Transcript WATER & THE CITY

WATER & THE CITY
All About Water
Keeps us alive
Moderates climate
Sculpts the land
Removes and dilutes wastes and pollutants
Recycled by the hydrological cycle
Humans are made up of over 60% water
It is a poorly managed resource
Water rich country: Canada (0.5% population with 1/5 of
freshwater)
Water poor country: China (1/5 population with 7% of
freshwater)
Hydrological cycle
• Powered by solar energy, water moves
through different stages and around the earth
• Evaporation from ocean----condensation in
the atmosphere-----precipitation over land--runoff and ground water recharge----back to
ocean
Surface runoff: precipitation that is not infiltrated
into the ground or evaporated back to the
atmosphere.
2/3 of annual runoff is lost by seasonal floods
and 1/3 is reliable runoff that we can count on
as a stable source of fresh water
The Hydrological Cycle
Watershed (or drainage basin): the region from which surface water
drains into a river, lake, wetland, or other body of water.
The Los Angeles River Watershed
Groundwater: water stored in the pores, fractures,, crevices, and
other places in soil and rock (one of the most important source of
fresh water)
Structure of underground
Zone of saturation: the spaces in rocks are completely filled with
water.
Water table: top of the zone of saturation
Aquifers: porous, water-saturated layers of sand, gravel, or bedrock
through which groundwater flows. (store water and provide the
underground conduit for groundwater flow)
Natural recharge: aquifers are replenished naturally by precipitation
that percolates downward through soil and rock (very slow, 3 feet
per year and no more than 1 foot per day).
Some aquifers get very little recharge and are nonrenewable
resource at human time scale. For example, in desert climate
zone, ground water was formed 15,000-30,00 years ago).
Groundwater Features
Water usages for human:
70% for irrigation (produce 40% of the world’s food),
20% in industry and residential use is 10%
Water distribution in United States:
Ample precipitation in the east and too little in the
west.
Problems in the east: flooding, occasional urban
shortages,and pollution.
Problems in the west: high evaporation and recurring
prolonged drought.
•In US, the average total water supply is 1.2 trillion
gallon per day (discharge of streams), total water
used in 1960 was 22% of total supply, the
consumption of water is about 5% of the total supply
(not returned after use)
Urbanization and water cycle
Water input:
Natural means: rivers, springs, precipitation, lakes
Engineering works: canals, wells, pipes, pumps,etc.
Once in the city, hydrological cycle works again
(evaporation, infiltration, consumption, runoff)
Two types of usage
1. Consumptive: remove water from the system and
depletes the outflow (5% total supply) (beverage
industry, evaporative cooler, etc.)
2. Nonconsumptive uses: water is returned to the
system undamaged theoretically (recreation,
navigation, cooling; generally results in modification
in chemical and thermal modification
Ways to provide more fresh water
1. Build dams and reservoirs to store runoff
2. Bring in surface water from another area
3. Withdraw groundwater and convert salt
water to fresh water (desalination)
4. Reduce water waster and import food to
reduce water use in growing crops and
raising livestock
Problems with Groundwater withdrawal:
(1)
land subsides (80% is related to underground
water usage) .(San Joaquin Valley southwest
of Mendota, CA; San Clarita Valley during Jan
4 to Aug 2, 1997)
http://water.usgs.gov/ogw/subsidence.html
(2) salt water intrusion: when fresh water is withdrawn at a
faster rate than it can be replenished, a draw down of the
water table occurs with a resulting decrease in the
overall hydrostatic pressure, salt water from the ocean
intrudes into the fresh water aquifer.
http://www.elmhurst.edu/~chm/onlcourse/chm110/outlines/saltintrusion.html
Desalination: removing dissolved salts from ocean or blackish
water in aquifers or lakes (slightly salty water)
Methods:
1.
Distillation: heating salt water until it evaporates, leaves
behind slats in solid form and condenses as fresh water
2.
Reverse osmosis: pumping salt water at high pressure
through a thin membrane with pores that allows water
molecules, but not dissolved salts to pass through
Problems:
(1) High costs for energy usage
(2) produces large quantities of briny wastewater that contains
lots of salt and other minerals (no where to disposal of without
causing environmental problems).
