May, 1918
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ORIGINAL PAPERS THE FERTlLIZING VALUE OF ACTIVATED SLUDGE’ B y GEORGS0.NASMITH AND G. P. MCKAY Received February 18, 1918
T h e most important problem remaining t o be solved i n t h e disposal of sewage is probably t h a t of economically dewatering t h e sludge. Since the discovery of t h e activated sludge method, t h e necessity of devising a method of dewatering this new type of sludge has become even more urgent for t h e reason t h a t activated sludge has marked fertilizing properties, as Bartow and Hatfield2 have pointed out. I n t h e activated sludge method of sewage disposal, finely divided air is blown through the sewage. After some time t h e sludge which settles out is found t o possess remarkable properties when agitated with fresh sewage b y the same method of aeration. The sludge has become “activated” and when blown in contact with fresh sewage t h e organic matter present in t h e latter is rapidly oxidized, practically all t h e intestinal bacteria destroyed, nitrates elaborated, a n d a stable effluent formed. “Activated” sludge, however, like ordinary sludge, contains 9 5 per cent of water, and still has t o be dewatered before i t can be satisfactorily handled. The treatment of sewage by this method is very promising for if t h e fertilizing value of t h e sludge is high, t h e revenue therefrom would help t o pay the cost of dewatering and disposing of the sludge. Furthermore, it is a question of conservation of t h e first magnitude, for if a fair proportion of t h e fertilizing value of t h e excreta from our cities and towns could be saved and turned back into t h e land it would be a great factor towards solving our fertilizer problem, particularly in conserving t h e supply of humus and nitrates, a n d increasing t h e fertility a n d productivity of t h e soil. I n December 191 j a small experimental activated sludge plant was started a t t h e Toronto Main Sewage Disposal Works, Morley Avenue. Dr. Adams and ’ M r . J . Scott, who at first operated t h e plant during my absence in France, soon proved t h a t Toronto sludge could be readily activated, and the plant has been i n operation ever since. A good deal of preliminary d a t a have been obtained for our own information i n case t h e city of Toronto should ever decide t o adopt t h e method on a large scale. Among other things, we have tested t h e value of activated sludge as a fertilizer. Bartow a n d Hatfield, in some experimental work t o determine t h e value of activated sludge as a fertilizer, made a number of experiments with the growth of wheat in pots. The activated sludge used by them gave t h e following analysis: Total Nitrogen = 6.3 per = 2 . 6 9 per cent. cent; P z O ~ By t h e use of one t o n of this sludge per acre, equivalent t o 1 2 0 lbs. of nitrogen, together with 5 tons of dolomite, ‘/zt o n of bonemeal, and 5 0 0 lbs. of potassium sulfate per acre, they obtained a yield of 36 t o 371/2 1
See communication from P. Rudnick in N o t e s and Correspondence. 8 (1916), 17.
’ TEISJOURNAL,
bu. of wheat per acre as against 13l/2 bushels per acre where the equivalent amount of nitrogen had been added in t h e form of dried blood. The straw also amounted t o over two tons per acre a s against less t h a n ”4 of a ton of straw per acre where dried blood h a d been employed as fertilizer. I n further tests as t o the value of sludge as a market garden fertilizer, these investigators used plots, each 2 f t . X 3 f t . , which were treated with equivalent quantities of sludge and dried blood per acre. They obtained a n increase in weight of 40 per cent in t h e
FIG I--SHOWING GROWTHON EXPERIMENTAL PLOTS,
JULY 18.
1917
lettuce and 1 5 0 per cent in the radishes, and the growth was much more rapid in t h e beds fertilized with activated sludge. They conclude from their experiments “ t h a t t h e nitrogen in ‘activated sludge’ is in a very available form, and t h a t activated sludge is valuable as a fertilizer.” Bartow and Hatfield, in determining t h e amount of fertilizer t o be employed, used as a basis t h e amount of nitrogen present. For instance, they used in their experiments t h e quantity of activated sludge a n d dried blood t h a t would yield 1 2 0 lbs. of nitrogen per acre.
