Aqueous chlorination of carbamazepine: Kinetic study and transformation product identification

Carbamazepine reactivity and fate during chlorination was investigated in this study. From a kinetic standpoint, a third-order reaction (first-order relative to the CBZ concentration and second-order relative to the free chlorine concentration) was observed at neutral and slightly acidic pH, whereas a second-order reaction (first order relative to the CBZ concentration and first order relative to the free chlorine concentration) was noted under alkaline conditions. In order to gain insight into the observed pH-dependence of the reaction order, elementary reactions (i.e. reactions of Cl₂, Cl₂O, HOCl with CBZ and of ClO⁻ with CBZ or of HOCl with the ionized form of CBZ) were highlighted and second order rate constants of each of them were calculated. Close correlations between the experimental and modeled values were obtained under these conditions. Cl₂ and Cl₂O were the main chlorination agents at neutral and acidic pH. These results indicate that, for a 1 mg/L free chlorine concentration and 1–10 mg/L chloride concentration at pH 7, halflives about 52–69 days can be expected. A low reactivity of chlorine with CBZ could thus occur under the chlorination steps used during water treatment. From a mechanistic viewpoint, several transformation products were observed during carbamazepine chlorination. As previously described for the chlorination of polynuclear aromatic or unsaturated compounds, we proposed monohydroxylated, epoxide, diols or chlorinated alcohol derivatives of CBZ for the chemical structures of these degradation products. Most of these compounds seem to accumulate in solution in the presence of excess chlorine.     

Transformation of phenazone-type drugs during chlorination

Chlorination is one of the most popular disinfection steps for water treatment in Europe. However, chlorine can react with pharmaceuticals and other micropollutants leading to either their elimination or by-products being formed. These by-products are frequently not identified and therefore the consequences of chlorination can be underestimated. In this work, the degradation of two analgesics and antipyretics, phenazone (antipyrine) and propyphenazone, during chlorination was investigated by liquid chromatography-mass spectrometry (LC-MS). A quadrupole-time-of-flight (Q-TOF) system was used to follow the time course of the pharmaceuticals, and also used in the identification of the by-products. The degradation kinetics was investigated at different concentrations of chlorine (1-10 mg/L), bromide (0-100 μg/L) and sample pH (5.7-8.3) by means of a Box-Behnken experimental design. Depending on these factors, half-lives were in the ranges: 0.9-295 s for phenazone and 0.4-173 s for propyphenazone. Also, it was observed that chlorine concentration was a significant factor for propyphenazone, resulting in increased degradation rate as it is increased. The transformation path of these drugs consisted mainly of halogenations, hydroxylations and dealkylations. After several days of reaction two derivatives remained stable for phenazone: chloro-hydroxy-phenazone and N-demethyl-chloro-hydroxy-phenazone and two for propyphenazone: N-demethyl-hydroxy-propyphenazone and N-demethyl-chloro-hydroxy-propyphenazone. Moreover, experiments conducted with real water matrices, tap and surface water, showed that reaction, and formation of by-products, can take place both at the emission source point (household) and during drinking water production.     

Comparative study of reactions of endocrine disruptors bisphenol A and diethylstilbestrol in electrochemical treatment and chlorination

Transformations of diethylstilbestrol (DES) and bisphenol A (BPA) in conventional chlorination and electrochemically (EC) treated solutions were examined using spectrophotometry and chromatographic analyses. EC treatment was carried out using an undivided EC cell with a PbO2 anode and a stainless steel cathode. EC-treatment and conventional chlorination caused DES and BPA to undergo a rapid degradation accompanied by the generation of low molecular weight chlorinated organic species indicative of the breakdown of DES and BPA. The identified compounds were predominated by chloroacetic acids (HAAs), but approximately 80% of the total organic halogen (TOX) was comprised by unidentified species. For EC treatment, the HAA yields were lower and HAAs were predominated by monochloroacetic acid (MCAA), while in the case of conventional chlorination, trichloroacetic acid (TCAA) was predominant and MCAA was virtually absent. The changes in the HAA speciation and yields were concluded to be caused by the EC-driven reductive dehalogenation which, however, did not affect the unidentified fraction of TOX. This indicated that the unidentified part of TOX was comprised by aromatic chlorinated forms of BPA and DES. Their resistance to degradation in EC reactors indicates that these compounds may be stable in conditions typical for drinking water treatment and distribution.     

