Sewerage and Sewage Treatment — Themes and Context

SEWERAGE AND SEWAGE TREATMENT

HAROLD E. BABBITT, M.S.

_Assistant Professor, Municipal and Sanitary Engineering, University of Illinois; Associate Member American Society of Civil Engineers_

NEW YORK JOHN WILEY & SONS, INC. LONDON: CHAPMAN & HALL, LIMITED 1922

Copyright, 1922, by HAROLD E. BABBITT, M.S.

PRESS OF BRAUNWORTH & CO. BOOK MANUFACTURERS BROOKLYN, N. Y.

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This book is a development of class-room and lecture notes prepared by the author for use in his classes at the University of Illinois. He has found such notes necessary, since among the many books dealing with sewerage and sewage treatment he has found none suitable as a text-book designed to cover the entire subject. The need for a single book of the character described has been expressed by engineers in practice, and by students and teachers for use in the class-room. This book has been prepared to meet both these needs. It is hoped that the searching questions propounded by students in using the original notes, and the suggestions and criticisms of engineers and teachers who have read the manuscript, have resulted in a text which can be readily understood.

The ground covered includes an exposition of the principles and methods for the designing, construction and maintenance of sewerage works, and also of the treatment of sewage. In covering so wide a field the author has deemed it necessary to include some chapters which might equally well appear in works on other branches of engineering, such as the chapter on Pumps and Pumping Stations. Special stress has been laid on the fundamentals of the subject rather than the details of practice, although illustrations have been drawn freely from practical work. The quotation of expert opinions which may be in controversy, or the citation of examples of different methods of accomplishing the same thing, has been avoided when possible in order to simplify explanations and to avoid confusing the beginner.

The work is to some extent a compilation of notes and quotations which have been collected by the author during years of study and teaching the subject. Credit has been given wherever due, and at the same time references have pointed out the original sources whenever possible. These references, which have been supplemented by brief bibliographies at the end of certain chapters, will be useful to the student and engineer interested in further study. Occasionally the original reference has been lost or the phraseology of a quotation has been so altered by class-room use, as to make it impossible to trace the original source, so that in some few instances full credit may be lacking.

The author is indebted to many of his friends for their criticisms and suggestions in the preparation of the manuscript; but he desires particularly to acknowledge the assistance of Professor A. N. Talbot, Professor of Municipal and Sanitary Engineering at the University of Illinois, and of Professor M. L. Enger, Professor of Mechanics and Hydraulics at the University of Illinois, in the entire work; also that of Mr. T. D. Pitts, Principal Assistant Engineer of the Baltimore Sewerage Commission during the construction of the Baltimore sewers, for his suggestions on the first half of the book; and to Mr. Paul Hansen, consulting engineer, of Chicago, and to Mr. Langdon Pearse, Sanitary Engineer of the Sanitary District of Chicago, for their help on the section covering the treatment of sewage; and to Professor Edward Bartow, Professor of Chemistry at the University of Iowa, for his review of the chapter on Activated Sludge; in general his thanks are due to all others who have furnished suggestions, illustrations, or quotations, acknowledgments of which have been included in the text.

URBANA, ILLINOIS, 1922.

PAGES 1. Sewerage and the Sanitary Engineer. 2. Historical. 3. Methods of Collection. 4. Methods of Disposal. 5. Methods of Treatment. 6. Definitions. 1–8

WORK PRELIMINARY TO DESIGN

7. Division of Work. 8. Preliminary. 9. Estimate of cost. METHODS OF FINANCING. 10. Bond Issues. 11. Special Assessment. 12. General Taxation. 13. Private Capital. PRELIMINARY WORK. 14. Preparing for Design. 15. Underground Surveys. 16. Borings. 9–23

17. Dry Weather Flow. 18. Methods for Predicting Population. 19. Extent of Prediction. 20. Sources of Information on Population. 21. Density of Population. 22. Changes in Area. 23. Relation between Population and Sewage Flow. 24. Character of District. 25. Fluctuations in Rate of Sewage Flow. 26. Effect of Ground Water. 27. Résumé of Method for Determination of Quantity of Dry weather Sewage. QUANTITY OF STORM WATER. 28. The Rational Method. 29. Rate of Rainfall. 30. Time of Concentration. 31. Character of Surface. 32. Empirical Formulas. 33. Extent and Intensity of Storms. 24–50

34. Principles. 35. Formulas. 36. Solution of Formulas. 37. Use of Diagrams. 38. Flow in Circular Pipes Partly Full. 39. Sections Other than Circular. 40. Non-Uniform Flow. 51–77

