INTRODUCTION TO BIOENGINEERING II BioE 411, AE/CE/BRT 511

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INTRODUCTION TO BIOENGINEERING IIBioE 411,
AE/CE/BRT 511

• J.(Hans) van Leeuwen
• T.H. Kim

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Instructor (33)

• Professor J. (Hans) van Leeuwen
• from/of the Lions
• Born in Gouda, Netherlands
• Grew up in South Africa
• Lived in Australia for 7 years
• Lived in Ames for 11 years
• Specialty Environmental and Bioengineering
• Industrial wastewater treatment and
  
• product development based on waste materials

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Research activities
Beneficiation of biofuel co-products by
cultivating fungi
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Ozonation applications
Selective disinfection Selective
oxidation Alcohol purification
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Keeping exotic aliens out of our ports
ET
Zebra mussels
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Human technological development
From scavengers
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to use of fire

• Use of fire was the turning
• point in the technological
• development of humans
• leading to extended diet
• food preservation
• better hunting
• agriculture
• industry
• Top of the food chain!

but, this ultimately led to
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Overpopulation
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P o l l u t i o n . .
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Pollution of a small stream
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Consequence of pollution
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and ecological disasters
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and more disasters
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Distribution of Earths water
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Dangers lurking in water
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Pollution from informal housing
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Waterborne diseases
Map by Lord John Snow of the cholera outbreak in
London in 1854 the Broad Street Epidemic. This
is considered the root of epidemiology.
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Spread of Cholera in London 1854
1-3 September 127 dead By 10 September
500 Ultimately 616 dead
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Cholera the rapid killer
SEM micrograph of Vibrio cholerae, a
Gram-negative bacterium that produces cholera
toxin, an enterotoxin, which acts on the mucosal
epithelium lining of the small intestine This is
responsible for the disease's most salient
characteristic, exhaustive diarrhea. Bottom
cholera toxin
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Examples of organisms secreting enterotoxins
Bacterial Escherichia coli O157H7 Clostridium
perfringens Vibrio cholerae Yersinia
enterocolitica Shigella dysenteriae
Staphylococcus aureus (?pictured)
Viral Rotavirus (NSP4) ? (Institute for
Molecular Virology. WI)
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Dissolved oxygen

Importance Why is oxygen in water
important? Dissolved oxygen (DO) analysis
measures the amount of gaseous oxygen (O2)
dissolved in an aqueous solution. Oxygen gets
into water by diffusion from the surrounding air,
by aeration (rapid movement), and as a product of
photosynthesis.
DO is measured in standard solution units such as
milligrams O2 per liter (mg/L), millilitres O2
per liter (ml/L), millimoles O2 per liter
(mmol/L), and moles O2 per cubic meter (mol/m3).
DO is measured by way of its oxidation
potential with a probe that allows diffusion of
oxygen into it.
The saturation solubility of oxygen in wastewater
can be expressed as Cs ? (0.99)h/88 x 482.5/(T
32.6)
For example, in freshwater in Ames at 350m and
20C, O2 saturation is 8.8 mg/L. (Check for
yourself, with ? 1)
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BOD
Biochemical oxygen demand or BOD is a procedure
for determining the rate of uptake of dissolved
oxygen by the organisms in a body of water
BOD measures the oxygen uptake by bacteria in a
water sample at a temperature of 20C over a
period of 5d in the dark. The sample is diluted
with oxygen saturated de-ionized water,
inoculating it with a fixed aliquot of microbial
seed, measuring the (DO) and then sealing the
sample to prevent further oxygen addition. The
sample is kept at 20 C for five days, in the
dark to prevent addition of oxygen by
photo-synthesis, and the dissolved oxygen is
measured again. The difference between the final
DO and initial DO is the BOD or, BOD5. Once we
have a BOD5 value, it is treated as just a
concentration in mg/L BOD can be calculated
by Diluted ((Initial DO - Final DO BOD of
Seed) x Dilution Factor BOD of seed (diluted
activated sludge) is measured in a control just
deionized water without wastewater
sample. Significance BOD is a measure of
organic content and gives an indication on how
much oxygen would be required for microbial
degradation.
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Oxygen depletion in streams
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DO sag definitions
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Cumulative oxygen supply demand
Plotting the two kinetic equations separately on
a cumulative basis and adding these graphically
produce the DO sag curve
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Streeter-Phelps Model

• Mass Balance for the Model
• Not a Steady-state situation
• rate O2 accum. rate O2 in rate O2 out
  produced consumed
• rate O2 accum. rate O2 in 0 0 rate O2
  consumed
• Kinetics
• Both reoxygenation and deoxygenation are 1st
  order
• Streeter, H.W. and Phelps, E.B. Bulletin 146,
  USPHS (1925)

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Kinetics for Streeter-Phelps Model

• Deoxygenation
• L BOD remaining at any time
• dL/dt Rate of deoxygenation equivalent to
  rate of BOD removal
• dL/dt -k1L for a first order reaction
• k1 deoxygenation constant, fn of waste
  type and temp.

See Kinetics presentation if unfamiliar
with the mathematical processing
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Developing the Streeter-Phelps
Rate of reoxygenation k2D D deficit in D.O.
k2 reoxygenation constant

• Where
• T temperature of water, ºC
• H average depth of flow, m
• ? mean stream velocity, m/s
• D.O. deficit
• saturation D.O. D.O. in the water

There are many correlations for this. The
simplest one, used here, is from OConnor and
Dobbins, 1958
Typical values for k2 at 20 C, 1/d (base e) are
as follows small ponds and back water 0.10 -
0.23 sluggish streams and large lakes 0.23 -
0.35 large streams with low velocity 0.35 -
0.46 large streams at normal velocity 0.46 -
0.69 swift streams 0.69 - 1.15 rapids and
waterfalls gt 1.15
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Combining the kinetics
Net rate of change of oxygen deficiency, dD/dt
dD/dt k1L - k2D where L L0e-k1t
OR
dD/dt k1L0e-k1t - k2D
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Integration and substitution
The last differential equation can be integrated
to
It can be observed that the minimum value, Dc is
achieved when dD/dt 0

, since D is then Dc
Substituting this last equation in the first,
when D Dc and solving for t tc
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Example Streeter-Phelps

• Wastewater mixes with a river resulting in a
• BOD 10.9 mg/L, DO 7.6 mg/L
• The mixture has a temp. 20 ?C
• Deoxygenation const. 0.2 day-1
• Average flow 0.3 m/s, Average depth 3.0 m
• DO saturated 9.1 mg/L
• Find the time and distance downstream at which
  the oxygen deficit is a maximum
• Find the minimum value of DO

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Solutionsome values needed

• Initial Deficit 
• Do 9.1 7.6 1.5 mg/L
• (Now given, but could be calculated from
  proportional mix of river DO, presumably
  saturated, and DO of wastewater, presumably zero)
  
• Estimate the reaeration constant
• k2 3.9 v½ (1.025T-20)½
• H3/2  

k2 3.9 x (0.3m/s)½ (1.02520-20)½
(3.0m)3/2  
0.41 d-1
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Solutiontime and distance
Note that the effects will be maximized almost 70
km downstream
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Solutionmaximum DO deficiency
Note that this BOD could have been calculated
from mixing high-BOD wastewater with zero or
near-zero BOD
The minimum DO value is 9.1-3.1 6 mg/L
Implication DO probably not low enough for a
fishkill, but if continued could lead to species
differentiation and discourage sensitives species
like trout.