1 The filtered water at peak hourly flow from a plant with coagulation, flocculation, and filtration has a pH
of 7.5 and temperature of 15°C. The
t10 in the clear well is 22 min, followed by transmission through a
pipeline for 4000 ft at a velocity of 5 ft/sec before entering the distribution system. What free chlorine residual is required in the water at the outlet of the clear well and pipeline? (The loss of residual concentration is likely to be negligible during the transmission time in the pipeline.)
2 The analysis of a water is as follows:
SO4
Mg++ = 1.0 meq/l = = 1.2 meq/l
HCO3
(a) Draw a milliequivalents-per-liter bar graph, list the hypothetical combinations of chemical compounds, and calculate the total hardness. (b) Calculate the chemical dose needed for excess lime softening.
(c) Draw a bar graph for the finished water after twostep precipitation softening by excess lime treatment with intermediate and final recarbonation, assuming 60 percent of the alkalinity is bicarbonate.Assume the practical limits of hardness removal for calcium to be 30 mg/l and magnesium to be 10 mg/l. (d) Calculate the chemical dose required for selective calcium carbonate removal to produce a finished water with a hardness of 120 mg/l.