Water Quality in Lakes

1
Water Quality in Lakes Streams

• CIVE 4312

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Introduction

• Water quality management is the science that
  predicts how much waste is too much for a body of
  water
• Assimilated- amount of waste that can be
  tolerated by a body of water
• Determined by knowing the type of pollutants
  discharged and their effect on water quality

3
Water Quality Management

• Water quality is affected by natural factors
• Historical uses in the watershed
• Geometry of the watershed area
• Climate of the region
• Good water quality protects drinking water as
  well as wildlife

4
Point Sources of Pollutants

• Point sources include domestic sewage and
  industrial wastes
• Point sources - collected by a network of pipes
  or channels and conveyed to a single point of
  discharge in receiving water
• Municipal sewage - domestic sewage and industrial
  wastes that are discharged into sanitary sewers -
  hopefully treated
• Point source pollution can be controlled by waste
  minimization and proper wastewater treatment

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Nonpoint Sources

• Urban and agricultural runoff that are
  characterized by overland discharge
• This type of pollution occurs during rainstorms
  and spring snowmelt
• Pollution can be reduced by changing land use
  practices

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Combined Sewer Flow

• Nonpoint pollution from urban storm water
  collects in combined sewers
• Combined sewers- carry both storm water and
  municipal sewage - older cities

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Combined Sewer Overflow

• Eliminating this involves
• Construction of separate storm and sanitary
  sewers
• Creation of storm water retention basins
• Expanded treatment facilities to treat the storm
  water
• Combined sewers are not prohibited by the U.S.
  because removal would disrupt streets, utilities,
  and commercial activities

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Oxygen- Demanding MATERIAL

• Dissolved Oxygen (DO)- fish and other higher
  forms of aquatic life that must have oxygen to
  live
• Oxygen- Demanding Material- anything that can be
  oxidized in the receiving water resulting in the
  consumption of dissolved molecular oxygen - BOD,
  COD
• Almost all naturally occurring organic matter
  contributes to the depletion of DO

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Nutrients

• Nitrogen and phosphorus are considered pollutants
  when too much present in high conc.
• High levels of nutrients cause disturbances in
  the food web
• Organisms grow rapidly at the expense of others
• Major sources of nutrients (N, P)
• Phosphorus-based detergent
• Fertilizer and agricultural runoff
• Food-processing wastes
• Animal and human waste

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Pathogenic Organisms

• Include bacteria, viruses, and protozoa from
  diseased persons or animals
• Water is made unsafe for drinking, swimming, and
  fishing
• Antibiotic-resistant bacteria are the most
  dangerous
• Bacteria are found in both urban and rural
  environments with no observable pattern

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Pathogenic Organisms

• Serious Outbreaks of these cause great suffering
• E. Coli - indicator of fecal coliform bacteria
• Salmonella (typhoid fever)
• Shigella (dysentery)
• Cryptosporidium - protozoa
• Giardia- protozoa

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Suspended Solids

• Suspended solids- organic and inorganic particles
  that are carried by wastewater into a receiving
  water
• A slower flow causes particles to settle and form
  sediment
• Colloidal particles- do not settle, cause an
  increase in the turbidity of surface water
• Organic suspended solids- exert oxygen demand
• Inorganic suspended solids- result from soil
  erosion

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Suspended Solids

• With an increase in the amount of sediment comes
• Increase of turbidity
• Decrease of light penetration
• Increase in amount of bacteria
• Increase in solids settled on the bottom which
  causes animal habitats to be destroyed

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Salts

• Total dissolved solids - TDS
• Water collects salt as it passes over soil during
  irrigation practice
• Too much salt can cause crop damage and soil
  poisoning
• Arid regions - west and south Texas

15
Toxic metals and toxic organic compounds

• Agricultural runoff contains pesticides and
  herbicides
• Urban runoff contains zinc - from tires
• Too many toxic metals and toxic organic
  substances can leave a body of water useless
• James River in Virginia
• Passaic River in New Jersey
• Toxic compounds can also make fish and shellfish
  unsafe to eat - As, Hg, Pb, and PCBs
• The new concern is pharmaceutical chemicals in
  water and wastewater

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Endocrine-Disrupting Chemicals (EDCs)

• These include
• Polychlorinated biphenyls
• Pesticides
• Phthalates
• No suitable method exists to
• characterize EDCs
• Can mimic estrogens, androgens, or thyroid
  hormones
• Interfere with regular animal reproduction
• Affects synthesis of hormones in the body

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Arsenic

• A naturally occurring element - As2O3 of real
  concern.
• Caused by minerals dissolving naturally from
  weathered rocks and soils - iron oxides and
  sulfides
• Causes many health effects such as
• Arsenic poisoning - interfere with ATP cycle
• Circulatory disorders
• Gastrointestinal upsets
• Diabetes
• Skin lesions possible skin cancers
• Created a huge problem in Bangladesh wells in 1992

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Arsenic - October, 2001

• EPA lowered the MCL from 50 to 10 ug/L
• Mostly a problem in western U.S. and the Midwest
  - naturally occurring
• Lifetime excess risk translates to 30/10,000
• Compares to other carcinogens - 1/105 to 1/106
• Major concern in water supplies now

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Heat Impacts

• An increase in the Temp of water can cause
• Increase in DO which leads to a deterioration in
  water quality
• Large fish kills
• Blocked migration of fish
• Altered genetic makeup in fish

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Taste and Odor Problems

• An increase in MTBE concentration in water
• Releases from USTs and watercraft engines
• Has impacted many lakes nationwide
• Created serious taste and odor problems
• City of Dallas shut down main water supply
  intakes due to largest pipeline spill in the U.S.
  in 2000
• City of Santa Monica closed main wells - 1999
• Many private wells impacted by MTBE

