Total Residual Chlorine Concentrations Research Articles

Short-Term Guideline Values for Chlorine in Freshwaters.

The current Australian and New Zealand default guideline value of 3 µg Cl/L for total residual chlorine in freshwaters is largely based on acute data converted to chronic data using a default acute to chronic ratio of 10, without consideration of chlorine decomposition. Given the rapid decomposition of chlorine, initially as hypochlorite and then as chloramine, it is appropriate to consider a guideline value based on short-term (acute) toxicity rather than one based on longer-term chronic data, as has been recommended for chlorine in marine waters. The literature on the fate of chlorine in drinking water discharged to freshwaters and on the ecotoxicity of total residual chlorine has been reviewed, and on the basis of this, revised default guideline values were derived for both hypochlorite and chloramine in freshwater using a species sensitivity distribution of toxicity data. The values for 95% species protection were 7 and 9 µg Cl/L as total residual chlorine, respectively. The former would apply to any total residual chlorine-containing effluent, but in the case of drinking water where dechlorination has been undertaken, the chloramine-based default guideline value is likely to be more appropriate. Both are likely to be conservative because they were largely based on toxicity testing under continuous flow-through conditions. They will apply at the edge of the mixing zone, and the variable receiving water concentration at this point might best be determined from a time-weighted average total residual chlorine concentration. Environ Toxicol Chem 2021;40:1341-1352. © 2021 SETAC.

2016 update Japanese Society for Dialysis Therapy Standard of fluids for hemodialysis and related therapies

The necessity of purification of dialysis fluids has been discussed since the 1980s. The Japanese Society for Dialysis Therapy (JSDT) presented a standard for dialysis fluid purification in 1995 and revised three times after that. Lastly, JSDT presented a new standard on microbiological management of fluids for Hemodialysis and related therapies in 2008 (the 2008 JSDT standard). It, however, specifies biological contaminants (ET and bacteria) alone.The society further revised the 2008 JSDT standard with the addition of the water quality standard for chemical contaminants and management standard for water treatment equipment in 2016 (the 2016 JSDT standard). This article describes the 2016 JSDT.Chapter 1 describes the water quality standard for biological contaminants without any modification of the standard values in the 2008 JSDT standard because the ultrapure dialysis fluid standard was met at 66.4% of all responder facilities in a 2014 survey conducted by the JSDT.Chapter 2 describes the water quality standard for chemical contaminants. Twelve items are specified in the standard, inasmuch as the toxic potentials of these chemicals have been verified, or are suspected. When the water treatment equipment is operated appropriately, chemical contaminants are appropriately removed from raw water and safe dialysis water is supplied to dialysis machines. However, chemical contaminants in raw water should be confirmed at least before installation of the water treatment equipment. In the daily management, water quality data on the source of raw water must be confirmed in each season of the year. If some chemical contaminants in source of raw water do not meet the water quality standard, the relevant chemical contaminants in dialysis water should be measured at least once a year.Chapter 3 describes the measurement of the residual chlorine. The concentration of total residual chlorine (total chlorine) in dialysis water should be less than 0.1 mg/L.The management standard for water treatment equipment is proposed in Chapter 4. Chapter 5 describes in detail the management.

Chlorination at Treatment Plant and Drinking Water Quality: A Case Study of Different Sectors of Islamabad, Pakistan

In the city of Islamabad, drinking water quality at the treatment plant usually meets the country’s hygienic standards. To provide protection against recontamination, concentration of total residual chlorine in treated water is maintained at levels from 0.2 to 0.5 mg/L in tap water of consumer end and rechlorination is not practiced. Some areas of the city have very low residual chlorine at consumer taps and little protection against secondary microbial contamination of water in pipelines. The analysis of the drinking water quality in the distribution network was carried out during March–August 2008 by collecting 80 water samples in triplicate from treatment plants and remaining of the residential taps. The collected samples were examined for total chlorine, free chlorine residual, chloramines, trihalomethanes, total organic carbon, total coliforms, fecal coliforms and turbidity. The water samples collected from sector F-6, F-10 and F-11 were found to be free of fecal contamination while in sectors E-7 and F-7 contamination was found at few stations among all the collected samples. Water samples collected from sectors F-8, G-9, G-8, I-9, and I-8 were highly contaminated with E. coli, at most of the sampling stations. Trihalomethanes and chloroform were detected at high concentrations in sector F-8.

