Reacteur a cellules nitrifiantes immobilisees sur garnissage aere a co- ou contre-courant. Etude experimentale et modelisationNitrification by attached-cell reactors aerated at co- or counter-current. Experimental data and modelling

Attached-cell reactors using a bed of granular material for wastewater treatment develop a high biomass concentration which allows an important reduction of the required residence time (Jeris et al., 1977; Elmaleh, 1982). In nitrification of ammonia containing wastewater, oxygen is currently the limiting substrate; in theory, 4.18 g of oxygen are required per 1 g of nitrogen (Painter, 1970). Oxygen can be added with hydrogen peroxide (Grigoropolou, 1980; Seropian, 1980; Yahi et al., 1982) which is nevertheless expensive and it seems better to transfer oxygen from a gas phase, i.e. air, to the liquid phase through a fixed bed (Charpentier, 1976).Two attached-cell reactors (Fig. 1) were operated in parallel for nitrification of ammonia containing synthetic wastewater (Table 2). Air was upflowed through a granular packing (Table 1) maintained in fixed bed while the liquid influent was injected at co- or counter-current.

1. (1) Owing to the high oxygen transfer properties of the system and to the fact that the thickness of biofilm is always less than 100 μm, the whole process was not limited by oxygen concentration of which remained larger than 7 mg l⁻¹ (Fig. 2a) (Bungay et al., 1969). Oxidised nitrogen ammonia is completely converted into nitrate (Fig. 2b). Experimental conditions are given in Table 3.

2. (2) The plot of ammonia conversion against air superficial velocity shows a maximum (Fig. 3) after which conversion decreases rapidly by overloading of the packing (Prost, 1965). Experimental conditions are given in Table 4.

3. (3) Process efficiency decreases when superficial upflow velocity is increased (Fig. 4).

4. (4) Complete abatement of inlet pollution is reached when nitrogen concentration is less than 25 mg l⁻¹ (Fig. 5) which corresponds to a volumetric loading up to 0.6 kg N (NH₄⁺) m⁻³ day⁻¹.

Moreover, the experimental data were fitted to a model based on classical assumptions (Roques, 1980; Grady, 1982; Atkinson and Fowler, 1974; Grasmick et al., 1979; Grasmick, 1982; Harremoes, 1976, 1978; Jennings et al., 1976; Williamson and MacCarty, 1976); i.e. zero order intrinsic kinetics and diffusion transport (Table 5), and recently developed (Grasmick, 1982; Rodrigues et al., 1984). This model provides, particularly, a very easy method to check its own use—in reaction regime and in diffusion regime—when time spans or inlet concentration are changed; experimental results can indeed be plotted in such a way that straight lines are obtained (Table 6). Figures 6 and 7 show the data obtained with the counter-current nitrification reactor when respectively inlet concentration and time spans are varied. The plotted straight lines show that the overall reaction is zero order and that, therefore, the biofilm is fully penetrated. A critical time span θ_c and a critical inlet concentration C_c, for which complete conversion is achieved, are then calculated, θ_c is theoretically proportional to C₁ which is verified in Fig. 8. The straight line θ_c vs C₁ can then be used in reactor design.     

Dissolved organic matter and the dissipation of chlorine in estuarine water and seawater

Dissolved organic matter in estuarine water and seawater collected in the summers of 1980 and 1981 in the James River, Virginia and the mouth of Chesapeake Bay were separated into fractions according to their nominal molecular weights (NMW) by ultrafiltration. Estuarine waters contained higher concentrations of dissolved organic carbon (DOC). Among the fractions, between 66–89% of the DOC was found in the fraction with NMW below 10,000. Estuarine waters also had higher chlorine demands. At a dose of 5 mg l⁻¹, in 23 h, about 90% of the added chlorine disappeared in estuarine waters, whereas, in seawater, only 60–75% of the chlorine had dissipated. At least two-thirds of the chlorine demand occurred in the first 5 h. About 10–30% of the chlorine demand may be attributed to the fraction with NMW above 10,000. The remaining chlorine demand was distributed almost equally between the fractions with ranges of NMW of 1000–10,000 and below 1000. If reactivity is measured in terms of organic chlorine demand (ΔClo) per unit weight of DOC, the fractions with lower NMW (< 1000 and 1000–10,000) always had a higher reactivity towards chlorine. Between these two fractions, the one with NMW between 1000 and 10,000 exhibited higher reactivity more frequently. The highest reactivity found was 1.4 mg ΔClo mg⁻¹ DOC.     

