Transcript Management of Non-Point Source Pollution CE 296B Sources of Pollutants - Part V

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Management of Non-Point
Source Pollution
CE 296B
Department of Civil Engineering
California State University, Sacramento
Lecture #9, March 3, 1998
Sources of Pollutants - Part V
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Recall that we were looking at the six categories of
pollutants:
1. Toxic inorganics - e.g. metals
2. Synthetic organics - e.g. solvents
3. Biostimulants - BOD, nutrients
4. Sediment - clay, silt, sand, gravel  Left off here
5. Pathogenic organisms - viruses, bacteria, protozoa
6. Trash - use your imagination
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And the framework for acquiring knowledge about
each category:
1. What are the sub-categories in each category
and what are representative members?
2. What are the origins of pollutants?
3. How pollutants are introduced to the flow
stream?
4. How pollutants behave in water? and here
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D. How do sediments behave in water? Divided
into three major groups, each one having it’s
own effect on water quality objectives and
beneficial uses:
• Transport of particles - Sedimentation
effects (mass loading).
• Adsorption of other materials - Major
determining factor for where toxic
substances end up and effect they have.
• Contribution to turbidity - Concentration
effects.
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
1. Transport of particles:
a. Two modes of transport• Suspended in the flow - Wetload
• Being pushed along the bottom - Bedload
b. Particle size distribution, wetload vs. bedload:
Obviously, wetload transport has a smaller
particle size distribution than bedload.
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Wetload Particle Transport
I. Questions associated with wetload particle transport
can be separated into two categories:
A. What is the largest, discrete, particle that will
remain in suspension?
Particles that are less than 1 µm in diameter are
colloidal and will remain in suspension as surface
forces are greater than body forces. It is the size of the
particle greater than 1 µm in diameter that will remain
in suspension.
B. How much aggregation of particles is taking
place?
The idea being that larger, aggregated particles are
more likely to become part of the bedload.
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Wetload Particle Transport
II. What controls the size of the largest, discrete
particle that will remain in suspension?
• For particles greater than 1 µm in diameter,
body forces are dominant. Unless held in
suspension physically by turbulence, the particle
will settle. Thus, as turbulence is proportional
to the Reynolds Number, the greater Reynolds
Number associated with the flow, the larger the
particle that will remain in suspension.
  D Where:  = Flow velocity
Re 
D = Stream width

µ = Fluid Viscosity
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Wetload Particle Transport
II. How much aggregation of particles is taking place?
Complex topic, but lessons learned from the
coagulation process apply here as well.
Aggregation is dependant on (among other things):
• The concentration of multivalent cations (Ca+2,
Mg+2) present. Higher concentrations mean
greater aggregation.
• The concentration of univalent cations (Na+, K+)
present. Higher concentrations mean less
aggregation.
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Wetload Particle Transport
II. How much aggregation of particles is taking place?
Complex topic, but lessons learned from the
coagulation process apply here as well.
Aggregation is dependant on (among other things):
(cont.)
• An appropriate velocity gradient (G).
– Too large a gradient, and shear forces will
tear aggregated particles apart.
– Too small a gradient, particles will have
inadequate opportunity to come into contact.
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Wetload Particle Transport
III. Thus, the amount of wetload, particulates that will
be transported rapidly, is dependant on:
A. The amount and composition of material
originally eroded.
B. The turbulence of the flow stream, either in a
natural or man-made channel.
C. The composition of electrolytes in the flow
stream.
IV. It is important to note that while fine particles are
suspended in the wet load, partitioning of metals
and synthetic organics to the solid phase is
enhanced.
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Bedload Particle Transport
I. Particles too heavy to remain in suspension may
still be transported along the bottom of a channel,
natural or man-made, by the force of the current
and the assistance of gravity.
Of interest in the examination of bedload transports
is:
• The mass flow rate of sediment in the
downstream direction.
• The fractionation of sediments by size as part of
the bedload transport process.
• The disposition of sediments when transport
ceases.
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Bedload Particle Transport
II. The mass flow rate of sediment in the downstream
direction is complex (translation, I don’t know
much about it yet). Factors include:
• The amount and type of erosion in the
watershed.
