Example 4-7: Single-stage softening A water with the ionic characteristics shown in the bar diagram below is to be softened to the minimum calcium hardness by the lime-soda ash process. Magnesium removal is not deemed necessary. 1. Calculate the chemical requirements and solids produced in milliequivalents per liter. 2. Draw a bar diagram for the finished water. 3. For a flow of 25,000 m³/d, calculate the daily chemical requirement and the mass of solids produced. Assume that the lime used is 90 percent pure and the soda ash is 85 percent pure. Ca²+ ISH- HCO3 3.5 mequiv/L mequiv/L Co 1.0 5.0 Mg²+ 6.0 SO²- Na* 8.0 8.0

An analysis of water from a surface source yields the following results: Ions Concentration (mg/l) Ca +2 Mg +2 HCO3 SO²- 60 18 91.5 96 The temporary hardness (as CaCO3) and permanent hardness (as CaCO3) present in the water are

Lake Bonaventure is a lake fed by the Saint Croix River.  The Acme smeting company discharges the heavy metal nickel into the lake.  The easy way to model the concentration of nickel is to assume the lake is well mixed.  It isn’t.  The lake has a mean depth of 30m, and during the summer a surface epilimnion of 5m develops, which breaks down for the winter.  (no calculations are required to answer the questions below) (A) Given what you know about the hydrology of lakes, what differences in concentration would there be if the smelter discharges at the surface or at a depth of 30m? (B) How would concentrations vary in the lake throughout the year? (C) What if you factor in the fact that the flow of the Saint Croix River is less during the winter?