Effect of oxidants on microalgal flocculation

The effects of chlorine, ozone and chlorine dioxide on Scenedesmus sp. cultures were studied. Algal cell viability and chlorophyll concentration decreased, and the concentration of dissolved organic substances increased with increasing applied oxidant concentration. Pretreatment with chlorine dioxide (1, 3 or 5 mg l⁻¹) or ozone (2.6, 4.6 or 8.1 mg l⁻¹) on algal cultures enhanced algal flocculation with alum, while prechlorination with 10 or 20 mg l⁻¹ increased the required dosage of alum by 15%. Scanning electron micrographs of oxidized cells revealed drastically adverse effects upon the cell surface architecture: in addition to the oxidation of noncellular organic materials, the oxidants damaged both cell surface structures and intracellular components. A model explaining the effects of the different oxidants on microalgal flocculation is suggested.     

Electroflottation et desinfection simultanee d'eaux residuaires urbaines

This reports presents the results of a simultaneous electroflotation and disinfection sewage treatment, after chemical coagulation and flocculation and in the presence of chloride ions at various concentrations. Theoretical studies had shown that anodic oxidation of chloride ions gives hyperchlorites (for pH 7.5) together with (if sufficient potential is provided) oxygen. A dynamic study was thus achieved. It appeared that for a given chloride concentration the chlorine production linearly increases with the current density and depends on the organic load (COD) and oxidation potential of the effluent (Figs 6, 7 and 8). The performances of the process were studied in the continuous mode on a small pilot plant, after treatment of the effluent with ferric chloride and an organic polymer (Fig. 2). In all experiments current density and chloride concentration were raised (respectively 100, 200, 300 A m⁻² and from 300 to 3000 mg l⁻¹). The results obtained showed that solid-liquid separation was improved over static clarification for 2 h (Table 3) and the disinfection efficiency was equal or better than that obtained with gaseous chlorine (Table 4, Fig. 9). For example at a 900 mg l⁻¹ chloride concentration the three current density used give treated water containing less than 10³/100 ml total coliforms (initial concentration 4.7 · 10⁷/100 ml). These results have direct applications to the design of electroflotation units where a better plug flow should be sought. Moreover this process produces highly concentrated sludges. The utilization of ATP (Adenosine Triphosphate) as an indicator of the viability of a biomass showed that the process is applicable to activated sludges with recycling. The experimental conditions required for this application are still uncertain and require further study.     

Caracterisation de la matiere organique dissoute presente dans les eaux en cours d'affinage: Influence des traitements appliques et du climat

