CE6503-ENVIRONMENTAL ENGINEERING I UNIT - I PART A. Collection works, Treatment works, Transmission works, Distribution works

Transcription

1 CE6503-ENVIRONMENTAL ENGINEERING I UNIT - I PART A 1. List out the components of a public water supply system. [N/D-15] Collection works, Treatment works, Transmission works, Distribution works 2. What do you mean by design period? [N/D-15] The future period for which a provision is mode in the water supply scheme is known as design period. Influencing factors: Useful life of pipes, equipment and structures. The anticipated rate of growth. If rate is more, design period will be less. The rate of inflation during the period of repayment of loans when inflation rate is high, a longer design period is adopted. Efficiency of component units. The more the efficiency, the longer will be design period. 3. State the assumptions made in an incremental increase method to forecast population. [M/J-16] Growth rate is assumed to be progressively increasing or decreasing, depending upon whether the average of the incremental increases in the past is positive or negative. The population for a future decade is worked out by adding the mean arithmetic increase to the last known population as in the arithmetic increase method and to this is added the average of incremental increases, once for first decade, twice for second and so on. Pn = P+nI + (n (n+1)/2)*r

2 PART B 1. The population of a town as per census record is furnished below. Forecast the population using the following methods: (i)arithmetical increase method (ii)geometrical increase method (iii) Incremental increase method. [N/D-15] YEAR POPULATION

3 ARITHEMATICAL INCREASE METHOD This method is based on the assumption that the population is increasing at a constant rate. The rate of change of population with time is constant. The population after n decades can be determined by the formula. Pn = P + n.c where P population at present n No. ofdecades c Constant determined by the average of increase of n decades YEAR POPULATION INCREASE IN POPULATION TOTAL AVERAGE 4833

4 YEAR POPULATION x 4833 = x 4833 = x 4833 = 36999

5 GEOMETRICAL INCREASE METHOD This method is based on the assumption that the percentage increase in population from decade to decade remains constant. In this method the average percentage of growth of last few decades is determined, the population forecasting is done on the basis that percentage increase per decade will be the same. The population at the end of n decades is calculated by Year Population Increase in Percentage increase in population population 4000 / x 100 = 50% / x 100 = 41.7% / x 100 = 32.4% TOTAL % AVERAGE % YEAR EXPECTED POPULATION / 100 x = / 100 x = / 100 x = 68524

6 INCREMENTAL INCREASE METHOD This method is improvement over the above two methods. The average increase in the population is determined by the arithmetical method and to this is added the average of the net incremental increase once for each future decade. Solution: Year Population Increase in Incremental population increase TOTAL AVERAGE ,250 The population at the end of the various decades shall be as follows: YEAR EXPECTED POPULATION ( ) x 1 = ( ) x 2 = ( ) x 3 = 40749

7 2. Enumerate and explain the characteristics of surface and ground water and state their environmental significance. [N/D-15] Water Sources The various sources of water can be classified into two categories: 1. Surface sources, such as a. Ponds and lakes, b. Streams and rivers, c. Storage reservoirs, d. Oceans (through Desalination). 2. Sub-surface or underground sources are a. Springs, b. Infiltration wells, c. Wells and Tube-wells. Source Water Characteristics Physical characteristics Water characteristics can be seen, smelled or tasted, generally the basis for customer complaints turbidity, taste/odour, colour, temperature. Chemical characteristics Can be organic, inorganic, and radioactive; includes ph. Health effects can be acute or chronic.includes chemicals that affect water s aesthetics. Biological characteristics Microorganisms present in water. Surface Water Characteristics Surface water changes depending on human activity, climatic changes and seasonal disturbances.

