L I E> R.ARY OF THE U N IVLRSITY Of ILLINOIS 628 I£65c ^0.4-8-50 ENGINEERING ISfoSsffi ill ,v LTSmAIr The person charging this material is re- sponsible for its return on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. University of Illinois Library 3 19 INTERIIBRARY *$&£&*** ... -G bv wra a. ei .fliMS i aSEifi » w Bsa J LOAN " .■ : L161— O-1096 Digitized by the Internet Archive in 2013 http://archive.org/details/critiqueondisinf50kapo 8). The second theory owes its origin to John Snow (18 13-l8£8) who was a medical practitioner in London. He was a keen observer of cholera epidemic in London in 1831-32 and actively studied its recurrence in I8I4.8. He published his observations in 181+9 as a pamphlet entitled 'On the Mode of Communication of Cholera. " During the epidemic of l8£lj.> his systematic investigations included the consumers of water from the Broad Street pump. This study published in another pamphlet showed that the number of deaths in each area corresponded to the degree of pollution of the part of the Thames River from which each company obtained its water. His definitive views on the spread of cholera can be summarized as follows: i) The "poison" of cholera enters the alimentary canal directly by mouth, and this "poison" is probably a specific living being derived from the excreta of a cholera patient; 2 ii) Cholera can be transmitted from person to person through soiling of the hands or through contaminated food and water; iii) In case of Broad Street pump water users, a damaged sewer made it possible for the dangerous wastes from cholera patients to permeate the ground and pollute wells or other supplies of water used by the community. Perhaps his most significant conclusion was that the cholera "poison" could be carried in water. However, he could not identify the infective agent. Snow's theory was supported by the establishment of the germ theory. However, it was substantiated only when Koch isolated and cultivated Vibrio cholerae in 1883. Thus began an important era in the history of public health which could be termed as the birth of modern sanitary engineering. From the history of the theory of spread of disease or infec- tion, the term "disinfection" as now applied to "the destruction of water- borne pathogens" is probably very apt (Fair 1968). It is obvious, there- fore, that "sterilization" (destruction of all living things in the medi- um sterilized. 1 ) must be distinguished from "disinfection. " The history of disinfection, at least its practice with or without intent, is as old as civilization. Baker (1°!$) cites others for reference to Sanskrit books in India wherein 'boiling', 'plunging hot metal into water 1 , 'exposure to sunlight' and 'filteration through charcoal' were expressed as "useful practices." He also mentions Aris- totle's (38U-323 B.C.) advice to Alexander the Great wherein he says: "Do not let your men drink out of stagnant poo Is... And when you carry water on the desert marches it should first be boiled to prevent its getting sour. " 3 The practice of boiling water appears to have been carried through Nero's reign (5U-68 A.D.), Paulus Aegineta's time (a medical man of seventh century Greece) and Khaze 's period (an important Mohammedan physician of the ninth century A.D.). Boiling water prior to drinking was probably the only practice universal to all civilizations. It is still respected, though not practiced. Among all the disinfectants which emerged during the bacterio- logical era following 1876, chlorine is the oldest and most widely used. In fact, until recently, chlorination was synonymous with disinfection. Sawyer (1967) points out that chlorination of water supplies on an emergency basis has been practiced since about 185>0. Baker (19U8) quotes Dr. Rohley Dunglinson in his 'Human Health" (Philadelphia, 1835) to say that chlorine was proposed to be used to make "the waters of Marshes potable. " In any case chlorination with a clear intent of disinfection of germs was adopted for public water supplies, though, on a limited scale, soon after the realization that water was a vehicle for many pathogenic germs. It is fortunate, however, that only a few of the numerous diseases which inflict man are water borne even though this number appears to be increasing with time owing to new discoveries. Table 1.1 shows the present situation with regard to many common diseases due to pathogenic bacteria and protozoa. The dates in this table are an indication of the rapid scientific progress following the statement of the germ theory. Tracing the history of disinfection further reveals how rapid were the efforts towards the annihilation of germ-causing diseases in many parts of the world. However, these efforts were highly controversial and generated severe opposition. Baker (l9k£>) has k recorded an almost complete chronicle of how chlorination came to be accepted as a standard water disinfectant in the U.S. and elsewhere in the world. Twenty years of trials and tribulations here and there culminated in the famous court case regarding chlorination at the Boonton, New Jersey water treatment plant (1908) . The decision uphold- ing the right of the city to chlorinate the public water supply provided the impetus for the spread of chlorination for disinfection. The Boonton plant is reputed to be the first in the U.S.A. to employ a permanent chlorinating plant although the Bubbly Creek plant in Chicago started the practice of chlorination a few days earlier. However, the credit of being the first to establish a permanent chlorinating plant in the world goes to the water works at Middelkerke, Belgium (1902). The practice of ozonation began about the same time as chlori- nation. However, chlorination became far more popular than ozonation in the U.S. Europeans, on the other hand, were more receptive to the use of ozone. It is still very popular there. Russia probably built the first ozonation plant in the world in 190H>-6 at Tzarskoe Selo - Tzar's village (Faber, 1961) although a number of patents and papers relating to ozonation were issued between 187U and 1905 in a number of countries. In the U.S.A. George A. Sopper, in the late 1890 "s, was the first engi- neer who recommended the use of ozone as a reliable disinfecting agent. The first ozonation tests were actually made in 1906 at an experimental filter plant at Jerome Park reservoir, New York City. That slight progress has been made by ozonation can be judged from the fact that only eight water works employed ozone during the period 1908-19l|.2. Of these, five plants abandoned its use soon after. Comparative progress of ozone in Europe can be seen from the fact that in 19l|0 there were 90 installations in France, lk in Italy, 5 in Belgium, k in England, 3 in Romania and one in Russia. Another agent that showed promise in the field of disinfection of water supplies was "ultraviolet rays. " Baker found the earliest mention of its success as a disinfecting agent in 1877 which described its attempted use at Marseilles, France. The first known installation of ultraviolet ray apparatus in the U.S.A. was at Henderson, Kentucky in 1916, notes Baker. However, this method of disinfection of water never became popular in the U.S.A. and has not received any recognition even now. On the other hand Faber (1961) notes that this system is "widely in practice in the Soviet Union. " Faber (l96l) found no known applications of bromine for the disinfection of drinking water supplies although it has good disinfecting ability and has been occasionally used for control of biological growths in industrial water supplies and swimming pools. Chang (1966), relating the history of iodination of water supplies, gives credit to Vergnoux who reported on the first rapid sterilization of water for troops in 1915>. Hinman and Hitchens, follow- ing this report, experimented with iodine and recommended its use in U.S.A. Iodine was later used by Dunham for disinfecting small water supplies in 1930 in the U. S. By 19U0 disinfection of drinking water by various physical and chemical means in general and by chlorine in particular, had achieved great popularity among the sanitary engineers and lot of practical knowledge about its application had been accumulated. But I u CD U o M •H +3 CO H (0 to CO CO 0) 0) o Q) o o o CD o >H >H *-r* >H H «H «H (1) CD IH o CO -p -p 5 iH 0) ■a cd •H & A ^ °a O ^ bO •n CD 1 o O O rt •H £ ,Q o o co •H $H X! •H W w w CD s & CO CO « CD CO 9 CO w to < m CO l-p M s E-t O m S pq i o o CO •H O cl CD H S 0) o CO CO CM CD O CM cn 1A vO CO On very little was known about the fundamental chemistry of the disin- fecting agents and the biology of the disinfecting action. Fortunately, during the early periods of the Second World War, in an effort to meet the urgent need for a suitable disinfecting agent for military use, particularly for the disinfection of canteen waters, a contract was awarded to Harvard University by the U.S. Army's Office of Scientific Research and Development (Committee on Medical Research) to make "studies and experimental investigations in connection with the dis- infection of water and related substances." The final report of this contract which was executed by Fair (Responsible Investigator) , Chang, Morris and many others, is an extensive study of almost all fundamental aspects of disinfection. Unfortunately the final report, as such, was never widely distributed due to its "restricted" classification. A portion of the findings did appear in a number of publications. In general this report dealt with the chemistry and biology involved in disinfections by chlorine, iodine and bromine. In the following years of the Second World War, the attention of the sanitary engineer turned to another focal point in the area of disinfection. In the late forties and thereafter, remarkable dis- coveries were made in the field of virology. Faced by serious viral epidemics which were largely believed to be due to water-borne infec- tious hepatitis (Mosley, 196£), (see Appendix A for definition of term "water-borne ") , the sanitary engineer was confronted by the twin problems of locating water-borne virus as well as their destruction. Much work has since been done but much more remains to be done. Table 1.2 lists various groups of virus which have been isolated from human feces. Some 8 of these are likely to be water-borne but this has yet to be proven in many cases (Berg 196k) . So far only the virus of infectious hepatitis is accepted as water-borne (Mosley 1965) . The study of disinfection is still in its infancy. In fact, the great advances in the field of virology in recent years demand that sanitary engineers must make a reappraisal of prevailing disinfection practice. Disinfection problems promise to increase substantially in the near future due to greater reuse of water in the face of gross pollu- tion in our surface waters. This review has been prepared as part of an effort to reawaken a wide interest in the field of water disinfection. No. TABLE 1.2 VIRUSES OBTAINED FROM FECES* Disease Associated Virus Group or Groups 1. Paralytic Poliomyelitis Poliovirus 2. Aseptic Meningitis Polio virus, Coxsackie Virus A & Virus B, and Echovirus 3. Pleurodynia Coxsackie Virus B 1*. Herpangina Coxsackie Virus A 5- Respiratory Echovirus, Adenovirus and Re o virus 6. Enteritis Echovirus, Re o virus 7. Rash Echovirus 8. Acute Infantile Myocarditis Coxsackie Virus B 9. Jaundice Infectious Hepatitis * This information is taken from "The Virus Hazard in Water Supplies " by G. Berg published in New England W. ¥. Association, 78:2:79 (June 1961*) . The listed viruses have been isolated from human feces and could be important in water supplies. However, infectious hepatitis is the only virus which has been conclusively proven to be water-borne, 10 Chapter 2 THE INFILTRATORS 2 . 