Sewage Disposal System PDF

SEWAGE DISPOSAL SYSTEM 4-1 The Sewage and its Disposal The collection and safe disposal of human wastes are among the most critical problems of environmental health. Recent statistical reports revealed that most of the water borne diseases such as dysentery, typhoid, diarrhea and other intestinal...

SEWAGE DISPOSAL SYSTEM 4-1 The Sewage and its Disposal The collection and safe disposal of human wastes are among the most critical problems of environmental health. Recent statistical reports revealed that most of the water borne diseases such as dysentery, typhoid, diarrhea and other intestinal disorders are prevalent in areas where there is no proper and scientific Sewage Disposal System It was reported that when human wastes are deposited in a pit, typhoid and dysentery causing organisms do not travel horizontally in the soil These harmful bacteria neither move by themselves, they were carried in some way These harmful organisms are carried somewhere through water flows, flies, rodents, cockroaches and other vermin which causes contamination The daily average volume of human waste or excreta per capita is about 80 grams of feces and 950 grams of urine When diluted with water at the rate of 30 to 100 gal- lons per day to form sewage, the solid content becomes a very small portion expressed in milligrams per liter. Of the total sewage solids, about 50% is organic and are subject to rotting Small as it is in the sewage, and as decomposition continues, it become odorous and dark in color. And whether fresh or stale, it contains harmful organism that causes diseases It is therefore important not only to know the different types of sewage disposal systems, but also to understand the scientific value of the system. Type of Sewage Disposal System Sewage disposal system has four types 1 The Cesspool 2 The Privy 3 The Septic Tank 4 The Public Sewer Line The Cesspool is a hole in the ground curbed with stones, bricks, concrete hollow blocks, or other materials laid in such a manner as to allow raw contaminated sew age to leach into the soil. The organic wastes accumulate and finally disposed of by disintegration process The Privy is a concrete sealed vault with a wooden shelter constructed for the collection of raw sewage The disintegration of excrement is accomplished in the same Inner as in a cesspool It is objectionable because of the danger of contaminating the source of water supply The Septic Tank is a device or receptacle used to expedite the decomposition of the elements contained in a raw sewage waste. Raw sewage consists of water, and setleable solid called organic materials that can be precipitated in a septic tank in a very short time The Public Sewer Line is a public sewage system, operated and maintained by the government consisting of a sewage treatment plant that conveys the raw sewage from buildings and houses to a disposal system. Of these four types of sewage disposal, the cesspool and the privy are already obsolete. The prevailing types recommended by the sanitary authorities are the Public Sewer line and the Septic Tank 4-2 Public Sewer Line The Public Sewer Line is classified into three types according to the kind of waste it disposes 1 The Combination Public Sewer 2\. The Sanitary Sewer 3\. The Storm Drain The Combination Public Sewer is the oldest type of public sewer that conveys both storm water and sanitary wastes. This type of public sewer is already obsolete and no longer allowed by sanitary authorities. The Sanitary Sewer is a public sewer facility that car. ries regular sanitary wastes only. It terminates in a modern sewage dispersal plant. Rainwater is not permitted to enter into this type of public sewer The Sanitary Sewer is classified into two types 1\. The Intercepting or Trunk Line Sewer 2\. The Tributary or Contributing Sewer The Intercepting Sewer is a sanitary sewer that conveys sanitary waste to a dispersal plant. It is commonly made of concrete pipe that varies in sizes from 0.60 to 3.00 meters in diameter. The pipes are laid underground to a minimum depth of about 3 meters, depending upon the natural contour of the ground The Tributary Sewer is classified as an intercepting 46er branch. The pipe is made of either vitrified clay or concrete pipe laid in an open trench. It is generally smaller in diameter installed not more than 3 meters below the street grade and terminate into the intercepting sewer The Storm Drain is another kind of public sewer Ime that carries storm water it terminates in a natural drain such as canals, lakes or rivers Manhole is classified as a device of the tuain and storm, sewer It serves as man\'s access for inspection, cleaning and repair. It is constructed out of bricks, stone, adobe or concrete at an interval distance from 75 to 150 meters. The manhole diameter varies from 90 to 120 centimeters provided with iron rungs to serve as ladder for the maintenance crew to reach the bottom It is provided with a well-fitted cover on top, leveled with the road surface, Sewage Ejector Sewage ejector refers to the pump that will discharge waste in the sump and transfer it to the house drain in- stalled overhead Sewage ejector is necessary when the public sewer line was installed at a depth from 2 to 4 meters below the street level. Large buildings with basement may have a deeper excavation making it difficult to drain its waste towards the main sewer by means of gravity. 