ENVIRONMENTAL ENGINEERING-I

Transcription

1 ENVIRONMENTAL ENGINEERING-I Prof. Rajesh Bhagat Asst. Professor Civil Engineering Department Yeshwantrao Chavan College Of Engineering Nagpur B. E. (Civil Engg.) M. Tech. (Enviro. Engg.) GCOE, Amravati VNIT, Nagpur Mobile No.: / ID:- rajeysh7bhagat@gmail.com Website:

2 Unit V 1) Disinfection : Purpose, Mechanism, criteria for good disinfectant, various disinfectants, their characteristics, disinfection by chlorination using different forms of chlorine. 2) Distribution systems: Requirements for a good distribution system, methods of distribution systems distribution systems and layouts of DS, appurtenance in water distribution system. 3) Leakage and leak detector. 4) Storage reservoirs for treated water: Types, capacity of reservoir, mass curve method.

3 Disinfection:- 1) Killing of pathogens 2) Sterilization is the process of killing of all bacteria 3) Materials & disinfectant used are called disinfectant 4) Disinfectant destroys microorganism by damaging cell wall of and inactivation of critical enzyme system responsible for metabolic activity.

4 Necessity:- 1) Water may contain bacteria & other micro-organism which may be pathogenic. It is therefore necessary to disinfect water to kill bacteria and other microorganism and thus prevent water borne diseases.

5 Requirements of Good Disinfectant:- 1) Effective in killing all the harmful pathogens 2) Readily available at reasonable cost 3) Safe to handle 4) Simple method of application 5) Harmless, unobjectionable, economical & easily available 6) Not required skilled labor 7) Not required costly equipment for its application 8) Kill all pathogens in reasonable time at a normal temperature 9) Protect against recontamination

6 Methods of Disinfection:- Physical Methods 1. Disinfection by Heat: Boiling of water 2. Disinfection by light: UV light 3. Sunlight is a natural disinfectant Chemical Methods 1. Chlorine 2. Bromine 3. Iodine 4. Ozone 5. Potassium Permanganate 6. Metal ions such as copper & silver 7. Treatment with excess lime

7 Boiling of Water 1) Bacteria killed by increasing temp C 2) Most effective methods 3) Impracticable to boiled large quantity of water 4) In case of epidemic consumers may boiled water for drinking 5) Cant take care of future contaminations

8 Ultra Violet Ray Treatment 1) Very costly & effective method. 2) Sun is most powerful source of UV rays but it requires a large exposure area & long time. 3) Hence generated by machines consisting of mercury vapour lamps enclosed in a quartz globe. 4) Effective disinfection water should be flow in a thin clear layer. 5) Depth water should not exceeds 10 cm. 6) Colorless & turbidity should not more. 7) No residual effects against re-contamination. 8) Unsuitable for large scale treatment plant. 9) Private building, institutes, hospitals, swimming pools, etc. 10) No color & taste developed.

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11 Treatment With Excess Lime:- 1) Enough lime to bring ph to 9.5 to kill bacteria 2) Removal up to 99 to 100 % 3) Re-corbonation is necessary

12 Iodine & Bromine Treatment 1) Dose = 8 mg/l. 2) Contact period = 5 minutes. 3) In the form of small pills. 4) More costly than chlorine hence used for small water supply. 5) Ex. Swimming pools, army, private plants etc. 6) Less irritating to the eyes than chlorine when used in swimming tank. 7) Provides longer lasting protection. 8) Reduced offensive taste and odors.

13 Halogen Group:

14 Ozone 1) More powerful as well as costly than chlorine. 2) Doesn't provide residual protection against recontamination. 3) Cant be stored. 4) Used on small scale. 5) Dose = 2 to 3 ppm. 6) Contact period = 10 minutes. 7) France and Russia on large scale. 8) Required skilled labor. 9) Gives pleasant and appealing appearance.

