2. Assume that the river has been selected as the source of raw water for the 2.0mgd demand.

a. Surface water has low alkalinity, high turbidity. The distribution system is cast iron pipe. What's the concern with using alum (Al₂(SO₄)₃) as the coagulant. What other chemical could be used?

b. A slow sand filter will follow the coagulation-flocculation-sedimentation. The organic content in the raw water supports a biofilm on the filter surface. How might this reduce the disinfectant dosage? What text Figure shows this?

c. The 4' thick filters run q=500 gpd/ft2. Find the total area of filter surface required to treat the 2.0 mgd. Also compute the hydraulic residence time in the filter.

d. The filtered water still has traces of ammonia and dissolved organics. Calcium hypochlorite Ca(OCl)₂ is used for disinfection. What's the advantage, what's the potential problem with using the hypochlorite rather than using ultraviolet (UV)?