Dissolved organic matter in treated surface waters (clarified, possibly ozonized, then GAC-filtered, Fig. 1), is fractionated by ultrafiltration into five molecular classes with MW < 300, 300–1000, 1000–5000, 5000–10000 or > 10,000. Dissolved organic carbon (DOC), oxidizability by KMnO₄ in hot alkaline medium and u.v. absorbances at 240, 254, 280, 300 nm are measured. Fourteen series of samples, distributed on an annual biological cycle are analysed (Figs 2 and 3); multivariate statistical analyses are performed.By PCA (principal component analysis), variations in water supplying the activated carbon units appear to depend for 47% on ozonation and temperature; but river flow rate and quantity of flocculant added are no longer responsible for such variations (Fig. 4). Three groups of water appear (Fig. 5), according to the applied ozone level (zero, medium, high); among the medium ozonized waters, the cold ones differ from temperate ones.Ozonation diminishes molecular size of compounds (Table 1): three major classes with MW < 5000 are present in non- or medium-ozonized waters, but only two, with MW < 1000, remain in highly ozonized waters. This treatment destroys MW > 10,000 and even 1000–5000 ones and yields MW < 300 products; it also minimizes u.v. absorbances and oxidizability. Seasonal variations occur in DOC content of medium ozonized waters, with maxima values in winter or spring and minima in summer or autumn (Fig. 6): occurrence of MW < 300 compounds follows that of DOC, but the presence of 5000–10000 ones is minimal in winter.Quality of GAC-filtered waters varies by 19% with temperature (Fig. 7); ozonation effects are minimized: only previously highly ozonized waters distinguished themselves from the others (Fig. 8). Waters, non or medium ozonized before GAC-filtration, are divided into cold, temperate and warm waters. One, two or three major classes of compounds with MW < 5000, remain in GAC-filtered waters, according to the ozone level applied previously. This filtration reduces DOC by 17%, decreases u.v. absorbances and oxidizability and gives water with the same 0.30 mg O₂ mg⁻¹ C ratio (Table 2): MW 1000–5000 class is much less oxidizable after ozonation-GAC filtration but, on the other hand, MW < 300 class appears rather less oxidizable without ozonation before biological filtration. DOC content in effluent follows that in influent (Fig. 9), but variations are less marked. Total efficiency of the filtration increases with temperature, but behaviour of compounds differs from one class to another: MW 300–1000 and 5000–10000 classes are the most affected; MW 1000–5000 is not really modified. Elimination of MW < 300 or 5000–10000 compounds depends on temperature and may be due to biological phenomena, a but that of 1000–5000 and > 10,000 classes, independent of this parameter, may be related to adsorption mechanisms.     

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.     

Chloration de composés organiques: demande en chlore et réactivite vis-a-vis de la formation des trihalométhanes. Incidence de l'azote ammoniacalChlorination of organic compounds: Chlorine demand and reactivity in relationship to the trihalomethane formation. Incidence of ammoniacal nitrogen

The purpose of this work is to contribute to knowledge of the condition of formation of volatile and non-volatile organochlorinated compounds during surface water chlorination. With this aim in view, the chlorination of a number of organic substances in diluted aqueous solutions (10⁻⁶-10⁻⁵ moll ⁻¹) and in a neutral medium was studied. Special attention was given to their reactivity in relation to the formation of trihalomethanes.The results obtained show great differences in the reactivity of chlorine towards chemical substances liable to be present in the waters. The high chlorine demands, 5–12 mol of chlorine per mol of compound after a 15 h reaction at pH 7, where obtained with those aromatic compounds having activating groups such as — OH and — NR₂ (phenol and aniline derivatives). On the other hand, a number of compounds (alipahitcs in general; acids, aldehydes, alcohols…) are relatively inert towards chlorination.As far as chloroform production is concerned, the study shows that many organic compounds are liable to lead to the production of low quantities of chloroform in a neutral medium (molar yields < 5%). However, only a few specific structures such as metapolyhydroxybenzenes and metachlorophenols constitute good precursors of the haloform reaction.The study of the formation kinetics of chloroform, carried out with some precursors of different reactivity: acetone, acetylacetone, resorcinol, phloroglucinol and 3,5-dichlorophenol allowed us to determine the kinetic constants of chloroform formation at pH 7.5 and 20° C:

