自由氯、氯胺和顺序氯化对饮用水消毒效果的试验研究

研究了自由氯、氯胺和顺序氯化三种消毒方式对大肠埃希氏菌和粪肠球菌的灭活效果.结果表明,自由氯浓度越高,对细菌的灭活速率和最终灭活率越大;氯胺浓度越高,对细菌的灭活速率和最终灭活率越大;顺序氯化消毒效果优于单独使用自由氯或氯胺时的消毒效果.同时,还探讨了pH和温度对三种消毒方式的影响.     

The effects of free chlorine and chloramine on growth and respiration rates of larval lobsters (Homarus Americanus)

The length, dry weight and standard respiration rate of larval lobsters (Homarus americanus) were monitored for 19 days following a 60 min exposure at 25°C to 1.0 mg I⁻¹ applied free chlorine and 1.0 mg I⁻¹ applied chloramine. Compared to control organisms, significantly lower increases in dry weight (P < 0.05) and significant reductions in standard respiration rates (P < 0.01) were measured among exposed organisms; greater differences were detected among chloramine exposed organisms. From these results it can be concluded that acute exposure to either free chlorine or chloramine results in subsequent reductions in growth and metabolic activity of larval lobsters.     

The effect of free chlorine on Burkholderia pseudomallei in potable water

Chlorine is widely used in public water supplies to provide a disinfection barrier. The effect of chlorine disinfection on the water-borne pathogen Burkholderia pseudomallei was assessed using multiple techniques. After exposure to chlorine viable bacteria were undetectable by conventional plate count techniques; however, persistence of B. pseudomallei was verified by flow cytometry and bacteria were recoverable following a simple one-step broth procedure. The minimum residual chlorine concentration and contact time as prescribed by potable water providers in Australia was insufficient to reduce a B. pseudomallei population by more than 2 log(10). Chlorine had a bacteriostatic effect only on B. pseudomallei; viable bacteria were recovered from water containing up to 1000 ppm free chlorine. This finding has practical implications for water treatment in regions where B. pseudomallei is endemic. Future work to assess the effect of alternative water disinfection processes either singly or in sequence is necessary.     

Comparison of bacterial regrowth in distribution systems using free chlorine and chloramine: a statistical study of causative factors

Bacterial regrowth was investigated over a 15-month period in distribution systems (DSs) of Durham and Raleigh in North Carolina. These two water utilities were chosen because they are adjacent to one another, have similar service area characteristics, and treat surface waters of similar characteristics with conventional processes (coagulation-sedimentation and dual-media filtration). The finished waters have similar chemical quality and regrowth potential as measured by assimilable organic carbon (AOC). The major difference in treatment is the choice of final disinfectants (chlorine in Durham and chloramine in Raleigh). Ten sampling sites (monthly sampling) were chosen in each system to give wide geographic coverage and correspondingly, a wide range of water residence times. Significant losses were observed in both chlorine and chloramine residual in the DSs that produced bacterial regrowth as measured by heterotrophic plate count (HPC). The frequency distributions for log HPC (133 observations from Durham and 135 observations from Raleigh) were statistically the same in the chlorinated and chloraminated DSs. A correlation analysis indicated that disinfectant residual is the most important factor determining HPC level. However, the resulting R2 value for a non-linear regression model that also included AOC, temperature, and pH as independent variables was less than 0.7. Bacterial regrowth as measured by HPC, is dependent upon a complex interaction of chemical, physical, and operational parameters that may not be captured by such a simple statistical relationship.     