1 Water-borne Pathogens Water is disinfected in order to destroy those organisms which are water-borne and are pathogenic to man. Pathogens have been found to exist among the following groups of organisms: A. Non-sporulating pathogenic enteric bacteria such as Eberthela typhosa , Shigella dysenteriae and Vibrio comma . An almost complete list of this type has been given in Table 1.1. B. Pathogenic Protozoa - The cysts of Bndamoeba histolytica , responsible for amebic dysentery, are probably the only water-borne pathogenic protozoa. Fair (1968) writes that other water-borne protozoa infections are "rare." C. Pathogenic Worms - Among these worms, cercariae of schistosomes and cyclops are the most important. D. Sporulating Bacterium - In this group, Bacillus anthracis is accepted as water-borne. E. Virus - The feeling that water is a very important vehicle in the transmission of human viruses is growing. So far, infectious hepatitis is the only virus which is accepted as water-borne by epidemiologists. The question of whether the virus of poliomyelitis and other enterovirus are water-borne is still a matter of contro- versy. 2.2 Conventional Test Organism The study of numerous non-sporulating pathogenic enteric 11 bacteria is often simplified by dealing with a non- pathogenic member of this group, Escherichia coli, an organism in human feces and generally somewhat more resistant to destruction than its pathogenic associates. (Harvard Report, 19k$) . This view has always been contested by some researchers (Kabler, ±9$1) , (Baumann, 1961) but no other organism has been proven to be equally or more reliable. Almost all the research on disinfection done in the U.S. has involved either Escherichia coli or a specific pathogen. Among the pathogenic protozoa cysts of Entamaeba histolytica being more resistant, have always been adopted as test organisms for disinfection studies. However, the reported incidence of water- borne amebic dysentery is very low in the U.S. Their removal by filtration or sedimentation is extremely satisfactory (Fair et al. 1968, Morris 1966). As a result, this organism is not often con- sidered as a test organism except in those cases where unfiltered water has to be disinfected or where the population of carriers of amebic cysts is large. Regarding its resistance to disinfectants, it is generally considered to be more resistant than E. coli (Morris 1966). Pathogenic worms in general and cercariae of schistosomes in particular are not effectively removed by conventional water treat- ment methods (Harringer, 19U9) and reliance has to be placed on dis- infection. Fortunately, schistosomiasis or cercariae dermatitis is of rare occurrence in the U.S. (Fair et al. 1968) and thus there is little need to consider the worms as a test organism. 12 2.3 Challenge of Virus The presence and survival of virus in water in general is no longer a controversial matter. Although infectious hepatitis is the only virus of human origin which has been conclusively proven to be water-borne, others have not been effectively disproved. (Mosley^ 196S>) . Berg (1965), in the introduction to 'Transmission of Viruses by the Water Route" poses the following questions on the status of virus in water supplies.* 1. Is there inherent in this situation a danger, albeit inapparent, to those who must use this water for drinking purposes? That is, are small quantities of viruses present in our drinking water? 2. If they are, how can we detect them? 3. If we ingest them, how much virus is needed to produce an infection? U. If small amounts of virus will produce infection, what proportion of those consuming such small amounts will become infected? 5. What viruses are important in water transmission? 6. To what extent are viruses of non-human origin important in human disease process? While all these questions remain unanswered, the matter of immediate concern to the sanitary engineer is whether or not virus poses greater danger to man through water route than does pathogenic bacteria with the present minimum standards? Chang (1968) points out that "water polluted by sewage, sewage effluent, or the like is 13 apt to carry enteric viruses (arid other pathogens), that floccula- tion, filtration, and marginal chlorination or ozonation (leaving very little or no residual) will probably not reduce the virus con- centration to a safe level for mass consumption, and that the con- form index used as the minimum standard will not ensure the safety of the water against viral infections." He further argues that only those viruses that grow in the intestinal wall of man and are discharged in large numbers in the feces deserve consideration. This criterion reduces them to the enteric group which comprises princi- pally the enteroviruses (poliovirus, coxsackievirus and echovirus) and the virus of infectious hepatitis. Unfortunately the infectious hepatitis virus has been reported to be the most resistant of all virus in the entire group. It does not lend itself to laboratory examination or cultivation (Berg 1965, Chang 1968). Accordingly, the dependence has always been placed on poliovirus (Weidenkopf 1958), Coxsackie virus (Clarke et al„ 195U) and adenovirus (Clarke, 1956) for experimental work. However, as Chang (1968) recommends, a slight margin of safety should be allowed on the assumption that the infectious hepatitis virus might be a little more resistant than the hardy enteroviruses. 2. U Relative Concentrations of Organic Virus in Water and Sewage Ho skins (1926) estimated that the number of coliforms dis- "A viral infection means establishment of parasitism in a host by the virus, whereas, a virus disease is an infection with overt symptoms and signs" (Chang 1968). Hi charged by an individual daily is of the order of UOO billion. On this basis Fair et al. (Harvard Report, 19U5) assumed that concen- trated sewage may at times contain about 100 million coliform bac- teria per 100 ml. Clarke (1962) reported that the mean coliform density in domestic sewage is U6 x 10 per 100 ml. But this high concentration may be present only in highly polluted waters. The density of Esch . coli in waters selected for public water supplies is probably a fraction of that in raw sewage. Streeter (1927) showed that the bacterial loading of a water supply prior to chlorination should desirably not exceed 50 Esch . coli per 100 ml if the treated water is to contain less than about one Esch . coli per 100 ml. It is, however, now felt that waters, prior to chlorination, may have bacterial counts which exceed 50 Esch . coli per 100 ml. Butterfield (191^3) used a density of 2000 bacteria per ml on the assumption that "it was not in excess of the number which might be expected in many waters. " Discussing the relative concentration of Eber . typhosa and Esch . coli in sewered area in which the annual typhoid rate is as high as 2000 per 100,000 population, Kehr and Butterfield (191j3) expected a ratio of 100 to 1,000,000. Due to its relative abundance and to its high resistance to disinfection, Esch . coli has been widely selected as a test organism. (There are other reasons also.) This is, however, a serious question as to whether the destruction of Esch . coli also reflects the destruction of water-borne virus. Recently, Geldreich et al., as quoted by Clarke et al. (1962), showed that the average coliform density feces per capita per day is 1.95 x ID . Using this data as well as Sabin's (1955) on virus, 15 Clarke (1962) found that the relative enteric virus density to coliform density in human feces is about 15 virus units for every million coliforms (a 1 to 65000 ratio) . In another extensive survey conducted at the Robert A. Taft Center and quoted by Clarke (1962) , a calculated density of 700 virus units per 100 ml of sewage and 0.15 to 1.5 virus units per 100 ml of polluted surface water was determined. Comparing his theoretical data with that of Kelly (1952), Clarke (1962) concludes that "the average enteric virus density in domestic raw sewage is probably 500 virus units per 100 ml, and in polluted surface water is not more than 1 virus unit per 100 ml. » 2.5 Interim Solution If the available data is accurate, it appears then that Esch . coli should continue to be the test organism so long as all enteric viruses are almost equal in resistance to various methods of disin- fection. However, Chang (1968) questions the validity of the data on virus on the basis of the following arguments: 1. There are a large number of sporadic cases of viral infec- tions, especially of virus (or viruses) of infectious hepa- titis and poliomyelitis, throughout the world showing there- by that a low level of transmission of virus is occurring in spite of water and wastexrater treatment in those areas. The situation is worse in less sanitated regions, due apparently to more severe pollution of the raw water and a lower water treatment efficiency. 16 2. So far we do not have a method suitable for the detection of enteroviruses in water, especially in small numbers. 3. The question of whether infectious hepatitis is caused by- one virus or a number of viruses is still unresolved. In addition, the relative resistance of the viruses has not been established. Pending the availability of such a method of viral detection and enumeration plus more information regarding the virus of infec- tious hepatitis, no reliable comparison can be made between a test organism such as Esch . coli and some representative virus. The following suggestions should be considered until then! 1. If polluted water is used as a source and if cases of enteric viral diseases occur without a known mode of trans- mission, the water treatment processes should be examined (Chang 1968). 2. Efforts should be undertaken to revise existing standards for Esch . coli established by U. S. Public Health Service. This should be done on the basis of existing data with an added safety factor (Personal communication - l) . 3. Wherever and whenever possible, especially in large cities where laboratory facilities are available, virus detection in the raw and finished water of municipal supplies with the present methods of detection should be a regular prac- tice. As far as possible, disinfection dosages should be determined on this basis if it exceeds the dosage presently required for the destruction of Esch . coli . (Personal communication - 1) . 