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Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Disinfection.

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1 Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Disinfection

2 Overview  Disinfection Options  Chlorine  Ozone  Irradiation with Ultraviolet light  Iodine  Silver  Disinfection mechanisms  Chicks law  CT  Problems with Disinfection  Disinfection-by-products  Tastes and odors  Real pathogens  Getting the right dose   Chlorine sources   Chlorine Chemistry  Metals  Water  Ammonia  Organics   The case for Chlorine  It kills stuff  Residual  Recontamination  Regrowth   Chlorine free  Some European cities

3 The Case for Chlorine  It kills stuff ( )  Residual  It’s the law… But is it a good idea?  Chlorine is the only available disinfectant that provides a residual  Recontamination  Does a chlorine residual provide protection against recontamination?  How much chlorine would be required?  Regrowth  Very few pathogens multiply in drinking water Revenge

4 Chlorine Based Disinfectants Contaminant MRDLG 1 (mg/L) 2 1 2 MRDL 1 (mg/L) 2 1 2 Potential Health Effects from Ingestion of Water Sources of Contaminant in Drinking Water Chloramines (as Cl 2 ) MRDLG =4 1 1 MRDL =4.0 1 1 Eye/nose irritation; stomach discomfort, anemia Water additive used to control microbes Chlorine (as Cl 2 ) MRDLG =4 1 1 MRDL =4.0 1 1 Eye/nose irritation; stomach discomfort Water additive used to control microbes Chlorine dioxide (as ClO 2 ) MRDLG =0.8 1 1 MRDL =0.8 1 1 Anemia; infants & young children: nervous system effects Water additive used to control microbes Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants. Maximum Residual Disinfectant Level Goal (MRDLG) - The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.

5 Chlorine  First large-scale chlorination was in 1908 at the Boonton Reservoir of the Jersey City Water Works in the United States  Widely used in the US  Typical dosage (1-5 mg/L)  variable, based on the chlorine demand  goal of 0.2 mg/L residual  Trihalomethanes (EPA primary standard is 80  g/L) 1  Chlorine concentration is measured as Cl 2 even when in the form of HOCl or OCl - Chlorine oxidizes organic matter 1)

6 Chlorine: The Rules  Minimum free chlorine residual in a water distribution system should be 0.2 mg/L. 1  For all systems using surface water or groundwater under the influence of surface water for supply, a detectable disinfectant residual must be maintained within the distribution system in at least 95% of the samples collected (or heterotrophic bacteria counts must be less than or equal to 500 cfu/ml as an equivalent) and at least 0.2 mg/L concentration of residual disinfectant (free or combined) entering the distribution system must be maintained. 2 1) 2)

7 Chorine isn’t always required  The European Union does not require disinfection. Of the 15 original European Union member states, only Spain and Portugal require disinfection in distribution systems. 1 1)

8 Life without Chlorine  Amsterdam stopped chlorinating in 1983  Chlorine chemistry council continues to lobby hard with scare tactics to discourage considering alternatives  False reports that cholera epidemic in Peru was caused by stopping chlorination

9 Why is a Residual Required? Why is Chlorine the only option?  Inactivating microorganisms in the distribution system  Treatment breakthrough  Leaking pipes, valves, and joint seals  Cross-connection and backflow  Finished water storage vessels  Improper treatment of equipment or materials before and during main repair  Intentional introduction of contaminants into distribution system  Indicating distribution system contamination (If residual chlorine is monitored continuously it might be possible to detect an increase in contamination from a decrease in chlorine.)  Controlling biofilm growth

10 Protection against recontamination?  Proponents of maintaining a disinfectant residual point to situations where residuals were not maintained and preventable waterborne disease outbreaks occurred. Haas (1999) argues that both a 1993 Salmonella outbreak caused by animal waste introduced to a distribution system reservoir and a 1989 E. coli O157:H7 outbreak could have been forestalled if distribution system chlorination had been in effect. Both of these outbreaks were due to bacterial pathogens that are sensitive to chlorine and could have been at least partially inactivated. 1 1)

11 Chlorine Demand vs. Total Organic Carbon 0.5 mg chlorine mg carbon Samples were incubated in the dark for 1 h at 10°C.

12 Chlorine Protection against Recontamination?  How much sewage would residual chlorine at 0.2 to - 0.5 mg/L protect you from?