340
T H E J O U 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 I I E M I S T R Y
The amount of phosphate or other ingredients present in the sludge was not concidered. TNI. V A I , U E
OF FLRTIIIZERS
Experience has proved t h a t t h e value oi fresh manure as a crop producer is from one third t o twothirds more effective t h a n rotted manure, because a certain proportion of the nitrogen and other in-
gredients have been leached out of the latter and lost. Manure has a greater fertilizing value than would he estimated from t h e amount of nitrogen, phosphoric acid and potash present. This greater value is due t o t h e large amount of humus present in t h e manure; humus is not found t o any extent in t h e commercial fertilizers, which are commonly purchased on their nitrogen, phosphoric acid or potash content. Humus is partly decomposed organic matter, such as decayed leaves. I t is found in large quantities in all fertile soils and is probably t h e most valuable constituent present, because i t is not only a source of nitrogen, b u t it helps t o keep t h e soil moist, loose and well aerated, as well as t o provide a medium ior the propagation of soil organisms so essential t o the growth of plant life. T h e chemical constituents in a iertilizer are not the only ones upon which its fertilizing value must be determined. It would be possible t o have the same amount of potash, nitrogen and phosphate in two differe n t fertilizers and yet obtain entirely different results upon plant growth. The availability of t h e food material for the assimilation oi the plant is a great factor. Thus ordinary septic sludge is not a good fertilizer ior immediate growth of plants, results obtained the first year being poor. But the trans-
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formation of t h e septic sludge taking place in the soil frees t h e plant fond material locked u p in this sludge and renders i t available, so t h a t i t becomes an excellent fertilizer the second year after i t has been dug into t h e soil. The experiences of a number of amateurs in Toronto who have been using ordinary septic sludge for several years in their vegetable and rose gardens, have quite established this fact. The truest test of fertilizers is not their content of nitrogen, phosphate or other chemical, b u t rather the availability of the chemicals present as food for growing crops and the actual increase in the yield brought about by t h e fertilizer. Hcre again t h e fertilizers must he differentiated according t o their ability t o produce immediate results. We must determine whether they are available through t h e growing season: whether they leave a residue of humus and other materials in the soil, and whether they bring about c.xhaustion oi the mineral elements of the soil or not. Activated sludge, when air-dried, is a dark brown, iriable, perfectly inoffensive material with a slightly earthy odor like t h a t of decayed leaves. I t consists largely of humus, b u t contains much more nitrogen, phosphoric acid and potash t h a n does ordinary barnyard manure. Furthermore, i t is crowded with millions of the nitrifying t y p e a i organisms so essential t o plant growth. I>or the reasons given above as t o the fertilizing value of manure, we have taken this for our standard of comparison and have not compared the fertilizing value of sludge with commercial iertilizers on a nitrogen, phosphoric acid or potash basis. T h e real single, final test of any fertilizer or manure is t h e increase in the yield produced by i t when compared with a n equivalent amount of barnyard manure.
I I k . III-I'L"STR*TrNo
TABLE
2
We selected ior our plot experiments a site on very t o our exaerimental -Door.. humus-free clav soil.. adiacent . plant.
The surface was scraped t o free it of any or-
T H E J O C ' R N A L OF I N D L T S 1 ' R I A L A N D E N G I N E E R I L V G C H E M I S T R Y
May, 1918
341
ganic matter present, and four inches of water-washed sand were then thoroughly incorporated with t h e soil t o a depth of t e n inches. This was done t o permit of aeration, t o prevent the soil baking in t h e sun, and t o make the soil friable. Six beds, each I O f t . X 4 ft., were then laid out and separated from the paths by boards placed edgewise in the ground. One bed was kept as a control, and no fertilizer added t o it. The second was treated mith 2 7 lbs. of airdried horse manure, and the other four each with 27 lbs. of air-dried sludge (equivalent t o r41/2 tons t o the acrc). This is summarized below: Quantity BED
No I No. 2 No. 3 No. 4 No. 5 No. 6
Air-dried Fertilizer Nose Manure
Activated sludse Sludge from old bed Ilumus-Brush filter Sludgetanks
Used
n
271bs. 271br. 271bs. 271b~. 27 Ibs.
Total
Total
Nitrogen PsOe Per cent Per cent 0 0 1.90 1.00 2.50 2.46 1.10 0.85 1.30 1.20 1.21 1.24
On May 18, 1917, the fertilizers were added and thoroughly incorporated with the soil, and on May 2 1 , the seeds were planted in all t h e beds. Seeds were used except in the case of tomatoes and Spanish onions. A fairly thick planting was made so t h a t plenty of seedlings would he available when thinning o u t , and a uniform number of strong seedlings of each variety could be left in each bed. As each row of vegetables was pulled from the several beds a t the same time, the complete plants, leaves a n d all, were placed in bags, labelled and brought t o the laboratory. After the removal of adherent earth the product of each bcd was weighed; the tops, in the case of root crops, n-ere then takcn offand weighed separately
lria. ~ - - - I L L U J T I I I T TABLH ~E 7
and the difference taken as the weight of the root. Kotes were also made as t o the quality of the crop. Before weighing, the crops were spread out on t h e floor i n their respective groups and photographed. The photographs, however, gave only a general idea of t h e difference in size of t h e various groups because of t h e fact t h a t the camera had t o be tilted, io consequence of which the rows closer t o t h e camera appear larger and the r o m farther away smaller t h a n they should be. The plan adopted worked very well in practicc and gave, we think, fair comparative results. Daily observations were made b y t h e man who looked after the beds, and who was himself a gardener, as t o appearance of the various vegetables, temperature, rainfall and cultivation. When he cultivated one bed he cultivated all the beds; if he watered one he watered all, and used the same amount of water, and when he pulled one variety he pulled t h a t variety from all the beds. I n this may we tried t o eliminate every factor which might give any advantage t o one bed over another, and t o remove cvery influence t h a t might have had any bearing on the growth of t h e plants except the actual efiect of the fertilizers themselves during the course of one season. 1 he folloxing are synopses of the results obtained:
,.
i - n ~ n r . ~n m s x m Acti- Morley N. Terrontu COD. vated Aue. c _ _ _ trot M a n w e Sludge Sliidge Humus Sludge 42 4ii 757 317 SS2 752 59 350 490 200 417 518 33 I05 267 117 165 234
TABLE
weigirt, totai--yrams
Weight, rwts-grams Weight, tops-grams 1ncreare in roois oYe/ E O , , . trol-percent . . . . . . . . . . . . . . Yield per acre- i o n s . . . . . . . . . . Weight, toial--grams Yield per acre-tons..