17 Chapter 3 OUR CHIEF SENTINELS 3.1 Introduction Until recently, it would not have been an exaggeration to say that "disinfection" has been almost synonymous with "chlorination. " The importance of chlorine as a disinfecting agent can be estimated from the figures reported by the United States Public Health Service (Thomas, 1953) which show that in 19U8, 1*3.9$ of all existing water treatment facilities employed chlorination as the only treatment. Cook (1965) reports further that in the same year 6135 plants repre- senting some 88$ of the existing facilities and serving more than eighty million people, employed chlorine disinfection alone or in conjunction with other treatment processes. This represents, accord- ing to him, more than 86$ of the population served by all community water supplies, both vriVth and without treatment, and some 96$ of the population receiving treated water. Although the situation has not changed much since that time, considerable interest in other disinfecting agents has developed. Other methods of disinfection which show great potential for the future include the following disinfectants: 1. Iodine 2. Ozone 3 . Bromine U. Ultraviolet rays In addition, the following methods of disinfections need be 18 explored further before they could be accepted as possible disin- fectants in the future: 5. Chlorine Dioxide 6. Silver 7. Copper 3.2 Disinfection by Halogens There are two major reactions which take place during disin- fection by the halogens. The first of these is a hydroloysis re- action: X 2 + HO «* HOX + H + + X" (1) The second is the ionization of the hypohalous acid formed during hydrolysis: - + (2) HOX * OX + H K } where X represents chlorine, iodine or bromine. These reactions are rapid and an equilibrium is formed almost at once in which varying quantities of the possible active species X - XOH and OX" are present (Harvard Report, ±9h$) . A knowledge of the equilibrium constants for the reactions would give: [HOX] (H + ) [X-] [X 2 ] = K, (3) and [HOX] i where K, = hydrolysis constant K. = ionization constant 19 The total analytical concentration, C, of the oxidizing halogen, in moles per liter, can be expressed by the relation: C = HOX + OX" + X (£) The analytical methods employed for the halogens determine the sum of the quantities of these three constituents and do not distinguish one specie from the other (Fair et al., 19h7) • Solving the above five equations, we get [X 2 ] = (H + ) [X-j C ( 1 ) (6) K h 1 + K./(H + ) + (H + ) r X"1 K h POX] = c( — i ) (7) * 1 + K ± /(H + ) + (H + ) [X-] K h [« = °\ ( ^1_^ ) (8) (H + ) V 1 + K./(H + ) + (H + ) [X"] K h Thus the concentrations of the three halogen components can be computed knowing the hydrolysis constant, the ionization constant, the pH of the solution, the total concentration of active halogen and the halide ion concentration. 3.3.1 Chemistry of Chlorination The hydrolysis and ionization constants for chlorine are: 1 K h =3.8x 10" 1 * at 20°C (Harvard Report ±9k$) K. = 3.3 x 10~ 8 at 20 °C Calculations using the equilibrium equations indicate that for all concentrations of chlorine used in water disinfection, the percentage of chlorine as Cl_ is so small that it can be disregarded. 20 In fact it is somewhat of a misnomer to call the process "chlorine- disinfection, " since Cl ? is present for less than a second in water. Based on above values of K. and K., Harvard Report (l9h$) reported the following relative amounts of hypochlorous acid and hypochlorite ion at various values of pH: TABLE 3.1 PERCENTAGES OF CHLORINE SPECIES PRESENT IN DILUTE CHLORINE SOLUTIONS AT VARIOUS pH LEVELS TITRABLE CHLORINE CONCENTRATIONS = 1 mg/1 _pH foEOGl #0C1 k and below 100 £ 99.7 0.3 6 96.8 3.2 7 75.2 2U.8 8 23.3 76.7 9 2.9 97.1 ID 0.30 99.7 11 0.03 99.97 Similar results were obtained by Wattie and Butterfield (19Wi). 21 Thus, for a particular temperature, the relative quanti- ties of hypochlorous acid and hypochlorite ion are a function of the hydrogen ion activity or pH. Since analytical methods so far available determine the sum of the two species, a knowledge of pH is required to determine the quantities of the individual species. It was probably an effort to be consistent with the analytical determination that the AWWA committee which prepared the chapter on "Chlorination and other disinfecting practices" for the manual on "Water Quality and Treatment" in the late forties introduced the terms, "free available chlorine" and "combined available chlorine."" Unfortunately, these terms are somewhat confusing and misleading. Although H0C1 is far more powerful a disinfectant than hypochlorite, the two are lumped together as part of the "free available chlorine" (Chang 1968). Berg (l°6U) complains of this as "poor semantics. " The AWWA Manual (l9£l) defines the terms as follows: "That chlorine existing in water as hypochlorous acid and hypoch- lorite ions is defined as free available chlorine. " "That chlorine existing in water in chemical com- bination with ammonia or organic nitrogen compounds is defined as combined available chlorine . " 22 3.3.2 Chlorine Demand and Chloramines The concentration of the chlorine available for disin- fection is greatly affected by the presence of oxidizable organic matter as well as nitrogenous substances. "Chlorine demand" may be defined as the quantity of chlorine involved in side reactions with substances in x^ater that consume or destroy chlorine residual. For- mation of chloramines is the result of side reactions of the disin- fectant with substances present in water that transform the active ingredient (HOCl) into 13H CI, HHCl- or NCI.. These chloramines are far less potent germicides than HOCl. Although this latter pheno- menon has a marked influence on the process of chlorination for dis- infection, it is not generally well understood. Morris (1967) points out that "as this survey of available data has shown, current know- ledge of the rates and mechanisms of reaction of dilute aqueous chlorine with nitrogenous compounds is very incomplete and scattered. " The following is a summary of the data which the literature reveals: (Sawyer (1967), White (1968), Fair (1968) Butterfield (19U6) ). 1. The three basic equations that govern the formation of chloramines are: NH 3 + HOCl - HHgCl (monochloramine) + H 2 (9) NHgCl + HOCl - MHClg (dichlor amine) + H 2 (10) HHC1 2 + HOCl - NCI (trichlor amine) + H 2 (11) According to these equations 3 moles of chlorine are required to react with each mole of ammonia. In practice only 2 moles are re- quired. 23 The addition of chlorine in water treatment practice beyond this amount required to react with ammonia is called 'break point chlorination. " Chlorination beyond the break point results in the formation of a "free chlorine residual. " 2. The rate of the equation (9) is highly dependent upon the pH of the solution. The maximum rate occurs at a pH of 8.3 and decreases rapidly at higher and lower pH values. 3. With molar ratios of chlorine to ammonia up to 1:1, both mono- and dichloramine are formed. The relative amounts of each are a function of pH, and greater proportions of dich- loramine appear at lower pH values according to the follow- ing expression: 2 HHgCl + H + * NH, + + NHC1 2 (12) Further increases in molar ratios result in the formation of the gases NCI, and N„ ? k» Chloramine residuals usually reach a maximum when 1 mole of chlorine has been added for each mole of ammonia. They then decline to a minimum value at a chlorine-to-ammonia ratio of 2:1. $, The germicidal powers of the chloramine s are different for different organisms. These shall be discussed later. Thus, the formation of chlor amines are dependent upon a number of factors such as pH, chlorine-to-ammonia ratio, temperature, contact time and salinity. 2k 3.3.3 Germicidal Properties of Chlorine and Its Various Species Ifliile the disinfection of water by chemical agents is a function of a number of variables, the following discussion is restricted to the resistance of a single organism to its destruction by one species of the disinfectant. Several other variables are assumed constant at that time: 1. The temperature of the water 2. The composition of the water 3. The concentration of the organisms U. Presence of other organisms Morris has done a survey of the literature for the compara- tive germicidal efficiencies of various disinfectants. (Personal communication -2). His analysis is presented in Table 3.2. TABLE 3.2 CONCENTRATIONS (mg/l) OF FORMS OF ACTIVE CHLORINE TO YIELD 99 PERCENT GERMICIDAL EFFECT IN 10 MINUTES AT 2$°C Organism H0C1 0CL~ NH g Cl Esch. coli 0.005 0.6 1.0 polio virus type 3 0.02 » 1 25.0 cysts 2.00 800 10 schistosomes 0.^-1.0 - o.k This data points out that hypochlorous acid is the principal disin- fecting agent irrespective of the type of organism. Hypochlorite ion and mono chlor amines are far less potent in their germicidal 2$ action. This is actually true :?or all temperatures and contact times. Dichloramine is slightly more powerful than mono chlor amine but neither compares with hypochlorous acid. These facts are amply supported by other sources in the literature (Butterfield (l9l|3), Chang (1968), Kabler (1951), Berg (19610, Kabler (l96l) ). 3.i|.l Chemistry of Iodination The equilibrium constants for the hydrolysis and ionization of iodine are: K. = 3 x 10" 13 at 25°C K. = k.$ x 10" 13 at 2^°C Using these values in equations 6, 7 and 8, Chang (1958) calculated the effect of pH on the reactions for total titrable con- centrations of iodine from 0.5 to 5>0.0 ppm. Three conclusions may be drawn from his calculations which were presented in graphical form: 1. As pH increases from 5>.0 to 8.0, molecular iodine (I ? ) hydrolyzes to form hypoiodous acid (HOI) . 2. As the titrable iodine concentration increases, hydrolysis takes place to a lesser degree. 3« Very little ionization of hypoiodous acid takes place at the pH values encountered in ordinary water disinfection practice. To illustrate these points, Table 3.3 has been prepared on the basis of curves presented by Chang. 26 TABLE 3.3 EFFECT OF pH ON THE HYDROLYSIS AND IONIZATION OF IODINE Titrable Iodine = 1 mg/1 Titrable Iodine = 5 me/1 % Concentration of % Concentration of PH h HOI 10" h HOI 10" 5 99 1 100 6 9$ 5 o - 93 2 7 67 33 90 10 8 20 80 « 1 5? h$ In addition to hydrolysis and ionization two other phenomena are important in iodine disinfection. They are of great significance because the products formed have practically no germicidal activity (Black (1965), Chang (1966) ). The first phenomenon is the forma- tion of iodate and iodide at or above a pH of 8 due to the instabi- lity of hypoidous acid. The reaction can be shown to take place as follows: 3 HOI + 2 (OH") ** HIO + 2H 2 + 21" (13) Wyss and Strandskov (19U5) showed, however, that this re- action is strongly influenced by the buffer used and the concentra- tion of titrable iodine. In case of carbonate buffer, which normally predominates in natural waters, this reaction is quite slow. More- over, below a concentration of 30 mg/1 of titrable iodine, the for- mation of iodate is not substantial. Black (1965) carried out studies on iodate formation at titrable iodine concentration in the range of 0.5 to 3.0 mg/1 and reported that no significant amounts of iodate 27 were formed in the concentrations and within a pH range of 5.0 to 9.0. The second important phenomenon which influences iodina- tion is the formation of tri-iodides or polyiodides. This reaction takes place in all iodine preparations used for disinfection which contains enough iodide to give an 1^:1" molar ratio of 1:1 or less. (Ill) (15) (16) The reaction taking place is i 2 + r - i 3 - h + V " V and so on ft] c 1 "] _. r [ V] ^ The value of K. at x 3 25' D C = l.k x tigated this reaction and has reported that the formation of the triiodide ion or higher iodides is insignificant at the iodide con- centrations likely to be found in water disinfection. This was earlier reported in the Harvard Report (19U5). 3.U.2 Chemical Demand and Formation of Iodamines The Harvard Report (19U5) states that: 1. Iodine demands of natural waters are of approximately the same magnitude as chlorine demands on a weight (mg/l) basis. On a molar basis, iodine demands are approximately 28^ of the chlorine demand. 