REFERENCES AND BIBLIOGRAPHY ON ACTIVATED SLUDGE
The following abbreviations will be used: A.S. for Activated Sludge, E.C. for Engineering and Contracting, E.N. for Engineering News, E.R. for Engineering Record, E.N.R. for Engineering News-Record, p. for page, and V. for volume.
No. 1. Cooperation Sought in Conducting A.S. Experiments at Baltimore, by Franks and Hendrick. E.R. V. 71, 1915, pp. 521, 724, and 784. V. 72, 1915, pp. 23, and 640. 2. Sewage Treatment Experiments with Aëration and A.S., by Bartow and Mohlman. E.N. V. 73, 1915, p. 647, and E.R. V. 71, 1915, p. 421. 3. A.S. Experiments at Milwaukee, Wisconsin, by Hatton. E.N. V. 74, 1915, p. 134. 4. A.S. in America, An Editorial Survey, by Baker. E.N. V. 74, 1915, p. 164. 5. Choosing Air Compressors for A.S., by Nordell, E.N. V. 74, 1915, p. 904. 6. A Year of A.S. at Milwaukee, by Fuller. E.N. V. 74, 1915, p. 1146. 7. A.S. Experiments at Urbana. E.N. V. 74, 1915, p. 1097. 8. Experiments on the A.S. Process, by Bartow and Mohlman. E.C. V. 44, 1915, p. 433. 9. Milwaukee’s A.S. Plant, the Pioneer Large Scale Installation, by Hatton. E.R. V. 72, 1915, p. 481 and E.C. V. 44, 1915, p. 322. 10. A.S. Experiments at Milwaukee, by Hatton. Journal American Waterworks Association and Proceedings Illinois Society of Engineers, 1916. Also E.R. V. 73, 1916, p. 255. E.C. V. 45, 1916, p. 104, and E.N. V. 75, 1916, pp. 262 and 306. 11. A.S. Defined. E.N. V. 75, 1916, p. 503, and E.N.R. V. 80, 1918, p. 205. 12. Status of A.S. Sewage Treatment, by Hammond. E.N. V. 75, 1916, p. 798. 13. Trial A.S. Unit at Cleveland, by Pratt. E.N. V. 75, 1916, p. 671. 14. Air Diffuser Experience with A.S. E.N. V. 76, 1916, p. 106. 15. Nitrogen from Sewage Sludge, Plain and Activated, by Copeland, Journal American Chemical Society, Sept. 28, 1916. E.N. V. 76, 1916, p. 665. E.R. V. 74, 1916, p. 444. 16. Tests Show A.S. Process Adapted to Treatment of Stock Yards Wastes. E.R. V. 74, 1916, p. 137. 17. Aëration Suggestions for Disposal of Sludge, by Hammond. Journal American Chemical Society, Sept. 25, 1916. E.R. V. 74, 1916, p. 448. 18. Cost Comparison of Sewage Treatment. Imhoff Tank and Sprinkling Filters vs. A.S., by Eddy. E.R. V. 74, 1916, p. 557. 19. Large A.S. Plant at Milwaukee. E.N. V. 76, 1916, p. 686. 20. A.S. Novelties at Hermosa Beach, Cal. E.N. V. 76, 1916, p. 890. 21. A.S. Experiments at University of Illinois, by Bartow, Mohlman, and Schnellbach. E.N. V. 76, 1916, p. 972.
CHAPTER XIX
ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION
275. The Miles Acid Process.—The Miles Acid Process for the treatment of sewage was devised and patented by G. W. Miles. It was tried experimentally at the Calf Pasture sewage pumping station, Boston, Mass., 1911 to 1914. In 1916 it was tried experimentally at the Massachusetts Institute of Technology, and it has been tested subsequently at other places, notably at New Haven, Conn., in 1917 and 1918. It is one of the most recent developments in sewage treatment and no extensive experience has been had with it. The process consists in the acidification of sewage with sulphuric or sulphurous acid, as the result of which the suspended matter and grease are precipitated and bacteria are removed. The equipment required for the process consists of devices for the production of sulphur dioxide (SO2), and for feeding niter cake or other forms of acid; subsiding basins; sludge-handling apparatus; sludge driers; grease extractors; grease stills; and tankage driers and grinders.
The first step is the acidification of the sewage. The period of contact with the acid is about 4 hours. Sulphurous acid seems to give better results than sulphuric because of the ease in which it can be manufactured on the spot. It seems also to be more virulent in attacking bacteria than an equal strength of sulphuric acid. In experimental plants the acidulation has been accomplished in different ways such as: by the addition of compressed sulphur dioxide from tanks; by the addition of sulphur dioxide made from burning sulphur; or by the roasting of iron pyrite (FeS2). The acidulation precipitates most of the grease as well as the suspended matter and results in a sludge which gives some promise of commercial value. In referring to the process R. S. Weston states:[[188]]
(1) It disinfects the sewage by reducing the numbers of bacteria from millions to hundreds per c.c.
