EnvEng3200-6200 – Fundamentals of Environmental Engineering Homework

Use the following water quality information for all problems.  A surface water has a pH of 8.1 and CO2 concentration of 1.1x10-5 M. The flow rate required for drinking water treatment to serve the nearby town is 1 MGD, and the water temperature is 18°C.

1. Based on the composition, determine the alkalinity, total hardness, and carbonate hardness in units of mg/L CaCO3.

2. Jar testing determined an optimum alum dose of 15 mg/L for particle removal.  Based on this dose, determine the (a) amount of natural alkalinity (mg/L as CaCO3) consumed, (b) the amount of alkalinity remaining, and (c) the amount of alum required (kg/yr).  

3. A mechanical rapid-mix tank is to be designed to add this alum with a detention time of 10 sec and a velocity gradient of 700 sec-1.  Determine the tank volume and power requirement.  The dynamic viscosity at 18°C is 1.053x10-3 N-sec/m2.

4. Particles resulting from the alum addition result in an average size of 100 µm diameter and a specific gravity of 1.05.  (a) Calculate the settling velocity if the density of water at 18°C is 998.6 kg/m3.(b) Determine the percent removal of these particles in a sedimentation basin with a depth of 2.5m, width of 4m, and length of 40m at the given flowrate.

5. Calculate the lime and soda ash dosage needed (in mg/L as CaCO3) (a) for selective calcium removal (i.e. to remove only calcium), (b) carbonate hardness removal, and (c) total hardness removal.

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