13 How much organic matter could be treated by residual Cl 2 ?  Take a town of 5000 people  Flow rate per person is about 3 mL/s*  Average flow rate is 15 L/s  Assume storage tank is half full when contamination event occurs  Small town storage tanks typically provides 1/3 day of storage – 432,000 L  Assume 0.2 mg/L Cl 2 residual – 0.4 mg/L C  173 gm of organic carbon * Based on consumption in Tamara, Honduras.

14 Effect of Chlorination on Inactivating Selected Bacteria BacteriaCl 2 (mg/l) Time (min) Ct Factor (mg-min/l) Reduction(%)Ct for pC* of1 Reference Campylobacter jejuni0.150.599.990.125Blaser et al, 1986 Escherichia coli0.23599.991.25Ram and Malley, 1984 Legionella pneumophila0.2560-9018.75999.4Kuchta et al, 1985 Mycobacterium chelonei0.7604299.9513Carson et al, 1978 Mycobacterium fortuitum 1.030 99.413.5Pelletier and DuMoulin, 1987 Mycobacterium intracellulare 0.156097017.2Pelletier and DuMoulin, 1987 Pasteurella tularensis0.5-1.053.7599.6-1001.6Baumann and Ludwig, 1962 Salmonella typhi0.563991.5Korol et al, 1995 Shigella dysenteriae0.05100.599.6-1000.2Baumann and Ludwig, 1962 Staphylococcus aureus0.80.50.4100--Bolton et al, 1988 Vibrio choleraeVibrio cholerae(smooth strain) 1.0< 1 100--Rice et al, 1993 Vibrio choleraeVibrio cholerae (rugose strain) 2.0306099.99912Rice et al, 1993 Yersinia enterocolitica1.030 9227Paz et al, 1993

15 Effect of Chlorination on Inactivating Selected Viruses VirusesCl 2 (mg/l) Time (min) Ct factor (mg-min/l) Reduction (%) Ct for pC* of1 Reference Adenovirus0.240-50 sec0.1599.80.06Clarke et al, 1956 Coxsackie0.16- 0.18 3.80.0699.60.025Clarke and Kabler, 1954 Hepatitis A0.421 99.990.105Grabow et al, 1983 Norwalk0.5-1.03022.5-- Keswick et al, 1985 Parvovirus0.23.20.64990.32Churn et al, 1984 Poliovirus0.5-1.03022.5100--Keswick et al, 1985 Rotavirus0.5-1.03022.5100--Keswick et al, 1985

16 Effect of Chlorination on Inactivating Selected Protozoa Protozoa Cl 2 (mg/l) Time (min) Ct Factor (mg-min/l) Reduction (%) Ct for pC* of1Reference Cryptosporidium parvum 80907200*907200Korich et al, 1990 Entamoeba histolytica 1.050 100--Snow, 1956 Giardia lamblia-- 68-38999.930AWWA, 1999 Naegleria fowleri0.5-1.0604599.9911de Jonckheere and van de Voorde, 1976 How many pathogens does it take to make you sick?

17 Inactivation of Shielded Pathogens  Many of the studies measuring inactivation of pathogens by disinfectants were conducted using dispersed pathogens  What happens if the pathogens are embedded in an organic particle?  Fecal contamination potentially contains pathogens embedded in protective organic matter

18 Cell Associated virus was inside fetal rhesus kidney derived cells 0.36 mg/L average free Cl 2 at pH 6 86 to get pC* of 4 is (86 min)*(0.36 mg/L)=31 (min mg/L) What do you conclude?

19 Conclusions from Virus in Kidney Cells  The rate of virus deactivation dropped significantly when the virus particles were inside kidney cells  The deactivation of embedded virus particles can not be described by a single first order reaction (________________)  What is controlling the rate of virus deactivation? Chicks Law is violated

20 Scales of the Embedded Virus 1000 nm Location Deactivation rate DispersedVery fast Inside cell with disrupted cell wall Slow Inside intact cell Very slow Virus particles are about 20 nm HOCl are about 0.2 nm 1  m

21 Mass Transport and Chlorine Protection  Chlorine must diffuse through cell contents to reach virus  Organic material inside the cell reacts with chlorine before it gets to the virus

22 Scale this up to a Fecal Aggregate  Turbid water could easily have organic particles that are 10 or even 100  m in diameter  The amount of organic matter in a small particle and the slow diffusion would provide long term protection for embedded pathogens 10  m

