## Questions For Thinking And Discussing

The following questions will challenge you and help to reinforce some of the principles presented in this chapter.

1. A waste stream from a pulp mill has an average concentration of 7.2 Lbs of water/Lbs of solids. A treatment plant to be designed will have a thickening stage that concentrates the stream to 1.8 Lbs of water/Lbs of solids with the production of a relatively clear overflow. Batch settling tests were conducted on different concentration slurries to ensure that the velocity of settling exceeds the upward flow of fluid at all concentrations normally encountered in the thickening of the specified feed. Tabulated results from these tests are given below Prepare an additional column for this table showing the estimated minimum area required for clear overflow in units of 1 ton/day/ft2 of solids feed. What is the minimum area to be used for design purposes?

 Mass Ratio Fluid to Solids Fluid Rising per Lbs Solids (Lbs/Lbs) Calculated Fluid Rising (ft3/hr) Measured Rate of Settling (ft/hr)