Chlorine Contact Time Research Articles

Iodate and Iodo-Trihalomethane Formation during Chlorination of Iodide-Containing Waters: Role of Bromide

The kinetics of iodate formation is a critical factor in mitigation of the formation of potentially toxic and off flavor causing iodoorganic compounds during chlorination. This study demonstrates that the formation of bromine through the oxidation of bromide by chlorine significantly enhances the oxidation of iodide to iodate in a bromide-catalyzed process. The pH-dependent kinetics revealed species specific rate constants of k(HOBr + IO(-)) = 1.9 × 10(6) M(-1) s(-1), k(BrO(-) + IO(-)) = 1.8 × 10(3) M(-1) s(-1), and k(HOBr + HOI) < 1 M(-1) s(-1). The kinetics and the yield of iodate formation in natural waters depend mainly on the naturally occurring bromide and the type and concentration of dissolved organic matter (DOM). The process of free chlorine exposure followed by ammonia addition revealed that the formation of iodo-trihalomethanes (I-THMs), especially iodoform, was greatly reduced by an increase of free chlorine exposure and an increase of the Br(-)/I(-) ratio. In water from the Great Southern River (with a bromide concentration of 200 μg/L), the relative I-incorporation in I-THMs decreased from 18 to 2% when the free chlorine contact time was increased from 2 to 20 min (chlorine dose of 1 mg Cl(2)/L). This observation is inversely correlated with the conversion of iodide to iodate, which increased from 10 to nearly 90%. Increasing bromide concentration also increased the conversion of iodide to iodate: from 45 to nearly 90% with a bromide concentration of 40 and 200 μg/L, respectively, and a prechlorination time of 20 min, while the I-incorporation in I-THMs decreased from 10 to 2%.

Artificial intelligence based modeling for predicting the disinfection by-products in water

Formation of trihalomethanes (THMs) in chlorinated waters poses high risk to humans. Strategies for the THM control require pre-knowledge of their levels in the water. Determination of the THMs in the laboratory experiments is very tedious, expensive, and time consuming. Hence, the development of new predictive models for the THM formation in the chlorinated water will be of immense help. This research presents the potential of the artificial neural network (ANN), support vector machine (SVM), and gene expression programming (GEP) modeling approaches to forecast the THM formation due to chlorination. To develop the models, a total of 63 data collected from the literature were used, wherein five parameters, such as dissolved organic carbon normalized chlorine dose, water pH, temperature, bromide concentration, and contact time were used as the input variables. The predictive and generalization abilities of the models were comprehensively evaluated using several statistical tests. The results revealed that the ANN, SVM, and GEP models are capable of capturing the complex nonlinear relationship between the water disinfection conditions and the corresponding THM formation in the chlorinated water. The optimal ANN, SVM, and GEP models yielded the root mean square error and coefficient of determination values of 0.09 and 0.998; 0.70 and 0.998; and 3.07 and 0.990 for training and 4.05 and 0.918; 3.66 and 0.935; and 3.63 and 0.933 for validation set, respectively. Sensitivity analysis results revealed that initial pH, contact time and temperature were the most significant factors that influence the THM formation during chlorination process. All the three models provide fairly promising approach for the prediction of the THM formation in water during the disinfection process. SVM model performed relatively better than the ANN and GEP models.

I-THM Formation and Speciation: Preformed Monochloramine versus Prechlorination Followed by Ammonia Addition

An increasing number of utilities in the United States have been switching from chlorination to chloramination practices to comply with the more stringent trihalomethane (THM) and haloacetic acid (HAA) regulations. This has important implications for disinfection byproduct (DBP) formation because the reactions of chlorine and monochloramine (NH(2)Cl) with natural organic matter (NOM) are not the same. In this study, iodinated trihalomethane (I-THM) formation from preformed NH(2)Cl and prechlorination (at two chlorine doses and contact times) followed by ammonia addition was compared. A representative bromide/iodide ratio of 10:1 was selected and four bromide/iodide levels (ambient, 50/5 or 100/10, 200/20, and 800/80 [μg/L/μg/L]) were evaluated. The results showed that I-THM formation was generally lower for prechlorination as compared to preformed NH(2)Cl due to the oxidation of iodide to iodate by chlorine. However, while prechlorination minimized iodoform (CHI(3)) formation, prechlorination sometimes formed more I-THMs as compared to preformed NH(2)Cl due to a large increase in the formation of brominated I-THM species, which were formed at much smaller amounts from preformed NH(2)Cl. I-THM concentrations and speciation for the two chloramination scenarios (i.e., preformed NH(2)Cl vs prechlorination followed by ammonia) depended on chlorine dose, contact time, bromide/iodide concentration, and NOM characteristics of the source water (SUVA(254)).