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18 Potassium Permanganate 1) Good for well water supply or water which is less contaminated. 2) 98 % removal of bacteria. 3) 100 % removal of cholera causing bacteria. 4) Rural areas. 5) Oxidizes organic matter and iron. 6) Pink color means organic matter present. 7) Dose = 1 to 2 mg/l. 8) Contact period = 4 to 6 hrs. 9) Cheap and quite useful.

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20 Silver Treatment 1) Removes algae. 2) Take care of future pollution. 3) Contact period = 15 minutes to 3 hrs. 4) No taste and no odor. 5) No harmful effect on human body. 6) Use of silver is very costly. 7) Generally not used for treating public water supplies.

21 Chlorination 1) Universally adopted. 2) Cheap, reliable & easy to handle. 3) Capable of providing residual disinfecting effects for long periods. 4) Ideal disinfectants. 5) Imparts bad taste. 6) Doesn t affect ph. 7) Not effective when water is alkaline.

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25 Purpose of Chlorination 1) To prevent the spread of diseases. 2) To remove bacteria, fungus, and other pathogens. 3) Oxidation of Iron, Fe and H 2 S. 4) Removal of taste and odor. 5) Oxidation of organic matter.

26 Factors Affecting Chlorination 1) Turbidity. 2) Metallic compound presence. 3) Ammonia compounds. 4) Temperature. 5) ph value. 6) Contact time. 7) Nature and concentration of bacteria.

27 Action of Chlorine Cl 2 + H 2 O HOCl + H + + Cl - HOCl H + + OCl - 1) When chlorine added it forms hypochlorus acid or hypochlorite ions. 2) HOCL & OCl accomplish disinfection. 3) It has an effect on micro-organism. 4) ph = 10 only OCl ions are found. 5) ph = 7 to 5 HOCL exist. 6) Chlorine doesn t reacts below ph = 5 & remains as elemental chlorine. 7) HOCl is 80 times more powerful than OCL. 8) Hence ph is maintained slightly less than 7.

28 Free Available Chlorine:- 1) Together HOCl and OCl is known as Free Available Chlorine 2) Free Cl 2 reacts with compounds such as ammonia, proteins, amino acids & phenols and form chloramines & chloro-derivatives which are called Combined Chlorine. 3) Combined chlorine also posses some disinfecting properties but less effective compared to free available chlorine.

29 Break Point Chlorination Two action:- I. Killing of bacteria. II. Oxidation the organic matter. Pure water has no chlorine demand. Raw water has chlorine demand. First stage :- killing of bacteria and metals & nitrites are oxidized Second stage :- forming of combined residual chlorine will gradually.increases. Chloramines have been recorded as a combined residual chlorine. Third Stage:- decrease in residual chlorine indicate the oxidation of organic matter. 1) At point C, gives bad taste & odor ( oxidation started). 2) At point D, bad smell & taste suddenly disappear. (oxidation completed)

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31 Break Point Chlorination 3) Point D represent the Break Point Chlorination 4) After this point, addition of chlorine results in increase in residual chlorine represented by line E with slope ) At break point true residual free chlorine is revealed. 6) Addition of chlorine beyond point D is break point chlorination 7) Gives ideas to ensure the desired amount of residual chlorine.

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33 Significance of Break Point Chlorination: 1) Removes taste and odor. 2) Have adequate effect on bacteria or pathogens. 3) Leave desired chlorine residual. 4) Removes Fe & Mn. 5) Oxidation of organic, ammonia & other compounds. 6) Removes color.

34 Forms of Chlorination 1) Plain chlorination 2) Pre-chlorination 3) Post chlorination 4) Multiple Chlorination 5) Super Chlorination 6) Dechlorination

35 Plain Chlorination 1) 0.5 to 1 mg/l. 2) Only chlorine treatment & no other treatment. 3) To remove bacteria, color, odor, etc. 4) Controls growth algae. 5) Clear water (turbidity less than 20 NTU) 6) In case of emergency.

36 Pre Chlorination 1) Application before treatment specially filtration. 2) Reduces the quantity of coagulants. 3) Reduces taste & odor. 4) Controls growth of algae. 5) Reduces bacterial load on filters. 6) Prevents decomposition of sludge in settling tanks.

