give an average most probable number of 970 per 100 ml. t o comply with the 95% requirement, compared with an average of 2240 per 100 ml. to meet the 80% requirement for the amperometric method. The limitations dictated by the statistical method are even better illustrated by comparing 15- and 30-minute contact periods for settled sewage. The unusually poor correlation for the longer contact period, as previously discussed, dictates the use of more chlorine than for the 15-minute period when o-tolidine is the control method. I t is necessary to provide higher residual chlorine for the longer contact period because the average must be reduced to 170 per 100 mi. while 970 per 100 ml. suffices for the 15-minute period, the 90% requirement being the controlling factor in both cases. Use of a chlorine method giving unnecessarily poor correlation means application of excessive quantities of chlorine and waste of money.
Summary and Conclusions The o-tolidine and two amperometric titration methods have been compared with respect to correlation between bacterial kill and residual chlorine for three types of domestic sewage. blodification of the usual amperometric titration failed to improve the correlation. In all samples the amperometric method indicated higher values than o-tolidine. I n trickling filter effluent correlation was equally good for both
methods, in spibe of the difference in absolute values of residual chlorine. I n settled sewage and chemical treatment effluent the amperometric method gave significantly better correlation. It is apparently less affected by organic matter. As most stream standards specify not only average bacterial count but also a statistical upper limit, poor correlation means an unnecessarily low average count and excessively high chlorine to comply with this limit.
References (1) American Public Health Association, New York, “Standard Methods for the Examination of Water and Sewage,” 9th ed., 1946. ( 2 ) Eliassen, R., Heller, A. S . ,a n d Krieger, H. L., Sewage Works J . , 20, 1008 (1948). (3) Eliassen, R., and Krieger, H. L . , SewaQe and Ind. Wastes, 22, 47 (1950). (4) Hoel, P. G., “Introduction t o Mathematical Statistics,” Xew York, John %‘iley & Sons, 1946. (5) Knox, IT. E., Stumpf, P. K., Dreen, D. E., a n d Auerbach, V. H., J . Bact., 5 5 , 4 5 1 (1948). (6) Marks, H. C., Joiner, R . R., and Stiandskov, F. B., Water and Sewage Works, 95, 176 (1948). ( 7 ) Ohio River Valley R7ater Sanitation Commission, Cincinnati, Ohio, “Bacterial Quality Objectives for t h e Ohio River,” 1961. (8) Siggia, S., and Edsberg, R. L., Anal. Chem., 20, 938 (1948).
RECEIYED for review November 21, 1952.
ACCEPTED December 3, 1952.
Disinf ectio Wastes by Chlorin H. Heukelekian, Robert Day1, and Raymond Manganelli NEW JERSEY AGRICULTURE EXPERIMENT STATION, RUTGERS UNIVERSITY, RUTGERS, N. J.
The purpose of this study was to obtain the best chemical yardstick of residual chlorine indicating the effectiveness of chlorination for disinfection of mixtures of wastes and sewage in terms of the most probable number (MPN) of coliform organisms remaining. The three methods of residual chlorine determinations used in this study were o-tolidine, modified starch iodide, and amperometric methods. The residuals obtained b y these methods with different dosages of chlorine applied to sewage; sewage plus spent yeast broth; sewage plus titanium pigment waste; waste from a chemical manufacturing plant; and municipal sewage containing large volumes of various industrial wastes were compared and correlated with the MPN of coliforms with the use of statistical methods. The results obtained indicated approximately similar magnitudes of residuals b y the modified starch iodide and amperometric methods with lower values for the o-tolidine method for nearly equivalent MPN of coliforms remaining. Statistical analyses of the results showed only a fair correlation between the residual chlorine determined b y the three methods employed and the coliform organisms remaining. This is primarily due to the inaccuracies of m.p.n. determinations which do not allow a more precise evaluation of the differences in the method of residual chlorine determinations.
