Review Questions for Exam 3

DISCLAIMER -- This is a list of questions to help you review. Test questions will probably not be in this format, and there may be questions on the exam that are not specifically included in this list. This list does, however, cover all the major topics of concern for this exam. If you can answer these questions, and think clearly, you should do well.


  1. Don't forget how to use the mass balance technique to analyze a system (e.g., sedimentation tank or wastewater treatment plant).
  2. Look at the class exercises and homework.
  3. When you see "calculation-type" questions, be sure to look at all angles of the calculation. In other words, if asked below, to calculate D given A, B, and C, be sure you can turn the problem around and calculate A, given B, C, and D. Also if asked to calculate A, check that you know what B, C, and D you need, and where you might get this information.

Water Resources and Natural Water Quality

  1. What's a beneficial use? List at least four.
  2. Who determines beneficial uses? How is this information used?
  3. What is pollution?
  4. What's the difference between point sources of pollution and nonpoint sources?
  5. What are the water quality problems associated with suspended solids?
  6. What is the main water quality effect of discharging (nontoxic) organic substances to a natural water body?
  7. What are the inorganic nutrients of concern in municipal and industrial discharges?
  8. What are the possible water quality effects of discharging organic nitrogen and ammonium to a natural water body? In other words, why might these discharges be regulated?
  9. What are the possible effects of discharging hot water to a stream?
  10. Who regulates the quantity and quality of discharges to natural water bodies in California? What is the legal basis of this authority?
  11. What is the technical basis for deciding allowable quantities and qualities in discharge requirements (NPDES permits)?
  12. Sketch the DO sag curve resulting from a wastewater containing an organic waste. What causes the DO to decrease? Where does the rate of oxygen removal due to organic degradation exceed the reaeration rate? Where does the reaeration rate exceed the rate of removal due to BOD? Where are they equal?
  13. Sketch the DO sag curve resulting from a waste stream without any organic waste.
  14. What two processes which affect DO in streams are not included in the DO sag eqaution developed in class?
  15. Why can't you use the DO sag curve presernted in class to model a lake?
  16. Practice using the DO sag equation, including temperature corrections for coefficients and mixing equations. Check your understanding of the nomenclature and variables. For example DO does not equal D0.
  17. Sometimes the DO sag equation gives you a deficit greater than the saturation concentration. What is the resulting DO concentration? Can this happen physically? If not, why does the equation give you this result?
  18. Check your understanding of how the model handles the equations for different reaches. Can you apply the equation to a river with two reaches? Can you apply the equation in a situation where physical parameters (T, kr, or kd) change partway down the river?