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38 Post Chlorination 1. Compulsory treatment. 2. Application of chlorine to water. 3. Standard forms of chlorination. 4. After filter and before it enters the distribution system. 5. Residual chlorine = 0.2 mg/l (1mg/L)

39 Multiple Chlorination 1) Application of chlorine at two or more points. 2) Consists of pre & post chlorination. 3) Highly contaminated water. 4) Large amount of bacteria.

40 Super Chlorination 1) Application of chlorine beyond the stage of break point. 2) At the end of filtration. 3) Whenever breakout of water borne diseases. 4) Dose = 10 to 15 mg/l. 5) Residual chlorine = 1 to 3 mg/l. 6) Necessary to remove the excess chlorine by dechlorination before supplied to the consumers.

41 De-Chlorination Removal of excess chlorine from water before supplying to consumers. Some residual chlorine should remains in water. I. Dechlorination by Aearation. II. Addition of some chemicals such as: 1) Sodium thio-sulphate, 2) Sodium bio-sulphate, 3) Sodium sulphite, 4) Activated carbon, 5) Pottassium permanganate, 6) Ammonia, 7) Sulphur dioxide

42 Testing of Chlorine Residuals 1) Orthotolidine Test. 2) Starch Iodide Test. 3) Chlorotex Test. 4) DPD test.

43 DPD Test (Diethylene-P-Phenylene Diamine) 1) Widely used in modern days. 2) DPD reagents used. 3) Comparators to compare the color. 4) 10 ml of sample in tube. 5) Add reagent and compare the color.

44 Orthotolidine Test 1) Commonly used to determine the residual chlorine. 2) 0.1 ml of orthotolidine solution is added to 10 ml of sample. 3) Compare the color with colored glass standard.

45 Chick s law Chick s law state that the number of organisms (y) destroyed in unit time is proportional to the number of organism (N) remaining Y α N ( N / No ) = e kt This is called Chick s Law

46 Que. 1) Calculate the quantity of bleaching powder required for disinfection 1 MLD of water. The dose of chlorine is 0.5 mg/l. Ans:- Assuming strength of bleaching powder = 30% Q = 1 MLD = L /Day Dose of chlorine = 0.5 mg / L Quantity of Chlorine required = 0.5 x = mg / Day = 0.5 Kg / Day 1 Kg of bleaching powder consists of 30 % of chlorine Total amount of bleaching powder required for 1 MLD water = 0.5 / 0.3 = 1.67 Kg

47 Que. 2) Chlorine used in treatment of 25 MLD of water is 9 Kg / Day. The residual chlorine after 10 minutes contact is 0.2 mg/l. Calculate the chlorine dose and chlorine demand. Ans:- Q = 25 x 10 6 L / day Quantity of chlorine = 9 Kg / Day Contact time = 10 minutes Dose of chlorine = ( 9 x 10 6 ) / ( 25 x 10 6 ) = mg / L Chlorine demand = chlorine dose residual chlorine = = mg /L

48 1) Continuous System:- Methods of Supply Water:- 1) Water is available to the consumers for all the 24 hours of a day. 2) Leads to the more wastage of water. 3) Minor leakages, long duration leads to great volume of water. 2) Intermittent System:- 1) Water is supplied to consumers only during some fixed hours of the day. 2) Most commonly adopted in India. 3) Adopted when sufficient pressure is not available or when sufficient quantity is not available.

49 Drawbacks of Intermittent System:- 1) If fire breaks during non-supply period, the rescue operation can not be effectively done. 2) Requires the small storage tank provision in individual houses. 3) During the non-supply period, the pressure in the supply line may fall below atmospheric pressure, this may lead to pollution or contamination. 4) Greater size of pipes will be required. 5) During non-supply period, the water taps may be left open unknowingly. 6) Staff required to operate no. of valves.