Comparison of chlorine and chloramine in the release of mercury from dental amalgam

The purpose of this project was to compare the ability of chlorine (HOCl/OCl⁻) and monochloramine (NH₂Cl) to mobilize mercury from dental amalgam. Two types of amalgam were used in this investigation: laboratory-prepared amalgam and samples obtained from dental-unit wastewater. For disinfectant exposure simulations, 0.5 g of either the laboratory-generated or clinically obtained amalgam waste was added to 250 mL amber bottles. The amalgam samples were agitated by end-over-end rotation at 30 rpm in the presence of 1 mg/L chlorine, 10 mg/L chlorine, 1 mg/L monochloramine, 10 mg/L monochloramine, or deionized water for intervals of 0 h, 2 h, 4 h, 8 h, and 24 h for the clinically obtained amalgam waste samples and 4 h and 24 h for the laboratory-prepared samples. Chlorine and monochloramine concentrations were measured with a spectrophotometer. Samples were filtered through a 0.45 µm membrane filter and analyzed for mercury with USEPA standard method 245.7. When the two sample types were combined, the mean mercury level in the 1 mg/L chlorine group was 0.020 mg/L (n = 25, SD = 0.008). The 10 mg/L chlorine group had a mean mercury concentration of 0.59 mg/L (n = 25, SD = 1.06). The 1 mg/L chloramine group had a mean mercury level of 0.023 mg/L (n = 25, SD = 0.010). The 10 mg/L chloramine group had a mean mercury level of 0.024 mg/L (n = 25, SD = 0.011). Independent samples t-tests showed that there was a significant difference between the natural log mercury measurements of 10 mg/L chlorine compared to those of 1 mg/L and 10 mg/L chloramine. Changing from chlorine to chloramine disinfection at water treatment plants would not be expected to produce substantial increases in dissolved mercury levels in dental-unit wastewater.     

Reactions of tetracycline antibiotics with chlorine dioxide and free chlorine

Tetracyclines (TCs) are a group of widely used antibiotics that have been frequently found in the aquatic environment. The potential reactions of TCs with common water disinfection oxidants such as chlorine dioxide (ClO₂) and free available chlorine (FAC) have not been studied in depth and are the focus of this study. The oxidation kinetics of tetracycline, oxytetracycline, chlorotetracycline and iso-chlorotetracycline by ClO₂ and FAC are very rapid (with large apparent second-order rate constants k_app = 2.24 × 10⁵-1.26 × 10⁶ M⁻¹ s⁻¹ with ClO₂ and k_app = 1.12 × 10⁴-1.78 × 10⁶ M⁻¹ s⁻¹ with FAC at pH 7.0) and highly dependent on pH. Species-specific rate constants are obtained by kinetic modeling that incorporates pH-speciation of TCs and the oxidants (for FAC), and reveal that TCs primarily react with ClO₂ and FAC by their unprotonated dimethylamino group and deprotonated phenolic-diketone group. The modest difference in reactivity among the four TCs toward the oxidants is consistent with expectation and can be explained by structural influences on the two reactive moieties. Product evaluation shows that oxidation of TCs by ClO₂ leads to (hydr)oxylation and breakage of TC molecules, while oxidation of TCs by FAC leads to chlorinated and (hydr)oxylated products without any substantial ring breakage. Results of this study indicate that rapid transformation of TCs by oxidants such as ClO₂ and FAC under water and wastewater treatment conditions can be expected.     

Combined toxicity of free chlorine, chloramine and temperature to stage I larvae of the American lobster Homarus americanus