DESIGN OF SEWERAGE SYSTEMS

41. The Plan. 42. Preliminary Map. 43. Layout of the Separate System. 44. Location and Numbering of Manholes. 45. Drainage Areas. 46. Quantity of Sewage. 47. Surface Profile. 48. Slope and Diameter of Sewers. 49. The Sewer Profile. DESIGN OF A STORM-WATER SEWER SYSTEM. 50. Planning the System. 51. Location of Street Inlets. 52. Drainage Areas. 53. Computation of Flood Flow by McMath Formula. 54. Computation of Flood Flow by Rational Method. 78–98

55. General. 56. Manholes. 57. Lampholes. 58. Street Inlets. 59. Catch-basins. 60. Grease Traps. 61. Flush-tanks. 62. Siphons. 63. Regulators. 64. Junctions. 65. Outlets. 66. Foundations. 67. Underdrains. 99–126

PUMPS AND PUMPING STATIONS

68. Need. 69. Reliability. 70. Equipment. 71. The Building. 72. Capacity of Pumps. 73. Capacity of Receiving Well. 74. Types of Pumping Machinery. 75. Sizes and Descriptions of Pumps. 76. Definitions of Duties and Efficiency. 77. Details of Centrifugal Pumps. 78. Centrifugal Pump Characteristics. 79. Setting of Centrifugal Pumps. 80. Steam Pumps and Pumping Engines. 81. Steam Turbines. 82. Steam Boilers. 83. Air Ejectors. 84. Electric Motors. 85. Internal Combustion Engines. 86. Selection of Pumping Machinery. 87. Costs of Pumping Machinery. 88. Cost Comparisons of Different Designs. 89. Number and Capacity of Pumping Units. 127–163

90. Materials. 91. Vitrified Clay Pipe. 92. Cement and Concrete Pipe. 93. Proportioning of Concrete. 94. Waterproofing of Concrete. 95. Mixing and Placing Concrete. 96. Sewer Brick. 97. Vitrified Clay Sewer Block. 98. Cast Iron, Steel, and Wood. 164–193

DESIGN OF THE SEWER RING

99. Stresses in Buried Pipe. 100. Design of Steel Pipe. 101. Design of Wood Stave Pipe. 102. External Loads on Buried Pipe. 103. Stresses in Circular Ring. 104. Analysis of Sewer Arches. 105. Reinforced Concrete Sewer Design. 194–210

CONTRACTS AND SPECIFICATIONS

106. Importance of the Subject. 107. Scope of the Subject. 108. Types of Contracts. 109. The Agreement. 110. The Advertisement. 111. Information and Instructions for Bidders. 112. Proposal. 113. General Specifications. 114. Technical Specifications. 115. Special Specifications. 116. The Contract. 117. The Bond. 211–232

118. Elements. WORK OF THE ENGINEER. 119. Duties. 120. Inspection. 121. Interpretation of Contract. 122. Unexpected Situations. 123. Cost Data and Estimates. 124. Progress Reports. 125. Records. EXCAVATION. 126. Specifications. 127. Hand Excavation. 128. Machine Excavation. 129. Types of Machines. 130. Continuous Bucket Excavators. 131. Cableway and Trestle Excavators. 132. Tower Cableways. 133. Steam Shovels. 134. Drag Line and Bucket Excavators. 135. Excavation in Quicksand. 136. Pumping and Drainage. 137. Trench Pump. 138. Diaphragm Pump. 139. Jet Pump. 140. Steam Vacuum Pumps. 141. Centrifugal and Reciprocating Pumps. 142. Well Points. 143. Rock Excavation. 144. Power Drilling. 145. Steam or Air for Power. 146. Depth of Drill Hole. 147. Diameter of Drill Hole. 148. Spacing of Drill Holes. SHEETING AND BRACING. 149. Purposes and Types. 150. Stay Bracing. 151. Skeleton Sheeting. 152. Poling Boards. 153. Box Sheeting. 154. Vertical Sheeting. 155. Pulling Wood Sheeting. 156. Earth Pressures. 157. Design of Sheeting and Bracing. 158. Steel Sheet Piling. LINE AND GRADE. 159. Locating the Trench. 160. Final Line and Grade. 161. Transferring Grade and Line to the Pipe. 162. Line and Grade in Tunnel. TUNNELLING. 163. Depth. 164. Shafts. 165. Timbering. 166. Shields. 167. Tunnel Machines. 168. Rock Tunnels. 169. Ventilation. 170. Compressed Air. EXPLOSIVES AND BLASTING. 171. Requirements. 172. Types of Explosives. 173. Permissible Explosives. 174. Strength. 175. Fuses and Detonators. 176. Care in Handling. 177. Priming, Loading, and Firing. 178. Quantity of Explosive. PIPE SEWERS. 179. The Trench Bottom. 180. Laying Pipe. 181. Joints. 182. Labor and Progress. BRICK AND BLOCK SEWERS. 183. The Invert. 184. The Arch. 185. Block Sewers. 186. Organization. 187. Rate of Progress. CONCRETE SEWERS. 188. Construction in Open Cut. 189. Construction in Tunnels. 190. Materials for Forms. 191. Design of Forms. 192. Wooden Forms. 193. Steel-lined Wooden Forms. 194. Steel Forms. 195. Reinforcement. 196. Cost of Concrete Sewers. BACKFILLING. 197. Method. 233–331

