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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 14, NO!.I €
Relation of Hydrogen-Ion Concentration to Fi It er -PlantOperati on‘ By William D. Hatfield WATERDEPARTMENT, CITYOB HIGHLAND PARK,MICHIGAN
M
ODERN chemistry ft is known that the p H value of a solution is a controlling factor The data in Series I, is aiding the waterin precipitating and filtering gelatinous materials. The work . Table I, show that the works chemist and reported below was undertaken to find that p H value at which best quantity of alum necessary results in coagulation, sedimentation, and filtration were obtained engineer to a new and more to produce a clear-cut floc under the conditions of operation of the Highland Park, Mich., accurate idea regarding is not dependent on the filtration plant. When similar data have been collected on numerous the coagulation of waters turbidity, and that in each piants operating under different conditions, the value of the p H with sulfate of aluminium. case good flocculation began determination to operation will become more definite. The alkalinity of a water a t a pH value of from 7.6 exists in two forms: (1) to 7.8. It does not necesthe hydrogen-ion concensarily follow that in the tration or pH value, and (2) the reserve alkalinity, which operation of a filter plant, where other factors as sedimenis the buffer value of the water. The latter has been deter- tation enter, more alum floc will not be necessary to adsorb mined as the methyl orange alkalinity, while the former is the higher turbidities. The data in Series I1 and 111, Table I, show that the quanthe value which apparently controls the complete precipitabities of alum necessary to produce a clear-cut floc are depention of aluminium from solution. Experiments in other fields of chemistry have shown that dent on the methyl orange alkalinity and not on the turbidity. the pH value of the solution is a controlling factor both in As in Series I, good flocculation in each case began at a pH the precipitation and filtration of gelatinous materials. If of from 7.0 to 7.8. This means that in cases of high alkait should be found possible to determine the proper pH linity large amounts of alum have to be used, not as a coaguvalue for the coagulation and filtration of a particular water, lant, but to neutralize the alkalinity of the water and bring we should have a simple method for controlling the alum the pH value down to 7.6 to 7.8, where flocculation begins. treatment. I n case of waters with high alkalinity, it may be The truth of this statement is shown from the data in Series economical to reduce the alkalinity by the addition of sul- IIa, Table I. The sample of water used was No. 4 of Series furic acid and thereby make a considerable saving in alum. 11, which had a turbidity of 45 p. p. m. and a methyl orange Colorimetric methods for the determination of pH values aIkalinity of 210 p. p. m. The original pH value of the water of water using the buffer solutions of Clark and Lubs2 or was greater than 9.0. Sulfuric acid was added to the water Sorenson3are most accurate for the trained chemist with good until the pH reduced to 8.2. Alum solution was then added to laboratory facilities, but the author highly recommends the a series of 500 ml. samples in quantities from 0 to 3.0 gr. Gillespie4 method, “without buffers,” for the average water- per gal. Good flocculation took place with from 0.75 to works laboratory. After the color standards are made up 1.00 gr. per gal. alum, again at a pH of 7.6 to 7.8. This same by the chemist, an operator with average intelligence can be mater, before treatment with acid, required 2.75 gr. per gal. taught that 5 or 10 ml. of the mixing chamber water plus a of alum for flocculation. TABLEI ‘certain number of drops of an indicator should have a cerMethyl Orange Gr. per Gal. pH of Treated Water tain color when matched with the standards. Alkalinity Alum to Coagulate at Which a Good Before beginning the experiments on the operation of the Sample Turbidity as CaCOs Sample Floc First Appeared Series Z--.Methyl orange alkalinity constant, turbidity variable pIant, preliminary laboratory tests were made on the precipi1 25 111 1.50 7 . 