LIBRARY. A & M COLLEGE- CAMPUS. E6-432-6M-L180 TEXAS AGRICULTURAL EXPERIMENT STATIIIN A. B. CONNER, DIRECTOR common STATION, BRAZOS COUNTY, TEXAS APRIL, 1932 3ULLETIN NO. 445 DIVISION OF CHEMISTRY The Composition and Fertilizing Value of Sewage Sludge AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS T. O. WALTON, President STATION STAFF i Administration: A. B. Conner, M. S., Director R. E. Karper, M. S., Vice-Director Clarice Mixson, B. A- Secretary M. P. Holleman, Jr., Chief Clerk J. K. Francklow, Asst. Chief Clerk Chester Higgs, Executive Assistant Howard Berry, B. S., Technical Asst. Chemistry: G. S. Fraps, Ph. D., Chief; State Chemist S. E. Asbury, M. S., Chemist J. F. Fudge, Ph. D., Chemist E. C. Carlyle, M. S., Asst. Chemist. T. L. Ogier, B. S., Asst. Chemist A. J. Sterges, M. S., Asst. Chemist Ray Treichler, M. S., Asst. Chemist W. H. Walker, Asst. Chemist Velma Graham, Asst. Chemist Jeanne F. DeMottier, Asst. Chemist R. L. Schwartz, B. S., Asst. Chemist C. M. Pounders, B. S., Asst. Chemist Horticulture: S. H. Yarnell, Sc. D., Chief **L. R. Hawthorn, M. S., Horticulturist H. M. Reed, M. S., Horticulturist J. F. Wood, B. S., Horticulturist L. E. Brooks, B. S., Horticulturist Range Animal Husbandry: J. M. Jones, A. M., Chief B. L. Warwick, Ph. D., Breeding Investiga. S. P. Davis, Wool Grader Entomology: F. L. Thomas, Ph. D., Chief; State Entomologist H. J. Reinhard, B. S., Entomologist R. K. Fletcher, Ph. D., Entomologist W. L. Owen, Jr., M. S., Entomologist J. N. Roney, M. S., Entomologist J. C. Gaines, Jr., M. S., Entomologist S. E. Jones, M. S., Entomologist F. F. Bibby, B. S., Entomologist S. W. Clark, B. S., Entomologist "E. W. Dunnam, Ph. D., Entomologist **R. W. Moreland, B. S., Asst. Entomologist C. E. Heard, B. S., Chief Inspector C. Siddall, B.~S., Foulbrood Inspector S. E. McGregor, B. S., Foulbrood Inspector Agronomy: E. B. Reynolds, Ph. D., Chief R. E. Karper, M. S., Agronomist P. C. Mangelsdorf, Sc. D., Agronomist D. T. Killough. M. S., Agronomist H. E. Rea, B. S., Agronomist B. C. Langley, M. S., Agronomist Publications: A. D. Jackson, Chief No. 1, Beeville, Bee County: R. A. Hall, B. S., Superintendent No. 2, Lindale, Smith County: P. R. Johnson, M. S., Superintendent **B. H. Hendrickson, B. S., Sci. in Soil Erosion **R. W. Baird, B. S., Assoc. Agr. Engineer No. 3, Angleton, Brazoria County: R. H. Stansel, M. S., Superintendent H. M. Reed, M. S., Horticulturist No. 4, Beaumont, Jefferson County: R. H. Wyche, B. S., Superintendent **H. M. Beachell, B. S., Jr. Agronomist No. 5, Temple, Bell County: Henry Dunlavy, M. S., Superintendent C. H. Rogers, Ph. D., Plant Pathologist H. E. Rea, B. S., Agronomist. S. E. Wolff, M. S., Botanist **H. V. Geib, M. S., Sci. in Soil Erosion **H. O. Hill, B. S., Jr. Civil Engineer No. 6, Denton, Denton County: P. B. Dunkle, B. S., Superintendent **I. M. Atkins, B. S., Jr. Agronomist No. 7, Spur, Dickens County: R. E. Dickson, B. S., Superintendent B. C. Langley, M. S., Agronomist No. 8, Lubbock, Lubbock County: D. L. Jones, Superintendent Frank Gaines, Irrig. and Forest Nurs. Teachers in the School of Agriculture Carrying G. W. Adriance, Ph. D., Horticulture S. W. Bilsing, Ph. D., Entomology V. P. Lee, Ph. D., Marketing and Finance D. Scoates, A. E., Agricultural Engineering A. K. Mackey, M. S., Animal Husbandry ‘Dean School of Veterinary Medicine. (V Qlxlaemnnillfi Veterinary Science: *M. Francis, D. V. M., Chief H. Schmidt, D. V. M., Veterinarian I. B. Boughton, D. V. M., Veterinarian "F. P. Mathews, D.V.M., M.S., Veterinaril W. T. Hardy, D. V. M., Veterinarian ————, Veterinarian Plant Pathology and Physiology: J. J. Taubenhaus, Ph. D., Chief W. N. Ezekiel, Ph. D., Plant Pathologist W. J. Bach, M. S., Plant Pathologist C. H. Rogers, Ph. D., Plant Pathologist Farm and Ranch Economics: L. P. Gabbard, M. S., Chief W. E. Paulson, Ph. D., Marketing C. A. Bonnen, M. S., Farm Management **W. R. Nisbet, B. S., Ranch Management **A. C. Magee, M. S., Farm Management Rural Home Research: Jessie Whitacre, Ph. D., Chief Mary Anna Grimes, M. S., Textiles Elizabeth D. Terrill, M. A., Nutrition Soil Survey: **W. T. Carter, B. S., Chief E. H. Templin, B. S., Soil Surveyor A. H. Bean, B. S., Soil Surveyor R. M. Marshall, B. S., Soil Surveyor **M. W. Beck, B. S., Asst. Soil Surveyor Botany: ' V. L. Cory, M. S., Acting Chief S. E. Wolff, M. S., Botanist Swine Husbandry: Fred Hale, M. S., Chief Dairy Husbandry: O. C. Copeland, M. S., Dairy Husbandman Poultry Husbandry: R. M. Sherwood, M. S., Chief J. R. Couch, B. S., Asst. Poultry Hsbdma Agricultural Engineering: H. P. Smith, M. S., Chief Main Station Farm: G. T. McNess, Superintendent Apiculture (San Antonio): H. B. Parks, B. S., Chief A. H. Alex, B. S., Queen Breeder Feed Control Service: F. D. Fuller, M. S., Chief James Sullivan, Asst. Chief D. Pearce, Secretary . Rogers, Feed Inspector . Kirkland, B. S., Feed Inspector . Reynolds, Jr., Feed Inspector . Moore, Feed Inspector Wilson, B. S., Feed Inspector Wickes, B. S., Feed Inspector MFWWFW u>Upm SUBSTATIONS No. 9, Balmorhea, Reeves County: J. J. Bayles, B. S., Superintendent No. 10, College Station, Brazos County: R. M. Sherwood, M. S., In Charge L. J. McCall, Farm Superintendent No. ll, Nacogdoches, Nacogdoches County: H. F. Morris, M. S., Superintendent “No. 12, Chillicothe, Hardeman County: J. R. Quinby, B. S., Superintendent **J. C. Stephens, M. A., Asst. Agronomist No. 14, Sonora, Sutton-Edwards Counties: W. H. Dameron, B. S., Superintendent I. B. Boughton, D. V. M., Veterinarian W. T. Hardy, D. V. M., Veterinarian O. L. Carpenter, Shepherd G. Babcock, B. S., Asst. Entomologist No. 15, Weslaco, Hidalgo County: W. H. Friend, B. S., Superintendent S. W. Clark, B. S., Entomologist W. J. Bach, M. S., Plant Pathologist J. F. Wood, B. S., Horticulturist No. 16, Iowa Park, Wichita County: C. H. McDowell, B. S., Superintendent L. E. Brooks, B. S., Horticulturist No. 19, Winterhaven, Dimmit County: E. Mortensen, B. S., Superintendent **L. R. Hawthorn, M. S., Horticulturist Cooperative Projects on the Station: J. S. Mogford, M. S., Agronomy F. R. Brison, B. S., Horticulture