Use of Lethal Short‐Term Chlorine Exposures to Limit Release of Nonnative Freshwater Organisms

AbstractFish hatcheries and other types of aquatic facilities are potential sources for the introduction of nonnative species of fish or aquatic invertebrates into watersheds. Chlorine has been suggested for use to kill organisms that might be released from the effluent of a facility. While acute LC50s (concentrations lethal to 50% of organisms exposed for up to 96 h) for chlorine are available for some species, short‐term LC100s for chlorine have not been determined. The objective of this study is to establish concentrations of chlorine that are lethal to 100% of organisms after brief (1‐, 5‐, or 15‐min) exposures. A total of 22 species were exposed to total residual chlorine concentrations (TRC) of 1, 10, or 25 mg TRC/L for 1, 5, or 15 min under static conditions followed by a 24‐h postexposure recovery period in water without the addition of chlorine. Concentrations of chlorine resulting in 100% lethality of organisms were established for all of the species tested except for four species of mollusks or for a beetle. Exposures for 5 to 15 min to 10–25 mg TRC/L were the lowest combined time–chlorine treatments under which all of the fish tested and the other invertebrates tested (17 species) exhibited 100% lethality by the end of the initial chlorine exposures or after the 24‐h recovery period.

低濃度残留塩素時の海生生物付着事例について

Cooling efficiency at coastal industrial plants with seawater-based cooling systems is often reduced due to water flow blockage caused by marine biofouling. Maintenance of a residual chlorine concentration of 0.1–0.3 mg/L for 18 h/day is known to be an effective countermeasure, but it is often impossible to maintain so high a concentration because of chlorine-induced corrosion and/or environmental considerations. There have been only a few reports examining the effects of low concentrations of residual chlorine, so we carried out a study to evaluate the marine biofouling potential at residual chlorine concentrations of 0.05 mg/L or less, and to identity any related problems. The study was conducted at a factory on the shore of Ise Bay, Japan, at which no residual chlorine was detected in the discharge water. For 63 days (27 Apr. to 29 Jun. 2010) we regularly observed the extent of marine biofouling on a coarse-mesh vinylon net placed parallel to the water flow inside a cooling-water pipe through which seawater with a total residual chlorine concentration averaging 0.055 mg/L (range: 0.02–0.12 mg/L) was run continuously. We also checked the condition of the net on 6 Dec. 2010 after 30 days of uninterrupted exposure to the water flow. In both cases, much biofouling was observed on the test net. Thus, low levels of residual chlorine, even when applied continuously, appear insufficient to prevent biofouling and an attendant reduction in cooling efficiency.

Spatio-temporal variability of tastes and odors of drinking water within a distribution system

The threshold of human perception in the detection of tastes and odors (T&O) relating to compounds in drinking water is variable. For example, chlorine can be detected at the ppm level and geosmin can be perceived at the ppt level. In this paper, sensory tests (using a human panel), physicochemical analyses (total and free residual chlorine, temperature, metals, geosmin, and 2-methylisoborneol (2MIB)) and microbiological analyses (algae, Actinomycetes and heterotrophic plate count) were performed for water samples collected during a seventeen-month period at ten different locations of a municipal distribution network of Quebec City (Canada). The results showed that different flavors(1) assessed by a panel and aggregated into global flavor intensity (GFI) vary considerably spatially and seasonally. Multiple regression analysis showed that the factors best explaining the variability of GFI are (in order) the season, the location, the concentration of total residual chlorine and the presence of cyanobacteria. Results also demonstrate that chlorine has a masking effect on other T&O.