23 Chlorine saves lives…  If you accept the “Chlorine eliminated Typhoid Myth”  Then you will likely recommend chlorination as the first line of defense in the Global South-  But in small systems (in the Global South)  Chlorine dose is generally not controlled based on a target residual dose  Surface water may currently be untreated and hence have high turbidity  that correlates with high chlorine demand  that contains pathogens embedded in organic particles

24 Getting the Right Dose: WHO on Chlorination  Chlorine compounds usually destroy pathogens after 30 minutes of contact time, and free residual chlorine (0.2–0.5 mg per liter of treated water) can be maintained in the water supply to provide ongoing disinfection.  Several chlorine compounds, such as sodium hypochlorite and calcium hypochlorite, can be used domestically, but the active chlorine concentrations of such sources can be different and this should be taken into account when calculating the amount of chlorine to add to the water.  The amount of chlorine that will be needed to kill the pathogens will be affected by the quality of the untreated water and by the strength of the chlorine compound used.  If the water is excessively turbid, it should be filtered or allowed to settle before chlorinating it (___________________________) Remove particles first! exposed

25 Chlorine Demand vs. Turbidity  Disclaimer – There is no solid connection between chlorine demand and turbidity  But – organic matter is often associated with particulate matter   If using the standard dose of 2 mg/L, then no residual above 15 NTU! Based on 6 watersheds in western Oregon

26 Turbidity and Chlorine  Chlorine test showing no residual after exposure to turbid tap water (left)

27 Chlorine Sources  On Site Production (electrolysis)  Chlorine gas (Cl 2 )  Liquid Bleach (NaOCl)  Calcium hypochlorite (1 mg Ca(OCl) 2 is equivalent to 0.65 mg of Cl 2 ) Bleach Concentration in terms of sodium hypochlorite (NaOCL) Bleach concentration in terms of Available Chlorine (As Cl 2 ) Additional Information (estimated) Wt. %Trade %Grams per literWt. % Trade % Grams per liter Density of the solution (lb/U.S. gal) Specific gravity of the solution 55.453. 1011.6115.89.511.0110.49.71.16 1518.6185.714.317.7177.010.31.24

28 How much Clorox should you add to a 5 gallon bucket or a 1L bottle?

29 Calcium hypochlorite  Relatively inexpensive  Easy to transport (high equivalent moles of Cl 2 per unit mass)  Less dangerous than chlorine gas  High calcium concentration results in insoluble calcium carbonate from exposure to the atmospheric CO 2 or dissolved carbonates.  Clogs tubing and float valves (submerged orifice works better to avoid contact with atmospheric CO 2 )

30 Chlorine Reactions Cl 2 + H 2 O  H + + HOCl + Cl - HOCl  H + + OCl -  The sum of HOCl and OCl - is called the ____ ______ _______ free chlorine residual +1-2+10Charges Hypochlorous acid Hypochlorite ion

31 Chlorine and pH  HOCl is the more effective disinfectant  Therefore chlorine disinfection is more effective at ________ pH  Dissociation constant is 10 -7.5  HOCl and OCl - are in equilibrium at pH 7.5 low HOCl  H + + OCl - pk

32 Chick’s Law  The death of microorganisms is first order with respect to time  Thus, the remaining number of viable microorganisms, N, decreases with time, t, according to:  where k is an empirical constant descriptive of the microorganism, pH and disinfectant used.  Integrating with respect to time, and replacing limits (N = N o at t = 0) yields: k is expected to be highly correlated with concentration

33 EPA Pathogen Inactivation Requirements  SDWA requires 99.9% inactivation for Giardia and 99.99% inactivation of viruses  Giardia is more difficult to kill with chlorine than viruses and thus Giardia inactivation determines the CT Concentration x Time Safe Drinking Water Act

34 EPA Credits for Giardia Inactivation Treatment typeCredit Conventional Filtration99.7% Direct Filtration*99% Disinfectionf(time, conc., pH, Temp.) * No sedimentation tanks

35 EPA Disinfection CT Credits Contact time (min) chlorinepH 6.5pH 7.5 (mg/L) 2°C10°C2°C10°C 0.5300178430254 115994228134 To get credit for 99.9% inactivation of Giardia : Inactivation is a function of _______, ____________ ______, and ___________. concentrationtime pH temperature Where did these numbers (to 3 significant digits) come from?