The results obtained during this work also show that the chlorine found in the chloroform produced from a precursor, represents only a small proportion of the chlorine demand. Even with a highly reactive precursor such as resorcinol. It was shown that the liberation of chloroform is accompanied by the formation of trichloroacetic acid (molar yield < 10%) and of monochloromaleic acid (molar yield 60%). Moreover, tetrahalogenated and pentahalogenated hydrocarbons (C₃Cl₄ and C₃ HCl₅) resulting from 3,5 -dichlorophenol chlorination were made manifest. As for the chlorin- ation of acetylacetone, a mechanism passing through the formation of 1,1-tri- chloroacetone was proposed.Lastly, in the general framework of the interactions between chlorine, ammonia nitrogen and the organic compounds which are frequently found in surface water chlorination, the study allowed us to show that the chlorination of highly reactive precursors (such as metapolyhydroxybenzenes and metachlorophenols) can lead to the production of important amounts of chloroform before reaching breakpoint. These results compared to the values of the velocities of the various reactions between chlorine and the ammoniacal compounds.     

Essais d'aerateurs: Enseignements tires de 500 essais en eau claire effectues dans 200 stations d'epuration differentes—I. Methodologie

Aeration represents the main part of energy consumption in the activated sludge process and the evaluation of aeration systems efficiency is becoming more important, especially as energy cost increases. Since 1972, CEMAGREF teams have carried out more than 500 non-steady state clean water tests in sewage treatment plants. The first aim of these measurements was to compare the results collected in plants with those predicted by manufacturers.The distribution of the different types of aerators tested in the field by the CEMAGREF is given in Table 1. All tests are conducted using tap water under non-steady state conditions: the initial dissolved oxygen (DO) level is brought down to zero by adding cobalt chloride as catalyst and sodium sulfite. When all the sodium sulfite has been used, the increase in water dissolved oxygen content is monitored vs time in various places in the tank by means of membraned probes.The graphical procedure used for estimating the oxygen transfer coefficient (K_La) is shown in Fig. 1; this procedure is usually called “log deficit method”. The results are expressed for “standard conditions” (θ = 10°C; P = 760 mm Hg). The influence of temperature on oxygenation capacity is illustrated in Fig. 2.The water quality parameters that may affect oxygen transfer are investigated: it appears that only the presence of surfactants, flocculated suspended solids, or high salinity (conductivity > 1500 μS cm⁻¹—Table 2) are liable to have any appreciable effect on oxygen transfer. The unflocculated SS, pH and alkalinity have no effect on oxygenation results in the common range of values occurring in the tests (Table 3).Authors differ about the operational procedure in non-steady state clean water test. After 7 years' field-measurements the CEMAGREF teams have developed their own recommendations about test procedures; their main conclusions are the following:Dissolved oxygen analysis: the differences observed between the results ( ) obtained simultaneously by Winkler titration of piped samples and those from in-tank probes never exceed 4% (Table 4). Reliable dissolved oxygen probes are suitable for accurate measurements of oxygen transfer.The number of sampling points should be no smaller than three for aeration tanks with a volume below or equal to 500 m³. It should be recommended to add one sampling point for every additional 500 m³.Location of sampling points requires attention. Differences may appear according to the locations of probes in the basin (Tables 5, 6 and 7).Sulfite pre-dissolution has no influence on results and should be avoided whenever possible.     

Evaluation of a sampler for liquid effluents

A design of automatic sampler for liquid effluent streams is described, which is based on the use of a rapidly circulating pumped stream of the liquid effluent. This stream passes through an interceptor vessel from which sub-samples may be taken iso-kinetically to provide a variety of sample types (e.g. snap, composite, flow-related). This interceptor may be conveniently located and may also be used to hold monitoring probes (pH, ion selective electrodes) which will provide continuous information on the composition of the effluent stream.This sampler system has been evaluated using simulated liquid effluents, chosen to represent cases in which it is difficult to acquire a truly representative sample. The cases chosen were:

1. (a) water containing up to 10,000 mg 1⁻¹ of finely divided inorganic solid;

2. (b) water containing 2000 mg l⁻¹ of sewage solids

3. (c) water containing dissolved, volatile organic solutes;

4. (d) water containing dispersed oil.