50 Water Supply System (Distribution System):- 1) Gravity system 2) Pressure or pumping system 3) Dual system or combined gravity & pumping system For efficient distribution it is required that water should reached to every consumer with required rate of flow.

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52 Gravity System:- Water flows due to gravitational force. When some ground, sufficiently high above the city area, is available, this can be utilized for the distribution system in maintaining pressure in water pipes. Suitable when source of supply such as lake, river or impounding reservoir is at sufficient height than city. No pumping is required, therefore it is the most reliable system. Water will have to be pumped during fires.

53 Pumping System:- Water is directly pumped in the mains. Number of pumps are required to meet the demand & if the power fails, the whole supply of the town will be stopped. Sometimes diesel pumps are used in addition to electric pump as standby.

54 Dual or Combined Gravity & Pumping System:- Water is stored in elevated service reservoir when demand is small. When demand is more then it is distributed as required. This system is more reliable and economical. Water comes from two sources one from reservoir & second from pumping station if demand increases.

55 Advantages of Dual or Combined Gravity & Pumping System:- Reliable. Economical. Efficient. Overall best system. During power failure, the balance water stored in the water will be supplied to the town. Pump has to work at constant speed, without any variation in their speed, this increase the efficiency of pumps.

56 Layout of Distribution System:- Depending upon the relative levels of the different zones of the city, the layout of the roads etc., the type of the distribution network is adopted or decided. I. Branch Network II. Loop Network There are four principal methods of layout of distribution system: 1) Dead End System or Tree System. 2) Grid Iron System or Reticulation System. 3) Circular System or Ring System. 4) Radial System.

57 PURPOSE OF A SYSTEM: To supply water at 1) adequate pressure and 2) flow. However, pressure is lost by the action of friction at the pipe wall. The pressure loss is also dependent on the 1) water demand, 2) pipe length, 3) gradient and 4) diameter.

58 Dead End System or Tree System:- 1) One main supply pipe from which originates a number of sub-main pipes. Each sub-main, then divides into several branch pipes called laterals. 2) From the laterals service connections are given to the consumers. 3) Adopted in older towns which developed in a haphazard manner without properly planned roads. 4) Water supply mains have then to be taken along the main roads & branches taken off wherever needed, thus resulting in the formation of a number of dead ends.

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60 Advantages of Dead End System or Tree System:- 1) Simple & easy design calculation. 2) Cheap & economical design. 3) Laying of pipe is simple. 4) Lesser number of cutoff valves are required. 5) Network can be extended easily. Disadvantages of Dead End System or Tree System:- 1) Stagnation of water. 2) Accumulation of sediments at the dead end. 3) Large number of scour valves are required at the dead ends. 4) Discharge available for fire fighting in the streets will be limited. 5) Less pressure in the remote parts. 6) In case of repairing, whole portion beyond that point will be required to be cut off completely.

61 Grid Iron System:- 1) Interlaced system or Reticulation system. 2) Mains, sub-mains & branches are all inter connected with each other. 3) In a well planned city, the roads are developed in a grid-iron pattern & pipes line in such places can follow them easily.

62 Advantages of Grid Iron System:- 1) Free circulation of water without any stagnation or sediment deposit. 2) Due to inter connection, water is available at each point with minimum loss of head. 3) Enough water is available for fire fighting. 4) In case of repairs, very small area of the distribution system is affected. Disadvantages of Grid Iron System:- 1) A large number of cut off valves are required. 2) The system requires longer pipes lengths & bigger diameter. 3) The analysis of discharge, pressure & velocities in the pipe is difficult. 4) The cost of laying water pipes is more. 5) The design is difficult.

63 Circular or Ring System:- 1) The supply main forms a ring around the distribution system as shown in the figure. 2) The branches are connected cross wise to the mains and also to each other. 3) The system is most suitable for the town or area having well planned streets and roads.

64 Advantages of Circular System:- 1) Large quantity of water is available for fire fighting. 2) Free circulation of water. 3) Water available with minimum loss of head 4) Very small area of system is affected while repairing. Disadvantages of Circular System:- 1) A large number of cutoff valves are required. 2) Requires longer pipe length & bigger diameter. 3) The analysis of discharge, pressure & velocity in the pipe is difficult. 4) Design is difficult.

