Page 99 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

54 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

PROBLEMS
3.1 Units and Dimensions
Examine the units used in the reporting forms in a treat-
ment plant. In particular, look at the units associated with
the different unit processes. Convert the units to SI.
3.2 Conversions of Units
Demonstrate several conversions of force to mass and
vice versa. Use fundamental units for the conversions,
not shortcuts. Appendix A provides a guide to units.
Examples of problems are listed:
a. Suppose an object shows a reading on a spring scale
of 5 lb. Determine its mass in kg. Determine the force
it exerts in N.
b. A motor has a power output of 3 hp. Determine its
power in watts.
3.3 Scenarios
Consider the design scenarios for a wastewater treatment
plant as a whole. Generate several scenarios that have to
FIGURE 3.8 Six slow sand filters to evaluate effect of design=
do with the ability of the plant to meet its effluent dis-
operating variables on removals of coliforms and Giardia cysts.
charge permit.
3.4 Spreadsheets
was different; e.g., for filter 2, the depth was half of the
Set up the scenario in 3 on an Excelt spreadsheet, show-
control filter depth; for filter 3, the temperature was main-
ing the structure for computation. Generate numerical
tained at 48C; for filter 4, the effective sand size was larger; for
solutions using hypothetical data.
filter 5, chlorine was added to minimize growth of organisms
3.5 Models
before seeding with coliforms and Giardia; filter 6 was main-
The Denver Marston Water Treatment Plant treats drinking
tained with nutrients added continuously for 12 months of
water drawn from the adjacent Marston Lake (near Quincy
operation.
Avenue on the south side of Denver). The plant experiences
algae blooms that interfere with coagulation and filtration.
Suppose that microscreening is a proposed treatment pro-
3.6 SUMMARY cess for removing the algae. A manufacturer has provided
While ideas and concepts of modeling are reviewed, any a pilot plant that you will use as the basis for a design.
practical implementation remains an art, i.e., there are 1. Outline an experimental program that you might pro-
pose.
no specific guidelines. A major node point in the develop-
2. State dependent variables.
ment of the field of process design was the publication of
3. Identify the independent variables.
the two books by Linvil Rich, i.e., Unit Operations in
4. Would you do any bench scale testing?
Sanitary Engineering, published in 1961 (Rich, 1961),
5. Would you visit any microscreen plants?
and Unit Processes in Sanitary Engineering, published
6. Would mathematical modeling have a place?
in 1963 (Rich, 1963). These books were responsible for
7. Describe plots that you would generate from the pilot
a paradigm shift toward chemical engineering approaches
plant operation.
and a definite departure from empiricism as the modus
8. Would you apply mathematical modeling for any
operandi.
aspect of your design? Describe.
At the same time, mathematical modeling, in the sense
9. Describe how you would arrive at a final sizing for a
of understanding fundamentals, became the quest of aca-
full-scale design.
demics. In addition to looking for empirical rules and con-
If you have any ideas for discussing the problem that
ducting ‘‘black box’’ experiments, the goal was to understand
vary from the above suggested responses, please feel free
and incorporate ‘‘mechanisms’’ into models, such as math-
ematical expressions involving kinetics, diffusion, turbu- to bring out the salient points as you feel appropriate.
lence, boundary layers, adsorption isotherms, equilibrium
constants, etc. GLOSSARY
The method of problem solving is the same for all engin-
eering problems, simple or complex. The problem must be Accuracy: The relationship between a measurement and a
stated clearly, the objectives stated, and the methods delin- ‘‘true’’ value. For example, if a turbidimeter is cali-
eated. Regardless of the character of the problem or the brated and reads the same as, say two or three stand-
method used, this simple procedure is common to all ards, it may be considered ‘‘accurate’’ (assuming the
problem solving. standard was prepared properly).