Ozonation and advanced oxidation of wastewater: Effect of O-3 dose, pH, DOM and HO center dot-scavengers on ozone decomposition and HO center dot generation

The decomposition of ozone in wastewater is observed starting 350 milliseconds after ozone addition. It seems not to be controlled by the autocatalytic chain reaction, hut rather by direct reactions with reactive moieties of the dissolved organic matter (DOM). A larger ozone dose increases ozone consumption prior to 350 milliseconds but decreases the rate of ozone decomposition later on; this effect is predicted by a second-order kinetic model. Transferred ozone Dose (TOD) is poorly correlated with ozone exposure (= integral[O-3]dt) indicating that TOD is not a suitable parameter for the prediction of disinfection or oxidation in wastewater. HO circle concentrations (> 10(-10) M) and R-ct (=integral[HO circle]dt vertical bar integral[O-3]dt > 10(-6)) are larger than in most advanced oxidation processes (AOP) in natural waters, but rapidly decrease over time. R-ct also decreases with increasing pre-ozonation doses. An increase in pH accelerates ozone decomposition and HO circle generation; this effect is predicted by a kinetic model taking into account deprotonation of reactive moieties of the DOM. DOC emerges as a crucial water quality parameter that might be of use to normalize ozone doses when comparing ozonation in different wastewaters. A rapid drop of absorbance in the water matrix-with a maximum between 255-285 nm- is noticeable in the first 350 milliseconds and is directly proportional to ozone consumption. The rate of absorbance decrease at 285 nm is first order with respect to ozone concentration. A kinetic model is introduced to explore ozone decomposition induced by distributions of reactive moieties at sub-stoichiometric ozone concentrations. The model helps visualize and comprehend the operationally defined "instantaneous ozone demand" observed during ozone batch experiments with DOM-containing waters

Formation of assimilable organic carbon (AOC) and specific natural organic matter (NOM) fractions during ozonation of phytoplankton

Ozonation of natural surface water increases the concentration of oxygen-containing low molecular weight compounds. Many of these compounds support microbiological growth and as such are termed assimilable organic carbon (AOC). Phytoplankton can contribute substantially to the organic carbon load when surface water is used as source for drinking water treatment. We have investigated dissolved organic carbon (DOC) formation from the ozonation of a pure culture of Scenedesmus vacuolatus under defined laboratory conditions, using a combination of DOC fractionation, analysis of selected organic acids, aldehydes and ketones, and an AOC bioassay. Ozonation of algae caused a substantial increase in the concentration of DOC and AOC, notably nearly instantaneously upon exposure to ozone. As a result of ozone exposure the algal cells shrunk, without disintegrating entirely, suggesting that DOC from the cell cytoplasm leaked through compromised cell membranes. We have further illustrated that the specific composition of newly formed AOC (as concentration of organic acids, aldehydes and ketones) in ozonated lake water differed in the presence and absence of additional algal biomass. It is therefore conceivable that strategies for the removal of phytoplankton before pre-ozonation should be considered during the design of drinking water treatment installations, particularly when surface water is used. (c) 2007 Elsevier Ltd. All rights reserved

Geant4 visualization: pBR322 plasmid DNA molecule irradiation by 20 MeV proton in liquid water

<p><strong>Geant4 simulation of pBR322 plasmid DNA irradiation by 20 MeV proton particle in liquid water.</strong></p> <p>Computer visualization of plasmid DNA irradiation in liquid water as modelled by the Geant4 Monte Carlo track structure code.</p> <p>pBR322 plasmid DNA geometry created using A. Vologodskii's group (see Huang, J., Schlick, T. and Vologodskii, T. (2001) Dynamics of site juxtaposition in supercoiled DNA. Proc. Natl. Acad. Sci. USA, 98, 968-973) was included in a Geant4-DNA physical and chemical stage simulation of liquid water sphere irradiation by a 20 MeV proton track.</p> <p>First the physical stage of radiation action is modelled; proton track is shown in green, yellow dots correspond to interaction events. Secondaries are followed down to thermalization.</p> <p>Next, the chemical stage simulation for first 100 ns is visualized. Individual chemical species diffusing in space and reacting with each other are shown as colour trails, the color codes chemical species type.</p> <p>Visualization combines the plasmid DNA geometry interface to A. Vologodskii's group code written by Václav Štěpán and the chem3 Geant4 example by M. Karamitros, S. Meylan, Y. Perrot and V. Štěpán.</p> <p>For more information about water radiolysis and chemical stage modelling using Geant4, please see  "Diffusion-controlled reactions modeling in Geant4-DNA" by M. Karamitros et al., doi:10.1016/j.jcp.2014.06.011</p

