Februarv. 1931
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
209
Technic of Stream-Pollution Investigations' F. W. Mohlman, T. L. Herrick, and H. Gladys Swope THES A N I T A R Y DISTRICT OF
CHICAGO,
XTESSIVE studies of the pollution of the Illinois River have been made by the Sanitary District of Chicago prior to and since the opening of the Drainage Canal in 1900. A survey was made by the U. S. Public Health Service in 1921 and 1922 ( I ) , and the data collected were used by the Engineering Board of Review of the Sanitary District of Chicago as a basis for extensive calculations concerning the present and future dilution requirements of this river. The Board of Review recommended that further and more extensive studies be made. These studies were started in 1925 and are still in progress. Attention has been directed primarily to a study of the oxygen balance as measured by the relation of dissolved oxygen and biochemical oxygen demand. I n the course of the studies many points of special interest have been investigated and improvements in the technic of sampling, analysis, and compilation have been made. It is the writers' intention, therefore, not to present any summarized average results showing conditions from month to month or year to year, but rather to select topics of more general interest, the discussion of which will be applicable to similar investigations of other streams. This discussion may serve to draw attention to certain factors which may have been overlooked in other investigations and, furthermore, the technic that has been adopted may be of some general interest.
E
Jomple
Figure 1-Selection
r'8
845
WABASH
AVB , C H I C A G O . ILL.
luted stream an hourly variation in concentration may occur similar to the well-known variation in concentration of sewage throughout the 24 hours. I n the lower reaches of the same stream the same, if not greater, variation may be found in the dissolved-oxygen content due to the presence of green and blue-green algae which give off large amounts of oxygen in the presence of sunlight. The great width of streams as compared with sewers and conduits makes it necessary to consider the advisability of taking samples a t various points across the stream. The sampler then has to decide whether to take top samples or bottom samples, a single sample in the channel, or three or more samples across the stream. After selecting the proper sampling location he must decide whether the hourly variation is large enough to require more than one sample during the 24 hours. The writers have found it necessary t o take more samples than one per day in order to obtain a true picture of the oxygen conditions of the Illinois River. although this may not be necessary in other streams. In selecting the sampling points a cross-sectional survey has been made a t practically all of the stations similar to the one reported here for Wesley City, just below Peoria. Current-meter tests were made a t various points across the stream and samples were taken a t the same points. These sarnples were analyzed for dissolved oxygen and biochemical
obtained
of S a m p l i n g P o i n t at Wesley City, Illinois River Investigations
With the exception of the studies made by the U. S. Public Health Service and the Engineering Board of Review, stream pollution surveys are usually of a somewhat qualitative nature, consisting of chemical, biological, and hydraulic observations which show the condition of a river a t various points, but which are not complete enough to serve as a basis for computation of oxygen balance, dilution ratios, or re-aeration coefficients. Since facilities were available for making a complete study of oxygen relations by use of a large number of samplers, the writers have been enabled t o obtain hourly samples of dissolved oxygen a t sixteen stations for a period of a year or more and a t ten stations for the last five years. Sampling The sampling of a large river presents more difficulties than the sampling of sewage or effluents. In a highly pol1 Received November 20, 1930. Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930.
oxygen demand and weighted averages were computed in order to determine the proper location of a single sampling point. The results of this survey a t Wesley City are shown in Figure 1. It will be noted that there would be an appreciable error at this location if a sample were taken at three points across the stream and averaged Likewise it was necessary to take a weighted rather than a straight average, as shown in Table I. The gagings have been checked several times and, while there is some change between low and high water, the actual distance the point has had to be moved has not been great. With regard to surface and bottom sampling, there may be more danger in this procedure than value. Unless the exact depth is known, the sampling can may approach too closely the beds of sludge deposits which are known to occur in the Illinois River. A deep sample will show a lower dissolved oxygen and higher biochemical oxygen demand than a surface sample, but it is a question whether this represents the condition of the flowing stream or merely a local condition.
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If the samples are taken too close to the bottom a very low dissolved oxygen may be obtained a t practically all places where sludge deposits are known to exist. Table I-Stream
Survey a t Wesley City
STATION FROM WEST
&DAY
BANK DISCHARGE B . 0. D . Cu. f t . / s e c . P. 9. m. 1 285 31.2 2 19.7 585 9.9 3 702 4 1180 7.8 1928 5 5.9 6 1916 3.4 2337 2.8 7 8 2234 2.1 1241 2.5 9 10 682 2.2 341 2.0 11
--
Total Average
13431
89.5 8.14
DISSOLVED U'EIGHTED OXYGEN B . 0 . D .