6 to 7 . 8 tation of aluminium hydroxide from a solution of filter alum, 2 75 111 1.50 7 . 6 to7.8 3 150 111 1.50 7 . 6 to 7 . 8 and on the coagulation of artificially prepared waters. Ti4 300 111 1.50 7 . 6 to7.S tration curves of an alum solution (0.855g. per liter) were 5 600 111 1.50 7 . 6 to 7 . 8 Series ZZ-Turbidity constant, methyl orange alkalinity voriable made with 0.1 N and 0.01 N sodium hydroxide, sodium bicar1 45 55 0.75 7 . 6 to 7 . 8 bonate, sodium carbonate, ammonium, and calcium hydroxide. 2 45 107 1.25 7 . 6 to 7 . 8 3 45 158 2.00 7 . 6 to 7 . 8 These curves show approximately the same deflection with 4 45 210 2.76 7 . 6 to 7 . 8 the central point in the drop of the curve a t a pH of 7.0. Series Ila-Samfile 4. Series I I , treated with N ~ S O to P P H of 8.2 1 45 .. 0 . 7 5 to 1 . 0 0 7 . 6 to7.8 The data in Table I were obtained by treating 500 ml. of Series Ill-Turbidity conslant, methyl orange alkalinity variable the samples of waters in beakers with quantities of alum vary1 150 23 No floc (7.4)‘ ing from 0 to 3.0 grain per gal. The waters were prepared 2 150 85 1.00 7 . 6 to 7 . 8 3 150 136 1 . 5 0 7 . 6 to 7 . 8 from distilled water, with fuller’s earth for turbidities, and 4 150 218 3.00 7 . 6 to 7 . 8 sodium bicarbonate for bicarbonate alkalinities. A freshly 7 4 was the pH value of the untreated water. 0 . 2 5 ar. per gal. of prepared alum solution (0.855 g. per liter) was used. One alum brought the p H to 7.1, but in no case was there a floc formed. milliliter of this solution in 500 ml. of water is equivalent to In Table I1 data are given on the treatment of 8 water 0.1grain per gal. having a turbidity of S5 p. p. m. and a methyl orange alkalinity of 112 p. p. m. A good, clear-cut floc which settled readily Presented before the Division of Water, Sewage, and Sanitation at the 63rd Meeting of the American Chemical Soclety, Birmingham, Ala,, April 3 was obtained between the pH values of 7.6 and 6.6 with apt o 7,1922. plications of alum from 1.5 to 6.0 gr. per gal. Below the J . Bact., 2 (1917), 1 , Clark, “The Determination of Hydrogen-Ion pH value of 6.45 the floc became feathery and did not settle. Concentration,” Willlams and Wilkins, 1920. The pH limits, within which the floc coagulated and settled 8 Biochem. Z.,24 (IglO), 387; Levy, ArLh Inlernal M e d . , 16 (1915), 389; Hawk, “Practical Physiological Chemistry,” 5th ed , p . 289, P. Blakissatisfactorily, coincide with those of Blums for the complete ,
1
1
2
ton’s Son & Co. 4 Soil Science, 9 (19201, 115; J . A m . Chem. S o c . , 4 2 (1920), 743.
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J . A m . C h e a . SOG., 96 (1913), 1499.
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Nov., 1922
precipitation of aluminium hydroxide. It is possible, however, that the complete precipitation of the aluminium also takes place a t p H values much lower than the limits given above. TABLEI1 (Sample of water used: alkalinity 112 p. p. m.; turbidity 85 p. p. m.1) Alum Added Character of p H Value of Solution in Gr. per Gal.? Coagulation Sedimentation 0.0 8.4 8.2 0.5 7.8 I .o .... 7.5 1.5 Good Good 2.0 Good Good 7.4 Good Good 7.0 3.0 6.8 ZJ .O Heavy Good Heavy Good 6.7 5.0 6.6 6.0 Very heavy Good 6.45 Not clear cut Fair 7 .O 6.35 Featherv Poor 8.0 Feathery Very poor 6.3 9.0 6.25 Peathery Very poor 10.0 Feathery Very poor 6.15 11 . o 1 The solution used was made by addition of sodium bicarbonate and fuller's earth to distilled water. 2 Further addition of alum solution gradually peptized the feathery flock until the solution showed a deep turbidity only. I
.
.
.
The chemical composition of the raw water for the Highland Park supply, taken from Lake St. Claire, is practically constant the year around. Rains have little or no effect on the turbidity and alkalinity, though high winds cause the turbidity to rise from the usual 5 to 20 p. p. m. to 100 to 200 p. p. m. Theee periods of high turbidity last only a few days. The bacterial content to the water ranges as follows: Agar 37O 10 to 1000 organisms per milliliter Agar 20' 100 to 15,000 organisms per milliliter ( B . coli average, 6 organisms per 100 ml.)