Aqueous chlorination of the antibacterial agent trimethoprim: reaction kinetics and pathways

Trimethoprim (TMP), one of the antibacterials most frequently detected in municipal wastewaters and surface waters, reacts readily with free available chlorine (i.e., HOCl) at pH values between 3 and 9 (e.g., the pH-dependent apparent second-order rate constant, k'(app)=5.6 x 10(1)M(-1)s(-1), at pH 7). Solution pH significantly affects the rate of TMP reaction with HOCl. The reaction kinetics in reagent water systems can be well described by a second-order kinetic model incorporating speciation of both reactants and accounting for acid-mediated halogenation of TMP's 3,4,5-trimethoxybenzyl moiety. Studies with the substructure model compounds 2,4-diamino-5-methylpyrimidine and 3,4,5-trimethoxytoluene show that TMP reacts with HOCl primarily via its 3,4,5-trimethoxybenzyl moiety at acidic pH, and with its 2,4-diaminopyrimidinyl moiety at circumneutral and alkaline pH. LC/MS product analyses indicate that the TMP structure is not substantially degraded upon reactions with HOCl. Instead, a wide variety of (multi)chlorinated and hydroxylated products are formed. Experiments with real drinking water and wastewater matrixes confirmed that substantial TMP transformation can be expected for conditions typical of wastewater and drinking water chlorination.     

Disinfection by-products formation and precursors transformation during chlorination and chloramination of highly-polluted source water: Significance of ammonia

Many studies have demonstrated the different trends of disinfection by-products (DBPs) formation between chlorination and chloramination. However, the reactions between precursors and disinfectants are widely assumed to be “black box” and the reasons for abovementioned difference are not well illustrated. This study focused on source water with high levels of natural organic matter (NOM) and bromide, and compared the transformation of NOM specific characteristics and the ratios of specific DBPs as an equivalent of chlorine to total organic halogen (TOX) among three disinfection scenarios of chlorination, chloramination and chlorine–chloramine sequential treatment (Cl₂–NH₂Cl process). A three-reaction-phrases model was proposed thereafter to illustrate the major reactions involved in, i.e., stage-I: rapid consumption of fast reactive sites (DOC₁), which transformed to slow reactive sites (DOC₂) and measured DBPs, i.e., trihalomethanes, haloacetic acids, etc; stage-II: oxidation and/or halogenation of DOC₂ into unknown TOX (UTOX) intermediates; stage-III: oxidation of UTOX intermediates into measured DBPs. The effect of ammonia was also quantified. Ammonia is observed to inhibit the formation of measured DBPs by 68–92%, 94–99%, and 92–95% of that in chlorination in Stage-I, II, and III, respectively, and the formation of UTOX is reduced by 2–80%, 60–94%, and 82–93% accordingly. These effects lead to the steady accumulation of DBPs intermediates such as UTOX, and to the elevated UTOX/TOX during chloramination and Cl₂–NH₂Cl process thereafter. The results illustrate the mechanism of ammonia participating in DBPs formation, and are valuable to fill in the gap between the transformation of precursors and the formation of different DBPs.     

