خيارات البحث
النتائج 2141 - 2150 من 4,309
Perspectives of Quantitative Risk Assessment Studies for Giardia and Cryptosporidium in Water Samples النص الكامل
2017
Balderrama-Carmona, Ana Paola | Gortáres-Moroyoqui, Pablo | Álvarez, Luis H. | Ulloa-Mercado, Ruth Gabriela | Leyva-Soto, Luis Alonso | Díaz-Tenorio, Lourdes Mariana
A quantitative microbial risk assessment method can be used to evaluate infections probabilities for microorganisms in a specific place. The methodology provides suitable information to generate strategies focusing on health problems. Giardia cysts (GC) and Cryptosporidium oocysts (CO) are considered emerging pathogens that can infect human and animals by ingesting contaminated food or water, where food and water are transport vehicles for these parasites. Studies for GC and CO have reported occurrences for these parasites in water up to 100%, and some of these studies documented a number of cases, about 403,000 people, infected worldwide. This review is focused on compiling the most relevant works assessing the risk for GC and CO and their presence in different water samples that are susceptible for direct and indirect human consumption. The annual risk infection probability for these parasites has been reported from different water sources, with a range between 1 × 10⁻⁶ and 1, while the world standard regulation is 1 × 10⁻⁴. The infection probability depends not only on water quality but also on water treatment implementations.
اظهر المزيد [+] اقل [-]Ammonia Recovery from Pig Slurry Using a Membrane Contactor—Influence of Slurry Pretreatment النص الكامل
2017
Zarebska, Agata | Karring, Henrik | Christensen, Morten Lykkegaard | Hjorth, Maibritt | Christensen, Knud Villy | Norddahl, Birgir
Pig slurry contains sufficient amount of nitrogen, phosphorus, and potassium for plant growth. If appropriately administered, this could substitute significant amounts of fertilizer. However, excessive fertilization with slurry causes environmental problems. To reduce environmental issues, solid-liquid separation or anaerobic digestion is needed to obtain a better distribution of nutrients. Solid-liquid separation produces a solid fraction rich in phosphorus and a liquid fraction containing ammonia, potassium, and high water content. Therefore, further concentration of ammonia is desired for any practical use. In this study, ammonia membrane stripping was carried out using polypropylene membranes and the impact of temperature, flow velocities, and liquid fraction pretreatment on the membrane contactor performance was tested. Sieved liquid effluents from a decanter centrifuge, a screw press, an AL-2 system (flocculation and filtration), and an anaerobic digester were tested. Since the properties of these liquid effluents vary, they might affect ammonia recovery. Thus, it is essential to investigate which effluent is most suitable as a feed for a membrane contactor and what is the cost of preprocessing. The mean ammonia mass transfer coefficient at 30 °C was found to be equal to 17 ± 2 × 10⁻³ m h⁻¹. At 50 °C, it was found to be equal to 29 ± 2 × 10⁻³ m h⁻¹ for all the tested effluents. This means that sieving after slurry separation or anaerobic digestion alleviates the influence the solid-liquid separation has on ammonia membrane stripping. However, the cost evaluation showed that solid-liquid separation using a decanter centrifuge followed by sieve draining is the cheapest of the methods investigated.
اظهر المزيد [+] اقل [-]Influence of Arsenic Stress on Physiological, Biochemical, and Morphological Characteristics in Seedlings of Two Cultivars of Maize (Zea mays L.) النص الكامل
2017
Du, Liyu | Xia, Xindi | Lan, Xiping | Liu, Miao | Zhao, Liyang | Zhang, Pan | Wu, Yan
Agricultural practices and industrial growth have contaminated the environment with heavy metals and many other harmful compounds. Arsenic (As) has been highlighted as a major heavy metal affecting growth and development of plants as well as causing severe human health hazards through food chain contamination. Most studies of heavy metal impacts address only one of these aspects, overlooking the effect of pollution on the plant as a whole. In this work, our objective was to determine the effect of arsenic stress on physiological, biochemical, and morphological characteristics in seedlings of two cultivars of maize with different arsenic tolerance. This study investigated the effects of varying levels of arsenic (As) stress on growth, enzymatic characteristics, and cell ultrastructure in seedlings of As-sensitive and As-tolerant maize cultivars (Shiyu No. 9 and Dongdan90, respectively) grown in hydroponic culture. Compared to Shiyu No. 9 at the same As concentration, Dongdan90 maintained higher values of biomass, shoot length, root length, and activity of superoxide dismutase, peroxidases, and catalase, but had lower malondialdehyde content, As accumulation, and non-protein thiol. High As concentrations inhibited the growth of both cultivars, while lower concentrations stimulated it. The As-tolerant cultivar also maintained the structural integrity of cells and tissues more efficiently under As stress. These findings demonstrate a link between the physiological and physical impacts of heavy metals on crop plants that paves the way for improved interventions to deal with heavy metal pollution.