I
N THE evaluation of the action of chlorine as a disinfecting agent the ultimate criterion should be the number of coliform organisms remaining in the effluent. The percentage reduction of coliform organism as a result of chlorination, although valuable as an index of efficiency, is not significant with respect to acceptability of the effluent from the regulatory standpoint whatever the standards may be. The coliform organisms remaining in the effluent after chlorination are determined by the dilution technique and are expressed in terms of most probable numbers. The technique of enumeration and mathematical expression on the basis of the most probable numbers are subject to great inherent inconsistencies even with a large number of replications which are not 1
Present address, Wallace & Tiernan Co., Inc.
1004
commonly employed under routine conditions. A sa basis of practical control of the chlorination process, the enumeration of coliform organisms has little value as the results are obtained some 4 days later. For these reasons a chemical short cut such as residual chlorine determination is employed under practical conditions to indicate the quality and the acceptability of the effluent. The residual chlorine determination is a test involving the contact of the chlorine with the substrate for a definite length of time. The portion of chlorine which has not reacted with the various ingredients in the substrate is then determined by one of several methods. There are a number of reactions which take place with the various materials in the substrate. The nature and concentration of these materials vary with the different substrates and even with the same substrate from time to time.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 45, No. 5
Water Treatment The most commonly employed tests for the determination of residual chlorine are the o-tolidine and starch iodide tests. The o-tolidine test measures the free chlorine and also the chloramines which are formed from the interaction of chlorine with ammonia present in the water. I n addition, organic chlorine compounds are formed, which with the chloramines have disinfecting powers different from those of free chlorine. Iron and sulfides also react with chlorine, producing products with
\
\
1. Spent yeast broth, representing soluble organic wastes 2. Titanium p i p e n t wastes, representing an inorganic waste consisting of sulfuric acid and ferrous sulfate 3. Organic chemical plant wastes containing dyes, pigments, pharmaceuticals, textile intermediates, and rubber chemicals 4. A sewage obtained from a municipal plant that receives a high percentage of laundry, dry cleaning, metal plating, dye house, printing and lithographing inks, asphalt and asbestos shingles, insula&on board, paint and varnish, and medical supply house wastes.
HIGHLAND PARK S WAGE
\ \
IO
-
I \
z
The work entailed obtaining these wastes from time to time from the respective plants. The three wastes obtained from industrial plants were mixed with settled domestic sewage in the ratios of 1 volume of waste to 9 volumes of sewage and 9 volumes of waste t o 1 volume of sewage. This step was considered necessary for the following reasons:
IO
0.1
0
2 RESIDUAL
4
6
- P P M.
Figure 1. Relationship between Various Types of Residuals and Average MPN in Chlorinated Highland Park Sewage Represented as Line of Best Fit
*
no disinfecting power. These and many other reactions between chlorine and various ingredients of the substrate reduce, either completely or partially, the disinfecting power of chlorine. Thus it is difficult t o predict the disinfecting capacity of chlorine on the basis of the residual chlorine test. The pH value also changes the rate and the direction of these reactions, adding another complicating factor. In disinfecting water these difficulties are not pronounced because the types and concentrations of materials capable of reacting with chlorine are few in number and low in concentration. However, sewage contains a relatively large variety and high concentration of organic and inorganic compounds which react with chlorine. Consequently the difficulties encountered when employing the residual tests as a method of controlling the bacterial quality of the effluent increase measurably. The complexity of sewage is also subject to variation because of the discharge of various types and concentrations of industrial wastes into municipal sewers; the wastes vary from time to time and place to place making the problem of the control of disinfection even more difficult. There are situations where disinfection of industrial wastes is practiced with or without prior treatment on the premises. This paper is a report of a preliminary study of the disinfecting power of chlorine in sewage containing various proportions of some typical industrial wastes. The work was sponsored by the subcommittee of the Federation of Sewage and Industrial Wastes Association, Committee on Standard Methods, under the chairmanship of W. Rudolfs. The work was done by members of American Cyanamid Go., Calco Chemical Division; Wallace & Tiernan Co.; and the Department of Sanitation staff a t Rutgers University. The committee has set forth immediate and ultimate objeotives: (1) Selection of residual chlorine determination (otolidine, starch iodide, or amperometric method) which can be best correlated with the bacterial quality of the effluents from several chlorinated industrial wastes and sewage mixtures. This
May 1953
Methods and Procedures The following wastes were selected as representative of the various types of wastes:
100
a 2
represents the factrfinding stage of the program and should lead, if necessary t o (2) modifying or improving the present methods, or developing new methods which will be specially and more or less generally applicable for the disinfection of sewage containing industrial wastes or of industrial wastes themselves.