WEIGHTED
DISSOLVED OXYGEN
P. p . m. 8892 11524 6950 9204 11375 6514 6544 4691 3103 1500 682
0.8 2.8 4.9 5.0 5.9 6.6 6.2 6.8 7.0 6.4 6.7
-
59.1 5.37
-_
228 1638 3440 5900 11380 12640 14500 15180 8678 4360 2285
-
70979 80229 5.2Sp.p.m. 5.97p.p.m.
Hourly Variations
The extent of hourly variations at Lockport is shown in Figure 2. These results indicate the magnitude of variation in the upper highly polluted part of the river. The U. S. Public Health Service ( I ) attempted to correct results of a single daily determination for the hourly variation in concentration and flow. For the past several years the hourly variation in flow has not been nearly so great as in 1921 and 1922, but the variation in dissolved oxygen and B. 0. D. has been large a t certain periods of the year. In addition to the hourly variation a t Lockport, a very marked daily variation has been noted throughout the week, with particularly low results each Monday, following the Sunday shutdown of industries in Chicago. The plotted daily results obtained a t Lockport through 1928 are shown in Figure 3. The weekly variation caused by industrial wastes is shown by the results for dissolved oxygen and B. 0. D. The rapid drop in dissolved oxygen in the early spring is noteworthy, likewise the slow increase during the fall. I n other polluted streams i t is probable that this rapid decrease in dissolved oxygen occurs a t the onset of warm weather. This effect is accelerated by the increased activity in sludge deposits following their dormant condition through the winter months. The hourly variation in dissolved oxygen due to photosynthesis occurs in the lower reaches of the upper Illinois River, between Chillicothe and Peoria, where the river widens out to form Lake Peoria. This phenomenon is by no means new, but was studied and reported by Professor Palmer in his classic studies of the Illinois River prior to and following the opening of the Drainage Canal in 1900. Typical results for two days in midsummer of 1927 a t Averyville are shown in Figure 4. The difference between a sunny day and a cloudy day is quite marked. The examples given above indicate that one must be very cautious in accepting a single daily sample a t a sampling station as representing the average conditions a t that point in the Illinois River. The differences are usually not great enough to warrant discarding analyses of single samples, particularly when they are reenforced by biological observations and field investigations, but the large differences found a t times from hour to hour make it advisable to recommend that such hourly variations be studied in all surveys of stream pollution. In our control of large sewage treatment works we would be unlikely to give much weight to analyses of a single catch sample. The collection of composite samples is of fundamental importance in sewage sampling Composite samples may frequently be of equal necessity in stream surveys.
Vol. 23, x o . 2
Biochemical Oxygen Demand
The &day 20' C. B. 0. D. test was used throughout these studies, but it was early recognized that it would be necessary to obtain information for rates of B. 0. D. on longer periods of incubation. In a previous publication (3)it was shown that, for Illinois River samples, no constant relation existed between the 5-day demand and either the complete firststage demand or in fact any longer period of incubation. The 5-day demand may, as it were, be "lifted" off the B. 0. D. curve a t almost any stage of oxidation; consequently, it is unsafe to use any fixed factor for calculation of longer or shorter periods of incubation. With this precaution in mind for several years weekly tests have been made a t each sampling station of rates of B. 0. D. with incubation a t 20" C. from 1 to 40 days. These curves indicate the degree of oxidation according to the point of inflection between the first and second stages. This occurs after 12 to 14 days a t 20" C. with freshly polluted water; increasing stabilization may be noted by the shortening of the first stage. Entrance of fresh pollution again extends the transitional period between the first and second stages. For example, the average of weekly 40-day demands extending over a year are shown for Averyville and Pekin in Figure 5. The transition occurs after 5 or 6 days above Peoria, but the influx of fresh pollution brings this up to 7 or 8 days a t Pekin. The writers
HOURS Figure 2-Hourly Variations in Dissolved Oxygen and Oxygen Demand, Lockport
have records far downstream which indicate that for samples far distant from fresh pollution the rates of B. 0. D. may approximate a straight line or the curve appears to be in the second stage, that of nitrogen oxidation. Curves at Chillicothe for summer and winter conditions are shown in Figure 6. The first stage is extended to 12 days in winter owing to the slower rate of oxidation, while in summer the more rapid oxidation shortens it to 5 days. While the information with regard to long-time rates of B. 0. D. has been considerably extended, it is still somewhat difficult to use these curves in a precise mathematical relationship. With more knowledge concerning the exact state of oxidation of the organic matter, it might be possible to use these curves with more confidence. The writers believe, however, that it is necessary to go beyond a mere consideration of the 5-day demand in studies of stream pollution.
