A surface water treatment plant at a winter resort city has been designed to process cold,...

A surface water treatment plant at a winter resort city has been designed to process cold, low-turbidity water by direct filtration based on the pilot-plant study described in Problem. The filtered water has a turbidity of less than 0.1 NTU, temperature of 10°C, and pH of 7.4 during the period of highest water consumption in the winter. Tracer analyses of the clear-well reservoir are illustrated in Figure 11.28. At the critical hourly flow of 3.0 mgd, t10 = 90 min. To comply with the EPA surface water disinfection regulation, what free chlorine residual must be maintained in filtered water at the outlet of the clear well? What would be the required dose of chlorine dioxide if it was used instead of chlorine?

Prooblem:

The data listed below are from a pilot plant study to determine turbidity and Giardia cyst removal from a cold, low-turbidity water (less than 1°C and 0.5 NTU in winter) by direct filtration using a cationic polymer as the coagulant [Reference 11, Chapter 10).The filter was a dual-media coal-sand bed, 2 ft by 2 ft square, operated for most test runs at a loading of approximately 12 m3/m2 • h (4.9 gpm/ft2) for durations in the range of 3-22 hr. During selected filter runs, Giardia cysts and coliform bacteria were injected into the raw water for 40-60 min and tested for presence in the filtered water. Calculate the percentages for Giardia cyst and coliform removals. Plot turbidity versus polymer dosage for both the raw water and filtered water on the same diagram. What is the least dosage of polymer for maximum turbidity removal? What appears to be an acceptable turbidity in the effluent to ensure 98%-99% t virtually iUU7o) Giardia cyst removal?