Chlorination of Sewage C. K. CALVEHT, Indiariapolis Sanitation Plant, Indianupolis, Ind
T
H E s e i v ~ ~ gof e Idianapolis, witli the exc,cpt.ioii of a p I,ll>tilD-CHl.ORlNE ~ E I I I Y & : I ~ 1)EYICES Y proxiniat.ely 3 $f. (:. I)., is delivered to the sewage Figure 1 is a pli~itograph of four chlorine delivery deplant for trcrttiiicnt. The quantity so delivered avervices which have been taken apart; tlie pieces are placed ages Jfi.8 $1, G. 11. All seaage wliicli readies tlic ~ ~ ? i ~ ; i ~ ~ , - i , r ~ ajilant l , i ~ i i ~inie i i t above the other in assembly order, so that each onr is clarified hy R conibinntiun (ifcotiretitrating swceiis aiid slips down into tlie one below to reach an cq~eratingposition, sodimentation. 1)oriiig the sunmior niw,ths tlic :&v:&d9. Glrasr jet with did& outside packing nuts. sludge plant is operated at its greatest capacity, wlricli rcW. Variable-orifice device. Chhrino control at top, eliloriire stilts i n the trt&mcrit of about 70 per cent of tlie sewage inlet at upper right, aatar inlet at middle fmiit, and water and flow. The reiirairidm of tlie sewage goes to the river with chiwine delivery point at extreme bottsrn. A 2-inch ~ I R S S cylinder fits on the lower p r t . nu oblier trentoimt than clarification. C. Metal jet with lead gasket joints. D. Glass jet with single inside packing nut. 1. Chlorine control head with chlorine entering at tlip, controlled by iiecdie valve and delivwcd t o jet helow. 2. Chlorine delivery jet. 3. W:rter head with chlorine enterinr: tliroudi ict above. and wzter eriterinr through side opening 4. Gage glsss held to d e r tiead with packing nut. The water Aows down thmu& this glass and out into a hose clamped on the bottom. T h e ehloririo is deliverel from the iet into the upper part oi the glass. Applying chlorine in this fashion results in its rermhing the scnege BS: (1) ice, (2) mster solution, and (3) gas; t h o relative amount of each depends on: (1) rnte of mixtwc wit,lr, (2) the volume of ly&ter,and (:3) t.emyerature.
Tlic chlorine froin chlorine ice is liberated relatively slowly and absorbed easily by the sewage. It is a simple matter to mix the solution of chlorine with the sewage, but the gas may rise through a shallow layer of sewage without being absorbed aiid so he lost. In one installation the mixture Ficrrne I , Cnt,orrrxr:
Ihi.wrnv
Dwrctis
I’riur tu the suiiiucr of 1930 B nuiiilw of observxtims Iiiid been made elsewlicre on tlie effect of ihliiriiie o n the 11. 0. I). of sewage. From those various picces of work it appeared that the chlorination of clarified sewage at Tlidianapolis rriiglit result in improved river conditions. Laboratory experiments, carried on a t Indianapolis iluriiig 1929 and again early in 1930, indicated that a reduction of j d a y 13. 0. U. might be expected, arnounting to perhaps 35 pcr ceiit of the total, and, on tho basis of l@de,y incubntion, a reduction of 15 to 20 per cent. In these experiments chlorine m’as applied to give at least a trace of residual after 10 minutes, the quantity being varied tliroughout the (lay on the hasis of the strength of sewage as indicated by the chloriiie demand. On the basis of the pnblislied rosults and the laburatory experiments made at Indianapolis, the use of chlorine during the summer of 1930 was determined with the 1 1 0 1 ~that river conditions might be improved until such time RS extensiiin of the activated-sludge plant could IJC redizeil. I n order to simplify the inntauation-amjiding the use of evaporators and autornatic gaseous chlorine machincs an eiTrxt was made to apply liquid chlorine so that the quantity iif chemical used might he increased to any desired point without material modification irf the installatian. A number of dovices were t.ried exi’criinent,:rlly, and fiiially two types of cliloriiie jet., were dcvehjnil. Both types require constant attentiou to maintain a uniform application of chlorine, but do not require expert operators. The stoppage of lines and jets, or orifices, lry a giiiiiiny substarice in the liquid chlorine offers some difficulty, but i t is believed that this can be overcome by the itre uf rather livge-area filters near the cliloriiie cylinders.
9
Fit;une .4.
R.
C.
2.