Water Treatment

  1. What are the typical constituents of concern (general classes) that cause us to treat surface water for drinking?
  2. For a typical surface water, sketch the treatment train for a conventional drinking water treatment plant. Label all of the unit processes. Describe what each unit process removes.
  3. Why are there few ground water treatment plants, compared to surface water plants? What are the typical constituents of concern that might cause you to treat ground water? What processes would you use?
  4. What is an MCL?
  5. What are the roles of the federal and state governments in regulating drinking water quality?
  6. What are the characteristics of a particle or fluid that affect settling velocity? (Look over Stokes' Law.)
  7. What is critical settling velocity? What is the relationship between critical settling velocity and overflow rate? Calculate the value of one, given the other.
  8. How does particle removal efficiency depend on critical settling velocity or overflow rate?
  9. What's the difference between discrete and flocculating settling?
  10. Size a settling tank based on overflow rate and/or detention time.
  11. Calculate sludge qualities or concentrations based on a mass balance analysis of a settling tank.
  12. What is a "stable" suspension and what makes it stable?
  13. What do chemical coagulants do?
  14. How do we determine the best chemicals and doses in coagulation/flocculation processes?
  15. Calculate the mass (or weight) of chemicals needed in a treatment process given the concentration and flow.
  16. What effect does alum have on alkalinity? Why is this a potential problem?
  17. What is the purpose of flocculation? How is it normally done?
  18. What does velocity gradient measure?
  19. Given appropriate data, calculate the G value for a given power input, or the power needed to establish a desired G value in a tank.
  20. How is it that a sand filter can remove particles smaller than the pore spaces between the sand grains?
  21. What is backwashing? Why is it done? What indicates that a filter needs to be backwashed?
  22. Why are dual media filters sometimes preferred over sand filters?
  23. Why is anthracite used instead of gravel as the top layer of dual media filters?
  24. Size a filter based on filtration rate and operating times.
  25. Estimate the concentration of suspended solids in backwash water based on a mass balance analysis of a filter.
  26. Describe the tytpical operating cycle of a filter. What causes the headloss?
  27. What is the difference between "free" and "combined" chlorine residual?
  28. Why is a chlorine residual left in water as it leaves a water treatment plant and enters the piping system? Why isn't a chlorine residula left in the effluent of a wastewater plant?
  29. Why is pH control important in using chlorine as a disinfectant?
  30. What is the potential problem with using chlorine as a disinfectant? To avoid this problem, what other disinfectants are sometimes used? Do the alternative disinfectants have any problems of their own?
  31. Why is there a contact time associated with disinfection?
  32. What is a Ct factor? How is it used?
  33. Why are plug flow tanks preferred for contact tanks?
  34. List two methods of softening water.
  35. Why might you use activated carbon in a water treatment train?
  36. Where and in what form do the pollutants end up in a conventional water treatment plant?

Wastewater Treatment

  1. What is pretreatment? Who can require it and why?
  2. What are "secondary" treatment standards (numerical values)?
  3. Sketch the treatment trains water ands sludge in a typical secondary treatment plant. Label the processes and indicate what each one does.
  4. Where and in what form do the pollutants end up in a typical secondary wastewater treatment plant?
  5. What general processes might be included as part of "advanced" treatment?
  6. What is the general strategy of biological treatment?
  7. Why are aerobic processes generally preferred over anaerobic ones (besides the smell)?
  8. What is MLSS, MLVSS, RAS, and WAS?
  9. Why is the sludge recycled in an activated sludge plant?
  10. What is sloughing in a trickling filter or RBC?
  11. What does a trickling filter filter (trick question)?
  12. What is the purpose of a secondary clarifier in a biological treatment plant?
  13. Why are activated sludge plants aerated and why isn't this done in trickling filters?
  14. What is sludge stabilization?
  15. List three sludge stabilization technologies and describe generally how they work.
  16. What is the differences between in inputs and products of aerobic and anaerobic treatment (or sludge stabilization) processes?
  17. Why don't wastewater treatment plants that use ponds usually have anaerobic digesters?
  18. What is thickening? Where in the treatment process is it used? Why is it used?
  19. What is dewatering? Where in the treatment process is it used? Why is it used?
  20. Size a primary settling tank based on average and peak conditions.
  21. Size an aeration basin based on F/M ratio.
  22. Size a trickling filter based on hydraulic and organic loading.
  23. Size a pond based on organic loading or hydraulic detention time.
  24. Size an anaerobic digester based on detention time or organic loading rate (same as ponds).
  25. In an activated sludge plant, calculate the waste sludge flow rate, based on solids retention time.
  26. In an activated sludge plant, calculate the recycle flow needed to maintain a specified level of MLSS.
  27. What is the difference between MLSS and MLVSS? Which one is easier to measure? Which one more closely approximates the concentration of mocroorganisms in an aeration tank?
  28. How do changes in various parameters (influent BPOD, temperarture, miccroorganism concentration, flow) affect how large an aeraqtion tank is needed? For a given tank size, how do these changes affect the effluent BOD concentreation?
  29. What hydraulic model do we use to model trickling filters? Can you solve a problem using the equation presented in class? (It's just like some of the mass balance problems we've done before.)