EFFECT OF ELECTROLYTIC TREATMENT OF BALLAST WATER ON CORROSION BEHAVIOR OF TANK STEEL

In order to regulate discharges of the ships' ballast water and reduce the risk of non-native species introduced from the ballast water,the international maritime organization(IMO) has developed international legislation,the ships' ballast water should be treated before discharge, and electrolysis has been developed as a promising method for ballast water treatment.However, the oxidative species such as Cl_2,HClO and NaClO generated during electrolytic treatment may not only kill the non-native aquatic species but also accelerate the corrosion of the ballast tank steel. In this paper,the effect of the total residual chlorine(TRC) concentration in 3.5%NaCl solution on the corrosion of Q235 steel was studied using mainly the open-circuit potential-time measurement (E_(OC)-t) and electrochemical impedance spectroscopy(EIS).Four TRC concentrations,0,5,10 and 20 mg/L,which are around the concentration proved to be effective for removal of non-native aquatic species,were tested.Both the E_(OC)-t and EIS results suggested that the corrosion of the Q235 steel in 3.5%NaCl solution with or without TRC can be divided into three stages:rapid oxidation of steel, coverage of metal surface by oxide film,and breakdown of the oxide film and initiation of corrosion. The negative shift of E_(OC) and reduction of charge-transfer resistance(R_(ct)) of the steel immersed in the solutions containing low TRC concentrations such as 5 and 10 mg/L demonstrated that the corrosion of steel is slightly enhanced.The enhancement of corrosion is due to the increase of the depolarization concentration present in the solutions.But for solution with higher TRC concentration such as 20 mg/L,both the E_(OC) and R_(ct) increased,suggesting retardation of the corrosion process.The retardation of corrosion can be attributed to the passivation of the steel surface due to the strong oxidation of the active species and the formation of compact corrosion product that covers the corrosion sites.This means that increasing TRC concentration to 20 mg/L does not accelerate the corrosion of the tank steel. Therefore,higher TRC concentration for on-board electrolytic treatment is allowable,which is beneficial for shortening the treating process and improving the removal efficiency.

Corrosion of marine carbon steel by electrochemically treated ballast water

Laboratory weight-loss measurements, electrochemical tests and SEM techniques were used to study the corrosive behaviour of electrolysed ballast water on marine carbon steel. Experimental results showed that for the mass concentration of Total Residual Chlorine (TRC) being 7.5mg/l, 17mg/l and 28mg/l respectively, the corrosion rates within seven days were 1.25, 1.46 and 1.7 times those in natural seawater. The corrosion rates decreased as time progressed. The corrosion rate in the electrolysed seawater is controlled by the cathodic process which is mass transfer controlled. The SEM observation showed that the topographies of carbon steel corroded in electrolysed ballast water with mass concentration of TRC 7.5mg/l and 17mg/l were characterised by denudation and rupture. Both the weight-loss and electrochemical tests revealed that the chlorinated seawater accelerated the corrosion rate and that this is consistent with result of the SEM observation

The decontaminative effects of acidic electrolyzed water for Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on green onions and tomatoes with differing organic demands

Acidic electrolyzed water (AC-EW) has strong bactericidal activity against foodborne pathogens on fresh vegetables. However, the efficacy of AC-EW is influenced by soil or other organic materials present. This study examined the bactericidal activity of AC-EW in the presence of organic matter, in the form of bovine serum against foodborne pathogens on the surfaces of green onions and tomatoes. Green onions and tomatoes were inoculated with a culture cocktail of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes. Treatment of these organisms with AC-EW containing bovine serum concentrations of 5, 10, 15, and 20 ml/l was performed for 15 s, 30 s, 1 min, 3 min and 5 min. The total residual chlorine concentrations of AC-EW decreased proportional to the addition of serum. The bactericidal activity of AC-EW also decreased with increasing bovine serum concentration, whereas unamended AC-EW treatment reduced levels of cells to below the detection limit (0.7 logCFU/g) within 3 min.