65 Radial System:- 1) City should have a radial road system. 2) Roads emerging from different centers, the pipe lines can be best laid in a radial method by placing the distribution reservoirs at these centers. 3) Water is taken from water main & pumped into the distribution reservoirs. 4) Water is then supplied through radially laid distribution pipes.

66 Advantages of Radial System:- 1) Ensure high pressure 2) Efficient water distribution 3) design is also simple 4) system gives quick service without much loss of head.

67 Requirements of Good distribution System:- 1) Ensure high pressure 2) Efficient water distribution 3) System gives quick service without much loss of head. 4) Large quantity of water is available for fire fighting. 5) Free circulation of water. 6) Water available with minimum loss of head 7) Very small area of system is affected while repairing. 8) Simple & easy design calculation. 9) Cheap & economical design. 10) Laying of pipe is simple. 11) Lesser number of cutoff valves are required. 12) Network can be extended easily.

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69 Leakage in Water Distribution 1) Waste" covers the quantity of water lost by leakage from water mains, service pipes and fittings, abandoned service pipes/ferrule connection etc. 2) Wastages in water supply systems are 20 to 40 % of total available supply. 3) By adopting proper techniques and doing systematic field work, it is observed that wastage can be reduced by 10 to 20 % of the total supply received. 4) Efforts are being made by the concerned authorities to increase supply hours and pressures, which in turn lead to more wastage. 5) Hence timely action on waste control is absolutely needed. Further, waste control measures will reduce cost as well as contamination. 6) Therefore it is necessary to study about leakages & its remedial measures to arrest leakages.

70 FACTORS AFFECTING LEAKAGES 1) High pressures: high pressure results in increased flow and thereby increase in wastage through leaks. 2) Poor quality of fittings/bad workmanship: Wastage of water can be controlled by strictly using fittings bearing ISI mark, or installing tested pipes and fittings. 3) Soil movement: Soil movement and particularly shrinkage may result in loosening the joints and causing fracture of the pipe due to unequal settlement. 4) Shock and water hammer: This can result in bursts due to undue high pressures. 5) Effects of traffic: Inadequate cushioning above the pipe line may cause damage due to traffic movements. 6) Age of pipes: Service life of C.I. mains is normally assumed as 75 years under normal conditions. The life of G.I. pipes will be about 10 years. 7) Damage to Pipes by other utility concerns: During construction activities may cause settlement of pipes, opening of joints, etc. Such situations can however be avoided by co-ordination and proper precautions.

71 METHODS OF DETECTION (i) Minimum night flow method: Minimum consumption is recorded by suitable bulk meters & Further detailed investigation are carried out. This method cannot be employed on intermittent water supply system. (ii) Stop tap method: Total flow of water into the zone is measured through revenue or a kent meter. All boundary sluice-valves and all stop-taps on connections are closed. This survey may have to be carried out by taking special supply during non-supply hours of the area. (iii) Sounding method : The zone under test is subjected to sounding again and again and repairs of leak points/appurtenances are carried out systematically. Pressures at 4-5 points are recorded before & after completion of survey. Success of this method is noted by the improvement in pressures. Less expensive and less time consuming.

72 Leak Detection 1) Visual: Customer Complaints Operational Staff (Look & Listen) 2) Sounding: Acoustic Listening Sticks Ground Microphones Electronic Listening Equipment Noise Loggers 3) Correlating: Leak Noise Correlator

73 INSTRUMENTS 1. Sounding rod 2. Electronic pipe locators 3. Electronic leak detector 4. Metal detector (for tracing buried sluice valves etc.) Locating leaks in using a sounding device placed on the surface of the ground, or above the alignment of water pipes. Water escaping through a hole in the pipe sets up vibrations which are transmitted to the ground and then picked up by the instruments which convert and magnify the vibrations to audible sounds.

