Vol. 9, No. 4
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
3 70
I n conclusion i t may be stated t h a t with a knowledge of t h e method a n d with strict attention t o detail, very accurate and reliable results may be obtained, and t h e fact t h a t i t is extremely delicate is a point in its favor. Accuracy, however, will come only with practice. LABORATORY OF
SAVANNAH
GUANOCOMPANY
SAVANNAH, GEORGIA
THERMOCLINE STUDIES AT KENSICO RESERVOIR' By FRANK E. HALE AND JOHN E. DOWD Received September 30, 1916
The new and enlarged Kensico reservoir is the storage reservoir for the new Catskill water supply nearest t o New York City. Owing t o t h e progress made on t h e dam, t h e reservoir was filled in t h e winter of 1915-16. Close watch was kept of t h e quality of t h e water in order t o utilize it a t t h e earliest possible moment. During construction t h e water of t h e Bronx watershed had been held back b y t h e Bronx a n d Rye Dykes and the Bronx supply fed from Rye Dyke. As soon as t h e quality of t h e water permitted, change of draught was made t o t h e new dam a n d filling continued over t h e Dykes in order t o conserve in t h e Catskill system as much of t h e winter and spring flow as possible. The problem was interesting in t h a t it is not t h e usual procedure t o use water from a reservoir without long standing and possibly blowing of bottom water after stagnation. TREATMENT OF RESERVOIR BOTTOM
Soil stripped from certain designated portions was used for filling areas of shallow flowage. Swampy areas were covered with sand and gravel t o a depth of 1 2 in. or more. The bottom and a margin of about 30 f t . outside t h e flow-line were cleared of all buildings, fences, trees, bushes, logs, stumps, high grass, tussocks or clumps of roots of bushes or grass, weeds a n d rubbish. Stone walls within t h e 30-ft. margin and t o a depth of 20 f t . below t h e flow-line were removed.
anything approaching t h e stagnation of summer is avoided. Water first flowed in from t h e Ashokan tunnel on November 2 2 , 1915,a n d continued steadily until January ~ j 1916, , when t h e water was 1 2 3 f t . deep. Filling was resumed February 21, 1916, and continued t o full reservoir level which was reached May 23, 1916. The water entering was of low turbidity and free from B. coli in I O cc., having seen long storage a t Ashokan reservoir. The water as it entered the reservoir stirred up the mud of t h e bottom with t h e result t h a t the whole volume of water in Kensico reservoir was muddy and showed B. coli in many of t h e tests in 0.1 cc. The turbidity contained fine silt which settled very slowly. The turbidity was still 30 p. p. m. a t t h e end of a month and naturally cleared more slowly in t h e deeper water. B. coli results improved with subsidence of turbidity and time of standing, tests in only I O cc. being obtained a t t h e end of 3 weeks and a t t h e end of 6 weeks being negative in I O cc. Special inspections were started by t h e Laboratory Division of t h e Department of Water Supply, Gas a n d Electricity, and special samples were taken on December 2 2 , 1915. Eight samples taken a t different points along the side of the reservoir had an average of only 36 bacteria per cc. (agar 3 7 ' C.) and no B. coli in I O cc. within 24 hrs., lactose bile test. I n 3 days' time t h e tests in I O cc. were positive in s/d of t h e samples. One only gave a test in I cc. These results proved t h e presence of attenuated B. coli only, its source being t h e disturbed mud of t h e reservoir. A p a t h was broken through the ice t o a point several hundred feet back of t h e intake a t t h e dam and samples taken f r 0 m . a row boat a t t h e surface and a t 50 ft. depth, the total depth of water being 82 f t . These samples were taken, as were all similar samples later, by t h e method employed for collecting dissolved oxygen samples, i. e . , allowing a larger bottle t o fill through a small bottle so t h a t t h e analysis of t h e water in t h e small bottle represents the actual conditions a t t h e
TABLEI-QUALITY OF WATERAT VARIOUSDRPTRS,KENSICORESERVOIR PHYSICAL CHEMICAL ANALYSIS 0 (Parts per Million)
EXAMPATION
."*E
s
Y
.*8 DATE Dec .22. 1915 Jan. 7, 1916
PLACE OF COLLECTION Surface 50 ft. Depth 82 ft. Bottbm 5 16 2v 34 Surface 25 ft. Depth 34.5 5 16 2u 4 16 2v 50 ft. Depth 35 117 ft. Bottom
.. . 0.116 0.038 0,002 0.15 0.106 0.024 0.002 0.15
8 2.2
6
u
gu
d 4 t
i
e
P
a d d
d
14 0.70 0.9 91.9 13.08 14 0.60 0.9 90.0 12.67
0.088 0.016 0.002 0.15 48 1.0 25 0.088 0.020 0.002 0.10 51 1.2 20 0.090 0.030 0.002 0.20 59 1.4 20
