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PHYSICS (541 journals)            First | 1 2 3 4 5 6 | Last

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences     Full-text available via subscription   (Followers: 5)
Philosophy and Foundations of Physics     Full-text available via subscription  
Physica B: Condensed Matter     Hybrid Journal   (Followers: 5)
physica status solidi (a)     Hybrid Journal   (Followers: 1)
physica status solidi (b)     Hybrid Journal   (Followers: 1)
physica status solidi (c)     Hybrid Journal   (Followers: 1)
Physica Status Solidi - Rapid Research Letters     Hybrid Journal   (Followers: 1)
Physical Communication     Hybrid Journal  
Physical Review C     Full-text available via subscription   (Followers: 17)
Physical Review Special Topics - Physics Education Research     Open Access   (Followers: 6)
Physical Review X     Open Access   (Followers: 4)
Physical Sciences Data     Full-text available via subscription   (Followers: 1)
Physics - spotlighting exceptional research     Full-text available via subscription   (Followers: 1)
Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B     Full-text available via subscription   (Followers: 2)
Physics and Chemistry of Liquids: An International Journal     Hybrid Journal  
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (Followers: 3)
Physics Essays     Full-text available via subscription  
Physics in Medicine & Biology     Full-text available via subscription   (Followers: 7)
Physics in Perspective     Hybrid Journal   (Followers: 1)
Physics International     Open Access   (Followers: 2)
Physics Letters A     Hybrid Journal   (Followers: 10)
Physics Letters B     Open Access   (Followers: 2)
Physics of Fluids     Hybrid Journal   (Followers: 24)
Physics of Life Reviews     Hybrid Journal   (Followers: 1)
Physics of Plasmas     Hybrid Journal   (Followers: 6)
Physics of the Dark Universe     Open Access  
Physics of the Solid State     Hybrid Journal   (Followers: 3)
Physics of Wave Phenomena     Hybrid Journal   (Followers: 1)
Physics Procedia     Partially Free   (Followers: 1)
Physics Reports     Full-text available via subscription   (Followers: 1)
Physics Research International     Open Access   (Followers: 1)
Physics Today     Hybrid Journal   (Followers: 19)
Physics World     Full-text available via subscription   (Followers: 3)
Physics-Uspekhi     Full-text available via subscription  
Physik in unserer Zeit     Hybrid Journal  
Physik Journal     Hybrid Journal  
Plasma Physics and Controlled Fusion     Hybrid Journal   (Followers: 2)
Plasma Physics Reports     Hybrid Journal   (Followers: 2)
Pramana     Open Access   (Followers: 9)
Preview     Hybrid Journal  
Proceedings of the National Academy of Sciences     Full-text available via subscription   (Followers: 436)
Proceedings of the National Academy of Sciences, India Section A     Hybrid Journal   (Followers: 3)
Progress in Materials Science     Hybrid Journal   (Followers: 18)
Progress in Planning     Hybrid Journal   (Followers: 1)
Progress of Theoretical and Experimental Physics     Open Access  
Quantum Electronics     Full-text available via subscription   (Followers: 2)
Quantum Measurements and Quantum Metrology     Open Access  
Quarterly Journal of Mechanics and Applied Mathematics     Hybrid Journal   (Followers: 3)
Radiation Effects and Defects in Solids     Hybrid Journal   (Followers: 1)
Radiation Measurements     Hybrid Journal   (Followers: 2)
Radiation Physics and Chemistry     Hybrid Journal   (Followers: 1)
Radiation Protection Dosimetry     Hybrid Journal   (Followers: 2)
Radiation Research     Full-text available via subscription   (Followers: 2)
Radio Science     Full-text available via subscription   (Followers: 3)
Radiological Physics and Technology     Hybrid Journal   (Followers: 1)
Reflets de la physique     Full-text available via subscription  
Reports on Mathematical Physics     Full-text available via subscription  
Reports on Progress in Physics     Full-text available via subscription   (Followers: 2)
Research & Reviews : Journal of Physics     Full-text available via subscription  
Research in Drama Education     Hybrid Journal   (Followers: 9)
Research Journal of Physics     Open Access  
Results in Physics     Open Access   (Followers: 1)
Reviews in Mathematical Physics     Hybrid Journal  
Reviews of Accelerator Science and Technology     Hybrid Journal  
Reviews of Geophysics     Full-text available via subscription   (Followers: 19)
Reviews of Modern Physics     Full-text available via subscription   (Followers: 16)
Revista Colombiana de Física     Open Access  
Revista Mexicana de Astronomía y Astrofísica     Open Access  
Revista Mexicana de Física     Open Access  
Revista mexicana de física E     Open Access  
Rheologica Acta     Hybrid Journal   (Followers: 3)
Russian Journal of Mathematical Physics     Hybrid Journal  
Russian Journal of Nondestructive Testing     Hybrid Journal   (Followers: 1)
Russian Physics Journal     Hybrid Journal  
Samuel Beckett Today/Aujourd'hui     Full-text available via subscription   (Followers: 2)
Science and Technology of Nuclear Installations     Open Access   (Followers: 1)
Science China : Physics, Mechanics & Astronomy     Full-text available via subscription  
Science China Physics, Mechanics and Astronomy     Hybrid Journal   (Followers: 1)
Science Foundation in China     Full-text available via subscription   (Followers: 2)
Scientific Journal of Physical Science     Open Access  
Scientific Reports     Open Access   (Followers: 11)
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of     Hybrid Journal   (Followers: 16)
Sensor Letters     Full-text available via subscription   (Followers: 1)
Sensors and Actuators A: Physical     Hybrid Journal   (Followers: 28)
Services Computing, IEEE Transactions on     Hybrid Journal   (Followers: 3)
Shock and Vibration     Hybrid Journal   (Followers: 7)
Shock Waves     Hybrid Journal   (Followers: 4)
Small     Hybrid Journal   (Followers: 8)
Software Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 20)
Solid State Physics     Full-text available via subscription  
Solid-State Circuits Magazine, IEEE     Hybrid Journal   (Followers: 1)
South African Journal for Research in Sport, Physical Education and Recreation     Full-text available via subscription   (Followers: 3)
Space Research Journal     Open Access   (Followers: 2)
Space Weather     Full-text available via subscription   (Followers: 3)
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy     Hybrid Journal   (Followers: 7)
Spectrochimica Acta Part B: Atomic Spectroscopy     Hybrid Journal   (Followers: 4)
Spectroscopy     Hybrid Journal   (Followers: 3)
Spectroscopy Letters: An International Journal for Rapid Communication     Hybrid Journal   (Followers: 3)
Sri Lankan Journal of Physics     Open Access  
Strain     Hybrid Journal   (Followers: 2)

  First | 1 2 3 4 5 6 | Last

Journal Cover Physics and Chemistry of the Earth, Parts A/B/C
   Journal TOC RSS feeds Export to Zotero [5 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1474-7065
     Published by Elsevier Homepage  [2570 journals]   [SJR: 0.423]   [H-I: 36]
  • Preparation of SPE hybrid mesoporous silica sorbents for the analysis and
           removal of organic pollutants in water
    • Abstract: Publication date: Available online 12 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): D.T. Maiga , T.A.M. Msagati , K.F. Kilulya , B.B. Mamba
      Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants that threaten the health of humans and the environment. PAHs are found naturally in the environment but they can also be man-made. PAHs are produced when products like coal, oil, gas, and garbage are burned in an incomplete burning process. PAH’s can be introduced into water bodies in several ways including industrial, domestic and commercial effluents, sewage, agricultural runoff and wastes. Monitoring of PAH’s in water is of great importance because of their mutagenic and carcinogenic properties. The aim of this study was to develop the hybrid mesoporous silica sorbents for the analysis and removal of organic pollutants (OPs) in water especially PAH’s. The determination of PAHs was performed using gas chromatography coupled to time of flight mass spectrometry (GCxGC-TOFMS). The hybrid materials were successfully synthesized using silica gel as a source of silica followed by modification with organic compounds. However the performance of the materials was evaluated using GCxGC-TOFMS for the determination of recovery PAH’s concentrations. At optimum conditions sorbent materials were able to remove 95.9±12.21% of the PAHs in spiked water samples at a laboratory scale.

      PubDate: 2014-10-13T00:40:06Z
  • Synthesis and application of reduced graphene oxide and molecularly
           imprinted polymers composite in a chemo-sensor for trichloroacetic acid
           detection in aqueous solution
    • Abstract: Publication date: Available online 8 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Rose W. Kibechu , Messai A. Mamo , Titus A.M. Msagati , S. Sampath , Bhekie B. Mamba
      This work presents the fabrication of a simple, cheap and fast thin film chemo sensor for detection of trichloroacetic acid (TCAA) in aqueous solutions. Reduced graphene oxide (RGO) based molecular imprinted polymers (MIP) chemo-sensor has been developed. The recognition of TCAA was achieved by imprinted polymers synthesized by copolymerization of 4-vinylpyridine (4-VP) and a crosslinking monomer ethylene glycol dimethacrylate (EDGMA) in acetonitrile using bulk polymerization method. Adsorption studies to determine the rebinding properties of the MIP with the template were conducted using ultra violet visible spectrophotometry (UV-Vis). The imprinted sensor exhibited high recognition ability and affinity for HAA in comparison with the non-imprinted one which was employed as a control, this indicated that the MIP could selectively rebind with TCAA. Reduced graphene oxide (RGO) was used to improve conductivity of the sensor; RGO was obtained from reduction of graphene oxide (GO) synthesized using modified Stauddmer and Hummers method. Polysulphone was used in solution blending of MIP and RGO to form a hybrid which was deposited between two gold plated electrodes by spin coating to form a thin film. The performance of the imprinted sensor was studied using a homemade circuit. The results demonstrate that the sensor based on TCAA-imprinted polymer is fast, cheap and sensitive screening method of TCAA in drinking water.

      PubDate: 2014-10-12T00:34:18Z
  • Analysis of Water Stable Isotopes fingerprinting to inform conservation
           management : Lake Urema Wetland System, Mozambique
    • Abstract: Publication date: Available online 2 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Franziska Steinbruch , Stephan M. Weise
      The present study focusses on the analysis of water stable isotopes to contribute to understanding the hydrology of the Lake Urema wetland system in central Mozambique towards conservation management. Lake Urema Wetland is located in the Gorongosa National Park at the southernmost extent of the East African Rift System and is situated entirely within the Urema catchment. Of particular concern to the park’s management is the understanding of hydrological processes as these may trigger transformations of ecosystems, habitat losses and wildlife migrations. Concerns over the Lake Urema wetland’s drying up and the trapping of sediments in the floodplain have been raised for some time by conservationists. Water samples were collected for stable water isotope analyses during the wet and the dry seasons for the period 2006 to 2010 from springs, boreholes, rivers, and Lake Urema. In addition monthly composite precipitation was collected at two rain gauges. The results show that Lake Urema is maintained throughout the dry season merely from water generated during the wet season. It receives water from wet season precipitation and the runoff generated from this precipitation. The water source areas of the lake are the Gorongosa Mountain and the Barue Basement geomorphological units. Consequently, the source of the sediments which have been trapped into the lake and the floodplain has to be identified in these two catchment areas and urgent action is required to rescue the lake. This water body constitutes a groundwater buffer system which supports a unique wetland landscape. The annual inundations’ processes leading to the recharge-drainage cycle in the floodplain are most sensitive to the deposition of sediments, changing hydraulic gradients, and reducing wet season inflows and increasing drainage rates.

