A practical theorem on using interferometry to measure the global 21-cm signal

The sky-averaged, or global, background of redshifted $21$ cm radiation is expected to be a rich source of information on cosmological reheating and reionizaton. However, measuring the signal is technically challenging: one must extract a small, frequency-dependent signal from under much brighter spectrally smooth foregrounds. Traditional approaches to study the global signal have used single antennas, which require one to calibrate out the frequency-dependent structure in the overall system gain (due to internal reflections, for example) as well as remove the noise bias from auto-correlating a single amplifier output. This has motivated proposals to measure the signal using cross-correlations in interferometric setups, where additional calibration techniques are available. In this paper we focus on the general principles driving the sensitivity of the interferometric setups to the global signal. We prove that this sensitivity is directly related to two characteristics of the setup: the cross-talk between readout channels (i.e. the signal picked up at one antenna when the other one is driven) and the correlated noise due to thermal fluctuations of lossy elements (e.g. absorbers or the ground) radiating into both channels. Thus in an interferometric setup, one cannot suppress cross-talk and correlated thermal noise without reducing sensitivity to the global signal by the same factor -- instead, the challenge is to characterize these effects and their frequency dependence. We illustrate our general theorem by explicit calculations within toy setups consisting of two short dipole antennas in free space and above a perfectly reflecting ground surface, as well as two well-separated identical lossless antennas arranged to achieve zero cross-talk.Comment: 17 pages, 6 figures, published in Ap

Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude

We estimate the 21 cm Radio Background from accretion onto the first intermediate-mass Black Holes between $z\approx 30$ and $z\approx 16$. Combining potentially optimistic, but plausible, scenarios for black hole formation and growth with empirical correlations between luminosity and radio-emission observed in low-redshift active galactic nuclei, we find that a model of black holes forming in molecular cooling halos is able to produce a 21 cm background that exceeds the Cosmic Microwave Background (CMB) at $z \approx 17$ though models involving larger halo masses are not entirely excluded. Such a background could explain the surprisingly large amplitude of the 21 cm absorption feature recently reported by the EDGES collaboration. Such black holes would also produce significant X-ray emission and contribute to the $0.5-2$ keV soft X-ray background at the level of $\approx 10^{-13}-10^{-12}$ erg sec$^{-1}$ cm$^{-2}$ deg$^{-2}$, consistent with existing constraints. In order to avoid heating the IGM over the EDGES trough, these black holes would need to be obscured by Hydrogen column depths of $N_\text{H} \sim 5 \times 10^{23} \text{cm}^{-2}$. Such black holes would avoid violating contraints on the CMB optical depth from Planck if their UV photon escape fractions were below $f_{\text{esc}} \lesssim 0.1$, which would be a natural result of $N_\text{H} \sim 5 \times 10^{23} \text{cm}^{-2}$ imposed by an unheated IGM.Comment: 10 pages, 7 figures, accepted to ApJ, replacement to match submitted versio

Le Traitement des Eaux de Consommation : La Nécessité d'une Recherche en Chimie de l'Eau