The differential effects of free chlorine and chloramine on stage I larvae of the American lobster Homarus americanus have been investigated in continuous flow bioassay units. Applied chloramine was more toxic than corresponding concentrations of applied free chlorine to lobster larvae with estimated lc₅₀ values at 25° of 16.30 mg/l applied free chlorine and 2.02 mg/l applied chloramine. The synergistic effect of temperature on the toxicity of both free chlorine and chloramine has also been demonstrated. Exposure to applied free chlorine at 20° resulted in no significant mortality of test organisms, whereas exposure at 30° resulted in an estimated lc₅₀ value of 2.50 mg/l. Applied chloramine was considerably more toxic with an estimated lc₅₀ value at 20° of 4.08 mg/l and at 30° of 0.56 mg/l.The action of each toxicant appeared to be an alteration of standard metabolic activity as revealed by changes in respiration rates during and after exposure to applied free chlorine and chloramine. Initial respiratory stress was detected during exposure to 0.05 mg/l applied chloramine and 5.00 mg/l applied free chlorine. Reductions in respiration rates 48 h after exposure were observed with exposure to all concentrations tested, similar results being obtained following exposure to 0.05 mg/l applied chloramine and 0.10 mg/l applied free chlorine. These results are indicative of the need for information in addition to that obtained in standard bioassays for an adequate assessment of chlorine toxicity.The apparent chlorine demand of the seawater used in this study was determined after removal of particulate and dissolved organics and ammonia. Approximately 18% of the applied level of free chlorine and chloramine was recovered as residuals, measured by amperometric titration; however, no reason for this low recovery has been determined. Until it has been established that undetected chlorine and chloramine in seawater do not result in the production of toxic compounds, both applied and residual levels should be reported in toxicity studies.     

Effects of temperature and biodegradable organic matter on control of biofilms by free chlorine in a model drinking water distribution system

This study used annular reactors (AR) to investigate, under controlled laboratory conditions, the effects of temperature and biodegradable organic matter (BOM) on the free chlorine residual needed to control biofilm accumulation, as measured by heterotrophic plate count (HPC) bacteria. Biofilm was grown on PVC coupons, initially in the absence of chlorine, at 6, 12, and 18 degrees C, in the presence and absence of a BOM supplement (250 microg C/L) added as acetate. During the early stages of chlorine addition, when no measurable free chlorine residual was present, a reduction in biofilm HPC numbers was observed. Subsequently, once sufficient chlorine was added to establish a residual, the biofilm HPC numbers expressed as log CFU/cm2 fell exponentially with the increase in free chlorine residual. Temperature appeared to have an important effect on both the chlorine demand of the system and the free chlorine residual required to control the biofilm HPC numbers to the detection limit (3.2 Log CFU/cm2). For the water supplemented with BOM, a strong linear correlation was found between the temperature and the free chlorine residual required to control the biofilm. At 6 degrees C, the presence of a BOM supplement appeared to substantially increase the level of free chlorine residual required to control the biofilm. The results of these laboratory experiments provide qualitative indications of effects that could be expected in full-scale systems, rather than to make quantitative predictions.     

Empirical model for disappearance of free oxidants in natural water with wide salinity and ammonia ranges

An empirical model for the disappearance rates of chlorine-induced free oxidants was developed. Both in seawater and river water, the disappearance of free oxidants occurred in two stages (stage I and II). The disappearance of free oxidants in stage II was considered to be the consumption by organic substances in natural water. The disappearance rate could be empirically explained by a second-order reaction of oxidants. The observed rate constant was decreased with the increase of the oxidant concentration after subtracting the decrease in stage I from the chlorine dose in natural water. Especially in seawater, the maximum persistence of oxidants could be estimated by the self-decomposition rate of hypobromite which was the disappearance rate in artificial seawater, and the rate constant was obtained as a function of bromide concentration. The disappearance in stage I, which was very rapid, was considered to be the reactions with reactive inorganic and organic substances in natural water. The minimum decrease, which was led to the maximum persistence in stage II, could be approximately expressed as the consumption by ammonia. Using our proposed model, the maximum persistence of free oxidants in natural water with wide salinity and ammonia ranges could be estimated.     

Impacts of water quality on chlorine and chlorine dioxide efficacy in natural waters

The impact of disinfection efficacy in natural waters was evaluated by performing disinfection assays using four untreated surface waters of various qualities and ultra-pure buffered waters as a baseline condition for comparison. Bacillus subtilis spores were spiked in these waters and disinfection assays were conducted at 22 degrees C using either free chlorine or chlorine dioxide. Assays using indigenous aerobic spores were also completed. The inactivation kinetics in natural and ultra-pure buffered waters were not statistically different (at p = 0.05) while using free chlorine, as long as disinfectant decay was taken into account. Filtering natural waters through a 0.45 microm did not improve the sporicidal efficacy of chlorine. For three out of the four waters tested, the efficacy of chlorine dioxide was greater in natural waters compared to that observed in ultra-pure buffered waters. Such results are consistent with previous observations using ultra-pure waters supplemented with NOM-extract from the Suwannee River. Similar to free chlorine results, the impact of filtration (0.45 microm) on the efficacy of chlorine dioxide was not statistically significant.     