February, 1931
INDUSTRIAL AND ESGINEERING CHEMISTRY
Figure 3-Average
211
Daily Results, Lockport, 1928
Effect of Sludge Deposits
The solids from untreated or partially treated sewage that accumulate in a stream settle to the bottom, there to form sludge deposits of more or less thickness and greater or less putrescibility. These sludge deposits are probably of more importance with regard to conditions of nuisance in polluted streams than any other single factor. The Engineering Board of Review found that their effect on the oxygen content of the Illinois River was of greater importance than the
sludge throughout the flowing river by ebullition of gas. As long as the sludge remains quiescent on the bottom of the river it probably has no great demand for oxygen, but as soon as the solids are carried up by discharge of gas a very rapid demand for oxygen occurs. A few simple laboratory experiments to illustrate these facts have been made by C. L. Adams in the Joliet laboratory. Samples of sludge from the Drainage Canal were quietly introduced through a pipet over the bottom of 8-ounce bottles which had been filled with oxygen-containing water. In the first experiment 10 cc. of sludge were placed in one bottle and 25 cc. in the other. After standing quietly a t 20" C. for 2 hours the oxygen content of the supernatant water was determined. It was found that there was a loss of only 0.2 p. p. m. in both bottles; the loss was no greater with 25 cc. than with 10 cc., the surface area being the same
HOURS Figure 4-Effect of S u n l i g h t on Dissolved Oxygen, Averyville, August, 1927
effect of the current discharge of sewage, practically all untreated. During July and August, 1922, sludge deposits between Chicago and Chillicothe consumed 1,270,000 pounds of oxygen per 24 hours, while the current flow of sewage consumed only 741,000 pounds per 24 hours. The study of sludge deposits is therefore one of the most important requirements of a stream survey. These sludge deposits may be mapped, classified, and analyzed, but it is difficult t o utilize the results in any satisfactory manner, because the relative importance of depth and area is not known. The writers' observations indicate that the depth of the deposits is not very important, but that the factors of most importance are the area of the deposits and the rate of dispersion of solid
DAYS Figure 5-Average R e s u l t s Year 1929 of Weekly 40-Day B 0. D. Determinatidns, Averyville a n d Pekin
in both cases. In two more bottles, however, which were inverted every 15 minutes for the first half-hour and a t intervals of 30 minutes thereafter, the sample containing 25 cc. of sludge had lost 6.5 p. p. m. while the one containing 10 cc. had lost only 3.5 p. p. m. These results show the great difference between quiescent and dispersed sludge.
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Vol. 23, No. 2
for the summer of 1925. The barometer dropped suddenly from 29.7 to 28.43 from September 8 to 9,1925. The B. 0. D. increased markedly and the dissolved oxygen dropped on the 9th a t Brandon’s Bridge, while at Morris, 221/2 miles downstream, the marked increase in pollution occurred the next day.
I a LL
Analytical Procedures
d
d
m
Figure 6-Average
DAYS S u m m e r a n d Winter 40-Day B. 0. D. Determinations, Chillicothe
Another test was made over a longer period of time. Each bottle received 25 cc. of sludge. One set was allowed to incubate for 33 hours. The results are shown in Table 11. The depletion of oxygen was very slow up until 22 hours. At some time between 22 and 33 hours, gas formed and carried a considerable quantity of sludge to the top. The depletion of oxygen was greatly increased by this dispersion, as shown by a loss of 3.6 p. p. m. from 22 to 33 hours, whereas only 2.6 p. p. m. had been lost during the first 22 hours of incubation, while the sludge remained quiescent on the bottom of the bottle. By way of comparison, one bottle under the same conditions as above was inverted once every half-hour. The oxygen was practically depleted in 3 hours, with only 0.4 p. p. m. remaining.