      PubDate: 2014-10-02T23:57:57Z
  • The Viability Assessment of Microcystis aeruginosa cells after
           co-culturing with Bacillus mycoides B16 Using Flow Cytometry
    • Abstract: Publication date: Available online 2 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): JR Gumbo , TE Cloete , GJJ van Zyl , JEM Sommerville
      Microcystis aeruginosa is the dominate cyanobacteria in freshwater bodies causing proliferation of toxic harmful algal blooms (HABs), worldwide. Thus a biological control method based on predatory bacteria is an alternative environmental solution to the control of these HABs, A Flow cytometric technique was used to assess the viability of Microcystis spp cells after deliberate co-culturing with a predatory bacterium, Bacillus mycoides B16. Under static conditions, B. mycoides had a lytic effect on Microcystis cells that resulted in a significant (p = 0.0000) population decline of 97% in six days. In contrast under turbulent conditions, B. mycoides had a lytic effect on Microcystis spp cells resulting in a significant (df = 5; t = -7.21; p= 0.0003) population decrease of 85% in the same time period. The Levene test also showed a significant (p = 0.0003) decrease in Microcystis cell numbers, which also coincided with a significant (t = 11.31; p = 0.0001) increase in B. mycoides cell numbers. This suggested that B. mycoides, a heterotroph, was utilizing the Microcystis as a source of nutrition. The effect of agitation may have contributed to the delay in cell lysis as it disturbed the physical contact between the predator and prey. The control samples showed a significant (df = 5; t = + 6.86; p = 0.0010) increase in Microcystis spp cell numbers. B. mycoides was able to lyse Microcystis spp cells under these conditions and may thus be considered as a potential biological control agent for the management of Microcystis spp harmful algal blooms.

      PubDate: 2014-10-02T23:57:57Z
  • Streamflow variation due to glacier melting and climate change in upstream
           Heihe River Basin, Northwest China
    • Abstract: Publication date: Available online 18 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Feng Wu , Jinyan Zhan , Zhan Wang , Qian Zhang
      Streamflow simulation is often challenging in mountainous watersheds because of incomplete hydrological models, irregular topography, immeasurable snowpack or glacier, and low data resolution. In this study, a semi-distributed conceptual hydrological model (SWAT-Soil Water Assessment Tool) coupled with a glacier melting algorithm was applied to investigate the sensitivity of streamflow to climatic and glacial changes in the upstream Heihe River Basin. The glacier mass balance was calculated at daily time-step using a distributed temperature-index melting and accumulation algorithm embedded in the SWAT model. Specifically, the model was calibrated and validated using daily streamflow data measured at Yingluoxia Hydrological Station and decadal ice volume changes derived from survey maps and remote sensing images between 1960 and 2010. This study highlights the effects of glacier melting on streamflow and their future changes in the mountainous watersheds. We simulate the contribution of glacier melting to streamflow change under different scenarios of climate changes in terms of temperature and precipitation dynamics. The rising temperature positively contributed to streamflow due to the increase of snowmelt and glacier melting. The rising precipitation directly contributes to streamflow and it contributed more to streamflow than the rising temperature. The results show that glacial meltwater has contributed about 3.25 billion m3 to streamflow during 1960-2010. However, the depth of runoff within the watershed increased by about 2.3 mm due to the release of water from glacial storage to supply the intensified evapotranspiration and infiltration. The simulation results indicate that the glacier made about 8.9% contribution to streamflow in 2010. The research approach used in this study is feasible to estimate the glacial contribution to streamflow in other similar mountainous watersheds elsewhere.

      PubDate: 2014-09-21T23:07:48Z
  • Streamflow forecasting for operational water management in the Incomati
           River Basin, Southern Africa
    • Abstract: Publication date: Available online 18 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): R.K.M. Sunday , I. Masih , M. Werner , P. van der Zaag
      If the future availability of water is uncertain to water managers, dam operators and water users, then an effective allocation among competing uses can be difficult. The difficulties can partly be alleviated by including streamflow forecasting as a tool for informed decision making. The Incomati basin in Southern Africa frequently experiences water shortages, and here streamflow forecasting can contribute to an improved water management. This paper explores the skill of streamflow forecasting and its usefulness in decision making in the Incomati basin. The study applies correlation and regression methods to forecast streamflow, and standard verification scores to evaluate the skill of the forecasts. Suitable statistical forecasting techniques were analysed and tested. The data used for forecasting include Sea Surface Temperature (SST), El Niño Southern Oscillation (ENSO), rainfall and streamflow. Results show that there is some scope for streamflow forecasting that can support water management decision making in the basin. The rainfall and streamflow of the previous months and/or season can be used to predict the streamflow in the next month and/or season with reasonable to good results. Results obtained during low flow periods (May-September) were found to be better than those obtained for the high flow periods (October-April). However, inclusion of ENSO and/or SST as an explanatory variable enhanced forecast skill, particularly during high flow periods. Forecasts were conducted for streamflow being in the below normal, above normal or normal terciles, with the forecasts for the extremes found to have better skill than forecast for the sreamflow being in the normal tercile. Forecasts for low flows demonstrated the best skills, with these being of most use to the allocation of the scarce water resources.

      PubDate: 2014-09-21T23:07:48Z
  • Quality of Drinking Water and Cholera prevalence in Ndirande Township,
           City of Blantyre, Malawi
    • Abstract: Publication date: Available online 18 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): John F. Kamanula , Omega J. Zambasa , Wellington R.L. Masamba
      Scarcity of safe drinking water is a big problem in Ndirande Township, City of Blantyre. Consequently, residents use unsafe sources of drinking water other than the potable water provided by Blantyre Water Board (BWB). This study was conducted from November 2007 to April 2008 to assess the quality of drinking water and cholera prevalence in Makata, Chinseu, Golio, Safalao and Newlines, in Ndirande Township. A survey using semi-structured questionnaire was conducted to gather information on the sources of drinking water and prevalence of cholera in the Township. Data on cholera cases and number of deaths in Ndirande Township which occurred between November 2007 and April 2008 was sourced from Ndirande Health Centre in Blantyre City. Water samples were collected from unprotected shallow wells, boreholes and taps and analysed for Escherichia coli, metals and non-metals. Data was analysed for pH, turbidity, total dissolved solids, sulphate, phosphate, nitrate, hardness, chloride, chromium, lead, cadmium, iron, sodium and potassium. Results showed that 85% of 150 respondents drink water from shallow wells, rain water and boreholes in addition to treated water provided by BWB. Only 15% of the respondents get water from BWB without supplementation from the other sources. Forty percent of the respondents indicated that they did not treat their water before consumption. Cholera cases (176), were prevalent throughout the study period with highest number (85) recorded in December 2007. Two deaths were recorded in November 2007. Over 80% of water samples from shall wells and boreholes contained E. coli. Concentrations of total dissolved solids, sulphates, sodium, potassium, lead, cadmium and chromium in all water samples were within the acceptable limits by World Health Organisation (WHO) and Malawi Bureau of Standards (MBS). Based on the results of this study, water from boreholes and shallow wells was heavily polluted with faecal matter, and therefore, not suitable for human consumption. Use of water disinfectants to treat well and borehole waters in the study area should be intensified. Furthermore, research on use of solar radiation to disinfect untreated water and use of plant materials, for example, Moringa oleifera seed kernel to clarify water should be investigated.

      PubDate: 2014-09-21T23:07:48Z
  • Efficiency of a constructed wetland in removing microbial contaminants
           from pre-treated municipal wastewater
    • Abstract: Publication date: Available online 17 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): H.J. Kipasika , J. Buza , Beatus Lyimo , W.A. Miller , K.N. Njau
      In most capital towns, urban wastewater discharging into environment is highly enriched in a wide range of microbial contaminants, thus threatening people’s health and the quality of the receiving basin water and other water for reuse. This study focused on evaluating the efficiency of the removal of faecal coliform indicator bacteria and salmonella spp. by Moshi Municipal urban wastewater treatment system composed of a constructed wetland (CW) system and waste stabilization ponds (WSP) operating in parallel. The CW system is a sub-surface flow type designed in the year 2002 for treating effluent from the second maturation pond of the treatment system. The study considered faecal coliform data taken in 2009 and 2012 and both salmonella and faecal coliform data taken in 2013 and 2014. Data generated monthly in 2009 and 2012 showed high variations in faecal coliform removal with a mean efficiency of less than 60 percent. The levels of faecal coliform from both the CW and the last maturation pond were below the acceptable limit. However, a similar investigation done in 2013 and 2014 on the removal of specific pathogen – salmonella spp. showed that the CW is discharging significantly higher amount of salmonella spp. than the maturation system. The treated wastewater is currently used for paddy farming, in this way exposing people to health risks. The results highlight the necessity for improving the system monitoring and also the management taking into consideration the end users of effluent water.

      PubDate: 2014-09-17T22:53:21Z
  • Benchmarking land use change impacts on direct runoff in ungauged urban
    • Abstract: Publication date: Available online 14 August 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Hasan Ozdemir , Emre Elbaşı
      This paper describes the results of benchmark testing of land use change impact on direct runoff using Soil Conservation Service –Curve Number (SCS-CN) model in two ungauged neighbouring urban watersheds (Çınar and Kadıyakuplu) in Istanbul, Turkey. To examine this impact, the model was applied to daily rainfall data using three different dated (1982, 1996 and 2012) hydrological soil groups and land use of the two ungauged urban watersheds. Finally, the impact of land use change and model performance were evaluated with the rainfall-runoff regression, the coefficient of determination and the NSE test using benchmark runoff data based on 1982 land use conditions. The results of the analysis indicate that the changing of land use types from natural surfaces to impervious surfaces has a significant impact on surface runoff. Additionally, remarkable spatial variations of the land use changes and their impact on the runoff in 1996 and 2012 were more detected in the Çınar watershed compared with the Kadıyakuplu watershed. The planning decision on land use of the watersheds, has vital role in these differences. The results of this research also reveal that change to intensive land use in urban watersheds has a significantly larger impact on runoff generation than those rainfall.