13.25
1 Presented at the 53rd Meeting. American Chemical Society, New York City, September 25 to 30, 1916.
Bact'l Mic'l
P
25 1.5 25
Designated areas within the 30-ft. margin a n d t h e reservoir bottom t o a depth of 35 ft. below t h e flowline were grubbed of stumps a n d roots. Material was burned, excrement removed, a n d chloride of lime used. T h e time of filling t h e reservoir was well chosen, late fall, since circulation continues all winter and
EXAMINATION
OXYGEN
13 0.40 0.4 93 13 0.50 0 4 13 0.50 0:4 92'
1i:25
Bacillus
coli ti$ad 0.1 in in in 1.0 10 p1
CC.
cc. cc.
15 0 0 0 37 0 0
+
15 15
1 1 0 0 0 20 1 1 0 0 0 100 0 1 9 0 0 0
depth sampled. These samples were given complete analysis, physical, chemical, bacteriological, and microscopical. Dissolved oxygen and free carbonic acid were also determined a t the reservoir. The results are shown in Table I. The temperature, oxygen-free carbonic acid and other determinations proved t h e water t o be of uniform character throughout. Microscopic organisms were practically absent, oxygen was abundant, 90
T H E J O C R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Apr., 1917
3-71
Previous experience with Croton Lake having indicated t h a t there would be no stagnation until summer, special sampling was discontinued until spring. Regular samples were taken 3 times weekly of surface and effluent a t t h e d a m a n d these remained of excellent quality. Common reference is made t o winter stagnation in reservoirs. It is t h e opinion of the writers t h a t under usual conditions there is no winter stagnation. I n our experience with Croton Lake a n d with Kensico Reservoir t h e water circulates and overturns all winter long even t o a temperature below t h a t of greatest density. The following table of temperatures taken by thermophone by t h e Boapcl of Water Supply substantiates this point : TABLE11-TEMPERATURE OF WATER AT VARIOUS DRPTHS,KENSICO RESERVOIR
DEPTHS Surface.. . , . . 7 f t....... . 22 f t . . , . . . . 62 f t . 102 f t . . , . . , . . . 122 ft. (bottom)
.. . . . . ........ .
SURFACE
1 ;
32.J
401-
i
- 20
o r DRAUGHT) DLCfMBLR 22,/9/5
(LowEST P y N r
!
-M
1
I ! 20 I- -i
'
I :
I
I
I
I
32
A!-
40
I1
? t'
h
5'
!
1 (LOWLST
-----1 ---
Ez
----
--.-.-.-.--
/oo
!
0
5
5 /O
OXYGZN
i1
Cfl4RT NG'l
QL-ALITY
I5
20
33.9 34.0 34.2 34.8
..
1.1 1.1 1.2 1.6
...
DEPTHS Surface 14 f t . 3 4 ft. 89 f t . 129 f t . 149 ft.
APRIL5. 1916 35.8 36.0 36.1 36.3 36.4
2.1 2.2 2.3 2.4 2.4
...
