| TABLE 74 | ||||||
|---|---|---|---|---|---|---|
| Sewage Analyses Showing Hourly, Daily, and Seasonal Variations in Quality | ||||||
| Place | Time Nitrogen | Total | Chlorine | Suspended Matter | Remarks | Reference |
| Marion, Ohio | Mid’t-noon, 5–21–06. | 45 | 53 | 190 | Industrial | 1 |
| Noon-mid’t 5–21–06. | 37 | 94 | 133 | Domestic | 1 | |
| Westerville, Ohio | Day | 10.2 | 76 | 118 | college town | 1 |
| Night | 2.6 | 74 | 41 | 1 | ||
| Columbus, Ohio | 1904–1905 | |||||
| Mid’t to 2 a.m. | 4.6 | 50 | 131 | 2 | ||
| 2 a.m. to 4 a.m. | 3.0 | 52 | 95 | 2 | ||
| 4 a.m. to 6 a.m. | 2.3 | 51 | 83 | 2 | ||
| 6 a.m. to 8 a.m. | 2.7 | 48 | 83 | 2 | ||
| 8 a.m. to 10 a.m. | 16.3 | 66 | 476 | 2 | ||
| 10 a.m. to noon | 11.4 | 100 | 324 | 2 | ||
| Noon to 2 p.m. | 11.3 | 86 | 246 | 2 | ||
| 2 p.m. to 4 p.m. | 12.3 | 78 | 246 | 2 | ||
| 4 p.m. to 6 p.m. | 22.0 | 78 | 368 | 2 | ||
| 6 p.m. to 8 p.m. | 8.2 | 71 | 209 | 2 | ||
| 8 p.m. to 10 p.m. | 7.8 | 80 | 120 | 2 | ||
| 10 p.m. to mid’t | 6.2 | 56 | 117 | 2 | ||
| Center Ave., Chicago. | Mid’t to 3 a.m. | 123 | 3 | |||
| 4 a.m. to 7 p.m. | 316 | 3 | ||||
| 8 a.m. to 11 p.m. | 608 | 3 | ||||
| Noon to 3 p.m. | 785 | 3 | ||||
| 4 p.m. to 7 p.m. | 717 | 3 | ||||
| 8 p.m. to 11 p.m. | 287 | 3 | ||||
| Columbus, Ohio | Sunday | 6.7 | 55 | 858 | 2 | |
| Monday | 9.1 | 66 | 1048 | 2 | ||
| Tuesday | 9.4 | 69 | 1024 | 2 | ||
| Wednesday | 9.6 | 68 | 1005 | 2 | ||
| Thursday | 9.2 | 66 | 990 | 2 | ||
| Friday | 9.2 | 67 | 1018 | 2 | ||
| Saturday | 9.3 | 67 | 1016 | 2 | ||
| Baltimore, 1907–1908 | Aug. 1 to Sept. 1 | 16.0 | 246 | 4 | ||
| Sept. 4 to Oct. 3 | 19.0 | 190 | 4 | |||
| Oct. 6 to Nov. 4 | 20.0 | 188 | 4 | |||
| Nov. 15 to Nov. 29 | 20.0 | 164 | 4 | |||
| Dec. 3 to Dec. 29 | 20.0 | 123 | 4 | |||
| Jan. 6 to Jan. 21 | 19.0 | 127 | 4 | |||
| Feb. 2 to Feb. 26 | 20.0 | 149 | 4 | |||
| Feb. 29 to Mar. 24 | 28.0 | 274 | 4 | |||
| Mar. 27 to April 29 | 25.0 | 165 | 4 | |||
| April 30 to May 26 | 19.0 | 104 | 4 | |||
| June 8 to July 11 | 15.0 | 88 | 4 | |||
| July 13 to Aug. 8 | 9.5 | 124 | 4 | |||
References: 1. 1908 Report of the Ohio State Board of Health. 2. Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905. 3. Report on Industrial Wastes from the Stock Yards and Packingtown in Chicago, by the Sanitary District of Chicago. 1921. 4. Report of the Baltimore Sewerage Commission, 1911.
