Review Questions for Exam
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.
- Don't forget how to use the mass balance technique to analyze
a system (e.g., sedimentation tank or wastewater treatment plant).
- Look at the class exercises and homework.
- 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
- What's a beneficial use? List at least four.
- Who determines beneficial uses? How is this information used?
- What is pollution?
- What's the difference between point sources of pollution and
- What are the water quality problems associated with suspended
- What is the main water quality effect of discharging
(nontoxic) organic substances to a natural water body?
- What are the inorganic nutrients of concern in municipal and
- 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?
- What are the possible effects of discharging hot water to a
- Who regulates the quantity and quality of discharges to
natural water bodies in California? What is the legal basis of
- What is the technical basis for deciding allowable quantities
and qualities in discharge requirements (NPDES permits)?
- 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?
- Sketch the DO sag curve resulting from a waste stream without
any organic waste.
- What two processes which affect DO in streams are not included
in the DO sag eqaution developed in class?
- Why can't you use the DO sag curve presernted in class to
model a lake?
- 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.
- 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?
- 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
- What are the typical constituents of concern (general classes)
that cause us to treat surface water for drinking?
- 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.
- 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
- What is an MCL?
- What are the roles of the federal and state governments in
regulating drinking water quality?
- What are the characteristics of a particle or fluid that
affect settling velocity? (Look over Stokes' Law.)
- What is critical settling velocity? What is the relationship
between critical settling velocity and overflow rate? Calculate
the value of one, given the other.
- How does particle removal efficiency depend on critical
settling velocity or overflow rate?
- What's the difference between discrete and flocculating
- Size a settling tank based on overflow rate and/or detention
- Calculate sludge qualities or concentrations based on a mass
balance analysis of a settling tank.
- What is a "stable" suspension and what makes it stable?
- What do chemical coagulants do?
- How do we determine the best chemicals and doses in
- Calculate the mass (or weight) of chemicals needed in a
treatment process given the concentration and flow.
- What effect does alum have on alkalinity? Why is this a
- What is the purpose of flocculation? How is it normally done?
- What does velocity gradient measure?
- Given appropriate data, calculate the G value for a given
power input, or the power needed to establish a desired G value in
- How is it that a sand filter can remove particles smaller than
the pore spaces between the sand grains?
- What is backwashing? Why is it done? What indicates that a
filter needs to be backwashed?
- Why are dual media filters sometimes preferred over sand
- Why is anthracite used instead of gravel as the top layer of
dual media filters?
- Size a filter based on filtration rate and operating times.
- Estimate the concentration of suspended solids in backwash
water based on a mass balance analysis of a filter.
- Describe the tytpical operating cycle of a filter. What causes
- What is the difference between "free" and "combined" chlorine
- 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?
- Why is pH control important in using chlorine as a
- 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?
- Why is there a contact time associated with disinfection?
- What is a Ct factor? How is it used?
- Why are plug flow tanks preferred for contact tanks?
- List two methods of softening water.
- Why might you use activated carbon in a water treatment train?
- Where and in what form do the pollutants end up in a
conventional water treatment plant?
- What is pretreatment? Who can require it and why?
- What are "secondary" treatment standards (numerical values)?
- Sketch the treatment trains water ands sludge in a typical
secondary treatment plant. Label the processes and indicate what
each one does.
- Where and in what form do the pollutants end up in a typical
secondary wastewater treatment plant?
- What general processes might be included as part of "advanced"
- What is the general strategy of biological treatment?
- Why are aerobic processes generally preferred over anaerobic
ones (besides the smell)?
- What is MLSS, MLVSS, RAS, and WAS?
- Why is the sludge recycled in an activated sludge plant?
- What is sloughing in a trickling filter or RBC?
- What does a trickling filter filter (trick question)?
- What is the purpose of a secondary clarifier in a biological
- Why are activated sludge plants aerated and why isn't this
done in trickling filters?
- What is sludge stabilization?
- List three sludge stabilization technologies and describe
generally how they work.
- What is the differences between in inputs and products of
aerobic and anaerobic treatment (or sludge stabilization)
- Why don't wastewater treatment plants that use ponds usually
have anaerobic digesters?
- What is thickening? Where in the treatment process is it used?
Why is it used?
- What is dewatering? Where in the treatment process is it used?
Why is it used?
- Size a primary settling tank based on average and peak
- Size an aeration basin based on F/M ratio.
- Size a trickling filter based on hydraulic and organic
- Size a pond based on organic loading or hydraulic detention
- Size an anaerobic digester based on detention time or organic
loading rate (same as ponds).
- In an activated sludge plant, calculate the waste sludge flow
rate, based on solids retention time.
- In an activated sludge plant, calculate the recycle flow
needed to maintain a specified level of MLSS.
- 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?
- 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?
- 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.)