Experimental Study on Secondary Effluent Disinfection with Ultrasound and Chlorine

Ultrasonic disinfection is safe and effective, but requires high power consumption. For economic considerations, ultrasound and chlorine can be combined to promote a wider range of applications. In this paper, we investigated the disinfection effect of secondary effluent with low-frequency ultrasound and sodium hypochlorite. The optimal conditions were determined by changing the ultrasound intensity, exposure time, chlorine dosage, and chlorine contact time. The results showed that ultrasound can significantly enhance the effects of chlorine disinfection. When the coliform bacteria is 106~107CFU/L, the dosage of chlorine at 4~6mg/l can meet the national discharge standard (less than 104 CFU /L). However, the chlorine dosage can be further reduced to 1~2mg/l if we add 30 s of ultrasonic radiation, thereby reducing the disinfection by-products. Orthogonal experimental results show that the relative importance of the disinfection factors: chlorine dosage&gt; ultrasonic irradiation time &gt;chlorine contact time&gt; ultrasound intensity.

Formation of halogenated C-, N-DBPs from chlor(am)ination and UV irradiation of tyrosine in drinking water

The formation of regulated and emerging halogenated carbonaceous (C-) and nitrogenous disinfection by-products (N-DBPs) from the chlor(am)ination and UV irradiation of tyrosine (Tyr) was investigated. Increased chlorine contact time and/or Cl 2/Tyr ratio increased the formation of most C-DBPs, with the exception of 4-chlorophenol, dichloroacetonitrile, and dichloroacetamideChloroform and dichloroacetic acid increased with increasing pH, dichloroacetonitrile first increased and then decreased, and other DBPs had maximum yields at pH 7 or 8. The addition of ammonia significantly reduced the formation of most C-DBPs but increased 4-chlorophenol, dichloroacetonitrile, dichloroacetamide, and trichloroacetonitrile yields for short prechlorination contact times before dosing ammonia. When UV irradiation and chlorination were performed simultaneously, the concentrations of the relatively stable C-DBPs increased, and the concentrations of dichloroacetonitrile, dichloroacetamide, and 4-chlorophenol decreased with increasing UV dose. This information was used to develop a mechanistic model for the formation of intermediate DBPs and end products from the interaction of disinfectants with tyrosine.

Formation and Decomposition of New and Unknown Polar Brominated Disinfection Byproducts during Chlorination

Brominated disinfection byproducts (Br-DBPs) are generally more cytotoxic and genotoxic than their chlorinated analogues. A great portion of total organic bromine in chlorinated drinking water is still unknown and may be ascribed to polar Br-DBPs. In this work, a novel approach, precursor ion scan using ultra-performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, was adopted and further developed for selective detection and identification of polar Br-DBPs, which made it possible to reveal the whole picture of the formation and decomposition of polar Br-DBPs during chlorination. Simulated drinking water samples with chlorine contact times from 1 min to 7 d were analyzed. Many new polar aromatic and unsaturated aliphatic Br-DBPs were detected and tentatively proposed with chemical structures, of which 2,4,6-tribromophenol, 3,5-dibromo-4-hydroxybenzoic acid, 2,6-dibromo-1,4-hydroquinone, and 3,3-dibromopropenoic acid were confirmed or identified with authentic standards. It was found that various polar Br-DBPs formed and reached the maximum levels at different chlorine contact times; high molecular weight Br-DBPs might undergo decomposition to relatively low molecular weight Br-DBPs or even finally to haloacetic acids and trihalomethanes. The decomposition of newly detected intermediate Br-DBPs (including molecular ion cluster m/z 345/347/349/351, 2,4,6-tribromophenol, and 3,5-dibromo-4-hydroxybenzoic acid) during chlorination was investigated in detail. The "black box" from the input of "humic substances + bromide + chlorine" through the output of "haloacetic acids + trihalomethanes" was opened to a significant extent.