Relationship of nutrient and residual chlorine concentration in treated wastewater with periphytic algae grown in a stream receiving treated wastewater

The ratio of the amount of treated wastewater to river water is increasing in urban areas due to the spread of sewage systems. Treated wastewater is also sometimes extensively used to create streams and other water environments in urban areas. Rivers, streams and other water environments provide valuable habitats for all kinds of aquatic species, but the relationship between such aquatic species and the quality of treated wastewater they inhabit is not clearly understood. This study was carried out to clarify the effect of the water quality of treated wastewater such as nutrients and residual chlorine on periphytic algae grown in a stream receiving treated wastewater using laboratory-scale experimental channels. The following results were obtained. (1) When the range of phosphate (PO4-P) concentration was 0.04 to 0.09 mg/L, the higher the PO4-P concentration, the higher the biomass of periphytic algae and the more dominant the Chlorophyceae. (2) When the range of total residual chlorine (TRC) concentration was 0.07 to 5.8 mg/L, the higher the TRC concentration, the lower the biomass of periphytic algae. When the range of TRC concentration was 0.93 to 5.8 mg/L, this tendency was more pronounced.

NaOCl produced by electrolysis of natural seawater as a potential method to control marine red-tide dinoflagellates

As part of the development of a method to control the outbreak and persistence of red tides using sodium hypochlorite (NaOCl), we investigated the effect of NaOCl on the survival of red-tide dinoflagellates, diatoms, heterotrophic protists, planktonic crustaceans, fin-fish, shellfish, and macroalgae. Because NaOCl introduced into natural waters would be subject to dilution, as well as breakdown in sunlight to NaCl, the survival of organisms was determined after 10 min exposure and 1 h exposure to NaOCl, and again after transfer to fresh seawater for 6 or 24 h. The lethal total residual chlorine (TRC) concentration that killed 50% of the test organisms (LC50) for the red-tide dinoflagellates Gymnodinium catenatum, Cochlodinium polykrikoides, Akashiwo sanguinea, Lingulodinium polyedrum, Prorocentrum micans, Alexandrium affine, and Gymnodinium impudicum ranged from 57 to 157 ppb for 10 min exposure and from 30 to 106 ppb for 1 h exposure. Complete mortality of all red-tide species occurred at TRC concentrations of ~ 500 ppb. The LC50 of the diatoms Skeletonema costatum and Thalassiosira rotula, 3083–3383 ppb for 10 min exposure and 3128–3433 ppb for 1 h exposure, were much higher than for red-tide dinoflagellates. But the LC50s of the heterotrophic dinoflagellates Polykrikos kofoidii and Oxyrrhis marina were similar to those of red-tide dinoflagellates. The ciliate Strombidinopsis sp. had LC50s of 306 ppb for 10 min exposure and 119 ppb for 1 h exposure, which are higher than those for dinoflagellates. The LC50s of the calanoid copepods Acarlia spp. and Pseudodiaptomus sp. were 1397–1493 ppb for 10 min exposure and 744–987 ppb for 1 h exposure, and those for larvae of the brine shrimp Artemia franciscana were 4905 ppb for 10 m exposure and 2814 ppb for 1 h exposure. The LC50s of juvenile gray mullet Mugil cephalus and juvenile black rockfish Sebastes schlegeli were 1234–1883 ppb for 10 min exposure and 1234–1440 ppb for 1 h exposure, whereas those of adult Manila clam Ruditapes philippinarum and spat of the abalone Nordotis discus were> 20,000 ppb. The LC50s of the macroalgae Griffithsia japonica (Rhodophyta) and Ulva pertusa (Chlorophyta) were 1519–12,365 ppb for 10 min exposure and 1085–12,558 ppb for 1 h exposure. The present study therefore suggests that, if NaOCl is introduced into waters containing red-tide organisms at TRC concentrations of 300–500 ppb for 10 min exposure and 200–400 ppb for 1 h exposure, red tides can be effectively controlled without serious harmful effects on other marine organisms, except heterotrophic dinoflagellates.

