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No attemDt has been made to cover the field of disinfectantsg or of-industrial hygiene.41 BIBLIOGRAPHY ,
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1-W. P. Mason, J . Ind. Eng. Chem., 7 (1917), 289. . 2-Wolman and Hannan, Chem. Met. Eng., 24 (1921), 728. ’ 44 (1922), 1435. 3-Buswell and Greenfield, J . A m . Chem. SOC., 4-Clark, Unpublished discussion, American Water Works Association ’ Convention, May 18, 1922. &Buswell and Edwards, Chem. Met. Eng., 26 (1922), 826; Howard and Hannan, Can. Eng., 41, 461. 6-Baylis, J. A m . Water Works Assoc., 9, 408. , ‘ 7-G. F. Catlett, Eng. Rec., 73 (1916),’741. , , 8-0. M. Smith, J. A m . Chem. SOC.,42 (19201, 460. . , 9-M. J. Pirnie, J . A m . Water Works Assoc., 9,247. ’ 10-P. J. West, J . Ind. Eng. Chem., 14 (19221, 601; ‘F. N. Speller, J. Frank. Inst., 193,515; P. J. Kestner, J . SOL.Chem. I n d . , 40 (1921), 57T.. , 11-J. Tillmans, Z,.Nahr.-Genussm., 38 (1919), 1. , 12-J. M. Kolthoff, Chem. Weekblad, 17, 390. . , Don, Engineering, 111 (1921), 769. ’ 13-J. 14--Chick, Proc. -Roy. Soc., 57B, 254. . . , 15-Wolman and Powell, Eng. News-Record, 86, 210; Gavett, Ibid., 1081. News-Record, 88, 266. 16-Eng. 17-Enslow and Wolman, J . Ind. Eng. Chem., 11 (1919), 209. ’ ’ 18-H. W. Streeter, J . A m . W a t h Works Assoc., 9 (1922), 157.’ 19-A. Gunthey-Schultze, 2. anorg. Chem., 116, 16; J . SOL:Chem. I n d . , 40 (1921), 526A; Hisschemoller, Rec. trav. chim., 40, 3.94; J . SOC;Chem. I n d . , 40 (1922), 526A. . . 2O--Jolles, Bev. pharm. Ges., 30 (1920); 421. .
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21-C. A . , 16 (1921), 1773, 910, 3354; 16 (1922), 2189 22-Fox and Gauge, J . SOC.Chem. I n d . , 41 (1922), 173”. 23-I,. Scheringa, Pharm. Weekblad, 57 (1920). 1481. . 24--Nichols, Ind. Eng. Chem., 12 (1920), 987; Bur. Standards, Sci. .Paper 367. 2 6 P r o c . A m . SOC.Civil Eng., 47, 653; Eng. News-Recovd, 87,392, 444; Rep. of Comm. 13 of A m . R y . Eng. Assoc., 23 (1921), 242; J . SOC.Chem. i n d . , 40 (1921), 159T; Eng. News-Record, 87, 771; J. Collins, J . Ind. Eng. Chem., 12 (1920), 1181; “A Half Century of Public Health.” Edited by ‘Ravenel, Jubilee Historical Volume of American Public Health Association. : 26-8th Report of Royal Commission on Sewage Disposal, Appendix, 182. , 27-E. J. Theriault and Hommon, U.S . Pub. Health Bull. 98, 71; U. S. Pub. Health Repts. 36, 1087. 28-Proc. A m . SOC.Civil Eng., 47, 617 (discussion in following number). 29-W. Donaldson, A m . J . Pub. Health, 11, 193; 12, 421. , 30-Eng. News-Record, 86, 513. 31-C. A , , 15 (1921), 3352. ’ 32-Gould, Proc. A m . SOC.Civil Eng., 47, 603; 48, 711, 991, 1269. 33-Richards and Weeks, Report from Water and Water Eng., 23, 500. . ’ 34--Ardern, “Second Report on Colloid Chemistry and I t s General Industrial Applications,” 1918, 81. 35-cox, Eng. News-Record, 87, 720. 36-Thompson, A’. J . . A g r . Expt. Sta., Bull. 352 (1921). U.S. Pub. Health Rept. 37, 1505. 37-Wagenhals, , . 38-Buswell and Weinhold, Paper, Philadelphia Convention, Am. Water Works Assoc., May 19, 1922. 39-Mohlman and Pearse, J . A m . Water Works Assoc., 9,311. 40-Fairbrother and Benshaw, J. Soc. Chem. I n d . , 41 (1922), 134T. 41-Pub. Health Repts., 37, 275; J. S. Owens, Proc. Roy. Soc., 101A, 18 to 37; J. SOC.Chem. I n d . , 41 (1922), 344A. ,
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Activated Sludge By Edward Bartow arid Gerald C. Baker DEPARTMENT OF CHEMISTRY, UNIVERSITY OF IOWA, IOWA CITY, IOWA
Experimental plants have been in operT I8 conceded that the activated sludge ation for some time at Urbana, Ill., the process is the most perfect method Calumet region of the Sanitary District of sewage disposal at the present of Chicago; this plant when completed will time. Its growth in America and Eurohave a capacity of 1,750,000 gal., and the pean countries has been quite widespread. plant of the Desplaines River district of Since the discovery of the process, early in the Sanitary District of Chicago, when 1914, the method has been adopted for completed, will treat the sewage from a several municipalities, and an exceedingly population of 30,000. large number of experimental plants have In