GATE PSUs- Environmental Engineering - one liners

Hello there,
How you doing? Here are one liners from Environmental Engineering which, might be helpful for your GATE and PSUs examinations.

• Turbidity is measured on Standard silica scale.
• On a standard silica scale, the turbidity in drinking water should be limited to 10 ppm.
• Residual chlorine in water is determined by starch iodide method and orthotolidine method.
• If the total hardness of water is greater than its total alkalinity, the carbonate hardness will be equal to total alkalinity.
• The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about 0.05 ppm to 0.5 ppm.
• The dissolved oxygen level in natural un-polluted  water at normal temperature is found to be of the order of 10 mg/lt.
• The velocity of flow of water in a sedimentation tank is about 15 to 30 cm/min.
• The length of sedimentation tank should not be more than 4B where, B is the width of the tank.
• The overflow rate for plain sedimentation tanks is about 500 to 750 liters/hour/m2.
• 75 percent of bacterial load can be removed from water by the process of plain sedimentation.
• The settling velocity of a particle in a tank depends upon the surface are of the tank.
• For a given discharge, the efficiency of sedimentation tank can be increased by increasing the surface area of the water tank.
• In general, the detention period is more and overflow rate is less for plain sedimentation as compared to sedimentation with coagulation
• The amount of coagulant needed for coagulation of water increases with increase in turbidity of water and decrease in temperature of water.
• Alum as a coagulant is found to be most effective when pH range of water is 6 to 8.
• The detention period in coagulation tanks is usually kept as 2 to 6 hours.
• The alum when added as a coagulant in water, decreases the pH value of water.
• Lime is the chemical most commonly used to increase the speed of sedimentation of sewage.
• In water treatment, rapid gravity filters are adopted to remove bacteria and colloidal solids.
• The rate of filtration in slow sand filters in million liters per day per hectare is about 50 to 60.
• The effective size of sand particles used in slow sand filters is 0.25 to 0.35 mm
• As compared to rapid sand filters, slow sand filters give slower filtration rate and higher efficiency in removal of bacteria.

Thanks for visit!

Reference: Civil Engineering Objectives - S P Gupta and S P Gupta.