Initial Chlorine Concentration Research Articles

Predictive Models for Available Chlorine Depletion and Total Microbial Count Reduction During Washing of Fresh‐Cut Spinach

ABSTRACT: Washing of fresh‐cut spinach with aqueous chlorine solutions eliminates foreign matter, removes cellular fluids produced by cutting and reduces the initial microbial contamination. Response Surface Methodology was used to evaluate the effect of initial chlorine concentration (25 to 125 ppm), water‐to‐produce ratio (10 to 26 L/kg) and washing time (2 to 8 min) on the total and available chlorine depletion and the total microbial count reduction after washing. All variables affect the chlorine depletion but the microbial count reduction was only influenced by initial chlorine concentration and washing time. Different combinations of the variables were determined by the predictive models to reduce microbial contamination assuring residual levels of chlorine in the washing solution.

Predicting the Formation of Chlorinated and Brominated By-Products

Although disinfection was one of the major public health advances in the last century and continues to be so in the twenty-first century, the disinfectants themselves may react with naturally occurring materials in treated water to form unintended by-products, which may themselves pose risks. This is of particular concern with regard to the use of chlorine. Generation of disinfection by-products (DBPs) has been shown to be a function of various factors including total organic carbon concentration, type of organic precursor, chlorination level, pH, temperature, reaction time, and UV-254 absorbance. Another factor affecting DBP formation is the presence and concentration of the bromide ion in the raw or finished water. Bromine substitutes for chlorine to produce bromine-containing homologues of the more familiar chlorine species. The current list of by-products targeted for regulation contains brominated and mixed bromine-chlorine species of total trihalomethanes and haloacetic acids. These are known to form in bromide-containing waters when chlorinated. To control chlorination DBPs therefore requires an understanding of the factors that influence their formation. This paper presents a model that can be used to predict the formation of chlorinated, brominated, and mixed species compounds based on initial chlorine concentration, chlorine consumption, bromide ion concentration, and pH. The model clearly shows that higher levels of bromide in the water favor the formation of brominated compounds. Brominated compounds also form faster than chlorinated compounds.

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.

Survival of Salmonella hadar after washing disinfection of minimally processed spinach.

Washing disinfection with chlorine is widely used to reduce the initial microbiological load during the preparation of minimally processed vegetables. The effects of initial concentration of chlorine, time and the liquid volume:produce weight ratio on the reduction of Salmonella counts on inoculated spinach were evaluated using response surface methodology. Initial chlorine concentration, time and the interaction between them had a significant effect on reduction of Salmonella populations. However, the liquid volume:produce weight ratio did not have significant effects. The highest Salmonella reduction was around 1.2-1.4 log at 125 ppm during 8 min regardless of the water:produce ratio. According to the results, chlorination reduced Salmonella hadar population, but the complete elimination from the produce was not achieved.

Factors which control bulk chlorine decay rates

Several computer programs for modelling water distribution networks have been developed which incorporate a facility for modelling chlorine decay. Problems have been experienced with the calibration and durability of these models due to both temporal and spatial variability in the decay constants. Chlorine will decay either due to reactions at the pipe wall or due to reactions in the bulk water. The aim of the work presented in this paper is to investigate the factors which influence bulk decay. Over 200 determinations of bulk chlorine decay against time were performed on waters taken from 32 sampling locations within the Severn Trent region, U.K. The bulk decay constant was observed to show significant variation with temperature, the initial chlorine concentration and the organic content of the water. An equation was derived relating these parameters which could be used to update the decay constants in network models and improve their durability.

Modelling of chlorine decay in municipal water supplies

This paper describes the effects which temperature and the initial chlorine concentration have on the chlorine decay in different water samples. It also reports the derivation of empirical formulae which describe these effects. The data show that chlorine decays more rapidly in fresh samples than in those which had been re-chlorinated with sodium hypochlorite to give a concentration of about 0.5 mg/l. The decay constants were found to be inversely proportional to the initial chlorine concentration in the former case and to the concentration added in the latter case. A combined first and second-order model is described which describes the decay more precisely than the conventional first-order model. Specifically, it shows that the chlorine decay is influenced by its initial concentration and explains why chlorine decays more rapidly in the initial stages. It also explains why the decay constant in the first-order model varies with the initial chlorine concentration.