2. There is no evidence for the reaction of iodine with ammonia or amino type substances in aqueous solutions. Similar findings were reported by Black (1965) . 28 3.U.3 Germicidal Properties of Iodine and Its Various Species As discussed in Section 3*k»l, of the five species of iodine which might exist in water upon its application in its commercial form, only molecular iodine and hypoiodous acid are important. These species alone are the powerful disinfecting agents. Comparing the disinfection efficiencies of the two species, Carrel et al. (195>7) reported that HOI is three to four times as active as I ? in killing Esch . coli. In the killing of spores (B. metiens), Wyss and Strandskov (l°U5) claimed that I ? is at least three times more effective than HOI. Clarke, et al. (I96I4.) showed that the viricidal efficiency of hypoiodous acid is J4O to 50 times as great as molecular iodine when tested against the hardy group of enteric virus. Chang (1967) compiled data for the time- concentration relationship for 99*97° destruction of the accepted test organisms from bacteria, protozoa and virus at 18 C. The titrable iodine con- centrations in mg/1 of Ip and HOI for a contact time of 10 minutes are given below. 29 TABLE 3.U CONCENTRATIONS OF IODINE SPECIES FOR 99.9/£ KILL FOR 10 MINUTES COOT ACT TIME AT l8°C Organism Molecular Iodine - mg/1 Hypoiodous Acid - mg/1 Esch . coli < 0.005 « 0.005 Poliovirus Type 1 > 20 0.5 E. histolytica 2.5 k*0 From this data it appears that molecular iodine is about twice as power- ful as hypoidous acid for cysts of E. histolytica , whereas hypoiodous acid is superior to I ? in the disinfection of bacteria and virus. 3.5 Disinfection with Bromine A survey of the literature reveals very little data on the use of bromine in the disinfection of water in general and on the chem- istry of bromine in particular. The Harvard Report (19U5) used the following values of the hydrolysis constant and ionization constants for calculating concentrations of bromine species in dilute aqueous solutions of bromine: K. = 5.8 x 10~ 9 at 25°C K. = 3.75 x 10~ 9 at 25°C The Harvard Report also indicates that the value of the ionization constant needs more study. Jolly (1966) reports the value of K. as -9 2.1 x 10 at room temperature. In any case, the values of the above constants are such that "within the range of pH values encountered found in water supply 30 XTOrk any one of the three possible species, i.e., Br ? , HOBr and OBr", may predominate." (Harvard Report, ±9h$) . The following are the concentrations of various bromine species in a solution con- taining 1 mg/1 of titrable bromine as recorded in the Harvard Report. TABLE 3.5 PERCENTAGES OF BROMINE SPECIES PRESENT IN DILUTE BROMINE SOLUTIONS AT VARIOUS pH LEVELS FOR TITRABLE BROMINE CONCENTRATION OF 1 mg/1 Species 3 k 5 6*** 7 8 9 10 11 Br 2 U5.3 11.8 1.5 0,2 HOBr 5U.7 88.2 98.5 99.6 98.0 83.3 33.3 U.8 0.5 OBr" 0.2 2.0 16.7 66.7 95.2 996 At higher pH values and at long contact times, there is further decomposition of hypobromite into bromate and bromide according to the equation: 3 OBr" - BrO " + 2 Br" As shall be discussed later, OBr", BrO " and Br" have very poor germicidal power and as such their formation is a positive drawback in bromine disinfection. It is, however, yet to be determined whether these reactions play an important role in dilute aqueous solutions. "■There is no evidence for the formation of compounds between bromine and ammonia in water solution" (Harvard Report, 19U5). It was then believed that these substances were completely hydrolyzed at the concentrations employed in water disinfection practice. 31 Galal-Gorchev and Morris (1965), however, hold the view that there is rapid reaction between bromine or hypobromite and ammonia in dilute buffered aqueous solutions which results in the formation of NH„Br, NHBr ? or NBr~, depending upon pH and molar ratio of ammonia to bromine. According to these investigators, NHJ3r predominates in alkaline solutions at high N/Br ratios, NHBr ? predominates in the pH range 6-9 with N/Br ratios about 5 to 20, and NBr, predominates in more acid solutions. NBr~ is found in mixtures up to pH 8 when two to three moles of bromine per mole of ammonia are allowed to re- act. Similar findings were reported earlier by a number of research- ers, primarily Johannesson (i960) . Since the formation of bromamines has been confirmed only recently, it appears that no work has been carried out with respect to their germicidal activity. The literature contains relatively few references to studies of the disinfecting efficiencies of Br ? and HOBr. In fact, Chang (1968) writes that "very little is known of the viricidal efficiency of HOBr. " Whatever data is available is not even accompanied by data on pH. Therefore, the concentra- tions of the bromine species present cannot be calculated. In general, bromine has been reported to be less viricidal than chlo- rine or iodine on a weight basis. Morris (Personal communication -2) found that the concentration of HOBr required to obtain a 99% kill in a contact time of 10 minutes at 20-25 C are 0.05 mg/1 and 10 mg/1 for Esch . coli and Endamoeba histolytica respectively. Marks and Strandskov (1950) reported the results of tests with B. metiens where molecular bromine was found more active than hypo- bromous acid. 32 On the "whole the germicidal behavior of bromine and its derivations are not very well known. 3.6 Ozonation Ozone disinfection is another method which has potential of an effective and economical technique. It has not been extensively used in the U.S. The chemical and physical properties of ozone are not yet adequately known. This is probably one reason which has obstructed the collection of consistent data on the germicidal properties of ozone. Ozone is a very powerful oxidizing agent and reacts more rapidly with organic substances than hypochlorous acid. This. may indicate that the disinfecting rate might be faster with ozone. However, at the same time, the "ozone demand" of natural waters would be expected to be larger than the corresponding chlorine demand. Another serious drawback of ozonation is its instability in solution. It decomposes into oxygen. Stumm (195>8) quoted his earlier work ( Stumm (l°5U) when he showed that this decomposition in aqueous solution is temperature dependent, is strongly catalyzed by trace concentrations of many organic and inorganic constituents of water and is especially dependent on the hydroxyl ion concentra- tion. For all these reasons there is no residual concentration of ozone in water distribution lines after ozonation. Regarding the germicidal efficiencies of ozone there are widely diverging reports in this literature. Stumm (1958) analyzes the data available and reports that, on the whole, ozone is a better 33 bactericidal, viricidal and cysticidal agent than hypochlorous acid when fudged on the basis of contact time alone. Morris (Personal communication - 2) finds the following repre- sentative figures in the analysis of the literature on ozonation: TABLE 3.6 CONCENTRATIONS OF OZONE FOR 9?p KILL IN 10 MINUTES AT 20-25 C Organism 0~ Concentration in mg/1 Esch. coli 0.001 (at 5°C) E ndamoeba histolytica 0.1 Poliovirus 0.03 (type not known) VI. Chang (1968) quotes Trahtman's unpublished data (1966) which showed that 99.9/> destruction of enteroviruses was achieved with 0.2 ppm of ozone. The temperature and contact time here not given. Faber (1961) quotes French sources which state that the Water Control Service of the city of Paris used 0.1 mg/1 of ozone for a contact time of $ seconds against 60,000 E. coli /ml. On the whole, it appears that ozone has disinfecting powers against the water-borne pathogens in water comparable to that of chlorine. However, much work is required to authenticate the avail- able information. 3.7 Other Processes All processes other than those already discussed, with the exception of the application of heat, are in their infancy. The boiling of water for disinfection purposes is an ancient process and 3k is a "safe and commendable practice where drinking water safety is a suspect," write Fair et al. (1968). All other methods may be said to be in an experimental stage. 3S Chapter 4 QUEST FOR THE BEST I4..I For over fifty years in the U.S. chlorine has been the domi- nant choice as a disinfectant for drinking water. It has performed so great a service to man that it has become a standard. It has gained such wide acceptance that any effort to substitute another agent in its place, even for experimental purposes, is reviewed with skepticism by those in waterworks practice. At the same time some researchers feel that other possible disinfectants may have more potential. U. 2 Criteria for Selection "What criteria should determine the choice of disinfectant for the disinfection of different waters? There are numerous variables which are involved. In this chapter consideration will be given to a few of the prominent factors which influence disinfection. Ao Physical and Chemical Characteristics of the Water to be Treated: (a) Chemical demand: In the practice of chlorination, the term "chlorine demand" refers to the amount of chlorine which must be added before a stable residual is formed. Since this forms an impor- tant fraction of the dose of a disinfectant, its determination is very important . If the demand for disinfectant is high, higher dosages of disinfectant may be uneconomical or have undesirable tastes and odors. Under such conditions, iodine, for which the chemical demand is low, or pre-ozonation might be considered. Chang (1968) refers to ozone 36 as "ideally suited for treating water prior to chlorination to re- duce the chlorine demand as well as the pathogen load, thus making the chlorination process more satisfactory and less objectionable on the basis of odor and taste. " Since ozonation must be performed on-the-spot, it may not always be applicable. For these reasons, iodine has been selected by the military for disinfection of water under field conditions. (b) Ammonium ion concentration: A knowledge of the ammonia-nitrogen concentration of the water to be disinfected is required. This information will permit the calculation of forma- tion of chloramines which may be less germicidal or have no disin- fecting power at all. On the other hand, iodine does not undergo reactions with nitrogenous matter (Harvard Report, 19hS; Black, 1965) . (c) pH: We have discussed in earlier chapters the in- fluence of pH on the hydrolysis, ionization and decomposition of a halogen in water. It has also been observed that these reactions transform the original substance into those which may or may not have any resemblance to the parent element. In the case of chlorine, for example, the increasing ionization of hypochlorous acid into hypoch- lorite ion with rising pH values reduces the disinfecting ability of the aqueous solution of chlorine. Fig. U.l has been prepared to present the influence of pH on chlorine, bromine and iodine solutions. They are based on data presented in Chapter 3 for 1 mg/1 of titr- able halogen. These curves show that pH 7.5 can be regarded as a critical pH for chlorination because at higher pH the hypochlorite 37 Principal Disinfecting Agents in Halogens are: 1. Hypochlorous Acid 2. Molecular tfronrine/Hypobromous Acid 3. Molecular Iodine/Hypoiodous Acid H cv o c u Sc pq iool k Total Titrable Halogen 1PPM 5 6 7 8^ 9 10 11 12 i i o o 1; W CM O H ' ■^ curve for iodine curve for chlorine curve for bromine 10- _|20_ 30- i40. 