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981.
Chang Liu Jianlin Luo Xiaona Li Qiang Gao Jianzhang Li 《Journal of Polymers and the Environment》2018,26(1):158-165
The effects of three compounded curing agents on the properties and performance of the urea-formaldehyde (UF) resin were investigated in this study. The compounded curing agents were prepared by mixing ammonium chloride with hexamethylenetetramine, citric acid, and oxalic acid respectively at a ratio of 1:1, named N-H, N–CA, and N–OA, respectively. The curing process, crystallinity, and physical properties were measured, and the three-ply plywood was fabricated to measure its prepress strength, wet shear strength, and formaldehyde emission. Results showed that the compounded curing agents N–CA and N–OA enhanced the initial viscosity, crosslinking density and thermal stability of UF resin. Additionally, the prepress strength of the plywood bonded by UF resin with N–CA and N–OA increased by 82 and 111% respectively compared to the UF resin with NH4Cl, and the wet shear strength increased by 14 and 16%, the formaldehyde emission decreased by 19 and 42% respectively. However, owing to the short pot-life of these curing agent limited their storage time, the curing agents N–CA and N–OA should be applied to fabricate plywood in winter for obtaining a better bond strength and a lower formaldehyde emission. While the UF resin with N–HT showed a suitable pot-life, so it could be applied to fabricate plywood in summer for long time storage and avoiding procuring problem. 相似文献
982.
Yuling Zhang Hanxiao Wei Yijian Jiang Shaoxin Kang Zhiguang Hu Jilong Wang 《Journal of Polymers and the Environment》2018,26(1):116-121
Poly(aspartic acid-itaconic acid) copolymers (PAI) is a new scale inhibitor for water treatment. Thus, it is necessary to investigate its biodegradability. The biodegradability of PAI was investigated through CO2 evolution tests under different conditions based on determination of carbon dioxide production. The investigation results showed that the degradation rate of PAI on day 10 and day 28 were respectively 38.7 and 79.5%, indicating that PAI was one kind of easily biodegradable scale inhibitors. With the increase in the content of itaconic acid in copolymerization process, the biodegradability of PAI was significantly reduced. In addition, the high biodegradability might be attributed to the existence of C–N bone-structure and more –COO–. Finally, Cu2+ could decrease the degradation percentage and the enzyme inhibition effect of Cu2+ was not the linear effect, but the “low-dosage effect”. 相似文献
983.
Silvina Vargas Gil Analia Becker Claudio Oddino Mónica Zuza Adriana Marinelli Guillermo March 《Environmental management》2009,44(2):378-386
Soil microbial populations can fluctuate in response to environmental changes and, therefore, are often used as biological
indicators of soil quality. Soil chemical and physical parameters can also be used as indicators because they can vary in
response to different management strategies. A long-term field trial was conducted to study the effects of different tillage
systems (NT: no tillage, DH: disc harrow, and MP: moldboard plough), P fertilization (diammonium phosphate), and cattle grazing
(in terms of crop residue consumption) in maize (Zea mays L.), sunflower (Heliantus annuus L.), and soybean (Glycine max L.) on soil biological, chemical, and physical parameters. The field trial was conducted for four crop years (2000/2001,
2001/2002, 2002/2003, and 2003/2004). Soil populations of Actinomycetes, Trichoderma spp., and Gliocladium spp. were 49% higher under conservation tillage systems, in soil amended with diammonium phosphate (DAP) and not previously
grazed. Management practices also influenced soil chemical parameters, especially organic matter content and total N, which
were 10% and 55% higher under NT than under MP. Aggregate stability was 61% higher in NT than in MP, 15% higher in P-fertilized
soil, and also 9% higher in not grazed strips, bulk density being 12% lower in NT systems compared with MP. DAP application
and the absence of grazing also reduced bulk density (3%). Using conservation tillage systems, fertilizing crops with DAP,
and avoiding grazing contribute to soil health preservation and enhanced crop production. 相似文献
984.