Investigation of the mechanism of chlorination of glyphosate and glycine in water

The chlorination reactions of glyphosate and glycine in water were thoroughly studied. Utilizing isotopically enriched (13C and 15N) samples of glycine and glyphosate and 1H, 13C, 31P, and 15N NMR spectroscopy we were able to identify all significant terminal chlorination products of glycine and glyphosate, and show that glyphosate degradation closely parallels that of glycine. We have determined that the C1 carboxylic acid carbon of glycine/glyphosate is quantitatively converted to CO2 upon chlorination. The C2 methylene carbon of glycine/glyphosate is converted to CO2 and methanediol. The relative abundance of these two products is a function of the pH of the chlorination reactions. Under near neutral to basic reaction conditions (pH 6-9), CO2 is the predominant product, whereas, under acidic reaction conditions (pH < 6) the formation of methanediol is favored. The C3 phosphonomethylene carbon of glyphosate is quantitatively converted to methanediol under all conditions tested. The nitrogen atom of glycine/glyphosate is transformed into nitrogen gas and nitrate, and the phosphorus moiety of glyphosate produces phosphoric acid upon chlorination. In addition to these terminal chlorination products, a number of labile intermediates were also identified including N-chloromethanimine, N-chloroaminomethanol, and cyanogen chloride. The chlorination products identified in this study are not unique to glyphosate and are similar to those expected from chlorination of amino acids, proteins, peptides, and many other natural organic matters present in drinking water.     

Characterization and identification of antiestrogenic products of phenylalanine chlorination

Recent studies have reported that chlorination increased the antiestrogenic activity of wastewater, suggesting that disinfection by-products (DBPs) formed during chlorination is a potential and important source of endocrine-disruptor. However, antiestrogenic DBPs have not been identified. In this study, the antiestrogenic activity after aqueous chlorination of phenylalanine solution was evaluated by yeast two-hybrid assay and antiestrogenic DBPs were also identified and characterized. For the first time, aqueous chlorination of phenylalanine was found to form antiestrogenic DBPs when the antiestrogenic activity of chlorinated phenylalanine solution (0.5 mmol L^?1) increased from undetectable to 57 μmol-tamoxifen (TAM) L^?1 with the increase in chlorine doses from 0 to 0.5 mmol-Cl₂ L^?1. This level decreased sharply when chlorine addition went over 0.5 mmol-Cl₂ L^?1. By fractionating DBPs of chlorinated phenylalanine solution into different fractions via semipreparative liquid chromatography, a key fraction with high antiestrogenic activity was discovered and collected. Based on analyses of mass spectrometry (MS) and nuclear magnetic resonance (NMR), the compound involved in this fraction (21 mg) was determined to be 2,4-diphenylcrotonaldehyde, which is newly identified as a relatively high antiestrogenic chemical.     

Investigating the chlorination of acidic pharmaceuticals and by-product formation aided by an experimental design methodology

The degradation of seven acidic drugs and two metabolites during chlorination was investigated by liquid chromatography-mass spectrometry (LC-MS). A triple-quadrupole (QqQ) system was used to follow the time course of the pharmaceuticals and by-products, while a quadrupole time-of-flight (Q-TOF) system was also used for the identification of the by-products. Under strong chlorination conditions (10 mg/L Cl₂, 24 h), only four of the target compounds were significantly degraded: salicylic acid, naproxen, diclofenac and indomethacine. The degradation kinetics of these four compounds were investigated at different concentrations of chlorine, bromide and pH by means of a Box-Behnken experimental design. Depending on these factors, measured pseudo-first order half-lives were in the ranges: 23-573 h for salicylic acid, 13-446 min for naproxen, 5-328 min for diclofenac and 0.4-13.4 min for indomethacine. Also, it was observed that chlorine concentration was the overall most significant factor, followed by the bromide concentration (except for indomethacine), resulting in increased degradation kinetics as they are increased. The degradation path of salicylic acid, naproxen and diclofenac consisted of aromatic substitution of one or two hydrogens by chlorine and/or bromide. Moreover, for diclofenac, two other by-products corresponding to a decarboxylation/hydroxylation pathway from the monohalogenated products were also identified. On the other hand, indomethacine degradation did not lead to halogenation products but to oxidation ones. The investigation of these by-products in real samples by LC-MS/MS (QqQ) showed that the halogenated derivates of salicylic acid occurred in all the drinking water and wastewater samples analysed.     