1. To ensure the presence of coliform organisms in the wastes 2. To determine whether the degree of dilution has an effect on the chlorine requirements 3. T o calculate the chlorine requirement of a waste after it has been discharged into a sewer.
The mixture of sewage and industrial waste obtained from a municipal plant was not diluted with sewage. 1000
100
f \
10
z a
r 10
01
0
I 2 RESIDUAL. P P M
3
Figure 2. Relationship between Various Ty es of Residuals and Average MPN in Ch&rinated Manville Sewage Represented as Line of Best Fit
The wastes were adjusted to p H 7.0 if needed before mixing with sewage in order to eliminate the pH variable. Three mixtures were prepared for each waste for each run, the one being the domestic sewage used as a diluent and the other two the 10 and 90% wastes. To a number of samples containing each of these mixtures, increasing quantities of chlorine water were added. At the end of 30 minutes of contact time the :esidual chlorine was determined by o-tolidine, amperometric, and acidified starch iodide methods. T o the remaining portion of the samples sufficient sodium sulfite was added t o destroy the excess chlorine, and coliform determinations were made by planting serially into lactose broth tubes triplicate portions of a number
INDUSTRIAL AND ENGINEERING CHEMISTRY
1005
of dilutions. The positive resumptive tests were confirmed after 48 hours at 37" C. in bri&ant green bile. The results are expressed as the most probable number (MPN) of coliform organisms on the basis of brilliant green bile broth positive tubes after an additional 48 hours incubation at 37" C. This constituted one run and the procedure was repeated ten different times with each waste mixture. The numbers of the coliform organisms in the nonchlorinated sewage and sewage and waste mixtures were also determined but are not presented in this paper.
1000
100
chlorine gives higher amperometric and starch iodide residuals than o-tolidine residuals with the same MPN. This is in accordance with the findings of Strandskov, Marks, and Horchler ( 3 ) ; Marks and Joiner ( I ) , and Marks, Joiner, and Strandskov ( 2 ) . Similar relationships are indicated with hfanville (Figure 2 ) and Rutherford sewage (Figure 3)-namely, that amperometric and starch iodide residuals are a t a higher level than orthotolidine residuals for a given MPN. The comparison of M P N on the basis of amperometric residuals for the three sewages is given in Figure 4, which indicates wide differences in the numbers of surviving coliforms with a given amperometric residual with different sewages. The effect of addition of 10% spent yeast broth to Highland Park sewage on the relationship between the three residuals and the MPN is shown in Figure 5 , on the basis of line of best fit. I n general, the results are similar to those obtained with sewage alone-namely in order to obtain a given M P N by chlorination, higher levels of amperometric and starch iodide residuals are indicated than with orthotolidine residuals. Such is not the case, however, for the mixture of Highland Park sewage and ti-
01 2
0
4
6
RESIDUAL- P P M
Figure 3. Relationship between Various Ty es of Residuals and Average MPN in Chgrinated Rutherford Sewage Represented as Line of Best Fit
The results of all ten runs for each mixture were grouped together on the basis of a number of ranges of coliform organisms remaining with the corresponding average chlorine residuals required to produce these results. The plot of the results, analyzed even in this manner, showed a wide scatter, and it was impossible to draw a line through the points. The line of best fit was calculated by the method of least squares using the direct relation of the log of M P N and the residual chlorine. I n one series of figures, all the results obtained for a given type of substrate with the three residuals are compared. I n the second series of figures the effect of the addition of a waste to the respective sewage is compared on the basis of one type of residual. Figure 1 shows the relationship between the three types of residuals and the M P N per ml. as the line of best fit for the results obtained with Highland Park sewage. T o obtain a given coliform M P N per ml. of say 100, 10, or 1, much lower o-tolidine residuals are required than amperometric or starch iodide residuals. On the basis of the latter two residuals more or less identical MPN, are obtained. I n other words, a given dosage of
Table I.