conjunction with the Corn Products been put in operation. The most notable Co., Argo, Ill., the Sanitary District of one8 in existence a t the present time are Chicago has also run an experimental at Davyhulme (Lancashire), Worcester, plant on starch wastes. This plant has a $tamford, Aeritree, Sheffield, Bradford, capacity of 25,000 gal. Tunstall, Blackpole (Worcestershire), Experimental plants using mechanical Whitney (Blanket Co.), St. Albans, Withagitation have been in operation a t Pasaington, Moreton (Dorsetshire), Birmingdena and Hermosa Reach, Calif. Works ham, Reading, Baguely, and Stoke-onare in the process of construction in MilTrent, in England. I n other countries, waukee which will treat the entire sewage the most notable ones are at Jamshedpur from that city, population 588,760, and (India), Sibpur (India), Holte (Denmark), at Indianapolis, Ind., population 314,000. Burmeister (Denmark), and Kimberly Other plants in the process of construction (South Africa). I n the United States the EDWARD BARTOW at the present time are Brisbane (Ausbest-known plants are at Houston, Texas, stralia), and Singapore (India). and Milwaukee, Miis. Rotheham, Hanley, and Mansfield (England) are considering NEWPLANTS schemes along the line of the Sheffield works. Low Angeles, Recently (April 1921) a plant has been installed a t Wood- .Calif., is also considering the adoption of the activated sludge stock, Ontario, to handle 1,500,000 imperial gal. per day, process for the treatment of sewage of that city. dry weather flow. A small plant has also been installed a t There are many other small plants and installations that Brampton, Ontario. could be mentioned, but lack of space does not permit. A plant was put in operation on October 18, 1921, at TYPES OF AERATION Gastonia, N. C., which treats 1,000,000 gal. sewage daily. There are in general two types or modifications of aeration: I n October 1921, an installation was put in operation to treat the waste (600,000-gal. daily flow) from the Decker (a) diffused air, and (6) mechanical agitation. The experimental plants in this country have practically all used Packing Plant at Mason City, Ia.
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THE JOURNAL OF INDUSTRIAL A N D ENGINEER€NG CHEiWSTRY
the diffused air treatment, which consists of blowing air through the sewage and sludge, after it has passed through filtros plates. Intermil tent aeration has been tried at Manchester, England, and elsewhere; this allows aeration for a certain length of time and then a rest, but has not proved successful in the saving of air. Cegain devices have also been tried for decreasing the amount of air necessary for the process. The Dorr-Peck process consists in aerating the sewage and sludge in a specially deqigned thickener, which effects diqtribution and circulation of the air bubbles in one chamber and causeq sedimentation in another. Aeration in less time and less air required was claimed, but the company very recently announced that the process had not met their expectations and they have decided t o carry the tests no further. The Trent 'devices consist of aeration and agitation of the sewage by drawing the sewage and air into the bottom of the actih,tion tanks. Distribution is by means of revolving perforatgd arms of the rotating lawn-sprinkling principle. Test Pasadena, Calif., and a similar process a t Hermosa process to take twice the time and cost more to operat ' the continuous air diffusion method-. Mechanical agitation, that is,' t h has proved successful a t Sheffield, England. These paddles suck the air through a tuhe'by creating a' vacuum, and rotation is carried for eight' hrs. By this method the sewage is brought in contact with the air a t i required ik, to mix the sewage andrippling the surface increases the s tion of thc air. The Sheffield sewa and experiments made elsewhere agitation alone will not pu activated sludge without t penditure of much more energy than the air-diffusion method; the original and maintenance costs also seem greater. It is the gcneral opinion that the continuous air diffusion method is preferred but that some aeration might be dispensed wit h provided some other form is used. .