Evaluating Free Chlorine Disinfection of Viruses in Recycled Water: Effects of Free Chlorine CT, Dose, Residual, and Contact Time

Evaluating Free Chlorine Disinfection of Viruses in Recycled Water: Effects of Free Chlorine CT, Dose, Residual, and Contact Time

Tracer studies with fluorescent-dyed microorganisms—A new method for determination of residence time in chlorination reactors

The Ct value, a product of free chlorine concentration and contact time, is the most significant factor in the disinfection of pathogenic microorganisms. Pulse introduction of a tracer at the reactor inlet and a collection of probes at the outlet are often used to determine contact time t from the residence time distribution (RTD) curve. Introduction of inert soluble tracers such as chloride, fluoride, and fluorescent dyes has long been considered sufficient to determine the flow-through path in chlorination reactors. It was generally agreed that the microorganisms are following the path of the soluble tracers.The current study compares RTD curves of soluble tracers with curves of viruses and bacteria under a hypothesis that residence time can be influenced by the size of the solute. Tracer studies were performed in a bench-scale chlorination contact tank with fluorescent dyes rhodamine B (RB) and acridine orange (AO), viruses MS2 and T4, and bacterium Escherichia coli. The viruses and bacterium were stained with RB and AO, respectively.An inverse relation between residence time and size of solute has been observed. Mean residence times of 10.8, 7.8, 7.1, and 6.1min were found for rhodamine B, MS2, T4, and E. coli, respectively. The RTD curves of labeled and native microorganisms closely resemble each other, and were significantly different from the RTD curves of soluble dyes. Fluorescence intensity of the dyes was found to be sensitive to free chlorine concentration C. A linear correlation over a free chlorine concentration between 0 and 3mg/L was found.Determination of contact time in chlorination reactors by fluorescent labeling of microorganisms is a novel, simple, fast, and convenient procedure. The staining can provide precise microorganism-specific residence time in a chlorination reactor; in that sense the new tool has the potential to replace the inert soluble tracers used so far in RTD experiments.

Mitigation of Alicyclobacillus spp. spores on food contact surfaces with aqueous chlorine dioxide and hypochlorite

The prevalence of Alicyclobacillus spp. and other spore-forming spoilage organisms in food handling and processing environments presents a sanitation challenge to manufacturers of products such as juices and beverages. The objectives of this study were to determine the efficacy of chlorine dioxide and sodium hypochlorite in killing Alicyclobacillus spores in situ and to evaluate the efficacy of various chlorine dioxide and hypochlorite sanitizing regimes on Alicyclobacillus spp. spores on stainless steel, wood, and rubber conveyor material. Five or two log CFU/ml spore concentrations were left in aqueous solution or inoculated onto stainless steel, rubber, or wood coupons and challenged with sanitizer for varied time intervals. After treatment, the coupons were placed in sterile sample bags, massaged with neutralizing buffer, and enumerated on Ali agar. Surfaces were also examined before and after treatment by scanning electron microscopy to confirm destruction or removal of the spores. For both five and two log CFU/ml spore concentrations, treatments of 50 and 100 ppm of chlorine dioxide and 1000 and 2000 ppm of hypochlorite, respectively, were the most effective. Of the range of chlorine dioxide concentrations and contact time regimes evaluated for all surfaces, the most effective concentration/time regime applied was 100 ppm for 10 min. Reductions ranged from 0 to 4.5 log CFU/coupon. Chlorine dioxide was least effective when applied to wood. Hypochlorite was not efficient at eliminating Alicyclobacillus spores from any of the food contact surfaces at any time and concentration combinations tested. Chlorine dioxide is an alternative treatment to kill spores of Alicyclobacillus spp. in the processing environment.

Effects of operating conditions on THMs and HAAs formation during wastewater chlorination

Disinfection is the last barrier of wastewater reclamation process to protect ecosystem safety and human health. However, the chlorination process results in the formation of mutagenic/carcinogenic disinfection by-products (DBPs) deriving from the reaction of the chlorine with organic compounds in wastewater. The effects of operating conditions (chlorine dose, contact time, reaction temperature and pH value) of chlorination on the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) in biologically treated wastewater samples were investigated in this study. The results indicated that the total THMs (TTHM) and total HAAs (THAA) increased exponentially with increasing chlorine dose, but there are discrepancies between the formation rates of TTHM and THAA. The THAA reached a peak at contact time of 2 h and thereafter decreased with extended time. The formation time of THMs depends on the wastewater content of quick or slow formers. The yields of bromated HAAs (as MBAA, BCAA, and BDCAA) would decrease markedly after the contact time over 2 h during wastewater chlorination, and were favored in low pH values of 4 and high pH values of 9 under certain contact time. In addition, the formation of MBAA, BCAA, BDCAA decreased gradually as reaction temperature increased from 4 to 30 °C in the chlorination of wastewater containing a certain concentration of bromide. The effects of operating conditions on THMs and HAAs formation during wastewater chlorination were completely different from those of surface water disinfection.