Deterioration of drinking water quality in the distribution system and gastrointestinal morbidity in a Russian city

Few studies have been conducted in Russia to assess the relationship between drinking water quality and gastrointestinal (GI) infections. In the city of Cherepovets, effluent water at the treatment plant usually meets the country's hygienic standards. To provide protection against secondary water contamination in the distribution system, concentrations of total residual chlorine in effluent water are maintained at levels from 1 to 2 mg l -1 . However, residual chlorine concentrations rapidly decline in the distribution system and rechlorination is not practiced. Some areas of the city routinely have very low residual chlorine at taps and little protection against secondary microbiological contamination of water in pipelines. A cross-sectional epidemiological study was conducted in Cherepovets to assess an association between decline in residual chlorine concentrations and risk of GI illness. This study included water quality monitoring and an extensive questionnaire survey of city residents. The results demonstrated a consistent spatial pattern of free chlorine decline in the distribution system. An interquartile range variability in free residual chlorine decline (0.22 mg l -1 ) was associated with 1.42 (95% confidence interval (CI) = 1.05, 1.91) relative risk of self-reported gastrointestinal illness after control for socioeconomic, hygienic and demographic parameters.

Improving the recoveries of unstable N-chloramines determined by liquid chromatography-postcolumn electrochemical detection.

Liquid chromatographic (LC) measurement of individual N-chloramines, which are key byproducts of wastewater and drinking water chlorination, could lead to more effective control of water disinfection. Such measurements are challenging because of analyte instability. A detector selective for N-chloramines is constructed based on postcolumn derivatization with iodide followed by reductive detection of the iodine product at a glassy carbon electrode. In flow injection (FIA) mode, the detector gives identical responses for a test set of four chemically diverse N-chloramines. In the LC mode, losses of the test compounds are observed when LC and FIA responses are compared and quantitated by introducing a relative response factor (RRF). Using the RRF, N-chloramine recoveries are evaluated as a function of multiple LC separation parameters. The highest recoveries are obtained using a reversed-phase (C18) column with an acetonitrile mobile phase and a pH 7.02 aqueous phosphate buffer. With these conditions, linear calibration curves are obtained for all test N-chloramines. The detection limits obtained are in the low 10(-7)-mol/L range, which is nearly tenfold better than previously reported and 10-1000-fold lower than total residual chlorine concentrations typically found in disinfected water and wastewater.

Effluent Total Residual Chlorine Decay in Outfall Pipe

Field and bench tests were conducted to determine the decay property of effluent total residual chlorine (TRC) in an outfall pipe. The pipe conveys secondary treated effluent from the Broward County North Regional Wastewater Treatment Plant to the Atlantic Ocean off the east coast of South Florida. During a field test effluent samples were taken and TRC concentrations were measured every 15 mins for 6 h at three stations along the inland portion of the outfall pipe. Results indicate that the effluent TRC decay can be described by first-order kinetics. The TRC overall decay constant is assumed to be the sum of static and dynamic decay constants. The overall decay constant, determined from the field tests, is one order of magnitude greater than the static decay constant determined from the bench tests. This suggests that TRC decay in the outfall pipe is dominated by chlorine consumption by the biofilm at the pipe wall. The removal of TRC during the effluent transport in the outfall pipe is estimated as 68% at the permitted flow rate of 2.9 m³/s.