It will be noted t h a t t h e colder temperatures are at t h e surface, t h a t on February 8, there was only a difference of 1.2' C. between t o p a n d bottom temperatures taken, and on April j, only 0.4' C. difference, a n d t h a t all t h e temperatures on April 5 are higher t h a n those on February 8, proving circulation from t o p t o bottom. The probable explanation of this circulation is t h a t water cooled below 4' C. becomes lighter and when i t again increases in temperature grows heavier u p t o 4' C. Any disturbance as b y wind then causes a n overturning which temperatures show is profound. Such appears t o be t h e case all winter. Only in t h e summer does t r u e stagnation t a k e place. T h e fact t h a t Kensico was filling most of t h e winter really has no bearing on t h e results in t h a t t h e same phenomenon has been noticed at Croton Lake and also there was no water running in from January 1 5 t c February 2 1 , a period of 5 weeks. Again t h e water entered a t t h e northern end a n d sampling was a t t h e southern end. The temperatures obtained on t h e different dates are shown in Table 111.
TEMPERATURC 'C
,rn,r&?co*
BOTTOM
I/ 7
1 6 " Q
POINT O f O R A U G H 7 ) 2 6 > LEGEND ! M/CR~SCOPIC o ~ f i ~ ~ s m s
FEBRUARY 8. 1916 32.7OF. 0.4' C .
25
- PPM - P PM
- OXYGEM.??M - 1EMPfRATUUt C'
WINTER C I R C U L A T I O N
OF KENSICORESERVOIR W A T E R AT VARIOUS D E P T H S
As t h e water rose difficulty was experienced with t h e pipe line bringing water from Rye Dyke a n d i t became necessary t o supplement a t t h e new dam. Service from Rye Dyke was soon discontinued a n d all draught taken a t t h e new d a m , t h e point of draught being 50 f t . off t h e bottom, t h e lowest available. Filling of t h e reservoirs, which was stopped January 15, was continued February 2 1 , a n d t h e Dykes flooded until t h e reservoir was practically full with a depth of I j j ft. on May 2 3 , 1916.
COMPLETE ANALYSES
On May 22, 1916,t h e first of a very complete set of analyses was started. Temperatures were taken by a thermophone of t h e Board of Water Supply, operated b y Mr. Glazer. The instrument was of t h e galvanometer type and readings could be made accurately t o 0.1' F. T h e instrument had been compared with standard thermometers a n d found t o be correct. Temperatures were read a t every 5 it. depth down t o I O O f t . , then a t every I O ft. depth. When the thermocline developed later its exact position was determined b y readings I f t . apart. Samples for other determinations were taken a t frequent intervals, including especially just above and just below t h e thermocline. Samples have also been taken from t h e effluent pipe each time, which have demonstrated t h a t t h e draught is actually a t t h e depth intended.
T H E J O U R N A L OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
372
Depth Ft.
1 5 10 15 20
May 22, 1 9 1 6 Temperatures Thermophone -Bottle55.1:F. -12.8'C. 55.8'F. 55.0 -12.8: 54.30 -12.4 54.0' -12.2' 52.9' -11.6'
......
...... ...... .. ....
25 30 35 40 45 50 55 60 65
70 75 80 85 90 95 100 105 110
iso
.... .... ....
-
4i:jo 4i:jo
......
......
.... .... .... .... .... .... ....
-13.2OC.
54.0°
-12.2O
.... .... ....
51.2" -10.7' 49.6' 9.8' 8.80 47.90 47.0' 8.3' 46.2" 7.9' 45.39 7.40 6.9' 44.5' 6.7' 44.0' 43.7' 6.5' 6.4' 43.6" 6.3' 43.4' 6.3' 43.3' - 6.2' 43.2O 6.2' 43.2' 43.2' 6.2' 43.1e 6.2O (Effl;ent) 42.6 5.9'
izo 4i:io iio 4 i : S o
146
....