36 CT equation for Giardia  C Cl = Free Cl 2 Residual [mg/L]  t contact = Time required [min]  pH = pH of water  T = Temperature, degrees C  pC* = -[Log(fraction remaining)] Note: These equations are NOT dimensionally correct! Chicks Law!

37 Disinfection Byproducts Contaminant MCLG 1 (mg/L) 2 1 2 MCL (mg/L) 2 2 Potential Health Effects from Ingestion of Water Sources of Contaminant in Drinking Water Bromatezero0.010 Increased risk of cancerByproduct of drinking water disinfection (plants that use ozone ) Chlorite0.81.0 Anemia; infants & young children: nervous system effects Byproduct of drinking water disinfection (plants that use chlorine dioxide ) Haloacetic acids (HAA5) n/a 6 6 0.060 Increased risk of cancerByproduct of drinking water disinfection Total Trihalomethanes (TTHMs) none 7 ---------- n/a 6 7 6 0.10 ---------- 0.080 Liver, kidney or central nervous system problems; increased risk of cancer Byproduct of drinking water disinfection What happens to residual chlorine when you drink it?

38 Dark side of chlorine  Bladder cancer in the US in 2011 - New cases: 69,250 - Deaths: 14,990 ( )  15% attributable to exposure to chlorination by-products ( )  1/139,000 people may die from bladder cancer from exposure to chlorination by- products

39 Tastes and Odors: Taste Thresholds  Complaints of the chlorine taste should not be discounted  Chlorine taste may prevent some consumers from using treated water  Need to convince consumers that the chemical taste is healthy???

40 Conclusions  Chlorine can inactivate many types of pathogens with inactivation efficiency a function of pathogen type, embedded protection, contact time, pH, dose…  Chlorination cannot replace particle removal for surface waters  If you can see cloudiness in a glass of water it is too dirty for chlorine!  Chlorine cannot make water contaminated with feces safe to drink  Efforts to prevent contamination of treated water all the way to the consumer’s mouth are very important!

41 Confusions  The importance of chlorine residual is unclear and there is evidence of negative health effects  Chlorine dosages should be kept as low as possible and it isn’t clear what the optimal target should be

42 Invitation to an Open House: Monday 12-3 HLS 150  ENGRI 1131 students have built 8 miniature computer controlled drinking water treatment plants.  You are invited to stop by during the open house in Hollister 150 and see what first year engineers can do to make clean drinking water!

43 Options post CEE 4540  CEE 4550 (full for spring 2012)  Help us build/test/implement ram pumps  Reduce the cost of AguaClara facilities  Build a demonstration plant that fits on a table top and that is a working model of all AguaClara processes from dose control to SRSF

44 Consider a Master of Engineering Degree  Take graduate level courses to gain a deeper understanding of environmental engineering  Take elective courses to broaden your skills  Work with a team on a design project (could be AguaClara or any of a number of projects offered by other faculty)

45 Quiz?  What have you learned in CEE 4540 that will be most important to you in 5 years?


47 The Case for a Residual  Disinfect any recontamination  Prevent bacteria growth in the treated water  Do pathogens grow in water?  “The real reason for maintaining residuals during treatment and distribution is to control microbiological growths when the water is biologically unstable.”  Control those non-pathogenic slime-forming organisms  “Current practice in North America tries to kill all microorganisms whenever possible”

48 Protection Against Recontamination  In order to be effective the following requirements must be met  The amount of chlorine demand must not exceed the residual  The pathogens must be dispersed (not associated with other particles)  This is unlikely if the contamination is faecal  The pathogens must be susceptible to chlorine Remember intermittent water supplies…

49 Growth of Bacteria in Water Distribution Systems  Consumption of dissolved oxygen  Increased heterotrophic plate counts or coliform counts  This does not imply a health risk  Decreased hydraulic capacity of the pipes  Formation of taste/odor compounds  Geosmin, mercaptans, amines, tryptophans, sulfates  Increased rates of pipe corrosion (for metal pipes) I don’t have any evidence that this biological growth has a significant public health impact extra

50 Pathogen Growth in Distribution Systems (CDC)  Biofilms are coatings of organic and inorganic materials in pipes that can harbor, protect, and allow the proliferation of several bacterial pathogens, including Legionella and Mycobacterium avium complex (MAC).  Mycobacterium avium complex, MAC, is an opportunistic bacterial pathogen, is resistant to water disinfection (much more so than Giardia cysts), and grows in pipe biofilms We need more data here! Is this a real public health threat? This is inconsistent with the purported (but apparently inconsequential) beneficial role of biofilms in SSF extra

51 WHO on Regrowth  There is no evidence to implicate the occurrence of most microorganisms from biofilms (excepting, for example, Legionella, which can colonize water systems in buildings) with adverse health effects in the general population through drinking water, with the possible exception of severely immunocompromised people  Water temperatures and nutrient concentrations are not generally elevated enough within the distribution system to support the growth of E. coli (or enteric pathogenic bacteria) in biofilms.  Thus, the presence of E. coli should be considered as evidence of recent faecal contamination.