5o_ 60 70 80 90_ 100 7 8 9 10 11 12 13 — PH -| FIGURE U.l. PERCENTAGES OF VARIOUS SPECIES AT DIFFERENT pH VALUES 38 concentration increases sharply. These high pH values are en- countered where softening is practiced. The iodine curve in the same figure reveals increasing hydrolysis of molecular iodine into hypoiodous acid with increasing pH. Hypoiodous acid predominates in the region, pH 7.3-9.0, after which it decomposes rapidly. Comparing the behavior of iodine with that of chlorine over this pH range, iodine has an advantage in that both hypoiodous acid and iodine are good disinfectants and, in fact, hypoiodous acid is a far better viricidal and bactericidal agent than iodine. Thus, iodine is effective over the entire pH range whereas chlorine becomes ineffective above pH 7.5>. The disinfecting powers of the species, HOBr and Br ? are not yet established. Thus, pH plays a major role in the selection of the disin- fectant in spite of the fact that the final choice would involve the ultimate economy, human reaction and safety. (d) Temperature: Temperature should not play a very criti- cal role in water disinfection basically because the temperature of the water usually available for disinfection does not vary widely. In addition the temperature effects on the rate of kill are parallel for almost all disinfectants and conform closely to the Van't-Hoff- Arrhenius equation (Harvard Report 19U5 ) • In the case of disin- fecting tablets, the water temperature does have an effect on the rate of solution. Berg (l°6U) reports that within the biological range, a 10 C decrease in temperature would increase the contact time for a given amount of viral destruction by 35>0 to l&Ofc in case of mole- cular Ip and by 200 to 300^ in case of chlorine. 39 E. Governing Organism: If a single organism is to be used, which organism should be regarded as the governing organism (one who would dictate the dosage or residual requirements of the disinfectant)? Considering the threat of the virus, Chang (1968) comments that 'we must base ourselves on circumstantial evidence, and not on epidemiologic dogma, in ascertaining the role of water supply in viral trans- mission in noneDidemic times. " The coliform index as the minimum standard should not be relied upon. Instead, the water should be made safe from viral infections without sacrificing other desirable properties. This can be illustrated by the example of a munici- pality reporting low level viral infection and whose treated waters have pH reactions around 8.5. Such a water can be disinfected sat- isfactorily with high dosages of chlorine. But, as an alternative, iodine can be used. In areas where waterborne amebic dysentery is reported to have a high incidence, it is improper to rely on chlorination unless it is accompanied by effective filtration and other treatment. This is because hypochlorous acid is a very poor cysticidal agent. On the other hand, molecular iodine, and not hypoiodous acid, is effective against Endamaeba histolytica . C. Odors and Tastes: Apparently it may not seem to be a critical element in our criteria at present. Tastes and odors might pose a serious problem in the near future. With increased stream pollution, larger doses of disinfectants and their residuals might become inevitable. Morris ho (i960) insists that "a minimum residual concentration of 1 to 2 ppm of free chlorine after 10 to 30 minutes of contact must become standard practice with all waters that have been subjected to any sizable degree of contamination. " Uith an increased concentration of chlorine for disinfection coupled with the presence of phenolic substances (even though USFHS has set an upper limit of 1 ppb on phenolic compounds'.) plus the formation of chloramines, the prob- lems of tastes and odors will increase. Such problems may be less severe with iodine but it does not appear to be absent. Black (l Q 65>) concludes that "when the concentration of elemental iodine is 1.5- 2.0 ppm, many people will be able to detect a taste, but it will not be an objectionable one. " This statement concedes that taste, whether sweet or otherwise, would be present in solutions containing molecular iodine, '..here iodine is to be used as a viricidal agent, it should be present in the form of hypoiodous acid which is highly viricidal. Since HOI has been reported to be a colorless and taste- less substance (Browne (1968)), this problem should be minimum at high pH. While ozone is not accepted as a full fledged disinfecting agent, it has great potential as a prechlorination agent both for the elimination of chlorine demand as x-rell as for the removal of color, odor and taste problems. Stumm (1958) stresses the great capability of ozone and Chang (1968) recommends the use of ozone prior to chlorine disinfection. Morris (1966), however, prefers superchlorination followed by dechlorination using agents such as S0 ? or activated carbon. Ill D. Concentration - Contact Time Relationships Flexibility in the selection of the concentration of the disinfectant for a corresponding contact time, during which the required percentage kill is obtainable, is desirable. Fair and Geyer (i960) reproduces from literature the following empirical formula: C n t - K p where C = concentration of the disinfectant t = time required to effect a constant percentage kill of the organism n = coefficient of dilution or a measure of the order of the reaction K = a constant n & K depend upon the organism being disinfected, tempera- ture and the disinfectant Values of n & K for some conditions have been reported (Berg 196k; Kimball 1953; Gurian 1956). S. Cost of Disinfection The cost of gaseous chlorine and iodine in 1961 was report- ed to be $0.0625 per pound and $1.10 per pound respectively (Chamber, 1961) . This would place the cost of iodination roughly 18 times higher than that of chlorination on purely purchase price basis. Beattie (1968) reported almost the same prices and cost proportion. Diaper (1968) reported on the cost of ozonation for water sterilization on the basis of 1 ppm of ozone. His analysis showed 1*2 that installation cost (which includes ozone generator and air pre- paration equipment and electrical equipment, but no construction work) is almost constant beyond a rated capacity of 10 mgd water treatment plants and is about $5000 per mgd treated. The capital cost up to 2 mgd plants is around c?l£,000 per mgd treated but then falls rapidly. The operating costs for ozonation chiefly depend upon the cost of electricity and was reported by him to be 0.10 per 1000 gallons at a dose of 1 ppm. This cost includes electrical con- sumption for ozone production and injection, air preparation and ancilliaries. The average cost for installation and operation based on a dosage of 1 ppm ozone over a period of 20 years at \$> interest plus taxes for a 10 mgd plant comes to 0.280 per 1000 gallons. On a personal communication with local water treatment plants with a peak capacity of 22 mgd (Smith, 1968), it was gathered that the cost of chlorination was about 0.20 per 1000 gallons. Mak- ing a rough comparison with ozonation costs, it appears that ozona- tion is only about 5>0$ more costly than chlorination. This means that even if ozonation is not indepently relied upon, preozonation followed by chlorination may be a feasible yet not a very uneconomi- cal proposition. This should, of course, ensure a more satisfactory disinfection than chlorination alone. On a rough estimation of the cost of iodination on the basis of purchase price of iodine and chlorine, it might cost around \x$/ 1000 gallons. Black (l°6£) has tried to offset this high cost of iodination on the following basis: U3 1. Iodine being a weak element chemically has substantially lower iodine demand both for organic matter content of most waters as well as for nitrogenous substances. 2. Iodide ion may be reconverted to the elemental form "by a wide variety of oxidizing agents, weak and strong." Presence or introduction of such an oxidizing agent should be able to increase the residual contact time with water manifold. He calls this idea "unique in water disinfection practice." Indeed it is so but the question refers back to how much price does one attach to this in- surance for public health. Another problem posed by this idea will be the discovery of an ideal oxidant which can be introduced in drinking water safety and without enhancing the overall cost sub- stantially. 3. Little decomposition of hypoiodous acid in the pH range and concentrations likely to be encountered in water disinfection practice is the third factor offered by him. Probably the compari- son is with the ionization of hypochlorous acid in chlorine solu- tions in the same pH range. While the comparison is well taken, it appears that this factor counts towards the determination of dosage of iodine in our criteria rather than as a separate evaluation. In addition to the above factors, one may agree to additional reduction due to greater acceptability of iodine by the user on the basis of lesser degree of odor, taste and color problems as well as elimination of safety hazards usually associated with the use of liquid chlorine. There are numerous accidents on record which have prompted plants to stop the use of liquid chlorine and to switch hk over to hypochlorites. One such organization was a sewage treat- ment plant in New York City which made this decision in 1963 (Cook, 1965). Of course, this decision cannot be easily made for a water treatment plant because of the seriousness of the purpose of disin- fection in water supply systems. The use of hypochlorite should raise the pH, thus converting hypochlorous acid into hypochlorite ion which has, comparatively, little germicidal power. Thus, the economic comparisons are not as easy as they apoear to be but need deeper investigations and realistic evaluations. U-3 Variables involved in "quest for the best" are many and complex. There may be a few more that can be added to the above list. However, the idea suggested here is that a flexible and critical approach based on the evaluation of the needs and avail- ability should be attempted rather than pursuing a rigid and biased line of thought. Chapter V THE PILL 5.1 There are many occasions when water disinfection must be practiced on a small scale and under adverse conditions. The need for a ready-to-use disinfectant is greatest during military opera- tions or at times of natural disasters when small groups of people or even individuals have to depend upon sources of water which might be contaminated. Even during peace time, campers, sportsmen and adventurers have need for a packaged, instant-disinfectant such as a tablet. This need was first recognized more than fifty years ago (Morris et al. , 1953). However, only a few preparations, usually consisting of iodine and chlorine, were in use at the be- ginning of the Second World War. At that time a team of scientists and engineers conducted an extensive investigation at Harvard Uni- versity under a contract with the Committee on Medical Research of the Office of Scientific Research and Development. The Harvard re- searchers (Harvard Report, 19U5) listed the following desirable properties of chemical disinfecting agents which are