MAINTENANCE OF SEWERS

198. Work Involved. 199. Causes of Troubles. 200. Inspection. 201. Repairs. 202. Cleaning of Sewers. 203. Flushing Sewers. 204. Cleaning Catch-basins. 205. Protection of Sewers. 206. Explosions in Sewers. 207. Valuation of Sewers. 332–351

COMPOSITION AND PROPERTIES OF SEWAGE

208. Physical Characteristics. 209. Chemical Composition. 210. Significance of Chemical Constituents. 211. Sewage Bacteria. 212. Organic Life in Sewage. 213. Decomposition of Sewage. 214. The Nitrogen Cycle. 215. Plankton and Macroscopic Organisms. 216. Variations in the Quality of Sewage. 217. Sewage Disposal. 218. Methods of Sewage Treatment. 352–371

219. Definition. 220. Conditions Required for Success. 221. Self-purification of Running Streams. 222. Self-purification of Lakes. 223. Dilution in Salt Water. 224. Quantity of Diluting Water Needed. 225. Governmental Control. 226. Preliminary Treatment. 227. Preliminary Investigations. 372–382

SCREENING AND SEDIMENTATION

228. Purpose. 229. Types of Screens. 230. Sizes of Openings. 231. Design of Fixed and Movable Screens. PLAIN SEDIMENTATION. 232. Theory of Sedimentation. 233. Types of Sedimentation Basins. 234. Limiting Velocities. 235. Quantity and Character of Grit. 236. Dimensions of Grit Chambers. 237. Existing Grit Chambers. 238. Number of Grit Chambers. 239. Quantity and Characteristics of Sludge from Plain Sedimentation. 240. Dimensions of Sedimentation Basins. CHEMICAL PRECIPITATION. 241. The Process. 242. Chemicals. 243. Preparation and Addition of Chemicals. 244. Results. 383–409

245. The Process. 246. The Septic Tank. 247. Results of Septic Action. 248. Design of Septic Tanks. 249. Imhoff Tanks. 250. Design of Imhoff Tanks. 251. Imhoff Tank Results. 252. Status of Imhoff Tanks. 253. Operation of Imhoff Tanks. 254. Other Tanks. 410–430

FILTRATION AND IRRIGATION

255. Theory. 256. The Contact Bed. 257. The Trickling Filter. 258. Intermittent Sand Filter. 259. Cost of Filtration. IRRIGATION. 260. The Process. 261. Status. 262. Preparation and Operation. 263. Sanitary Aspects. 264. The Crop. 431–464

265. The Process. 266. Composition. 267. Advantages and Disadvantages. 268. Historical. 269. Aëration Tank. 270. Sedimentation Tank. 271. Reaëration Tank. 272. Air Distribution. 273. Obtaining Activated Sludge. 274. Cost. 465–479

ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION

275. The Miles Acid Process. ELECTROLYTIC TREATMENT. 276. The Process. DISINFECTION. 277. Disinfection of Sewage. 482–493

278. Methods of Disposal. 279. Lagooning. 280. Dilution. 281. Burial. 282. Drying. 495–505

AUTOMATIC DOSING DEVICES

283. Types. 284. Operation. 285. Three Alternating Siphons. 286. Four or More Alternating Siphons. 287. Timed Siphons. 288. Multiple Alternating and Timed Siphons. 506–512

SEWERAGE AND SEWAGE TREATMENT

CHAPTER I INTRODUCTION

=1. Sewerage and the Sanitary Engineer.=—Present day conceptions of sanitation are based on the scientific discoveries which have resulted so much in the increased comfort and safety of human life during the past century, in the increase of our material possessions, and the extent of our knowledge. The danger to health in the accumulation of filth, the spreading of disease by various agents, the germ theory of disease, and other important principles of sanitation can be counted among the more recent scientific discoveries and pronouncements. Experience has shown, and continues to show, that the increase of population may be inhibited by accumulations of human waste in populous districts. The removal of these wastes is therefore essential to the existence of our modern cities.

