Laboratory Control of Water

Transcription

1 Apr., 1936 Laboratory Control of Water Purification Plants * HARRY E. JORDAN, F.A.P.H.A. Chemical Engineer, Indianapolis Water Company, Indianapolis, Ind. \/JE who are engaged in the con- VV trol of public water supplies do not know everything about the quality of water, but enough is known to build and operate purification plants so that public water supplies are seldom unsafe. The phrase, " enough is known," must be taken precisely at its real content. The reference is to the state of knowledge; not to the application of that knowledge, because it is fairly evident that, in recent years, whenever a public water supply has not met all of the requirements of safety to the consumers, the failure was not due to the lack of knowledge. It was occasionally due to the lack or inavailability of equipment, but more often due to the simple failure -of a responsible personnel to use its knowledge and the equipment intelligently. We may properly digress for a time into a discussion of problems of water works personnel-problems associated with its frequent lack of training and often with the lack of real interest. One of the interesting developments of recent years has been that, in many plants over the country, the men engaged in water supply operations are taking voluntary training when the requirements of the state in which they work do not make it necessary. The * Read before the Laboratory Section of the American Public Health Association at the Sixtyfourth Annual Meeting in Milwaukee, Wis., October 8, fact that only 3 states at the beginning of this year required that their purification plant operators be regularly trained and licensed is in itself evidence of the fact that the people, since the first glow of interest in sanitary progress at the beginning of the century, have settled back into a state of complacency and lack interest in the training and qualifications of public service personnel, especially those associated with the vital task of public water supply. Again, lack of interest on the part of water works operators that frequently interferes with the proper operation of purification plants, is purely a by-product of the political control under which so many water works plants operators- work. Men in charge of properties, or divisions of water works departments, are in operating positions not because of any fitness for the work, but because they happen to be, shall we say, precinct committeemen of the victorious political party. These impediments to the application of the knowledge that we have of the adequate control of water purification plants, affect the content of this discussion, but are somewhat tangential. The title is " Laboratory Control of Water Purification Plants." Fortunately for our purposes, Webster defines the laboratory as " the workroom of a chemist." That introduces pre- [4121

2 cisely the idea that is essential to the consideration of this topic. The entire purification plant is the workroom of the chemist. A purification plant is a laboratory that cannot be separately directed. I was somewhat amazed a to receive a communication from the head of a water department of a city of over 100,000 population, saying that a campaign was being waged by a consulting laboratory in his community to obtain a contract to carry on the laboratory work of his purification plant. The rejoinder is obvious to me, that if the water department wished to contract for the operation of a purification plant with a consulting concern, the operation to include definite and complete control, with certain criteria as to costs, etc., in the contract, the proposal might be entertained, but to detach the laboratorv control from the routine operation of a purification plant is inconceivable. The spirit of the water works laboratory must be the spirit of intelligently trained curiosity, and the moving spirit of a purification plant must be the application of that training and intelligent curiosity in an attitude of never being quite satisfied that things are right until they have been shown to be right. That type of control starts with the -moment that the raw water enters a plant. The first observation is that of the visible physical load, or turbidity, of the raw water. The referee contact with this observation may be carried on in the laboratory, but the practical hour to hour performance (and the per- -formance must be from hour to hour and not from day to day) should be in the hands of shift employees. They can be trained to do the work, especially if they know that their work is being adequately and frequently checked by the laboratory staff. The next step is the performance of simple field tests as to the adequacy of preliminary treatment. When Streeter's WATER PURIFICATION PLANTS4 Vol research indicated to all of us that practically two-thirds of the bacterial removal in the purification plant was effected before the water went to the filters, it should have made plain that the importance of control of preliminary operations needs to be emphasized. These field tests may be so simple as the trial filtration of the coagulated water to see that the finely divided material has been collected in the floc. The process may be extended to jar stirring tests, with varied doses of coagulant. They may even go so far as combination of these latter tests with tests for residual alumina. Wherever a test of this type is made, the control laboratory should do no more than referee the performance of those tests by the shift operators, or the laboratory should be staffed and in direct contact with the operators every hour of the day. Relatively few plants need to indulge in the latter type of organization. The great majority of plants are operated and the tests are adequately made by reasonably intelligent workmen. Performance of tests according to a definite outlined routine must be required at regular intervals on every shift. The next very valuable piece of field mechanism is the simple turbidimeter (Tyndall ray type indicator) so well developed by Bayliss in his work at Baltimore. This has an amazing capacity to indicate deviations from normal performance on the part of filter units and to flash emphatically to the eye and mind of an operator that something has occurred to break down the satisfactory performance of the sand layer. Its use does not require college training. The men simply need to be taught to correlate the indications given with past performance of the plant. In a purification plant where normal performance results in a turbidity of about 1/10 p.p.m., a deviation only up to '2 p.p.m. will be very evident, and