L'objectif principal de cet article est de montrer que les travaux de recherche en chimie de l'eau sont absolument nécessaires à la compréhension des phénomènes régissant la qualité des eaux de consommation produites et distribuées, ainsi qu'au développement de technologies innovantes dans le domaine du traitement de ces eaux. Pour l'atteindre, il a été choisi de présenter trois exemples des recherches menées à l'Université de Poitiers et à l'École Polytechnique de Montréal : deux exemples de recherche fondamentale, sur les matières organiques naturelles et sur les mécanismes d'oxydation par les radicaux hydroxyle et un exemple de la recherche d'application, sur l'évolution de la qualité de l'eau lors de son traitement biologique par ozonation couplée à la filtration sur charbon actif en grains.The main purpose of this paper is to demonstrate that a better understanding of chemical reactions and a better technologies development for the drinking water treatment absolutly needs research in water chemistry. In order to reach this objective, two examples of recent fundamental research works in water chemistry and one example of research applied to drinking water treatment have been selected.The first one concerns a fundamental research on characterization and analysis of natural organic matter. Nowadays, the main analytical tools used for quantification of NOM are DOC (BDOC for the biodegradable fraction) and UV-absorbance. However, a better knowledge of NOM would be useful to predict water quality and determination of doses of some treatment chemicals, such as coagulants and oxidants. This paper presents some data about (i) NOM fractionning by XAD macroporous resins and relationship between UV-absorbance and 13C-NMR, and (ii) study of chlorination of the isolated fractions. Based on these results, one can suppose that aquatic NOM could be soon easily fractionnated and characterized by simples analytical tools. However, many research works are still necessary, particularly on the field of relationships between data of "heavy" analytical tools (13C-NMR, pyrolysis/GC/MS, etc.) and more simple others (UVA/DOC, BDOC, fluorescence etc.).The second paragraph of the paper relates oxidation mechanisms by hydroxyl radicals. In ozonation of drinking water, currently applied in the drinking water treatment, OH radicals production is a necessary consequence, considered as the main action of ozone by some authors. So, disinfection quality, bromate production, BDOC formation, pesticides removal will never be entirely understood as long as hydroxyl radicals participation in ozonation processes will not be really cleared up. To illustrate this purpose, the example of ozonation of a free aminoacid (glycine) by molecular ozone and by OH radicals is shown. Oxidation by "pure" OH radicals, produced by radiolysis, as compared to oxidation by molecular ozone, (at acidic pH in the presence of radical scavengers) shows that two mechanisms are really different. So, some works published some years ago, mixed up the two pathways. Such mechanisms on aminoacids oxidation should allow to understand some more descriptive data on water disinfection and pesticides oxidation.The third example concerns the changes of water quality during ozone/GAC treatment. It is well known that ozonation of naturel waters leads to an enhancement of water biodegradability, in terms of BDOC increase. So, if this BDOC is not removed in the plant, it can be the origin of bacteria regrowth in distribution system. The solutions are either to include, after ozonation step, a biological treatment step on activated carbon (BAC), or to increase chlorination doses applied in final disinfection. The effects of BAC treatment on BDOC and ozonation by-products removals, in the case of the drinking water treatment plant of Sainte-Rose (City of Laval, Quebec, Canada), are described. Finally, taking into account the cost of such a process, the last paragraph of this paper gives some recommandations for conception on BAC treatment.As for general conclusion, some new research topics in water chemistry for the drinking water treatment are enumerated and some ideas about organization and development of applied and fundamental researches in water chermistry for the drinking water treatment, are given

Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics

The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other long-lived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the large-scale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later

Oxydation de S-triazines par les procédés d'oxydation radicalaire. Sous-produits de réaction et constantes cinétiques de réaction

