A) Explain why the presence of alkalinity in raw source water is important for coagulation. Demonstrate you answer using detailed chemical reactions.

b) A raw surface water source with a minimum 12oC design temperature and an alkalinity of 80 mg/L of CaCO3 is planned to be treated for turbidity removal at a water treatment plant. Jar tests showed that the optimum alum dose for turbidity removal is 45 mg/L. Is adequate alkalinity available for complete reaction between alum and water to occur? If no, how much alkalinity should be added in mg/L as CaCO3. Demonstrate your answer with stoichiometric reactions and calculations.

c) What are the three most common destabilization mechanisms for colloids in turbid water, and when

would you expect each of these to occur during a coagulation process?

d) Design a rapid mix unit process (aka, coagulation tank) to mix the alum dose in (b) with raw water, considering a design flowrate to be 2MGD. The water treatment plant manager desires to operate two rapid mix tanks at all times, that will also account for redundancy. The maximum mixing time will be 30 seconds, however, if one tank is out of service, the mixing time must not be less than 10 seconds. Assume minimum design temperature to be 12 oC.

Your design should include the dimensions of each tank and the power imparted to each mixer to achieve a G of 1,000 sec-1 per tank.
Draw a simplified diagram to demonstrate how you will be splitting the flow between the two tanks that you sized.