Occurrence and Mammalian Cell Toxicity of Iodinated Disinfection Byproducts in Drinking Water

An occurrence study was conducted to measure five iodo-acids (iodoacetic acid, bromoiodoacetic acid, (Z)-3-bromo-3-iodo-propenoic acid, (E)-3-bromo-3-iodo-propenoic acid, and (E)-2-iodo-3-methylbutenedioic acid) and two iodo-trihalomethanes (iodo-THMs), (dichloroiodomethane and bromochloroiodomethane) in chloraminated and chlorinated drinking waters from 23 cities in the United States and Canada. Since iodoacetic acid was previouslyfound to be genotoxic in mammalian cells, the iodo-acids and iodo-THMs were analyzed for toxicity. A gas chromatography (GC)/negative chemical ionization-mass spectrometry (MS) method was developed to measure the iodo-acids; iodo-THMs were measured using GC/high resolution electron ionization-MS with isotope dilution. The iodo-acids and iodo-THMs were found in waters from most plants, at maximum levels of 1.7 microg/L (iodoacetic acid), 1.4 microg/L (bromoiodoacetic acid), 0.50 microg/L ((Z)-3-bromo-3-iodopropenoic acid), 0.28 microg/L ((E)-3-bromo-3-iodopropenoic acid), 0.58 microg/L ((E)-2-iodo-3-methylbutenedioic acid), 10.2 microg/L (bromochloroiodomethane), and 7.9 microg/L (dichloroiodomethane). Iodo-acids and iodo-THMs were highest at plants with short free chlorine contact times (< 1 min), and were lowest at a chlorine-only plant or at plants with long free chlorine contact times (> 45 min). Iodide levels in source waters ranged from 0.4 to 104.2 microg/L (when detected), but there was not a consistent correlation between bromide and iodide. The rank order for mammalian cell chronic cytotoxicity of the compounds measured in this study, plus other iodinated compounds, was iodoacetic acid > (E)-3-bromo-2-iodopropenoic acid > iodoform > (E)-3-bromo-3-iodo-propenoic acid > (Z)-3-bromo-3-iodo-propenoic acid > diiodoacetic acid > bromoiodoacetic acid > (E)-2-iodo-3-methylbutenedioic acid > bromodiiodomethane > dibromoiodomethane > bromochloroiodomethane approximately chlorodiiodomethane > dichloroiodomethane. With the exception of iodoform, the iodo-THMs were much less cytotoxic than the iodo-acids. Of the 13 compounds analyzed, 7 were genotoxic; their rank order was iodoacetic acid >> diiodoacetic acid > chlorodiiodomethane > bromoiodoacetic acid > E-2-iodo-3-methylbutenedioic acid > (E)-3-bromo-3-iodo-propenoic acid > (E)-3-bromo-2-iodopropenoic acid. In general, compounds that contain an iodo-group have enhanced mammalian cell cytotoxicity and genotoxicity as compared to their brominated and chlorinated analogues.

Development and Interpretation of Disinfection Byproduct Formation Models Using the Information Collection Rule Database

Multiple linear regression models were used to examine relationships between water quality, treatment, and disinfection byproduct (DBP) formation in Information Collection Rule field data. Finished water models were specified using a cross-validation approach based on data for 225 free chlorine treatment plants. Turbidity, bromide, temperature, alkalinity, total organic carbon, ultraviolet absorbance at 254 nm, pH, chlorine residual, chlorine consumed, and chlorine contact time were employed as independent variables. Important trends within the trihalomethane, dihaloacetic acid, and trihaloacetic acid classes were observed. Bromide was a significant predictor for all DBP species and its influence changed in sign and magnitude with the extent of bromine substitution. A similar pattern followed by alkalinity suggested it plays an important role as an indicator of natural organic matter hydrophobicity and reactivity. Chlorine consumed and organic precursor variables were significant predictors in almost all DBP species models, exhibiting trends opposite to those for alkalinity and bromide. Temperature was the most significant variable in chloroform and chloral hydrate models and its significance declined with increasing bromine substitution within the trihalomethane class. pH had a strong positive influence on chloroform formation, a negative influence on trihaloacetic acid formation, and no influence on dihaloacetic acid formation.