L'étude bibliographique montre que l'oxydation de l'atrazine en milieu aqueux par 03, 03/H202, 03/UV, H202/UV et TiO2/UV ne permet qu'une dégradation limitée du pesticide (pas d'ouverture de l'hétérocycle azoté). Ces procédés d'oxydation conduisent aux mêmes sous-produits d'oxydation. Les composés N-déalkylés, les acétamido-s-triazines et l'hydroxyatrazine constituent les premiers sous-produits de dégradation de l'atrazine. Une oxydation plus poussée conduit par des réactions de N-déalkylation, d'hydroxylation et de déamination à la formation de produits finals relativement stables comme la déséthyldésisopropylatrazine, l'amméline, l'ammélide et l'acide cyanurique. La distribution des différents sous-produits en cours d'oxydation dépend du procédé d'oxydation utilisé, des conditions de mise en oeuvre du procédé (dose d'oxydants ou d'UV, longueur d'onde d'irradiation,...), des caractéristiques des eaux de dilution (pH, pièges à radicaux hydroxyles,...).Les études cinétiques indiquent que l'atrazine est relativement réfractaire à une oxydation par l'ozone moléculaire (constante cinétique de l'ordre de 6 l mol-¹ s-¹ à 20 °C) et est assez réactive vis-à-vis des radicaux hydroxyles (constante cinétique de l'ordre de 2,5 10·9 mol-¹ s-¹ à 20 °C). En ce qui concerne les constantes cinétiques de réaction des radicaux hydroxyles sur les autres s-triazines, les résultats montrent que les méthylthio s-triazines sont beaucoup plus réactives que les méthoxy s-triazines qui sont elles mêmes légèrement plus réactives que les chloro et hydroxy s-triazines. Parmi les sous-produits d'oxydation de l'atrazine, la déséthyldésisopropylatrazine et l'acide cyanurique sont très réfractaires à une oxydation par les radicaux hydroxyles et par l'ozone moléculaire.In this paper, oxidation studies of s-triazines in aqueous solution by advanced oxidation processes (O3, O3/H2O2, O3/UV, H2O2/UV, et TiO2/UV) have been reviewed.Oxidation by-products of atrazine:Several investigators have shown that N-dealkylated (deethylatrazine and deisopropylatrazine) and acetamido-s-triazines are the primary oxidation by-products of atrazine by O3 and by O3/H2O2 (table 1; fig. 1a). Under conditions which favored the production of hydroxyl radicals (03/H2O2), trace amounts of hydroxyatrazine may also be formed. These primary by-products are subsequently degraded to give complete N-dealkylated, deamined, dehalogenated and hydroxylated s-triazines (deethyldeisopropylatrazine, ammelide ammeline, cyanuric acid,...) (table 1). For example, oxidation of deethylatrazine by O3/H2O2 yields deethyldeisopropylatrazine as the major by-product (fig. 1b). Identical by-products are produced by photochemical oxidation (O3/UV, H2O2/UV and TiO2/UV) (table 2; fig. 4 and 5). UV photolysis of atrazine at 253.7 nm (monochromatic radiation) yields hydroxyatrazine as the major product (=0.95 -1.0 mole of hydroxyatrazine formed / mole of atrazine photolysed (fig. 4a) whereas N and N,N'-dealkylated, deaminated and hydroxyderivatives are produced by UV irradiation in the presence of ozone, hydrogen peroxide (fig. 4b) or photosensitisers.The s-triazine ring is found to be resistant to chemical and photochemical oxidation. Pathways for the degradation of atrazine by molecular ozone (fig. 2) and by hydroxyl radical (fg. 3) are proposed.Kinetic rate constants:The second-order kinetic rate constants for the reaction of molecular ozone and of hydroxyl radical with atrazine have been determined by several authors from competitive experiments or from kinetic models The rate constants for the reaction of ozone which have been measured (~ 61 mol-¹ s-¹ at ~ 20°C) indicate that molecular ozone is not very reactive towards atrazine. The rate constants which have been determined for the reaction of hydroxyl radical with atrazine by using different modes of generation of hydroxyl radicals (O3 + OH-; O3 + H2O2; PhotoFenton; H2O2 + UV) are in the order of 2 10[exp]9 - 2.5 10[exp]9 l mol-¹ s-¹ at ~ 20°C (table 3).Rate constants for the reaction of hydroxyl radical with other s-triazines have been determined from competitive kinetic experiments. The relative rate constants show that methylthio s-triazines are far more reactive than methoxy s-triazines, which in turn are more reactive than chloro and hydroxy s-triazines (table 4). The kinetic data also confirm that deethyldeisopropylatrazine and cyanuric acid are very refractory to the oxidation by hydroxyl radical

Oxydation d'un acide humique aquatique par le bioxyde de chlore. Incidences sur une post-chloration et sur un traitement au charbon actif