(2) If the drying of the sludge and the extraction of the grease can be accomplished economically, it is possible that a large part, if not all, of the cost of the acid treatment may be met by the sale of the grease and fertilizer recovered from the sewage.
(3) The use of so strong a deodorizer and disinfectant as sulphur dioxide would prevent the usual nuisances of treatment works.
(4) The addition of sulphur dioxide to the sewage also avoids any fly nuisance, which is a handicap to the operation of Imhoff tanks and trickling filters.
The amount of acid used varies with the quality of the sewage and the desired character of the effluent. At Bradford, England,[[189]] 5,500 pounds of sulphuric acid are used per million gallons, producing about 2,340 pounds of grease or 0.43 pound of grease per pound of sulphuric acid. At Boston only 0.215 pound of grease were produced per pound of sulphuric acid. The difference is probably due to the great difference in the amount of grease in the raw sewage. In the East Street sewer at New Haven, Conn.,[[190]] only 700 pounds of acid are used per million gallons of sewage as the alkalinity is only 50 p.p.m. This amount of acid secures an acidity of 50 p.p.m. whereas in the Boulevard sewer 1,130 pounds of acid had to be added to produce the same result. The results obtained by the experiments conducted by the Massachusetts State Board of Health in 1917 are shown in Table 97. The character of the sludge from the same tests is shown in Table 98. After acidification[[191]] the sewage contains bisulphites and some free sulphurous acid, with some lime and magnesium soaps which are attacked by the acid liberating the free fatty acids. Part of the bisulphites and sulphurous acid are oxidized to bisulphates and sulphuric acid. It was found as a result of the New Haven[[191]] experiments that the presence of sulphur dioxide in the effluent caused an abnormal oxygen demand from the diluting water and that this difficulty could be partly overcome by the aëration of the effluent after acidulation and sedimentation, without prohibitory expense. The effluent and sludge are both stable for appreciable periods of time and are suitable for disposal by dilution. The character of the sludge as determined by the New Haven tests[[192]] is shown in Table 99.
| TABLE 97 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Average Analysis of Sewage Entering Boston Harbor, before and after Treatment, July 17 to September 27, 1917 | |||||||||
| (Eng. News-Record, Vol. 80, p. 319) | |||||||||
| Sample | Parts per Million | Bacteria, Millions | |||||||
| Ammonia | Kjeldahl Nitrogen | Chlorine | Oxygen Consumed | ||||||
| Free | Albuminoid | ||||||||
| Total | Total | Diss. | Total | Diss. | 20° | 37° | |||
| Paddock’s Island | |||||||||
| Raw sewage | 14.0 | 3.3 | 1.8 | 6.8 | 3.6 | 134 | 23.1 | 1.86 | 4.15 |
| Settled Sewage | 12.2 | 1.6 | 1.1 | 3.5 | 2.2 | 15.4 | |||
| Acidified and settled sewage | 20.9 | 5.2 | 3.9 | 10.0 | 7.5 | units 94 | units 91 | ||
| Deer Island | |||||||||
| Raw sewage | 23.3 | 8.2 | 4.8 | 16.8 | 8.9 | 3100 | 87.3 | 2.63 | 1.50 |
| Settled sewage | 21.1 | 5.6 | 3.9 | 10.7 | 7.3 | 62.2 | |||
| Acidified and settled sewage | 20.9 | 5.2 | 3.9 | 10.0 | 7.5 | units 147 | units 85 | ||
| Calf Pasture | |||||||||
| Raw sewage | 18.0 | 4.5 | 2.0 | 9.7 | 4.1 | 3254 | 41.2 | 1.89 | 0.98 |
| Settled sewage | 19.1 | 2.3 | 1.4 | 4.9 | 3.3 | 25.8 | |||
| Acidified and settled sewage | 17.8 | 2.4 | 1.6 | 4.9 | 3.3 | units 277 | units 149 | ||
The success of the Miles Acid Process in comparison with other processes is dependent on the commercial value of the sludge produced. The New Haven experiments indicate that 16 to 21 per cent of the grease in the sludge is unsaponifiable and seriously impairs the value of the process.