Synergistic inactivation of Cryptosporidium parvum using ozone followed by free chlorine in natural water

The synergistic effect of sequential exposure to ozone followed by free chlorine on inactivation of Cryptosporidium parvum oocysts suspended in natural waters was studied in bench-scale batch reactors. Animal infectivity using neonatal CD-1 mice was used to measure oocyst inactivation. The synergistic effect measured in two alkaline (pH 8.1) natural waters was statistically significant but was considerably smaller than previously reported in buffered de-ionized water at pH 6.0. Temperature, ozone primary treatment level, and water type did not have measurable impacts on the synergistic effect. Efforts to increase the synergistic effect by reducing the pH from 8 to 6 by acid addition were unsuccessful. In the two low alkalinity (pH 6.0) natural waters tested, the measured synergistic effect was greater than in the alkaline waters, but was still less than that measured previously in buffered de-ionized water. It was concluded that the synergistic effect reduction in the natural waters tested was due in part to alkalinity and in part to other unidentified water quality characteristics. Sequential treatment with ozone followed by free chlorine may only be a feasible strategy for achieving synergistic C. parvum inactivation credit for water treatment facilities with natural waters having a low pH (near 6.0).     

Inactivation of Cryptosporidium parvum oocysts with ozone and free chlorine

The objective of this study is to investigate the synergy involved in the sequential inactivation of C. parvum oocysts with ozone followed by free chlorine at 1-20 degrees C. Primary ozone and free chlorine inactivation curves are characterized by an initial lag-phase, followed by one or two post-lag-phase segments, the first segment at a faster rate than the second, of pseudo-first-order inactivation. The kinetics of primary inactivation with ozone and free chlorine has a relatively strong temperature dependence, and vary both with oocyst lot and oocyst age. Synergy is observed for the sequential inactivation of C. parvum oocysts with ozone/free chlorine. Ozone pre-treatment results in the disappearance of the lag-phase and the occurrence of a secondary free chlorine inactivation curve with generally two pseudo-first-order segments, the first segment at a faster rate than the second. The kinetics of both secondary segments is significantly faster than the post-lag-phase rate of inactivation with free chlorine alone. The temperature dependence for both phases of the secondary free chlorine inactivation kinetics is weaker compared to that for primary inactivation with ozone or free chlorine. As a result, the level of synergy in sequential disinfection with ozone/free chlorine increases with decreasing temperature within the range relevant to drinking water utilities. Good agreement is found between the kinetics determined using the modified in-vitro excystation method of viability assessment and animal infectivity data recently reported in the literature for both primary inactivation with ozone, and sequential disinfection with ozone/free chlorine.     

Management of chlorine dosing rates in urban water distribution networks using online continuous monitoring and modeling

The aim of this study is to present the results of a research which was undertaken to manage chlorine dosing rates in a real water distribution network using online continuous monitoring and modeling. The study area was divided into 18 district metered areas (DMAs) where the water pressure and flow rate measurements to each DMA were online and continuous. Besides, online water quality sensors were installed at eight different locations and a bimonthly water quality measurement and sampling program was carried out. The data sets required to set, calibrate and verify the hydraulic and chlorine models were derived from the online continuous monitoring and sampling program. Eight chlorine management scenarios that take into consideration the extreme conditions found out during the online monitoring and sampling were utilized. The study revealed that online monitoring provides excellent data sets for chlorine modeling and management that enables automatic application of chlorine dosing.     