.... ....
46.Sa
.... ....
.... ....
.... .... .. .. .. ..
....
45.0° 43.2'
.. .... .... .... .... .... ....
....
-5.60
....
-5.40
-.... 5.40 -.... 5.40
....
44.00
.... ....
....
....
TABLEI11 29,1916Temperatures Thermophone 1/a 75.1: F. 23.9; C. 5 73.2 22.9 10 72.9' 22.7' 22.4' 15 72.4' 16 7 1 . 5 O 21.90 17 66.4' 19.1O 171/z 64.3; 17.9O 20 62.4 16.9O
--June Depth Ft.
.... .... .... .... .... .... .... ....
. . . . . .
25 30 35 40 45 50 55 60 65 70
.... ....
.... .... .... ....
-8.2'
.... .... .... .... .... .... ....
75
80 85 90 95
-7.2' -6.2'
100
105 110 115 120 125 130 135 140 145 150
....
.... .... .... .... .... .... .... -6.7'
56.1' 52.9' 51.8: 50.5 48.6O 47.00 45.30 44.4O 43.7O 43.40 43.2O 43.00 42.9O 42.7' 42.5' 42.4O 42.3O 42.15' 42.05' 41.95O 41.9z0 41.9 41.85O 41.8 41.8' 41.8O
.......
.*..
....
Depth Ft.
Temperatures Thermophone
....
13.4' 11.6' 11.00 10.3O 9.2' 8.3' 7.4Q 6.9O 6.5' 6.3a 6.2O 6.1' 6.1' 5.90 5.8' 5.8' 5.70 5.6' 5.6O
--August 31. 1916-Depth Temperatures Ft. Thermophone '/a 75.6: F. 24.2; C. 5 75.6 24.2 24.2' 10 75.6' 15 75.2' 24.0" 20 74.0' 23.3' 21 73.70 23.2' 22 73.59 23.1' 22.3' 23 72.1' 20.3' 24 68.5' 25 65.7' 18.7' 30 58.0' 14.4; 35 55.50 13.1 40 53.2' 11.8' 45 51.90 11.10 50 50.50 10.3' 55 48.6' 9.2' 60 47.40 8.6' 65 46.3' 7.90 70 45.30 7.40 75 44.50 6.9' 80 44.2O 6.8' 85 43.8' 6.6' 90 43.40 6.3' 95 43.1' 6.2' 100 42.9' 6.1' 105 42.8O 6.O0 110 42.8O 6.0'
iio
5.50
5.50 5.50 5.50
5.40 5.40
5.40
.......
The analyses made May 2 2 are shown in Table 2 shows t h e temperatures, oxygen, free carbonic acid, and microscopic organisms. It is evident from t h e chart t h a t a thermocline had begun t o form a t about 2 0 f t . depth. Oxygen was abundant a t all depths and microscopic organisms a t a minimum. Comparison of t h e small bottle temperatures with t h e thermophone proved t h a t the samples came from t h e depth intended. Some change of temperature in t h e deep samples is occasioned while drawing up through t h e warmer water. This difference becomes greater as t h e surface temperatures become higher. TAB] ;E IV-QUALITY
OF
PHYSICAL
EX~UINATION
4i:io
....
5.90
....
ii6 42:40 i46 4 i : J o iio
5.80
.......
....
155 44.4O
IV. Chart No.
....
5.90
....
6.30 6.9'
The tubes were so arranged t h a t t h e bottles took 2 min. t o fill, and i t took only about one-half minute t o lower t o t h e depth desired. The analyses show the water t o be of remarkably uniform character from t o p t o bottom. On June 29, 1916,samples were again taken. The results, shown in Table I V and on Chart No. 3, indicate t h a t marked changes have taken place. A distinct thermocline has formed a t 16 ft. depth with great increase of temperature of the surface water. Microscopic organisms have increased above t h e thermocline. Free carbonic acid has increased below the thermocline
WATER A T VARIOUS DEPTHSA T KEXSICORESERVOIR BACTERIOLOGICAL MICROSCOPICAL EXAMINATION EXAMINATION of Standard Units CHEMICAL ANALYSIS per Cc. (Parts per Million) '0 IMPORTANT = Liti 5 GENERA g OR
.