Dissolution kinetics of copper, white metal and natural chalcocite in Cl 2/Cl − media

In order to explain the model of kinetics control on the dissolution of metallic copper, white metal, and natural chalcocite, the effects of the stirring speed, pH, initial chlorine and chloride concentrations, particle size, and temperature were investigated. The kinetics appear to be mass transport-controlled in conditions of full suspension of the particles, with activation energies of 17.9 kJ/mol (4.3 kcal/mol), 23.3 kJ/mol (5.6 kcal/mol), and 22.4 kJ/mol (5.4 kcal/mol) for copper, chalcocite, and white metal, respectively. The dependence of pH, temperature, and chloride concentration indicate that the rates were essentially determined by the concentration of chlorine.

Copper extraction from reverberatory and flash furnace slags by chlorine leaching

The effects of the stirring speed, temperature, initial chlorine and chloride concentrations, particle size, addition order of the reactants and slags on the copper and iron dissolution from reverberatory and flash furnace slags were investigated. Extractions in the range of 75 and 80% Cu and about 5% Fe were obtained at room temperature. The most significant parameters were the particle size and the initial chlorine concentration. A mineralogical characterization of the reverberatory and flash smelting slags, using X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) coupled to an X-ray energy dispersive spectrometer (EDS) and microanalysis (EPMA), was made. This characterization indicated that most of the copper is in the form of metallic copper, chalcocite, bornite and other complex sulphides of very small size, mainly 5–10 μm. Iron is present principally as the matrix of a vitreous phase, fayalite and magnetite. An average only 0.2–0.4% of the copper was found in the silicate phases.

Evaluation of the disinfection potential of low chlorine concentrations in tap water using immobilised enterococcus faecium in a continuous flow device

A simple continuous flow device in which bacteria were immobilised on membrane filters and flushed with tap water with free chlorine residuals of 0.05, 0.1, 0.2 and 0.4mg/L at pH 7.7 and 10°C, has been used for disinfection experiments with faecal streptococci. A 99.99% reduction of Enterococcus faecium was observed between 3.4–5.2min (0.05mg/L), between 2.8–4.1min (0.1mg/L), between 1.7–3.1min (0.2mg/L) and between 0.8–2.1min (0.4mg/L). CT-products covered a range of 0.17 (0.05mg/L, lower limit) up to 0.85mg/L/min (0.4mg/L, upper limit). The test system is suggested as a more reliable alternative to batch experiments when the disinfection potential of low chlorine concentrations acting for several minutes has to be evaluated. The system cannot be used to demonstrate exact reduction kinetics but it allows the calculation of CT values and the evaluation of the disinfection potential of chlorinated water at any point of a distribution system where initial chlorine concentrations may have already remarkably declined.

Reduction of Aqueous Chlorine by Organic Material

Aqueous chlorine, used to reduce surface bacteria populations on carcasses of slaughter animals after evisceration, during chilling, and after transport, dissipates in the presence of organic matter. This study characterized the amount of residual chlorine present when aqueous HOCI was exposed to bovine serum albumin, bovine lean muscle, porcine adipose tissue, or Trypticase soy agar (TSA) surfaces. Test chlorine solutions, made using Ca (OCl)2, contained 0, 50, 100, 200, 400, 800, 1,600, or 3,200 ppm chlorine, the latter two concentrations being used only in the case of albumin. Chlorine depletion by albumin was almost instantaneous, but was influenced by the amount of albumin present and the initial chlorine concentration. Chlorine exposed to organic surfaces was reduced most readily by lean muscle, then by TSA, and least by adipose tissue. Available chlorine was reduced by about 62% when the volume of aqueous chlorine was 22 ml/cm2 of lean muscle and by about 89% when the volume of aqueous chlorine was 0.69 ml/cm2. With increasing exposure time, the exposure to lean and fat decreased available chlorine by an average of about 10% in 4 min, 27% in 32 min, and 45% in 96 min. Thirteen pure bacterial cultures and two mixed cultures associated with meat were exposed to aqueous chlorine to characterize the effectiveness of the chlorine. All cultures except Bacillus cereus and Enterococcus faecalis were destroyed within 15 s by 3 ppm chlorine. Based on the data, the authors conclude that (a) available chlorine reduction is dependent on exposure time, chlorine concentration, and amount/source of organic material and (b) bacterial inactivation by aqueous chlorine is species specific. These data are of value for estimating chlorine dose for carcass decontamination during washing/chilling and for confirming that bacterial resistance to HOCI is species specific.

