carbon nanotube network and using nanoparticle fixation technology for the removal of viruses.The pore size of the nanofilter was approximately 38 nm and the measured flow rate ranged from 21.0 to 97.2 L/(min·m~2)under a pressure of 1–6 kgf/cm~2 when the amount of loaded carbon nanotube-silver composite was 1.0 mg/cm~2.The nanofilter was tested against Polio-,Noro-,and Coxsackie viruses using a sensitive real-time polymerase chain reaction assay to detect the presence of viral particles within the outflow.No trace of viruses was found to flow through the nanofilter with carbon nanotube-silver composite loaded above 0.8 mg/cm~2.Moreover,the surface of the filter has antibacterial properties to prevent bacterial clogging due to the presence of 20-nm silver nanoparticles,which were synthesized on the carbon nanotube surface.     

Occurrence and bioaccumulation of polybrominated diphenyl ethers in sediments and paddy ecosystems of Liaohe River Basin, northeast China

Concentrations of 16 polybrominated diphenyl ether(PBDE) congeners were measured in river sediments, paddy soils and three species of paddy-field organisms(crab, loach and carp) collected from the Liaohe River Basin, northeastern China. The total contents of PBDEs(∑_(16)PBDEs) in sediments and paddy soils were in the ranges of 273.4–3246.3 pg/g dry weight(dw), and 192.1–1783.8 pg/g dw, respectively. BDE 209 was the dominant congener both in sediments and paddy soils. The concentrations of ∑_(16)PBDEs in sediments were significantly higher than those in the adjacent paddy soils, indicating a potential transport of PBDEs from river to paddy ecosystems via river water irrigation. The biota–soil accumulation factor(BSAF) was calculated as the ratio between the lipid-normalized concentration in paddyfield organisms and the total organic carbon-normalized concentration in paddy soil. The average BSAF values of ∑15PBDEs followed the sequence of crab(3.6) loach(3.3) carp(2.1). BDE 154 had the highest BSAF value, and a parabolic trend between BSAF values of individual PBDE congeners and their log KOWvalues was observed. In view of the fact that crab had the larger BSAF value and higher lipid content, the ecological risk and health risk for crab cultivation in paddy fields should be of particular concern.     

Effects of elevated atmospheric CO2 concentration and temperature on the soil profile methane distribution and diffusion in rice–wheat rotation system

The aim of this experiment was to determine the impacts of climate change on soil profile concentrations and diffusion effluxes of methane in a rice–wheat annual rotation ecosystem in Southeastern China. We initiated a field experiment with four treatments: ambient conditions (CKs), CO₂ concentration elevated to ~ 500 μmol/mol (FACE), temperature elevated by ca. 2°C (T) and combined elevation of CO₂ concentration and temperature (FACE + T). A multilevel sampling probe was designed to collect the soil gas at four different depths, namely, 7 cm, 15 cm, 30 cm and 50 cm. Methane concentrations were higher during the rice season and decreased with depth, while lower during the wheat season and increased with depth. Compared to CK, mean methane concentration was increased by 42%, 57% and 71% under the FACE, FACE + T and T treatments, respectively, at the 7 cm depth during the rice season (p < 0.05). Mean methane diffusion effluxes to the 7 cm depth were positive in the rice season and negative in the wheat season, resulting in the paddy field being a source and weak sink, respectively. Moreover, mean methane diffusion effluxes in the rice season were 0.94, 1.19 and 1.42 mg C/(m²·hr) in the FACE, FACE + T and T treatments, respectively, being clearly higher than that in the CK. The results indicated that elevated atmospheric CO₂ concentration and temperature could significantly increase soil profile methane concentrations and their effluxes from a rice–wheat field annual rotation ecosystem (p < 0.05).