ENV EXAM 5 - King Saud University College of Engineering...

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King Saud University CE 442 Water & Wastewater Treatment College of Engineering 1 st Semester 1425-1426H / 2004-2005G Civil Engineering Department Section: 1026, Dr. W. Zahid Final Examination (aid sheet is provided) Time allowed: 3 hours Student Name : …………………………………………………. Student Number : …………………………………………...…. ةيلصفلا لامعلأا : ................ يئاھنلا ناحتملإا .............. : ةيئاھنلا ةجردلا ................. : Question One (20%) Answer with true (T) or false (F): ( ) (1) The presence of coliform bacteria in water supplies indicates fecal contamination of water. ( ) (2) Temporary hardness is caused by the presence of calcium and magnesium sulfates and chlorides. ( ) (3) Both the BOD and COD are used to determine the organic strength of wastewater. ( ) (4) Water alkalinity is a measure of its ability to resist changes in pH when a strong acid is added. ( ) (5) Groundwater is usually more hard than fresh surface water. ( ) (6) Addition of alum (aluminum sulfate) to water decreases its pH. ( ) (7) Soda ash (Na 2 CO 3 ) is used to remove carbonate hardness of water. ( ) (8) Softening of water by the ion exchange process can reduce hardness to zero. ( ) (9) The reverse osmosis process involves the forced transfer of water through a semi-permeable membrane from a solution of a lower to one of higher concentration. ( ) (10) Ozone is the most widely used disinfectant for drinking water. ( ) (11) Chlorine existing in water as hypochlorous acid and hypochlorite ion is called “combined available chlorine”. ( ) (12) Due to the low pH involved, excess-lime softening assists in removing pathogens if any is present. ( ) (13) Stabilization ponds are suitable for treating small flows of wastewater. 1
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( ) (14) The main objective of the secondary treatment of wastewater is to reduce the level of soluble inorganics remaining after the primary treatment. ( ) (15) The main disadvantage of anaerobic treatment of wastewater is the large production of sludge. ( ) (16) Disinfection of water with chlorine is more effective at a pH of 7.5 than at pH 6.5. ( ) (17) A mixed liquor having a SVI (sludge volume index) in the range 50-150 exhibits good settling. ( ) (18) The main purpose of sludge stabilization (digestion) is the removal of water. ( ) (19) In the activated sludge process, a portion of the settled solids in final settling tanks is returned to aeration tanks in order to maintain the desired concentration of micro-organisms in the aeration tanks. ( ) (20) Bacteria are the most common microorganisms found in domestic wastewater (sewage). Question Two (10%) Note one method/process only (without explaining) by which each of the following can be reduced or controlled: (1) Pathogens in water: …………………………………………………………………………… (2) Dissolved gases in water: ……………………………………………………………………… (3) Excess calcium and magnesium bicarbonates in water: ………………………………………..
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