WV. R. Horlacher, Ph. D., Genetics J. H. Knox, M. S., Animal Husbandry A. L. Darnell, M. A., Dairy Husbandry iAs of March 1, 1932. "In cooperation with U. S. Department of Agriculture. Sewage sludge is a by-product from the purification of the _ sewage at several hundred towns and cities of Texas. Two types of sewage sludge are produced: the digested sludge and the activated sludge. Digested sludge is the sludge pro- duced from the sewage of most of the towns and cities in Texas, while activated sludge is produced by only one or two. Digested sludge is low in plant foodt containing, on the average, 1.9 per cent nitrogen, 1.6 per cent total phos- a phoric acid, and 0.2 per cent potash, in the dried condition. The results of a number of pot experiments here reported indicate that the nitrogen of digested sludge has an avail- ability of about half the availability of the nitrogen of cottonseed meal. Dried digested sludge closely resembles farmyard manure in composition. It has sufficient plant food, of sufficient availability, to justify its use in a manne-r similar to that of ordinary farm manure. Digested sludge may be utilized by farmers who live near enough to sewage disposal plants to be able to haul it away to advantage. Dried activated sludge contains about 5 per cent nitrogen and 2 per cent available phosphoric acid. The nitrogen of activated sludge has a good availability to crops, about equal to that of cottonseed meal, and it also passes the chemical tests for activity. Dried activated sludge has about 70 per cent of the fertilizing value of cottonseed meal, and it can be used as a fertilizer in the same way as cotton- seedr meal, either alone or mixed with other materials. CONTENTS - Introduction y Kinds of sewage sludge g Fertilizing constituents of sludge Other constituents of sludges Availability of the nitrogen of sewage sludge Pot experiments to estimate the availability of the nitrogen in sludge.-__.i a Discussion of results of the pot tests Nitrification of sewage sludge Utilization of sewage sludge I Summary References ULLETIN NO. 445 APRIL, 1932 l THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE G. S. FRAPS. ' VSewage sludge is a by-product from the purification of sewage, produced - large quantities by a number of Texas towns. The lawsuof Texas forbid contamination of streams or water courses with sewage. This fact lecessitates the purification of sewage before it is discharged, by prac- ally every incorporated city or town in Texas with a population of over 000. A certain amount of solid matter, or sewage sludge, is formed in ‘1- process of purification. As there are several hundred municipalities grifying sewage, large quantities of sewage sludge are produced, which ust be utilized or otherwise disposed of. Activated sludge is known to gyve fertilizing value; most of the sludge produced in Texas is digested y’ udge. If this digested sludge could be used economically for fertilizing lurposes or otherwise, it would aid the municipality in the troublesome roblem of disposing of the sludge. If it could be used as a fertilizer to pply plant food, its use should also be of advantage to the farmer or ‘rdener. The chief object of the work here presented was to ascertain digested sludge might be used for fertilizing purposes. f; The value of a fertilizer is considered to be chiefly due to the nitrogen, hosphoric acid, and potash it contains, and upon the extent to which these plant foods can be taken up by plants. While it is known that, under ex- jkeptional conditions, other elements have a value to crops, at the present time this need seems to occur in small relatively isolated areas. The fer- f, ilizing value of sewage sludges depends upon the percentages of total fnitrogen, available phosphoric acid, and water-soluble potash they contain and also on the availability of the nitrogen in them. If the plant food r annot be taken up by plants, it obviously has no value to them. KINDS OF SEWAGE SLUDGE i l The first step in the purification of sewage is the removal of most of the k suspended material, or raw sludge, either by settling, or by settling and ll the action of organisms. Two widely different kinds of sludge are produced and must be disposed of. The disposal of the sludge is sometimes trouble- l some and expensive. ' Digested Sludge. In the Imhoff type of process which produces digested o sludge, the raw sludge is retained in closed tanks and undergoes "an exten- S‘ sive decomposition. Bacteria and other organisms develop and break down the organic matter, converting the less resistant material into gases and soluble materials. The least resistant material is destroyed, and the more resistant material remains. The digested sludge, therefore, consists largely of material which has resisted the action of the bacteria, and its organic matter could not be expected to decay rapidly in the soil. For this reason also, its content of plant food is low and the availability of the plant food a : 11w WW7»"is~.,vw-,r;,,1",,.,n,$.,. V 6 BULLETIN NO. 445, TEXAS AGRICULTURAL EXPERIMENT STATION can be expected to be lOW. Most of the sludge produced from the pu cation of sewage in Texas is digested sludge. ‘ ' Activated Sludge. In the activated-sludge process, the sewage is se with activated sludge and air is passed through the mixture. There is i extensive growth of protozoa and other organisms, which take up some, the dissolved material in the sewage. The organisms adhere to the ‘A pended solids, and cause them to settle (3). If the sludge introduced properly active, the sewage is clarified in 6 to 24 hours. The sludge c sists partly of solid organic material from the sewage and partly of b0, of the organisms which produce the clarification and take up some of dissolved constituents'of the sewage. For this reason, it contains m nitrogen thandigested sludge, decays more readily in the soil, and its food can be expected to be more readily available than the plant food ‘p, the digested sludge. There are a number of plants in Texas which I the activated process of purification, but most of them digest the