Cette étude de laboratoire a eu pour but d'examiner la réactivité du bioxyde de chlore sur un acide humique d'origine aquatique en solution aqueuse et en milieu neutre (pH = 7,5) et de préciser en particulier l'incidence d'une préoxydation chimique au CIO2 sur les potentiels de formation de composés organohalogénés (trihalométhanes, acides dicloroacétique et trichloroacétique, chlore organiquement lié) et sur l'adsorbabilité du carbone organique sur charbon actif.Les résultats obtenus montrent que radian du bioxyde de chlore sur racide humique Pinail à l'obscurité, conduit à des faibles abattements du carbone organique dissous (< 10 %) et de l'absorbance UV à 254 nm (de l'ordre de 30 %) et conduit à des productions potentiel es en composées organohalogénés très nettement inférieures à celles formées par chloration. De plus, une préoxydation chimique au bioxyde de chlore permet de diminuer d'une manière très significative la production de composés organohalogénés au cours d'une post-chloration et semble améliorer l'adsorbabllité du carbone organique sur charbon actif.L'oxydation de l'acide humique par le bioxyde de chlore s'accompagne, par ailleurs, de la formation de chlorites (0,65 mg/mg de CIO2 consommé) qui peuvent ensuite être oxydés en chlorates au cours d'une post-chloration ou réduits en chlorures par un traitement au charbon actif.Enfin, les résultats obtenus font apparaître que le mécanisme d'oxydation de composés organiques parle bioxyde de chlore en présence de la lumière ainsi que les interactions entre le bioxyde de chore, les chlorites, la matière organique et le charbon actif méritent d'être plus précisément étudiés.Chlorine dioxide has drawn much recent attention as an alternative disinfectant and oxidant for drinking water to replace chlorine because of its powerful disinfecting ability and its limited capacity to produce organohalogenated compounds. However, the use of chlorine dioxide leads to chlorite (ClO2-) and chlorate (ClO3-) as inorganic oxidation by-products which are reported to have toxic effects on humans. The reactions of ClO2 with simple organic compounds (phenols, aliphatic and aromatic amines...) produce polar compounds such as quinone, ketones, aldehydes and carboxylic acids while oxydation by-products of dissolved organic matter of surface waters (in particular humic substances) are largely unknown. Consequently, the aim of this work was to obtain a better understanding of the effects of the use of chlorine dioxide in drinking water treatment To this end, experiments were carried out with dilute aqueous solutions of an isolated aquatic humic acid (Pinail humic acid, PHA) and the objectives of this present study were :- To evaluate the ClO2 demand and to determine the productions of chlorite, chlorate and of organohalogenated compounds such as trihalomethanes (THMs), dichloroacetic and trichloroacetic acids (DCA, TCA) which are the main organohalogenated products formed by chlorination.- To show the effects of chlorine dioxide preoxidation on organic halide formation potentials (postchlorination) and on the removal of dissolved organic carbon (DOC) by activated carbon. In addition, reactions of chlorite with chlorine or with activated carbon were also examined.EXPERIMENTALPniail humic acid was dissolved in phosphate buffered ultra-pure water (pH = 7.5). Oxidation and adsorption experiments were carried out in headspace-free bottles, at 20 ± 1 °C and in the dark. Stock solutions of chlorine dioxide (4-6 g l-1) and of chlorine (6-10 g l-1) were prepared in the laboratory and titrated by iodometry. Residual chlorine dioxide concentration in PHA solutions was determined by spectrophotometric measurement at 360 nm and by two colorimetric methods : the chlorophenol red and the ACVK methods. Concentrations of DOC and of total organic chlorine or halogen (TOCI, TOX) were measured using a DOHRMANN DC 80 carbon analyser and a DOHRMANN DX 20 A TOX analyser equipped with a microcoulometric cell, respectively. THMs, DCA and TCA were determined by a gas chromatograph equipped with a 63 Ni electron capture detector after extraction by pentane for the THMs, and methylation in ether phase for DCA and TCA. Inorganic chlorine species were analysed by HPLC with a UV detector (ClO2-) or by chromatography (Cl-, ClO3-).RESULTS• Oxidation of PHA by ClO2The results showed that PHA consumed about 2 mg of ClO2/mg of DOC after a reaction time of 24 hours (fig. 1) and that there is a rapid consumption of ClO2 during the first 30 minutes of the reaction (fig. 2) Oxidation by ClO2 had no effect on DOC concentration (DOC removal : < 10 %) and led to a significant decrease (about 30 %) of the UV-absorbance at 254 or 270 nm (fig. 1 and 2), and to productions of ClO2- (0,65 mg of ClO2-/mg of ClO2 consumed) which were independant of the applied oxidant dose and of the reaction time.Furthermore, after a 72 hour reaction time in the dark, chlorine dioxide ([ClO2]0 = 5 mg l-1, [PHA]0 = 5 mg l-1, DOC = 2,6 mg l-1) produces very small amounts of chloroform (< 5 µg l-1), DCA (5 µg l-1) and TCA (5 µg l-1) and organochlorinated compounds (TOCl : 36 µg/mg DOC) compared to chlorine oxidation (tableau 1). However, in the presence of sunlight, ClO2 is rapidly photodecomposed (fig. 3) and the photodegradation products of ClO2 allow bromide oxidation (fig. 11) and lead to higher productions of organohalogenated compounds such as THMs (fig. 4).• Chlorine dioxide preoxidation followed by chlorinationAs shown in figure 5, chlorine dioxide preoxidation reduces the production of organohalogenated compounds and the chlorine demand during postchlorination. For a preoxidant dose corresponding to the ClO2 demand of PHA, the decrease in the formation potentials of CHCl3, DCA, TCA and TOCl was about 40-50 %. These results confirm the similarity of the action of chlorine dioxide and chlorine on aromatic structures which have high electron density carbons and which constitute probably the most reactive precursors of organohalogenated by-products.As far as chlorite concentration is concerned, the results showed that chlorite formed during the preoxidation step was completely oxidized to chlorate during postchlorination, under the experimental conditions used in this study (chlorine dose : 40 mg l-1; contact time : 24 or 72 hours). Because of the reactions of chlorine eh chlorine and with residual chlorine dioxide, a small increase in the chlorine demand was observed when PHA solutions were heavily preoxidized (fig. 5).• Chlorine dioxide preoxidation followed by activated carbon treatmentBatch experiments were carried out with a powdered activated carbon (PAC, granulometry : < 80 µm) which was obtained by crushing a commercial granular activated carbon (CECA 40,12 x 40 mesh). Once equilibrium was achieved (contact time : 10 days), adsorption isotherms indicated that chlorine dioxide preoxidation increases the absorbability of DOC on activated carbon (fig; 4tableau 2). Furthermore, chlorite in oxidized PHA solutions was reduced by PAC to chloride. The capacity of CECA 40 activated carbon for ClO2- reduction to Cl- was about 170 mg ClO2-/g of PAC (fig. 7). Other experiments showed that chlorite may react with specific surface groups on PAC to produce inorganic carbon (fig. 7) and with PHA only in the presence of PAC as shown the DOC and UV-absorbance curves in figure 8 and the increase of TOX concentration in the liquid phase in figure 9. Thus the observed increase in DOC absorbability on PAC after a chlorine dioxide preoxidation may be attributed to cheminal interactions between PAC, chlorite, residual chlorine dioxide and adsorbed organic matter and requires further study