II
13 16 17 19 21 23 25 27 28 September. 1930
I h s U L T s O f I’IANT OPBRATION ANI, AFTER CHLoRINhTION
Chlorine demand of s e w w e Chlorine supplied t o ~ e w . * p e R . 0.D. 01 aewage
D. E.
1
3
6
7
Ootuber
HEFORE, DURING. B. 0.D. uf,effluenC Detention time
F. Air per gallon
~
of solution, ice, and gas wae delivercd below filtros tile, under
wliicli the ice and solution passed, and through which the gas escaped in fine bubbles into the sewage. Very little loss of chlorine occurred judging from the odor in the sewer bclow the point at which application was made. lfighly chlorinated sewage loses its chlorine ii agitated irnmediatdy after application, such as falling over a dam or traveling a t high velocity over a steep grade. In order to mix the chlorine mure thoroughly and intimately with the sewage, a second device was employed: 92
January, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
This device consisted of a 30-inch vitrified tile with the upper end sealed, and the lower end supported about 8 inches from the floor of the sewer. The mixture of chlorine solution, ice, and gas was delivered through a hose under the tile and well toward the top. Another hose line led from the very top of this tile
n
100 1
93
tirely, the B. 0. D. reduction would have been improved but little. This observation is substantiated by the B. 0. D. reduction figures on days when free chlorine remained more than 10 minutes. TABLEI. REDUCTION OF IMMEDIATE CHLORINE DEMAND AND DAY B. 0.D. OF CLARIFIED SEWAGE BY CHLORINATION (July 26 to September 12, 1930)
IMMEDIATE DEMAND
TIXE
500
9 A.M. 1 P.M. 4p.x.
19 22 25
August
28
31
3
6
9
12 15
18 21
24
September, 1930
27 30
FIGURE 3. B. 0. D. IN COMBINED PLANTEFFLUENT AND RIVERCONDITION 4 .
B. C.
D.
B 0. D. disoharged from plant per day River discharge Minimum dissolved oxygen in river Chlorine in combined plant effluents a t outfall (oh1orin;ition discontinued September 12, 1930)
Number of determina- Clantions fied 5.8 9.0
36 37
9.0
28
B . 0. D. Clarified and chlo- Reducrinated tion % .-
5-DAY
Clanfied and chlo- Reducrinated tion % ._ 1.7 71 2.9
Clarified 184 298 268
68 67
3.0
166 275 249
9.8
7.7
7.1
Chlorine was applied to the influent to the activatedsludge plant a t a point very near that a t which the return sludge entered. The concentration of chlorine was held sufficiently low to avoid more than traces coming in contact with the activated sludge, although it was not all combined a t this point. Figure 2 shows the results of plant operation before, during, and after chlorination. A glance shows that there was no improvement in operation during the chlorination period. Neither is the increase in detention period and air per gallon in the latter part of September due to chlorination. It is a seasonal change and is anticipated. The color and appearance of the activated sludge seemed to be improved during the chlorination period. Indianapolis sewage is quite fresh when it arrives a t the treatment plant. It is probable that chlorination of septic 4ewage might result in a much greater reduction in B. 0. D.
back t o the suction side of a Duriron injector. Thus, any gas delivered to the tile was drawn back through the injector, mixed again with water, and delivered to the line as solution. Any gas not absorbed by the water was drawn back through the injector a second time. With this arrangement, chlorine was applied to the sewage with no loss of the gas.
EFFICIENCY OF ;~PPLICATION OF CHLORINE It appears from the examination of individual figures that large doses of chlorine may not reduce B. 0. D. in the same proportion as small doses. It appears too that, chlorine may combine with substances in the sewage to render it inactive to starch-iodide tests and yet reduce the B. 0. D. inappreciably. Any attempt to determine the efficiency of application a t Indianapolis is affected by the above conditions. Period averages, when excess chlorine was common, indicbate that about 60 per cent of the chlorine applied can be accounted for as free chlorine or satisfied chlorine demand. Actually the whole amount of chlorine used, calculated to parts per million, equals almost exactly the average immediate chlorine demand of the sewage a t 9 A. M., 1 P. M.,and 4 P. iv. However, during much of the time the chlorine demand was materially less than the average, and the application of chlorine was a t an excessive rate. It is difficult t o arrive a t an estimate of the efficiency of application. Laboratory determinations were made three times daily (during the peak load period) of the B. 0. D. and chlorine demand, before and after chlorination. S o work was attempted to show what compounds resulted from f he reaction between the chlorine and the sewage constituents. Tests were made for free chlorine each hour by the starch-iodide method. Table I shows the reduction noted in the chlorine demand and 5-day B. 0. D. It is seen that the chlorine demand is reduced from seven to ten times as much as the B. 0. D. Even though the chlorine demand had been satisfied en-
1
2
3
4
5
6
Minimum D. 0. in river (p. p. m.)