intended for use under field conditions: A. This should be made available as a tablet of such size as to permit use of a single or at most two tablets for a small quantity of water. B. The technique of applying the disinfectant should be simple of management, substantially foolproof, and not unduly time consuming. U6 C. The agent should disintegrate or dissolve quickly and liberate its active ingredient or ingredients rapidly in order to free as much time as possible for the kill. D. Dosages should preferably be such as to ensure disinfec- tion of all kinds of natural waters to be treated without testing for residual concentrations of the disinfectant. E. The treated water should be acceptable to the user. In other words, odor, taste and appearance of the water should not be objectionable and foods and beverage powders or con- centrates placed in the water should not be changed in normal appearance or flavor. F. The treated water should not be toxic or otherwise unde- sirably physiologically active during periods of reasonable use. The water, furthermore, must not interfere with essential prophylactic or therapeutic medication. G. The treated water should not be corrosive to water con- tainers. H. The disinfecting agent should be stable under conditions of storage and actual use. I. The ingredients required in compounding the disinfectant should be economically and strategically available. J. Manufacture of the chemical agent should lend itself to large scale preparation with normally available chemical and pharmaceutical equipment. hi $.2 Ingredients of a Tablet Apart from disinfectant, a tablet must have substances which help either in the manufacture or its dissolution or promotion of disinfecting process. These ingredients could be classified as follows: A. Filler A filler or an excipient is always required in pharmaceutical practice to give the tablet adequate bulk. A number of fillers are available but a disinfecting tablet must employ one which is soluble (to preserve the clarity of the treated water), and at the same time should not be hygroscopic and should be inert to the disinfecting chemical. As shall be discussed later, the halazone tablet has sodium chloride as an excipient. A number of soluble nitrates, phosphates, acetates and sulfates could also be usefully employed. B. Buffer The selection of a buffer to promote the disinfecting action of the agent is very important. For example, for any chlorine compound to be an effective disinfectant, it is essential that the pH of the chlorinated water be less than 8. Above pH 8, the predominance of hypochlorite ion seriously reduces the disinfection capability. Similarly, where iodine is used, the pH of the solution should not be less than 7. Otherwise, the viricidal efficiency of hypo- iodous acid will be sacrificed. Sometimes, the buffer also U8 serves as a filler. This is true of globaline tablets which employ disodium dihydrogen pyrophosphate as a buffer as well as an excipient. C. Lubricant The function of this ingredient is to lubricate the punches of tablet-making machines. Talc is a popular lubricant. Calcium or magnesium stearate are also some- times added. The purpose cf a lubricant may sometimes be performed by the filler itself. D. Swelling Agent The use of certain colloidal clays, such as bentonite. promotes the disintegration of tablets by quick swelling in water causing the tablet to burst. This clay is chemically inert but physically very active. 5.3 Test Organism Emergency conditions demand that the disinfecting agent or tablet should be capable of killing the most resistant water-borne pathogen. The Harvard Report (l Q U5) states in this regard that "leaving out of consideration the virus of infectious hepatitis, the cysts of Entamoeba histolytica appear to be the most resistant water-borne pathogens that must be dealt with in the water disin- fection and so appear to determine the pattern of accomplishment that must be established both in the laboratory and in the field. " Much work has since been carried out on various human enteroviruses and the results confirm the earlier observations that cysts of Entamoeba histolytica offer greater resistance than any enteric h9 virus, including infectious hepatitis, to the disinfecting action of chlorine (Harvard Report, 19U5) • Morris (l°66), for instance, quotes other investigators who state that the concentrations of H0C1 needed to yield 995* germicidal effect in 10 minutes at 5 C for virus and cysts are 0. 002-0. k ppm and 10 ppm respectively. Chang (1966) presents data for iodine which shows that for a con- tact period of 10 minutes at 18 C and 99*% kill, the concentra- tions of I ? and HOI needed for poliovirus Type I and E. histolytica are shown in Table f>.l. TABLE 5.1 Species Poliovirus Type I E. histolytica Iodine 20 mg/1 2.5 mg/1 Hypoiodous Acid 0.1*5> mg/1 k mg/1 This data indicates that for effective disinfection of cysts and virus with reasonable doses of iodine, both molecular iodine and hypoiodous acid should be present in solution. It is interesting to note here that at pH 7> a dilute solution of iodine contains almost equal percentages of molecular iodine and hypoiodous acid (Black et al., 1965). This fact underscores the role the buffer has in a disinfecting tablet containing iodine. $.h Tablets in Use There are currently two tablets being used for water disin- fection in the U.S. The halazone tablet has been in use prior to 5o and during World War II. The disinfectant employed is a chlorine compound. The other tablet, globaline, xtfhich contains an iodine- based disinfectant, is used by the U.S. Armed Forces for the dis- infection of canteen waters. This tablet was developed by the Harvard researchers and has many advantages over the halazone tablet for this purpose. A. Standard Halazone Tablet - Composition and Reactions The composition of this tablet is as follows: Halazone ---------_-- = £.30 mg Soda Ash, dried = £.18 mg Boric Acid = 11.92 mg Sodium Chloride --'------ = 111;. 00 mg Weight per Tablet ------- = 136. k0 mg The chemical name of halazone is p-dichlorosulfonami dobenzoic acid. It reacts with water to release hypochlorous acid up to £0/£ of the titrable chlorine present. One tablet dissolved in a quart of water produces a titrable chlorine" concentration of 2.3 ppm and a maximum concentration of H0C1 (as Cl^) of 1.1 ppm. The reaction of the halazone in water is as below: C1 2 N0 SC,H, C00H + HgO — »» CI HNOgSCgH, COOH + H0C1 The Harvard researchers (Harvard Report, 19h$) defined titrable chlorine as the total oxidizing power of the material or solution under consideration which is effective in oxidizing iodide ion to iodine in dilute acetic acid solution, expressed as ppm of ele- mental chlorine. 51 In this tablet sodium chloride is the filler and the remaining two compounds form an alkaline buffer. B. Globaline Tablet - Composition and Reactions The Globaline tablet derived its name from a chemical compound which was developed by the Harvard researchers. The Harvard Report (19U5) refers to globaline as triglycine hydro- periodide, (IH-CH COOH). • HI . I . The formulation was later modified to tetraglycine hydroperiodide (HH^CHpCOOH), HI • 1.2l;l 2 (Summary Report, 19U6). This compound provides l|2.32/£ titrable iodine and 5>9.1|2^ total iodine. The composition of the globaline tablet is as below: tetraglycine hydroperiodide - - - - = 19.3 to 21 mg disodium dihydrogen pyrophosphate - = 82. £ to 92.3 mg (Ua 2 H 2 P 2 7 ) talc -------------- — = not more than 6 mg weight per tablet ------- — = 110 to 120 mg One tablet dissolves in a quart of water to give 8 ppm of titrable iodine. The talc is employed as a lubricant and disodium dihydrogen pyrophosphate works as an acid buffer as well as an excipient. This acid buffer serves to lower the pH of natural waters for it was then thought that elemental iodine was more germicidal in general than its main hydrolysis product, hypoiodous acid. As discussed earlier, Chang (1966) has shown that while molecular iodine is an excellent cysticidal agent, it has poor viricidal properties. On the other hand, hypoiodous acid requires about 52 double the dose of molecular iodine for killing cysts under the same conditions, but is about I;0 times as viricidal as iodine. These results indicate the need for the presence of both I„ and HOI in reasonable concentrations in water for effective disinfec- tion of all organisms rapidly. S> . 5 Comparison of the Two Tablets The Harvard Report (19U5) provides sufficient data on almost all properties of the two tablets discussed. The following is a summary of some of this data: ^.5.1 Dissolution Time Field studies employing soldiers in acceptability tests indicated that they considered rapid solubility of tablet as a primary criterion for acceptability. They were impatient with agents that required a waiting period of more than 10 minutes. For field simulation, the tablet to be tested was placed in a liter volumetric flask containing tap water at 23 C. The stoppered flask was then inverted end-over-end continuously, causing the tablet to drop through water until it was dissolved. These tests showed that while globaline disintegrated and dis- solved in less than one minute, standard halazone tablets re- quired 73§ minutes. Thus, in the case of halazone, the actual con- tact time betxreen the disinfectant and the organism is 25g minutes, if 10 minutes is taken as the total time a soldier will wait. It may be mentioned here that the disintegration of the tablets is not primarily a function of the disinfecting agent but rather of the filler and expanding agent used in the tablet. Since 53 halazone contains sodium chloride "which hardens or "sets up" with time, it suffers from a low rate of solution. As for the solu- bility of halazone itself, it was tested at different pH values. The results showed that the solubility was low and constant up to a pH of about U. Above this pH, the solubility increased quite rapidly, either because of hydrolysis of the dichlor group or through ionization of the carboxylic acid group. For example, some values were as follows: pH 3.8 5.5 5.6 halazone solu- bility, grams/ liter 0.09 0.83 1.200 These figures indicate that a change in the filler now employed in Halazone might improve the dissolution time of the tablet markedly. On the other hand, the use of disodium dihydrogen pyrophosphate as a buffer and free-flowing filler in the globaline tablet was a marked improvement even though the solubility of glo- baline compound itself is far greater than that of halazone. Glo- baline has a solubility of 380 grams per liter of distilled water. A. Effect of Storage and Humidity on Dissolution Time In general tests showed that storage at ll|0 F and room humidity did not affect the dissolving properties of the tablets tested. B. Effect of Temperature on Dissolution Time In general, lowering of the water temperature increased the time of dissolution for both the tablets substantially in accordance with the Van't Hoff-Arrhenius formulation. Some of the dissolution 5U 10°C 20°C 30°C 1.9 min 1.2 min 0.8 min 9.5 min 8 min 6.5 min times obtained were: Globaline Halazone 5.5.2 Cysticidal Dose Cysticidal doses of globaline and halazone tablets were determined in Cambridge tap water alone or with the addition of interfering substances that might be present in natural polluted water. The cyst density was 60 per ml of water. This density is considered to be far higher