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SETTLING - Certain improvements aver plain sedimentation are claimed for Rettling sludge. Dorr thickeners have been successfully used. These sedimentation tanks are circular in diameter and have a smooth bottom with a slight slope toward the center. A revolving scraper collects the sludge continuously, scraping it toward the center of the t,ank, from which it is removed by a pump or by gravity without the interruption of the operation of the thickener.
DEWATERING SLUDQE AND SLUDGE DRYIXG These are the biggest problems yet unsolved, but very promising advances have, however, been made within the last few months, and complete solution is hoped for in the near future. Filter pressing and certain types of centrifuges have given promising results under varying conditions. Lagooning has also been somewhat satisfactory, but in this method the fertilizing value of the sludge is lost. Certain recent developmenls have been made, both in England and in this country, in filter pressing. I n England it has been found possible to reduce 98 to 99 per cent moisture sludge to 75 per cent by spreading it on paper-makers' gauze or very fine screen gauze and applying a slight vacuum to the under surface: the thin cake thus produced can be readily dried in the air. In this country experiments with certain types of American filters (Oliver and American) embodying the same principle have recently given very satisfactory results.
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Dewaterinq by plate presses and squeeze presses (Worthington or Bcrringan) has given promising result.. with sludge that has been treated before filtration. At Milwaukee by adjusting the reaction to a certain hydrogen-ion concentration with sulfuric acid, and by adding chromium or aluminium sulfate, the rate of pressing has been greatly increased. A solid bowl centrifuge (Besco-Ter-Meer) has given much more promising results than other centrifuges at Milwaukee. This centrifuge is continuous and automatic in operation, and is devoid of all screens. It build.. up a cake againqt n solid stationary plate and unloads it automatically. It has been posqible to reduce the moisture to 72 to 75 per cent. With this machine the water does not pass through the cake but out over the top; the effluent contninq a rather high percentage of the lighter and finer solids. Thew are those who believe that a centrifuge will be so perfected that it will solve the dewatering problem. Another recent advance in the dewatering treatment of sludge is the Maclachlan process, or modifications of it. In this process the sludge is treated with sulfur dioxide, generated by burning sulfur, and live steam. In the Mac-> lachlan process at Houston, Tex., the sulfur dioxide and live steam are applied to the activated sludge for 25 min., raising its temperature from 80" to 135" 3'. The sludge float4 to the top and can be readily filter-pressed, yielding a cake with as low as 74 per cent moisture; the treated sludge may be dried on filter bedq. Jackson and Doman report that the filtered sludge dries readily on hard, impervious ground W lied in depths varying from 4 to 16 in. Dehydrati s appear in'all cases ivithin 24 hrs. At the end of the first day the moisture is reported as 77.1 per cent, in 3 days 59.7 per cent, and in 3 arks. 26.4 per cent. The present trend in dewatering sludge seems in the direction of conditioning the sludge rather than the improvement of mechanical devi'ces. Besides drying the sludge on beds with disposal in the lagoons, direct heat driers have been used with more or less success for the drying of filter-press and centrifuge cake. Drying experimentP have been carried out with both direct and indirect heat driers, and indications are that drying in either form is an expensive process. It is generally agreed, however, that after the first 20 per cent of the water is removed the qludge more readily parts from the remainder.
FERTILIZING VALUE Dried sludge has been proved by various investigators1 to have an excellent fertilizing value. The nitrogen content of the sludge has been shown to be equal in fertilizing value to the nitrogen of ammonium sulfate or dried blood, when applied to grains and vegetables. These results have also been borne out at Rothamsted. The nitrogen content of the sludge varies from about 4 per cent to 7 per cent, depending upon the type of sewage treated. It has been shown a t hlanchester that 21 per cent of the nitrogen of the wet sludge is immediately available for plant food, while only 8.L5 per cent of the nitrogen of airdried sludge and only 4.6 per cent of that dried at 100" C. are immediately available. Heat drying lowers the percentage of nitrates considerably. One of the new developments is irrigation and fertilization with wet activated sludge. It is possible to dispose of the sludge already in liquid form by means of a system of mains and service pipes. The present indications are that the sale of fertilizer will partially, if not wholly, offset the cost of the dewatering and drying of the sludge, jf these problems are properly solved, but no surplus applicable to the operation of the plant can be expected. 1
Bartow and Hatfield, Nnsmith, and others.