7
8
FIGURE 4. EFFECT OF B. 0. D. LOADON RIVER CONDITION IN 1930 x. With ohlorine 0. Without chlorine
than was noted in this work, and that under such conditions it might improve materially the operation of a biologictreatment plant. ACTIVATED-SLUDGE PLANT Since it was obvious, from an examination of the B. 0. D. reduction effected by chlorination of the clarified sewage and from river inspection, that chlorination was not solving
INDUSTRIAL AND ENGINEERING CHEMISTRY
94
the problem, it was determined to chlorinate so heavily that free chlorine would be maintained in the river itself, with the hope that longer contact and greater concentration might improve the river. For this purpose, advantage was taken of the volume of the effluent from the activatedsludge plant, chlorinating it as well as the clarified sewage, both of which enter the river through the same sewage outfall. Two main factors control river condition-the organic load added and the dilution afforded by the stream. No account is taken, in this discussion, of the distance, time, or reaeration afforded by riffles, since they are practically the same for the chlorinated and unchlorinated periods. The B. 0. D. in the combined plant effluent and the river condition are shown in Figure 3. The organic load and dilution are shown as thousand pounds of 20-day B. 0. D. discharged from the plant per day, and the river discharge in second feet. The measure of river condition is taken as the minimum dissolved oxygen within the first 6 miles of river flow, which is the part most affected. In order to determine the effect of chlorine applied to the sewage, the residual chlorine in the entire plant effluent is also shown. An examination of this graph shows that, with a material reduction in the organic load or an increase in the river discharge, there is a resultant increase in the dissolved oxygen. It will be noted that this increase comes a day late on the graph, approximately this time elapsing between the discharge of sewage and the taking of the sample. In one instance the increase in the minimum oxygen occurs following a day on which no chlorine was applied, although there is no connection between the two conditions. There appears to be no material change in the oxygen content in the river on account of chlorination of sewage and plant effluent.
Vol. 24, KO.1
not warrant the expenditure of much money for chlorine or any other treatment agent. Figures 5 and 6 show the relation of B. 0. D. poundage to river condition between stations 8 and D during days of chlorination and no chlorination. The data for the 4 days shown were chosen on account of similar B. 0. D. and river discharges. When the oxygen content of the river a t any point is higher on one day than another, it is on account of the relative river flows or B. 0. D. load, whether chlorine was being used or not. iin,
5
70 1 d Y
z
0
5
i l
,d
,/'
30
...
____.____ ___-. ---.--..,
%__
10 C
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1 2 3 4 5 6
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7 8 9 101112131415DE F G H Station
FIcunr. 6. DISPOLYED OXYGEN IN WHITERIVER,SEPTEMBER 7 AND 23,1930
There is always danger in drawing general conclusions. The matter presented here is on the basis of the experience gained in using 150,000 pounds of chlorine in one summer. METHODS
dl0
1 -
C
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u
1
s
I
2 3 4 5
I
3
I
a
I
I
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6 7 8 9101112131415DEFGH Station
OXYGEN 1N WHITE HI\ E R , SEPFIGURE5. DISSOLVED TEMBER
*B. 0. D., pounds Second feet *Residual chlorine, p. p. m. A . Chlor mated B . Unchlorinated
5
AND
19, 1930 SeDt. 4 45,927 266 3.0
SeDt 18 45,896 287 0
* I n sewage effluent. Figure 4 is made on the basis of minimum oxygen content in the first 6 miles of river flow for various thousand pound per day loads of 5-day B. 0. D., both with and without the addition of chlorine. On the assumption that the 5-day B. 0. D. of the clarified sewage may be reduced 10 per cent, it is seen that chlorination can be expected to produce very little improvement in river condition. Assuming, for instance, that the daily load amounts to 50,000 pounds of 5-day B. 0. D., and that it may be reduced 10 per cent, or to 45,000 pounds, the improvement in the dissolved oxygen in the river amounts to only 0.12 p. p. m. Assuming again that a reduction of B. 0. D. of 25 per cent could be obtained, and the B. 0. D. load reduced to 37,500 pounds per day, the improvement in the river amounts to 0.4 p. p. m. of dissolved oxygen. Such a small increase certainly does
ImmDIATE CHLORINEDEMAKD.In a liter beaker are placed 400 cc. of a 500-cc. sample. Chlorine solution (1 cc. = *1.0 mg. chlorine), standardized hourly, is run in quickly in not more than 0.5-cc. amounts until free chlorine appears, as shown by the starch-iodide test used as an outside indicator. The remainder of the 500-cc. portion is added, and the titration continued, using smaller portions of chlorine solution a t the end. B. 0. D. Standard method. Aged aerated distilled water is used for dilution. OXYGENDISSOLVED.Nodified Winkler.
COXCLUSION~ The summer's work leads t o the belief that: 1. Chlorine under proper conditions may be applied as a liquid instead of as a gas. 2. The chlorination of Indianapolis sewage reduced the 5-day B. 0. D. no more than 10 per cent. 3. Chlorination of clarified sewage resulted in no material improvement in the activated-sludge process. 4. Summer improvement of the White River effected by chlorination can be expected to be negligible with a B. 0. D. load of, or greater than, 25,000 pounds per day. ACKNOWLEDGMENT The work of preparing the data for this report was done by D. E. Bloodgood, whose splendid assistance is gratefully acknowledged. RECEIVED April 18, 1931. Presented before the Divislon of Water, Sewage, and Sanitation Chemietry a t the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 t o April 3, 1931.
