Water Quality Water Quality in Lakes & in Lakes & StreamsStreams

Dr. Philip BedientDr. Philip Bedient

IntroductionIntroductionWater quality management is the

science that predicts how much waste is too much for a body of water

AssimilatedAssimilated- 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

Water Quality Water Quality ManagementManagement

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

Point Sources of Point Sources of PollutantsPollutants

Point sources include domestic sewage and industrial wastes

Point sources -Point sources - collected by a network of pipes or channels and conveyed to a single point of discharge in receiving water

Municipal sewage -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

Nonpoint SourcesNonpoint 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

Combined Sewer FlowCombined Sewer Flow Nonpoint pollution from urban storm water

collects in combined sewers Combined sewers-Combined sewers- carry both storm

water and municipal sewage - older cities

Combined Sewer Combined Sewer OverflowOverflow

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

Oxygen- Demanding Oxygen- Demanding MATERIALMATERIAL

Dissolved Oxygen (DO)-Dissolved Oxygen (DO)- fish and other higher forms of aquatic life that must have oxygen to live

Oxygen- Demanding Material-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

NutrientsNutrients

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

Pathogenic OrganismsPathogenic 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

Pathogenic OrganismsPathogenic OrganismsSerious Outbreaks of these cause great suffering

E. Coli - indicator of fecal coliform bacteria Salmonella (typhoid fever) Shigella (dysentery) Cryptosporidium - protozoa Giardia- protozoa

Suspended SolidsSuspended Solids 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 sedimentsediment

Colloidal particles-Colloidal particles- do not settle, cause an increase in the turbidity of surface water

Organic suspended solids-Organic suspended solids- exert oxygen demand

Inorganic suspended solids-Inorganic suspended solids- result from soil erosion

Suspended SolidsSuspended 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

SaltsSalts Total dissolved solids -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

Toxic metals and toxic Toxic metals and toxic organic compoundsorganic 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

Endocrine-Disrupting Endocrine-Disrupting Chemicals (EDCChemicals (EDCss))

These include Polychlorinated biphenyls Pesticides Phthalates

No suitable method exists to characterize EDC’s

Can mimic estrogens, androgens, or thyroid hormones

Interfere with regular animal reproduction Affects synthesis of hormones in the body

ArsenicArsenic 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

Arsenic - Arsenic - October, 2001October, 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

Heat ImpactsHeat 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

Taste and Odor Taste and Odor ProblemsProblems

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

Water quality Water quality management in riversmanagement 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:1) Measuring pollutants levels (x,z, t)2) Predicting their effect on the water quality3) Determining background water quality that

would be present without human intervention4) Evaluate the levels acceptable for intended

uses of the water

River Pollution ImpactsRiver Pollution Impacts

Waste Input Receptor

Simple Mass BalanceSimple Mass Balance

Waste Input Qw, Cw

C = Qw Cw + Qs Cs

Input rate - Output rate - decay rate = Accumulation rate

Stream Qs, Cs

Steady state conservative system

Qs + Qw

Simple Mass BalanceSimple Mass Balance

Waste Input Qw = 5 m3/sCw = 40 mg/L

C = 20 (10) + 40 (5)

Input rate - Output rate - decay rate = Accumulation rate

Qs = 10 m3/s

Cs = 20 mg/L

Steady state conservative system

(10 + 5)

26.67 mg/L

Transport characteristics Transport characteristics that affect concentrationthat affect concentration

• Velocity

• Dilution (mixing)

• Dispersion

• Degradation (mass loss)

• Adsorption (to soils)

• Sedimentation (to bottom)

• Aquatic Life (attached)

v

Effect of Oxygen-Effect of Oxygen-demanding wastes on demanding wastes on

riversrivers 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

Biochemical oxygen Biochemical oxygen demanddemand

Biochemical oxygen demand (BOD)-Biochemical oxygen demand (BOD)- oxidation of an organic compound is carried out by microorganisms using the organic matter as a food source

Biossay-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

Biochemical oxygen Biochemical oxygen demanddemand

Aerobic decomposition-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 = -kLLt = Lo e-kt where Lo = ultimate

BOD

BODBOD Ultimate 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

Nature of the wasteNature 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

Ability of Organisms to Ability of Organisms to use wasteuse 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

TemperatureTemperature 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:

1) Temperature of receiving water throughout the year

2) Comparing data from various locations at different T values

Temperature EqnsTemperature Eqns The BOD rate constant is adjusted to the

temperature of receiving water using this:

kT=k20()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.

5 day Bod test5 day Bod test

1) A special 300 mL BOD bottle is filled with a sample of water that has been appropriately diluted and inoculated with microorganisms

2) Blank samples containing only the dilution water are also placed in BOD bottles and sealed

3) The sealed BOD bottles containing diluted samples and blanks are incubated in the dark at 20°C for the desired number of days

4) After five days has elapsed, the samples and blanks are removed from the incubator and the dissolved oxygen concentration in each bottle is measured.

Dissolved Oxygen DODissolved 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

Do Sag CurveDo 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

Use of Ponds for Water Quality

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

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

Dt = DOs - DO

DO

X

Critical DO