- From the equations, determine the lowest concentration of oxygen in
the stream?
This minimum can be obtained by substituting the test data into eq.
11, and the answer is 4.1 ppm.
- From the graph (oxygen sag curve) and data table of the model, determine
the lowest concentration of oxygen in the stream?
The answer is 4.17 ppm.
- Determine the time and location of the lowest oxygen concentration.
(Thibodeau)
By setting the first derivative of eq. 11 to zero, the critical time is:
tc = {1/1k'A /h - k'''B}*ln{(1k'A/hk'''B)*[1 -
DAš([(1k'A/h)-k'''B]/k'''BrBš]}
tc = 18 sec
Lc = v*tc
- What is the importance of the lowest concentration of oxygen in the
stream?
This minimum should not be less than the oxygen concentration to
sustain aquatic life in the stream. The students can determine the types
and levels of higher life forms in a stream with the minimum concentration
of oxygen. For example, catfish needs about 3.8 ppm or trout needs about
6 ppm.
- How can you increase the minimum point of oxygen concentration on the
oxygen sag curve of the model?
By changing such elements as the amount of pollutants, season, flow of
stream, mechanical mixing, and/or surface area of water.
- Experiment: Design and build an aeration system to increase the
transfer water. Optimize the size-cost-power by calculating the size of
aeration system, the best type of equipments and cost.
Teachers: Oxygen can be transferred:
- from bubbles to liquid water (aspirators)
- from atmosphere to water droplets (waterfalls)
- from atmosphere to water interphase (quiet turbulent, sheets films, etc.)
- Problem:(This problem is taken from class work developed by Dr.
Craig Myler, Professor of Chemical Engineering, University of Maryland
Baltimore County.)
This morning, the headlines of local news paper read: "ACME Chemicals
kills catfish!" As a head engineer for the ACME company, it is going to be
up to you to talk to the press this evening. You phone the plant and are
told that no upsets have occured and nothing but non- toxics have been
discharged. The sampling data from the previous day show the following:
- Water saturated with oxygen above the plant (9.37 ppm)
- Average depth = 20 ft
- Width = 10 ft
- Velocity = 2 ft/sec
- Temperature = 17šC
- Distance to catfish kill is 0.5 mile
- 1k'A = 1.65x10-3 ppm.ft/sec
- k'''B = 7.38x10-5 ppm/sec
- Catfish need 3.8 ppm of DO to survive
What are you going to tell your boss? the press? and the public?
ACME did not kill the fish. The minimum dissolved oxygen is 4.10 ppm.
- Experiment: Determine k'''B in laboratory with Lamotte's
Dissolved Oxygen Test Kit or DO Standardized Methods for starch
simulation.
Procedure: The purpose of this section is to provide a general
guide to the teachers. The teachers must supervise students and provide
detailed procedures to each section of the experiment. In this
experiment, starch is the organic pollutant.
- Make a 4 % sollution of starch.
- Let the starch solution cool to room temperature.
- Install a pump to circulate the solution as an aeration system to change flow rate, surface area of water, etc.
- Determine the DO with Lamotte's Dissolved Oxygen Test Kit or DO Standarized Methods
in time interval. DO Standardized Methods can be found in Standard Methods for the
Examination of Water and Waste Water by Greenberg, Clesceri, and Eaton (Page 498 -
4103). Lamotte's Test Kit can be purchased by calling (800) 344-3100 or (410) 778-3100.
- Determine the concentration of starch in the solution with UV/VIS spectrophotometric methods and potassium iodate.
- Calculate and interpretate the data according to DO Standardized Methods can be found in Standard Methods for the Examination of Water
and Waste Water by Greenberg, Clesceri, and Eaton (Page 10-31 to 10-40).
- What are the assumptions used by this model?
Constant biosphere
Constant chemical reactions
Constant rate of absorption
Constant surface area
Constant velocity
Constant volume
Homogenous system
Neglect of other absorptions
Neglect of other O2 usage such as fish and plants
O2 input by other means
Solubility or other equilibrium
This model can be extended by expanding any one of the above assumptions.