activa ' ’_ sludge in tanks, and thereby produce digested sludge as the final produ FERTILIZING CONSTITUENTS OF THE SLUDGE The fertilizing constituents of_a number of samples of dried sewa sludge, as collected in Texas, are given in Table 1. The composition of moist or wet sludge would of course be lower, in proportion to the quanti of water present. The composition of the sludge depends upon the co_ position of the raw sewage, the particular tanks and apparatus used '} the treatment, the time and temperature of the digestion of solids, a, other factors. Consequentlypa variation in the composition of the slud is to be expected between different places, and between different times :- the same place. The digested sludge contains 0.88 to 2.99 per cent of nitrogen with a‘ average of 1.87 per cent. iThe total phosphoric acid varies from 0.47 3.74 per cent, with an average of 1.57 per cent. The available phosphori I acid, in the samples analyzed varies from 0.21 to 2.30 per cent in the digeste sludge, with an average of 1.07 per cent. The potash varies from 0.02 ‘- 1.44, with an average of 0.24 per cent. " The activated sludge contains 3.59 to 5.54 per cent of nitrogen, usualli over 5 per cent. It not only contains more nitrogen than the digested sludge,_ but it is more nearly uniform in composition. It conitains practically potash. It contains about 2.5 per cent of total phosphoric acid, and usually. f1 over 2 per cent of available phosphoric acid. Activated sludge contains about 70 per cent as much nitrogen as cottonseed meal. e Either type of sludge contains sufficient plant food to justify applying it to the soil. OTHER CONSTITUENTS OF THE SLUDGES I Constituents other than the fertilizing elements are shown in Table 2. A It is to be noted that the sludges contain high percentages of ashpranging i‘ 7 THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE _ m . . , . . . . . , . . . . . . . . . . . . 1 mud ................. ..=oAw:ofl||smoE 3 63.3w Aafifimfim v25 mmim . . , . . . . . . . . . . . .. QWN 3.... coAwsofliwwsAm wwfiwipua AEEQ AmmAm w?“ . . , . . . . . . . .. a mmd :6 .... 1mm?» wmxfiw3mem .325? wwfifi/Euwv wficwmaoig mmwvm 2.... . . . . , . . . . . . , . . . . . . . . . .. $4. ............................................. .. Ezwomlwmwsz Awfi>so< oAmmm m3. . . . . . . . . . . . . . . . . . . . . . . .. EA ............................................. -- Evaflamlwizm wwfigzfi» mifi EB NN. EA N». m: mm.” ............................................ .- =8msomiwwsz Amzwzunz» wEwA .... 1 Aw. . .. AAA A3. lwwwsa A6§>$Q< $2; :3 AN. $A 5.. EA 5A 88 mug? wfiwwwmm wwfifiwi» .... .. mm. NQN 3mm oAcofilw swwlomusi uwpmwwmm 93mm HM . . . , . . . . . , . . . . . . .- mm. mm. .............................................. 1 8am Amlwfizi AmsmwwAm _ 8&3 . . . . . . . , . . . . . . . . .. 3N 3A omwm AmTlwuAzzm AxswwwAnA 3mm» Awd mm. . . . , . , , . . , ,. 3A 2.5 ................................................... z wfiniwlbuwzfim wwpwwwmfi mwmAm mm...» AA. 5. m6. SA 3A ............................ =¥AAwQ|wwA5Aw EOSEH v5» cwzwuéw mvoAm .... .. 2. ma. mm. mNA 3A noAAwAm wuwzouiwiaw ow .... .. Jpsmmwafl wmoflwwn Awwis woamwmfiv wwwiw woawommfi wAoAm AA. Aw. mm. wAA mmA .............................................. JEEEm wwwzaolwfifi. 3 JAAAmwoAQ wwuswmn nwwmfl wwawwuflv mwwfiw wouwwmmfi mAoAm .... .- AA. moA i. omA 3A wuwzoolmzmw om dnfimmoan wwubwwn nwwfls vouwwumw wwwfiw woamwwmQ wAoAm - .. mm. 3A am. 3A EA ............................................. ..Efi§.m wwwzoofwfiww 2 daflmmwum wwofiww» HQUCB. wmpwwmmw wmufim UQwwQMMQ wfioam $4. ma. 5A A»... wmA 5A ............................................. 13am AHLwwAAAw wwAmwwAQ N85 A3. 5. o2 3A 3;“ fiflm ..................................................... ; oowglowcs? wwAwwwAQ AAoAm AAEA S. AmA mm. AKA EA .......................................... .. BAAESQAULwwAAAw wwawowAnA A805 $4. 3. AéA AN. wNA mwA ......................................... x ofinwm cwmLwwsAw wwpwwwmfl owAcw 5d 5. 3A mm. 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N444 N4..NN ....... 14.44.241.441; 444.441.49.444. 4§$N4m . 4.44.45 _ 54444444444 44.44444 034940 mcawouiwm in 054d m4 mo: M442 3.443 44.0.4 umnfisz 3.44.40 44344494444 4.4444 haouwuonwQ 4494M .4449. uomllwmwgm wMQBww mo manwdumamcoo 482444434402 d @3449 f .'-*‘Tv.~v~rvi l, _ THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE 9 from 33 to 76 per cent. The ash consists chiefly of material insoluble in f i l i‘ g v amounts of lime. The nitrogenous constituents are not shown shown in Table 1 were calculated to protein, by multiplying the nitrogen acids, but also contains some iron and aluminum oxides, and appreciable Next to protein, the grease makes up the chief constituent of the organic part of the sludge, in most cases, though it is low in some of The sludge contains some pentosans and some crude fiber. the samples. in the table, but if the nitrogen by 6.25, the protein would seem to be the ingredient present in next largest a quantity to the ash. The organic constituents of sludge do not constitute a especially good materials for the formation of humus in the soil. i dated sludge, AVAILABILITY OF NITROGEN OF SEWAGE SLUDGE Several workers have estimated the availability of the nitrogen of activ- both by means of pot experiments and by chemical methods. Noer, in Wisconsin (12/7) in pot experiments found that 36 per cent of the nitrogen of activated sludge was taken up by oats, compared with 39 to 44 per cent from cottonseed meal, and 46 per cent from dried blood. Ex- tensive field experiments also indicated that the plant food in activated sludge has a good availability and is effective for use on plants. Haskins (5) in Massachusetts found 68 per cent of the nitrogen of activated sludge was taken up by millet, compared with SOIper cent of that of dried blood, and 68 per cent of that of cottonseed meal. Reynolds (13) in Texas found that activated sludge increased the yield of cotton 17 per cent and the yield of corn 13.9 per cent. Haskins (4) also found activated sludge to pass the chemical tests both by the neutral permanganate