52 WHO on Regrowth (2)  Viruses and the resting stages of parasites (cysts, oocysts, ova) are unable to multiply in water.  Relatively high amounts of biodegradable organic carbon, together with warm temperatures and low residual concentrations of chlorine, can permit growth of Legionella, V. cholerae, Naegleria fowleri, Acanthamoeba and nuisance organisms in some surface waters and during water distribution Where is the original research for these conclusions?

53 WHO Recommendations for Chlorine as Sole Treatment  Low turbidity (<30 NTU) and low chlorine demand  Low turbidity probably means good quality groundwater (from a spring or from a well)  For effective use; pre-treat turbid water  Pre-treat means using a particle removal technology first  Surface water would generally not meet the NTU requirement  Chlorine requires process control (feedback based on residual chlorine concentration)

54 Pathogen Poisson Process Probability  Suppose we have an average pathogen concentration of C in our drinking water  Suppose we drink volume V  What is the probability that we will ingest k pathogens?  Suppose V = 1 L, C = 2/L, what is probability of ingesting exactly 2 pathogens?

55 Probability of k Pathogens  What is probability of k < (dose)?  Let dose = 15  Find cumulative probability for k=14 CV=15 45% chance of not getting sick!

56 Find probability that k>0 CV=1 For CV = 1, P k>0 = 0.63 For CV = 0.001, P k>0 = 0.001 (converge for small CV)

57 Effect of Pathogen Dose  What happens if the pathogen dose is 10 rather than 1?  Let’s assume that the concentration of this new pathogen is 10 times as great (CV=0.01)  What is the probability that you ingest 10 or more?  Pathogens with an infectious dose of 1 are potentially quite harmful even at very low concentrations!  Pathogens with an infectious dose>1 are not dangerous at low concentration! For CV = 0.001, P k>0 = 0.001 For CV = 0.01, P k≥10 = 3x10 -27

58 Waterborne Disease Outbreaks in the US (1985)  G. lamblia was the most frequently identified pathogen for the seventh consecutive year, causing three (20%) of 15 waterborne outbreaks.  In each of the outbreaks, as in well-characterized waterborne outbreaks of giardiasis in the past, water chlorination had been maintained at adequate levels to make outbreaks of bacterial diseases unlikely, but the lack of an intact filtering system capable of filtering Giardia cysts, distribution system problems, and mechanical deficiencies allowed drinking water to become a vehicle of giardiasis.

59 Waterborne Disease Outbreaks (1993)  The majority of outbreaks (68%) during 1991-1992 were classified as AGI of unknown etiology  Water sampling showed the presence of coliforms and/or deficiencies in chlorination for 91% of these outbreaks  24 outbreaks (71%) were associated with contaminated untreated or inadequately treated groundwater  Two outbreaks were associated with treatment deficiencies in water systems using UV light for disinfection  Three protozoal outbreaks during 1991-1992 occurred in systems that were equipped with chlorine disinfection and met EPA coliform standards but were not equipped with filtration If you believe chlorine is what prevents waterborne disease outbreaks, then you will look for deficiencies in chlorination

60 Waterborne Disease Outbreaks (1993)  Four of the six surface water systems associated with WBDOs were equipped with filtration.  In three of these outbreaks, raw water quality had deteriorated because of sewage effluents that were not appropriately diluted as a result of low stream flows during dry weather.  During the outbreaks associated with these systems, filtration deficiencies were noted, with elevated turbidity in finished water.  Decreased filtration efficiency combined with deterioration in raw water quality also contributed to the WBDO in Milwaukee (1993). It appears that chlorination was unable to provide an effective barrier when filtration failed