Impact of Ozone and Biological Filtration on Water Quality Parameters in Arlington, Texas

The City of Arlington began experiencing atypical water quality problems beginning in 1999 after ozonation and biofiltration were added to the existing conventional treatment processes. These problems included high chloramine residual decay rates, system nitrification and elevated manganese levels in the finished water. This study reviewed literature, existing plant and system data and collected additional data to determine if modifications to the plant and system processes would resolve these water quality problems. Results demonstrated that chloramine stability is improved with increased free chlorine contact time at a pH near 8.3. Improved biofiltration by nurturing the biomass in the filters also improves chloramine stability as well as eliminating the breakthrough of manganese at the filters. Careful monitoring and minimizing water age in the distribution system can also reduce water quality issues.

Free chlorine demand and cell survival of microbial suspensions

The utility of chlorine residual and chlorine demand as a surrogate for microbial contamination in the water distribution system was evaluated. The chlorine demanded by and cell survival of pure culture suspensions of Escherichia coli, Staphylococcus epidermidis, and Mycobacterium aurum were quantified in solutions with initial free chlorine concentrations of 0.20, 0.40, and 0.80 mg/L. The chlorine demand increased with initial concentration of cells and free chlorine for all species. At equivalent initial cell concentrations, chlorine demand was greatest for M. aurum, followed by S. epidermidis and E. coli. The chlorine contact time required for a 3-log inactivation of E. coli, S. epidermidis, and M. aurum was calculated as 0.032±0.009, 0.221±0.080, and 42.9±2.71 mg min/L, respectively. The ultimate chlorine demand and cell survival were directly proportional. No chlorine demand was observed at cell concentrations less than 10 5 CFU/mL for E. coli or 10 4 CFU/mL for S. epidermidis. M. aurum demanded chlorine at all initial cell concentrations including 10 3 CFU/mL, which was the detection limit of the cell quantification assay. Chlorine demand was determined to be a suitable surrogate indicator of the organisms studied and its utility may be enhanced in locations of the water distribution system that maintain a higher free chlorine residual.

정수처리긍정에서 소독부산물인 트리할로메탄의 생성모델

We have been proposed model equation which is able to predict the trihalomethane producing concentration formation, that is one of byproduct, in the water treatment processes. In proposed model, the effects of trihalomethane factors like chlorine contact time, pH, temperature, TOC and UV-254 are considered. The concentration of the trihalomethane produced is proportion to the contact with chlorine, pH of water, temperature of water TOC and UV-254, respectively. This proposed model could be predicted the formed concentration of trihalomethanes by trihalomethane factors.

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.

Chlorine inactivation of adenovirus type 40 and feline calicivirus.

Ct values, the concentration of free chlorine multiplied by time of contact with virus, were determined for free-chlorine inactivation experiments carried out with chloroform-extracted (dispersed) and non-chloroform-extracted (aggregated) feline calicivirus (FCV), adenovirus type 40 (AD40), and polio virus type 1 (PV-1). Experiments were carried out with high and low pH and temperature conditions. Ct values were calculated directly from bench-scale free-chlorine inactivation experiments and from application of the efficiency factor Hom model. For each experimental condition, Ct values were higher at pH 8 than at pH 6, higher at 5 degrees C than at 15 degrees C, and higher for dispersed AD40 (dAD40) than for dispersed FCV (dFCV). dFCV and dAD40 were more sensitive to free chlorine than dispersed PV-1 (dPV-1). Cts for 2 log inactivation of aggregated FCV (aFCV) and aggregated PV-1 (aPV-1) were 31.0 and 2.8 orders of magnitude higher than those calculated from experiments carried out with dispersed virus. Cts for 2 log inactivation of dFCV and dAD40 in treated groundwater at 15 degrees C were 1.2 and 13.7 times greater than in buffered-demand-free (BDF) water experiments at 5 degrees C. Ct values listed in the U.S. Environmental Protection Agency (EPA) Guidance Manual were close to, or lower than, Ct values generated for experiments conducted with dispersed and aggregated viruses suspended in BDF water and for dispersed viruses suspended in treated groundwater. Since the state of viruses in water is most likely to be aggregated and associated with organic or inorganic matter, reevaluation of the EPA Guidance Manual Ct values is necessary, since they would not be useful for ensuring inactivation of viruses in these states. Under the tested conditions, dAD40, dFCV, aFCV, dPV-1, and aPV-1 particles would be inactivated by commonly used free chlorine concentrations (1 mg/liter) and contact times (60 to 237 min) applied for drinking water treatment in the United States.

