The formation of stable organic chloramines during the aqueous chlorination of cytosine and 5-methylcytosine

The interaction of aqueous hypochlorous acid with the aminopyrimidines, cytosine and 5-methylcytosine has been investigated. Analysis of the reaction mixtures indicated substantial formation of chlorine substitution and addition products with little reduction of chlorine to chloride. Very high levels of combined chlorine were observed. Ultraviolet spectra showed complex patterns of behaviour with peak shifts and intensity changes occurring in some cases and full loss of aromaticity in others. The latter process was suggestive of addition of HOCl to double bonds with formation of chlorohydrins. The behaviour was found to depend on reaction pH and chlorine to base ratios. Thin layer chromatography revealed complex patterns of stable chloramine formation with the reaction mixture complexity tending to increase with increasing pH and FAC/base ratios. Chemical ionization mass spectra disclosed the existence of a number of organic chloramines containing up to three chlorine atoms and, in the case of 5-methylcytosine a major ring cleavage and rearrangement product of as yet undefined structure. The half-life for the decay of the combined chlorine was found to be approx. 3.9 days and to be independent of precursor compound and pH.     

The kinetics and products of the chlorination of caffeine in aqueous solution

The kinetics and products of the reaction between aqueous hypochlorous acid and caffeine have been evaluated. The reaction was found to be dependent on pH only to the extent that it influences the fraction of FAC which is in the form of HOCl. The kinetics were found to be well represented by the expression: The rate constant had a value of 162 ± 32 M⁻² s⁻¹. For each mol of caffeine consumed, 6.3 mol of FAC were consumed. The chlorination reaction proceeded primarily by ring cleavage and rearrangement forming nonoaromatic nitrogen heterocycles. 8-Chlorocaffeine was unequivocally identified as an aqueous chlorination product but was found to be formed only to a small extent and under rather limited conditions. No stable organic chloramines were formed.     

UV-induced effects on chlorination of creatinine

Ultraviolet (UV) irradiation is commonly employed for water treatment in swimming pools to complement conventional chlorination, and to reduce the concentration of inorganic chloramine compounds. The approach of combining UV irradiation and chlorination has the potential to improve water quality, as defined by microbial composition. However, relatively little is known about the effects of this process on water chemistry. To address this issue, experiments were conducted to examine the effects of sequential UV₂₅₄ irradiation/chlorination, as will occur in recirculating system of swimming pools, on disinfection byproduct (DBP) formation. Creatinine, which is present in human sweat and urine, was selected as the target precursor for these experiments.     

Formation of organic chloramines during water disinfection - chlorination versus chloramination

Many of the available studies on formation of organic chloramines during chlorination or chloramination have involved model organic nitrogen compounds (e.g., amino acids), but not naturally occurring organic nitrogen in water. This study assessed organic chloramine formation during chlorination and chloramination of 16 natural organic matter (NOM) solutions and 16 surface waters which contained dissolved organic nitrogen (DON). Chlorination rapidly formed organic chloramines within 10 min, whereas chloramination formed organic chloramination much more slowly, reaching the maximum concentration between 2 and 120 h after the addition of monochloramine into the solutions containing DON. The average organic chloramine formation upon addition of free chlorine and monochloramine into the NOM solutions were 0.78 mg-Cl₂/mg-DON at 10 min and 0.16 mg-Cl₂/mg-DON at 24 h, respectively. Organic chloramine formation upon chlorination and chloramination increased as the dissolved organic carbon/dissolved organic nitrogen (DOC/DON) ratio decreased (i.e., DON contents increased). Chlorination of molecular weight (10,000 Da) fractionated water showed that molecular weight of DON would not impact the amount of organic chloramines produced. Comparison of three different disinfection schemes at water treatment plants (free chlorine, preformed monochloramine, and chlorine/ammonia additions) indicated organic chloramine formation could lead to a possible overestimation of disinfection capacity in many chloraminated water systems that add chlorine followed by an ammonia addition to form monochloramine.     

