CE/ENVE 347-Spring 2004 5. (15 points) For a flow rate of 1.2 m/s, how many rapid sand filters are needed to accommodate a loading rate of 140 m'(dm³)? Each filter bed has a surface area of 10 m x 10 m. How should this design be adjusted to accommodate the need to backwash filters (just comment on needed adjustments, you do not need to provide an adjusted number of filters)? 6. (15 points) The Long Term 2 Enhanced Surface Water Treatment Rule requires that 99% of Cryptosporidium should be inactivated during drinking water treatment. If a drinking water treatment plant uses ozone at a concentration of 2.0 mg/L for primary disinfection of water at 20°C, what contact time (in minutes) is needed to achieve sufficient Cryptosporidium inactivation? (Hint: You will need to use Table 6-15 from your textbook units for values in this table are mg/L min. Use Table 6-16 if you are referring to the 5th edition.). 7. (20 points) A chemical analysis of a surface water with pH-10.5 yields the following data: Ion Ca Mg2+ HCO CO₂² Concentration (mg/L) 90 30 165 244 a) Determine the alkalinity, expressed in mg/L as CaCO3. b) Determine the hardness in mg/L as CaCO3. How would you characterize this water based on hardness (refer to the slides from class or from Lab #3)!

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