Characteristics of aerosol types during large-scale transport of air pollution over the Yellow Sea region and at Cheongwon,Korea, in 2008 总被引:1,自引:0,他引:1
Episodes of large-scale transport of airborne dust and anthropogenic pollutant particles from different sources in the East
Asian continent in 2008 were identified by National Oceanic and Atmospheric Administration satellite RGB (red, green, and
blue)-composite images and the mass concentrations of ground level particulate matter. These particles were divided into dust,
sea salt, smoke plume, and sulfate by an aerosol classification algorithm. To analyze the aerosol size distribution during
large-scale transport of atmospheric aerosols, aerosol optical depth (AOD) and fine aerosol weighting (FW) of moderate imaging
spectroradiometer aerosol products were used over the East Asian region. Six episodes of massive airborne dust particles,
originating from sandstorms in northern China, Mongolia, and the Loess Plateau of China, were observed at Cheongwon. Classified
dust aerosol types were distributed on a large-scale over the Yellow Sea region. The average PM10 and PM2.5 ratio to the total
mass concentration TSP were 70% and 15%, respectively. However, the mass concentration of PM2.5 among TSP increased to as
high as 23% in an episode where dust traveled in by way of an industrial area in eastern China. In the other five episodes
of anthropogenic pollutant particles that flowed into the Korean Peninsula from eastern China, the anthropogenic pollutant
particles were largely detected in the form of smoke over the Yellow Sea region. The average PM10 and PM2.5 ratios to TSP
were 82% and 65%, respectively. The ratio of PM2.5 mass concentrations among TSP varied significantly depending on the origin
and pathway of the airborne dust particles. The average AOD for the large-scale transport of anthropogenic pollutant particles
in the East Asian region was measured to be 0.42 ± 0.17, which is higher in terms of the rate against atmospheric aerosols
as compared with the AOD (0.36 ± 0.13) for airborne dust particles with sandstorms. In particular, the region ranging from
eastern China, the Yellow Sea, and the Korean Peninsula to the Korea East Sea was characterized by high AOD distributions.
In the episode of anthropogenic polluted aerosols, FW averaged 0.63 ± 0.16, a value higher than that in the episode of airborne
dust particles (0.52 ± 0.13) with sandstorms, showing that fine anthropogenic pollutant particles contribute greatly to atmospheric
aerosols in East Asia. 相似文献
985.
Radon ((222)Rn) is a carcinogenic gas produced by the radioactive decay of radium ((226)Ra). It has been reported that soil and soil-gas are primary factors that could cause indoor radon problems. Six sites were selected for this study--Sanbook, Gangcheon, Jikyeong, Choojung, Geumsung and Homyoung--each was classified according to bedrock type. In order to investigate soil-gas radon activities and radon emanating power, innovated active and passive detecting methods were developed and applied under both field and laboratory conditions. Statistical analysis of results confirmed that the radon activity values measured using either active or passive methods under field or laboratory conditions could be interchangeable with each other. 相似文献
986.
987.
Pambrun V Marquot A Racault Y 《Environmental science and pollution research international》2008,15(7):592-599
Background, aims, and scope Sometimes, urban wastewaters convey a more or less significant part of toxic products from industries or the craft industry.
Nitrifying activity can be affected by these substances, implying higher ammonia concentrations in the outlet effluent and
contributing to toxicity for the aquatic environment. Moreover, the more stringently treated wastewater standards now require
a reliable treatment for nitrogen. One of the key issues is the identification of the inhibition behavior of nitrifying bacteria
facing a toxic substance. This new understanding could then finally be integrated into models in order to represent and to
optimize wastewater treatment plants (WWTP) operation in cases involving ‘toxic scenarios’.
Materials and methods The toxic substances studied in this work, cadmium and 3.5-dichlorophenol (3.5-DCP), are representative of chemical substances
commonly found in municipal sewage and industrial effluents and symbolize two different contaminant groups. The effects of
Cd and 3.5-DCP on nitrification kinetics have been investigated using respirometry techniques.
Results IC50 values determination gives concentrations of 3.1 mg/L for 3.5-DCP and 45.8 mg/L for Cd at 21 ± 1°C. The variation to
low temperature seems to have no real effect on IC50 for DCP, but induces a decrease of cadmium IC50 to 27.5 mg/L at 14°C.
Finally, specific respirometric tests have been carried out in order to determine the potential effect of these toxic substances
on the nitrifying decay rate b
a
. No significant effect has been noticed for Cd, whereas the presence of 3.5-DCP (at IC50 concentration) induced a dramatic
increase of b
a
at 20°C. The same behavior has been confirmed by experiments performed in winter periods with a sludge temperature around
12°C.
Discussion The target substances have different modes of action on activity and mortality, notably due to the abilities of the contaminant
to be precipitated, accumulated, or even to be progressively degraded. Studies realized at low temperature confirmed this
assumption, and put in evidence the effect of temperature on toxic substances capable of being biosorbed. However, the change
in the sludge sample characteristics can be pointed out as a problem in the investigation of the temperature effect on nitrification
inhibition, as biosorption, bioaccumulation, and predation are directly linked to the sludge characteristics (VSS concentration,
temperature) and the plant operating conditions (loading rates, sludge age, etc.).
Conclusions This work brings new understandings concerning the action mode of these specific contaminants on nitrifying bacteria and,
in particular, on the role of temperature. The experiments lead to the determination of the IC50 values for both toxic substances
on biological nitrification. The inhibition mechanisms of Cd and 3.5-DCP on nitrifying activity have been simply represented
by a non-competitive inhibition model.