method and by the alkaline permanganate method. Tests made in connection with ‘the Texas work here reported on 3 samples of activated sludge showed that over 80 per- cent of the nitrogen was soluble in neutral permanganate solution, and the nitrogen of acti- vated sludge therefore passed the chemical test for availability. These tests show that while the nitrogen of activated sludge is not as available as that of dried blood, it has a good availability and is suitable for use as a fertilizer either alone or as an ingredient of a mixed fertilizer. While tests of the availability of the nitrogen of digested sludge, have been made (1, 2, 8, 11, 14, 15), no exact tests have come to the attention of the author. The high value of activated sludge seems to be definitely established (5, 8, 12) ; so the work on the availability of nitrogen in sewage sludge here reported has been directed chiefly to that in digested sludge. POT EXPERIMENTS TO ESTIMATE THE AVAILABILITY OF NITROGEN IN SEWAGE SLUDGES The efficiency of the nitrogen in a fertilizer can be measured by the quantity of nitrogen taken from a definite amount of it by a crop grown in pot experiments, compared with the quantity of nitrogen taken up from a definite quantity of a standard fertilizer under the same conditions. The weight of the dried crop is sometimes used as a measure of the effect of 10 BULLETIN NO. 445, TEXAS AGRICULTURAL EXPERIMENT STATION the fertilizer, but as the percentage of nitrogen in the crop may vj with the different treatments, the Weight of the crop would not necessa . be in proportion t0 the amount of nitrogen taken up and cannot be c“ sidered to be a satisfactory measure of the availability of the nitro The Weight of nitrogen taken up by a crop grown on the soil or sand without any addition of nitrogenous fertilizers, should also be ducted from the weights of nitrogen .taken up by the crops grown the fertilizer being studied in order to get the net effect of the additi, Phosphoric acid, potash, and sometimes other plant foods, should be ad’ to all the pots in sufficient amounts to ensure that nitrogen is the limiti element. '3 The pot experiments here reported were conducted by the usual meth used in_this laboratory. Each pot containing 5,000 grams of soil or say‘, ' received additions of dicalcium phosphate and potash salts, and the vario . nitrogenous materials in amount equivalent to 0.1 gram of nitrogen in _ cases, but 0.15 gram of nitrogen wasapplied in some of the experimen The sand received, in addition, magnesium sulphate and sodium chlorii The plants were watered three times a week, or oftener, if needed, u} were kept in a greenhouse. At the end of about two months, the plan were cut, dried, weighed, and subjected to analysis. ‘é Eight different soils or sands were used. The sand or soils used we i selected as being low in nitrogen and are described as follows: " No. 22194. Builders sand, containing .003 per cent nitrogen, and with .40 per cent basicity to acid. No. 31116. Washed silica sand, quartz. No. 31185. Hidalgo clay loam, 7 to 19 inches deep, from Frio county, containing 0.89 per cent nitrogen, with a basicity to acid of 10.0 per cent. No. 31887. Duval fine sandy loam, 7 to 19 inches deep, from Frio county, containing .039 per cent nitrogen, and with a basicity of 0.15 per cent. No. 31889. Webb fine sandy loam, 7 to 19 inches deep, Frio county, containing .083 per cent nitrogen, with a basicity of 0.95 per cent. ’ No. 33124. Moscow fine sandy loam, 0 to 3 inches deep, Polk county, containing .047 per cent nitrogen and with a basicity of .20 per cent. No. 33131. Bowie fine sandy loam, 7 to 15 inches deep, Polk county, containing .020 per cent nitrogen and with a basicity of .01 per cent. No. 33135 Susquehanna fine sandy loam, 7 to 18 inches deep Polk county, containing .025 per cent nitrogen with a basicity of .07 per cent. DISCUSSION OF RESULTS OF THE POT TESTS Detailed results of the tests are given in Tables 3, 4, and 5. A summary/i of the results is given “in Table 6, which shows the net amount of nitrogen: _ taken up by the plants, expressed in percentage of the amounts addedfi Table 7 contains‘ the comparative availability of the nitrogen in the-Q various materials, compared with that of nitrate of soda equal to 100.1? That is to say, the quantity of nitrogen taken from the nitrate of soda‘ 11 THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE .... .. Mmfi. £2. $2. 2. v2 Z 5w Nd ism a. QSSZ m ..... .. $3. 3. Haw Z Eu Nd .326 mo vfififiZ . . ..... Si. 3. i: Z Em Nd g3 we QFEZ ZEN...“ Ra... $1 Q5 Z Eu 3A6 63$. Jwwfi wwwaafioo 6N 5 . . . . . . . . . . . . .- 3:5. mo. mdfl z EM wbad dwfimw Jwws UwwmGoaaOU mUN mm . . ...... memo. S. N: Z EM 2A6 63$ Jawfi wwefiofioo mom 3 WW». mmww MMWZ. 22. . 5. f: Z Em £5 5%“ dwwfim wfiwzfié 5N Q . . . . . . . . . . . . .. .33. ma. 9M3 Z EM mad AZNNw 6E5? wait/Gm)‘. Zmu an . ...... .- 2.2. 3. Q3 Z Em £5 éZmmw awwzw wwfizai 5N 3 Cm QM? 8w... 5%. S. W3 Z Em I. ism w. 0225A m ..... .. $2. E. 93 Z EM Z6 éwom mo oaafizZ . . ..... .. 3M8. Ev. 52 Z Em I. 5E5 mo 8.332 mwn mmwc. wmwm... .58. S. d2 Z Eu mm... 63$ :68 wwwwzctoo mom . . . . . . . . . . . . .- m3... mm. 13 Z EM wwo. 63mm 16E uwwmaofioO mow . . ...... .. 5.8. 2. i: Z Em ma... 63$ :38 wwwaapaoo mo» wmw A55. mm. W3 Z Em mfid 58S wwwzm wwfizpi 5w . ....... . . S8. 3. Q: Z Em mid 65$ wwcflm wB~>n6< 5m . . . . . . . . . . . . . . . . . .. www... .2. W5 Z Em mfid 55$ @951 wB~>$v< 5w . . . . . . . . . . .. owmc. m5? wm. Pa.“ ocoZ O m M . . . . . . . . . . .. 3.2. S. g wcoZ o N ...... .- 9%? S: ME 3oz o H U0h®>OUOH cououflfl iwwoufi: iowcafifl ucwu 3n Em ZQAEZC Z mo mam wEwMU flowofifiz mono COTZUQQ mfioflwmoufiz uom pcwo uwk EMU wuwao>< dkw . 33mm wcwmlbwciw 0wa>>ow 50C 2.5a .3 wwpo>ouon cwwoafiZ .m mix? .1. ..,.[L>. N 0 I T A T S T N E M I R E P X E L A R U T L U c Y1 R G A S A X E T 5, 4 4 0 N N I T E L L U B 12 .... .. 3N? >35. NS... NN. . mNwo. 2w. mmwm_w mafiwzfiz» m mMQ NN o . $3.. S. 3. Nw H wwfizfié m $5 NN . . . . . . . . . w: $8 $8. £4 i Qwwfifimwmwmmwwudw m $5 NN mwm $8. N5 . 5 N. $5 5N S. S... . 