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Note for Environmental Engineering - EE by ramya shri

  • Environmental Engineering - EE
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UNIT-1 ENVIRONMENT The term environment is defined as all the systems namely atmosphere, lithosphere, hydrosphere (non living components) and biosphere (living components) surroundings us. It includes air, water, food, the pollutions, waste materials and other ecological problems, which effect the life and health of human beings and other life. Environmental engineering is concerned with the control of all those which exercise or may exercise deleterious effect on his development, health and sundial with the consideration of the physical, economic and social impact of the control measures applied. Environmental engineering deals with the application of engineering principles to the control, modification and adaption of the physical, chemical and biological factors of the environment in the interest of man’s health, comfort and social wellbeing. In this textbook, some aspects of environmental engineering, such as ecology, water supply systems, waste water treatment and disposal, rural sanitation and air pollution are presented. If proper arrangements for the collection, treatment and disposal of all the wastes produced from the town or city such as water from bathroom, kitchens, lavatory basins, house and street washings, from various industrial processes semi liquid wastes of human and animal excreta, dry refuse of house and street sweepings, broken furniture, crockery, wastes from Industries etc are not made, they will go on accumulating and create (i) Buildings and roads will be in danger due to accumulation of spent water in their foundation (ii) Disease causing bacteria will bread up in the stagnate water (iii) Drinking water will be polluted. Total insanitary conditions will be developed in the town or city and it will become impossible for the public to live in the town or city. Therefore in the interest of the community of the town or city it is most essential to collect, treat and dispose of all the waste products of city in such a way that it may not cause any problem to the people residing in the town. Table 1.1. illustrates waste products of town or city (outlines of sanitary engineering). OBJECT OF PROVIDING SEWERAGE WORKS: The following are the aims and objects of sewage disposal. 1. Proper disposal of human excreta to a safe place, before its starts decomposition and may cause insanitary conditions in the locality 2. To take out all kinds of wastewater from the locality immediately after its use, so that mosquitos, files, bacteria etc may not breed in it and cause nuisance. 3. Final disposal of sewage on land or in near by watercourses after some treatment so that receiving land or water may not get polluted and unsafe for its further use. 4. As far as possible the fertilizing elements of sewage may be used in growing crops through farming and getting some income in addition to the disposal of sewage 5. In unsewered areas, the treatment of sewage from individual houses, should be done by septic tank or other suitable means and the effluent should be disposed of.

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6. If the sewage is disposed of on land, it should have such s degree of treatment that it may not affect the sub-soil in anyway. DEFINITIONS OF TERMS-SULLAGE, SEWAGE, SEWER AND SEWERAGE: Sullage: The liquid waste from latrines, Urinals stable etc is known as sullage. Sewage: The term sewage is used to indicate the liquid waste from the community and it includes sullage, discharge from latrines, urinals, stable etc industrial waste and storm water. Sewer: The underground conducts or drains through which is conveyed are known as the sewers. Sewerage: The entire science of collecting and carrying sewage by water carriage system through sewers is known as sewerage. Garbage: The term indicates dry refuse which includes decayed fruits, grass, leaves, paper pieces, sweepings, vegetables etc. Refuse: The term refuse is used to indicate all kinds of dry wastes of the community (i.e.,) street and house sweepings, garbage etc. CLASSIFICATION OF SEWAGE: 1. Storm Sewage: Which includes surface runoff developed during and immediately after rainfall over the concerned area. 2. Sanitary Sewage: Which includes the liquid wastes of domestic and industrial places. This sewage is extremely foul in nature and required to be disposed of very carefully. SYSTEMS OF SEWERAGE METHODS: 1. CONSERVANCY SYSTEM: In this system various types of refuse and storm water are collected, conveyed and disposed off separately by different methods in this system. This method is also called dry system and is in practice from very ancient times. This is method is adopting in small towns, villages and undeveloped portions of large city even it is out of date system. In this method garbage or dry refuse is collected from the dustbins and conveyed by trucks or covered carts once or twice in a day. All the uncombustible portions such as sand, dust, clay, ashes etc are used for filling low lying areas and combustible portions such as dry leaves, waste paper, broken furniture etc… are burnt. The decaying fruits, vegetables, grass are first dried and then disposed of by burning or in the manufacture of manure. Human excreta or night soil is collected in separate liquid and semi-liquid wastes by animal drawn carts, trucks or tractor trailors and buried in trenches. After 2-3 years the buried night soil is converted into an excellent manure which can be used for growing crops. In this system sullage and storm water are also carried separately in closed or open drains upto the point of disposal, where they are allowed to mix up with streams, rivers or sea.