      PubDate: 2014-08-16T20:15:43Z
  • Preconcentration and spectrophotometric determination of polyDADMAC in
           treated water by insitu co-precipitation with naphthalene
    • Abstract: Publication date: Available online 27 July 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Isaac W. Mwangi , J. Catherine Ngila , Patrick Ndungu , T. Msagati
      Polydiallyldimethylammonium chloride (polyDADMAC) is a water-soluble cationic polyelectrolyte used as a flocculant in water treatment works. Unreacted traces in water react with chlorine to produce a carcinogenic compound during the disinfectation process. This study reports on a preconcentration procedure and spectrophotometric determination of polyDADMAC at trace levels in treated water by insitu co-precipitation with naphthalene with a view to come up with an analytical tool that will be used by water works to routinely monitor the polycation in an effort to supply safe water to consumers. Preconcentration of polyDADMAC polyelectrolyte in water at trace levels was achieved by co-precipitating the polyelectrolyte with naphthalene. This resulted in the formation of a water insoluble adsorbent with a high affinity for azo dyes. The formation of this material was based on multilayer assembly of organic polyelectrolyte systems resulting to multilayers through a layer-by-layer self-assembly process. The co-precipitate was formed by mixing aqueous solutions containing varying concentrations of polyDADMAC with different volumes of solutions containing 0.75 g of naphthalene dissolved in acetone. The resulting respective precipitates were packed in different glass columns and a solution of the dye was eluted through each column. The contents of each column were then dissolved in 10 mL of dimethylformamide (DMF) and the absorbance readings of the resulting solutions recorded. The wavelength of maximum absorption was found to be 540 nm at pH 12.0. A linear calibration for polyDADMAC solutions was obtained with a correlation coefficient of 0.976. The detection limit was found to be 1.90 x 10-4 μg mL-1 and the method was applied to determine the concentration of polyDADMAC residue in treated water.

      PubDate: 2014-07-28T18:58:27Z
  • Mechanisms and modelling of waste-cement and cement-host rock interactions
    • Abstract: Publication date: 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 70–71
      Author(s): Diederik Jacques , Barbara Lothenbach , Erich Wieland

      PubDate: 2014-06-18T15:59:57Z
  • Implementing water science research to benefit all
    • Abstract: Publication date: 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 67–69
      Author(s): Hodson Makurira , Benjamin Mapani , Dominic Mazvimavi , Marloes Mul , Barbara Tapela , Victor Wepener

      PubDate: 2014-06-18T15:59:57Z
  • Radial diffusion of radiocaesium and radioiodide through cementitious
    • Abstract: Publication date: Available online 21 April 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M. Felipe-Sotelo , J. Hinchliff , D. Drury , N. Evans , S. Williams , D. Read
      The function of the backfill material in a geological disposal facility (GDF) is to chemically condition the environment of the near field and thereby chemically retard the transport of the radionuclides present in the waste. This function of the backfill material is usually referred to as chemical containment. Diffusion experiments are being carried out over periods up to four years to assess the diffusion of Cs, Ni, Eu, Th, U and I (as I-) through Nirex Reference Vault Backfill (NRVB). The method uses cylinders of NRVB (40 mm diameter, 40-45 mm height) which can be doped via a central well with the radionuclides of interest. Diffusion occurs radially into a surrounding solution already pre-equilibrated with the cement. This paper shows the results obtained during the first two years for experiments undertaken using 137Cs and 125I- tracers with and without carrier. Comparison is made to tritiated water under identical experimental conditions. Breakthrough of Cs and I- occurred within the first week of the experiments, reaching steady state in the surrounding solution after 20 to 50 days. The maximum concentrations expected from the original inventories based on a simple dilution calculation have not been reached, indicating that retention in the matrix has occurred; ranging from 10% to 40% for Cs, and up to 50% for I-. Corresponding experiments using a solution containing cellulose degradation products (CDP) showed an increased diffusion for both Cs and I. Migration profiles have been obtained and the relative retention of each radionuclide has been confirmed using digital autoradiography. The results indicate that, for both isotopes, migration occurs through the cement matrix rather than through microfissures. However, whereas Cs is homogeneously distributed within the blocks, there is evidence of zones of preferential I- accumulation even where concentrations in solution have reached steady state. Transport modelling using GoldSim has replicated experimental observations, producing comparable partition ratios (Rd) to those reported in the literature.

      PubDate: 2014-04-29T06:45:15Z
  • Constraints from sulfur isotopes on the origin of gypsum at
           concrete/claystone interfaces
    • Abstract: Publication date: Available online 4 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Catherine Lerouge , Francis Claret , Christophe Tournassat , Sylvain Grangeon , Stéphane Gaboreau , Bernard Boyer , Daniel Borschnek , Yannick Linard
      Two in situ concrete/claystone interfaces were sampled at the laboratory level in the Andra Meuse/Haute Marne (France) Underground Research Laboratory (URL) in order to study five years of interactions between Callovian–Oxfordian (COx) claystone and two cementitious materials (concrete bottom slab and shotcrete on the walls of the main gallery), with a specific focus on sulfur. Combined mineralogical, chemical and sulfur isotopic investigations were carried out to define the degree of the perturbation of the sulfur system in the claystone and in both the cementitious materials. At both interfaces, results show that the main perturbation on the claystone side is the formation of scarce μm-sized gypsum, the sulfur content of which is essentially derived from pyrite oxidation. The distribution of gypsum is highly correlated with the fissure network of the damaged zone due to excavation of the gallery. Its presence is also often associated with a loss of cohesion of the concrete/claystone interface. Due to the small amounts of gypsum and its μm-size, measurements were performed by ion microprobe. Adaptations were needed on account of the reactivity of gypsum and sulfates in general under the beam. The use of ion microprobe analysis provided evidence of high local isotopic heterogeneity that could be attributed to kinetic fractionation effects. Some analyses suggest a minor contribution of dissolved sulfates in pore water of claystone and possibly of concrete. The perturbation on the concrete side is marked by a significant increase in the bulk sulfur content within three millimeters of the interface with the claystone, showing a sulfur gradient from claystone to concrete. The main objective of this work was to define the extent of the chemical and mineralogical perturbations, taking into account in situ URL conditions, i.e. hydrodynamic conditions (shotcrete sprayed on the gallery walls and subjected to ventilation of the galleries), damaged zone of claystone induced by excavation and multi-scale heterogeneity. This identifies the relevant parameters to better constrain predictive reactive transport models of concrete/claystone interactions at a realistic scale.

      PubDate: 2014-04-29T06:45:15Z
  • Estimation of design floods in ungauged catchments using a regional index
           flood method. A case study of Lake Victoria Basin in Kenya
    • Abstract: Publication date: Available online 20 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Joel Nobert , Margaret Mugo , Hussein Gadain
      Reliable estimation of flood magnitudes corresponding to required return periods, vital for structural design purposes, is impacted by lack of hydrological data in the study area of Lake Victoria Basin in Kenya. Use of regional information, derived from data at gauged sites and regionalized for use at any location within a homogenous region, would improve the reliability of the design flood estimation. Therefore, the regional index flood method has been applied. Based on data from 14 gauged sites, a delineation of the basin into two homogenous regions was achieved using elevation variation (90-m DEM), spatial annual rainfall pattern and Principal Component Analysis of seasonal rainfall patterns (from 94 rainfall stations). At site annual maximum series were modelled using the Log normal (LN) (3P), Log Logistic Distribution (LLG), Generalized Extreme Value (GEV) and Log Pearson Type 3 (LP3) distributions. The parameters of the distributions were estimated using the method of probability weighted moments. Goodness of fit tests were applied and the GEV was identified as the most appropriate model for each site. Based on the GEV model, flood quantiles were estimated and regional frequency curves derived from the averaged at site growth curves. Using the least squares regression method, relationships were developed between the index flood, which is defined as the Mean Annual Flood (MAF) and catchment characteristics. The relationships indicated area, mean annual rainfall and altitude were the three significant variables that greatly influence the index flood. Thereafter, estimates of flood magnitudes in ungauged catchments within a homogenous region were estimated from the derived equations for index flood and quantiles from the regional curves. These estimates will improve flood risk estimation and to support water management and engineering decisions and actions.

      PubDate: 2014-04-29T06:45:15Z
  • Connectivity influences on nutrient and sediment migration in the Wartburg
           catchment, KwaZulu-Natal Province, South Africa
    • Abstract: Publication date: Available online 17 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Kipkemboi J. Kollongei , Simon A. Lorentz
      Non-point-source (NPS) pollution of surface and groundwater by sediment and nutrient loads emanating from agricultural catchments is a prominent environmental issue, with major consequences on water supply and aquatic ecosystem quality. The concept of connectivity has proved invaluable in understanding migration of NPS pollutants in catchments. Observations of sediments or suspended solids (SS), nitrate (NO3) and phosphorous (P) fluxes alongside stable water isotope sampling were made on a nested basis at field and catchment (41km2) scales for a series of events in the Wartburg catchment, South Africa. The nested catchment scale sampling was focused on control features in the stream network, including road crossings, farm dams and wetland zones. The analyzed stable water (δ18O and δ2H) isotopes results were used to interpret the connectivity of the contributing land forms and the stream network. The results reveal the dominant influences of farm dams and wetlands in limiting the downstream migration of sediment and nutrients for all but the most intense events. Certain events resulted in mixing in the dams and larger resultant outflow than inflow loads. These occurrences appear to be as a result of combinations of reservoir status, catchment antecedent conditions and rainfall depth and intensity. The nutrients loads between Bridge 1 and Bridge 2 stations reflect the bedrock control, where contributions from sugar cane hillslopes between these stations are not retained, even in the short wetland upstream of Bridge 2. Isotope analyses reveal that the headwaters, comprising 70% of the catchment area, contribute as little as 29% of the total catchment discharge, due to impoundments in this area. However, this contribution varies significantly for different events, reaching a maximum of 78% of the catchment discharge. It can therefore be concluded that nutrients and sediment migration in the Wartburg catchment is greatly influenced by connectivity. The δ18O and δ2H water isotopes can be used to assess the contributions of different sources of water which impact the transport of nutrients and sediments in catchments.

      PubDate: 2014-04-29T06:45:15Z
  • Exploring the effectiveness of sustainable water management structures in
           the Upper Pungwe river basin
    • Abstract: Publication date: Available online 1 March 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): B. Nyikadzino , P. Chibisa , H. Makurira
      The study endeavoured to assess the effectiveness of stakeholder structures and their participation in sustainable water resources management in the Upper Pungwe river basin shared by Zimbabwe and Mozambique. The study sought to assess the level and effectiveness of stakeholder, gender and the vulnerable groups representation in sustainable water resources management as well as the whole stakeholder participation process. The study employed both qualitative and quantitative methods for data collection and analysis. Sampling data was obtained from 15 stakeholder representatives (councillors) constituting Pungwe Subcatchment Council, 30 water users ranging from small scale to large scale users and professionals in water resources management. Two different questionnaires and three structured interviews were administered during the study. Water permit database, financial reports and other source documents were also analysed. The study established that the sustainability and effectiveness of stakeholder structures and their participation in water resources management is being compromised by lack of stakeholder awareness. Water utilisation is very high in the subcatchment (99%) while women participation is still low (20%). The study therefore recommends the use of quotas for the participation of women in stakeholder structures. Stakeholder structures are encouraged to intensify stakeholder awareness on issues of river protection, efficient water use and pollution control. Further research is recommended to be carried out on the effectiveness of stakeholder structures in combating water pollution and enhancing river protection.