493 730 5.04 7
T~a1.l;2-HLan 31 238
.......
.. ........
239
606
778
.........
L~TTUC~ 484
667 1461 1.9 3.88
. . . . . . . . . . . . . . . . . . . . . . . . . . .
T A ~ 3-1,I;TTvcE. L ~
.....
Weight. totrl--grarnr.. 75 Increase OIirr control-per cent... . . . . . . . . . . . . . . . . . . . Yield per aere---fons..
........
Gamm RAPIDS Mhsing 524 155
277
248
Miasins 598
269
228
Miasins
IO6
............
T H E J O U R N A L O F I L V D U S T R I A L A N D ENCILVEERI.\~C
342
TABLB +BEANS 290 525
Weight, total-grams ....... 256 Increase oyer control-per cent S i d d per acre-tons.. . . . . . . . .
......................
357
15.6 105 1.78 3.16
377
531
.3 9. . 4. . 4. 7.. 2. .107.
TABLB S-BBETS
Weight, tot3il-grams ....... 79 1796 3437 1160 Weisht,roots-erams ....... 24 730 1737 437 Increase OYer control-per cent ...................... 2941 7137 1304 Yield per acretons.. 5 . 8 5 13.90 'I'A~LE6--L*rs R I ~ ~ S H E S Weieht, total--grams ....... 32 7.5 315 472 Weight. roais---gr"ms ....... I8 43 179 283 Increase OYer contro1-per cenf. ..................... 139 894 1470 Yield ~ c acre-tons.. r TABLt3 7-TOMRTOIIS W e i ~ h f tota-grams , 29 422 1654 164 N ~or.tomatoes ............ 2 9 15 2 Average weight of single iomato-giams ............ 14% 47 110 82 Increase DYer cootm-per cent ...................... 1355 5603 466 Yield per acre-tons.. . . . . . . . . 5 . 0 7 19.9 TABLR 8-Cnnx"Ts Weiebt, totsl-.gianis.. 885 1680 1535 1425 Increase 0"er contro1-per cent ...................... 96 80 66 Yield ptr a c r e t o n s . . . . . . . . . . 20
2012 891
2945 1169
3612
4770
285 197
738 452
1006
2410
533
1184 13
.........
........
.......................
.......
6
89
91
1738
3983
1560
2695
.........
.....
82
.........
'rani.- ~ - - O ~ ( ~ O N SS,Y I N Z S X (16 Weight, toCal--grams . . . . . . . 41 96 280
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this t h o , mndc a good showing and indicated t h a t aerobic action and nitrification of this sludge had taken place in t h e earth, rendering this fertilizer available as a plant food. TABLE 7--The tomatoes xcre picked October 2. During the growing season the tomato plant i n the activated sludge bed had been most vigorous; thc tomatoes had also ripened first. on the beds treated with activated sludge a n d S o r t h Toronto sludge. The activated sludge bed gave tbe greatest number and t h e greatest total weight of tomatoes. The activated sludge gave a yield of 300 per cent in excess over t h a t of the manure bed, showing t h a t a c t i v a k d sludge is a n ideal fertilizer for tomatocs. The yield from the plot fertilized with Korth Toronto sludge was considerably behind the activated sludge, though away ahead of the manurc plot.
215 32.4
nns)
142 08 OYPi control-per c e n i . . . . . .. . . . . . . . . . . . . . . . 134 583 246 64 Yield per acre-tons.. . . . . . . . . 1.2 3.4 TABLEIII---ONIONE, RED WEATXIKIIELD (8 Bssr) Wright, toiaI---granir . . . . . . . 67 110 720 239 223 1nrrease D Y e r Coiltroi~~P" cenf . . . . . . . . . . . . . . . . . . . . . . 64 974 256 235 Yield per acre---fons., . . . . . . . . 1.3 8.7 T ~ ~ ~I i-oNioas, ~ . K D I ~ ~ ~ I ~ ~~~~s S (8 s m ) Weizht, totd---grams ....... 67 124 232 260 184 1ncrrase Over 'Oo,.rol---yer ~ p . t ...................... 85 246 288 174 Yield p a acre-tons 1.5 2.8 . . . . . . 1ncre:rre
327
......
700 3.9
......
527 5. I
..
o x TAH1.T.S
CSII