ノニルフェノールの塩素およびオゾンによる分解

Alkylphenols are used in various industries in Japan. These substances are found to be endocrine disruptors that affect the gonad system. One alkylphenol that is often detected in the aquatic environment and has been found to have an estrogenic effect is nonylphenol (NP). The objectives of this study were to degrade NP using chlorine and ozone, the two major disinfectants used in treatments of drinking water and wastewater, and to investigate the effects of other coexisting substances. The results showed that NP in buffered water could easily be degraded by chlorine and ozone. The presence of ammonia however affected the degradation of NP by chlorine. Humic acid showed a negative effect on the removal of NP by chlorine and ozone but the effect of humic acid was small. Comparison of the amount of total chlorinated carbon (TOX) formed during chlorination of buffered NP solution and of sewage effluent was likewise conducted. Under normal chlorination conditions, the amount of TOX formed per mg dissolved organic carbon (DOC) was higher in buffered NP solution (138μg-Cl/mg-DOC) than in sewage effluent (84μg-Cl/mg-DOC). The results of the study further showed that 15-min chlorine contact time considerably decreased the NP concentration and its estrogen receptor binding effect. The aromatic ring however was not decomposed. Degradation of the aromatic ring was only observed after 24-h contact time. Ozone contact time of 1-min was found to degrade the aromatic ring.

Bactericidal effect of chlorine on Mycobacterium paratuberculosis in drinking water.

One possible route of transmission of Mycobacterium paratuberculosis from cattle to humans is via contaminated water supplies. The aim of this work was to determine whether this organism can survive standard water treatment processes. Two strains of M. paratuberculosis (bovine strain, NCTC 8578 and human strain Linda, ATCC 43015) were subjected to various chlorine concentrations (0.5, 1.0 and 2.0 microg ml(-1)) for 15 and 30 min. Chlorine test solutions were made up in two types of water, sterile water that had been deionized and subjected to reverse osmosis (DRO) and DRO water containing MgCl(2), CaCl(2), NaHCO(3) and bovine serum albumin (0.3% w/v), the latter to mimic conditions the organism would experience in commercial water treatment operations. The data showed that when initial inoculum levels were high (10(6) cfu ml(-1)) neither M. paratuberculosis strain was completely killed at the free chlorine concentrations and contact times applied. Log10 reductions in the range 1.32-2.82 were observed. The greatest log(10) reduction in cell numbers (2.82 and 2.35 for the bovine and human strains, respectively) was observed at the highest chlorine concentration (2 microg ml(-1)) and longest contact time (30 min). This work highlights the need for further research into the survival of M. paratuberculosis during water treatment.

Removal of Taste and Odour Compounds by Conventional Granular Activated Carbon Filtration

Abstract In recent years, musty-earthy tastes in drinking water have become a seasonal problem (September to November) for communities that draw their water from the upper St. Lawrence River. The source of the problem is attributed to the presence of geosmin and 2-methylisoborneol (MIB) at concentrations ranging from 5 to 60 ng/L. In 1997 and 1998, the Cornwall Water Purification Plant added granular activated carbon (GAC) to conventional gravity filters to control taste and odour compounds. We report on a study to test the efficiency of these conventional GAC-capped filters to reduce geosmin and MIB concentrations in finished water as a function of filter age, initial chlorine residual and contact time. GAC–capped filters removed on average 60% of the MIB and 80% of the geosmin from the source water after 2 and 12 months of filter operation. However, testing after 24 months operation showed reduced efficiency. Amounts removed ranged between 13 and 20% (15% average) for MIB and 50 to 57% (54% average) for geosmin in these filters. Testing also suggested that filter efficiency was greater with longer contact times and with higher chlorine residuals (in the range 0.1 to 0.6 mg free Cl2/L). In addition to carbon age, chlorine residual and contact time, flow channelization and slow release of the taste and odour compound load (particularly MIB) from the GAC bed may affect apparent filter efficiency.