      PubDate: 2014-04-29T06:45:15Z
  • Potential of weight of evidence modelling for gully erosion hazard
           assessment in Mbire District – Zimbabwe
    • Abstract: Publication date: Available online 28 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): F. Dube , I. Nhapi , A. Murwira , W. Gumindoga , J. Goldin , D.A. Mashauri
      Gully erosion is an environmental concern particularly in areas where landcover has been modified by human activities. This study assessed the extent to which the potential of gully erosion could be successfully modelled as a function of seven environmental factors (landcover, soil type, distance from river, distance from road, Sediment Transport Index (STI), Stream Power Index (SPI) and Wetness Index (WI)) using a GIS-based Weight of Evidence Modelling (WEM) in the Mbire District of Zimbabwe. Results show that out of the studied seven factors affecting gully erosion, five were significantly correlated (p <0.05) to gully occurrence, namely; landcover, soil type, distance from river, STI and SPI. Two factors; WI and distance from road were not significantly correlated to gully occurrence (p >0.05). A gully erosion hazard map showed that 78% of the very high hazard class area is within a distance of 250m from rivers. Model validation indicated that 70% of the validation set of gullies were in the high hazard and very high hazard class. The resulting map of areas susceptible to gully erosion has a prediction accuracy of 67.8%. The predictive capability of the weight of evidence model in this study suggests that landcover, soil type, distance from river, STI and SPI are useful in creating a gully erosion hazard map but may not be sufficient to produce a valid map of gully erosion hazard.

      PubDate: 2014-04-29T06:45:15Z
  • Characterization and radionuclide retention properties of heat-treated
    • Abstract: Publication date: Available online 3 March 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): B. Kienzler , C. Borkel , N. Finck , S. Heck , S. Hilpp , M. Schlieker , V. Metz , M. Plaschke , E. Soballa , T. Cron , A. Miassoedov
      This study was performed to obtain insight into the characteristics of contaminated cementitious materials which may result from a light water reactor core melt down accident. Such material arose in a huge amount from the Fukushima disaster. We analyzed the elemental and mineralogical composition of similar, heat-treated material and investigated its radionuclide retention properties. We present the radionuclide retention properties of concrete samples which originally were part of an experiment using a thick-walled concrete recipient that had been heated by simulating a reactor melt down. Batch sorption experiments have been performed with the elements Cs(I), Co(II), and Eu(III) in seawater under aerobic conditions. Sorption coefficients were measured: Rs (Eu) ∼5800mlg−1 and Rs (Co) ∼110mlg−1. A tentative value for Cs was determined, adulterated by the relatively high release of Cs from the concrete itself.

      PubDate: 2014-04-29T06:45:15Z
  • A versatile pore-scale multicomponent reactive transport approach based on
           lattice Boltzmann method: Application to portlandite dissolution
    • Abstract: Publication date: Available online 13 April 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Ravi A. Patel , Janez Perko , Diederik Jacques , Geert De Schutter , Klaas Van Breugel , Guang Ye
      A versatile lattice Boltzmann (LB) based pore-scale multicomponent reactive transport approach is presented in this paper. This approach is intended to capture mineral phase and pore structure evolution resulting from geochemical interactions applicable, for example to model microstructural evolution of hardened cement paste during chemical degradation. In the proposed approach heterogeneous reactions are conceptualized as pseudo-homogenous (volumetric) reactions by introducing an additional source term in the fluid node located at the interface adjacent to a solid node, and not as flux boundaries as used in previously proposed approaches. This allows a complete decoupling of transport and reaction computations, thus different reaction systems can be introduced within the LB framework through coupling with external geochemical codes. A systematic framework for coupling an external geochemical code with the LB including pore geometry evolution is presented, with the generic geochemical code PHREEQC as an example. The developed approach is validated with a set of benchmarks. A first example demonstrates the ability of the developed approach to capture the influence of pH on average portlandite dissolution rate and surface evolution. This example is further extended to illustrate the influence of reactive surface area and spatial arrangement of mineral grains on average dissolution rate. It was demonstrated that both location of mineral grains and surface area play a crucial role in determining average dissolution rate and pore structure evolution.

      PubDate: 2014-04-29T06:45:15Z
  • Competition behaviour of metal uptake in cementitious systems: An XRD and
           EXAFS investigation of Nd- and Zn-loaded 11 Å tobermorite
    • Abstract: Publication date: Available online 23 January 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M. Vespa , R. Dähn , E. Wieland
      Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. Cement is used to condition and stabilize the waste materials and to construct the engineered barrier systems (container, backfill and liner materials) of repositories for radioactive waste. In this study, bulk-X-ray absorption spectroscopy (XAS) was used to investigate the uptake mechanism of Nd on the crystalline C-S-H phase 11 Å tobermorite in the presence of Zn (co-absorbing metal), and vice versa, as potential competitor under strongly alkaline conditions (pH=12.5-13.3). The Zn and Nd concentration in all samples was 50 000 ppm, whereas the reaction times varied from one to six months. Extended X-ray absorption fine structure (EXAFS) data of the Nd LIII-edge indicate that the local structural environment of Nd consists of ∼7-8 O atoms at 2.42 Å, ∼7-8 Si at ∼3.67 Å and ∼5-6 Ca at ∼3.8 Å, and that this environment remains unchanged in the presence and absence of Zn. In contrary, Zn K-edge EXAFS data exhibit distinct differences in the presence and absence of Nd as co-absorbing element. Data analysis indicates that Zn is tetrahedrally coordinated (∼ 4 O at ∼1.96 Å) and the obtained structural data in the simultaneous presence of Nd and Zn are consistent with the formation of mixed Zn surface complexes and Zn bound in the interlayer remaining in these positions also with prolonged reaction times (up to 6 months). However, without the co-absorbing element Nd, strong structural changes in the uptake mechanisms of Zn are observable, e.g., after 3 month reaction time Zn-Zn backscattering pairs can be observed. These findings suggest that Nd has an influence on the incorporation of Zn in the tobermorite structure. In addition, the results of this study indicate that competitive uptake of metal cations with similar sorption behaviour by C-S-H phases can take place, deserving further attention in future assessments of the safe disposal of radioactive wastes in cement-based repositories.

      PubDate: 2014-01-24T10:11:25Z
  • Docking 90Sr Radionuclide in Cement: An Atomistic Modeling Study
    • Abstract: Publication date: Available online 16 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Mostafa Youssef , Roland J.-M. Pellenq , Bilge Yildiz
      Cementitious materials are considered to be a waste form for the ultimate disposal of radioactive materials in geological repositories. We investigated by means of atomistic simulations the encapsulation of strontium-90, an important radionuclide, in calcium-silicate-hydrate (C-S-H) and its crystalline analogue, the 9 Å-tobermorite. C-S-H is the major binding phase of cement. Strontium was shown to energetically favor substituting calcium in the interlayer sites in C-S-H and 9 Å-tobermorite with the trend more pronounced in the latter. The integrity of the silicate chains in both cementitious waste forms were not affected by strontium substitution within the time span of molecular dynamics simulation. Finally, we observed a limited degradation of the mechanical properties in the strontium-containing cementitious waste form with the increasing strontium concentration. These results suggest the cement hydrate as a good candidate for immobilizing radioactive strontium.
      Graphical abstract image Highlights

      PubDate: 2013-12-19T08:39:42Z
  • Conceptual Model Analysis of Interaction at a Concrete – Boom Clay
    • Abstract: Publication date: Available online 13 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Sanheng Liu , Diederik Jacques , Joan Govaerts , Lian Wang
      In many concepts for deep disposal of high-level radioactive waste, cementitious materials are used in the engineered barriers. For example, in Belgium theengineered barrier system is based ona considerable amount of cementitious materials as buffer and backfill in the so-called supercontainer embedded in the hosting geological formation. A potential hosting formation is Boom Clay. Insight in the interaction between the high-pH pore water of the cementitious materials and neutral-pH Boom Clay pore water is required. Two problems are quite common for modeling of such a system. The first one is the computational cost due to the long timescale model assessments envisaged for the deep disposal system. Also a very fine grid (in sub-millimeter), especially at interfaces has to be used in order to accurately predict the evolution of the system. The second one is whether to use equilibrium or kinetic reaction models. The objectives of this paper are twofold. First, we develop an efficient coupled reactive transport code for this diffusion-dominated system by making full use of multi-processors/cores computers. Second, we investigate how sensitive the system is to chemical reaction models especially when pore clogging due to mineral precipitation is considered within the cementitious system. To do this, we selected two portlandite dissolution models, i.e., equilibrium (fastest) and diffusion-controlled model with precipitation of a calcite layer around portlandite particles (diffusion-controlled dissolution). The results show that with shrinking core model portlandite dissolution and calcite precipitation are much slower than with the equilibrium model. Also diffusion-controlled dissolution smooths out dissolution fronts compared to the equilibrium model. However, only a slight difference with respect to the clogging time can be found even though we use a very small diffusion coefficient (10-20 m2/s) in the precipitated calcite layer.

      PubDate: 2013-12-15T03:31:45Z
  • OpenGeoSys-Gem: A numerical tool for calculating geochemical and porosity
           changes in saturated and partially saturated media
    • Abstract: Publication date: Available online 8 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Georg Kosakowski , Norihiro Watanabe
      Reactive transport codes that use a Gibbs Energy Minimization (GEM) to solve chemical equilibria are uncommon. We present a new coupling of the Richards flow module of the Finite Element (FE) based OpenGeoSys code with the GEM based chemical solver GEMS3K. The coupled code is highly parallelized using an overlapping domain decomposition approach in combination with execution of multiple threads that solve chemical equilibria in parallel. FE reactive transport schemes are often affected by spurious concentration oscillations. We effectively suppress these oscillations with a linearized algebraic flux corrected transport (FCT) algorithm. An application example is presented which investigates the evolution of material interfaces in a deep geological repository for nuclear waste. The example uses all features of the new coupled code: flow and multi-component transport in variably saturated media, and a very complex chemical setup which makes extensive use of (non-linear) solid solution formulations for mineral phases.

      PubDate: 2013-12-11T07:49:59Z
  • Combining thermodynamic simulations, element and surface analytics to
           study U(VI) retention in corroded cement monoliths upon &gt; 20 years
           of leaching
    • Abstract: Publication date: Available online 9 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): C. Bube , V. Metz , D. Schild , J. Rothe , K. Dardenne , M. Lagos , M. Plaschke , B. Kienzler
      Retention or release of radionuclides in a deep geological repository for radioactive wastes strongly depends on the geochemical environment and on the interaction with near-field components, e.g. waste packages and backfill materials. Deep geological disposal in rock salt is one of the concepts considered for cemented low- and intermediate-level wastes. Long-term experiments were performed to observe the evolution of full-scale cemented waste simulates (doped with (NH4)2U2O7) upon reaction with relevant salt brines, e.g. MgCl2-rich and saturated NaCl solutions, and to examine the binding mechanisms of uranium. Throughout the experiments, concentrations of major solution components, uranium and pH values were monitored regularly and compared to thermodynamic equilibrium calculations, which indicate that close-to-equilibrium conditions have been achieved after 13-14 years duration of the leaching experiments. Two of the full-scale cemented waste simulates were recovered from the solutions after 17-18 years and studied by different analytical methods to characterize the solids, especially with respect to uranium incorporation. In drill core fragments of various lateral and horizontal positions of the corroded monoliths, U-rich aggregates were detected and analyzed by means of space-resolved techniques. Raman, μ-XANES and μ-XRD analyses of several aggregates demonstrate that they consist of an amorphous diuranate-type solid. Within error, calculated U solubilities controlled by Na-diuranate (Na2U2O7·H2O) are consistent with measured U concentrations in both, the NaCl and the MgCl2-system. Since uranophane occurs also in the corroded monoliths, it is proposed that a transition towards the thermodynamic equilibrium U(VI) phase is kinetically hindered.