Evaluation of the disinfection potential of low chlorine concentrations in tap water using immobilised Enterococcus Faecium in a continuous flow device

A simple continuous flow device in which bacteria were immobilised on membrane filters and flushed with tap water with free chlorine residuals of 0.05, 0.1, 0.2 and 0.4mg/L at pH 7.7 and 10°C, has been used for disinfection experiments with faecal streptococci. A 99.99% reduction of Enterococcus faeciam was observed between 3.4–5.2mm (0.05mg/L), between 2.8–4.1mm (0.1mg/L), between 1.7–3.1mm (0.2mg/L) and between 0.8–2.1mm (0.4mg/L). CT-products covered a range of 0.17 (0.05mg/L, lower limit) up to 0.85mg/L/min (0.4mg/L, upper limit). The test system is suggested as a more reliable alternative to batch experiments when the disinfection potential of low chlorine concentrations acting for several minutes has to be evaluated. The system cannot be used to demonstrate exact reduction kinetics but it allows the calculation of CT values and the evaluation of the disinfection potential of chlorinated water at any point of a distribution system where initial chlorine concentrations may have already remarkably declined.

Use of alternative disinfectants, individually and in combination, in aquacultural wastewater treatment

The inactivation effect of chlorine, iodine, ozone and UV irradiation was compared between phosphate buffered saline and waste water collected from a fish farm, with the fish-pathogenic bacterium Aeromonas salmonicida subsp. salmonicida as the model organism. In addition, the effect of combining chlorine, iodine or ozone with UV was evaluated. A tenfold increase in initial chlorine concentration, from 0.2 to 2.0 mg l−1. had to be applied to maintain the same level of inactivation in waste water as in PBS. Iodine was less efficient than chlorine in PBS. by demanding a concentration of 1.0 mg l−1 to obtain the same rate of inactivation as with 0.2 mg l−1 chlorine. However, no difference between the two halogens was evident in the low-quality water. An initial ozone concentration of 0.1 mg l−1 in PBS caused a rapid drop in bacterial viability for the first 20 s after which the curve levelled off. By continuous ozonation of waste water, a residual oxidant concentration of about 0.3 mg l−1 had to be established before a rapid inactivation was observed. The UV inactivation profiles in PBS and waste water were almost identical, with a 99.9% reduction in viability after 48 and 50 s. respectively. When UV irradiation was combined with chlorine, a less than additive effect, as compared with the sum of individual death rates by the two treatments, was observed. The corresponding UV/iodine combination at least gave an additive effect in both water qualities. No increment in inactivation rate in PBS was observed when ozone was used in combination with UV, as compared with ozone alone.

Effect of dimethylsulfoxide as a masking agent for aqueous chlorine in the determination of oxychlorines

The aim of this work was to demonstrate that dimethylsulfoxide (DMSO) is an excellent masking agent for aqueous chlorine in the determination of other oxychlorines. By the addition of excess DMSO, specific absorbance of free chlorine disappeared, and the oxidation of iodide to iodine by chlorine was completely prevented. Chlorine dioxide, chlorite and chlorate were not affected by the co-existence of excess DMSO, but chlorosulfamic acid, showed results comparable to free chlorine. By using ion chromatographic analysis of the mixed solution of free chlorine and DMSO, chloride was recovered as the only anionic species and its molar concentration was approximately twice the initial chlorine concentration. DMSO seems to reduce and mask chlorine completely, without affecting other oxychlorines. Chlorine and DMSO reacted in the molar ratio of 1:1 The reaction seemed to be second-order. The rate constant was larger at a lower pH, and it was dependent not on a concentration of total chlorine, but on that of hypochlorous acid. The redox potential of DMSO was higher at a lower pH, and only hypochlorous acid would have a redox potential high enough to oxidize DMSO in acidic conditions. These results suggest that DMSO reacts with hypochlorous acid stoichiometrically. In practical use, DMSO may be successfully used as a masking agent for aqueous chlorine.