Because of this constancy of chemical composition and the ease of handling the bacteriological purification, it is possible to run the plant for a month at a definite alum treatment and study the relation of p H values to the efficiencies of coagulation, sedimentation, and filtration, without worrying about changes in alkalinity or sudden gross pollution of the raw water. The raw water has a methyl orange alkalinity of 83 p. p. In. The p H value of the water in the summer months is as high as 8.4 and gradually decreases with temperature until a t 1O C . it is 7.8. This gradual lowering may be due to the increased content of carbon dioxide in the water during the winter months. T a b k I11 contains data on the coagulation and pH values of the treated water collected a t the end of the mixing chamber when different amounts of alum were added. The same results have been obtained in laboratory beaker experiments. Coagulation takes place at a p H of 7.6, confirming the data on the artificially prepared water. In all experiments it is
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noticeable that flocculation in beakers requires considerably more time than in the mixing chamber. The reason for this has not been ascertained. It is probably due to a number of differing factors, as stirring, volume, presence of floc nuclei, concentration of alum solution added, etc. TABLE I11 Alum Added Gr. per Gal. 0.0 0 2 0.3
pH Valiie of Treated Water 8.4 8.2 8.0 7 8
0 4
~
7;65 7.6 7.67.55 7.4+ 7.4 7.47.3 7.2 7.15
0.5 0.6 0.63 0.69 0.77 0.81
0.88 0.95 1.01 1.19
Character of Floc a t End of Mixing Chamber None None Very faint Faint . . ~ ~ ~ . Poor
Fair
Good Large Large Laree Large Large Large Large
TABLE IV-COAGULATION
OF RAWWATER I N BEAKERSJANUARY 16, 1922. ORIGINALTEMPERATURE 1 . O o C. (Last column contains data on the floc in influent to filters in February 1922 showing comparison to beaker experiments) Time t o Form Floc in Alum Added p H Value of Influent in Gr. per Gal. Treated Water Floc in Beakers None 0.0 7.8 None in 3 hrs. None in 3 hrs. Very few small parti0.2 7.65 cles of floc Considerable minute 0.4 7 6 None in 3 hrs. particles of floc 7.4 Fair floc in 3 hrs. Large quantity of fair0.6 sized floc Good floc in 1 hr. Excellently coagulated 7.35 0.8 and settled Excellently coagulated Good in 30 min. 7.2 1.0 and settled 1.25 7.2Good in 30 min. Excellently coagulated and settled 1 50 7.06 Good in 3 min. Excellently coagulated Heavy in 30 min. and settled
At winter temperatures the p H values of the treated mater, as well as the raw water, are lowered as is seen on comparing Tables I11 and IV. The time of reaction, both in beakers and in the mixing chamber, is prolonged. The last column in Table IV shows that coagulation takes place after the water leaves the mixing chamber, and also shows the point where good sedimentation takes place. Although the initial pH of the raw water is 0.6 lower in the winter than in the summer, as the alum treatment approaches 1.0 gr. per gal., the p H values approach 7.2 both for winter and summer. Table V contains data on the operation of the filter plant from August 1, 1921, to January 14, 1922. The data on the hours of filter service are reliable and best indicate the efficiency of operation. The data on removal of bacteria expressed by percentage are of less value because the raw water count is often very low. Table V shows that under the conditions of
OPERATION OF HIGHLAND PARKFILTER PLANT BEFORE CLEANING SEDIMENTATION BASIN (August 1, 1921, to January 14, 1922) Per cent Per cent c o s t of Bacterial Bacterial Average Hrs. of Treatp H Value Efficiency of Efficiency Filter Service Per cent ment per Raw Treated' Sedimentatifn of Filtratirp Coarse Fine? Washwater Million No. of Temp. Turbid- Alum in DATES Days 'C. ity Gr.perGa1. Water Water 20 37 20 37 Sand Sand Used Gallons Aug. 1 t o 17 Sept. 13 to 16, 1921 21 28 10 0.60 22 8.4 7.6 31 1.72 $1.81 34 20 Sept. 17 t o d c t . 20, 1921 16 0.68 .. 8.0 7.5 36 27 1.36 1.87 Oct. 22 to Nov. 25. 1921 36 12 31 0.78 87 46 33 8.0 59 67 87 1.15 2.02 7.4 December 1 t n 31 '1921 31 19 0.92 4 58 90 7.8 73 97 40 1.02 7.3 61 2.28 January 5 t o 13: i922 9 1.5 1.07 11 52 7.8 . . 9 7 . 5 52 35 1.09 2.56 7.2 .. January 14 to 17, 1922 4 1.5 1.19 15 46 43 98.5 90 33 2.83 7.15 7.8 1.11 48 1 p H values have been run on raw, mixed, settled, filtered, and chlorinated waters. The p H values of the last four are always identical as collected a t this plant. 2 Eight of the filter beds are made of a coarse Red Wing sand and four are made of a finer Cape May sand. The bacterial efficiencies of the two sands are about the same, but the fine sand gives fewer hours of service, TABLEV-DATA
O N THE
..
..
(89:)
THE OPERATION O F THE HIGHLAND PARK FILTER PLANT AFTER CLEANING (February t o April 1922) Per cent Per cent Bacterial Bacterial p H Value Efficiency of Efficiency of No. of Temp. Turbid- Alum in Raw Treated Sedimentation Filtrationo Days O C . ity Gr.per Gal. Water Water 200 370 20' 37 10 1.5 3 0.21 7.8- 7.7 0 0 74 70 8 2.0 8 0.42 7.8 7.6 15 26 88 98 8 2.0 12 0.62 7.8- 7.423 21 81 86 2.5 8 17 0.75 7.8 64 55 7.395 96 4 8.0 24 0.95 7.9- 7.2 85 83 95 98
TABLEVI-DATA
DATES February Y.4 to 23 1922 February 24 to M6rch 3, 1922 March 4 to 11 1922 March 12 to l b 1922 April 13 t a 16, is22
(g)
ON
SEDIMSNTATION
BASIN
Average Hrs. of Filter Service Per cent Coarse Fine Wash Water Sand Sand Used 67 46 0.80 55 35 0.89 58 37 1.34 0.99 61 46 66 47 0.70
c o s t of Treatment per Million Gallons $0.69 1.17 1.73 1.89 2.45
