Questions For Thinking And Discussing

1. What should be the pressure across an ultrafiltration module, in order to achieve a permeate flux of 400 Liter/m2-day. The clean membrane resistance is 2.4 X 1010 1/m.

2. If the pressure drop across a tubular membrane is 2.8 bars, determine the permeat velocity across the membrane module. The thickness and the porosity of the deposit are 2 mm and 40 %, respectively. The average diameter of the partices is 5 microns. The initial membrane resistance is estimated to be 1.7 X 1010 1/m.

3. The energy requirements for the desalination of brackish waster based on RO is typcially around 9 kWh/m3. Develop a simplified calculation basis for multistage distillation and compare the energy requirements for the two techniques. All things being considered equal, which of these approaches might best be described as pollution prevention technology. The following process flow scheme applies to a distillation operation.

Condensed Purified Water

Saltwater Feed -ยป

Preliminary Filtering

Brine solution recycle

Brine solution purge

4. Explain the various mechanisms that result in fouling membrane surfaces.

5. Consider a typical electrodialysis process. What will happen if the electrodes on either side are interchanged? Explain the performance of the modified system.

6. Compute the osmotic pressure for a typical sea water.

7. An electrodialysis cell has the following dimensions (110 cm X 60 cm x 0.04 cm (thickness), and is used to treat water with a throughput velocity of 10 cm/sec. The product concentration is 0.0092 eq/Liter. The cell current efficiency is 0.892. Resistance across the cell is 0.205 ohm. The influent concentration is 125 mg/Liter of NaCl. Calculate the following: (a) cell current, (b) cell power output, (c) the cell voltage, and (d) the energy consumption per equivalent of product transferred.

8. The following data was obtained from a series of pilot tests for a microfiltration process, in which the incoming particles have an average size of 3 microns. Determine the following: (a) Prepare a plot of time versus permeate flow and deposit resistance. Examine these results and establish a basis for recommending when the process should be backwashed. Discuss these recommendations and your criteria; (b) Calculate the time averaged permeate flux between the start of filtration till the time of backwashing. Assume that this time averaged permeate flux will remain constant for the remainder of the runs, and compute the membrane area required for treating a surface water source of capacity 1 Mliter/day (Hint: apply Simpson's rule to performing a curve fitting of the data); (c) If the average particle size of particles in the influent is 8 microns, compute the flux at 35 minutes. Compare this flux with the corresponding flux obtained with the 3 micron particles. Discuss the implication of these results in a commercial water treatment facility.

Time, min. Deposit porosity Deposit thickness, cm

9. Develop some pollution prevention options for the disposal of brine or salt solution derived from a desalting operation.

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