Model studies in aqueous chlorination: The chlorination of phenols in dilute aqueous solutions

A study of the chlorination of four phenols in dilute aqueous solution at initial pH's of 6.0 and 3.5 is described. Extensive chlorination is observed under these mild reaction conditions. Identification of the products indicates that the reactions occurring involve chlorination to more highly chlorinated phenols, oxidation to chlorinated p-benzoquinones, chlorine addition to the aromatic ring to form chlorinated 2,5-cyclohexadienones, and addition of 2 moles of chlorine or one each of chlorine and hypochlorous acid to give chlorinated cyclohexenones and chlorinated hydroxycyclohexenones.     

Bromine tracer study of the chlorination with hypochlorite in a buffered and a non-buffered aqueous solution containing chloride, bromide and phenol as model compound

A tracer study of the chlorine-induced bromination of phenol in buffered (pH = 6.0 and 8.0) and in non-buffered (initial pH = 7.0) aqueous solutions is described. In the non-buffered solution about 8 at.% bromine containing compounds could be isolated from the reaction mixture; for the buffered system at pH 6.0 and 8.0 the figures were 17 and 47 at.% respectively.Two types of compounds were found in the reaction mixtures; halogen containing phenols and compounds of a non-phenolic character.     

Kinetics of aqueous chlorination of some pharmaceuticals and their elimination from water matrices

Apparent rate constants for the reactions of four selected pharmaceutical compounds (metoprolol, naproxen, amoxicillin, and phenacetin) with chlorine in ultra-pure (UP) water were determined as a function of the pH. It was found that amoxicillin (in the whole pH range 3-12), and naproxen (in the low pH range 2-4) presented high reaction rates, while naproxen (in the pH range 5-9), and phenacetin and metoprolol (in the pH range 2.5-12 for phenacetin, and 3-10 for metoprolol) followed intermediate and slow reaction rates. A mechanism is proposed for the chlorination reaction, which allowed the evaluation of the intrinsic rate constants for the elementary reactions of the ionized and un-ionized species of each selected pharmaceutical with chlorine. An excellent agreement is obtained between experimental and calculated rate constants by this mechanism.The elimination of these substances in several waters (a groundwater, a surface water from a public reservoir, and two effluents from municipal wastewater treatment plants) was also investigated at neutral pH. The efficiency of the chlorination process with respect to the pharmaceuticals elimination and the formation THMs was also established. It is generally observed that the increasing presence of organic and inorganic matter in the water matrices demand more oxidant agent (chlorine), and therefore, less chlorine is available for the oxidation of these compounds. Finally, half-life times and oxidant exposures (CT) required for the removal of 99% of the four pharmaceuticals are also evaluated. These parameters are useful for the establishment of safety chlorine doses in oxidation or disinfection stages of pharmaceuticals in treatment plants.     

Ozonation of pyrene in aqueous solution

The reaction of pyrene with ozone was studied in aqueous solution at low (10–200 μg l⁻¹) substrate concentration and with ozone concentrations (5 mg l⁻¹) approximating to those used in potable water treatment. Degree of reaction and the formation of polyaromatic/aromatic reaction products were assessed using a technique of solvent extraction and derivatisation with gas chromatographic (GC), gas chromatographic-mass spectrometric (GC-MS), high performance liquid chromatographic (HPLC) and u.v. spectrometric analysis of extracts. A freeze drying/derivatisation technique with GC and GC-MS analysis was employed for the isolation/identification of short chain polar aliphatic reaction products. Substantial destruction of pyrene was recorded within 1 min of reaction with ozone. Polyaromatic/aromatic compounds did not persist; reaction products are likely to be short chain polar aliphatic compounds. Products of this type were isolated but not identified in the study.     

Sorption and desorption of pyridine-clay in aqueous solution

Sterile, radiochemical procedures were applied in a study of the cationic exchange processes occurring during pyridine sorption onto highly-purified sodium kaolinite and sodium montmorillonite particulates of colloidal dimensions. Sodium desorption is directly related to increased protonation. Hydrogen ion exchange dominates at pH < 3. Maximum pyridium sorption occurs at pH 4.0–5.5. At pH > 7.0 neither pyridium nor hydrogen exchange occurs. Previously sorbed pyridium desorbs from the clays as a function of time and solution pH with maximum desorption at pH 1 and 11 and minimum near pH = pK_a = 5.25. Pyridine desorption is much slower than sorption at comparable pH and clay:organic ratio. The extent of desorption is also directly related to the number of stages and/or the volume of solution. Particulate charge, zeta potential, changes are greatest between pH 1–4 with coagulation and charge reversal at pH ≅ 2 if the pyridine concentration is < cation exchange capacity, CEC. Pyridine concentration in excess of CEC induces coagulation through the “cage effect”.     