-NITROGEN
.-a
-m
July 28. 1916-
7-
Vol. 9, No. 4
AS-
.-8
h
3
0
*" g%
c
v M
W
d
5/22 Surface 25 ft. 50 ft. 100 ft. 150 ft. 105 ft.(E$&unl) 6/29 Surface 16 ft. 24 ft. 50 ft. 79 ft. 105 ft.(Efluent) 150 ft. 7/28 Surface 20 ft. 25 ft. 50 ft. 7 5 ft. 105 ft. 125 ft. 1.50ft. 8/31 Surface 20 ft. 30 ft. 50 ft. 75 ft. 105 ft.(E&ent) 125 ft. 150 ft.
3 2 2 2 2 2 2 2 2 1 1 1 1 3 3 2 1 1 3 1 6 2 2 2 1 1
13 12 12 12 12 12 12 15 11 11 11 11 15 12 14 11 10 9 13 11 160 9 10 6 6 6
; 5 12
440
0 0 0 0 0 0 lo lu lV 1V
lv lU
1u 0 0 0
0
0 0 0
3v le
le IC IC
le IC
le IC
0.180 0.0200.004 0.00 48 14 34 1.3 20 13 0.1700.025 0.002 0 . 0 0 48 14 34 1.3 20 13 0.110 0.025 0.002 0.05 48 14 34 1.3 20 13 0.060 0.0300.002 0.00 48 14 34 1.3 20 13 0,1200.025 0,004 0.05 48 14 34 1.3 30 13 0.065 0.020 0.042 0.05 48 14 34 1.3 20 13 0.195 0.000 0.000 0 . 0 0 46 18 28 1.4 23 18 0.155 0.005 0 . 0 0 0 0.00 49 21 28 1.6 23 18 0.170 0 . 0 0 0 0.000 0.05 40 16 24 1.5 23 18 0.065 0,0500.002 0.10 41 14 27 1.4 22 16 0.065 0.1000.004 0.05 42 16 26 1 . 3 20 15 0.075 0.100 0.006 0.10 47 16 31 1.4 21 17 0.120 0.080 0.006 0.05 46 17 29 1.4 21 17 0.190 0.0000.002 0.05 . . . . . . . 1.8 26 16 0.215 0.020 0,0020.05 50 18 32 1.8 23 16 0.185 0.110 0.002 0.05 49 17 32 1.5 26 16 0.135 0.030 0.002 0.05 . . . . . . . 1.5 23 14 0.150 0,0200.006 0 . 0 5 46 20 26 1.5 26 14 0.190 0.005 0.008 0.10 42 14 28 1.5 23 12 0.145 0.015 0.008 0.10 . . . . . . . 1.5 25 14 0.150 0.060 0.018 0.15 1.8 . . 34 0.115 0.005 0.002 0.15 49 . 0.110 0.010 0.002 0.10 49 0.095 0.005 0.002 0.10 48 . . 0.075 0,005 0.002 0.10 43 ,. 0.0800,0050.002 0.10 51 0.040 0,005 0.002 0.10 58 .. 0.055 0.005 0.002 0.10 45 .. 0.1900.685 0.002 0.15 100
.......
... .. ..