95.. Q5 Wwum 33min N. $5 ¢N . , . . . . . . . . . . . . mmmm $8. $5 5 N1 _ 5.8.895 N. $5 2 . . . . , . . . . . . . . . . . . . . . .. $2.. i: Wm Nuns? @885. m mMQ m3 Q $2.. NNA 5 wwwim wwiwmmn N $5 S. . . . . . . . . 5.. mmm. $8. N5 .3 . M25 wwfiwwmn N $5 m: . . . . . . . . . . . . . . . . . . . . .. 3S. 5A m; mwws? Nfimwwmo N mvwm 3 o £8. N5 5 ............................... =2: .0 . N32 wwfiwém N $5 E . , , . . . , . . :5. N: 5 ..coSw@w QMQSOU dzxm dz .mwwfl~m wwuwwwmfi m wMQ 2 . . , . . . . . . . . . . . . . . . . . ., W2... NNA 5 EQKNNw QNBBQ NEON an awwwm wwmwwm w mwm w. Q2 NNS. NON? Nfim. Wfi i EEM wwwzoo .255 dz 63.2w Ezmwwwa 5 $5 a . . . . . . . . . . . . .. Nwm .55. 23 a2: wwwzzzéo 2m$5 N v.3. . $8. 3. NN ................................................... L 2c wwwwcofibo Smomm w ..... . wwww mmwm. 35o. mo; H6 Eu . two“: wwowcofioo 2w$5 b . . . . . . . . . . . . . . . . . . . . .. .33.. 24 .3. z 8w Ca Mam u. 8922 Nzmm w . . . . . . . . . . . . : omvc. woA wfl ..:.........::.:,..:.::AZ EM fiov aw we wpwhzz QZMQ m . . . . . . . . . . . . .- mwmw. 23o. 3A w. . ....H..@.- wow mo QQFSMZ NZMQ w . . . . . . . . . . . . . . . . . . . . .- ZS. S; o; .. . 282 Qwfi N 2.2. No.5 A...» z . . . . . . . . . . . . . .. mmmfi wwaumlrouo» coflzwww Z Z 5w A w no 0.5m: >2 o 5w Z E H5 3 F36 w an acme hum n50 QWEEJ» 52w ammo 5Q Z m%>.%o c3235 msocowoafim~ ofiwfieflk: 8m 63$ 22$ so FNou an uwhtroomn cowofitz A. wish. 13 THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE _ _ . 1N2 N39 v N59 W N59 _ 3.. N N.N2 ................................ .6522» NNNHN .d2 62.3w N. w22 N 2.2 N39 _ N39 _ N39 _ NN.. N N22 ............................ ..d::>add.~w .205 .d2 62.2w N $22 N . . . . . . . . . . . . .. a _ N35. _ N2. _ N2 d=€ddd2o .255 .d2 .6255 N N22 M. You woNe. NNNo. 2wN9 NN.. __ N422 13E 000225200 0M2 w . . . . . . . . . . . . .. _ _ $2.9 3.. _ 9S E2: 2662:5062 022 N N.NN NNNN. NNNd. _ N15. NN.. _ 9NN ................................................... 1.2.2. Nd @6622 .222 2. . . . . . . . , . . . . ; _ N NNS. 2.. __ fiNN Nd ddfi:2 @222 N . . . . . . . . . . . . .. NNN9 2N9 _ 2N. _ 2N 262 22 N . . . . . . . . . . . . .. _ 5N6. Nd. _ S. .. 262 22 2 . N ¢N2NN .d2 26w N2 N69 N.NN? NNNo. NN. N.N .......................... dwdm :2 .22N .d2 62.3w N22 2 . . . . . . . . . . . . .. 2NN9 NN. N.N dwdm r2 28S d2 625% m22 N 9cm ddNd. NNNd. NNNd. NN. N2 .............................................. .. 1.68 Nddmdddddo 022 N . . . . . . . . . . . . .. NNN9 NN. NN 2N2: Ndddddfido 022 N. N.NN N.NN? N35. 0mg. NN. 9N2 . wcow we 3532 NZMQ w . . . . . . . . . . . . .. = N39 NN. k N.N2 26w Nd 622:2 @222 N 2N 259 NNN9 NNN9 NN. NN .................................. =8§> NSHN .d2 632w N m22 N. . . . . . . . . . . . . . . . .. 3N9 NN. _ N.N .................................. .6285 £32m d2 62.3w N N22 N . . . . . . . . . . . . . .. NNN9 NNNd. _ NN. _ 2N 262 22 N . . . . . . . . . . . . . . . . . . . . .. NNN9 NN. N2. .. . 262 22 2 NNNHN dZ zdm N.N NNN9 NNN9 _ 3N9 NN. N4. ............................. .. dddm 22 .285 d2 62.3w N22 2 . . . . . . . . . . . . . . . . . . 3N9 N9 _ N4. dwdm 22 28$ d2 22.3w @022 3 NAN N2Nd. oNNo. NNNd. dN. N2 ...................................................... -665 dddmcdfido 022 N . . . . . . . . . . . . . . . . . . . . .. NNN9 oN. :2 2.2026660 022 N 2.8 2N9 NNNd. NNNN. NN. _ N2 ...................................................... .203 Nd d:2:2 @0222 N . . . . . . . . . . . . . . . . . . . . .. NNS. NN. _ Ni 26d 2d 62.52 N222 N Ni N39 NwNo. N56. 2N. NS .................................. -835 NSHN d2 62.3w N m22 N. . . . . . . . . . . . . .. .. 2NN9 NN. _ NN ddd? .N:2N d2 62.3w N m22 N . . . . . . . . . . . . .. 5N9 N2N9 NN. _ 2N 262 22 N . . . . . . . . . . . . . . . . . . . . .. N39 NN. N N4. 262 22 2 N N.NN?“ dZ mdm N.NN 3N9 NNN9 NNN9 NN. 4 2N ................................ .. 62.2 22 .235 .d2 62.3w N22 N N.NN NNN9 N26. 3N9 NN. _ N2: ................................................... .. 16E wddmcdfido 022 N .... .. _ 2.3.9 2N. _ 2N :2: dddwcdfido 0M2 N. 9S 3N9 NNNN. _ NNN9 A NN. _ N62 ................................................... .. 26d Nd 82:2 2.0222 N ? _ 3N9 _ 2N. _ 2N2 .................... .... .............................. -208 2d ddd§2 N222 N 9S N29 _ 3N9 3N9 _ NN. N2. ................................... 18d? d3?“ d2 62.3w N mM2 N. .... .. 7 _ 5N9 ‘ NN. _ N.N 022$ .N22N ..0Z 02.2w N mMQ N . . . . . . . . . . . . .. N NNNN. _ 3N9 N9 _ 9:. 262 22 N .... .. _ m NNN9 _ NN. _ 9N 262 22 2 _ _ N NNNHN d2 =dw 6029,0002 Z .20 2020 2m 20.20 @200 . Eu 2022.222 @200 20m. 220w i ZEM E Z i .202 Z l 20.20 20223000 92020202272 20M 020.52% 02.224 madhw . :55 620w msoi?» 2o 2302M 2.200 .3 002.2582 zomonfiz .m 320B N m T A T S T N E m R E P X E L A R U T L U C 1|. R G A S A X E T 5, fix 4 0. N N I T E L L U B 14 “ma”... m2... wis. 3. vHm EAZ EM m3 ¢E>m=>>o~m 45am .oZ $3.2m H man m HWMH Emu. $3. 25m. 3.. m5. .... :AZ EM m3 noomaom $2M .oZ 365w m 9E w . . . . . . . . . . . . . . . . . . .. 3mm. Hv. w? EEAZ EM m3 coomzom 41.35 .oZ $2.2m m mam v m1: $2. m5... $2. 2.. 3a ...... z AZ EM m3 9:34 ammo“ .oZ $9.2m o. mmo w . ..... .. $28. mm. Nam ......... HZ EM m1 @524 $33 dZ 62.2w H. mMQ m W3 mag. 2.6. Hams. 3.. mdm ................................................... .. HQoE wwwmcofioo own H. . . . . . . . . . . . . . . : $2.. 5i vdH ..................................................... .. 13E HowmwcofioO 0mm m. . . . . . . . . . . . . z was. $2.. HQ. ._._.H..H mcoZ MG N . . . . . . . . . . . . . . . . . . . . 1 $2. Hw. méH .. wcoZ MG H mfimm dZ mow HSH $2. 22.. was. 5.. m1: EAZ EM m3 oacwm 5m .223 .oZ .9355 N woE 2 . . . . . . . . . . . . . . . . . . . . ; $8. 3% mzmH EAZ EM m1 otcwm cam .223 .oZ dwufim m man m wdH $2. mmwo. _ M38. 5.. W»: EAZ EM m3 ¢E>2~Bo~m 433 .oZ JMHVZm H $5 w . . . . . . . . . . .. .. _ m3? 2.. _ WE AAZ Em 5o @E>w=>>o.~m A53 d2 62.2w E $5 L. oHm oHmo. Ewe. _ wmvo. 3.. vdH ................................................. : 13E wwwmnoaooo 0M9 m. . . . . . . . . . . . . x _ £2. mw. o.mH HowwmcofioO DMD m wéw $2.. £3. $3. mm. v.3 .................................................... .lmH.om Ho wofinzz wZMmH H. . . . . . . . . . . . . . . . . . . . . : 33o. 3.. 