Mutagenicity and alkylating activity of the aqueous chlorination products of humic acid and their molecular weight fractions

Fluka humic acid used as a model substrate in these studies was analysed for elemental and the oxygen-containing functional groups. It was chlorinated at C:Cl molar ratios of 1:1 and 1:0.3 and subsequently separated into molecular weight fractions by ultrafiltration. The freeze-dried, chlorinated humic acid and the respective molecular weight fractions were analyzed for TOC, TOX, alkylating activity using 4-(p-nitrobenzyl)pyridine and mutagenicity by the Ames/Salmonella/microsome assay with strains TA-98 and TA-100. Results indicated that predominantly non-volatile, direct-acting mutagenic and/or alkylating agents were formed during humic acid chlorination and that these agents were unevenly distributed among the various molecular weight fractions. Formation of mutagenic and alkylating agents were highly dependent upon level of chlorination and total organic carbon. Higher levels of mutagenic and alkylating activities were produced with increasing concentration of chlorine in the range of 0.4-1.2 chlorine equivalents per mole of carbon. However, both these activities in the freeze-dried, chlorinated humic acid solutions containing the non-volatiles or the fresh solutions decreased gradually with increasing pH and storage time, apparently due to degradation and hydrolysis of some of the components.     

酸性水溶液对建筑材料影响现状研究综述

对环境污染产生的酸雨对建筑材料的腐蚀作用进行了分析,从酸性水溶液对建筑材料性能影响的研究现状和进展方面进行了论述,从而避免酸性水溶液对建筑材料的腐蚀,以提高建筑材料的强度。     

Sonochemical decomposition of dibenzothiophene in aqueous solution

Dibenzothiophene is decomposed rapidly by sonication in aqueous solution. Decomposition of dibenzothiophene follows a first-order reaction kinetics. The rate constant was found to increase with increasing ultrasonic energy intensity, temperature, and pH and decrease with increasing initial dibenzothiophene concentration. The activation energy was 12.6 kJ/mol in the temperature range of 15–50°C, suggesting a diffusion-controlled reaction. Hydroxydibenzothiophenes and dihydroxydibenzothiophenes were identified as reaction intermediates. It is proposed that dibenzothiophene is oxidized by OH radical to hydroxy-dibenzothiophenes and then to dihydroxy-dibenzothiophenes. Kinetic analysis suggests that approximately 72% of the dibenzothiophene decomposition occurred via OH radical addition. A pathway and a kinetic model for the sonochemical decomposition of dibenzothiophene in aqueous solution are proposed.     

Odor effects of pyridine-montmorillonite in aqueous solution

The threshold odor response of individuals to aqueous solutions of pyridine with and without the presence of sodium montmorillonite was determined at 24 and 40°C. At 24°C there was a significant olfactory effect at pyridine-clay concentrations that produced no effect at 40°C. The olfactory effect depended on the relative sensitivity of the panelists.     

Stability of chlorine dioxide in aqueous solution

Chlorine dioxide in unbuffered aqueous solution at pH 9 and 25°C decomposes to chlorate, chlorite, chloride and oxygen by coupled slow and rapid reactions. The initiation of the second rapid decomposition depends on the initial chlorine dioxide concentration and ionic strength of the solution. Chloride ion has a catalytic and inhibiting effect, changing the product distribution to a 1:1 molar ratio of chlorate and chlorite, thus increasing the oxidizing potential of chlorine dioxide. In buffered solutions at pH 8.8 the reaction is pseudo-second order, yielding chlorate and chlorite as products.     

The production of bromophenols resulting from the chlorination of waters containing bromide ion and phenol

The formation of 2,4,6-tribromophenol is shown to result from the chlorination of water containing phenol and bromide ion at pH 7.4. Direct bromination with hypobromous acid is compared with bromination by hypochlorous acid and bromide ion. Under conditions where HOCl is not limiting, a higher yield of bromine substitution products can be expected from bromination by HOCl + Br⁻ than by direct bromination by HOBr.     