61 A fatal waterborne disease epidemic in Walkerton, Ontario  An estimated 2,300 people became seriously ill and seven died from exposure to microbially contaminated drinking water in the town of Walkerton, Ontario, Canada in May 2000  The Walkerton operators were asked to provide a chlorine residual (majority to be free chlorine) of 0.5 mg/L after 15 min.  Evidence at the Inquiry revealed that chlorine dosage practice at Well #5 was insufficient to achieve a 0.5 mg/L residual even in the absence of any chlorine demand.  Although the evidence did not allow for an estimate of the chlorine demand at the time Well #5 was contaminated, it was reasonable to assume that the contamination causing this outbreak was accompanied by a chlorine demand sufficient to consume entirely, or almost entirely, the low chlorine dose thereby allowing inadequately disinfected water into the distribution system Evidence that chlorination that doesn’t produce a residual doesn’t provide protection

62 Calicivirus - An Emerging Contaminant in Water  Annual estimates among adults in the U.S. reveal approximately 267 million episodes of diarrhea leading to 612,000 hospitalizations and 3,000 deaths  In the last 3 decades it has become increasingly clear that viral agents are responsible for much of this public health burden  Human caliciviruses (HuCVs) have been estimated to cause 95–96% of nonbacterial gastroenteritis outbreaks (Fankhauser et al., 1998; K.Y. Green et al., 2000).  These viruses are considered ubiquitous in nature and stable in the environment, thereby increasing their propensity to spread and cause disease

63 Calicivirus  Four genera  Lagovirus  Vesivirus  Norwalk-like viruses (Noroviruses or NLVs)  Sapporo-like viruses (Sapoviruses or SLVs)  Single structural protein that makes up the viral capsid  27-40 nm in diameter Cause disease in humans

64 Norovirus: Infectious Dose  Human volunteer feeding studies have determined the number of viral particles needed to initiate infection is 10 to 100  The infectious dose may well be the result of mass transfer limitations in the gut  i.e. the virus needs to be transported to the villi in the gastric mucosa and attach to initiate infection  Thus it is likely that 1 viral particle is sufficient to initiate infection Huffman, D. E., K. L. Nelson, et al. (2003). Weber-Shirk

65 Norovirus: Clinical Illness and Diagnosis  The most common symptoms of NLV infections include mild to moderate diarrhea, abdominal cramps, and nausea (Adler and Zickl, 1969; Hedberg and Osterholm, 1993).  Other symptoms may include headache, malaise, chills, cramping, and abdominal pain. Stools typically do not contain blood or mucus.  The onset of illness is generally within 24 to 28 h of exposure with a relatively short duration of illness (12 to 60 h).  Adult infection with NLV can be distinguished from bacterial pathogens such as Salmonella and Shigella due to its characteristic projectile vomiting (Adler and Zickl, 1969; Caul, 1996)

66 Norovirus: Inactivation  A 1-log reduction in the RTPCR signal of Norwalk virus was observed after treatment with 2 mg/L monochloramine at pH 8 for 3 h  Norwalk virus appears to be fairly resistant to free chlorine and monochloramine

67 Chlorine Disinfection Mechanisms*  Oxidation of membrane-bound enzymes for transport and oxidative phosphorylation  Oxidation of cytoplasmic enzymes  Oxidation of cytoplasmic amino acids to nitrites and aldehydes  Oxidation of nucleotide bases  Chlorine substitution onto amino acids  DNA mutations  DNA lesions *It is possible that none of these mechanisms have been documented (more likely)

68 Ammonia Reactions  Substitution reactions…  The combined chlorine maintains its oxidizing potential  Total chlorine is combined chlorine plus free chlorine NH 3(aq) + HOCl  NH 2 Cl+ H 2 O NH 2 Cl + HOCl  NHCl 2 + H 2 O -3 +1 Combined chlorine extra

69 Breakpoint Chlorination  Removal of ammonia by chlorination  Oxidizing equivalents of chlorine are consumed 2NH 3(aq) + 3HOCl  N 2 + 3Cl - + 3H 2 O -3 +1 0 extra

70 Does Chlorine Completely oxidize organic matter?  Oxidation states  Carbon in organic matter (-4)  Carbon in carbon dioxide (+4)  Chlorine in HOCl (+1)  Chloride (-1)  Therefore should take 4 moles of chlorine (Cl 2 ) per mole of organic carbon  23.6 g chlorine/g organic carbon 4HOCl + CH 4  CO 2 + 2H 2 O + 4Cl - + 4H + NO! extra

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