Etude sur les acides fulviques extraits d'eaux superficielles françaises - Extraction, caractérisation et réactivité avec le chlore

Après avoir présenté quelques données bibliographiques sur les substances humiques aquatiques, l'extraction de plusieurs substances humiques issues de onze eaux de surface françaises, est discutée en terme de rendements d'extraction. Quelques paramètres de caractérisation des acides fulviques sont présentés et en particulier, l'analyse élémentaire, l'absorption UV, les fonctions carboxyles et les potentiels de réactivité avec le chlore. Concernant la chloration, une attention particulière a été portée d'une part sur la nature produits organo-chlorés formés et d'autre part sur les corrélations qui existent entre la nature des acides fulviques et leur potentiel de réactivité avec le chlore.Numerous procedure for the isolation of aquatic humic substances are described in literature. The first part of this study presents the extraction of fulvic and humic acids from eleven French surface waters, using XAD 8 macroreticular resin as developed by TRURMAN and MALCOLM (1981). The results are discussed in terms of extraction yield and fulvic acid/humic acid mass ratio.The second part of the paper presents some structural parameters of the extracted fulvic acids such as elemental analysis, UV-absorbance, carboxyle-function content and in some cases of fulvic acids, infrared spectrum and apparent molecular weight investigated by ultra filtration.The third part of the work concerns the study of fulvic acids chlorination. Firstly, the gas chromatography - mass spectrometry analysis of one chlorinated fulvic acid allowed us to identify some chlorination by-products and especially chloroform, dichloro-acetic and trichloroacetic acids and some other chlorinated aliphatic acids. Secondly, the chlorine reactivity potentials of each fulvic acids were determined and results are discussed in terms of chlorine consumption, chloroform and total organohalides formation potentials. Some relationships are established between the chlorine reactivity potentials and UV-absorbance of the extracted fulvic acids