Recommendations and perspectives Other experiments carried out in a continuous lab-scale pilot plant should be done with a proper control of the operating
conditions and of the sludge characteristics in order to better understand the mechanisms of nitrification inhibition for
each contaminant. Finally, these first results show that toxic substances can have an effect on the growth rate but also on
the decay rate, depending on the characteristics of the toxic substance and the sludge. This eventual double effect would
imply different strategies of WWTP operation according to the behavior of the contaminant on the bacteria. 相似文献
988.
Si-Yu Zhang Paul N. Williams Jinming Luo Yong-Guan Zhu 《Frontiers of Environmental Science & Engineering》2017,11(1):1
Arsenic (As) is a pervasive environmental toxin and carcinogenic metalloid. It ranks at the top of the US priority List of Hazardous Substances and causes worldwide human health problems. Wetlands, including natural and artificial ecosystems (i.e. paddy soils) are highly susceptible to As enrichment; acting not only as repositories for water but a host of other elemental/chemical moieties. While macroscale processes (physical and geological) supply As to wetlands, it is the micro-scale biogeochemistry that regulates the fluxes of As and other trace elements from the semi-terrestrial to neighboring plant/aquatic/atmospheric compartments. Among these fine-scale events, microbial mediated As biotransformations contribute most to the element’s changing forms, acting as the ‘switch’ in defining a wetland as either a source or sink of As. Much of our understanding of these important microbial catalyzed reactions follows relatively recent scientific discoveries. Here we document some of these key advances, with focuses on the implications that wetlands and their microbial mediated transformation pathways have on the global As cycle, the chemistries of microbial mediated As oxidation, reduction and methylation, and future research priorities areas. 相似文献
989.
Genetic diversity and population structure of the Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis> in its native range 总被引:1,自引:0,他引:1
Liying Sui Fumin Zhang Xiaomei Wang Peter Bossier Patrick Sorgeloos Bernd Hänfling 《Marine Biology》2009,156(8):1573-1583
The Chinese mitten crab Eriocheir sinensis is an indigenous and economically important species in China, but can also be found as invasive species in Europe and America.
Mitten crabs have been exploited extensively as a food resource since the 1990s. Despite its ecological and economic importance,
the genetic structure of native mitten crab populations is not well understood. In this paper, we investigated the genetic
structure of mitten crab populations in China by screening samples from ten locations covering six river systems at six microsatellite
loci. Our results provide further evidence that mitten crabs from the River Nanliujiang in Southern China are a genetically
differentiated population within the native range of Eriocheir, and should be recognized as a separate taxonomic unit. In contrast, extremely low levels of genetic differentiation and
no significant geographic population structure were found among the samples located north of the River Nanliujiang. Based
on the reproductive biology of mitten crabs and the geography of their habitat we argue that both natural and human-mediated
gene flow are unlikely to fully account for the similar allele frequency distributions at microsatellite loci. Large population
sizes of mitten crabs suggest instead that a virtual absence of genetic drift and significant homoplasy of microsatellite
alleles have contributed to the observed pattern. Furthermore, a coalescent-based maximum likelihood method indicated a more
than two-fold lower effective population size of the Southern population compared to the Northern Group and low but significant
levels of gene flow between both areas. 相似文献
990.
This study investigated the presence of total mercury (Hg) and organic mercury levels in the muscle of 19 common fresh water
fish species captured from river Ganges, West Bengal, India. The total mercury level found in our study may not cause any
toxic effect, but the methyl mercury (MeHg) level in some freshwater fish species was surprisingly very high and toxically
unacceptable. The results of mercury analysis in various specimens indicated that some fish muscles tended to accumulate high
levels of Hg, and approximately 50–84% of Hg was organic mercury. A strong positive correlation between mercury levels in
muscle with food habit and fish length (age) was found. Wallago attu possessed the highest amount of organic mercury in their muscle tissues, and it was 0.93 ± 0.61 μg Hg/g of wet weight. Whereas
in small-sized fishes Eutropiichthys murius, Puntius sarana, Cirrhinus mrigala, Mystus vittatus or Mystus gulio, and Tilapia mossambicus, it was below the detection limit. Contamination in Catla catla (0.32 ± 0.11), Anguilla bengalensis bengalensis (0.26 ± 0.07 μg Hg/g), Chitala chitala (0.25 ± 0.18), Rita rita (0.34 ± 0.14), and Ompok pabda (0.26 ± 0.04) was also above the 0.25 μg Hg/g of wet weight, the limit set by the PFA for the maximum level for consumption
of fish exposed to MeHg. Though in Labeo rohita (0.12 ± 0.03), Mastacembelus armatus (0.17 ± 0.02), Pangasius pangasius (0.12 ± 0.16), Bagarius bagarius (0.12 ± 0.01), and Clupisoma garua (0.1 ± 0.01), concentration was below the recommended level, in Lates calcarifer (0.23 ± 0.0) and Mystus aor (0.23 ± 0.1), it was threatening. Interestingly, a low concentration of Hg was found in post-monsoon samples. 相似文献