Role of discontinuous chlorination on microbial production by drinking water biofilms

Microbial quality in water distribution systems is strongly affected by the development of microbial biofilms. Production and release of microbial cells by the biofilm affect microbial levels in the water column and in some cases this fact constitutes a public health concern. In this study, we attempt to analyze in which way the existence of different episodes of chlorine depletion affects both biofilm formation and microbial load of an artificial laboratory system. The work was carried out using two parallel packed bed reactors both supplied with running tap water. One of the reactors was used as a control and was permanently exposed to the action of chlorine. In the other reactor, chlorine was neutralized at selected times during the experiment and for periods of variable length. During the experiment the concentration of total and viable cells from the effluent was monitored at the exit of each of the reactors. The data obtained were used to estimate microbial production from the biofilms. As an average, release of microbial cells to the water phase increased tenfold in the absence of chlorine. The results also indicate that disinfectant efficiency against the biofilm was not recovered when chlorine returned to normal levels after each event of chlorine neutralization. Cell viability in the water phase in the presence of chlorine was low at the beginning of the experiment but increased 4 orders of magnitude after five neutralization periods. Therefore, subsequent episodes of chlorine depletion may accelerate the development of microbial communities with reduced susceptibility to disinfection in real drinking water systems.     

Chlorination of pure bacterial cultures in aqueous solution

The fate and distribution of chlorine in aqueous solutions containing four pure bacterial cultures was studied. Solutions were subjected to chlorination at different initial free chlorine concentrations. Resulting concentrations of residual chlorine were determined by both DPD/FAS titration and membrane introduction mass spectrometry (MIMS). In all cases, false-positive breakpoint chlorination curves, probably attributable to the formation of chloroorganic-N compounds, were observed by DPD/FAS titration, while little or no inorganic residual chloramine was found by MIMS. Free chlorine was observed in similar quantities by both methods after chlorine demand by bacterial cellular materials in solution was satisfied. These results indicated the residual chloramines existed in the form of organic chloramines; these compounds are generally recognized as being poor antimicrobial agents. Further investigation confirmed that the bacterial cells were the source of organic-N compounds. The kinetics of chlorination of pure bacterial suspensions was also studied. The pattern of residual chlorine decay following chlorination of the bacterial suspensions indicated rapid initial free chlorine consumption, followed by slow free chlorine consumption, with trace quantities of inorganic chloramine being formed.     

Decomposition of diazinon in aqueous solution by ozonation

The decomposition of diazinon in aqueous solution by ozonation was studied under various solution pH values, gaseous ozone dosages, gaseous pressure, alkalinity levels and solution temperatures. Ozonation has been shown to be feasible for achieving nearly complete decomposition of diazinon within 1 h. The surface tension of aqueous solution was found to be affected by the dissolved diazinon and influenced the oxidation mechanism of diazinon by ozonation in aqueous solution. The gas–liquid reaction model was well used to describe the transfer and reaction behaviors of reacting species in the system. The quasi-global kinetics based on a simplified consecutive reaction scheme was developed to describe the temporal behavior of diazinon decomposition in aqueous solution by ozonation.     

Kinetic modeling of electro-Fenton reaction in aqueous solution

To well describe the electro-Fenton (E-Fenton) reaction in aqueous solution, a new kinetic model was established according to the generally accepted mechanism of E-Fenton reaction. The model has special consideration on the rates of hydrogen peroxide (H(2)O(2)) generation and consumption in the reaction solution. The model also embraces three key operating factors affecting the organic degradation in the E-Fenton reaction, including current density, dissolved oxygen concentration and initial ferrous ion concentration. This analytical model was then validated by the experiments of phenol degradation in aqueous solution. The experiments demonstrated that the H(2)O(2) gradually built up with time and eventually approached its maximum value in the reaction solution. The experiments also showed that phenol was degraded at a slow rate at the early stage of the reaction, a faster rate during the middle stage, and a slow rate again at the final stage. It was confirmed in all experiments that the curves of phenol degradation (concentration vs. time) appeared to be an inverted "S" shape. The experimental data were fitted using both the normal first-order model and our new model, respectively. The goodness of fittings demonstrated that the new model could better fit the experimental data than the first-order model appreciably, which indicates that this analytical model can better describe the kinetics of the E-Fenton reaction mathematically and also chemically.