Host Growth Can Cause Invasive Spread of Crops by Soilborne Pathogens

Invasive soilborne plant pathogens cause substantial damage to crops and natural populations, but our understanding of how to prevent their epidemics or reduce their damage is limited. A key and experimentally-tested concept in the epidemiology of soilborne plant diseases is that of a threshold spacing between hosts below which epidemics (invasive spread) can occur. We extend this paradigm by examining how plant-root growth may alter the conditions for occurrence of soilborne pathogen epidemics in plant populations. We hypothesise that host-root growth can 1) increase the probability of pathogen transmission between neighbouring plants and, consequently, 2) decrease the threshold spacing for epidemics to occur. We predict that, in systems initially below their threshold conditions, root growth can trigger soilborne pathogen epidemics through a switch from non-invasive to invasive behaviour, while in systems above threshold conditions root growth can enhance epidemic development. As an example pathosystem, we studied the fungus Rhizoctonia solani on sugar beet in field experiments. To address hypothesis 1, we recorded infections within inoculum-donor and host-recipient pairs of plants with differing spacing. We translated these observations into the individual-level concept of pathozone, a host-centred form of dispersal kernel. To test hypothesis 2 and our prediction, we used the pathozone to parameterise a stochastic model of pathogen spread in a host population, contrasting scenarios of spread with and without host growth. Our results support our hypotheses and prediction. We suggest that practitioners of agriculture and arboriculture account for root system expansion in order to reduce the risk of soilborne-disease epidemics. We discuss changes in crop design, including increasing plant spacing and using crop mixtures, for boosting crop resilience to invasion and damage by soilborne pathogens. We speculate that the disease-induced root growth observed in some pathosystems could be a pathogen strategy to increase its population through host manipulation. © 2013 Leclerc et al.ML thanks the Institut Technique franc¸ais de la Betterave industrielle (ITB) for funding this project. CAG and JANF were funded by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Sous-produits de réaction formés lors de la filtration sur charbon actif de composés phénoliques en présence d'ions chlorite

L'étude des interactions entre les ions chlorite, un charbon actif en grains (CAG CECA 40) et des composés phénoliques (phénol et para-nitrophénol) a été réalisée à partir d'expériences de filtration sur mini-colonnes de CAG de solutions aqueuses de chlorite et du composé organique en mélange ([C102-] inf=50 mg.l-¹; [Composé Organique]jnf=200 µmol.l-¹ ; 3 g de CAG; Vitesse de filtration: 3,7 m.h-¹). Les résultats obtenus ont permis de montrer que la présence de chlorite conduit à une augmentation des capacités du CAG vis-à-vis de l'élimination du phénol et du para-nitrophénol. Cette augmentation résulte de réactions chimiques entre le composé organique et les sous-produits de décomposition des ions chlorite par le charbon actif. Les analyses par couplage CG/SM des extraits issus des charbons actifs à la fin des filtrations ont permis de mettre en évidence la présence de nombreux composés adsorbés sur le charbon actif. Les composés identifiés résultent de réactions d'oxydation, de deshydroxylation, de carboxylation, d'halogénation, d'hydroxylation et de dimérisation. L'action des ions chlorite sur le charbon actif peut conduire à la formation de radicaux à la surface du charbon actif ou en solution capables de réagir avec les composés organiques pour former les sous-produits observés.The use of chlorine dioxide for the chemical preoxidation of potable water with high oxidant demand requires that the major inorganic byproduct, chlorite, in the treatment system be removed, owing to the potential toxicity of this oxychlorine species. Granular Activated Carbon (GAC) filtration, in converting chlorite ions into chloride, appears to be an interesting approach, but very few data are available concerning possible interactions in the presence of organic matter. The present research was designed to examine the influence of phenolic compounds on the efficiency of activated carbon in removing chlorite and to study the reactions between chlorite, activated carbon and organic molecules. Laboratory experiments have been carried out with relatively high substrate concentrations in order to identify the resulting byproducts.Materials and Methods.Filtrations of solutions containing chlorite and a phenolic compound (phenol or para nitrophenol; [Organic Compound]inf=200 µmol.L-¹;[C102-] inf=50 mg L-¹; pH=7.2); were performed using 1- cm i.d. glass columns packed with 3.0 g of GAC CECA 40 (Flow rate: 3.7 m.h-¹). Inorganic species were analysed by HPLC, with an anion column and a conductimetric detector for chloride and chlorate, and with a C-18 column and a UV detector for chlorite. Phenol and para nitrophenol were also analysed by HPLC, in the reverse mode. At the conclusion of the filtrations, the Total Organic Halogen (TOX) adsorbed on the carbon was determined after combustion of the carbon and measurement of the liberated halides with a micro coulometer (Dohrmann DX20). In order to identify organic reaction byproducts, carbon samples were Soxhlet extracted with methylene chloride and half of the extracts were methylated with diazomethane. Identification of the organic products was then carried out by gas chromatography / mass spectrometry with a DB5 capillary column and a quadrupolar hyperbolic filter system CPV/MS.Results and Discussion.Effects of phenol and p nitrophenol on removal of chlorite by GAC. The effluent curves from columns that received solutions containing both chlorite and an organic solute (columns A and B; fig. 1) showed that the presence of phenol or p nitrophenol in the influent decreases the capacity of GAC to remove chlorite.Effect of chlorite on removal of phenol and p nitrophenol. An increase in the cumulative removal of the organic solute was observed for columns A and B compared with columns that received solutions of the phenolic compound only (fig. 2; table 11). p benzoquinone was found in the eff1uent of column A fed with a chlorite phenol solution (fig. 3).Formation of organic byproducts by reactions between chlorite and phenol or p nitrophenol in the presence of GAC. TOX analyses showed that interactions between chlorite, GAC, and phenol or p nitrophenol led to the production of organohalogenated compounds. These data clearly demonstrate that halogenation reactions take place in the GAC bed and that a fraction of the total amount of phenol or p nitrophenol removed can be due to chemical reactions. GC/MS analyses of GAC extracts of columns A and B (tables IV and V) indicated that the phenol chlorite GAC reactions yield a variety of organic byproducts that are produced by hydroxylation and carboxylation of the aromatic ring by oxidation to quinones, by chlorine substitution and by dehydroxylation and dimerization reactions. Fewer products could be identified in the reaction between p nitrophenol, chlorite, and GAC. Since chlorite is unreactive with phenol and p nitrophenol in neutral aqueous solution, the formation of these organic byproducts can be attributed to reactions between phenol or p nitrophenol present in the GAC pore solution or adsorbed on GAC and the chemical species (Cl· ClO·, ClO2, HOCl (ClO-), surface free radicals ...) generated from the reaction of chlorite and carbon. Thus, aromatic acids could come from radical processes between adsorbed molecules and carbon surface functional groups oxidized by chlorite. The formation of dimers can also be explained by a freeradical mechanism. The reactions between Cl·, ClO· radicals or radicals present on the GAC surface, with organic compounds produce organic radicals via H atom abstraction or one electron transfer. Organic radicals such as phenoxy radicals or other aromatic radicals can then undergo dimerization by carbon-oxygen or carbon-carbon coupling. The formation of organochlorinated compounds can be explained by the reaction of chlorine (HOCl, ClO-) and chlorine radicals with organic molecules present in the solution. However further investigation is needed in order to evaluate if such compounds can be formed on GAC filters and then desorbed in the effluent in thc case of drinking waters pretreated with chlorine dioxide