The greatest need of a modern city is its water supply. Without it city life would be impossible. The next most important need is the removal of waste matters, particularly wastes containing human excreta or the germs of disease. To exist without street lights, pavements, street cars, telephones, and the many other attributes of modern city life might be possible, although uncomfortable. To exist in a large city without either water or sewerage would be impossible. The service rendered by the sanitary engineer to the large municipality is indispensable. In addition to the service necessary to the maintenance of life in large cities, the sanitary engineer serves the smaller city, the rural community, the isolated institution, and the private estate with sanitary conveniences which make possible comfortable existence in them, and which are frequently considered as of paramount necessity. Training for service in municipal sanitation is training for a service which has a more direct beneficial effect on humanity than any other engineering work, or any other profession. W. P. Gerhard states:

_A Sanitary Engineer_ is an engineer who carries out those works of civil engineering which have for their object:

(_a_) The promotion of the public and individual health;

(_b_) The remedying of insanitary conditions;

(_c_) The prevention of epidemic diseases.

A well-educated sanitary engineer should have a thorough knowledge of general civil engineering, of architecture, and of sanitary science. The practice of the sanitary engineer embraces water supply, sewerage, and sewage and garbage disposal for cities and for single buildings; the prevention of river pollution, the improvement of polluted water supplies; street paving and street cleaning, municipal sanitation, city improvement plans, the laying out of cities, the preparation of sanitary surveys, the regulation of noxious trades, disinfection, cremation, and the sanitation of buildings.

The need of the work of the sanitary engineer in the provision of sewers and drains is thrust upon us in our daily experience by the clogging of sewers, the flooding of streets by heavy rains, filthy conditions in unsewered districts, increased values of property and improved conditions of living in sewered districts, and in many other ways. The increasing demand for sewerage and the amount of money expended on sewer construction is indicated by the information given in Table I.

=2. Historical.=—An ordinance passed by the Roman Senate in the name of the Emperor about A.D. 80, states:

I desire that nobody shall conduct away any excess water without having received my permission or that of my representatives; for it is necessary that a part of the supply flowing from the delivery tanks shall be utilized not only for cleaning our city, but also for flushing the sewers.[1]

Neither the sewers mentioned nor the distributing pipes of the public water supply were connected to individual residences. The contributions to the sewers came from the ground and the street surface. The streets were the receptacles of liquid and solid wastes and were often little more than open sewers. A promenade after dark in an ancient, medieval, or early modern city was accompanied not only by the underfoot dangers of an uneven pavement or an encounter with a footpad, but with the overhead danger from the emptying of slops into the streets from the upper windows. Sewers were used for the collection of surface water; the discharge of fecal matter into them was prohibited. The problem of the collection of sewage remained unsolved until the Nineteenth Century.

POPULATION TRIBUTARY TO SEWERAGE SYSTEMS

──────────────────────────────────────┬──────────┬──────────┬────────── │ 1905[2] │ 1915[3] │ 1920[4] ──────────────────────────────────────┼──────────┼──────────┼────────── Population discharging raw sewage into│ │ │ the sea or tidal estuaries │ 6,500,000│ 8,500,000│ Population discharging raw sewage into│ │ │ inland streams or lakes │20,400,000│26,400,000│ Population connected to systems where │ │ │ sewage is treated in some way │ 1,100,000│ 6,900,000│ Population connected with sewerage │ │ │ systems │28,000,000│41,800,000│46,300,000 ──────────────────────────────────────┴──────────┴──────────┴──────────

The development of the London sewers was commenced early in the Nineteenth Century. The sewerage system of Hamburg, Germany, was laid out in 1842 by Lindley, an English engineer who with other English engineers performed similar work in other German cities because of their earlier experience in English communities. Berlin’s present system dates from 1860. The construction of storm-water drains in Paris dates from 1663.[5] They were intended only as street drains but are now included in the comprehensive system of the city. The first comprehensive sewerage system in the United States was designed by E. S. Chesbrough for the City of Chicago in 1855. Previous to this time sewers had been installed in an indifferent manner and without definite plan. The installation of a comprehensive sewerage system in Baltimore in 1915 marks the completion of installation of sewerage systems in all large American cities.

In the early days of sewerage design it was considered unsafe to discharge domestic wastes into the sewers as the concentration of so much sewage was expected to create great nuisances and dangers to health. That the fear that the concentration of large quantities of sewage would create a nuisance was not ill founded is proven by the conditions on the Thames at London in 1858–59. Dr. Budd states:[6]

For the first time in the history of man, the sewage of nearly three millions of people had been brought to seethe and ferment under a burning sun in one vast open _cloaca_ lying in their midst.