      PubDate: 2013-12-11T07:49:59Z
  • Dissolution kinetics of C-S-H gel. Flow-through experiments
    • Abstract: Publication date: Available online 4 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Ana Trapote-Barreira , Jordi Cama , Josep M. Soler
      C-S-H gel dissolution kinetics was studied by means of flow-through experiments under CO2-free atmosphere at room temperature (23 ± 2 °C). The starting C-S-H gel was obtained by hydration of commercial C3S (3CaO·SiO2) and consisted of 67 wt% C-S-H with a Ca/Si ratio of 1.7 ± 0.1 and 33 wt% portlandite. Based on the changes in aqueous chemistry and in the C-S-H solid, it was observed that the C-S-H gel dissolves incongruently when the Ca/Si ratio is high and congruently as the Ca/Si ratio decreases to the tobermorite stoichiometric Ca/Si ratio of 0.83. First, a dissolution rate law for C-S-H gel with Ca/Si ratio equal to 0.83 is proposed based on the dissolution rates normalized to the final BET surface area. Additionally, reactive transport modeling of the changes in aqueous chemistry allowed the fitting of the rate constants for C-S-H with Ca/Si ratio ranging from 1.7 to 0.83. Solid examination by SEM-EDX and EPMA before and after the experiments showed some variability of the Ca/Si ratios of the analyzed particles, suggesting the existence of compositional domains with variable Ca/Si ratios. 29Si MAS NMR spectra showed an increase in polymerization of the reacted C-S-H, and also the formation of Si-rich domains in some cases, mainly under slow flow conditions. Inhibition of the rates in these cases will have to be further investigated.

      PubDate: 2013-12-07T06:23:02Z
  • Reactive Transport Modelling of Organic Complexing Agents in Cement
           Stabilized Low and Intermediate Level Waste
    • Abstract: Publication date: Available online 28 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Henrik von Schenck , Klas Källström
      The Swedish final repository for short-lived radioactive waste (SFR 1) is located at Forsmark in Sweden. It holds low and intermediate-level operational waste from the Swedish nuclear power plants, as well as industrial, research-related, and medical waste. A variety of low molecular weight organic compounds are present in the waste or in its matrix. Such compounds can also be formed by chemical degradation of organic macromolecules. These organics can ligate to metal atoms forming stable complexes and also adsorb to the surface of cement, thereby influencing the net release of radionuclides from the repository. This motivates the study of the concentration distribution of complexing agents in the repository as a function of time. The following paper reports the results of mass transport modelling, describing the transport of complexing agents through the cementitous matrix in the rock vault for intermediate-level waste in the SFR 1 repository. Nitrilotriacetate (NTA) and isosaccharinate (ISA) have been investigated, where the former is considered to be non-sorbing and non-reacting, while the latter is produced from cellulose degradation and adsorbs strongly to cement. The 3D model considers advection, diffusion, and sorption of solvated species in cement pore water over a time period of 20000 years. The model accounts for the spatial distribution of the flow field in the repository structure and also considers changing groundwater flow during the investigated time period. It is found that 99% of the NTA is removed after approximately 4000 years, while 90% of the ISA is retained in the rock vault after 20000 years. The maximum pore water concentration of ISA is found to be 8.6 mol/m3 after approximately 2300 years, based on the degradation of the deposited amounts of cellulose. Over the investigated time scale, the ligands retained in the repository can redistribute across several waste compartments where the organic compounds were not originally deposited. In the case of ISA this effect is dampened due the influence of sorption.

      PubDate: 2013-12-02T11:22:31Z
  • Application of polysulfone/cyclodextrin mixed-matrix Membranes in the
           removal of natural organic matter from water
    • Abstract: Publication date: Available online 1 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): F.V. Adams , E.N. Nxumalo , R.W.M. Krause , E.M.V. Hoek , B.B. Mamba
      The removal of natural organic matter (NOM) by polysulfone/β-cyclodextrin polyurethane (PSf/ β-CDPU) mixed matrix membranes (MMMs) was investigated in order to establish the effect of the addition of β-cyclodextrin polyurethane (β-CDPU) in polysulfone (PSf) membrane on the rejection of NOM (humic acid) and the fouling resistance of MMMs. It was found that the effective pore sizes and molecular-weight-cut-off (MWCO) of hand-cast PSf membranes were improved by β-CDPU addition due to its large pore size and its conical structure being capable of allowing easy passage of water molecules. An increase in pure water flux was achieved with increase in β-CDPU concentration in the PSf MMMs. Furthermore, the pure water flux of the hand-cast PSf membrane improved from 12 to 137 l/m2h when the applied pressure was increased from 0.62 to 2.41 MPa. The highest NOM removal efficiency achieved was 69% based on TOC measurements whereas a 76% NOM removal efficiency was attained as calculated from UV254 analysis. Fourier transform infrared (FT-IR) spectroscopy analyses confirmed the absence of -OH and -CH groups on all membranes after NOM rejection. This accounted for the increase in contact angle obtained after rejection tests. It is suggested that solution-diffusion mechanism is responsible for NOM filtration/rejection process. In addition, scanning electron microscopy (SEM) micrographs (after NOM rejection tests) revealed that the addition of β-CDPU in PSf resulted in improved antifouling properties based on the agglomeration of NOM on the membrane surfaces.
      Graphical abstract image

      PubDate: 2013-12-02T11:22:31Z
  • Experimental characterization of cement-bentonite interaction using core
           infiltration techniques and 4D computed tomography
    • Abstract: Publication date: Available online 27 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): F. Dolder , U. Mäder , A. Jenni , N. Schwendener
      Deep geological storage of radioactive waste foresees cementitious materials as reinforcement of tunnels and as backfill. Bentonite is proposed to enclose spent fuel drums, and as drift seals. The emplacement of cementitious material next to clay material generates an enormous chemical gradient in pore water composition that drives diffusive solute transport. Laboratory studies and reactive transport modeling predict significant mineral alteration at and near interfaces, mainly resulting in a decrease of porosity in bentonite. The goal of this project is to characterize and quantify the cement/bentonite skin effects spatially and temporally in laboratory experiments. A newly developed mobile X-ray transparent core infiltration device was used, which allows performing X-ray computed tomography (CT) periodically without interrupting a running experiment. A pre-saturated cylindrical MX-80 bentonite sample (1920 kg/m3 average wet density) is subjected to a confining pressure as a constant total pressure boundary condition. The infiltration of a hyperalkaline (pH 13.4), artificial OPC (ordinary Portland cement) pore water into the bentonite plug alters the mineral assemblage over time as an advancing reaction front. The related changes in X-ray attenuation values are related to changes in phase densities, porosity and local bulk density and are tracked over time periodically by non-destructive CT scans. Mineral precipitation is observed in the inflow filter. Mineral alteration in the first millimeters of the bentonite sample is clearly detected and the reaction front is presently progressing with an average linear velocity that is 8 times slower than that for anions. The reaction zone is characterized by a higher X-ray attenuation compared to the signal of the pre-existing mineralogy. Chemical analysis of the outflow fluid showed initially elevated anion and cation concentrations compared to the infiltration fluid due to anion exclusion effects related to compaction of the bentonite core that was adjusting to the experimental conditions. Subsequently, the OPC fluid is fully buffered, and a gradually decreasing ionic strength is observed as a result of progressive consumption of hydroxide at the mineral reaction front.

      PubDate: 2013-11-28T11:26:04Z
  • In-situ interaction between different concretes and Opalinus Clay
    • Abstract: Publication date: Available online 27 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): A. Jenni , U. Mäder , C. Lerouge , S. Gaboreau , B. Schwyn
      Interactions between cementitious materials and claystone are driven by chemical gradients in pore water and might lead to mineralogical modifications in both materials. In the context of a radioactive waste repository, this alteration might influence safety-relevant clay properties like swelling pressure, permeability, or specific retention. In this study, interfaces of Opalinus Clay, a potential host-rock in Switzerland, and three concrete formulations emplaced in the Cement-Clay Interaction (CI) Experiment at the Mont Terri Underground Laboratory (St. Ursanne, Switzerland) were analysed after 2.2 years of interaction. Sampling techniques with interface stabilisation followed by inclined intersection drilling were developed. Element distribution maps of the concrete-clay interfaces show complex zonations like sulphur enrichment, zones depleted in Ca but enriched in Mg, strong Mg enrichment adjacent to the interface, or carbonation. Consistently, the carbonated zone shows a reduced porosity. Properties of the complex zonation strongly depend on cement properties like water content and pH (ordinary Portland cement vs. low-pH cement). An increased Ca or Mg content in the first 100 μm next to the interface is observed in Opalinus Clay. The cation occupancy of clay exchanger phases next to the ordinary Portland cement interface is depleted in Mg, but enriched in Na, whereas porosity shows no changes at all. The current data suggests migration of CO2/HCO3 -, SO4 2-, and Mg species from clay into cement. pH decrease in the cement next to the interface leads to instability of ettringite, and the sulphate liberated diffuses towards higher pH regions (away from the interface), where additional ettringite can form.

      PubDate: 2013-11-28T11:26:04Z
  • Detection of Chloroform in water using an azo dye-Modified
           β-Cyclodextrin – Epichlorohydrin Copolymer as a Fluorescent
    • Abstract: Publication date: Available online 9 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Phendukani Ncube , Rui W.M. Krause , Bhekie B. Mamba
      Chlorination disinfection by-products (DBPs) in water pose a health threat to humans and the aquatic environment. Their detection in water sources is therefore vital. Herein we present the detection of chloroform, a DBP, using a molecular fluorescent probe. The detection was based on the quenching of fluorescence of the probe by chloroform due to host-guest complex formation between β-cyclodextrin in the probe and the chloroform molecule. The stability constant for the host-guest complex was high at 3.825 x 104 M-1. Chloroform quenched the fluorescence of the copolymer the most compared to the other small chlorinated compounds studied, suggesting that the probe was more sensitive to chloroform, with a sensing factor of 0.35 compared to as low as 0.0073 for dichloromethane. There was no interference from other chloroalkanes on the quenching efficiency of chloroform. The probe was used to detect chloroform in dam water as well as in bottled water. Detection of chloroform in both water samples using the probe was possible without chemically treating the water samples which may introduce other pollutants.
      Graphical abstract image Highlights

      PubDate: 2013-11-13T10:30:52Z
  • X-ray micro-diffraction studies of heterogeneous interfaces between
           cementitious materials and geological formations
    • Abstract: Publication date: Available online 28 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): R. Dähn , D. Popov , Ph. Schaub , P. Pattison , D. Grolimund , U. Mäder , A. Jenni , E. Wieland
      In the present study the challenge of analyzing complex micro X-ray diffraction (microXRD) patterns from cement-clay interfaces has been addressed. In order to extract the maximum information concerning both the spatial distribution and the crystal structure type associated with each of the many diffracting grains in heterogeneous, polycrystalline samples, an approach has been developed in which microXRD was applied to thin sections which were rotated in the X-ray beam. The data analysis, performed on microXRD patterns collected from a filled vein of a cement-clay interface from the natural analogue in Maqarin (Jordan), and a sample from a two-year-old altered interface between cement and argillaceous rock, demonstrate the potential of this method.