• The bottom composition (roughness) - a
smoother surface yields a greater transport rate.
• The flow velocity - higher velocity yields a
greater transport rate.
• The slope - a steeper slope yields a greater
transport rate.
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Discussion Break
Based on what you have seen, and knowledge of
gravity flow system design, how efficiently will
sediments, of all sizes, be transported once they
enter the system?
Focus of BMP’s?
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Bedload Particle Transport
III. The fractionation of sediments by size. Consider
the diagram:
At periodic states of
equilibrium, the
potential energy of each
Streambed at quasi-equilibrium
particle is nearly equal.
Particle 1, m1
m1gh1 = m2gh2 = m3gh3
Particle 2, m2
h1
So
Particle 3, m3
h2
h3
Thus, along the streambed, natural or man-made, there
will be a sorting out of particles by size to satisfy first
law concerns. So, gravel deposits, sandbars, mudflats!
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Discussion Break
All other things being equal, where would you
expect to find the greatest concentration of toxic
substances?
Basis: Mass of contaminant per mass of dry soil
(mg/kg)
Gravel Beds?
Sandbars?
Mudflats?
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Bedload Particle Transport
III. The disposition of sediments when transport
ceases. Two different types of issues are
addressed:
A. Are the effects of sediment deposits positive or
negative?
• Positive:
– Spawning grounds and beaches (gravel / sand)
– Entombment of toxic substances
• Negative:
– Filling of wetland habitat type effects
– Impairment of navigation
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Bedload Particle Transport
III. The disposition of sediments when transport
ceases. Two different types of issues are
addressed: (cont.)
B. Are the deposits permanent or temporary?
If they are permanent, the same issues
discussed previously will be valid.
If temporary:
• Will a large flow event, clearing out the deposit
cause a “shock loading” problem downstream?
• Will the inevitable large flow event “clean out” a:
– positive deposit (beach, spawning ground)?
– negative deposit (clogged wetland)
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
2. Adsorption of toxic substances to particles.
Two different aspects to this topic:
• How much and how tightly are toxic
substances bound to particulate material?
• Is this removing toxic substances from liquid
phase and thus making them less bioavailable
or is this concentrating toxic substances in one
place (the bottom sediments)?
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
3. How much and how tightly are toxic
substances bound to particulate material?
In other classes, substaintial effort
has/is/will be made on behalf of partitioning
of metals, synthetic organics to the soil
matrix (or activated carbon). The
equilibrium relationships developed there
only applies to the circumstance pore water
within a matrix.
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
3. How much and how tightly are toxic
substances bound to particulate material?
(cont.)
Many of the same principles apply to
adsorption of metals and synthetic organics
to soil particles suspended in a water matrix,
but the equilibrium equations do not.
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
3. How much and how tightly are toxic
substances bound to particulate material?
(cont.)
New, yet to be developed relationships may
describe the equilibrium between liquid
phase concentrations and adsorbed phase
amounts for metals and synthetic organics
with respect to soil particles suspended in a
water column.
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
3. How much and how tightly are toxic
substances bound to particulate material?
(cont.)
Factors that would be considered in such a
relationship:
•
•
•
•
Concentration of solids
Clay fraction
Organic fraction
Temperature
•
•
•
•
Hardness
Mixing
Contact time
pH
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V. The fourth category of pollutant to examine is
sediment. (cont.)
D.How do sediments behave in water? (cont.)
4. Finally, wetload sediment transport
contributes to increased turbidity. In
addition to being a water quality objective,
turbidity can:
• Have a negative effect on fish. Particulate
material and gills do not mix.
• Although the correlation is very poor, turbidity
measurements can be a surrogate measure for
sediment concentration.
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Recall that we were looking at the six categories of
pollutants:
1. Toxic inorganics - e.g. metals
2. Synthetic organics - e.g. solvents
3. Biostimulants - BOD, nutrients
4. Sediment - clay, silt, sand, gravel
On to here 
5. Pathogenic organisms - viruses, bacteria, protozoa
6. Trash - use your imagination
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And the framework for acquiring knowledge about
each category:
1. What are the sub-categories in each category
and what are representative members?
2. What are the origins of pollutants?
3. How pollutants are introduced to the flow
stream?