3 AMERICAN JOURNAL OF PUBLIC HEALTH 414 A pr., 1936 while the average consumer will have no knowledge of the change, and while it is' unlikely that such change will haveany adverse physiological effect upon the consuming public, the deviation is indicative of the immediate necessity of reviewing the purification processes which have preceded this stage in the treatment. By and large, the average plant performance will produce a safe drinking water if the indication given by the fine turbidimeter is good, and if the next observation, that of the amount of residual chlorine, is regularly made and adequately controlled. There is the strong fortress of plant control. A great deal of attention in the forthcoming edition of Standard Methods has been given to the determination of chlorine. The precision, or attempted precision, of statement of this test is designed to meet the needs of the laboratory, but in the day to day control of purification plants, if the laboratory reviews the hourly observations of residual chlorine at least once a day and correlates the plant observations with the laboratory records; the field tests do not need to be carried on with the precision that should be expected in the laboratory. At the same time, the field tests probably have a more direct bearing on the overall efficiency of plant operations than do the laboratory tests. When it is stated that the field tests do not need to be performed with the precision required of a laboratory test, one does not imply that basic considerations as to reasonable accuracy in handling reagents, reasonable cleanliness of apparatus, reasonable care in the handling of samples, should not be fulfilled. It is not implied that anyone can neglect the care of the orthotolidine solution, or expose reagents, standards and test samples to direct sunlight, nor by any means should one neglect to hold the sample treated with orthotolodine in the dark until the color development is complete. These important phases of the chlorine test can- be just as well understood by the shift men as by the expert chemist. It is necessary to confess a considerable degree of astonishment at the fact that, in spite of the directions in previous issues of Standard Methods against exposure to sunlight, many laboratories have been found to carry on all of their work and keep their permanent standards in the direct sunlight. Occasionally, one is led to think that possibly the simpler minded laborer of the plant could be used to read Standard Methods to the trained chemist, so as to be sure that the latter paid attention to all of the detail that he should. We have travelled through a purification plant controlling the preliminary treatment of the water, observing the residual turbidity after filtration and checking the efficiency of chlorination. Perhaps some of you will be shocked when it is implied that many of the other tests which we all make are " window dressing." That term is used to irritate some of you. Every operating test beyond the above brief list should be examined in the light of this question-" Just what does it contribute to the successful operation of the plant? " Obviously, if ammonia or carbon treatment is being used for taste improvement, and if prechlorination is practised, the laboratory staff will add to its daily routine the task of reviewing, by odor and associated tests, the efficiency of the dosage. Set dosages and foolish economy produce consumer bad will. Set dosages at fool-proof high rates waste money. The laboratory naturally must balance needs with dosage. The field of historical record of plant performance is the establishment of bench marks by which the value of the field tests above enumerated can be de-