Cinetiques de l'action bactericide des chloroisocyanurates sur trois bacteries: pseudomonas aeruginosa, streptococcus faecalis et staphylococcus aureus

The efficiency of chloroisocyanurates in swimming pool disinfection has been demonstrated by a number of authors (Andersen, 1965; Kolwalski and Hilton, 1966; Robinton and Mood, 1967; Fitzgerald and der Vartanian, 1969). The disinfection rate was seen to slow down during studies on different bacteria; this was attributed to the existence of a weak concentration of free chlorine (HOCl + ClO −). However, since these studies were carried out when the aqueous chemistry of chloroisocyanurates was not completely elucidated, the specific action of chloroisocyanurates was difficult to determine. This, in part, was due to the large number and variety of experimental procedures and analytical methods for chlorine measurements, and to the lack of specificity of the methods employed. We studied the action of chloroisocyanurates on three environmental strains: S. faecalis, S. aureus, Ps. aeruginosa and on one collection strain: Ps. aeruginosa—CIP. Disinfection tests were carried out in the laboratory, in pH and temperature conditions typically found in swimming pools (pH 7.5, 25°C). The initial concentration of total chlorine varies from 0.5 to 2.5 mg I −1, for concentrations of isocyanuric acid, H 3Cy, from 25 to 360 mg 1 −1. With these concentrations, free chlorine (HOCl + ClO −) does not exceed 3% of total chlorine (that is, less than 0.08 mg 1 −1). We used an easy and rapid method of dosage which distinguishes between “available chlorine” [(HOCl + ClO −) + (chlorine from isocyanurates, H nCl mCy p−)] and “total chlorine”: absorption spectrophotometry after reaction with the N-diethylparaphenylenediamine (DPD). We adopted a common method for monitoring simultaneously, chlorine concentration and bacterial count. In this way, we studied the kinetics of selected bacteria inactivation, relative to H 3Cy concentration and for different levels of available chlorine.

Effects of initial active chlorine concentrations on the Antarctic ozone spring depletion

Several one‐dimensional model experiments have been conducted in order to simulate the observed downward trend of total ozone and the shape of ozone profiles in the Antarctic during the austral spring. The results underline the fact that the O3 depletion is quadratically sensitive to the amount of active chlorine, which we have expressed as the fraction (F) of Clx that is in active form by polar sunrise. For F = 1, this result is largely independent of the occurrence of heterogeneous chemistry after polar sunrise since all of the processing has already occurred. The main O3 loss is due to formation and photolysis of Cl2O2, the mechanism first suggested by Molina et al. [1987]. By comparison, using Brx levels similar to currently measured values, it was found that the BrO + ClO reaction plays a less important role in O3 depletion. The depth of the O3 minimum in spring appears to be related to the vertical extent of the region chemically processed by polar stratospheric clouds as well as the absolute levels of active Clx; more extensive vertical regions result in larger bite outs of the O3 profile. This may account for the difference in O3 minimum between 1986 and 1987. Simulations involving downward vertical transports are unable to reproduce observed decreases in total O3. We speculate that low trace gas mixing ratios of species such as N2O may be remnants of the previous summer and fall conditions, rather than signatures of downward transport during the springtime ozone depletion.

The Effects of Residual Chlorine, Temperatures and Salinities on the Development of Pacific Oyster (Crassostrea gigas)

Chlorination to eliminate oysters and other fouling organisms in the cooling system of a coastal power plant may cause undesirable effects on nearby oyster farming areas. This study was aimed at determining the effect of residual chlorine on the development of Pacific oyster Crassostrea gigas under various temperature and salinity regimes. Fertilized eggs at first polar stage and four larval stages - blastula, trochophore, veliger, and D-larva - were exposed to combinations of five initial chlorine concentrations (0 to 2.52 mg.I-1) at four temperatures (19° to 28°C) and three salinities (18 to 34 ppt) for one hour. Up to second order multiple regression models were constructed to evaluate and compare the resistance of various life stages of oyster to the residual chlorine. The resistance to chlorine increased with salinity for all stages. Except for first polar eggs and D-larvae, resistance increased with temperature. First polar eggs had the highest resistance to chlorine and trochophore the lowest. Chlorina­tion at 1.392-2.953 mg.1-1 eliminated 90% of the oyster fouling in the cooling system of power plants. Chlorine concentration below 0.01-0.028 mgJ-1 reduced the impact on oyster culture.

Decay of chlorine in diluted municipal effluents

Laboratory studies were conducted to develop a model for the overall decay of total residual chlorine (TRC) under various conditions in the natural streams. This model assumes that a portion of the initial chlorine concentration is used to satisfy the immediate chlorine demand and the remainder is subject to gradual decay.The important parameters influencing the gradual decay of TRC, after mixing in the rivers, were found to be photolysis, evaporation, free radical oxidation, temperature, and turbulence. The decay rate is catalyzed by ultraviolet light and increases significantly as the ratio of area to volume of the container increases. The average level of turbulence in streams is found to approximately double the decay rate obtained under quiescent conditions. Key words: residual chlorine, natural streams, decay, evaporation, photolysis, turbulence, temperature effect, municipal effluents.