9S awom mo wHFSHZ MZMQ m ...... .. $2. $2. 3.. 9w mnoZ MD m . . . . . . . . . . . . . . . . . . . . : 2.2. 2.. cs . ocoZ MQ H . H23 d2 mow wwawioow» Z mo no.6 cm no.3 “Emu EM uwnEHE ammo nmnH EHwM Z EM EH Z awn Z _ no.6 l Eowfiwww mfiomwMoafi Z uonH wMano>< ®MduQ>< mEwnw _ 5a. n . Howscmuconvlmmow msompfi» no =>>o~M F30 %Q ©0h0>OQUk CQMOHHMZ .m QHQNP... 15 E G D . U L S E G . A W E S __ ......................... zioamflowm Jqmmfim dz Qwwflim uwumfigodw F 3.. E . . . . . . . . . . . . . . . . . . . .. 5.82am O pm 26w: QGDOEN @352; 2mg .02 03.3w wmsséi .1. ..................... .. iouwdom dfiwum .02 @253 wwfiésfi» Hy vu 1.. ............... :io$duw wmwioO dvflom dz wwqsfim wwpmwwmn L v ............... ecofimaaw wwwzov .30?" .02 @252 wfiwwwfi A o .... ................ .. oficwm flaw. awgm d2 wwwim wwfiwfia V c Z ..................... =2s>mc>>o~m 43g d2 ~25? wwiwfin .... .... 3 mfi ............................... :w¢2§< dmmfim .02 wuwiw ufimammm G l: .1. w. wfi ......................... im-ZT/iwwhmv Jcoam dz wwmfiiw wwpmwwmm m W“ 2 NH ........................... zomwmm mm ASE dZ wmwim ufiwwwfi Z o -.. m ................................. .533 fiim d2 awwim uwamwwfi M l. mm m- W. mm ................................. ..€c:oEw Bnsouv 13E wwwéotao H. N.» 1 5 mm .................................................................. .. i2: wwwwaouuoo R mm fifi .................................. eflufldofiw @1303 dfiow m0 wafixz E E _ E ........................................................ ........ .33 i. 83:2 F E i. S 3 Q _ S _ D N , A in? 22m £5” Hfifi qfim» _ 2&5 _ 22m _ mwfim N _ W .950 Mo no.3 3S E wo~w>oooa wwwwd cwwoafi: mo wwmmacwouoh 6 ~35. I S O P. M . O C E H T 16 BULLETIN NO. 445, TEXAS AGRICULTURAL EXPERIMENT STATION was taken to be 100, and the quantities taken up by the crops from the other materials was expressed in percentages of this amount. With soil 33135, the standard was taken to be 45 per cent availability of nitrogen in cottonseed meal. The availability of the nitrogen of the digested sludge in some cases was very low, in one case it was better than that of cottonseed meal, while in other cases is was nearly as good. The average of all the experiments on digested sewage sludge, gives an availability of 19 for its nitrogen compared with 100 for nitrate of soda, and 47 for cottonseed meal. If the results. on sand 31116 are omitted, the comparative availability of the nitrogen of digested sludge is 23. The availability of the nitrogen of digested sewage sludge is about one-half of that of cottonseed meal and one-fourth of that of nitrate of soda. It is also less than that of barnyard manure, given by Lipman, Blair and Prince (9, 10) as about 50 per cent of that of nitrate of soda. However, this includes the residual effect of several years of application of the manure and was not confined to the first crop, as is the work here reported. While digested sewage sludge is not suitable for use in commercial fertilizers, on account of the low availability of the nitrogen and its low content of plant food, the dry sludge can be used locally to advantage, unless the cost of hauling is excessive. The three pot experiments on the activated sludge gives its nitrogen an availability of about 55 per cent compared with about 50 for cotton seedmeal and 100 for nitrate of soda. The pot experiments on, activated sludge confirm the work of other investigators and show that it has a good availability to plants, being approximately equal to cottonseed meal in this respect. NITRIFICATION OF SEWAGE SLUDGE Plants are incapable of directly absorbing and utilizing the nitrogen in most organic compounds. For this reason, the nitrogenous compounds of cottonseed meal, sewage sludge, and other organic materials, must be de- composed, and changed into ammonia and nitrates, before the nitrogen can be of any service to plants. The production of nitrates from three samples of sewage sludge was compared with that produced from cottonseed meal in a number of soils. For the purpose of this work, material equivalent to 0.1 gram of nitrogen (equivalent to 500 parts per million of soil) was mixed with 200 grams of soil and water equal to one-half its saturation capacity, and incubated four weeks at 35°C. The soil was then mixed and nitrates determined by the phenol-disulphonic acid method. The quantity of nitric nitrogen in a sample of soil with no addition, incubated at the same time and under the same conditions, was deducted in order to correct for the nitrates produced by the soil alone (See Table 8). There was considerable variation in the capacities of the various soils to convert the nitrogen in the added material to nitrates. The nitric nitro- gen produced from the cottonseed meal varied from 16 to 321 parts per million of soil as shown in Table 8. The nitric nitrogen produced from l7 THE COMPOSITION ‘AND FERTILIZING VALUE OF SEWAGE SLUDGE pm Amy wmwfim woumowmw 0mduo>< 2 Aw." =3 Jmwgw vwamwwmu owduw>< 3 .uuv3oxo 3:..." v53 dwwfim wwfiwwmw wumuw>< _ ....... a S mm . confine!“ 63$ dZ owns? wwunfiuodw a. E. 1-. .3 ............................. .. ccfisofl 23m: acacia 25.53 imam dZ ~25: wwewzafi. 3 :1 -... , av . ........ ..:o»m:om damn dz 03.3w 03.8534 3 ..: i- :.- 3 .... .-.3w owwfloO irfiom dz dmwgw uBmwwmQ o :4 . o .... 5.3m mMwSoU 4.23m .02 owwni wwumwwmfi 3 2.. A. ...-..o:5m cwm .233 dZ 633m umsawmmn i" 3 mu ..-.wE>m=Bo.~m J33 62 63.3w H6335 3 5 m» ............ .2534 dmfim 62 6mg? vwuwommfi S“ s" .... ...... -.o_z>=w3w .25.?” .02 Jwvgm wfimwwa 3 5 § 3 ¢ ......... -.omam EH A88 dZ 633m woomwwmfi 3 . m w 9. .....-.---......oow>P a8; .02 63.3w ufimwwmn 3 8 .............. =$c~6E¢ “x452: <85 wwwmaofico 5 m“. S. 5 5 .3 U. 3 .2. .. 13E wwwzaauco 3H 2: ................ ..A.._E6Ew 2.303 86m we wodhumz 2:" o3 o3 o3 o3 o3 o3 o3 .................................................. lwwow we muuufiz £3” 35w 3.4m» awfim :61." £2” 33m 23$ owuu0>4 .02 =8 dz mom dZ mom dZ mow dz mom dz =5 SZ =8 dz 23w wawwmnm mu wwom HO Qwdhvmfi HO nwwouamfl lam? UUHGAMEOO omwfim ouu3om u o nomonfifi a. SEQEE>< H 03H? 18 BULLETIN NO. 445, TEXAS AGRICULTURAL EXPERIMENT STATION a Nu w _ Hm ....................................................................................... “wwmcaso smacks: mo pcwu 3m .3 w: 3,. __ “EH ............................................. 