0
2
6
4
AMPEROMETRIC RESIDUAL -
P
P M
Figure 4. Comparison of Amperometric Residuals os. MPN in Three Sewages Represented as Line of Best Fit
tanium pigment xaste where the three lines of best fit are closer together (Figure 6). With 10% chemical waste the amperometric and starch iodide results were also in close agreement. A direct comparison of the effect of addition of 10% yeast broth and of 10% titanium pigment waste on the relationship between o-tolidine residuals and MPN on the basis of the line of best fit is given in Figure 7 . The addition of 10% yeast broth had little, if any, effect on the chlorine requirement to give a stipulated number of coliform organisms. But M ith the addition of 10yo titanium pigment waste, significantly higher o-toli-
Summary Table of Correlations Z = a variable directly dependent on r )
( r l = square of the coefficient of correlation r.
Residual Type
Highland Park Sewage
z
OT 0.217 St+rch iodide 0.196 Amperometric 0.256 Critical difference
..
1006
-0,505
Spent Yeast Waste
10% Titanium
Waste
r2 0.289
z
-0.589
10% T2
0.209
z
-0.494
90% -Z r2
..
-0.476
0.306
-0,622
0.149
-0.406
..
-0.557
0.316
-0,634
0.327
-0.640
0.384
0.44
..
0.43
..
0.43
..
.. ,
,
.. ..
Manville Sewage sa
0.35
Z -0.68
Chemical Waste
10% 1'2
z
0
90% __-
Rutherford
Sewage ____
1'2
Z
rp
Z
0
0
0
0.533
-0.93
0.33
-0.654
0.235
-0.529
0.06
.
0.533
-0.93
0.387
-0.726
0.278
-0.587
0
0
0.476
-0.85
0.40
..
..
0.41
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
.
..
0.37
Vol. 45, No. 5
Water Treatment dine residuals were required t o produce equivalept MPN per ml. A similar comparison is made in Figure 8 for Manville sewage alone and with 10% chemical waste on the bakis of amperometric residual, showing the effect of the waste in increasing the residuals required to produce stipulated coliform organisms in the effluent.
\
dine yielded an intermediate value, indicating that for this waste mixture the amperometric method is somewhat more reliable than the other two methods. For Manville sewage r2 values were somewhat higher than for Highland Park sewage with no definite superiority of one method over another. The addition of 10% chemical waste to Manville sewage decreased the values of r2, which for o-tolidine residual was zero, indicating no correlation. The highest r2 values were obtained with Rutherford sewage, with no definite superiority of one type d residual over another. The variable, 2, is directly dependent on r and is used t o test, the hypothesis that each method of residual determination measures the disinfecting properties of the residual with equal precision. A probability of 5% is used to denote significance. The critical difference of two 2 values, to indicate a significant difference of the corresponding correlation coefficients, is alsogiven in Table I. With the exception of one case, differences were not greater than the critical difference, indicating a lack of significant differences in the various methods of measuring the disinfecting power as indicated by the three methods of determining residuals. In other words, all the methods had equal significance, and one method could not be selected as being superior to another.