      PubDate: 2013-11-01T10:30:21Z
  • Determination of Volatile Fatty Acids in Wastewater by Solvent Extraction
           and Gas Chromatography
    • Abstract: Publication date: Available online 30 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Nontando T. Mkhize , Titus A.M. Msagati , Bhekie B. Mamba , Maggy Momba
      The purpose of this study was to develop a liquid-liquid extraction method for the analysis of volatile fatty acids collected at the elutriation units of Unit 3, 4 and 5 at Johannesburg Water-Northern Works Wastewater treatment plant. Liquid-Liquid extraction (LLE) method employing dichloromethane (DCM) and methyl-tert-butyl- ether (MTBE) as extracting solvents was used during the quantitative analysis of volatile fatty acids namely acetic, propionic, butyric, isobutyric, valeric, isovaleric and heptanoic acid. The detection of the extracts was by gas chromatography coupled to a mass spectrometer operating under electron ionization mode (GC-EI-MS). The results showed that MTBE was a better extraction solvent than DCM as it gave much higher recoveries (> 5 folds). On the other hand, the overall reactor performance for all the three units in the period when the samples were collected, which was measured by the ratio of propionic to acetic acid was good since the ratio o did not exceed 1.4 with the exception of the samples collected on the 3rd of October where the ratio exceeded 1.4 significantly. The concentration of acetic acid, another indicator for the reactor performance in all three units was way below 800 mg/L thus the digester balance was on par.

      PubDate: 2013-11-01T10:30:21Z
  • Spatial-Temporal Variability In Water Quality and Macro-Invertebrate
           Assemblages In The Upper Mara River Basin, Kenya
    • Abstract: Publication date: Available online 26 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Fidelis Kilonzo , Frank O. Masese , Ann Van Griensven , Willy Bauwens , Joy Obando , Piet N.L. Lens
      Tropical rivers display profound temporal and spatial heterogeneity in terms of environmental conditions. This aspect needs to be considered when designing a monitoring program for water quality in rivers. Therefore, the physico-chemical composition and the nutrient loading of the Upper Mara River and its two main tributaries, the Amala and Nyangores were monitored. Initial daily, and later a weekly monitoring schedule for four months spanning through the wet and dry seasons was adopted. Benthic macro-invertebrates were also collected during the initial sampling to be used as indicators of water quality. The aim of the current study was to investigate the physico-chemical status and biological integrity of the Upper Mara River basin. This was achieved by examining trends in nutrient concentrations and analysing the structure, diversity and abundance of benthic macro-invertebrates in relation to varying land use patterns. Sampling sites were selected based on catchment land use and the level of human disturbance, and using historical records of previous water quality studies. River water pH, dissolved oxygen, electrical conductivity (EC), temperature, and turbidity were determined in situ. All investigated parameters except iron and manganese had concentration values within allowable limits according to Kenyan and international standards for drinking water. The Amala tributary is more mineralized and also shows higher levels of pH and EC than water from the Nyangores tributary. The latter, however, has a higher variability in both the total phosphorus (TP) and total nitrogen (TN) concentrations. The variability in TP and TN concentrations increases downstream for both tributaries and is more pronounced for TN than for TP. Macro-invertebrate assemblages responded to the changes in land use and water quality in terms of community composition and diversity. The study recommends detailed continuous monitoring of the water quality at shorter time intervals and to identify key macro-invertebrate taxa that can be used to monitor changes of the water quality in rivers of the Mara basin as a result of anthropogenic changes.

      PubDate: 2013-10-28T13:12:43Z
  • Microwave-Induced Synthesis Of B-Cyclodextrin/N-Doped Carbon Nanotube
           Polyurethane Nanocomposites For Water Purification
    • Abstract: Publication date: Available online 25 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Sello P Masinga , Edward N Nxumalo , Bhekie B Mamba , Sabelo D Mhlanga
      The fabrication of polymer nanocomposites for the removal of organic species in aqueous media is achieved using conventional methods. However, these methods are expensive and deteriorating to the environment due to high energy demands and high organic solvent volume requirements. This work discusses the synthesis of nanocomposite polymers of β-cyclodextrin (β-CD) and nitrogen-doped carbon nanotubes (N-CNTs) under microwave irradiation for the first time. This novel method is efficient, greener and time saving. Typically, the reaction to prepare β-CD polymers takes about 24 h. Here we report a novel method to synthesize the polymers in 10 min. N-CNTs were synthesized via chemical vapour deposition method (CVD) using a 10 wt% Fe-Co/CaCO3 catalyst. The N-CNTs were found to contain ∼ 2 at% nitrogen by CN analysis. The N-CNTs were of high purity and were oxidized with acid functional groups (-COOH, -CO, -OH) using nitric acid under reflux. Zeta potential studies indicated that the quantity of acid functional groups increases with increase in acid treatment times. The functionalised N-CNTs (fN-CNTs) were then polymerized with β-CD using hexamethylene diisocyanate as the functional cross-linker in a microwave under an inert gas atmosphere. The polymers showed an efficient removal of p-nitrophenol from spiked water samples as confirmed by UV-Vis spectroscopy.
      Graphical abstract image Highlights

      PubDate: 2013-10-28T13:12:43Z
  • The Seasonal influence on the spatial distribution of dissolved selected
           metals in Lake Naivasha, Kenya
    • Abstract: Publication date: Available online 23 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Joseph Nyingi Kamau , Anthony Gachanja , Catherine Ngila , Johnson Michael Kazungu , Mingzhe Zhai
      Lake Naivasha is the only freshwater Lake in Rift Valley, in Kenya. It lies in a fertile semi-arid basin. The Lake has no surface water outlet and is presumed to be under stress. Dissolved metals are directly taken up by bacteria, algae, plants, and planktonic and benthic organisms. Dissolved metals can also adsorb to particulate matter in water column and enter aquatic organisms through various routes. Cadmium, copper, lead and zinc may bioaccumulate within lower organisms, yet they do not biomagnify up the food chain as do mercury and selenium. This study reports on the levels and distribution of dissolved heavy metals and investigates the influence of physicochemical parameters on metal mobilization. The bioavailability of selected metals was investigated by relating the levels of dissolved metals to that in fish. Water abstraction for irrigation and domestic use, compounded with organic matter inflow will affect physicochemical parameters and hence influences the mobilization of heavy metals. Dissolved Zn correlated highly with sediment pH (r=0.67) indicating that dissolution increases with increase in pH. In addition, the fact that the pH also correlated positively with organic matter r=0.50, Eh r=0.63, temperature r=0.56 and dissolved oxygen r=56, would suggest that organic bound Zn contributed significantly to the concentration of dissolved Zn. In situ flux experiments indicated that the fringing papyrus reeds located along the shores of Lake Naivasha provided sites for metal immobilization due to their coprecipitation on redox sensitive

      PubDate: 2013-10-24T09:34:55Z
  • Assessing Indigenous Knowledge Systems and Climate Change Adaptation
           Strategies in Agriculture: A Case Study of Chagaka Village, Chikhwawa,
           Southern Malawi
    • Abstract: Publication date: Available online 16 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Emmanuel Charles Mkomwa , Miriam Kalanda Joshua , Cosmo Ngongondo , Maurice Monjerezi , Felistus Chipungu
      In Malawi, production from subsistence rain fed agriculture is highly vulnerable to climate change and variability. In response to the adverse effects of climate change and variability, a National Adaptation Programme of Action is used as framework for implementing adaptation programmes. However, this framework puts limited significance on indigenous knowledge systems (IKS). In many parts of the world, IKS have shown potential in the development of locally relevant and therefore sustainable adaptation strategies. This study was aimed at assessing the role of IKS in adaptation to climate change and variability in the agricultural sector in a rural district of Chikhwawa, southern Malawi. The study used both qualitative data from focus group and key informant interviews and quantitative data from household interviews and secondary data to address the research objectives. The study established that the local communities are able to recognize the changes in their climate and local environment. Commonly mentioned indicators of changing climatic patterns included delayed and unpredictable onset of rainfall, declining rainfall trends, warming temperatures and increased frequency of prolonged dry spells. An analysis of empirical data data corroborates the people’s perception. In addition, the community is able to use their IKS to adapt their agricultural systems to partially offset the effects of climate change. Like vulnerability to climate change, IKS varies over a short spatial scale, providing locally relevant adaptation to impacts of climate change. This paper therefore advocates for the integration of IKS in programmes addressing adaptation to climate change and vulnerability. This will serve to ensure sustainable and relevant adaptation strategies.

      PubDate: 2013-10-20T09:31:27Z
  • Validation of Remotely Sensed Rainfall over Major Climatic Regions in
           Northeast Tanzania
    • Abstract: Publication date: Available online 19 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Fredrick Mashingia , Felix Mtalo , Michael Bruen
      Increase in population has resulted in pressure for more land and water use for food security in northeast Tanzania. This calls for proper understanding of spatial-temporal variations of quality and quantity of water to ensure sustainable management. The number of hydrometeorological stations such as rainfall stations and flow measuring stations has not increased and even the functioning of the existing ones is deteriorating. Satellite rainfall estimates (SRE) are being used widely in place of gauge observations or to supplement gauge observations. However, rigorous validation is necessary to have some level of confidence in using the satellite products for different applications. This paper discusses the results of application of SRE over a data scarce tropical complex region in northeast Tanzania. We selected river catchments found in two different climatological zones: the inland region mountains (ie. Kikuletwa and Ruvu basins) and the coastal region mountains (ie. Mkomazi, Luengera and Zigi basins), characterized by semi arid, sub humid to humid tropical climate. Thus, the validation sites were ideal for testing the different SRE products. In this study, we evaluated two gauge corrected high resolution SRE products which combine both infrared and passive-microwave estimates; the National Oceanographic and Atmospheric Administration Climate Prediction Center (NOAA-CPC) African Rainfall Estimation (RFE2) and the Tropical Rainfall Measuring Mission product 3B42 (TRMM-3B42) using station network. The accuracy of the products was evaluated through a comparison with available gauge data. The comparison was made on pair-wise (point to pixel) and sub-basin level with the reproduction of rainfall volume, rainfall intensity and consistency of rain and no-rain days. The SRE products performed reasonably well over both regions in detecting the occurrence of rainfall. The underestimation was mainly ascribed to topology and the coastal effect. Whereas, the overestimation was mainly ascribed to evaporation of rainfall in the dry atmosphere under the cloud base. Local calibration of satellite-derived rainfall estimates and merging of satellite estimates with locally available rain-gauge observations are some of the approaches that could be employed to alleviate these problems. Although, the products did not show strong correlation to the observed rainfall over the complex tropical mountainous catchments considered, they have high potential to augment gauge observations in data sparse basins.