4-3 The Septic Tank Septic Tank is a receptacle or vault used to collect organic waste discharged from the house sewer. The main function of a septic tank is to liquefy and precipitate solid waste purifying odorous materials Sewage that was discharged into the tank is retained and during its retention period, about 60% to 70% of the suspended solid of the sewage is removed largely by sedimentation to form a semi-liquid substance called sludge. The sludge accumulates at the bottom of the septic tank. Parts of the solids are formed into floating scum. Both the scum and the sludge are processed by anaerobic bacteria and transforming them into liquid and gases This process is called digestion. The solid matter is reduced in sizes and consequently changed in character The septic tank therefore, combines two processes, sedimentation in the upper portion of the tank and anaerobic decomposition of the accumulated sludge at the bottom Decomposition of organic matter from human waste is a bacteriological process caused by Aerobic bacteria called aerobes 2 Anaerobic bacteria called anaerobes 3 Facultative bacteria The life process of Aerobic bacteria is in the presence of material oxygen. The Anaerobic bacteria on the other hand, functions in the absence of free oxygen. Likewise, Facultative bacteria also functions even with or without free oxygen. These three types of bacteria have no relation to disease. They thrive naturally in sewage, and will function when conditions are favorable in terms of Food Supply 2 Temperature 3\. Moisture However, even when conditions are favorable, these bacteria will cease to exist in the presence of antiseptics of disinfectants And to discharge large amount or volume of waste and water containing disinfectants, oil and grease the septic tank will affect and disturb the bacterial activities therein and may then destroy the purpose for which the septic tank is constructed The human waste of excreta are decomposed, until the organic matters are transformed into materials that could no longer be utilized by the bacteria in their life process. The process of decomposition is regarded as stabilization. Decomposition caused by anaerobic bacteria which is sometimes referred to as putrefaction, is accompanied by bad odors. On the other hand, aerobic decomposition is not accompanied by unpleasant odor. A sewage that turn dark and smell unpleasantly due to anaerobic decomposition is called Septic, Decomposition caused by aerobic bacteria is accomplished with no definite time and could be within a matter of hours 4-6 Location of Septic Tank Location of the septic tank shall observe the following considerations 1. The septic tank may be located closer to the build- ing it will serve, providing a minimum distance of 2.00 meters from the outside wall 2. As much as possible, the septic tank should not be located closer to the doors or windows 3. Septic tank should be at least 15 meters away from any source of water supply. The farther the better 1. here should be no contamination of ground sur- face that may enter into the spring of wells 2. There should be no contamination of surface water Requirements for a Satisfactory Disposal of Human Waste 3. The surface soil should not be contaminated 4. Excreta should not be accessible to animals, flies, cockroaches, vermin and the like 5. There should be no odor and unsightly conditions 6. The methods used should be simple and economical in terms of construction operation 4- Safety Precautions In most cases septic tanks are poorly aerated or ventilated It lacks free oxygen. Under this condition, an individual entering into a septic tank for making repairs or cleaning purposes, may meet almost instant death. Septic tank may contain harmful and dangerous gases When repair work or cleaning is to be made, be sure that the septic tank is well ventilated, by removing the manhole cover few days in advance of the work Another precaution is to supply fresh air inside the tank, while work is being done Remember that the tank may contain inflammable gases that might be ignited to cause a terrific explosion. If light is needed to work in the dark, an electric emergency light with properly insulated cord should be used. In the absence of electric supply, a flashlight powered by dry cell battery is equally safe. 4-8 Sewage Treatment The effluent removed from the septic tank is still in the stage of objectionable matter Although these organic matters have been removed, and many of the objectionable gases have been eliminated, still it contains countless number of harmful anaerobic bacteria and objectionable chemical compounds in solution that must be disposed of There are several methods and processes wherein sew ages may be treated. And those that are most commonly used are the activated sludge process, and the trickling or sprinkling filter processes The detailed scientific analysis of sewage treatment is beyond the scope of this subject in plumbing. But in passing, it is worth mentioning that the treatment of municipal sewage is a complex problem involving scientific aspects outside the sphere of plumbing The design and construction of a modern sewage disposal plant requires engineering training in all the phases of natural science Civil works for the design and construction of the structure, mechanical for the construction of equipment plus an extended knowledge of chemistry. physics and bacteriology