Effect of chlorination condition and permeability of chlorine species on the chlorination of a polyamide membrane

Most studies on membrane chlorination have been investigated in an unpressurized chlorination mode, even if the polyamide membrane was continuously exposed to chlorine under high operating pressure in real water/wastewater treatment plants. In this study, performance changes due to polyamide membrane chlorination were investigated in both pressurized and unpressurized chlorination modes. Chlorination in an unpressurized mode showed a flux increase at high pH and a flux decline at low pH due to the compaction and swelling of the polyamide chains, respectively. On the other hand, chlorination performed in a pressurized mode decreased the water flux in both acidic and alkaline conditions, showing that compaction is overwhelming compared to swelling. The permeability of HOCl, a dominant species at low pH, through the polyamide membrane was pH independent and almost similar to the system recovery, but the permeability of OCl⁻, which is dominant at high pH, was maxima at a neutral pH. The different performance behaviors of membranes chlorinated at various pH conditions in the presence or absence of applied pressure could be explained by the permeability of chlorine species and compaction/swelling of polymer chains after chlorination. The effect of membrane chlorination on the chemical property changes at the two different modes was confirmed using attenuated total reflection Fourier transform infrared analysis, and a conceptual model of performance change was proposed to explain the performance discrepancy between the two chlorination modes.     

Photodegradation study of three dipyrone metabolites in various water systems: identification and toxicity of their photodegradation products

The photochemical behaviour of three relevant metabolites of the analgesic and antipyretic drug dipyrone, 4-methylaminoantipyrine (4-MAA), 4-formylaminoantipyrine (4-FAA) and 4-acetylaminoantipyrine (4-AAA), was evaluated under simulated solar irradiation (Suntest system). For 4-MAA, different aqueous solutions (synthetic seawater, freshwater and Milli-Q water) as well as different operational conditions were compared. According to the experimental results, 4-MAA resulted as being an easily degraded molecule by direct photolysis, with half-life times (t1/2) ranging from 0.12 to 0.58 h, depending on the irradiation conditions. Faster degradation was observed in synthetic waters, suggesting that the photolysis was influenced by the salt composition of the waters. However, no effect on the degradation rate was observed by the presence of natural photosensitizers (dissolved organic matter, nitrate ions). 4-FAA and 4-AAA showed slower photodegradation kinetics, with t1/2 of 24 and 28 h, respectively. A study of photoproduct identification was carried out by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) (ESI positive mode), which allowed us to propose a tentative photodegradation pathway for 4-MAA and the identification of persistent by-products in all the cases. Finally, the application of an acute toxicity test (Daphnia magna) showed an increase in toxicity during the photolytic process, a consequence of the formation of toxic photoproducts.     

Fate of toxic cyanobacterial cells and disinfection by-products formation after chlorination

Drinking water sources in many regions are subject to proliferation of toxic cyanobacteria (CB). Chlorination of source water containing toxic cyanobacterial cells for diverse treatment purposes might cause cell damage, toxin release and disinfection by-products (DBP) formation. There is limited information available on chlorination of different toxic CB cells and DBP formation potentials. This work: (1) determines the extent of lysis and toxins/taste and odor compound release in chlorinated natural water from CB cells (Anabaena circinalis, Microcystis aeruginosa, Cylindrospermopsis raciborskii, and Aphanizomenon issatsckenka) from laboratory cultures and natural blooms; (2) assesses the rates of oxidation of toxins by free chlorine under environmental conditions; (3) studies the DBP formation associated with the chlorination of CB cell suspensions. With chlorine exposure (CT) value of <4.0 mg min/L >60% cells lost viability causing toxin release. Cell membrane damage occurred faster than oxidation of released toxins. Kinetic analysis of the oxidation of toxins in natural water revealed significant differences in their susceptibility to chlorine, saxitoxins being the easiest to oxidize, followed by cylindrospermopsin and microcystin-LR. Furthermore, concentrations of trihalomethanes and haloacetic acids (<40 μg/L) and N-nitrosodimethylamine (<10 ng/L) as chlorination by-products were lower than the guideline values even at the highest CT value (220 mg min/L). However, the DBP concentrations in environmental bloom conditions with very high cell numbers were over the guideline values.     