Chlorine Dynamics and Ambient Toxicity in Receiving Streams

This study was conducted to better understand total residual chlorine (TRC) dynamics and ambient toxicity in two chlorine‐contaminated streams in eastern Tennessee. The study used stepwise logistic analysis of Ceriodaphnia survival and water quality factors measured in 169 7‐d chronic toxicity tests of water from four sites in one stream to determine the factors significantly affecting the survival. The 7‐d mean concentrations of TRC and a measure of day‐to‐day variation in TRC concentration in each test were included as dominant factors in explaining Ceriodaphnia mortality. The logistic regression model correctly predicted the mortality or survival in individual Ceriodaphnia in 89.9% of the cases and had a low rate of false positives and false negatives. A simpler pass‐or‐fail model, which used a Ceriodaphnia survival criterion of 60%, yielded slightly better results (correctly predicted outcomes, 91.7%). We also measured TRC concentrations in situ by monitoring at two sites in one of the streams and at one site in the other stream. This monitoring showed that TRC concentrations in both streams varied approximately three‐fold in daily cycles, with TRC concentrations at night greater than those during the day. Laboratory and field experiments indicated that the diel cycles in TRC were probably driven by sunlight and stream periphyton. Two key points emerged from this study. First, the analysis show that logistic regression can be used effectively to relate temporally varying chemical conditions to the outcomes of static‐renewal ambient toxicity tests. In some situations, this method of analysis is more appropriate than other methods, such as ANOVA, that there are used to evaluate dose‐response patterns. Second, diel changes in TRC in streams, apparently caused by sunlight and periphyton, can be large and have important implications for predicting the fate and ecological effects of this widespread contaminant.

Minnows can acclimate to total residual chlorine

AbstractObservations in a chlorine‐contaminated stream in eastern Tennessee revealed several species of fish in areas where total residual chlorine (TRC) concentrations were often great enough to be lethal, based on the results of other studies. We used in situ and laboratory experiments to test the hypothesis that minnows could acclimate to TRC. Acclimation was assessed by time‐to‐death for fish exposed to a single lethal regime of TRC. In in situ experiments, striped shiner and central stoneroller minnows collected from East Fork Poplar Creek at a TRC‐contaminated site and a site farther downstream, where TRC was below detection, were caged at sites in the stream where TRC concentrations were either nil or great enough to be lethal. At the cage with high TRC, minnows collected from the “TRC‐contaminated” site survived two to four times longer (15.8 h vs. 6.1 h) than the same species from the “TRC‐free” site. In laboratory experiments, golden shiner minnows were exposed to TRC in a stepwise increasing concentration regime (0.04 mg/L during week 1, 0.08 mg/L during week 2, and 0.12 mg/L during week 3) before being challenge‐tested with a lethal concentration of TRC. Minnows that had been previously exposed to TRC survived longer than controls in each test, and the magnitude of the mean time to death increased as the TRC concentration and duration of exposure increased (1.2‐, 2.5‐, and 3.9‐fold increases for weeks 1, 2, and 3, respectively). Another experiment with golden shiner minnows showed that a 21‐d exposure to TRC at a low concentration (0.04 mg/L) only slightly increased their tolerance to TRC. Thus, several minnow species apparently can acclimate, fairly rapidly, to TRC. This study may help explain why fish kills are less common than expected in TRC‐contaminated streams.

Chlorine Tolerance of Mesocyclops (Cyclopoida: Cyclopidae) Copepods and Three Container-Breeding Species of Mosquitoes

Sodium hypochlorite (NaOCI) tolerance characteristics of Mesocyclops aspericornis (Daday), Mesocyclops longisetus (Thiebaud), Aedes aegypti (L.), Culex quinquefasciatus Say, and Anopheles farauti Laveran (sibling species no. 1) were investigated by measuring their mortality in response to total residual chlorine concentrations ranging from 0.0 to 2.0 ppm. Of the two Mesocyclops species evaluated, M. aspericornis showed the greatest sensitivity to chlorinated water, with an LD50 value of 0.47 ppm total residual chlorine. M. longisetus exhibited the greatest suitability for treatment of chlorinated stored water, with an LD50 value of 1.01 ppm total residual chlorine. Cx. quinquefasciatus , Ae. aegypti , and An. farauti had LD50 values of 0.71, 1.07, and 1.35 ppm total residual chlorine, respectively. The laboratory findings were compared with a field study of chlorine levels in water tanks targeted for treatment with Mesocyclops in Fortaleza (3° 45′ S, 38° 35′ W), Brazil.