In all cases it proved practical to obtain samples which were representative in composition of the liquid being tested; comparison in all cases was with snap samples taken simultaneously from appropriate points in the loop system.The sampler appears to be generally suitable for use with most types of liquid effluents. The several components of the sampler should be constructed of materials which are inert to the effluent.     

Chlorine demand in deep sea-water

Samples of deep sea-water were obtained at 25, 250 and 2000 m from the Sargasso Sea. The chlorine demands in these samples at any given contact time decrease with the depth at which the sample was obtained. The dissipation of chlorine occurs in two phases. The consumption rate of chlorine is similar in all three samples during the second phase at about 1 × 10⁻⁴ mg l⁻¹ min⁻¹. The difference in chlorine demand is caused primarily by the decrease in the organic chlorine demand, which occurs during the first phase of reactions, with depth reflecting the decreasing amount and increasing inertness of dissolved organic matter. The organic chlorine demands at 25, 250 and 2000 m are 0.9, 0.5 and 0.4 mg l⁻¹ respectively. These organic chlorine demands are significantly lower than those observed in coastal sea-waters with similar dose of added chlorine of about 5 mg l⁻¹. If sea-waters from various depths are available, deeper sea-water would be preferred as a coolant because of its smaller chlorine demand and lower initial temperature.     

Reactions of chlorine with inorganic and organic compounds during water treatment-Kinetics and mechanisms: a critical review

Numerous inorganic and organic micropollutants can undergo reactions with chlorine. However, for certain compounds, the expected chlorine reactivity is low and only small modifications in the parent compound's structure are expected under typical water treatment conditions. To better understand/predict chlorine reactions with micropollutants, the kinetic and mechanistic information on chlorine reactivity available in literature was critically reviewed. For most micropollutants, HOCl is the major reactive chlorine species during chlorination processes. In the case of inorganic compounds, a fast reaction of ammonia, halides (Br(-) and I(-)), SO(3)(2-), CN(-), NO(2)(-), As(III) and Fe(II) with HOCl is reported (10(3)-10(9)M(-1)s(-1)) whereas low chlorine reaction rates with Mn(II) were shown in homogeneous systems. Chlorine reactivity usually results from an initial electrophilic attack of HOCl on inorganic compounds. In the case of organic compounds, second-order rate constants for chlorination vary over 10 orders of magnitude (i.e. <0.1-10(9)M(-1)s(-1)). Oxidation, addition and electrophilic substitution reactions with organic compounds are possible pathways. However, from a kinetic point of view, usually only electrophilic attack is significant. Chlorine reactivity limited to particular sites (mainly amines, reduced sulfur moieties or activated aromatic systems) is commonly observed during chlorination processes and small modifications in the parent compound's structure are expected for the primary attack. Linear structure-activity relationships can be used to make predictions/estimates of the reactivity of functional groups based on structural analogy. Furthermore, comparison of chlorine to ozone reactivity towards aromatic compounds (electrophilic attack) shows a good correlation, with chlorine rate constants being about four orders of magnitude smaller than those for ozone.     

The impact of combined sewer overflows on the dissolved oxygen concentration of a river

As described in the preceding paper by Harremoës (Harremoës, Water Res.16, 1093–1098, 1982) it is important to distinguish between removal and degradation of organic matter for non-steady-state discharges to rivers. These effects were investigated to determine the impact of combined sewer overflows on the dissolved oxygen concentration of a small river. Two different effects on the DO-concentration in the receiving river were observed during and after the passage of the bulk of combined sewage discharged at an existing outlet:

1. 1. An immediate effect caused mainly by degradation of the soluble BOD-fraction in the water body and by direct absorption and degradation of organic matter at the bottom.

2. 2. A delayed effect caused by degradation of adsorbed soluble, colloidal and fine particulate organic matter. After the passage of the bulk discharge a delayed effect on the DO-concentration in the river would be observed. This delayed effect lasted 12–24 hours after the discharge event.