اظهر المزيد [+] اقل [-]Quantitative Assessment of PM2.5 Sources and Their Seasonal Variation in Krakow النص الكامل
2017
Samek, Lucyna | Stegowski, Z. | Furman, L. | Styszko, K. | Szramowiat, K. | Fiedor, J.
In industry areas of Poland such as Silesia or urban sites like Krakow and some other cities, the levels of pollutants frequently breach air quality standards. Particulate matter (PM) is the most important constituent of atmospheric pollution. Beginning on 1st February 2014 until 31st January 2015, the samples of fine particulate matter PM₂.₅ (aerodynamic diameter of particles less than or equal to 2.5 μm) were collected at a site in the south-eastern Krakow urban background area. During this period, 194 samples were taken. The samples showed daily variation of PM₂.₅ concentration. From these data, monthly variations were estimated and presented in this paper. Monthly integrated data are more representative for the Krakow urban background and show seasonal variation of PM₂.₅ pollution. The lowest monthly concentration value was found for August 2014—about 10 μg m⁻³, the highest for February 2014–70 μg m⁻³, whereas the average annual value was about 31 μg/m³. Utilizing X-ray fluorescence method, concentrations of 15 elements for each sample were determined and 8 inorganic ions were analyzed by ion chromatography. Additionally, the samples were analyzed for black carbon (BC). Receptor model PMF (positive matrix factorization) was used for source identification and apportionment. The modeling identified six sources and their quantitative contributions to PM₂.₅ total mass. The following sources were identified: combustion, secondary nitrate and sulfate, biomass burning, industry or/and soil and traffic. Finally, monthly variations of each source are presented.
اظهر المزيد [+] اقل [-]Synthesis and Metal-Ion Uptake Properties of a New Dithiocarbamate-Base Resin النص الكامل
2017
Sarikahya, Hasan | Scalzo, Rachel D. | Alawaed, Abdulkhaliq | Niri, Vadoud | Damkaci, Fehmi
A new dithiocarbamate-base resin was synthesized utilizing the reaction between carbon disulfide and immobilized amines on the fully cross-linked side of the styrene-maleicimide (SMI) copolymer. The sorption characteristics of the synthesized resin for copper, lead, nickel, zinc, and cadmium ions were investigated, using atomic adsorption spectroscopy (AAS). The sorption capacity of the resin for each metal ion was studied as a function of pH and time. The optimum pH range for sorption of the metal ions was between 4 and 6. The capacity of the resin for the metal ions decreases in the following order: Cu(II) ≈ Pb(II) > > Zn(II) > Ni(II) > Cd(II). The sorption rate of the metal ions in the resin decreases in the following order: Zn(II) > Ni(II) > Cd(II) > Pb(II) > Cu(II). The affinity of the resin for the ions was also studied using a mixture of the heavy metal ions. The capacities of the new resin, especially for copper and lead, are significantly higher than previously studied resins. Additionally, it was shown that desorption of the captured ions from the resin within 24 h can be done using 1 M nitric acid solution.
اظهر المزيد [+] اقل [-]Remediation of Radiocesium-137 Affected Soil Using Napiergrass Under Different Planting Density and Cutting Frequency Regimes النص الكامل
2017
Kang, Dong-Jin | Ishii, Yasuyuki | Tazoe, Hirofumi | Isobe, Katsunori | Higo, Masao | Hosoda, Masahiro | Yamada, Masatoshi | Tokonami, Shinji
This study investigated the use of napiergrass (Pennisetum purpureum Schum.) to remediate soils highly contaminated with radiocesium-137 (¹³⁷Cs) in the town of Namie, Fukushima Prefecture, which is located around 9 km northwest of the Fukushima Daiichi Nuclear Power Plant, Japan. Field experiments were performed to investigate the remediation effects using two sites (paddy or upland grassland) as replicates, three planting densities (low, medium, and high density), and two different cutting frequencies (cut once or twice a year) over 2 consecutive years. Napiergrass can be more efficient than sorghum for ¹³⁷Cs remediation. The maximum ¹³⁷Cs removal ratio (CR, %) in napiergrass achieved with high-density planting (11 plants m⁻²) was between 0.32 and 0.57%. However, cutting frequency did not affect the CR. Higher biomass leads to a dilution of ¹³⁷Cs in cutting frequency. Therefore, we suggest that the greatest CR could be achieved through a high above ground biomass (high-density planting).
اظهر المزيد [+] اقل [-]Influences of Coal Ash Leachates and Emergent Macrophytes on Water Quality in Wetland Microcosms النص الكامل
2017
Olson, LeifH. | Misenheimer, JohnC. | Nelson, ClayM. | Bradham, KarenD. | Richardson, CurtisJ.