Investigation of CPE/PVC morphology via STEM

Microscopic characterization of the phase morphology of poly(vinyl chloride) (PVC) modified with chlorinated polyethylene (CPE) is vital to understanding the blend physical properties. A 2-3 week CPE selective staining technique, developed by Fleischner et al., has been the mainstay for recent TEM investigations of CPE/PVC. Several researchers employing this method have reported a network structure of CPE surrounding primary PVC particles.Rapid electron beam-induced dehydrochlorination of chlorinated polymers prohibits TEM examination of unstained sections. Chemical changes resulting from such dehydrochlorination of polymers was addressed recently by Vesely and Finch. In this study we investigated unstained thin sections, obtained at ambient temperature with a diamond knife, by scanning transmission electron microscopy (STEM) on a JEOL 2000 FX.As the STEM micrographs show (Figs. 1-3), sufficient contrast was available to distinguish CPE (light phase) from the PVC matrix (dark). Differences in initial chlorine concentration and rates of beam-induced mass loss most likely account for the contrast between phases.

Studies on the effects on municipal wastewater on the growth of Porphyra yezoensis. V. Effects of chloramine on the growth of Porphyra yezoensis (Rhodophyta).

Four kinds of chlorinated soultions were investigated to identify the causative substance (s) inhibiting the growth of Porphyra yezoensis thalli. The inhibitory effects were measured in terms of the length and the number of dead cells in Porphyra yezoensis thalli. Tests were conducted by cultures dosed chlorinated municipal sewage effluent, chlorinated ammonium solution, chlorinated municipal sewage effluent after nitrification and chlorinated ion exchanged water, respectively, each culture being subjected to shaking. Chlorinated municipal sewage effluent and chlorinated ammonium solution showed rather severe inhibitory effects on the growth of Porphyra yezoensis thalli as compared to chlorinated municipal sewage effluent after nitrification and chlorinated ion exchanged water. EC50 (10-day) values (in initial chlorine con-centration)for chlorinated municipal sewage effluent, chlorinated ammonium solution and chlorinated ion exchanged water were 0.016mg Cl/l, 0.014-0.020mg Cl/l and 1.4mg Cl/l, respectively. The chlorinated municipal sewage effluent after nitrification did not show any adverse effects on the growth of Porphyra yezoensis thalli. It was determined that only mono-chloramine formed in both chlorinated municipal sewage effluent and chlorinated ammonium solution, and that no chloramine is present in both chlorinated effluent after nitrification and chlorinated ion exchanged water. Therefore, monochloramine was considered to be a causative substance to the growth of Porphyra yezoensis thalli. Above mentioned results suggest that complete nitrification is suitable measures to reduce the adverse effects of chlorinated muni-cipal sewage effluent on the growth of Porphyra yezoensis thalli.

都市下水の養殖ノリの生育に及ぼす影響に関する研究 ＩＶ 養殖ノリの生育に及ぼす塩素殺菌都市下水処理水の影響

The effects of chlorinated effluent of activated sludge treatment on the growth of Porphyra yezoensis were investigated with different chlorinated effluent-dosed culture media and different chlorine-dosed, diluted Provasoli's Enriched Seawater (PES) culture media as a control, by means of a shaking culture. To clarify the effect of the chlorinated effluent on the Porphyra thalli, the length of thalli were measured every two days, and the number of dead cells in a thallus were counted under a microscope 4-10 days after the start of the culture followed by an erythrosine staining. Initial chlorine concentrations which manifested a 50% growth effect and 50% dead cell in chlorinated effluent-dosed culture and chlorine-dosed diluted PES culture were 0.025-0.035mg Cl2/l and 0.06mg Cl2/l, and 0.75-0.95mg Cl2/l and 1.5-3mg Cl2/l, respectively. The growth effect and dead cells manifestation were dependent on the initial chlorine concentrations in both cultures. It was found by the amperometric method that chlorine was free chlorine in the diluted PES culture and combined chlorine in the chlorinated effluent-dosed culture. Although both residual chlorines disappeared with the passage of time, the removal rate of combined chlorine was slower than that of free chlorine. The above mentioned results suggest that the strong toxicity may be caused by the reaction products of chlorine with organic substances in the effluent.