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100
I
I
1
4
6
I
In order to establish the statistical validity of the results obtained, a summary of the correlations for all the results is presented in Table I. The index of correlation, ya, represents the coefficient of correlation squared. For Highland Park sewage r2 varies from 20 to 26% for the three types of residuals, indicating 1000
1
I
1 1 10 % TITANIUM
ASTE
l l
100
t
\
1
I
\
0.1
0
2
0.T RESIDUAL P P M
Figure 7. Effect of Adding lOyo Spent Yeast Broth and 10% Titanium Pigment to Domestic Sewage on Relationship between o-Tolidine Residuals and MPN Represented as Line of Best Fit
IO
z a I
Discussion IO
I
0
4
I
S P P M
I
12
RESIDUAL Figure 6. Relationshi between Various Ty es of Residuals an$ Average MPN in Chgrinated Mixture of 10% Titanium Pigment in Sewage Represented as Line of Best Fit
that this extent of variation in MPN can be attributed to variation in the residual. The t-2 for the 10% mixture of titanium pigment waste shows a variation from 29 to 31% for the three residuals. With 10% spent yeast broth the amperometric residual gave an r* value of %?yo',, starch iodide 15%, and o-toliMay 1953
The results show little definite superiority of one method of determining residual chlorine over another in respect t o the MPN in the chlorinated effluent of various sewage and industrial waste mixtures on the basis of statistical analyses. I n determining the efficiency of chlorination and in the control of the process, one chemical method seems to be as good as another. The residual values to be maintained for given stipulated coliform organisms in the effluent are higher for amperometric and starch iodide residuals than for the o-tolidine method. This by itself might constitute a slight advantage in favor of the amperometric and starch iodide methods as a method of control, because frequently with zero o-tolidine residuals, the numbers of coliform organisms are quite low and may in some instances be lower than the required standards for effluents. The presence of industrial wastes and sewage does not seem t o affect this general conclusion in regard to the lack of superiority of one method over another as a chemical index of the efficiency
INDUSTRIAL AND ENGINEERING CHEMISTRY
1007
of disinfection. There are, however, other considerations which make one method more useful than another. With colored wastes, colorometric methods such as o-tolidine and starch iodide methods are impossible. This was true with 90% concentrations of spent yeast broth. The amperometric method is not subject t o this disadvantage. Even in the absence of definite color in the substrate, color comparisons with the ortho tolidine method are not accurate because of the turbidity. Moreover, there is always the personal equation, which is not a factor with the amperometric method. 1000
100
-
P
'
IO
a z
I
10
01
0
2
4
6
AMP. RESIDUAL P.P M.
Figure 8. Effect of Adding 10% Chemical Waste to Domestic Sewage on Relationship between Amperometric Residuals and MPN Represented as Line of Best Fit
ten replications in a series were made with sewage obtained at different times from the same plant and the mixtures were made with wastes obtained from the respective plants a t different times, it seems reasonable to attribute some of the inconsistencies to the variation in the cornpositicy and concentration of the samples.