Disinfectant decay and disinfection by-products formation model development: chlorination and ozonation by-products

Comprehensive disinfectant decay and disinfection by-product formation (D/DBP) models in chlorination and ozonation were developed to apply to various types of raw and treated waters. Comparison of several types of models, such as empirical power function models and empirical kinetic models, was provided in order to choose more robust and accurate models for the D/DBP simulations. An empirical power function model based on dissolved organic carbon and other parameters (Empirically based models for predicting chlorination and ozonation by-products: haloacetic acids, chloral hydrate, and bromate, EPA Report CX 819579, 1998) showed a strong correlation between measured and predicted trihalomethane (THM) and haloacetic acid (HAA) formation for raw waters. Internal evaluation of kinetic-based models showed good predictions for chlorine decay and THM/HAA formation, but no significant improvements were observed compared to the empirical power function model simulations. In addition, several empirical models for predicting ozone decay and bromate (ozonation disinfection by-product) formation were also evaluated and/or developed. Several attempts to develop kinetic-based and alternative models were made: (i) a two-stage model (two separate decay models) was adapted to ozone decay and (ii) an ozone demand model was developed for bromate formation. Generally, internal evaluation of kinetic-based models for ozone decay showed significant improvements, but no significant improvements for the simulation of bromate formation were observed compared to the empirical power function model simulations. Additional efforts were performed to reduce the gaps between specific models and their actual application. For instance, temperature effects and configuration of ozone contactors were considered in actual application.     

Effects of ozone pre-treatment on diclofenac: Intermediates, biodegradability and toxicity assessment

Diclofenac (DCF), a common analgesic, anti-arthritic and anti-rheumatic drug, is one of the most frequently detected compounds in water. This study deals with the degradation of diclofenac in aqueous solution by ozonation. Biodegradability (BOD₅/COD ratio and Zahn-Wellens test), acute ecotoxicity and inhibition of activated sludge activity were determined in ozonated and non-ozonated samples. Liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOF-MS) was used to identify the intermediates formed in 1 h of ozonation. Eighteen intermediates were identified by these techniques and a tentative degradation pathway for DCF ozonation is proposed.Experimental results show that ozone is efficient at removing DCF: > 99% removal (starting from an initial concentration of 0.68 mmol L^− 1) was achieved after 30 min of ozonation (corresponding to an absorbed ozone dose of 0.22 g L^− 1, which is 4.58 mmol L^− 1). However, only 24% of the substrate was mineralized after 1 h of ozonation. The biodegradability, respiration inhibition in activated sludge and acute toxicity tests demonstrate that ozonation promotes a more biocompatible effluent of waters containing DCF.     

Chlorination kinetics of glyphosate and its by-products: modeling approach

Chlorination reactions of glyphosate, glycine, and sodium cyanate were conducted in well-agitated reactors to generate experimental kinetic measurements for the simulation of chlorination kinetics under the conditions of industrial water purification plants. The contribution of different by-products to the overall degradation of glyphosate during chlorination has been identified. The kinetic rate constants for the chlorination of glyphosate and its main degradation products were either obtained by calculation according to experimental data or taken from published literature. The fit of the kinetic constants with experimental data allowed us to predict consistently the concentration of the majority of the transitory and terminal chlorination products identified in the course of the glyphosate chlorination process. The simulation results conducted at varying aqueous chlorine/glyphosate molar ratios have shown that glyphosate is expected to degrade in fraction of a second under industrial aqueous chlorination conditions. Glyphosate chlorination products are not stable under the conditions of drinking water chlorination and are degraded to small molecules common to the degradation of amino acids and other naturally occurring substances in raw water. The kinetic studies of the chlorination reaction of glyphosate, together with calculations based on kinetic modeling in conditions close to those at real water treatment plants, confirm the reaction mechanism that we have previously suggested for glyphosate chlorination.     