+
70 0 0.20 0.8 11.2 12 0 0 0 0.05 1.5 10.8 17 0 0 0 ...: 1.5 10.8 0.2s 1.5 11.2 10 0 0 14 0 0 0 0.25 2.3 11.2 20 0 0 0.25 2.3 11.5 6 0 0 0 0.10 0.2 9.5 160 0 0 0.15 1.1 9.2 5 0 0 0 0.15 3.0 8.6 130 0 0 0.15 4.6 9.5 9 0 0 0 0.20 3.4 10.2 9 0 0 0 0.25 3.4 10.6 3900 0 0 0 9.4 0.20 3.8 . . . . 0.38 7.78 3 0 0 + f 520 0 0.30 2.66 7.78 120 0 0 0.30 4.56 6.04 150 0 0 4.56 7.45 6 0 n 0.35 4.56 8.61 5 0 0 6 0.60 4.56 8.78 . . . . 4.56 8.45 150 0 0 . . . . 15.20 1.90 130 0 7.40 100 0 0 6.67 175 0 0 0 640 0 0 2.20 830 0 0 5.20 115 0 0 0 7.24 7.20 40 0 7.32 540 0 0 0 320 0 0 0.57
+
....
+
+ + +
. 270 220 190 270 200 180 250 350 360 360
. 70 45 5 5 35 30 15 40 30 35 25 15 40 . . . . 2700 110 120 610 170 . . 110 80 40
.... .... .... .... ....
.. .. .. .. .. .. .. .. .. .. ..... .. .. .. .. .. ..... .. .. .. .. .. .... .... . . . . . .... ....
2950 900 330 190 130 240 90 50.. . . 10 .. 80 290 80 140 280 40 3900 4020 320 3700 3770 220 1800 1870 360 520 320 . . . . . 460 190 370 180 100 675 30 150 270 120 510 2400 . . . . . 460 125 480 130 820 .... 80 1050 50 750..... 115 520..... 60 5 7 0 . . . . . . . . . 40 570 . . . . . .... .... 30 2500
.....
0
a -5-
0-15-20-
25-Ter-perature 'C.
l
5
I
374
T H E JOCR,VAL O F IAVDCSTRI.4L A S D E;VGIlVEERIXG C H E M I S T R Y
a n d amorphous matter. Microscopic organisms have greatly increased above t h e thermocline a n d somewhat below, t h e curve conforming t o t h e temperat u r e curve very closely. Free ammonia showed certain changes also, increasing from zero a t t h e surface t o a maximum just below t h e thermocline, reducing again t o a minimum at point of draught (105 ft.) a n d increasing again t o t h e bottom, Nitrite a n d nitrate showed a slight increase from t o p t o bottom. For t h e first time B . coli appeared in both samples above t h e thermocline, also a t mid depth and a t bottom. T h e numerous regular samples taken of t h e effluent have, however, only a few times given a positive test for B . c o l i in I O cc. Another odd feature is a slight rise in temperature a t t h e bottom, probably due t o earth temperature. While not sufficient t o cause overturning in t h e quiet water of t h a t depth, this probably accounts for t h e gradual increase during t h e summer in t h e temperat u r e of t h e water below 7 5 ft. depth. On August 31, 1916, another set of samples was taken. T h e results are shown i n Table I V a n d on Chart N o . 5. T h e thermocline is sharply formed a t 23 f t . depth. The oxygen dip below t h e thermocline a n d a t t h e bottom is striking. This is accompanied by heavy amorphous matter at both points due t o t h e death of microscopic organisms which for some reason have almost disappeared a t all depths. Particularly striking is t h e reciprocal relationship between t h e oxygen a n d t h e free carbonic acid, t h e latter increasing greatly just below t h e thermocline a n d exceedingly a t t h e bottom. The bottom sample also shows a n exceedingly high color with accompanying high iron. The turbidity, free and albuminoid ammonia, amorphous matter, oxygen, a n d free carbonic acid all show t h e effect of stagnation a n d leaching of t h e bottom. T h e albuminoid ammonia decreased from t h e surface t o t h e point of draught and then increased t o t h e bottom. T h e amorphous matter increased from t h e surface t o t h e sample just below t h e thermocline, where oxygen is low, then decreased, t o increase again a t t h e bottom. The water was in satisfactory bacteriological condition throughout. T h e increase in temperature a t t h e bottom, extending for 1 5 f t . , is again noticeable. In conclusion attention is called t o t h e fact t h a t , although t h e reservoir was recently filled, draught