Cosmic Microwave Background Constraints on the Duration and Timing of Reionization from the South Pole Telescope

The epoch of reionization is a milestone of cosmological structure formation, marking the birth of the first objects massive enough to yield large numbers of ionizing photons. However, the mechanism and timescale of reionization remain largely unknown. Measurements of the cosmic microwave background (CMB) Doppler effect from ionizing bubbles embedded in large-scale velocity streams—known as the patchy kinetic Sunyaev-Zel'dovich (kSZ) effect—can be used to constrain the duration of reionization. When combined with large-scale CMB polarization measurements, the evolution of the ionized fraction, x-bar_(e), can be inferred. Using new multi-frequency data from the South Pole Telescope (SPT), we show that the ionized fraction evolved relatively rapidly. For our basic foreground model, we find the kSZ power sourced by reionization at ℓ = 3000 to be D^(patchy)_3000 ≤ 2.1 μK^2 at 95% confidence. Using reionization simulations, we translate this to a limit on the duration of reionization of Δz≡z_(x-bar)_e=0.20 - z_(x-bar)_e=0.99≤4.4 (95% confidence). We find that this constraint depends on assumptions about the angular correlation between the thermal SZ power and the cosmic infrared background (CIB). Introducing the degree of correlation as a free parameter, we find that the limit on kSZ power weakens to D^(patchy)_3000 ≤ 4.9 μK^2, implying Δz ≤ 7.9 (95% confidence). We combine the SPT constraint on the duration of reionization with the Wilkinson Microwave Anisotropy Probe measurement of the integrated optical depth to probe the cosmic ionization history. We find that reionization ended with 95% confidence at z > 7.2 under the assumption of no tSZ-CIB correlation, and z > 5.8 when correlations are allowed. Improved constraints from the full SPT data set in conjunction with upcoming Herschel and Planck data should detect extended reionization at >95% confidence provided Δz ≥ 2. These CMB observations complement other observational probes of the epoch of reionization such as the redshifted 21 cm line and narrowband surveys for Lyα-emitting galaxies