Application of a neural observer to phenols ozonation in water: simulation and kinetic parameters identification

Presented in this study, a dynamic neural network (DNN) is employed to estimate the states dynamics of the phenols-ozone-water system. A new technique based on the dynamic neural network observer (DNNO) with relay (signum) term is applied to estimate the decomposition dynamics of phenols and to identify their kinetic parameters without any mathematical model usage. The decomposition of phenols (phenol (PH), 4-chlorophenol (4-CPH) and 2,4-dichlorophenol (2,4-DCPH)) and their mixture by ozone, realized in a semi-batch reactor, is considered as a process with uncertain model ("black-box"). Only one parameter monitoring, namely, the ozone concentration in gas phase in the reactor outlet, is measured during ozonation. The variation of this variable is used to obtain the summary characteristic curve for the phenols ozonation. Then, using the experimental decomposition dynamics of phenols and of their mixture, obtained by HPLC method, the proposed DNNO is applied to estimate the ozonation constants of phenols at the different pH 2-12. A good correspondence between the decomposition dynamics and the estimated ones by DNNO is obtained.     

Effect of chlorination on endotoxin activities in secondary sewage effluent and typical Gram-negative bacteria

Wastewater reuse is a viable and attractive method to address water shortage problems. However, wastewater can have high endotoxin activity. Endotoxins are toxic inflammatory agents and are considered a risk factor for wastewater reuse. In this study, the effect of chlorination on endotoxin activity in secondary sewage effluent was evaluated by Limulus (Tachypleus tridentatus) Amebocyte Lysate assay. It was found that chlorination could not decrease endotoxin activity of secondary effluent effectively under the conditions employed in this study. Chlorination of a pure cultured Gram-negative bacterium (Escherichia coli), and a Gram-negative bacterium isolated from secondary sewage effluent, resulted in a significant increase in endotoxin activity, suggesting that the presence of Gram-negative bacteria contributed substantially to endotoxin activity, masking any potential reduction that may be attributable to chlorination. Furthermore, the activities of both free and cell-bound endotoxins in pure culture increased significantly during chlorination due to cell wall damage induced by chlorination.     

Inactivation and reactivation of antibiotic-resistant bacteria by chlorination in secondary effluents of a municipal wastewater treatment plant

Reports state that chlorination of drinking water and wastewater affects the proportions of antibiotic-resistant bacteria by potentially assisting in microbial selection. Studies on the effect of chlorination on like species of antibiotic-resistant bacteria, however, have shown to be conflicting; furthermore, few studies have inspected the regrowth or reactivation of antibiotic-resistant bacteria after chlorination in wastewater. To understand the risks of chlorination resulting from potentially selecting for antibiotic-resistant bacteria, inactivation and reactivation rates of both total heterotrophic bacteria and antibiotic-resistant bacteria (including penicillin-, ampicillin-, tetracycline-, chloramphenicol-, and rifampicin-resistant bacteria) were examined after chlorinating secondary effluent samples from a municipal wastewater treatment plant in this study.Our experimental results indicated similar inactivation rates of both total heterotrophic bacteria and antibiotic-resistant bacteria. Microbial community composition, however, was affected by chlorination: treating samples with 10 mg Cl₂/L for 10 min resulted in chloramphenicol-resistant bacteria accounting for nearly 100% of the microbial population in contrast to 78% before chlorination. This trend shows that chlorination contributes to selection of some antibiotic-resistant strains. Reactivation of antibiotic-resistant bacteria occurred at 2.0 mg Cl₂/L for 10 min; specifically, chloramphenicol-, ampicillin-, and penicillin-resistant bacteria were the three prevalent groups present, and the reactivation of chloramphenicol-resistant bacteria exceeded 50%. Regrowth and reactivation of antibiotic-resistant bacteria in secondary effluents after chlorination with a long retention time could threaten public health security during wastewater reuse.     