4 Vol. 26 WATER PURIFICATION PLANTS 415. termined. We will probably all agree upon the bacteriological record as the principal one that meets this need. Shall that record include an enumeration of the bacteria? Koch's rule No. 2 was " To allow a complete and constant control of the bacterial efficiency of filtration, the filtrate from each single filter must be examined daily." The simplest record form which this examination can take is that of the bacterial count. At the same time it is likely to be indicative of all the facts that one needs to know about the individual filter. Is its performance equal to that of the other units? Has there been some misadventure in the sand layer? The 370 count will reasonably answer those questions. Shall we apply the 370 count to finished water and to distribution samples? The answer is in the affirmative, but not for the reason that would probably be given by many. The enumeration of bacteria in distribution samples frequently evidences lack of circulation, if the count is high. Lack of circulation might result in unpleasant tastes and odor, causing consumer complaints. The bacterial increase is likely to occur before the taste and odor develop. As a means of determining the hygienic efficiency of filtration, it is doubtful that the bacterial count has great value. With other conditions unchanged, there is considerable evidence that with a bacteria count in finished water of 10 or 100 or 1,000, no consumer reaction will result. The tradition persists that high counts are associated with lack of safety. High counts of heterogeneous organisms probably indicate improper operating control. High counts of homogeneous groups of organisms may indicate a simple unloading, or too long storage, or too little draft from a main. When we make an estimate of the presence and density of members of the coli-aerogenes group, we are building up the historical record that is most serviceable as a bench mark in plant operation. To what extent should coli-aerogenes records be accumulated? Under present-day conditions one can reasonably expect of a well controlled purification plant that an accurate record of coli-aerogenes density under all load conditions in the raw water, especially the peak loading, be made. One can also assume that with a somewhat lesser degree of accuracy, water in the various intermediate processes of purification should be checked. The filter effluent before final chlorination should, in the United States, be checked with the Treasury Standards, namely, the examination of five 10 ml. portions, to the end that, as a general operating result, the filtered water before final chlorination meets -the requirements of the Treasury Standard. In other words,- there should be a shade of disappointment on the part of the plant superintendent if the efficiency of the prior phases of the purification process has not been great enough to make chlorination unnecessary, except as a final extra factor of safety. The water as delivered by the plant should not only be examined, in the United States, in the five 10 ml. portions of the Treasury Standard, but also an equal number of 100 ml. portions should be examined. The reason is that if the plant operator sets as his yard-stick the simple terms of the Treasury Standard, he has no data aside from compliance or noncompliance with the standard. If, however, he sets as his yard-stick the absence of coli-aerogenes organisms from the great majority of the 100 ml. portions examined, he not alone has an added feeling of assurance, but when deviations occur that indicate the presence of the group in the 100 ml. portions, they should occur before such deviations would appear in the 10 ml. portions, thus an opportunity may be given to review and correct the

5 AMERICAN JOURNAL OF PUBLIC HEALTH 416 Apr., 1936 faults in the procedure that led to the deviation in the larger samples examined. The finished water plantings should also extend to an equal number of 1 ml. portions. Only in this way will an adequate appraisal of maximum density be had when and if some misadventure reduces the normal efficiency of operation. An intelligent operator who feels the weight of his responsibility to the thousands of people dependent upon him for safe water will not omit any finding of fact that, even temporarily unpleasant, eventually adds to the records that make future operation safer. The useful working tool given laboratory workers by the option of confirmation of coli-aerogenes by planting in selective liquid media makes possible the production of a greater volume of mathematically defensible records. With the development of correlative data that indicate the close approximation of the confirmed technic adopted with the full complete test, the operator will find himself in a position to appraise more intelligently the significance of steps in plant operation in the terms of coli-aerogenes density. American practice with relation to coli-aerogenes group definition puts a somewhat higher requirement upon water supply methods than is common to many other countries. We are all familiar with the discussion that has gone on for a number of years with relation to the use of certain selective media for primary planting of water samples. The broad implication of the use of lactose broth, as contrasted with selective broths, is that by using the former, not only are certain coliaerogenes forms that are freqtuently called " attenuated " incltuded in the findings, but also a class of organisms which probably are not essentially associated with human sewage pollution but with processes of destruction of vegetation. If the goal is set of removing all these from the finished water, instead of removing only the definite fecal strains of coli, the hygienic quality of the supply automatically becomes higher. Certain studies in this country, have indicated that the sanitary survey correlates better with the coliaerogenes findings from primary planting in a selective medium than with similar findings from primary planting in the more catholic lactose broth. In other words, it is evident that definitely bad sanitary backgrounds of samples are associated with positive findings in the selective media, and that the routine process in this country includes those doubtful cases of sanitary surveys where perhaps there is no specific evidence that could be correlated with the presence of the coliaerogenes group. But can we not agree that those border-line conditions should be improved? American water supply practice has met fairly well the financial and physical requirements necessary under the present method of measuring water quality, and while the correlation of the sanitary survey may be a bit more definite, if the other method is followed,. it is also evident that the degree of protection to the consumer against adverse conditions would be lessened just in the degree that the laboratory control of water supplies narrowed itself to search for more specific organisms. Perhaps when political control of water departments is not so obvious, when the training of purification plant operators is more widely insisted upon, and when a shade more knowledge is at hand as to the precise meaning of some of the tests we make, it may be possible to narrow the category of organisms that we call coli-aerogenes; but that time is not yet here. We have mentally travelled through the purification plant; observed the shift men making many necessary