was begun almost at once a n d all through t h e summer deep draught has been maintained at 5 0 f t . from t h e bottom. T h e water obtained has been clear, cold (43O F . ) , free from B . coli a n d low in bacteria. Microscopic organisms have been avoided, although heavy growths have occurred at t h e surface of a t y p e producing on decay disagreeable pig-pen odors. The water has also .contained abundant oxygen. The draught of 2 7 t o 30 m. g. d. has h a d no effect whatever on t h e water in t h e Reservoir. Similar results with larger draught have been obtained a t Croton Lake for several years. The fact of continuous winter circulation is also
T‘ol. 9 , NO.4
emphasized although t h e d a t a here presented in connection with Kensico Reservoir is not as complete as i t should be. The progressive changes in character of the water a t various depths accompanying t h e formation of t h e thermocline have been striking. Just below t h e thermocline and a t t h e bottom oxygen has diminished t o near exhaustion. Elsewhere i t has been abundant. Reduction in oxygen has been accompanied by increase in free carbonic acid, t h e two curves being reciprocally opposite i n character. The free carbonic acid was at a minimum above t h e thermocline, increasing below. Microscopic organisms increased greatly with increase of temperature above t h e thermocline. A slight increase in temperature in t h e bottom water was noticeable, a phenomenon we have never noticed elsewhere. MT. PROSPECT LABORATORY, DEPARTMENT OF WATERSUPPLY FLATBUSH AVE.AND EASTERN PARKWAY BROOKLYN, NEWYORK
IS THE RECOVERY OF THE NITROGEN IN SEWAGE SLUDGE PRACTICABLE?’ By WILLIAMR COPELAND
The answer t o t h e question as t o whether i t is or is not practicable t o recover t h e nitrogen in sewage a n d sewage sludge will depend upon three factors: (I) The amount of nitrogen contained. ( 2 ) The cost of recovering a n d disposing of t h e nitrogen. (3) T h e market value of t h e nitrogen. Sewage m a y be defined for t h e purposes of this article as t h e liquid a n d water-borne wastes discharged into t h e city sewers through drains from houses, buildings, factories a n d streets, together with more or less water which seeps into t h e sewers from t h e ground. In view of t h e great variety of sources a n d modes of collection of such waste liquors, sewage contains a variety of elements t h a t change in composition with t h e source, season of yea:, day of t h e week and hour of t h e day. As nitrogen is a n important constituent in many of t h e compounds, such as fecal matter, urine, horse manure, hair, meat scraps, etc., in sewage, t h e amount varies widely, both in regard t o t h e portion which is dissolved a n d t o t h e portion held in suspension by t h e liquid. Recovery of nitrogen, from t h e standpoint of this paper, has t o do principally with t h e nitrogen in suspension, because t h a t is t h e portion which appears in t h e greatest quantity in t h e sludge. T h e total obtained will vary both with t h e treatment process used and with t h e volume contained b y t h e raw sewage. T o illustrate these points t h e following d a t a are taken from Rletcalf a n d Eddy’s “American Sewerage Practice,” Volume 3: TABLEI-COMPOSITION
SOURCEOF SAMPLE
OF
DRYSEWAGE
SLUDGE
PER CENT
SLUDGE OBTAINED F R O M NITROGEN 2.85 . . Plain sedimentation 1.40 Septic tank . 1.22 Imhoff tank , 1.20 Imhoff tank , 2.77 . . . , Chemical precipitation
.. .. . . . . . . . ... . .... ..... ... ... ............. .. ... . .. .. . .
Frankfort-am-Main. Columbus, Ohio.. , Essen.. . , . . , Philadelphia, , , . . Worcester, Mass.. ,
1 Presented at the 53rd Meeting of the American Chemical Society. New York City, September 25-30, 1916.