      PubDate: 2013-10-20T09:31:27Z
  • Coping with droughts and floods: A Case study of Kanyemba, Mbire district,
    • Abstract: Publication date: Available online 19 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): G. Bola , C. Mabiza , J. Goldin , K. Kujinga , I. Nhapi , H. Makurira , D. Mashauri
      Most of Southern Africa is affected by extreme weather events, droughts and floods being the most common. The frequency of floods and droughts in Southern Africa in general, of which the Zambezi River Basin is part of, has been linked to climate change. Droughts and floods impact on the natural environment, and directly and indirectly impact on livelihoods. In the Middle Zambezi River Basin, which is located between Kariba and Cahora Bassa dams, extreme weather events are exacerbated by human activities, in particular the operation of both the Kariba and the Cahora Bassa reservoirs. To understand better, whether, and in what ways extreme weather events impact on livelihoods, this study used both quantitative and qualitative research methods to analyse rainfall variability and coping strategies used by households in the river basin. Data collection was done using semi-structured interviews, focus group discussions and structured questionnaires which were administered to 144 households. An analysis of rainfall variability and Cahora Bassa water level over 23 years was carried out. The study found that perceptions of households were that average rainfall has decreased over the years, and dry-spells have become more frequent. Furthermore, households perceived flood events to have increased over the last two decades. However, the analysis of rainfall variability revealed that the average rainfall received between 1988 and 2011 had not changed but the frequency of dry-spells and floods had increased. The occurrence of floods in the study area was found to be linked to heavy local rain and backflow from Cahora Bassa dam. The study found that households adopted a number of strategies to cope with droughts and floods, such as vegetable farming and crop production in the floodplain, taking on local jobs that brought in wages, planting late and livestock disposals. Some households also resorted to out-migration on a daily basis to Zambia or Mozambique. The study concluded that coping mechanisms were found to be inflexible and poorly suited to adapt to floods and droughts. The study recommends the implementation of adaptation measures such as the cultivation of drought-resistant crop varieties, irrigation and off-farm employment opportunities.

      PubDate: 2013-10-20T09:31:27Z
  • Calibration, Performance, Parameter Indentifiability and Uncertainty
           Analysis of a 2 – Parameter Parsimonious Monthly Rainfall-Runoff
           Model in Two Catchments in Zimbabwe
    • Abstract: Publication date: Available online 10 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): D.T. Rwasoka , C.E. Madamombe , W. Gumindoga , A.T. Kabobah
      Hydrologic modelling lies at the core of hydrology and water resources management. Attempts at gaining a holistic grasp on model robustness, hydrologic theory and processes have inadvertently led to models that are not-well structured or too complex to apply in arid and semi-arid catchments and in Africa, in particular. In view of this, this paper reports on the application of a monthly parsimonious hydrologic model in two catchments in Zimbabwe, the Nyatsime and Upper Save river catchments. The two (2) parameter monthly parsimonious GR2M model was applied. The inputs were rainfall and potential evapotranspiration. Measured discharge was used for calibration and validation. Calibration and uncertainty analysis were done using the Differential Evolution Adaptive Metropolis (DREAM) algorithm. The performance of the GR2M model was evaluated using ten (10) model performance metrics. Parameter indentifiability was analysed on the basis of the shape of the posterior distribution of parameters. Parameter and total uncertainty were analysed in the context of the formal Bayesian DREAM approach. The 10 performance evaluation metrics showed that the model performed satisfactorily during calibration and validation in terms of the overall fit of observed and simulated data, low flows and the runoff volumes. The NSE was > 0.85, the Kling-Gupta Efficiency (KGE) was > 80% and Volume Efficiency was > 59% during calibration. Slight performance drops were noted during validation except for the NSE in Nyatsime catchment whilst the KGE remained relatively high. The validation NSE was > 0.65, the Kling-Gupta Efficiency (KGE) was > 71% and Volume Efficiency was > 55%. Calibrated parameters values showed good time-stability and were well identifiable with posterior parameter distributions having Gaussian shapes. Parameter uncertainty, in relation to total uncertainty was low. Parameter uncertainty constituted about 7% of the total uncertainty region. It was concluded that, although the model only had two parameters, the model performed quite satisfactorily in the simulation of monthly flows which makes it a good tool for operational hydrology and water resources modelling, planning and management in most data poor regions.

      PubDate: 2013-10-12T09:30:59Z
  • Direct Spectrophotometric Detection of the Endpoint in Metachromatic
           Titration of Polydiallyldimethylammonium Chloride in Water
    • Abstract: Publication date: Available online 10 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): B. Gumbi , J.C. Ngila , P.G. Ndungu
      Polydiallyldimethylammonium chloride (poly-DADMAC) is a water soluble polymer that easily ionizes when dissolved in water. This cationic polyelectrolyte is mainly used as a flocculant within the water treatment industry, but little is known of its toxicological properties or its fate in the environment. It is often assumed that the polyelectrolyte sorbs onto solid surfaces in the water treatment stream and may be removed with the sludge or by a sand bed filter; which may not always be the case. In any event, reliable analytical techniques are needed for the determination of poly-DADMAC in matrices of environmental relevance. Metachromatic polyelectrolyte titration was used to quantify poly-DADMAC in model and tap water samples. We compared a routine visual titration method with a direct spectrophotometric technique that uses a dip probe, spectrometer, and computer. The direct spectrophotometric technique allowed for the determination of titration curves at 634 nm and 510 nm, whereby the later value has never been successfully utilised in the literature. The method simplifies the data analysis, and our recovery and matrix interference experiments demonstrate that the method is accurate, precise, and robust. The detection limit for this method was 0.1 mg L-1 in model water and 0.5 mg L-1 in tap water. The limit of quantification for both water matrices was 0.5 mg L-1.

      PubDate: 2013-10-12T09:30:59Z
  • Preparation of antifouling polyvinylpyrrolidone (PVP 40K) modified
           polyethersulfone (PES) ultrafiltration (UF) membrane for water
    • Abstract: Publication date: Available online 5 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Banele Vatsha , Jane Catherine Ngila , Richard M. Moutloali
      This study reports the fabrication of polyethersulfone (PES) membrane using the phase inversion method in the presence of polyvinylpyrrolidone (PVP, 40K) as pore-forming agent. The membranes were made from two PES concentration types i.e. 16 and 18 wt.%. The effect of high molecular weight PVP concentration (2 to 10%) was examined in order to obtain a membrane with good performance i.e. high water flux and reasonable Bovine Serum Albumin (BSA, protein model solution) rejection. The optimised membranes were characterised by ATR-FTIR, AFM, SEM, contact angle and dead-end membrane filtration tests. It was found that PVP moieties have positive influence in the prepared PES membranes. SEM surface and cross-sectional images were used to observed morphological changes as PVP content was varied. The pore sizes increased with PVP content for membranes prepared from 16 wt.% PES polymer, whereas at the higher PVP content in 18 wt.% PES membrane, pore sizes tend to decrease or completely disappear. The CA decreased gradually for the 16 wt.% PES with increasing PVP content whereas in the 18 wt.% PES the CA decreased initially before tapering off or increasing slightly. The rejection of BSA solution by both neat PES and PVP-containing PES membrane was above 85%. AFM surface topography exhibited increase in roughness value with PVP content. FTIR/ATR spectra corroborated the functional composition of neat PES and PVP molecule dispersed on PES membrane backbone. The results attained confirmed the potential industrial application of PVP molecule to minimise fouling tendencies.

      PubDate: 2013-10-08T09:31:15Z
  • Reactive-transport modeling of fly ash-water-brines interactions from
           laboratory-scale column studies
    • Abstract: Publication date: Available online 4 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): John M. Mbugua , J. Catherine Ngila , Andrew Kindness , Molla Demlie
      Dynamic leaching tests are important studies that provide more insights into time-dependent leaching mechanisms of any given solid waste. Hydrogeochemical modeling using PHREEQC was applied for column modeling of two ash recipes and brines generated from South African coal utility plants, Sasol and Eskom. The modeling results were part of a larger ash-brine study aimed at acquiring knowledge on (i) quantification and characterization of the products formed when ash is in contact with water-brines in different scenarios, (ii) the mineralogical changes associated with water-brine-ash interactions over time, (iii) species concentration, (iv) leaching and transport controlling factors. The column modeling was successfully identified and quantified as important reactive mineralogical phases controlling major, minor and trace elements’ release. The pH of the solution was found to be a very important controlling factor in leaching chemistry. The highest mineralogical transformation took place in the first 10 days of ash contact with either water or brines, and within 0.1 meter from the column inflow. Many of the major and trace elements (Ca, Mg, Na, K, Sr, S(VI), Fe, are leached easily into water systems and their concentration fronts were high at the beginning (within 0.1 meter from the column inflow and within the first 10 days) upon contact with the liquid phase. However, their concentration decreased with time until a steady state was reached. Modeling results also revealed that geochemical reactions taking place during ash-water-brine interactions does affect the porosity of the ash, whereas the leaching processes lead to increased porosity. Besides supporting experimental data, modeling results gave predictive insights on leaching of elements which may directly impact on the environment, particularly ground water. These predictions will help develop scenarios and offer potential guide for future sustainable waste management practices as a way of addressing the co-disposal of brines within inland ash dams and heaps.

      PubDate: 2013-10-08T09:31:15Z
  • Assessing the relationship between water quality parameters and changes in
           landuse patterns in the Upper Manyame River, Zimbabwe
    • Abstract: Publication date: Available online 7 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): J. Kibena , I. Nhapi , W. Gumindoga
      For the past 30 years, the increases in population pressure and external influences, such as economic growth, have accelerated the demand for land within the Upper Manyame River catchment in Zimbabwe which has caused substantial changes in landuse. The general objective of this research was to assess the impacts of landuse activities on the water quality of the Upper Manyame River which drains the rural and urbanized part of the catchment up to flow gauging station C21. Landcover data for the month of April in years of 1984, 1995, 2003 and 2011 were acquired from available Landsat TM and ETM images and were classified through the maximum likelihood digital image classification using the supervised classification approach. The status of water quality of the Upper Manyame River was also assessed through analyses of historical concentrations and pollution loads for TP, DO, BOD5, EC, PO4-P and TN at the Environmental Management Agency (EMA) gauging station CR21 sampling point for 1996, 2000/1 and 2008/9. Water quality of 15 monitoring sites comprising 25 water quality parameters were monitored monthly from January to June 2012. These locations were selected to reflect a wide array of landuse for both the dry and wet seasons. The results indicated that there was an increase in pollution load from 1995-2012; for TP from 130 kg/day to 376 kg/d, and for TN from 290 kg/day to 494 kg/d. This indicates high pollution levels which have severe impacts on downstream users. Significant deviations occurred in DO (0.1 - 6.8) mg/L, COD (11 - 569) mg/L, BOD5 (5 - 341) mg/L, PO4-P (0.01 - 4.45) mg/L, NH3-N (0.001 - 6.800) mg/L and EC (38 - 642) μS/cm. These values indicate sewage contamination. Hydrologic Response Unit and Buffer Analysis were used to determine the dominant landuse which contributes to a certain water quality. Results of digital image classification indicate that woodland/forest, grassland and bareland decreased between years 1984 to 2011 by 24.0 %, 22.6 % and 31.7 % respectively. This was mainly due to expansion or increase of agriculture and urban areas by 24.4% and 41.6 % respectively over the same time period. It was concluded that settlements and agricultural areas are the ones mainly affecting the water quality in Upper Manyame River with a Pearson’s correlation coefficient of r = 0.97 for COD and r = 0.78 for TSS respectively. It was also observed that the water quality status of the Upper Manyame River and its tributaries is very poor and the level of pollution generally increases from upstream to downstream. The results obtained provided baseline information which may be used in the development of appropriate water quality management systems in the catchment. Thus the study recommended a combined programme of point source control and landuse modification.