217. Sewage Disposal.—Previous to the development of the water-carriage method for removing human excreta and other liquid wastes the solid matter was disposed of by burial and the liquid wastes were allowed to seep into the ground or to run away over its surface. Following the development of the water-carriage system, which necessitated the development of sewers, the problem of ultimate disposal was rendered more serious by the concentration of human excreta together with a large volume of water. The unthinking citizen believes the problem of sewage disposal is solved when the toilet is flushed or the bath tub is drained. The problem may more truly be said to commence at this point.
It would appear that the simplest method of disposal of sewage would be to discharge it into the nearest water course. Unfortunately the nature of sewage is such that it may be either highly offensive to the senses or dangerous to health or both, when discharged in this manner. Only the most fortunate communities are favored with a body of water of sufficient size to receive sewage without creating a nuisance.
The problems of sewage disposal are to prevent nuisances causing offense to sight and smell; to prevent the clogging of channels; to protect pumping machinery; to protect public water supplies; to protect fish life; to prevent the contamination of shell fish; to recover valuable constituents of the sewage; to enrich and to irrigate the soil; to safeguard bathing and boating; for other minor purposes; and in some cases to comply with the law. Sewage may be treated to attain one or more of these objects by methods of treatment varying as widely as the objects to be attained.
218. Methods of Sewage Treatment.—In studying the subject of sewage treatment it must be borne in mind that it is impossible to destroy any of the elements present. They may be removed from the mixture only by gasification, straining or sedimentation. Their chemical combinations may be so changed, however, as to result in different substances than those introduced to the treatment plant. It is with these chemical changes that the student of sewage treatment is interested.
The methods of sewage treatment can be classified as mechanical, chemical and biological. These classifications are not separated by rigid lines but may overlap in certain treatment devices or methods. Mechanical methods of treatment are exemplified by sedimentation, and screening. Chemical precipitation and sterilization are examples of chemical methods. The biological methods, the most important of all, include dilution, septicization, filtration, sewage farming, activated sludge, etc. If for any reason it is desired to treat sewage by more than one of these methods the procedure should follow as nearly as possible the order of the occurrence of the phenomena in the natural biolysis of sewage. For example, in one treatment plant the sewage would first pass through a grit chamber where the coarse sediment would be removed, then through a screen where the floating matter and coarse suspended matter would be removed, then to a sedimentation basin where some finer suspended matter might settle out, then to a digestive tank where the solid matter deposited would be worked upon by bacterial action and partially liquefied. Simultaneous to the liquefaction of the deposited solid matter the liquid effluent from the digestive tank might proceed to an aërating device to expedite oxidation, then to an aërobic filter, and finally to disposal by dilution.
CHAPTER XIV
DISPOSAL BY DILUTION
219. Definition.—Disposal of sewage by dilution is the discharge of raw sewage or the effluent from a treatment plant into a body of water of sufficient size to prevent offense to the senses of sight and smell, and to avoid danger to the public health.
220. Conditions Required for Success.—Among the desired conditions for successful disposal by dilution are: adequate currents to prevent sedimentation and to carry the sewage away from all habitations before putrefaction sets in, or sufficient diluting water high in dissolved oxygen to prevent putrefaction; a fresh or non-septic sewage; absence of floating or rapidly settling solids, grease or oil; and absence of back eddies or quiet pools favorable to sedimentation in the stream into which disposal is taking place. The conditions which should be prevented are: offensive odors due to sludge banks, the rise of septic gases, and unsightly floating or suspended matter. In some instances the pollution of the receiving body of water is undesirable and the sewage must be freed from pathogenic organisms and the danger of aftergrowths minimized before disposal. Such conditions are typified at Baltimore, where the sewage is discharged into Back Bay, an arm of Chesapeake Bay. One of the important industries of the state of Maryland is the cultivation of oysters. The pollution of the Bay was therefore so objectionable that careful treatment of the Baltimore sewage has been a necessary preliminary to final disposal by dilution. It is unwise to draw public water supplies, without treatment, from a stream receiving a sewage effluent, no matter how careful or thorough the treatment of the sewage. The treatment of the sewage is a safeguard, and lightens the load on the water purification plant, but under no considerations can it be depended upon to protect the community consuming the diluted effluent.