8 1. Turbidity 2. Biological 3. Chemical 4. Physical 5. Living organisms 6. Radiological contaminants 7. Industrial/ commercial 8. Sediment 9. Decaying animal/vegetation 10. Hydrocarbons Groundwater Characteristics 1. Iron 2. Manganese 3. Fluoride 4. Calcium 5. Sulfate 6. Magnesium 7. Arsenic 8. Hydrogen sulfide 9. Nitrate 10. Radiological contaminants

9 3. Explain the laboratory procedure to determine chlorides,turbidity, sulphates,and odour. [M/J-16] CHLORIDE Presence in Natural Waters Dissolution of salt deposits Discharges of effluents Oil well operations Sewage discharges Irrigation drainage Sea water intrusion in coastal areas Methodology : An Argentometric Method Principle Chloride is determined in a natural or slightly alkaline solution by titration with standard silver nitrate, using potassium chromate as an indicator. Silver chloride is quantitatively precipitated before red silver chromate is formed. Chloride mg/l = (A-B) x N x x 1000 ml sample Where A = ml AgNO3 required for sample B = ml AgNO3 required for blank N = Normality of AgNO3 used Sulphate Significance Occurs in natural water High concentration of Sulphate laxative effect (enhances when sulphate consumed with magnesium) Problem of scaling in industrial water supplies Problem of odour and corrosion in wastewater treatment due to its reduction to H2S Method Spectorphotometric Method Principle: Sulfate ions are precipitated as BaSO4 in acidic media (HCl) with Barium Chloride. The absorption of light by this precipated suspension is measured by spectrophotometer at 420 nm or scattering of light by Nephelometer Calculate mg / L SO4 = mg SO4 x 1000 ml sample DETERMINATION OF SULPHATE. Sulphates can be determined by 1. Gravimetric method with ignition of residue. 2. Gravimetric method with drying of residue. 3. Turbidimetric method. 1. Gravimetric Method with Ignition of Residue Principle Sulphate is precipitated in hydrochloric acid medium as barium sulphates by the addition of barium chloride. The precipitation is carried out near the boiling temperature and after a period of digestion the precipitate is filtered; washed with water until free of chlorides, ignited and weighed as barium sulphates.

10 Procedure 1. Take 250 ml of the sample in a conical flask. 2. Adjust the acidity with HCl to 4.5 to 5 using a ph meter or the orange colour of methyl red indicator. 3. Then add an additional 1 to 2mL HCl. 4. Heat the solution to boiling and while stirring gently, add barium chloride solution slowly until precipitation appear to be completed. Then add about 2 ml in excess. 5. Digest the precipitate at 80 C to 90 C preferably overnight but for not less than 2 hours. 6. Filter the contents in the flask through an ashless filter paper. 7. Wash the precipitate with small portion of warm distilled water until the washing is free of chloride as indicated by testing with silver nitrate nitric acid reagent. 8. Place the precipitate along with filter paper in a crucible after finding its empty weight and dry it. 9. Keep the crucible in a muffle furnace and ignite at 800 C for 1 hour. 10. Cool in a desiccator and weigh. 11. Find weight of the barium sulphate precipitate. 2. Gravimetric Method with Drying of Residue If organic matter is not present in the sample, first method can be done without igniting and instead drying the residue and weighing. 4. Turbidimetric Method Principle The turbidimetric method of measuring sulphate is based upon the fact that barium sulphate tends to precipitate in a colloidal form and that this tendency is enhanced in presence of a sodium chloride hydrochloric acid solution containing glycerol and other organic compounds. The absorbance of the barium sulphate solution is measured by a nephelometer or turbidimeter and the sulphate iron concentration, determined by comparison of the reading with a standard curve. Procedure 1. Measure 100 ml or suitable portion of the sample into a 250 ml Erlenmeyer flask. 2. Add 5 ml of conditioning reagent and mix it by placing on a magnetic stirrer. 3. Add a spoonful of barium chloride crystals and begin timing immediately. 4. Stir at constant speed exactly for one minute. 5. After stirring pour some of the solution into the absorption cell of the photometer, and measure the turbidity at 30 second intervals for four minutes. 6. Usually maximum turbidity occurs within two minutes and the reading remains constant thereafter for 3 to 10 minutes. So, take reading with maximum turbidity occurring in within four minutes. 7. Prepare a calibration curve. The standards are prepared at 5 mg/l increments in the 0 40 mg/l sulphate range and their turbidity or absorbance read. 8. Absorbance versus sulphate concentration is plotted and a curve is obtained. 9. Finding the absorbance for a given sample, the concentration of sulphates in the solution is determined with the help of calibration curve. Observation Weight of filter paper =... Sample no. or Volume of the Empty weight Wt. of crucible + Wt. of BaSO4 mg/l description sample (ml) of the crucible residue after ignition precipitated SO4 + filter paper + filter paper 50 A Comprehensive Laboratory Manual for Environmental Science and Engineering Calculation SO4 in mg/l = mg of BaSO ml of sample =... Results Sample no. or description mg/l of SO4 Discussion Turbidity Turbidity is caused due to presence of suspended and colloidal matter in the water. The character and amount of turbidity depends upon the type of soil over which the water has moved ground waters are less turbed than the surface water.turbidity is a measure of resistance of water to the passage of light through it. Turbidity is expressed as NTU (Nephelometric Turbidity Units) or PPM (parts per million) or Milligrams per litre (mg/l). Turbidity is measured by