The storage of coal combustion residue (CCR) in surface water impoundments may have an impact on nearby water quality and aquatic ecosystems. CCR contains leachable trace elements that can enter nearby waters through spills and monitored discharge. It is important, therefore, to understand their environmental fate in affected systems. This experiment examined trace element leachability into freshwater from fly ash (FA), the most common form of CCR. The effects on water quality of FA derived from both high and low sulfur coal sources as well as the influences of two different emergent macrophytes, Juncus effusus and Eleocharis quadrangulata, were evaluated in wetland microcosms. FA leachate dosings increased water electric conductivity (EC), altered pH, and, most notably, elevated the concentrations of boron (B), molybdenum (Mo), and manganese (Mn). The presence of either macrophyte species helped reduce elevated EC, and B, Mo, and Mn concentrations over time, relative to microcosms containing no plants. B and Mo appeared to bioaccumulate in the plant tissue from the water when elevated by FA dosing, while Mn was not higher in plants dosed with FA leachates. The results of this study indicate that emergent macrophytes could help ameliorate downstream water contamination from CCR storage facilities and could potentially be utilized in wetland filtration systems to treat CCR wastewater before discharge. Additionally, measuring elevated B and Mo in aquatic plants may have potential as a monitoring tool for downstream CCR contamination.
اظهر المزيد [+] اقل [-]Functionalization of Cotton by RGO/TiO2 to Enhance Photodegradation of Rhodamine B Under Simulated Solar Irradiation النص الكامل
2017
Landi, S. Jr | Carneiro, J.O. | Fernandes, F. | Parpot, P. | Molina, J. | Cases, F. | Fernandez, J. | Santos, J.G. | Soares, G.M. B. | Teixeira, V. | Samantilleke, A.P.
Reduced graphene oxide (RGO) and titanium dioxide (TiO₂) nanoparticles were immobilized on cotton textile substrates to produce self-cleaning textiles. Varying number of layers of RGO and TiO₂ nanoparticles were coated by a facile method, and their photocatalytic potential was evaluated by measuring the degradation rate of rhodamine B (Rh-B) in an aqueous solution in a photoreactor under simulated solar irradiation. X-ray diffraction (XRD) and zeta potential measurements of starting materials were studied as they are crucial for innovative methods of functionalization. The study confirms that it is possible to ensure a good adhesion of nanoparticles on textile samples without the use of a resin. The application of varying number of RGO and TiO₂ coatings has influence on photocatalytic properties of functionalized cotton textile substrates. The energy band gap of the samples reduces from 3.25 to −3.20 eV with the number of RGO coatings. All five de-ethylated intermediates of Rh-B during the photocatalytic degradation were identified using a high-performance liquid chromatography–mass spectrometry method. The experimental results show that, in general, the higher the number of RGO coatings is, the higher the photocatalytic efficiency (η) of the functionalized substrate is (η=87% for three RGO coatings on TiO₂).
اظهر المزيد [+] اقل [-]Conventional as well as Emerging Arsenic Removal Technologies—a Critical Review النص الكامل
2017
Mohanty, Debasis
Arsenic poisoning from contaminated drinking water has evolved as one of the major health hazards in recent times. High concentrations of arsenic in water and soil have been found in many parts of the world. Developing countries like Taiwan, Chile, Argentina, Bangladesh, Nepal and Vietnam are most affected by the contamination of groundwater with arsenic. These countries also cannot afford expensive and large-scale treatments to remove arsenic from drinking waters to acceptable limits (10 ppb, as recommended by WHO and US EPA). The aim of this review is to summarize low-cost, effective conventional technologies currently described in the literature for arsenic removal that can be used in the third world and developing countries, compare them with the emerging technologies and discuss their advantages and disadvantages along with a brief analysis of arsenic chemistry.
اظهر المزيد [+] اقل [-]Application of Thermally Treated Crushed Concrete Granules for the Removal of Phosphate: A Cheap Adsorbent with High Adsorption Capacity النص الكامل
2017
Kang, Ku | Lee, Chang-Gu | Choi, Jae-Woo | Hong, Seong-Gu | Park, Seong-Jik
The aim of this study was to investigate phosphate removal using crushed concrete granules (CCGs). The CCGs were thermally treated at different temperatures (300, 500, 700, and 900 °C) for 3 h under anoxic conditions. The results showed that CCGs thermally treated at 700 °C (700TT-CCGs) were the most effective for the removal of phosphate. The equilibrium adsorption data fitted well the Langmuir isotherm model with a maximum phosphate adsorption capacity of 21.522 mg/g, higher than that of granular adsorbents in the literature. In pH experiments, phosphate adsorption by 700TT-CCGs decreased as initial pH increased from 3 to 5, but sharply increased above pH 5 (final pH 9.1), which was favorable for the formation of calcium phosphate precipitate. The effect of competing anions on phosphate adsorption follows the order: HCO₃⁻ > SO₄²⁻ > NO₃⁻, which is consistent with the reverse order of the shared charge. Column experiments showed no breakthrough of phosphate in the column packed with half 700TT-CCGs and half sand for over 300 h. This study demonstrates that CCGs can be used for phosphate removal from aqueous solution after thermal treatment, which is a simple and cheap way to improve the phosphate removal capacity of CCGs.
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