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ADVANTAGES AND DISADVANTAGES: ADVANTAGES: 1. Initial cost is low, because storm water can pass through open drains. 2. The quantity of sewage reaching at the treatment plant before disposal is low. 3. The sewer section is small and no deposit of silting because storm water goes in open drains DISADVANTAGES: 1. Possibility of storm water may mix with sewers causing heavy load on treatment plant. 2. In crowded lanes it is difficult lay two sewers or construct drains roadside causing great inconvenience to the traffic. 3. More land is required for human excreta. 4. Liquid refuse may get on access in the sub soil and pollute the underground water. 5. Aesthetic appearance of city cannot be increased. 6. Decomposition of sewage causes insanitary conditions which are dangerous to the public health. 7. This system is completely depends upon the mercy of sweepers at every time and may possibility of spreading of diseases in the town if they are on strike. 2. WATER CARRIAGE SYSTEM: In this system, the excremental matters are mixed up in the large quantity of water and are taken out from the city through properly designed sewerage systems where they are disposed off after necessary treatment in a satisfactory manner. The sewage so formed in water carriage system consists of 99.9 percentage of water and 0.1 percentage of solid matters. All the solid matters remain in suspension in the sewage and donot change the specific gravity of water. So all the hydraulic formulae can be directly used in the design of sewerage system and treatment plants. This system is universally used nowadays because of the following advantages. MERITS AND DEMERITS OF WATER CARRIAGE SYSTEM: The following are the merits of water carriage system. 1. It is hygienic method because all the excremental matters are collected and conveyed by water only. 2. There is no nuisance in the streets of town and risk of epidemics reduced because of underground sewerage system. 3. Less space is occupied in crowded lane as only one sewer is laid 4. Self cleaning velocity can be obtained even at less gradients due to more quantity of sewage. 5. The land required for the disposal work is less as compared to conservancy system. 6. This system doesnot depend on manual labour at every time except when sewers get choked. 7. The usual water supply is sufficient and no additional water is required in water carriage system. 8. Sewer after proper treatment can be used fro various purposes.

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DEMERITS The main disadvantage of this system is the wastage of water (99.9% of water). 1. This system is very costly in initial cost. 2. The maintenance of this system is also costly. 3. During monsoon large volume of sewage is to be treated compared to remaining period of year. COMPARISION OF CONSERVANCY AND WATER-CARRIAGE SYSTEMS: CONSERVANCY SYSTEM WATER-CARRIAGE SYSTEM 1. Very cheap in initial Cost 1. It involves high initial cost 2. Due to foul smell from latrines, they are to be constructed away from the living room 2. As there is no foul smell, latrines remain clean and neat and hence are constructed with room. 3. The aesthetic appearance of the city cannot be increased 3. Good aesthetic appearance of the city can be obtained. 4. Storm water is carried in usually surface drains, hence no problem of pumping the storm water 4. Sewage is treated before disposing of ,it may or may not require pumping it depends on the topography of the town. 5. The quantity of waste liquid reaching the disposed point is less, hence it can be disposed of without any treatment. 5. Large quantity of sewage highly polluted in nature, it requires its treatment before disposal so it is costly process. 6. This system is fully dependent on the human agency 6. This system is not dependent on the human agency 7. As sewage is disposed of without any 7. Sewage is treated upto required degree of treatment it may pollute the natural water courses sanitation. 8. For burying of excremental matter, large area 8. Less area is required as compared to is required. conservancy system. TYPES OF SEWERAGE SYSTEM AND THEIR SUITABILITY: The sewerage system are classified as follows: (a) Combined system (b) Separate system (c) Partially separate system (a) COMBINED SYSTEM:

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