21
Water quality management in rivers

• Main goal is to control the discharge of
  pollutants so that water quality is not degraded
  above the natural background level
• Controlling waste involves
• Measuring pollutants levels (x,z, t)
• Predicting their effect on the water quality
• Determining background water quality that would
  be present without human intervention
• Evaluate the levels acceptable for intended uses
  of the water

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River Pollution Impacts
Receptor
Waste Input
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Simple Mass Balance
Input rate - Output rate - decay rate
Accumulation rate
Steady state conservative system
Stream Qs, Cs
C Qw Cw Qs Cs
Qs Qw
Waste Input Qw, Cw
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Simple Mass Balance
Input rate - Output rate - decay rate
Accumulation rate
Steady state conservative system
Qs 10 m3/s Cs 20 mg/L
26.67 mg/L
C 20 (10) 40 (5)
(10 5)
Waste Input Qw 5 m3/s Cw 40 mg/L
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Transport characteristics that affect
concentration

• Velocity
• Dilution (mixing)
• Dispersion
• Degradation (mass loss)
• Adsorption (to soils)
• Sedimentation (to bottom)
• Aquatic Life (attached)

v
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Effect of Oxygen-demanding wastes on rivers

• Depletes the dissolved oxygen in water
• Threatens aquatic life that require DO
• Concentration of DO in a river is determined by
  the rates of photosynthesis of aquatic plants and
  the rate of oxygen consumed by organisms

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Biochemical oxygen demand

• Biochemical oxygen demand (BOD)- oxidation of an
  organic compound is carried out by microorganisms
  using the organic matter as a food source
• Biossay- to measure by biological means
• BOD is measured by finding the change in
  dissolved oxygen concentration before and after
  bacteria is added to consume organic matter

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Biochemical oxygen demand

• Aerobic decomposition- when organisms use oxygen
  to consume waste
• The rate at which oxygen is consumed is directly
  proportional to the concentration of degradable
  organic matter remaining at any time
• BOD is a first order reaction L BOD
• dL/dt -kL
• Lt Lo e-kt where Lo ultimate BOD

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BOD

• Ultimate BOD- maximum amount of oxygen
  consumption possible when waste has been
  completely degraded
• Numerical value of the rate constant k of BOD
  depends on
• Nature of waste and T
• Ability of organisms in the system to use the
  waste

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Nature of the waste

• Materials that are rapidly degraded have large
  BOD constants
• Materials that degrade slowly are almost
  undegradable in the BOD test
• BOD rate constant depends on the relative
  proportions of the various components
• Easily degradable organics are more completely
  removed than less readily degradable organics
  during wastewater treatment

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Ability of Organisms to use waste

• Many organic compounds can be degraded by only a
  small group of microorganisms
• The population of organisms that can most
  efficiently use wastes predominates
• BOD test should always be conducted with
  organisms that have been acclimated to the waste
• This created a rate constant that can be compared
  to that in the river

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Temperature

• Oxygen use speeds up as the temperature increases
  and slows down as the temperature decreases
• Oxygen use is caused by the metabolism of
  microorganisms
• BOD rate constants depend on
• Temperature of receiving water throughout the
  year
• Comparing data from various locations at
  different T values

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Temperature Eqns

• The BOD rate constant is adjusted to the
  temperature of receiving water using this
• kTk20(?)T-20
• T temperature of interest (in C)
• kT BOD rate constant at the temperature of
  interest(in days -1)
• k20 BOD rate constant determined at 20 C (in
  days -1)
• ? temperature coefficient.

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5 day Bod test

• A special 300 mL BOD bottle is filled with a
  sample of water that has been appropriately
  diluted and inoculated with microorganisms
• Blank samples containing only the dilution water
  are also placed in BOD bottles and sealed
• The sealed BOD bottles containing diluted samples
  and blanks are incubated in the dark at 20C for
  the desired number of days
• After five days has elapsed, the samples and
  blanks are removed from the incubator and the
  dissolved oxygen concentration in each bottle is
  measured.

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Dissolved Oxygen DO

• If the discharge of oxygen- demanding wastes is
  within the self-purification capacity, the DO is
  high
• If the amount of waste increases, it can result
  in detrimental changes in plant and animal life
• Aquatic life cannot survive without DO
• Objective of water quality management is to
  assess the capability of a stream to absorb waste

36
Do Sag Curve

• DO concentration dips as oxygen-demanding
  materials are oxidized and then rises as oxygen
  is replenished from atmosphere and photosynthesis
• Major sources of oxygen
• Reaeration from the atmosphere
• Photosynthesis of aquatic plants
• Factors of oxygen depletion
• BOD of waste discharge
• DO in waste discharge is less than that in the
  river
• Nonpoint source pollution
• Respiration of organisms and aquatic plants

37
Use of Ponds for Water Quality
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Oxygen Deficit Equation
Define deficit D DOs - DO in mg/L L
ultimate BOD (mg/L) V (dD/dx) kd L - kr
D Where kd deoxygenation rate constant
(day-1) kr reaeration rate
constant (day-1) Since t x / V, can write the
above in time as dD/dt kd L - kr D
(reaeration vs oxygen use) Solution to this eqn
gives the DO sag curve
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Oxygen Deficit Equation
At t 0, D Da and L La - Initial
values Solving the equation for Dt deficit at
any time t Dt kdLa e-kd t - e-kr t
Da e-kr t
Kr - kd
Critical DO
Dt DOs - DO
DO
X