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77 ADVANTAGES IN ARRESTING LEAKAGES Wastage of water can be saved and utilized by the consumers who are badly in need of it. This results in additional revenue to the Water Authority. Water can be supplied to the consumers at better pressures. Cost involved in pumping will be reduced. Contamination will be considerably reduced especially in intermittent supply system. Requirements by consumer can be assessed more realistically. During survey operations, unauthorized tapping could be detected.. We can keep constant checking on working of sluice-valves and other appurtenances for efficient operation. Authority can know the weak areas in the distribution system. This valuable information may useful for future planning.

78 I. Educating the public: There are some tendencies are like REMEDIAL MEASURES 1) when fresh supply is received, then throw store water to store fresh water 2) Not to turn off taps after the supply hours are over, 3) wash clothes with taps running, 4) use excessive water for gardening etc. 5) Washers and taps are not replaced in time. These tendencies can be reduced by giving lectures, showing slides in cinema-houses, posters, discussions on radio /T.V. etc.

79 (ii) Metering: All quantity of water even for domestic use should be supplied through meters. Extensive metering will reduce the wastage. (iii) Curb on aid: Government should finance or assist water supply schemes of Municipalities only if waste control measures are introduced by the Water Authorities. (iv) Enforcement by law: This has to be done by making provisions in Municipal Acts and By-laws. (v) Punishment: If wastage is not checked, then water connection should be cut off. Restoration can be done after repairs and heavy penalty.

80 Distribution Reservoir or Storage Reservoir: - Service reservoir store the treated water to supply the water during fire breakdowns, repairs, etc & also to help in absorbing the hourly fluctuations in the normal water demand. Surface reservoir, elevated reservoir, stand pipe, Steel tank, RCC tank, Masonry tank etc.

81 Purpose of Distribution Reservoir: - To absorb the hourly variation in demand & allow the WTP & Pump to operate at a constant rate. To maintained the desired & constant pressure in the distribution main & network. To facilitate disinfection of water. To provide storage for emergencies such as breakdown of pumps, fire, etc. To achieve economy by reducing the size of pumps, pipe lines and treatment units. To facilitates the pumping of water shift wise without affecting the supply.

82 Surface Reservoir: - Surface reservoir are circular or rectangular tanks, constructed at ground level or below the ground level. Ground reservoir. Made up of masonry or concrete. Constructed in two or more compartments so that one unit can be cleaned or repaired while other units are in operation.

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84 Elevated Reservoir: - Constructed of RCC or Steel. Overhead Tank. Circular, elliptical, rectangular, conical shape. Provided with top cover, ladders & manholes for inspection & cleaning purpose. Combined gravity and pumping system for water distributions are adopted. Water is pumped into reservoir from WTP and then supplied to the consumer.

85 Stand Pipe: - Elevated tanks without any erected towers for resting the tank body. Tall cylindrical shell resting directly on the ground. 15 to 30 m high and 10 to 15 m in diameter. Used when sufficient head is not required. Location should be on the hills or high grounds.

86 Capacity of storage: - The storage capacity is based on the following three requirements. 1) Balancing or Equalizing storage. 2) Breakdown storage. 3) Fire storage. Minimum Capacity of storage:- The minimum volume of water to be stored in reservoir to buffer the fluctuation in demand ie to balance the variable demand. When a storage reservoir is to be designed for the purpose of balancing or equalizing the flow. Its storage capacity can be determined by two methods. 1) Hydrograph Method 2) Mass Curve Method 3) Analytical Solution

87 Mass Curve Method: - 1) A mass curve of demand is the cumulative demand curve and is obtained by continuously adding the hourly demands and plotting these against time. 2) Mass demand curve continuously rises. 3) Steepness of the mass curve indicates a higher rate of demand, while flat portion shows the lower rate of demand. 4) First of all, mass curve of supply is drawn and superimposed by the demand curve. 5) The amount of balancing storage can then be easily determined by adding the maximum ordinates between the supply and demand lines.

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