6 Vo'l. 26 WATER PURIFICATION PLANTS 417 routine tests vital to good performance; we have set up the technically trained staff as a referee group, principally engaged in training and maintaining the efficiency of the operator as a bench chemist. We have observed that the technical staff, in making additional tests, has made them because each one had been shown to contribute definitely to the excellence of performance of the plant. They have also made records in terms of bacterial efficiency, and have correlated' these records with the simple field tests. What else is there for the technical staff to do? A' great deal.' They are engaged in research studies preparing to meet the' problems of tomorrow. A New Method for Estimating Population THE March 9 issue of New York State Health News describes a new device for estimating population increase: The population of New York State on July 1, 1935, was 13,226,417 and will increase by July 1, 1936, to 13,345,909, according to a recent estimate by the Division of Vital Statistics, State Department of Health. These figures are based upon the assumption that the relative growth of the population of the cities and counties of the state since the last federal census of 1930 was the same as that of the entire country. The estimates previously employed by the department were computed by the " arithmetical method," which assumes that the annual increase in population after a census is equal to the average annual increase during the last intercensal period. The new estimate for the state for 1935 is less by 468,000 than the estimate formerly used. The new figures admittedly have the single virtue of being, on the whole, less inaccurate than those hitherto used. The division is now investigating the possibility of a permanent solution of this most important problem through the development of sources of local authentic information, by means of which the estimates could be currently modified in keeping with the movement of population. Under normal conditions the arithmetical method produces reasonably satisfactory results. The years following 1930, however, were clearly not normal. The growth of the population has definitely slowed down because of the continued decrease in the birth rate and the almnost complete cessation of foreign immigration. In the 10 year period the net immigration averaged over 300,000 a year, while in the 5 year period the number of aliens who departed from this country exceeded the number of aliens admitted by almost a 4 million. One has to consider also the important additional fact that as a result of the depression the movement of population within the country has undergone a marked change. In , as a direct consequence of rapidly diminishing opportunities for employment, the hitherto prevalent movement from country into city was reversed. There is reason to believe that because of improvement in the economic situation, the trend after 1933 has again become cityward. Under these conditions, arithmetical estimates had no longer the degree of dependability that was formerly attached to them. It was felt inadvisable, however, to make any change in the established procedure because there was hope that a federal census might be taken in This expectation has not materialized and it was therefore necessary to abandon the arithmetical estimates as being entirely too high and misleading. Various experiments led the Division of Vital Statistics to decide, until a better way could be found, to adopt with slight modifications the method developed by the Census Bureau, according to which " the' computed increase in the population of the country as a whole [is] distribu-ted among the states, cities, and counties in proportion to the share which each of these areas had in the increase between 1920 and 1930."