I n order to round out the chemical investigations daily analyses have been made of the river water for nitrites, turbidity, and pH. The nitrite determination has been made primarily in order to determine when, if ever, it is necessary to use the permanganate-oxalate modification of the Winkler method. The writers’ procedure has been to use this modification when the nitrite content exceeds 0.1 p, p. m., which occurs only rarely. The turbidity cannot well be measured in composite samples extending over a week or longer, and likewise the pH must be determined immediately. For sanitary chemical analysis 10-day composites have been shipped to the main laboratory in Chicago for complete analysis. While the results of these analyses are of interest, they have not been of any great value for purposes of computation of stream conditions.
Table 11-Consumption of Oxygen b y Quiescent Sludge 22 33 3 HOURS 10 6 DISSOLVED 3 OXYGEN HOURS HOURS HOURS HOURSH o u ~ sMIXED ~ P . 9 . m . P . 9 . m . P.9.m. P . 9 . m . P . Q . ~ P. . 9 . m . 8.4 8.4 8.4 8.4 Initial 8.4 8.4 5.8 2.2 0.4 6.4 Remaining 8.3 7.5 6 . 2 8.0 2.6 Consumed 0.1 0.9 2.0 a Sludge at top of bottle.
It thus appears that the oxygen demand of sludge deposits is greatly intensified when the solids are gas-lifted. I n a practical way this phenomenon has been noted in the upper part of the Illinois River, with a falling barometer serving as the agent of dispersion. As the sludge lies quietly on the
25
d 320
DAYS - S E P T , 1925
Figure 7-Effect of Falling Barometer on Dispersion of Sludge t h r o u g h Flowing River
bottom of the river i t is filled with gas and is under a delicate equilibrium with respect to gravity. A rapidly falling barometer will permit the gas to expand, thus bringing large volumes of sludge to the surface. The results of such occurrences have been noticed in sudden waves of gas attacks a t Morris, shortly below the polluted Lake Joliet in the upper part of the river , A typical example is shown in Figure 7
Figure (I-Average Monthly Results 1929, of pH Value a t Various Illinois River S a m p i i n g Stations
For a complete stream investigation it is desirable to have biological and bacteriological studies. With regard to the Illinois River,which is not used for drinking purposes throughout its length, the latter studies are not of primary importance. Biological studies are, however, of considerable value. The writers have relied on the excellent biological studies that have been made for many years by the Illinois State Department of Natural History in cooperation with the Illinois State Water Survey, and also there is information of great value in the biological studies made by W. C. Purdp, of the U. S. Public Health Service, during 1921 and 1922. In studies of dilution water for B. 0. D. determinations some preliminary results obtained with synthetic dilution water consisting of distilled water to which has been added 500 p. p. m. sodium bicarbonate have been reported i n a former article (3). It was found necessary to develop such a synthetic water on account of the great variety of waters available in the cities where the branch laboratories of the Sanitary District were established. These tap waters were mostly from deep wells, some containing iron, others containing comparatively large amounts of ammonia and nitrate nitrogen, and others containing a variable amount of organic matter, I n view of the excellent results with the sodium bicarbonate water this has been used for the past three or four years, a t first with 500 p. p. m. sodium bicarbonate and more recently with 300 p. p. m. The reduc-
February, 1931
I,VDUSTRIAL AND ENGINEE'RIATG CHEMISTRY
tion in concentration was made in order to obtain a less alkaline water. The pH of the 300 p. p. m. sodium bicarbonate was usually between 7.7 and 8.3. The results of approximately 1900 determinations of p H in the Illinois River laboratories of the Sanitary District of Chicago for 1929 are shown in Figure 8. These curves indicate that, with the exception of Lockport and Morris, the pH generally varied between 7.5 and 8.2. In view of this rather alkaline reaction of the river water it has been concluded that the use of the sodium bicarbonate water is preferable to that of distilled or tap water. Proposed improvement of this synthetic water has been discussed elsewhere ( 2 ) . The selection of the dilution water for B. 0. D. tests in stream-pollution studies depends upon many local conditions, particularly the suitability of the available tap water. Where such
213
waters vary or give high blanks or cannot be stabilized successfully, it is our belief that synthetic water is preferable. I n the course of the work on the Illinois River various types of incubators have been studied. The general practice is to use an air-tempered incubator, but very good results have been obtained by G. R. Barnett a t the Peoria laboratory with a water bath thermostatically controlled. The results indicate that such a water bath can be controlled much more accurately than an air incubator of the type used by the writers and the cost of operation is less. Literature Cited (1) Hoskins, Ruchhoft, and Williams, U. S. Pub. Health Service, Bull. 171 (1927). (2) Mohlman, Sewage TVoorks J., 2, 375 (1930). (3) Mohlman, Edwards, and Swope, IND. END. CHEM.,19, 242 (1928).