4. How pollutants behave in water?
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VI.The fifth category of pollutant to examine is
pathogens.
A. Define what pathogens are:
A pathogen is a microscopic entity that if a
sufficient dose is transmitted to a human, a
disease will ensue. Three broad categories of
pathogens exist:
1. Viruses
2. Procaryotes
3. Eucaryotes
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Viruses
• Viruses (from the Latin virus - poisonous substance)
are infectious nucleic acid encapsulated in a protein
coat.
• A virus reproduces by invading a cell, where
replication takes place. The cell then dies releasing
many copies of the virus.
• A philosophical debate exists as to whether a virus is
alive. After all as an entity, it has no metabolic
functions. All it does is invade another cell and let
the that cells metabolic machinery do all the work
for reproduction.
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Viruses
• In most cases a virus has a specific type of cell it is
capable of invading.
• Viruses are small. The size range is 20 - 350 m.
50 m is typical.
• Traditional methods of detecting viruses involve
tissue cultures, looking to see in the correct type of
cells grown in culture are infected.
• This makes detection in water samples extremely
difficult.
• Example water borne pathogen - Polio
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Discussion Break
Why do you think it is so difficult to detect viruses
in water samples?
Policy implications?
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Procaryotes
• Procaryotes, loosely bacteria, are single celled
organisms capable of metabolic functions that do not
have a nucleus.
• Structure
Cell Membrane
Cytoplasm
DNA
• Typical Size
2 µm
0.8 µm
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Procaryotes
• By far, the largest source of biomass on the planet.
• As bacterial species are difficult to differentiate by
morphology, bacteria are usually classified by the
biochemical processes they do best.
• Most schemes to detect bacteria are centered on
isolating species based on biochemical tests. Does
the bacteria perform a particular biochemical
process.
• A major problem with this approach has been that
many species will perform a given biochemical
process.
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Procaryotes
• Pathogenic bacteria can be vectored many ways, but
we are interested in water borne pathogens. The
most likely source of bacterial pathogens in water is
fecal matter.
• Examples of water borne pathogens:
– Cholera: Vibrio cholerae
– Typhus: Salmonella typhi
The pathway for infection is the same for both species.
After an infected host contaminates a water supply, the
richest source being fecal matter, a victim ingests water
that contains a large enough number of viable organisms
to become infected.
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Eucaryotes
• Eucaryotes, loosely protozoa, are organism where
the cell(s) have a nucleus.
• Size: Huge variation, but much larger than bacteria.
• Reproduce much slower than bacteria, and thus
occur in much lower numbers.
• Many fewer viable organisms are required to cause
an infection.
• Are far tougher than bacteria or viruses. Can
withstand environmental stress better and are more
resistant to disinfection.
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Eucaryotes
• Often are parasitic. Treatment is notoriously
difficult.
• Because of:
– Low population densities, and
– Poorly understood biochemistry
are very difficult to detect.
• Example pathogens:
– Giardia lambilia
– Crytposporidium
– Entamoeba histolytica
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Eucaryotes
• The life cycle of these organisms are usually poorly
understood. It is often assumed, without proof, that
the major source of contamination is fecal matter.
• Other than minimizing fecal matter, a difficult chore
for wild animals in any case, source control
measures are hard to come by for eucaryotic
organisms.
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Discussion Break
Diarrhea kills more people worldwide than any other
cause.
In the U.S., it is not a big problem.
How real do you think the problem of water borne
disease is in this country?
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VI.The fifth category of pollutant to examine is
pathogens. (cont.)
B. Overview of detection of pathogens in surface
waters:
1. The number of possible pathogens is huge.
Each pathogen has a specific test associated
with it. Many of those tests are difficult and
expensive to perform.
2. A solution to this problem was put forward
at the turn of the century. That solution is
still the regulatory standard.
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VI.The fifth category of pollutant to examine is
pathogens. (cont.)
B. Overview of detection of pathogens in
surface waters: (cont.)
3. The idea was to test for an organism that
was found in fecal material, but that had no
other source.
4. Scientists searched for a biochemical
process that only took place in the intestinal
tract of warm-blooded animals. The choice
was the fermentation of lactose in the
presence of bile salts.