11 1) Turbidity rod or Tape 2) Jacksons Turbidimeter 3) Bali s Turbidimeter The Sample to be tested is poured into a test tube and placed in the meter and units of turbidity is read directly on the scale by a needle or by digital display. Drinking water should not have turbidity more than 10 N.T.U. This test is useful in determining the detension time in settling for raw water and to dosage of coagulants required to remove turbidity. 1) Turbidity rod or Tape: Turbidity rod is used for measuring turbidity of water in the field. It consists of a graduated aluminium rod, about 20.3 cm in length, at the upper end of which is attached a graduated non-stretchable tape of about 12.2 cm long. At the lower end of the aluminium rod, a screw containing a platinum needle and a nickel ring is inserted. The graduated tape has a mark at its top end specifying the position of eye during the test. In order to find the turbidity, the lower end of the rod is gradually immersed in water whose turbidity is to be determined. Eye is kept constantly at the marked position and the platinum needle is watched. The rod is moved slowly in water till the platinum needle just disappears from the vision due to turbidity of water. The reading of the graduated tape near the water surface directly gives turbidity in p.p.m. the rod gives only rough value of the turbidity of water. 2) Jacksons Turbidimeter This is a laboratory apparatus which is used to measure turbidity when it is more than 100 p.p.m. it consists of a metal stand holding a metal container and a graduated glass tube in it. A standard candle is placed below the stand. The water sample is poured in the sample and the image of the flame of the standard candle is seen through the turbid water in the glass tube. The level of water in the glass tube is gradually increased till the image of the flame ceases to be seen. The height of the water column, measured in the graduated glass tube provides the measure of the turbidity of the water. The longer the light path of 21.5 cm corresponds to 11 JTU while light path of 10.8 cm corresponds to 200 JTU where 1 JTU= 1 p.p.m. 3) Bali s Turbidimeter This is a very accurate and is preferred when the turbidity of the sample is less than 5 units. It consists of a galvanized iron box in which two glass tubes are kept at one end and a 250 watt bulb with reflector is placed at the other end. One tube contains standard solution of known turbidity while in the other tube the water sample is kept. The tube is held firmly in a platform with beveled holes at its bottom end. The tubes are surrounded on all its four sides by blue cobalt plates and at its bottom by a white opal glass plate. Because of blue cobalt plates, blue light is cast in both the tubes, and a comparison is made. If the light differs, another tube containing standard solution of different turbidity is introduced in the place of the first one till the color in both the tube matched. The standard solution at this stage give the turbidity of the given water sample. The turbidity is expressed either as p.p.m or BTU both being equivalent. Colour Colour in water is usually due to organic matter in colloidal condition but some times it is also due to mineral and dissolved organic impurities. The colour produced by one milligram of platinum in a litre of water has been fixed as the unit of colour. The permissible colour for

12 domestic water is 20ppm on platinum cobalt scale. The colour in water is not harmful but objectionable.

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