      PubDate: 2013-10-08T09:31:15Z
  • Impact of spatial input data resolution on hydrological and erosion
           modelling: recommendations from a global assessment
    • Abstract: Publication date: Available online 5 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): V. Chaplot
      The need to precisely describe the characteristics of a landscape is well-known in mathematical modeling from different environmental disciplines. Because spatial input data, such as climate, relief and soil maps are costly to obtain, especially when large areas are considered, several research studies have investigated the extent to which the resolution of these can be reduced. Yet, a consensus has not been reached on the question of models’ sensitivity to the whole range of spatial input data and for different environmental conditions. This issue was illustrated with the analysis of existing results from 41 watersheds from 30 research studies using the Soil and Water Assessment Tool (SWAT). Because these studies were not consistent in the type of spatial input data considered and the range of resolutions, an application of SWAT was performed in a flat 2,612 ha flat watershed of central Iowa (USA) where the sensitivity of runoff (R), NO3-N (N) and sediment (SED) yields was tested for changes in the resolution of all the required spatial input data (digital elevation model: DEM: 20-500m; n=12; number of rain gauge: NRAIN from 1 to 13; n=8; soil map: SOIL: 1/25,000-1/500,000; n=3) and in the number of watershed sub-divisions (NSW from 4 to 115; n=4). At the flat watershed, a Canonical Correlation Analysis with 67.4% of data variance explained by the two first variates, revealed that R and SED predictions were affected, mostly by NSW (r=0.95), followed by SOIL (r=0.18). N loads were the most sensitive to RAIN (r=0.76) and DEM (r=0.41), followed by SOIL (r=0.23) and NSW (r=-0.17). The Kolmogorov–Smirnov statistic (KS), that describes the significance of resolution changes for a considered spatial input data, showed that the model’s sensitivity was greater for SSW below 261ha, for 30<DEM<100m and across the whole range of NRAIN. Finally, the analysis of watersheds with different sizes and environmental conditions revealed that the minimum spatial input data resolution needed, to achieve accurate modeling results can be predicted from watersheds’ terrain declivity and mean annual precipitation. These results are expected to help modelers weight the level of investment to be made in generating spatial input data and in subdividing their watersheds as a function of both watersheds’ environmental conditions and desired level of accuracy in the output variables.

      PubDate: 2013-10-08T09:31:15Z
  • Stability studies of commercial ZnO engineered nanoparticles in domestic
    • Abstract: Publication date: Available online 7 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): E.F.C. Chaúque , J.N. Zvimba , J.C. Ngila , N. Musee
      Most wastewater treatment plants (WWTPs) employ activated sludge processes to treat wastewater. The bacteria found in these systems degrade organic matter but are very sensitive to toxic compounds such as heavy metals, among others. The impact of emerging contaminants, such as engineered nanoparticles (ENPs) on the treatment efficiency of WWTPs is yet to be fully elucidated. The effects of physicochemical parameters; the pH and ionic strength on ZnO ENPs in domestic wastewater were investigated to establish their fate and behaviour in wastewater treatment systems, as well as potential release into the environment if they pass untreated. Our findings showed a decrease in zinc concentration in the filtrate as pH and ionic strength increased which indicated its possible removal through the abiotic, biosorption, and biosolid settling mechanisms. This phenomenon was further confirmed by transmission electron microscopy (TEM) images which showed agglomerates of ZnO ENPs in wastewater compared with de-ionized water. The dynamic light scattering (DLS) analysis of ZnO ENPs suspension in the wastewater showed their stability over a period of 2-h, with energy dispersive X-ray (EDS) analysis showing the presence of zinc on the sludge surface, while X-ray diffraction (XRD) analysis confirmed the presence of ZnO ENPs in the sludge over typical wastewater pH ranges. The results of this study will inform the integrated water management on the impact of nanotechnology based industries and the best approach in handling wastewater treatment products.

      PubDate: 2013-10-08T09:31:15Z
  • An analsis of factors contributing to household water security problems
           and threats in different settlement categories of ngamiland, botswana
    • Abstract: Publication date: Available online 7 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Krasposy Kujinga , Cornelis Vanderpost , Gagoitseope Mmopelwa , Piotr Wolski
      Globally, water security is negatively affected by factors that include climatic and hydrological conditions, population growth, rural-urban migration, increased per-capita water use, pollution and over-abstraction of groundwater. While Botswana has made strides in providing safe and clean water to its population since independence in 1966, over the years a combination of factors have contributed to water security problems in different settlement categories of the country (i.e., primary, secondary, tertiary and ungazetted settlements) in general and in the district of Ngamiland in particular. To study water security problems differentiated by settlement category, this study employed quantitative data collection methods (i.e. household structured questionnaires) and qualitative data collection methods (i.e. key informant interviews, observation, focus group discussions and informal interviews), complemented by a review of relevant literature. Water security in all settlements is affected by status of the settlement, i.e. gazetted or ungazetted, climatic and hydrological factors and water governance challenges. In large villages such as Maun, factors threatening water security include population growth, urbanization, management challenges, old water supply and distribution infrastructure, increased demand for individual connections and changing lifestyles. Small gazetted and ungazetted settlements encounter problems related to limited sources of water supply as well as salinity of groundwater resources. In order to enhance water security in different settlement categories, Botswana has to develop a comprehensive water resources management strategy underpinned by integrated water resources management principles aimed at addressing factors contributing to water security problems. The strategy has to be settlement category specific. Large villages have to address factors related to demographic changes, urbanization, management challenges, water supply infrastructure and the introducing of water demand management activities. Households in small villages need provision of water from more sustainable sources while ungazetted settlements need better access to clean water.

      PubDate: 2013-10-08T09:31:15Z
  • Impacts of Climate Change on Water Resources in Southern Africa: A Review
    • Abstract: Publication date: Available online 2 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Samuel Kusangaya , Michele Lynn Warburton , Emma Archer Van Garderen , Graham P.W. Jewitt
      The Intergovernmental Panel on Climate Change concluded that there is consensus that the increase of atmospheric greenhouse gases will result in climate change which will cause the sea level to rise, increased frequency of extreme climatic events including intense storms, heavy rainfall events and droughts. This will increase the frequency of climate-related hazards, causing loss of life, social disruption and economic hardships. There is less consensus on the magnitude of change of climatic variables, but several studies have shown that climate change will impact on the availability and demand for water resources. In southern Africa, climate change is likely to affect nearly every aspect of human well-being, from agricultural productivity and energy use to flood control, municipal and industrial water supply to wildlife management, since the region is characterised by highly spatial and temporally variable rainfall and, in some cases, scarce water resources. Vulnerability is exacerbated by the region’s low adaptive capacity, widespread poverty and low technology uptake. This paper reviews the potential impacts of climate change on water resources in southern Africa. The outcomes of this review include highlighting studies on detected climate changes particularly focusing on temperature and rainfall. Additionally, the impacts of climate change are highlighted, and respective studies on hydrological responses to climate change are examined. The review also discusses the challenges in climate change impact analysis, which inevitably represents existing research and knowledge gaps. Finally the paper concludes by outlining possible research areas in the realm of climate change impacts on water resources, particularly knowledge gaps in uncertainty analysis for both climate change and hydrological modelling.

      PubDate: 2013-10-04T09:30:56Z
  • A multiplier-based method of generating stochastic areal rainfall from
           point rainfalls
    • Abstract: Publication date: Available online 1 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): J.G. Ndiritu
      Catchment modelling for water resources assessment is still mainly based on rain gauge measurements as these are more easily available and cover longer periods than radar and satellite-based measurements. Rain gauges however measure the rain falling on an extremely small proportion of the catchment and the areal rainfall obtained from these point measurements are consequently substantially uncertain. These uncertainties in areal rainfall estimation are generally ignored and the need to assess their impact on catchment modelling and water resources assessment is therefore imperative. A method that stochastically generates daily areal rainfall from point rainfall using multiplicative perturbations as a means of dealing with these uncertainties is developed and tested on the Berg catchment in the Western Cape of South Africa. The differences in areal rainfall obtained by alternately omitting some of the rain gauges are used to obtain a population of plausible multiplicative perturbations. Upper bounds on the applicable perturbations are set to prevent the generation of unrealistically large rainfall and to obtain unbiased stochastic rainfall. The perturbations within the set bounds are then fitted into probability density functions to stochastically generate the perturbations to impose on areal rainfall. By using 100 randomly-initialized calibrations of the AWBM catchment model and Sequent Peak Analysis, the effects of incorporating areal rainfall uncertainties on storage-yield-reliability analysis are assessed. Incorporating rainfall uncertainty is found to reduce the required storage by up to 20%. Rainfall uncertainty also increases flow-duration variability considerably and reduces the median flow-duration values by an average of about 20%.

      PubDate: 2013-10-04T09:30:56Z
  • Hydration of a silica fume blended low-alkali shotcrete cement
    • Abstract: Publication date: Available online 24 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Barbara Lothenbach , Daniel Rentsch , Erich Wieland
      Ettringite and C-S-H are the main hydrates formed during the hydration of the low-alkali cement “ESDRED” consisting of 60% CEM I, 40% microsilica and 4.8% set accelerator. Small quantities of portlandite and hemicarbonate present as intermediate phases destabilise within a few weeks. The use of a set accelerator leads to massive ettringite precipitation, a moderate decalcification of C-S-H and reduction of pH due to presence of dissolved formate. The slow reaction of the silica fume during hydration decalcifies the C-S-H and decreases the alkali concentration to 30 mM and the pH value of the pore solution to 11.5 after 1 year and longer. The further reaction of the silica fume is expected to be slow and to result in a decrease of pH to 11. Further, the destabilisation of ettringite to thaumasite is expected. The long-term stability of C-S-H and the pH of approximately 11 make ESDRED a good candidate for usage in contact with the clay-based barriers of a repository for radioactive waste.

      PubDate: 2013-09-26T14:00:43Z
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