1 \ ‘ ..................... 1 Awv wwwww>< _ E m3 fi __ Hmm . . . . \ . . . . ‘ . . . . . zmpcmou nwppom 0B6 E52 ma? nwfiom mmmfim 3 3H o mm ................................................ zficsou 33cm ab?» Ridm; >20 3mm oziwi< wwmfim 5 i. o é E ...................................................... .. muczou mouwum 0.24. 5E2 35mm 9S.“ cfifisq Sémw 3 m2 3 m3 .................................................... zficsoo @9232 0B5 5E3 wwcam mam“ @5232 mmmmw E mm o mm .................................................................. ..z»::ou aim Si-» .25“: 335m o5.“ new? mwwfim m. 2: om fiw ....... : . nucsoo oirm Kmfié .553 >20 owfimwmm mwwfim mm m2 mm $5 ........................................................................................ .. >250» oih upho SEQ 03h mwwfim 3 3H Y“ _7 m» ...................................... .............. ‘unucsou uwfiom 0.2% .252 35mm wcfl 05.554 mmmHm omwfiw coma wmzmfl 13E $9,552 wwumwwmfl wmwgm mwwfiw wwwmiopuoO znowwnonmfl @8890 wwfiwfin E . Sm o c9 1.: 5Q m pan mSw wsoia> E ww s w wwFSww 50h mo: 0.5 some» E vi _ . w w P u .2. a w . . w ~ m m. m. p. . PZ w 5 H. THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE 19 the Waco digested sludge varied from 64 to 136 parts per million. The nitric nitrogen produced by the other two samples varied from 0 to 58 and from 30 to 65 parts per milllion. In some cases, more nitrates were pro- duced from the sludge than from the cottonseed meal. As previously pointed out by the author (4), the production of nitrates alone is not a good measure of the availability of nitrogen in an organic fertilizer, while the production of nitrates and ammonia together is a much better measure. This is due chiefly to differences in the capacity 10f different soils to convert ammonia into nitrates. It was not practical ‘(to determine both ammonia and nitrates produced in the experiments here reported; they were, in fact, performed with the object of ascertaining fthe effect of the various materials upon nitrification in different soils, and not with the object of measuring the availability of the materials. However, they afford some indications that nitrification of these materials fvaries in different soils, that different samples of sewage sludge may pro- iduce widely different quantities of nitrates, and that the results vary with different soils. UTILIZATION OF SEWAGE SLUDGE Dried activated sludge is a nitrogenous fertilizer in fertility content (similar to cottonseed meal, and it can be used in the same way. It contains iabout 5 per cent of nitrogen, compared with 6.88 for 43 per cent protein cottonseed meal. Dried activated sludge contains less plant food than cottonseed meal, about 0.7 as much, and as its nitrogen has aboiut the same availability as that of cottonseed meal, dried activated sludge may be i5 considered, on an average, to have 0.7 the value of cottonseed meal. It ‘ can be used as a fertilizer in the same way cottonseed meal is used. It can be applied alone to soils which need nitrogen, at the rate of 300 i to 700 pounds to the acre or more. It can be mixed with superphosphate for use in soils which need phosphoric acid as well as nitrogen. It can be mixed with superphosphate and potash salts to make a complete fertilizer but is usually used in combination with other nitrogenous fertilizers, ion account of its low content of plant food. Sandy soils east of the {Brazos river, in general, need both phosphoric acid and nitrogen, A gmixture of 1,000 pounds of activated sludge (5 per cent nitrogen), 1,000 it pounds of 20 per cent superphosphate, and 100 pounds of muriate of potash . will give (in 2,100 pounds) the equivalent of 1,000 pounds of a 5-10-5 ferti- ilizer or of 1,250 pounds of a 4-8-4 fertilizer, for home use. This has 4a good ratio of plant food for ordinary farm or garden use. Dried activated sludge is being sold by the City of Milwaukee, Wisconsin, § under the name of Milorganite, and by the City of Houston, Texas, under .g the name of Hu-Actinite. Dried digested sewage sludge contains much more plant food than ordinary mixed farm manure (6), and a little more than either dried hen ' manure or dried sheep manure (see Table 9). It is not as good a material i, to furnish humus for the soil as farm manure, as it contains much less 20 BULLETIN NO. 445, TEXAS AGRICULTURAL EXPERIMENT STATION _ _ .-.- m6 m6 _ m6 ...................................................................................................... aowspwiw dpscmfi Gash 3 66 m; _ m4 ......................................................... : wuscwi no: wwifi S v6 m6 m6 ................................................................................................. zwpscwi 000cm 650w swwnh 2. H6 N6 v6 ..................................................................................................... :w.~::.wE 300 620m smwfim E. w6 m6 m6 ....... -. .. ..-..o.§cwE 030s 620m smwfim ,6 m6 § 6A 6A ...................................................................................................... aAwwEE wwwfiw 0030MB 6:00 .60 paws .59 £50 .60 ammo .80 .5603 Amdaom i 060-0121“ cwmoafiz $93 130E .2555 5.5m mo 0066300500 f?» 60.35800 032m wwumwwmw womb... mo iomfiwoqioO 6 03am. THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE 21 organic matter capable of forming humus. Wet digested sludge contains less plant food than the dry digested sludge, in proportion to the quantity of water present. The availability of the nitrogen in digested sludge is about half that of nitrogen in cottonseed meal; while low, the availability of the nitrogen is sufficiently high to justify its utilization. Dried digested sludge does not contain enough plant food to justify its commercial use or shipment to any distance. Its manurial value is sufficiently high for those in a vicinity of a sewage disposal plant to take advantage of the opportunity to utilize it. Partly