The result we all know. Stench so foul we may well believe had never before ascended to pollute this lower air. Never before at least had a stink risen to the height of an historic event.... For months together the topic almost monopolized the public prints.... ‘India is in revolt and the Thames stinks’ were the two great facts coupled together by a distinguished foreign writer, to mark the climax of a national humiliation.[7]

The problem of sewage disposal followed the more or less successful solutions of the problem of sewage collection. In England the British Royal Commission on Sewage Disposal was appointed in 1857 and issued its first report in 1865. The first studies in the United States were started in 1887 by the establishment of an experiment station at Lawrence, Massachusetts, where valuable work has been done. The station is under the State Board of Health, which issued its first report containing the results of the work at the station, in 1890.

Various methods of sewage treatment preparatory to disposal have been devised from time to time. Some have fallen into disuse, such as the A. B. C. (alum, blood and clay) process, and others have taken a permanent place, such as the septic tank. The unsolved problems of sewage collection, and the number of persons still unserved by sewerage and sewage disposal opens a wide field to the study and construction of sewerage works.

=3. Methods of Collection.=—The method of collection which involves the removal of night soil from a privy vault, the pail system which involves the collection of buckets of human excreta from closets and homes, indoor chemical closets, and other makeshift methods of collection are of extreme importance where no sewers exist, but they are not properly considered as sewerage systems or sewerage works. These methods of collection are generally confined to rural districts and to outlying parts of urban communities. They require constant attention for their proper conduct and little skill for their installation, the principal requirements being to make the receptacles fly-proof.

The pneumatic system was introduced by Liernur, a Dutch engineer.[8] It is used in parts of a few cities in Europe, but it is not capable of use on a large scale. It consists of a system of air-tight pipes, connecting water closets, kitchen sinks, etc., with a central pumping station at which an air-tight tank is provided from which the air is partly exhausted. As little water as possible is allowed to mix with the fecal matter and other wastes in order not to overtax the system. Solid and liquid wastes are drawn to the central station when the waste valve on the plumbing fixture is opened.

The collection of sewage in a system of pipes through which it is conducted by the buoyant effect and scouring velocity of water is known as the water-carriage system. This is the only method of sewage collection in general use in urban communities. In this system solid and liquid wastes are so highly diluted with water as either to float or to be suspended therein. The mixture resulting from this high dilution follows the laws of hydraulics as applied to pure water, or water containing suspended matter. It will flow freely through properly designed conduits and will concentrate the sewage wastes at the point of ultimate disposal.

=4. Methods of Disposal.=—Sewage is disposed of by dilution in water, by treatment on land, or occasionally by discharging it into channels that contain no diluting water. Some form of treatment to prepare sewage for ultimate disposal is frequently necessary and will undoubtedly be required in a comparatively short time for all sewage discharged into watercourses. The solid matters removed by treatment may be buried, burned, dumped into water, or used as a fertilizer.

If the volume of diluting water, or the area and character of land used for disposal are not as they should be, a nuisance will be created. The aim of all methods of sewage treatment has so far been to produce an effluent which could be disposed of without nuisance and in certain exceptional cases to protect public water supplies from pollution. Financial returns have been sought only as a secondary consideration. A few sewage farms and irrigation projects might be considered as exceptions to this as the value of the water in the sewage as an irrigant has been the primary incentive to the promotion of the farm.

It is to be remembered that since the aim of all sewage treatment is to produce an effluent that can be disposed of without causing a nuisance, the simplest process by which this result can be attained under the conditions presented is the process to be adopted. No attempt is made to _purify_ sewage completely, or on a practical scale to make drinking water.

=5. Methods of Treatment.=—Screening and sedimentation are the primary methods for the treatment of sewage. By these methods a portion of the floating and settleable solids are removed, preventing the formation of unsightly scum and putrefying sludge banks. Chemicals are sometimes added to the sewage to form a heavy flocculent precipitate which hastens sedimentation of the solid matters in the sewage. The process in these methods is mechanical and the solid matters removed from the sewage must be disposed of by other methods than dilution with the sewage effluent. More complete methods of treatment are dependent on biologic action. Under these methods of treatment complete stabilization of the effluent is approached, and in the most complete treatment an effluent is produced which is clear, sparkling, non-odorous, non-putrescible, and sterile. Sterilization of sewage, usually with chlorine or some of its compounds, has been used, not to reduce the amount of diluting water necessary, but to reduce the number of pathogenic germs and to minimize the danger of the transmission of disease.