than the highest conceivable concentra- tion of cysts in sewage. This estimate is based on an area of high endemicity, say 50, c j, where the ratio of amoebic cysts to E. coli would be of the order of 1 to 100,000. (The number of coliform organisms discharged by an individual is estimated to be about 1;00 billion per day and an infected individual would discharge cysts in numbers varying from several hundred to some ten million per day.) This ratio would make the number of cysts in concentrated sewage about 10 /ml. The tests with globaline gave the following results: TABLE 5.2 Kind of Water Temp °C Contact Time, Minutes Initial .pH. Final % Cystici- Cysticidal dal Dose Residual Tablet/Qt. I? -ppm Tap Tap Tap Tap Tea Infusion 3 10 23 28 23 25 15 10 5 8.0 to 9.0 8.0 to 9.0 8.0 to 9.0 8.0 to 9.0 7.2 6.5 6.6 7.3 6.65 6.U 7.5 6.9 7.5 7.5 8.7 The above data certifies that one tablet of globaline should be able to disinfect all cysts, pathogenic bacteria and spores. No conclusive tests were carried out against organisms of infectious hepatitis and other enteroviruses. Nevertheless, it is possible now to estimate the viricidal capacity of waters disin- fected with globaline. At 10 C, the initial pH of tap water was lowered to 6.6 with one globaline tablet thereby leaving a residual of 6.9 ppm of iodine. At pH 6.6, about $% of the titrable iodine is in the form of HOI (Chang, 1958). As a result, the hypoiodous acid concentration is about 0.35 ppm. This amount of HOI may not be sufficient to be viricidal. The high concentration of titrable iodine and the use of an acidic buffer result, therefore, in a high cysticidal efficiency but lower viricidal capacity. The tests with halazone tablets showed that at room tem- perature about 5 tablets per quart of water were required to destroy all cysts in 10 minutes, whereas 2^ tablets would do so in 30 min- utes. In moderately to heavily polluted water at the same tempera- 56 ture, 7 tablets were needed for 10 minutes contact time and about 5 to do so in 30 minutes. Larger dosages of these tablets are re- quired for the following reasons: A. This tablet can release a maximum concentration of titrable chlorine equal to 2.5 ppm and H0C1 equal to 1.25 ppm. This is far less than the dose required under adverse conditions. Morris (1966) reports that 10 ppm of H0C1 are required for 99% kill of E. histo - lytica in 10 minutes at 5 C. B. The halazone tablet has an alkaline buffer to aid in dis- solving the compound. Unfortunately, at high pH the predominant species of chlorine is 0C1~ which is about 100 times less cysticidal than H0C1. C. The dissolution time of the halazone tablet is slow; T^s minutes at room temperature. Halazone has a great advantage in that H0C1 reportedly is an excellent viricidal agent (Morris, 1966; Kabler et al., 1961). It may be safe to assume, therefore, that if a certain dose of H0C1 is cysticidal, it is also sufficient for all types of enterovirus. In summary, a major improvement which appears to be possible in the preparation of tablets containing halazone is the inclusion of an acidifying agent which will not affect the solu- bility of the compound. 5.5.3 Acceptability of Tablets by Users The acceptance of the disinfecting agent by the user is probably as important as its germicidal action. The user may hesi- tate to use the agent because of (a) unpleasant taste, odor or color, (b) adverse physiological reaction, or (c) excessive time for disin- fection. 57 A. Unpleasant Taste, Odor or Color Tastes and odors may be caused either by the tablet itself in water or by its combination with beverage powders. For purposes of comparison, the Whipple Scale of intensity of odors and tastes (Whipple, 1927) was adopted as a yardstick to determine the relative palatability of the tablets. Investigators (Harvard Report, 19U5) used four tablets of halazone providing about 10 ppm of titrable chlorine and one tablet of globaline pro- viding 8 ppm of titrable iodine per liter of boiled distilled water at 23 C. The pH was varied with citric acid, dihydrogen disodium pyrophosphate or sulfuric acid. The water was tested by seven to fourteen subjects. The results obtained indicate that in the "pH range commonly encountered, " the globaline was more acceptable than halazone. In fact, in this range of pH, globaline produced "faint" to "distinct" intensity of odor and taste whereas halazone treated water had "decided" to "very strong" range on the Whipple scale. The "objectionable thresholds" were also determined in boil- ed distilled water at 23 C and the results were as follows: Compound Percent of Normal Cysticidal Dose at which "Objectionable Threshold" is Reached pH halazone globaline From this it is apparent that globaline would reach the "objectionable threshold" only if 2 tablets were used as is pre- scribed for heavily polluted waters. h 5 6 7 8 9 50 Uo 25 25 25 25 _ 200 wm 200 _ „ 58 As for the effect of pH upon tastes and odors, it was deduced, though not conclusively, that minimum tastes and odors were produced at the pH values attained when the tablets are added to neutral, unbuffered waters. To study the effect of temperature on the tastes and odors, tests were made at temperatures of l£ C, 23 C, and 30 C. The results indicate that the intensity increased with temperature but did not become objectionable even at 30 C, although at that temperature no water is pleasant to drink. All observers agreed that the coldest drink was the most palatable. With regard to the effect of disinfection on beverage powders, no specific tests were then made with either of the two tablets.* B. Adverse Physiological Reaction The physiological response of the use of iodinated water has long been a matter of concern. A number of laboratory as well as field studies have been reported. Studies were conducted at: 1. Department of Pharmacology, Harvard University (Dr. Otto Krayer) 2. Division of Pharmacology, Food and Drug Administration 3. Army Medical Research Laboratory, Fort Knox k* Naval Installations, Marshall Islands Hurst and Bird (1968) have now found, however, during their field tests with globaline that soft drink mixes are used in the field to make contaminated water more palatable. 59 All of these investigations were performed using iodine in concentrations equivalent to or in excess of those used in the field purification process. The tablets themselves were not used in these tests. The first three studies or their conclusions have been described in the Harvard Report (19U5) whereas the fourth study has been reported by Morgan and Karpen (1953) . While the first three studies indicate in general that the ingestion of iodine- disinfected water by healthy male adults should have no injurious effect, the analysis of data in the fourth study revealed no evi- dence of weight loss, failure of vision, cardiovascular damage, altered thyroid activity, anemia, bone marrow depression, renal irritation, sensitization to iodine, predisposition to diseases of the skin, or impaired wound healing. A more exhaustive study is now underway at Gainesville, Florida, under Dr. A. P. Black where far lower dosages of iodine are being used. Partially reported results indicate that there is no evidence that iodine, under the experimental conditions employed, has had any detrimental effect on general health or thyroid function (Black et al., 1965; Black et al., 1968).""" C. Excessive Time of Disinfection As reported earlier, the acceptability tests show that the soldiers in the field are impatient with disinfectants which take Chang (1968), however, suggests that the tests should be extended to pregnant women, infants and small children to know their re- action to small amounts of iodination over a long period of time. 60 more than 10 minutes to complete their action. In other words, the dissolution should take place in a matter of seconds to leave about 10 minutes contact time for sterilization. Obviously hala- zone tablets which require more than 7 minutes for solution, have to compensate for a shortened contact time by higher dosage. Globaline, on the other hand, is reported to dissolve in less than a minute, thus leaving most of the 10 minute time for disinfection. 5.5.U Thermal Stability of Tablets Water disinfecting tablets designed for global use must be capable of withstanding extremes in air temperature as well as heat developed in storage warehouses. To test the stability of globaline, accelerated storage tests at lliO F and room humidity were carried out to determine the rate at which tablets decompose and at what rate active ingredients are dissipated. Tests on globaline powder indicate that it lost about 30$ of its iodine after one month and about 60$ after two months. On the other hand, results of experiments with halazone tablets indicated that no appreciable loss of available chlorine occurred after 20 days at II4Q F. Therefore, the halazone tablet can be described as thermally stable. %•$.$ Resistance to Humidity To determine the relative stability of tablets in humid atmospheres, they were subjected to tests at humidities of 100$, 1% and $$% at room temperature. The gain in weight after certain time intervals at room temperature was measured. 61 At 10C$ humidity globaline appeared to be more stable than halazone as the former retained 37$ of original iodine and the latter 2h» 1% of original chlorine after the same number of days. At 7% humidity as well as $$% humidity, globaline appeared to be less hygroscopic. Over long periods of time at 32$ humidity, globaline again proved to be a stable substance. 5.5.6 Simulated Field Test In order to gauge resistance to humidity and thermal stability during actual use in the field, bottles of globaline and halazone tablets, with and without cotton plugs, were placed in a control room held at 80 to 90% humidity and approximately 80 F. Every two hours during the day each bottle was opened for a minute and a tablet was drawn. Over a three-week period, none of the com- pounds showed an appreciable loss of strength, and there was little variation between the bottles with or without cotton plugs. 5.6 Corrosion of Metals To see the effect of halazone and globaline disinfected waters on the materials of canteens, a series of experiments was conducted on aluminum and steel canteens. To perform accelerated tests, the strength of solutions was quadrupled. Thus, the globaline solution contained 32 ppm of titrable iodine and the halazone solution had 20 ppm of titrable chlorine. Two types of tests were conducted, drip tests and immersion tests. 5.6.1 Drip Tests In the drip tests, the solutions were allowed to drop 62 upon the experimental metal and run down it for about 9 hours each day over a period of 36 to 50 days. The same solution was used over and over again, but it was freshly re concentrated each day with the respective tablets. The loss in metal was assumed to be an indica- tion of corrosion. The results showed that the steel canteen metal was much more resistant to corrosion than the aluminum metal. Upon aluminum, globaline appears to be more corrosive than halazone, al- though upon steel, the action of globaline is less pronounced than that of halazone. £.6.2 Immersion Tests In normal immersion tests with the same solutions of glo- baline and halazone tablets, the former was less corrosive than the latter on steel canteen but the reverse was true in case of aluminum canteens. 