Only 4% of the discharged organic matter was degraded during passage of the investigated stretch of the river, approx. 4 km. On the other hand about 35% of the discharged organic matter was removed by transfer to the bottom sediments. The rest was carried past the stretch of river investigated. This results in a rate of adsorption from the water phase of k = 9 m day⁻¹. The deposited organic matter was degraded with a first order reaction rate of K₄ = 0.75 day⁻¹.     

Cinetiques et mecanismes de l'action oxydative de l'hypochlorite sur les acides α-amines lors de la desinfection des eaux

In the field of water treatment, one increased concern over the quality of the environment requires an understanding of the fate of compounds generated by the addition of chemicals. One area of considerable interest is the stability of chlorine compounds produced when chlorine is added to natural water or swimming pool water. It is desirable to be able to predict the lifetimes of these harmful compounds under various conditions. In this study we examine for a range of hypochlorite α-amino acid ratios and pH, the kinetics and mechanism of the decomposition of α(N-chloro) and α(N,N-dichloro) amino acid, one of the products of chlorination.The interaction of chlorine with amino acids has been studied by several investigators Langheld (1909) was the first who discussed the decomposition of the α(N-chloro) amino acids. He noted that hypochlorous acid salts react with α-amino acids in the same manner as they do with amines to form monochlorinated or dichlorinated derivatives. Then, the decomposition of chloro-amino acids leads to the corresponding aldehydes or ketones, ammonia, carbonic acid, and sodium chloride. As an intermediate step Langheld assumed an imine formation.Wright (1936) and Pereira et al. (1973) have investigated the decomposition products of α(N,N-dichloro) amino acids. Their results indicate rapid formation of carbon dioxide, chloride ion, and the corresponding nitrile.Recently, many authors have investigated the rates of α(N-chloro) amino acids decomposition and the stability of its products (William and Wendy, 1979; Yoshiro et al., 1980; Le Cloirec-Renaud, 1984). However, they have neither differentiated between the decomposition of α(N-chloro) amino acid and α(N,N-dichloro) amino acid, nor have they demonstrated the combined effect of pH and molar ratio of hypochlorite and α-amino acid.In this study the hypochlorite oxidation of simple α-amino acids in aqueous solution has been investigated in the dark. The concentration of α(N-chloro) amino acid and α(N,N-dichloro) amino acid was monitored by DPD-fast titrimetric method and by measuring the absorbance at 255 and 293 nm respectively, this is illustrated in Figs 3 and 4. These results and the amino acids determination (O-phtalaldehyde—2 mercapto ethanol method) suggest that the intermediates α(N-chloro) and α(N,N-dichloro) amino acid are formed rapidly at an initial stage. Then, they decompose spontaneously by first order kinetics as shown in Table 1, to give a mixture of aldehyde and nitrile.When equimolar (1:1 mmol) amounts of hypochlorite and amino acid are used at pH 7, only aldehyde, carbon dioxide, chloride and ammonia are formed. However the corresponding nitrile compound appears, when operating condition allow the formation of α(N,N-dichloro) amino acid (acid pH or basic aqueous solutions with high molar ratio of hypochlorite and amino acid). This is illustrated in Table 2. The rate constant shows a dependence on pH, which is caused by the various forms that can arise from addition of protons to or removal of protons from the amino and carboxyl groups of the molecule William and Wendy, 1979). We assume an intermediate step of imine for the decomposition of both compounds: α(N-chloro) and α(N,N-dichloro) amino acid (scheme 6). The reaction should be considered as a spontaneous decarbonylation followed by a rapid hydrolysis of the imine. Scheme 7 illustrated how α(N,N-dichloro) amino acid can lead to the corresponding nitrile and aldehyde, however the α(N-chloro) amino acid gives only the corresponding aldehyde.The products of decomposition of α(N-chloro) amino acid are relatively stable in aqueous solution. Although we noted at pH = 3.5–5 that aldehyde react with chloramines and lead to the formation of corresponding nitrile, as shown in scheme 9.It appears that α(N-chloro) and α(N,N-dichloro) amino acid formed during the chlorination of natural or swimming pool water will degrade in a few hours to what are probably irritating products (like as aldehydes). The production of decomposition are a function of molar ratio of hypochlorite and amino acid and pH. However, since most natural water has a pH in the range of 5.5–9, there will be little variation of the rate of decomposition with pH. It seems that it is only temperature dependent.     