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Some Interrelationships of Plankton and Bacteria in Natural Purification of Polluted Water' C. T. Butterfield and W. C. Purdy U. S. PUBLIC HEALTH SERVICE,CINCINNATI, Oar0
Based on the results of a series of biological and A preceding paper ( 1 ) has HE abstraction of dischemical experiments, the theory is advanced that the described the p r e p a r a t i o n solved o x y g e n froni chief function of certain plankton in the biochemical and characteristics of a simple polluted water during oxidation process is to keep the bacterial population r e p r o d u c i b l e dextrose-pep the natural purification procreduced below the saturation point and thus to provide tone solution. Unless otheress is a well-known phenome conditions suitable for continuous bacterial multiwise stated, this standard non. It is also well known plication and as a result provide for more complete m e d i u m was used in the that the amount of dissolved oxidation. studies here reported. oxygen used up is definitely Support is given to this theory of the function of the related to the amount of polOxygen Depletion in Abplankton by the results obtained in experiments where lution present. While these sence of All Living the limiting numbers of bacteria were reduced by facts in regard to the natuOrganisms physical and by chemical means. Such reductions in ral purification of polluted bacterial numbers were invariably followed by renewed Suitable tests were made water are definitely known, bacterial multiplication and oxidation. to determine the extent of the mechanism by which the o x y g e n d e p l e t i o n in the oxidation is accomplished is only assumed. For instance, if a portion of polluted water is dilute medium: (a) in the absence of all biological forms, examined many bacteria and plankton are found. If all of and (b) in the presence of dead cells of B. aerogenes. No these organisms are killed or removed from the water, oxida- appreciable oxygen depletions were observed in 10 days. tion ceases. The part that each of these biological factors Oxygen Depletion in Presence of Bacteria Only plays in the progress of events, together with their interreactions, constitute the subject of this study. Studies were carried on with B. aerogenes and with bacteria Purdy and Butterfield (S), in their study on the effect of plankton animals upon bacterial death rates, showed quite other than B. aerogenes. All were in pure culture. The clearly that certain of the protozoa are responsible for the major portion of the work was done with B. aerogenes in an destruction of large number of bacteria in the natural puri- attempt to establish definitely the deoxidizing properties of fication process. Unfortunately their bacteria and plankton this organism under standard conditions, so that, in turn, results were not complemented with collateral data on the the effect and the function of the plankton, growing in pure chemical changes produced. culture and in combination with B. aerogenes, might also be I n the present work preliminary studies were made with definitely established. heterogeneous combinations of bacteria and plankton. With B. aerogenes, procedure was as follows: The dilute These studies, while instructive, presented too many vari- standard medium was prepared in 10-liter quantities, and ables to be of real value. sterilized. After cooling and vigorous agitation, the medium Further studies, with adequate control, were next under- was inoculated with B. aerogenes. The temperature of the taken t o determine oxygen depletion in a medium containing carboy of inoculated medium was next adjusted to approxino living organisms; oxygen depletion when bacteria only are mately 20 O C., the contents thoroughly mixed, then allowed present, in pure culture and in mixed culture; oxygen de- to stand quiescent a few minutes to permit escape of enpletion when no bacteria, but plankton only, are present; and trained air. The inoculated medium was siphoned to sterile oxygen depletion when bacteria and plankton are both pres- dissolved oxygen bottles with elaborate precautions to preent, in pure culture and in mixed culture. vent contamination. The dissolved oxygen bottles filled in this procedure were Received September 20, 1930. Presented before the Division of numbered in consecutive order. Initial determinations were Water, Sewage, and Sanitation Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930. made of the bacterial and dissolved oxygen contents of some