dried digested sludge should be handled in about the same way as farm manure. It may be appliedi broadcast at the rate of 10 to 40 tons to the acre, and turned under or harrowed in before the crop is planted. It should not be applied to growing cultivated crops. On some soils, it . would be advisable to supplement it with 200 pounds of superphosphate to the acre or even a complete fertilizer may in some cases be used with advantage to supplement it. Activated sludge as it comes from the tank, when it usually contains 98 to 99 per cent water, may be applied to land near the sewage plant by {means of ditches and irrigating furrows. Wet digested sludge, which contains 87 to 90 per cent water, may be applied in a similar way, though ' additions of water may be necessary to cause it to flow readily. ACKNOWLEDGMENT . Some of the samples used in this work were furnished by Mr. E. W. , Steel and Mr. P. J. Zeller, of the Department of Municipal and Sanitary Engineering, A. & M. College of Texas. Mr. S. E. Asbury, E. C. Carlyle, A. J. Sterges, T. L. Ogier, W. H. Walker,-and other members of the staff did the laboratory work or other work involved in this investigation. SUMMARY 5 Sewage sludge is a by-product from the purification of sewage and is produced by several hundred cities and towns in Texas. Digested sludge is produced by most of the sewage purification plants in Texas, and is the residue from the extensive decomposition of the organic matter of the sewage. It is composed chiefly of ash and of in~ soluble organic matter which has resisted the processes of decomposition. The activated sludge is produced by only one or two cities in Texas. _. It is produced by the decomposition of sewage andsettling of the sewage solids by means of protozoa and other organisms. It consists of insoluble solids from the sewage and the bodies of organisms. _ Sewage sludge is variable in composition. Its composition depends upon the composition of the sewage and on the time and temperature of the ‘ treatment, as well as on the details of the treatment and of the particular l apparatus used. Activated sludge is less variable than digested sludges. é. Dried digested sludge contains, on an average, about 1.9 per cent nitrogen, r ' W“ 3lM~"-wvw‘»a-_:-~»=qw1,~,,,.",.,,...W,lu... 22 BULLETIN NO. 445, TEXAS AGRICULTURAL EXPERIMENT STATION 1.6 per cent total phosphoric acid, of which about 1.1 per cent is avail- able and 0.5 per cent insoluble, and 0.2 per cent potash. Activated sludge when dried usually contains over 5 per cent of nitrogen and 2 per cent of available phosphoric acid, with about 0.2 per cent of potash. It has about 70 per cent of the fertilizing constituents of cotton- seed meal. The dried sludges contain 33 to 76 per cent of ash, chiefly insoluble in acid. They also contain appreciable amounts of nitrogenous material, and variable, though large, amounts of grease. Some pentosans and crude fiber are also present. The availability of the nitrogen of sewage sludge was estimated by means of pot experiments on eight different soils or sands. The availability of the nitrogen of digested sewage sludge was variable, and averaged about one-half of that of cottonseed meal. The availability of the nitrogen in the activated sludge was about equal to that of cottonseed meal. This agrees with the conclusions of other investigators as to the value of activated sludge as a fertilizer. The nitrogen of activated sludge also passes the chemical tests for activity. The nitrification of sewage sludge varied in different soils, being quite low in some soils and much better in others. Dried activated sludge is a nitrogenous fertilizer similar to cottonseed meal and has about seven-tenths of its value. It can be used alone or in the preparation of mixed fertilizers. Dried digested sewage sludge contains somewhat more plant food than farmyard manure but is a poorer source of humus. The availability of its nitrogen is about half that of cottonseed meal. It can be utilized in field or garden crops in the same way as farm manure by those suf- ficiently near to a sewage disposal plant to be able to haul it at a low cost. REFERENCES 1. Bodler, J., 1924. Fertilizer experiments with fine waste and mixed fertilizers as a beginning for the industrial use of municipal sewage, garbage, and sewage sludge. Gsudhts. Ingen., 417-266-279 Abstract in Exp. Sta. Record, 52:121. 2. Brenchley, W. E. & Richards, E. H., 1920. The fertilizing value of sewage sludge. Jour. Soc. Chem. Indus., 39:177 T. 3. Cramer, R., 1931. The role of protozoa in activated sludge. Ind. & Eng. Chem. 23:309. 4. Fraps, G. S., 1908. The production of active nitrogen in the soil. Texas Agr. Expt. Sta., Bul. 106. 5. Haskins, H. D.,‘1930. Nitrogen availability. The American Ferti- lizer, 72:15 (January). 6. Heck, A. F., 1931. Conservation and availability of the nitrogen in farm manure. Soil Science, 31:335. 7. Kadish, V. H., 1928. Milorganite. A new fertilizer material. Ind. 11. 12. 14. 15. THE COMPOSITION AND FERTILIZING VALUE OF SEWAGE SLUDGE 23 & Eng. Chem. 20:9. Keefer, C. E., 1930. English and German sewage treatment. News Record 105, 162-5. Lipman, J. G. & Blair, A. W., 1918. Twenty years’ work on the availability of nitrogen in nitrate of soda, ammonium sulphate, dried blood, and farm manures. Soil Sci. 5:291. Lipman, J. G., Blair, A. W. & Prince, A. L., 1928. Field experiments on the availability of nitrogenous fertilizers. Soil Sci. 26:1. Muller, J. F., 1929. The value of raw sewage sludge as fertilizer. Soil Science, 28:423. Noer, O. J., 1926. Activated sludge: its production, composition, and value as a fertilizer. Jour. Am. Soc. of Agron. 18:953. Reynolds, E. B., 1930. Activated sludge as a fertilizer for cotton and corn. Jour. Amer. Soc. Agron. 22:537. Rudolfs, W., 1930. Annual report of the department of sewage disposal for the year ending June 30, 1929. New Jersey Sta. Bul. 502. Stokes, W. E., Leukel, W. A. & Barnette, R. M., 1930. Effects of irrigation with sewage effluent on the yields and establishment of Napier grass and Japanese cane. Florida Agr. Expt. Sta., Bul. 215. Eng.