Oxidative transformation of micropollutants during municipal wastewater treatment: Comparison of kinetic aspects of selective (chlorine, chlorine dioxide, ferrate, and ozone) and non-selective oxidants (hydroxyl radical)

Chemical oxidation processes have been widely applied to water treatment and may serve as a tool to minimize the release of micropollutants (e.g. pharmaceuticals and endocrine disruptors) from municipal wastewater effluents into the aquatic environment. The potential of several oxidants for the transformation of selected micropollutants such as atenolol, carbamazepine, 17α-ethinylestradiol (EE2), ibuprofen, and sulfamethoxazole was assessed and compared. The oxidants include chlorine, chlorine dioxide, ferrate^VI, and ozone as selective oxidants versus hydroxyl radicals as non-selective oxidant. Second-order rate constants (k) for the reaction of each oxidant show that the selective oxidants react only with some electron-rich organic moieties (ERMs), such as phenols, anilines, olefins, and deprotonated-amines. In contrast, hydroxyl radicals show a nearly diffusion-controlled reactivity with almost all organic moieties (k ≥ 10⁹ M⁻¹ s⁻¹). Due to a competition for oxidants between a target micropollutant and wastewater matrix (i.e. effluent organic matter, EfOM), a higher reaction rate with a target micropollutant does not necessarily translate into more efficient transformation. For example, transformation efficiencies of EE2, a phenolic micropollutant, in a selected wastewater effluent at pH 8 varied only within a factor of 7 among the selective oxidants, even though the corresponding k for the reaction of each selective oxidant with EE2 varied over four orders of magnitude. In addition, for the selective oxidants, the competition disappears rapidly after the ERMs present in EfOM are consumed. In contrast, for hydroxyl radicals, the competition remains practically the same during the entire oxidation. Therefore, for a given oxidant dose, the selective oxidants were more efficient than hydroxyl radicals for transforming ERMs-containing micropollutants, while hydroxyl radicals are capable of transforming micropollutants even without ERMs. Besides EfOM, ammonia, nitrite, and bromide were found to affect the micropollutant transformation efficiency during chlorine or ozone treatment.     

Formation equation of halogenated organic compounds when water is chlorinated

Various halogenated organic compounds are formed by chlorination of water. In this study, formation of organic compounds halogenated from a reagent humic acid and extract of a leaf mold were examined under various conditions. The following overall formation equation was obtained from empirical data under the practical wide range when free chlorine remained.

[TOX]=k_TOX[TOC][Cl₂]_ot^β.

Here, [TOX] is the concentration of total organic halogen after t h in units of mg chlorine per liter; [TOC] and [Cl₂]_o are concentrations of total organic carbon and dosed chlorine in units of mg per liter; k_TOX is the rate constant and and β are parameters. From the values of k_TOX, and β, the character of organic substances i.e. precursor of halogenated organic compounds, in water can be evaluated. The values k_TOX, and β for humic acid are 0.053, 0.28 and 0.13, and the values for extract of the leaf mold are 0.032, 0.36 and 0.15, respectively. The activation energies are 10 kJ mol⁻¹ and 11 kJ mol⁻¹ for the reactions of humic acid and leaf mold extract, respectively.     