Kinetics and mechanisms of formation of bromophenols during drinking water chlorination: assessment of taste and odor development

Halophenols are often reported as off-flavor causing compounds responsible for medicinal taste and odor episodes in drinking water. To better understand and minimize the formation of 2-bromophenol and 2,6-dibromophenol which have low odor threshold concentrations (OTCs, 30 and 0.5 ng/L, respectively) a kinetic data base for the chlorination and bromination of phenols was established by combination of kinetic measurements and data from literature. Second-order rate constants for the reactions of chloro- and bromophenols with chlorine and bromine were determined over a wide pH range. The second-order rate constants for bromination of phenols are about three orders of magnitude higher than for chlorination. A quantitative structure activity relationship (QSAR) showed a good comparability of second-order rate constants from this study with those published previously for different phenol derivatives. The quantification of product distribution of the formed halophenols demonstrated that chlorine or bromine attack in ortho position is favored with respect to the para position. A kinetic model was formulated allowing us to investigate the influence of chlorine dose and some water quality parameters such as the concentration of phenol, ammonia, bromide and the pH on the product distribution of halophenols. The kinetic model can be applied to optimize drinking water chlorination with respect to phenol-born taste and odor problems. In general, high chlorine doses lead to low concentrations of intermediate odorous chlorophenols and bromophenols. An increase in the ammonia or phenol concentration leads to a higher consumption of HOCl and therefore greater final concentration of intermediate bromophenols. The presence of higher bromide than phenol concentration also facilitates the rapid bromination pathway which leads to further bromination of 2,6-dibromophenol to higher brominated phenols. Laboratory-scale experiments on taste and odor formation due to the chlorination of phenol- and bromide-containing waters have confirmed the trend of the model calculations.     

Formation, adsorption and separation of high molecular weight disinfection byproducts resulting from chlorination of aquatic humic substances

A significant portion of the unidentified disinfection byproducts (DBPs) in chlorinated drinking water can be attributed to high molecular weight (MW)-chlorinated DBPs (above 500 Da) that may have adverse health effects. In this work, issues on the formation, adsorption and separation of high MW-chlorinated DBPs were investigated by introducing radioactive (36)Cl into humic substance samples. The results show that the amount of high MW-chlorinated DBPs during chlorination decreased with the increase of contact time from 1 to 120 h, increased with the increase of pH from 5.5 to 9.5, and was less in the ultrafiltered samples from Suwannee River fulvic acid than from Suwannee River humic acid. The high MW-chlorinated DBPs were found to be effectively adsorbed by activated carbon and be possibly reduced to Cl(-) by activated carbon, but not to be readily desorbed from the activated carbon. Those high MW-chlorinated DBPs were demonstrated to be incapable of resolution into discrete peaks by any of the three liquid chromatography columns studied. The significant implications of these results are discussed.     

Occurrence and removal of pharmaceuticals and hormones through drinking water treatment

The occurrence of fifty-five pharmaceuticals, hormones and metabolites in raw waters used for drinking water production and their removal through a drinking water treatment were studied. Thirty-five out of fifty-five drugs were detected in the raw water at the facility intake with concentrations up to 1200 ng/L. The behavior of the compounds was studied at each step: prechlorination, coagulation, sand filtration, ozonation, granular activated carbon filtration and post-chlorination; showing that the complete treatment accounted for the complete removal of all the compounds detected in raw waters except for five of them. Phenytoin, atenolol and hydrochlorothiazide were the three pharmaceuticals most frequently found in finished waters at concentrations about 10 ng/L. Sotalol and carbamazepine epoxide were found in less than a half of the samples at lower concentrations, above 2 ng/L. However despite their persistence, the removals of these five pharmaceuticals were higher than 95%.