5.7 Conclusions The globaline tablet was developed as a result of a tremendous effort on the part of scientists and engineers at Harvard. It has satisfied most of the criteria set for a disinfecting tablet. The halazone tablet suffers from serious drawbacks which limit its efficiency. However, since the production of these tablets, much work has been done on the subject of disinfection and many miscon- ceptions have been corrected. It may be possible, therefore, to re-evaluate the potency of these products and make further improve- ments. Globaline was produced on the basic assumption that molecular iodine alone is germicidal (and not its hydrolysis products) and 63 that cysts of E. hystolytica represent the test organism. Molecular iodine is still known to be an extremely good cysticidal agent but it has been proven by several researchers (Chang, 1966; Kabler, et al., 1961) that it is much less viricidal. The Harvard Report (19U5) assumed that "the destruction of virus by disinfectants appear to be of the same order of magnitude as that of most patho- genic nonsporulating bacteria. " Since this assumption has been dis- proven (Morris, 1966; Kabler et al., 1961) it would be useful to evaluate the viricidal power of globaline tablets. As discussed in paragraph £.5>.2, due to the effect of disodium dihydrogen pyrophos- phate (acidic buffer) in lowering the pH of the water, the hypoio- dous acid content produced of the water may be so low that it may be insufficient to kill any virus present. This situation points to an area of possible improvement in the globaline tablet. The substitu- tion of an alkaline buffer (pH 8) would yield about 1|C$ HOI and 6Q% molecular I ? . At room temperature the globaline tablet was expected to dis- solve in less than a minute. Studies at the University of Illinois (0 'Connor, 1967) have indicated that it may take longer, perhaps from 3 to k minutes. However, this experimentation was done on tablets which had been manufactured a few years earlier. The dis- crepancy may be ascribed either to the adverse effect of storage on the solution properties of the tablet or the pressure exerted by tableting machines. Since these factors are difficult to control, further studies to find a more suitable swelling agent are indicated. An alternative would be an effort to make the tablet effervescent. 6U This problem is one that involves the psychology of the thirsty soldier and improvements towards a more satisfactory solution should be constantly pursued. Color, taste and odor problems are associated with the use of globaline tablets but not to an extent that it is alarming. In fact, these signs are significant as they indicate the presence of a fair amount of residual iodine. The halazone tablet, at present, is not a suitable disinfecting agent for military use. Not only because little titrable chlorine is released, but also because most of the chlorine released ionizes into 0C1~ due to the presence of an alkaline buffer. Since OCl" is about 100 times less cysticidal than H0C1, the efficiency of the chlorine is greatly reduced. The alkaline buffer was added to in- crease the rate of solution of halazone which is very low at low pH values but increases markedly above a pH of 6. It might be possible, therefore, to prepare a reasonably soluble tablet buffered at a pH of 6 rather than 8 or 9. The solubility might further be enhanced by the addition of a swelling agent or by making it an effervescent tablet. Comparing iodine and chlorine based tablets as disinfectants for small water supplies, the former appears to have advantages over the latter for the following reasons: 1. On molar basis, iodine is more cysticidal than hypo chlorous ' acid. 2. Iodine has very little organic demand as compared to chlorine . (6 3. Chlorine has a strong affinity for nitrogenous matter, whereas iodine has almost none. U. Both predominant forms of iodine, molecular iodine and hypoiodcnis acid, are efficient germicides. They form an excellent combination for cysts and enterovirus. On the other hand, where chlorine is used, hypochlorous acid alone is a good germicide while OCl" is a poor disinfectant, Finally, the present practice of packaging 50 tablets of globa- line in a single bottle may also be subject to improvement. Once opened for the use of first tablet, the remaining tablets may start to "set up" or harden. In addition, the disinfecting agent may be lost. With the tremendous improvements in packaging techniques and materials, it may not be difficult to devise a package which con- tains one or two tablets. Alternately, the use of a powder pillow may be a solution to the problems of stability and solubility. 66 Chapter 6 POINTS TO PONDER 6 1 Introduction The following discussion is an attempt to prepare a list of some of the many problems facing disinfection of public water supplies which appear to be very urgent and need attention in the near future „ It is the opinion of the writer that research on dis- infection of water is in a period of comparative stagnation. This view is supported by an informal survey which shows that very few universities and government research institutions are conducting research on problems associated with water disinfection. In the private sector, the situation is even worse „ The response of promi- nent chemical companies producing disinfecting chemicals to inquiries about new or improved disinfectants for water was negative „ This may be regarded, within limitations, as a reflection on the feeling pre- valent in the water works industry that all disinfection problems are solved. 6 2 Biological Standards for Potable Water The USPHS (1962) standards for the biological quality of drink- ing water are based on a limitation of the numbers of the coliform group in water. A question exists as to whether or not these limits ensure the absence of water-borne pathogenic virus in addition to other pathogens. The numbers of virus in water supplies is believed to be increasing due to continued low level transmission of viral infection in many communities in spite of adherance to the established standards. Mosley (1965) comments that "we must consider, therefore, 67 the possibility that present standards of water treatment are not adequate to prevent low levels of virus from intermittently pro- ducing what appear to be sporadic cases of infectious hepatitis and other viral diseases." Chang (1968) endorses Mosley's idea and suggests the establishment of an entero-virus index which is, of course, beyond reach until a reliable virus detection method is standardized. Until such a time, Chang suggests two procedures to be followed separately or in combination: 1. "If polluted water is used as a source and if cases of enteric viral diseases, i^e. infectious hepatitis, occur without a known mode of transmission, . . . steps should be taken to ensure the safety of the finished water. " (Chang, 1968). 2. A tentative enterovirus index should be established for communities where viro logical services are available, where with the help of presently known methods of detection and quantification (Chang, 1968) monitoring may be practiced. This will involve establishing enterovirus coliform group ratios in the water and might indicate the necessity for an upward revision of existing water supply standards. Morris (1966) suggests that "some better index than the number of coliform organisms must be found for the assessment of the hy- gienic quality of treated water supplies. " As an interim solution, he suggests the revival of the old total plate count at 20 C which should indicate the presence of some sporulating organisms which are even more resistant to chlorination than viruses. An appropriate 68 decrease in their number might well serve as an indicator of viricidal activity. The importance of viral challenge can be estimated from Berg *s (l%6) speculation that some viruses, when infecting unnatural hosts, may produce cancers in these hosts. He maintains that there is no proof available that viruses of other than human origin cannot enter and infect human cells. 6.3 Disinfection Capacity As discussed in earlier chapters, the terms 'residual free chlorine" and "residual combined chlorine" do not provide a clear picture of the disinfecting capacity of the aqueous solutions unless they are properly interpreted by subsequent calculation. Any attempt to replace these terms may have to wait for new analytical techniques which directly measure concentrations of each individual species present in the solution. The same is true for iodine and bromine solutions. The misleading nature of these terms in waterworks practice needs to be corrected meanwhile. An interim solution to the problem is the provision of tables or nomograms or even specially designed slide rules for the operator, which would calculate the actual 'U. Thus, with decreasing quality and increasing quantity requirements, more attention must be given to water disinfection. Moss (1967) writes in his preface to •The Water Crisis" that "for the next generation of Americans, I believe it is not an exaggeration to say that water - its competing uses and the conflicts that arise out of those uses - may be the most critical natural problem. " It is realized that his concern here is for the water resources in the nation as a whole but the drinking water is of no small importance. The role of the disinfection in the future is obvious. Merely increasing the production of chlorine, in particular and disin- fectants, in general, will not solve our problems. A more rational attitude should be developed toward disinfection and scientific 73 efforts should be intensified tc obtain disinfectants which are functional over the range of conditions encountered in water treat- ment and which are economical at the same time. Y/ith more stringent standards of acceptability, our search for an ideal disinfectant must continue. 7k APPENDIX DEFINITION OF TERM 'WATER-BORNE " The definition of the term "water-borne" has always been a matter of controversy. In an effort to resolve this situation, Mosley (1965) has tried to make it more broad-based. His approach is as follows: 1. "An agent may be considered as frequently water-borne if elimination of this route causes a significant reduction in the total incidence of the disease it produces." To place an agent at this level of occurrence indicates that control of waterquality plays an important part in control of the disease. 2. An infectious agent would be considered only occasionally water- borne if elimination of water as a vehicle made no appreciable difference in the total amount of disease, other than in limited areas for limited periods of time. The possibility of water- borne transmission, however, would require serious consideration in any epidemiological investigation. It would also be necessary to maintain water quality standards which would prevent supplies from serving as a vehicle for such agents, even though these standards would not contribute to overall control. 3. Finally, an infectious agent would be defined as rarely water- borne if few episodes were found, especially if these occurrences were the result of proximate contamination or unusual circum- stances . 75 BIBLIOGRAPHY Note: The following abbreviations are used in the bibliography. App. Micro.: Applied Microbiology JAWWA: Journal American Water Works Association JNEWWA: Journal New England Water Works Association P.H. 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