In this essay we will discuss about:- 1. Standards for Quality of Treated Water 2. Objects of Treatment 3. Considerations for Public Water Supply 4. Treatment Processes.
Essay # 1. Standards for Quality of Treated Water:
The treatment process should be designed such that, they should treat the water up to the desired standard for which it is to be used.
Table 10.1 gives the standards of quality for domestic water supplies. The standards given in the table for water are for ideal and safe public supplies. In the towns and small cities of the underdeveloped countries, in the beginning due to shortage of funds the full treatments may not be possible.
But the design of the treatment processes must be done for the complete treatment, and the construction may be done in stages according to the availability of the funds. Care should be taken in the beginning of treatment process to remove all the disease bacteria to avoid any serious water-borne disease.
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Table 10.2 gives the average water quality standards for process water for some important industries. The water coming in intimate contact with the manufacturing process of the industries should be of required quality as given in table 10.2. The water used in pulp or paper industries must be free from iron, manganese and hardness. But the water required for breweries, distilleries and bakeries should be slightly hard.
The water to be used in steel rolling mills should be free from chloride. The water to be used in textile industries should be free from dissolved solids, colour, hardness, iron and manganese, as they may cause strains, spots on the cloths and may damage its quality.
Under normal conditions the water fit for drinking is used in various industrial processing, except few industries, in which further treatment is done to meet their requirements. Usually all such extra treatments are done by the concerned industries themselves, and city water works are not concerned with such treatments.
Essay # 2. Objects of Treatment:
The main object of the treatment processes is to remove the impurities of raw water and bring the quality of water to the required standards.
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The objects may be summarized as follows:
(i) To remove the dissolved gases, murkiness and colour of water,
(ii) To remove the unpleasant and objectionable tastes and odours from the water,
(iii) To kill all the pathogenic germs, which are harmful to the human health,
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(iv) To make water fit for domestic use as cooking and washing, and various industrial purposes as dyeing, brewing, steam generation etc.,
(v) To eliminate the tuberculation and corrosive properties of water which affects the conduits and pipes.
Essay # 3. Considerations for Public Water Supply:
For the public water supply of a town or particular area, the following points should be considered:
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1. The selection of such source of water should be done, which can provide sufficient quantity of water in all the seasons.
2. As far as possible source should be at such place, from where water can flow under gravitational force, to the water works.
3. The quantity of water in the source, should also meet the future demand of the town.
4. The quality of raw water available at the source, should be good and it should require minimum treatments before supplying it to the public.
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5. The location of the water-works should be such that as far as possible, the water should flow under gravitational force to the buildings of the town, and may reach 10-15 m high.
6. In case if locality of the town is at higher level, it is always economical to supply the water in this area by pumping, whereas the remaining town may be supplied at minimum required pressure.
7. The provision of impounding reservoir is made only when its construction at higher elevation is economical. The minimum daily flow of river should also be more than the daily water demand.
Essay # 4. Treatment Processes:
The treatment processes directly depend on the impurities present in water.
For removing various types of impurities the following treatment processes are used:
The character and degree of treatment will directly depend upon the nature of water or indirectly on the source. The water of surface sources generally contains large amount of impurities, therefore, they will require all the treatments stated above. Mostly screens are fixed in the intake works; therefore, it is not necessary to have separate screening plant.
Sometimes the water of lakes or impounding reservoirs are free from suspended matter, therefore, it will require filtration and disinfection only. Ground waters, which are usually clear, may require only disinfection and chemical treatment for the removal of pathogens, iron removal, softening etc. Sometimes ground water contains dissolved hydrogen sulphide which gives very bad odour, and requires its removal.