Geant4-DNA visualization: Evolution of 1 keV electron track in liquid water in space and time

<p>Geant4-DNA generated track of 1 keV electron, followed up to 100 ns during chemical stage.<br>Using pre-release Geant4 10.1 code.</p> <p>First, the physical stage of radiation action is modeled, using Geant4-DNA physics. 1 keV electron track is fully slowed down and thermalized in a 150 nm sphere of liquid water.</p> <p>Yellow points correspond to interaction events in liquid water.</p> <p>Next, the chemical stage simulation for first 100 ns is visualized. Individual radical species diffusing in space and reacting with each other are shown as colour trails, the color coding chemical species type.</p> <p>References:</p> <p>Geant4 10.0, patch 01, Geant4 DNA chemistry code e964ead.<br>Code using the chem3 example by M. Karamitros, S. Meylan, Y. Perrot and V. Štěpán, video rendered by V. Štěpán on March 31, 2014.</p> <p>Internal ref: chem3-100ns-1kev-e</p> <p> </p

Preparation of modified RNA sequences for biological research

Our group is working on the development of reliable access to biol. relevant, long, and modified RNA sequences. Here, we briefly present the chem. synthesis of such sequences with 2'-O-triisopropylsilyloxymethyl (= 2'-O-tom) protected ribonucleoside phosphoramidites, their template-directed enzymic ligation, and some examples of modified nucleotides, designed to promote structural and biol. studies. [on SciFinder (R)

Evaluation of early radiation DNA damage in a fractal cell nucleus model using Geant4-DNA

The advancement of multidisciplinary research fields dealing with ionising radiation induced biological damage - radiobiology, radiation physics, radiation protection and, in particular, medical physics - requires a clear mechanistic understanding of how cellular damage is induced by ionising radiation. Monte Carlo (MC) simulations provide a promising approach for the mechanistic simulation of radiation transport and radiation chemistry, towards the in silico simulation of early biological damage. We have recently developed a fully integrated MC simulation that calculates early single strand breaks (SSBs) and double strand breaks (DSBs) in a fractal chromatin based human cell nucleus model. The results of this simulation are almost equivalent to past MC simulations when considering direct/indirect strand break fraction, DSB yields and fragment distribution. The simulation results agree with experimental data on DSB yields within 13.6% on average and fragment distributions agree within an average of 34.8%

Geometrical structures for radiation biology research as implemented in the TOPAS-nBio toolkit

Computational simulations, such as Monte Carlo track structure simulations, offer a powerful tool for quantitatively investigating radiation interactions within cells. The modelling of the spatial distribution of energy deposition events as well as diffusion of chemical free radical species, within realistic biological geometries, can help provide a comprehensive understanding of the effects of radiation on cells. Track structure simulations, however, generally require advanced computing skills to implement. The TOPAS-nBio toolkit, an extension to TOPAS (TOol for PArticle Simulation), aims to provide users with a comprehensive framework for radiobiology simulations, without the need for advanced computing skills. This includes providing users with an extensive library of advanced, realistic, biological geometries ranging from the micrometer scale (e.g. cells and organelles) down to the nanometer scale (e.g. DNA molecules and proteins). Here we present the geometries available in TOPAS-nBio

Prediction of DNA rejoining kinetics and cell survival after proton irradiation for V79 cells using Geant4-DNA

International audiencePurpose:Track structure Monte Carlo (MC) codes have achieved successful outcomes in the quantitative investigation of radiation-induced initial DNA damage. The aim of the present study is to extend a Geant4-DNA radiobiological application by incorporating a feature allowing for the prediction of DNA rejoining kinetics and corresponding cell surviving fraction along time after irradiation, for a Chinese hamster V79 cell line, which is one of the most popular and widely investigated cell lines in radiobiology.Methods:We implemented the Two-Lesion Kinetics (TLK) model, originally proposed by Stewart, which allows for simulations to calculate residual DNA damage and surviving fraction along time via the number of initial DNA damage and its complexity as inputs.Results:By optimizing the model parameters of the TLK model in accordance to the experimental data on V79, we were able to predict both DNA rejoining kinetics at low linear energy transfers (LET) and cell surviving fraction.Conclusion:This is the first study to demonstrate the implementation of both the cell surviving fraction and the DNA rejoining kinetics with the estimated initial DNA damage, in a realistic cell geometrical model simulated by full track structure MC simulations at DNA level and for various LET. These simulation and model make the link between mechanistic physical/chemical damage processes and these two specific biological endpoints