Summary and Conclusions A subcommittee of the Standard Methods Committee of the Federation of Sewage and Industrial Wastes Associations has undertaken to evaluate the various methods of residual chlorine determination as applied to selyage and industrial wastes using the coliform organisms as the ciiterion or, in other words, to select the chemical test for residual chlorine which most consistently indicates the objective sought-namely, the production of a bacteriologically acceptable effluent. This paper is based on data obtained by three collaborating laboratories coordinated by the subcommittee and is of preliminary nature. The objective of this study was to determine the effect of some representative industrial wastes, when mixed TTith domestic settled sewage in different proportions, on the relationship between the orthotolidine, starch iodide, and amperometric residuals and the coliform organisms. The wastes selected were (1) spent yeast broth representing highly organic soluble waste; (2) titanium pigment waste representing inorganic waste containing ferrous sulfate and sulfuric acid; (3) waste from a chemical manufacturing plant; and (4) municipal sewage containing a large variety and high percentage of industrial wastes. The domestic sewage and 10 and 90% volume concentrations of the wastes were chlorinated with various dosages of chlorine water and after 30-minute contact periods the residual chlorine was determined by the three methods, and the coliform organisms were enumerated by standard methods on the basis of confirmed test, using triplicate portions per dilution. The procedure was replicated ten times with each serage and waste mixture using different samples obtained from the same sources. The plots of coliform MPN versus the various types of residuals showed a wide scatter, and accordingly the relationship betaeen coliform MPN and various residuals are presented on the basis of line of best fit computed by the method of least squares. The results on this basis show the following:
The starch iodide end point is indefinite and fades, whereas the amperometric end point is sensitive to one drop of iodine. For these incidental reasons there is a distinrt advantage in favor of the amperometric method. The latter, hon-ever, is a newer method and not all the conditions to eliminate possible interferences have been carefully studied. In the course of this study, 1. Generally the starch iodide and amperometric residuals are for instance, with 90% titanium maste the pH value should be nearly of the same order of magnitude in relation to a stipulated adjusted to 6.5 to 7.0 prior to the titration instead of pH 3.5, number of coliforms in the chlorinated effluent and are a t a higher level than the o-tolidine residuals. which was suitable for lower concentrations and for other wastes. 2. The relationship between the MPN surviving and the reThis phenomenon appears to be related to the solubility of siduals on the basis of the line of best fit is not the same for the iron a t different pH values. sewage obtained from different sources in this study. A difficulty arises from another source not related to the re3. The addition of 10% spent yeast broth did not significantlv increase the residuals required for various stipulated coliform levsidual determinations but associated with high chlorine dosages els, but 10% titanium pigment waste and 10% chemical waste required with certain wastes for effective disinfection. With had a decided effect in this respect. high concentrations of certain high chlorine-requiring wastes, 4. With 90% of the spent yeast broth and titanium pigment such as 90% titanium pigment waste and 90% spent yeast waste i t was impossible to determine the o-tolidine and starch iodide residuals, but by the amperometric method the residuals broth mixtures, the chlorine added drives the pH to 3.0 or less, could be determined a t these high concentrations of waste. thus creating a second bactericidal factor. 5 , Statistical analysis of the results show only a fair correlaIrrespective of these difficulties, the major source of trouble in tion between residual chlorine determined by the methods emdisenfection studies is the extreme variations obtained in the ployed and the kill of coliform organisms. m.p.n. With three replications per dilution and ten repetitions results, when pooled for a given substrate, demonstrated an exLiterature Cited treme scatter which could not be overcome by averaging on the (1) Marka, Henry C., and Joiner, Robert R., Anal. Chem., 20, 1197 basis of a range of colifornis in the effluent nor on a statistical (1948). basis. It is believed that the coliform test is less sensitive and ( 2 ) Marks, Henry C.,Joiner, Robert R., and Strandskov, Frede B., subject to greater variations than the chemical determinations Wuter & Sewage W o r k s , 95, 185 (1948). which were used for the evaluation of disinfection. It, therefore, (3) Strandskov, Frede B., Marks, Henry C., and Horchler, Donn H., appears that before a final answer can be given in regard to the Sewage Works J., 2 1 , 2 3 (1949). selection of the best chemical tests as an indicator of the efficiency ACCYIPTED JANUARY 9, 1952. RECEIVED for Review October 15, 1942. of disinfection and the production of an effluent corresponding Paper of the Journal Series, New Jersey Agriculture Experilnent Station, t o a stipulated number of coliform organisms, the method of Rutgers Univeraity, the State University of New Jeraey, Department of Sanitation. enumerating these organisms must be improved. Since the 1008 INDUSTRIAL AND ENGINEERING CHEMISTRY VoI. 45, No. 5