Effect of fluctuating low‐level chlorine concentrations on valve‐movement behavior of the asiatic clam (Corbicula fluminea)

AbstractAsiatic clams (Corbicula fluminea) exposed to water from the upstream section of East Fork Poplar Creek (Oak Ridge, TN), a stream receiving chlorine‐containing industrial discharges, were monitored for changes in valve movement patterns. Individual clams were attached to an automated valve‐movement monitoring apparatus and suspended in flow‐through tanks located streamside. Valve‐closure behavior of two clams exposed to untreated water was compared to that of two clams exposed to dechlorinated water for two 18‐d periods. Chlorine concentrations in untreated water exhibited a pronounced diurnal cycle, fluctuating between a mean daily minimum of 0.02 mg/L total residual chlorine (TRC) during the day and a mean daily maximum of 0.07 mg/L TRC at night during the second monitoring period. In over 2,300 fifteen‐minute intervals, clams closed for 0.70 of the intervals while exposed to untreated water, but closed for only 0.22 of the intervals while exposed to dechlorinated water. Treatment differences in valve closure were tested by repeated‐measures ANOVA. A significant treatment effect (p = 0.026) on valve closure was found in the first monitoring period. Graphical analysis of valve‐closure records revealed die! cycles that differed between treatments. Clams in untreated water usually opened only near midday, when TRC concentrations were lowest. Clams in dechlorinated water opened more often, for longer periods, and appeared to respond to dawn and dusk changes in light. The valve‐closure behavior of clams in untreated water effectively minimized tissue exposure to waterborne TRC, presumably reducing toxic effects. Valve‐closure monitoring in conjunction with other studies may help estimate the effect of tissue isolation on the toxicity or bioaccumulation of waterborne chemicals. Such estimates could improve prediction of toxicological or ecological consequences of stressful conditions on bivalves.

Residual chlorine decay in a broad, shallow river

Field investigations into the mixing and decay of discharge plumes containing total residual chlorine (TRC) concentrations of 2.0 mg/l were conducted in the North Saskatchewan River downstream from two water treatment plants in the City of Edmonton, Canada. Environmental concentrations of TRC within the receiving body were found to be a function of the hydraulic mixing characteristics of the receiving stream and of the chemical decay of residual chlorine. In-stream TRC concentration profiles resulting from steady-state discharges were monitored at downstream locations. Dilution of the plume by the receiving stream was quantified by calibrating a two-dimensional mixing model to the mixing characteristics of the North Saskatchewan River using results obtained from steady-state dye-tracer studies using Rhodamine WT. First-order decay coefficients for TRC within the North Saskatchewan River were obtained by modelling the chlorinated plume mixing and fitting a first-order decay coefficient to the observed field data. Gross first-order decay coefficients attributed to all chlorine sinks except dilution and adjusted to a standard temperature of 20°C were found to be, at two different locations, 20 and 28 d −1.

Behavioral responses of marked snails as indicators of water quality

AbstractBehavioral responses of the common stream‐dwelling operculate snail Elimia clavaeformis were used to provide information about streamwater quality in in situ tests. These snails were found to be advantageous for such tests because they can be collected easily, individually marked, and transferred to other stream sites for release and recapture experiments.In noncontaminated stream sites, Elimia tended to disperse upstream. The rate of net movement was variable, but typically ranged from 0.5 to 5 m/d. Water velocity and food level influenced the movement patterns of the snails in 24‐ and 48‐h field experiments in noncontaminated stream sites. Rates of movement in the laboratory were temperature dependent, and increased from about 1.0 cm/min at 9°C to 2.2 cm/min at 24°C.In contaminated streams, snails showed clear evidence of stress: They moved downstream, and in some sites either withdrew into the shell or were unable to retract the foot or attach to a substrate. The maximum distance that Elimia traveled downstream in 24 h in a contaminated stream site was 17.5 m.In laboratory streams, Elimia moved downstream when exposed to 0.02 mg/L total residual chlorine (TRC); the time required to immobilize these snails declined rapidly as TRC concentration increased. Behavioral characteristics of snails that may be useful for water quality assessments include turnover time (the time needed for a snail to right itself after being turned onto its back), the rate and direction of dispersal or immobilization.