Sewage treatment

“ It produces a better effluent than any other known process of sewage treatment except land treatment or intermittent sand filtration; it can be built upon a comparatively small area; it produces no objectionable odors or flies; it produces a sludge of sufficient value to meet the cost of its reduction to a fertilizer and therefore relieves the city of the difficult, complicated and wasteful method of sludge disposal common to all other processes ”

“ While there have been some demands for the absolute sterilization of sewage, many sanitarians believe that any artificial method of sewage treatment will not esthetically render the final effluent fit for ingestion, and practically all authorities agree that final discharge of sewage need not be in this perfect condition. ”

“ 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. ”

“ The control of sewage treatment plant effluents so as to avoid the poisoning of fish life or the contamination of shell fish is likewise important. The study of plankton and macroscopic life in the treatment of sewage is an open field for research.
216. Variations in the Quality of Sewage.—The quality of sewage varies with the hour of the day and the season of the year. Some of the causes of these variations are: changes in the amount of diluting water due to the inflow of storm water or flushing of the streets or sewers ”

“ The principal advantage of septic action in sewage treatment is the relatively small amount of sludge which must be cared for compared to that produced by a plain sedimentation tank. The sludge from a septic tank may be 25 to 30 per cent and in some cases 40 per cent less in weight, and 75 to 80 per cent less in volume than the sludge from a plain sedimentation tank. The most important results of septic action and the greatest septic activity occur in the deposited organic matter or sludge. ”

“ For who would deny that masonry or concrete tanks and the materials contained in the same are artificial products—i.e. products formed by man—and that land is a natural product—i.e. formed by nature—and that further the soil is the natural home of bacteria. Hence it must be perfectly clear, even to a casual observer, that the line of demarcation drawn by the Commissioners between all known systems of sewage purification is a correct and legitimate one, and that all objections to such a division are based on misconceptions. ”

“ How extremely simple it all is!” was the remark of a recent visitor at a sewage farm—which encourages me to venture on publication of the most recent discussions on a “problem” complicated by engineers, chemists, bacteriologists and inventors of systems, who have raised clouds of dust through which it is difficult for ratepayers and district councillors to find their way to “the best practical and available means of sewage disposal.” ”

“ In addition to this it must be understood that, owing to the great losses by evaporation and by growing plants, which are continually at work on sewage farms, especially during the summer months, when, as a rule, the flow of water in the brook that takes the effluent is smallest, the quantity of the effluent from the natural treatment is probably only from one-half to one-third that resulting from the artificial treatment, which is a point of very great importance. ”

“ Before any sewage scheme is conceived a very careful survey of the neighbourhood ought to be made by a person who knows the requisites of a site for sewage disposal, especially if land irrigation is intended, because natural advantages of site both for tanks, main carriers, roads, etc., may make all the difference in the world in expense and efficiency not only in first cost of works but also in their use afterwards. ”

“ Sewerage is the name of the system of conduits and appurtenances designed to carry off the sewage. It is also used to indicate anything pertaining to sewers.
A difference is made between sanitary sewage, storm sewage, and industrial wastes. Sanitary sewage, sometimes called domestic sewage, is the liquid wastes discharged from residences or institutions, and contains water closet, laundry and kitchen wastes. Storm sewage is the surface run-off which reaches the sewers during and immediately after a storm. Industrial wastes are the liquid waste products discharged from industrial plants. ”

“ The main purpose of home sewerage works is to get rid of sewage in such way as (1) to guard against the transmission of disease germs through drinking water, flies, or other means; (2) to avoid creating nuisance. What is the best method and what the best outfit are questions not to be answered offhand from afar. A treatment that is a success in one location may be a failure in another. In every instance decision should be based upon field data and full knowledge of the local needs and conditions. An installation planned from assumed conditions may work harm. ”

“ The matters in solution will partly, after removal out of the liquid, be retained by the absorbing powers of the soil in the pores, a process that is due to physical and chemical agencies.
Absorbing powers gradually ripen.
It is well known that land which is being treated with sewage for the first time does not purify sewage so well as land that has been under systematic treatment for some time, and this is probably due to the absorbing powers, which gradually ripen until they have reached their maximum of efficiency. ”

“ It is convenient to divide sewage purification into two processes, the preliminary process and the final, or finishing process, and, while the preliminary process, in itself, never accomplishes purification, yet it is of considerable value in facilitating and increasing the rate and efficiency of that purification. The most common preliminary treatment is sedimentation, by which the larger solids in suspension are allowed to settle in a tank or tanks so that the filter beds later used are relieved from the accumulation of those deposits. ”

“ Where no sand is available, or where its use would be uneconomical, broken stone may be used to ensure final treatment. With stone, on account of its large voids, the enclosure must either be water-tight, and the outlet pipe must be provided with 13a valve or other device so that the sewage under treatment may be held in the enclosure or tank long enough to deposit the solids in suspension and to be acted on by the bacteria concerned. ”