溶解氧对含氨氮地下水生物除铁除锰效果的影响

采用生物滤柱进行了地下水除铁除锰效果的研究,通过检测滤柱不同滤层深度Mn^2＋、Fe^2＋、NH4^＋-N与DO浓度的变化,研究了各离子的去除效果与DO的关系,并对比了不同DO水平和不同滤速时离子的去除情况。结果表明,铁比锰和氨氮更优先被去除,滤速越低,溶解氧消耗越多。     

长距离给水管网氯胺消毒的控制研究

以某市第二水源工程供水管网为研究对象,通过测定余氯和茵落总数,考察了氨、氯质量比和出厂水余氯浓度对长距离给水管网氯胺消毒效果的影响。结果表明,在氨、氯质量比为1：4．5时,通过适当提高出厂水余氯浓度,可以有效改善长距离输水管网中的水质,避免增加中途加氯设备,以及便于水厂管理。     

Reactions of free chlorine with substituted anilines in aqueous solution and on granular activated carbon

Aqueous HOCl reacted with substituted anilines to form chlorinated derivatives. Some debromination and bromination products were also detected from two brominated anilines. When granular activated carbon was present, many additional products were formed. These compounds fall into several different groups: (1) N-acylation products, (2) N-carbomethoxylation products, (3) N=N dimerization products and (4) deamination and hydroxylation products.     

Effects of stratification on chloramine decay in distribution system service reservoirs

Water quality in chloraminated distribution systems is affected by microbial activity, particularly due to nitrifiers that accelerate chloramine decay. In summer, continuous thermal stratification increases retention time and lowers chloramine residual in some parts of a system service reservoir (tank), relative to fully mixed conditions. According to temperature and chemical indicators, cooling in winter destratifies these reservoirs naturally. Traditional (chemical) indicators of nitrification also suggest that destratification occurs with respect to microbiological activity. In contrast, the microbial decay factor (F_m) method, which separates microbiological and chemical decay in bulk water, identifies strong microbial stratification, even in winter. F_m can also be used to predict the exacerbated loss of chloramine residual in the following summer, which enables early intervention by system managers to minimise such loss, and so maintain an adequate residual through the distribution system.     

多水源供水管网余氯优化控制研究及应用

为解决供水管网节点余氯浓度过高问题,建立了基于水力优化调度模型的余氯优化控制系统.将建立的余氯优化控制模型应用于SY市多水源供水系统,得到了各水厂不同时段的供水量、氯投加量及节点余氯浓度等信息.优化后的各水源供水量变化较大,平均氯投加量由2.226 mg/L降至2.191 mg/L,表明该模型在多水源供水管网余氯优化控...     

Trihalomethanes formation in point of use surface water disinfection with chlorine or chlorine dioxide tablets

In remote or underdeveloped areas, natural disaster emergencies and armed conflict zones, point‐of‐use surface water disinfection with chlorine tablets provides microbiologically safe water, but disinfection by‐products such as trihalomethanes (THMs) are formed. While the health risks from THMs are much less than the risks from consuming microbiologically unsafe water, it is nonetheless desirable to understand and minimise THM formation. We show that THM concentrations in surface water samples from the Northern British Isles disinfected with chlorine tablets increased with contact time, in some cases to significantly exceed EU, US EPA and WHO drinking water guidance values after more than an hour. More stagnant water from ponds and lochs had higher THM formation than river water. Doubling the chlorine tablet dose slightly enhanced THM formation, and passing water through coffee filter paper reduced it. Chlorine dioxide tablets produced minimal amounts of THMs.     

氯氨供气管路积液问题分析与应对

针对正压加氨浮子堵塞问题,进行了加氨管线温度检测和氨气性质分析。结果表明,加氨管线中氨气受温度和压力影响再次液化是堵塞加氨浮子的原因,根据堵塞原因采取了一系列控制措施,并对水厂加氨（氯）管线的设计和安装需要注意的问题提出了建议。