Predicting disinfection by-product formation potential in water

Formation of regulated and non-regulated disinfection by-products (DBPs) is an issue at both potable water and wastewater treatment plants (W/WWTPs). Water samples from W/WWTPs across the USA were collected and DBP formation potentials (DBPFPs) in the presence of free chlorine and chloramine were obtained for trihalomethane (THM), haloacetic acid (HAA), haloacetonitrile (HAN), and N-nitrosodimethylamine (NDMA). With nearly 200 samples covering a range of dissolved organic carbon (0.6-23 mg/L), ultraviolet absorbance (0.01-0.48 cm⁻¹ at 254 nm wavelength), and bromide (0-1.0 mg/L) levels, power function models were developed to predict the carbonaceous DBP (C-DBP) and nitrogenous DBP (N-DBP) precursors spanning 3 orders of magnitudes. The predicted THM and HAA formation potentials fitted well with the measured data (analytical variance of less than 22%). Inclusion of dissolved organic nitrogen (DON) into the HANFP model improved the predictions. NDMAFP was the most difficult one to predict based upon the selected water quality parameters, perhaps suggesting that bulk measurements such as DOC or UVA₂₅₄ were not appropriate for tracking NDMAFP. These are the first such DBPFP models for wastewater systems, and among the few models that consider both C-DBPs and N-DBPs formation potentials from the same water sources.     

Assessment of an amperometric membrane probe for determining free residual chlorine in saline cooling waters

Cooling water at coastal and estuarine power stations is chlorinated to inhibit mussel growth in the intakes to the condensers and a means of automatically monitoring the free residual chlorine concentration is desired so that the dosage can be precisely maintained at 0.2 μg ml⁻¹ Cl₂. The Delta Scientific model 82124 amperometric membrane probe has been tested in the laboratory for its suitability for this application. The probe had a linear response to hypochlorous acid over the range 0–5 μg ml⁻¹, but was not specific for free residual chlorine, as chloramines also produced a response. The main product of the chlorination of sea water is bromine, to which the probe is about five times more sensitive than to hypochlorous acid. Although the probe can be calibrated with bromine, its response is then much noisier than that obtained with hypochlorous acid. The salinity of the sample influences the reading obtained at a given concentration of oxidant: increasing the salinity increases the reading obtained with hypochlorous acid but decreases that obtained with bromine.     

Electroflottation et desinfection simultanee d'eaux residuaires urbainesSimultaneous electroflotation and disinfection of sewage

This reports presents the results of a simultaneous electroflotation and disinfection sewage treatment, after chemical coagulation and flocculation and in the presence of chloride ions at various concentrations. Theoretical studies had shown that anodic oxidation of chloride ions gives hyperchlorites (for pH 7.5) together with (if sufficient potential is provided) oxygen. A dynamic study was thus achieved. It appeared that for a given chloride concentration the chlorine production linearly increases with the current density and depends on the organic load (COD) and oxidation potential of the effluent (Figs 6, 7 and 8). The performances of the process were studied in the continuous mode on a small pilot plant, after treatment of the effluent with ferric chloride and an organic polymer (Fig. 2). In all experiments current density and chloride concentration were raised (respectively 100, 200, 300 A m^?2 and from 300 to 3000 mg l^?1). The results obtained showed that solid-liquid separation was improved over static clarification for 2 h (Table 3) and the disinfection efficiency was equal or better than that obtained with gaseous chlorine (Table 4, Fig. 9). For example at a 900 mg l^?1 chloride concentration the three current density used give treated water containing less than 10³/100 ml total coliforms (initial concentration 4.7 · 10⁷/100 ml). These results have direct applications to the design of electroflotation units where a better plug flow should be sought. Moreover this process produces highly concentrated sludges. The utilization of ATP (Adenosine Triphosphate) as an indicator of the viability of a biomass showed that the process is applicable to activated sludges with recycling. The experimental conditions required for this application are still uncertain and require further study.