“ Passing now to the aerobic stage of sewage purification we find it universally admitted, that a good loam resting on very porous sand or gravel, affords the best medium for work by the oxygen-loving nitrifying organisms [Pg 6] when they are supplied with constantly moving liquid sewage, and given intermittent periods for the aeration of the pores of the soil. ”

“ Concerning land treatment, the Commissioners observe, “We doubt if any land is entirely useless,” but further on they observe that peat and stiff clay lands are generally unsuitable for the purification of sewage. ”

“ 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. ”

“ Sludge Disposal and Value Authorities are generally agreed that the sludge problem is the center of the entire sewage problem, because it causes more trouble and is the most expensive part of the treatment. ”

“ Some of the substances contained in raw sewage remain in the bed, no matter how carefully the sewage has been previously strained, and these, in combination with the slimy surface coating of the component particles, the accumulation of mineralised substances in the pores, the consolidation of the bed, the disintegration of the filling material, and the liquid retained, lead gradually but surely to the silting or sludging up of the bed. ”

“ But even separate sanitary sewers are often overloaded by having to serve greater populations than they were designed for, which means that their escape valves may leak raw sewage more or less continuously into surface watercourses and that the quality of treatment given the sewage that does reach the treatment plant signifies less than it ought to. ”

“ When town sewage is pumped through a long rising main, it can often be spread on the land in its really crude state, and if the soil is clay ploughed up to receive it the sludge is most beneficial to its texture. ”

“ 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. ”

“ Little guidance can be taken from the personal feeling of the persons immediately interested. The opinion of the riparian owner 5 miles down stream may differ materially from the popular will of the voters of a city, and it is likely to receive a more favorable hearing from the court. Statutes and legal precedents are the safest guides.
226. Preliminary Treatment.—If the sewage to be disposed of by dilution contains unsightly floating matter, oil, or grease, no amount of oxygen in the diluting water will prevent a nuisance to sight, or the formation of putrefying sludge banks. ”

“ 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. ”

“ Most authorities now agree that before turning sewage upon land, a preliminary treatment is required to remove as much as possible of the suspended matter, and then reduce the latter by subsidence in liquefying or septic tanks, so that the quantity remaining in the effluent is so small and finely divided that it may be readily decomposed and oxidized by bacterial action without risk of clogging the surface or interstices of the land upon which it may discharge. ”

“ Where the outfall sewage enters the disposal works provide a pair of open catch-pits (or grit-chambers) , each twice as wide as, and 2 feet deeper than the sewer, with sluices allowing the sewage to pass through one pit at a time in its free course, while the other pit is being dried and the deposited detritus dug out. ”

“ Standards of purity have been studied by many societies and various suggestions have been made. All agree that the sewage after treatment should not deteriorate the stream into which it flows. Watson advocates under certain conditions an effluent that will not putrefy on being kept for seven days at a uniform temperature of 80 degrees F. and that does not contain more than three parts per 100,000 of suspended solid matter. ”

“ The problem of treatment is the question of so modifying the character of a large volume of dirty water that it shall neither injure the quality of any drinking-water into which it may be discharged, nor cause objectionable odors, nor present disagreeable appearances in any body of water into which it may be emptied. ”

“ When it is remembered that less than one-half of the organic matter in sewage is in suspension and that the best results in any sort of a tank succeed in depositing only one-half of those suspended solids, it can readily be seen that a tank, whether called septic or settling, cannot be a complete method of treatment. In reality, such a tank does little more than take out from the sewage the greasy material and a certain proportion of the suspended matter. ”

“ A separate system of sewers is one in which only sanitary sewage or industrial wastes or both are allowed to flow. Storm sewers carry only surface drainage, exclusive of sanitary sewage. Combined sewers carry both sanitary and storm sewage. ”

“ It is easy to see how the popular idea of incompatibility has arisen in a case like that above stated of the Camp Farm tenant, eating up year by year all the fertility stored up in the land during the previous period, and letting nearly all the sewage run to waste, because its scientific application would cost much in thought and labour. ”

“ It is frequently more advantageous to discharge sewage into a swiftly moving stream, however, regardless of the conditions of self-purification, as the undesirable conditions which may result occur far from the point of disposal and may be offensive to no one. ”

“ In dealing with the sewage question during the last century, it will be an advantage to distinguish between the theory and practice of sewage purification, as such a division of the subject will render it less complicated and will tend to avoid misconceptions. ”

“ Dealing with the artificial processes from a chemical point of view, the Commissioners are of opinion that it is practicable to produce by these processes alone, either from sewage or from certain mixtures of sewage and trade refuse, effluents which might be discharged without fear of creating a nuisance, and that in consequence the Local Government Board would be justified in modifying, under proper safeguards, the present rule as regards the application of sewage to land. ”