| TABLE 98 | ||||||
|---|---|---|---|---|---|---|
| Average Amount of Sludge and Fats Obtained from Sewage Entering Boston Harbor after Eighteen Hours Sedimentation With and Without Acidification | ||||||
| (Eng. News-Record, Vol. 80, p. 319) | ||||||
| Paddock’s Island | Deer Island | Calf Pasture | ||||
| Sedimentation | Sedimentation | Sedimentation | ||||
| Plain | Acidulated | Plain | Acidulated | Plain | Acidulated | |
| Pounds of SO2 used per million gallons of sewage treated | 818 | 1513 | 1189 | |||
| Dry sludge per million gallons | 782 | 959 | 1709 | 1939 | 1208 | 1427 |
| Per cent Nitrogen in sludge | 3.10 | 3.38 | 3.57 | 3.45 | 3.18 | 2.83 |
| Per cent fats in sludge | 27.30 | 27.30 | 24.60 | 19.40 | 24.30 | 26.30 |
| TABLE 99 | |||||
|---|---|---|---|---|---|
| Character of Miles Acid Sludge at New Haven | |||||
| (Eng. News-Record, Vol. 81, p. 1034) | |||||
| East Street Sewer | Boulevard Sewer | ||||
| Length of run in days | 25 | 24 | 44 | 70 | 29 |
| Total sewage treated, thousand gallons | 260 | 239.4 | 407.8 | 602.2 | 145.5 |
| Gallons wet sludge per million gallons sewage | 3750 | 4025 | 3200 | 2600 | 5375 |
| Specific gravity | 1.067 | 1.048 | 1.054 | 1.061 | |
| Per cent moisture | 86.6 | 88 | 86.3 | 85.7 | 92.5 |
| Pounds of dry sludge per million gallons sewage | 503 | 483 | 439 | 368 | 403 |
| Ether extract, per cent dry sludge | 23.7 | 24.0 | 29 | 32.6 | 30.9 |
| Ether extract, pounds per million gallons | 119 | 116 | 127 | 120 | 124 |
| Volatile matter, per cent dry sludge | 47.2 | 51.2 | 57.3 | 63.8 | 78.5 |
| Nitrogen, per cent dry sludge | 1.6 | 1.6 | 2.4 | 2.0 | 3.0 |
The conclusions reached as a result of the New Haven experiments are:[[193]]
Our experience with New Haven sewage lends no color to the hope that a net financial profit can be obtained by the use of the Miles Acid Process, except with sewage of exceptionally high grease content and low alkalinity. They do, however, suggest that for communities where clarification and disinfection are desirable—where screening would be insufficient and nitrification unnecessary—the process of acid treatment comes fairly into competition with the other processes of tank treatment, and that it is particularly suited to dealing with sewages that contain industrial wastes, and to use in localities where local nuisances must be avoided at all costs and where sludge disposal could be provided for only with difficulty.
The conclusions reached as a result of the Chicago experiments are:[[194]]
The results on hand indicate that treatment of this sewage with acid results in a somewhat greater retention of fat. An apparent reduction in the oxygen demand over that resulting from plain sedimentation, while remarkable, is probably not real, being simply due to a retardation of decomposition by the sterilization of the bacteria present, the organic matter being left in solution.... However, there appears the added cost of acid treatment and the cost of recovery of the grease, as well as the uncertainty of the price to be received for the grease recovered.
The cost of the treatment is estimated by Dorr to be $18 per million gallons, and the value of the sludge obtained from the Boston sewage as $24 per million gallons, giving a net margin of profit of $6 per million gallons. At New Haven, the total return is estimated at $7.09 per million gallons. Based on the production of sulphur dioxide by burning sulphur (assumed to cost $36 per long ton) and on drying from 85 per cent to 10 per cent moisture with coal assumed to cost $7.50 per ton, it appears that the acid treatment of sewage should be materially cheaper than either the Imhoff treatment or fine screening under the local conditions. A comparison of the cost of the treatment of the East Street and the Boulevard sewage at New Haven and the Calf Pasture sewage in Boston is given in Table 100. The cost of construction was estimated by Dorr and Weston in 1919 as greater than $15,000 per million gallons of sewage per day capacity.
| TABLE 100 | ||||||||
|---|---|---|---|---|---|---|---|---|
| Estimated Cost of Sewage Treatment at New Haven and Boston by Three Different Processes | ||||||||
| Cost in Dollars per Million Gallons Treated | ||||||||
| (Engineering and Contracting, Vol. 51, p. 510) | ||||||||
| Miles Acid Process | Imhoff Tank and Chlorination | Fine Screens and Chlorination | ||||||
| East Street | Boulevard | Calf Pasture | East Street | Boulevard | Calf Pasture | East Street | Boulevard | |
| Tanks and Buildings Int. and Dep. | 2.47 | 2.47 | 2.47 | 5.28 | 4.44 | 4.60 | 4.60 | |
| Acid treatment | 6.93 | 10.74 | 18.65 | |||||
| Drying sludge | 2.09 | 2.04 | 10.34 | |||||
| Degreasing sludge | 1.78 | 1.91 | 9.12 | |||||
| Superintendence | 1.06 | 2.65 | 1.06 | 0.46 | 1.15 | 0.47 | 1.15 | |
| Labor on tanks and screens | 1.00 | 1.00 | 1.00 | 1.20 | 1.50 | 1.42 | 2.05 | |
| Disposal of sludge or screenings | 1.00 | 1.00 | 0.50 | 0.50 | ||||
| Chlorination | 4.05 | 4.05 | 4.05 | 4.05 | ||||
| Gross cost | 15.50 | 20.98 | 42.75 | 11.99 | 12.14 | 11.03 | 12.35 | |
| Revenue | 6.57 | 10.66 | 47.59 | |||||
| Net cost | 8.93 | 10.32 | 4.84 | 11.99 | 12.14 | 11.03 | 12.35 | |