Better solution:
1. reduce waste water: 2/3 of water is wasted, can be reduced to 15%
(evaporation, leaks, and other losses)
2. Water recycle
Karst Topography: Sinkholes
Early development stage
Later development-horizontal
Flood plain development
Floodplain Features
Figure 11.21
Flood: water in a stream overflows its normal channel and spills
into the adjacent area (floodplain)
Benefits: provide productive farmland, recharge groundwater,
and help refill wetland.
Causes in Increased floods in City
1. Increases in percentage of impervious surfaces (reduce
infiltration and increase surface runoff)
2.
Paving, straightening, or “improving” stream channels
(reduces the time lag between rainfall and runoff)
3.
Landscaping and subdivision of the land into building sites
(shorten distance in water flow and thus time lag)
4.
Filling in and human settlement of flood plains (reduces
space for storing flood water)
Urban Flooding
Figure 11.28
New Orleans Flooding after Hurricane Katrina
Water pollution: any chemical, biological, or physical
change in water quality that has a harmful effect on
living organisms or makes water unsuitable for
desired uses.
1.
infectious agents/cause diseases ; example: bacteria,
viruses, parasites; sources: human and animal wastes
2.
oxygen-demanding wastes/deplete dissolved oxygen
needed by aquatic species ; Example : biodegradable
animal wastes and plant debris ; sources : sewage,
animal feedlots, food processing facilities, pulp
mills
3.
Plant nutrients/cause excessive growth of algae and
other species; example: nitrates (NO3-) and
phosphates (PO43- ); source: sewage, animal wastes,
inorganic fertilizers
4.
organic chemicals/toxins to aquatic systems;
example: oil, gasoline, plastics, pesticides, cleaning
solvents; source: industry, farms, households
5.
inorganic chemicals/toxins to aquatic systems;
example: acids, salts, metal compounds; sources:
industry, households, surface runoff
6.
Sediments/disrupt photosynthesis, food webs, other
processes; example: soil, silt; source: land erosion
7.
thermal/make some species vulnerable to disease;
heat; sources: electric power and industrial plants.
On June 22, 1969, an oil slick and debris in the Cuyahoga River caught
fire in Cleveland, Ohio, drawing national attention to environmental
problems in Ohio and elsewhere in the United States.
Impact on water quality and temperature on streams
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average nitrates content is 14 times greater; detergent content is 9 to 18 times greater,
amount of dissolved solids is 3-4 times greater in the urbanized Nassau County
stream, New York;
Urban streams are much warmer in summer (5°-8°C and up to 10°C) and
somewhat cooler (1.3°C to 5°C) in winter than their rural counterparts due to
increases in storm runoff, decreases in groundwater recharge, and removal of
vegetation around the banks.
Eutrophication: natural nutrient enrichment of lakes, mostly from runoff of plant
nutrients such as nitrates and phosphates from surrounding land.
Cultural eutrophication: human activities greatly accelerate the input of plant
nutrients to a lake (near urban or agricultural area; farmland, animal feedlots, urban
areas, mining sites, treated and untreated municipal sewage, atmosphere). Promote
growth of dense growth or bloom of organisms. These plant life reduce lake
productivity by decreasing the solar energy input needed by phytoplankton that
support fish. When algae die, the bacteria depletes dissolved oxygen in the surface
layer of water near the shore and in the bottom layer. Eventually produce gaseous
decomposition products such as smelly, highly toxic hydrogen sulfide and flammable
methane.
Development of Drainage and sewage disposal system
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Ancient Rome constructed drainage system to drain storm water runoff
(to rivers and estuary) only. (“It is not uncommon to threw wastes out
of the window onto street and to the people passing by”). (Privies
(outdoor toilets) were used, but their contents frequently oozed through the
basement walls of the occupied apartments beside them. In other places,
wastes were simply heaped on the ground or placed in pits in the centers of
courtyards; some courtyards were covered with filth up to the doorways of the
houses.)
In nineteen century, combined sewers were used. (Organic waste load
decomposed after entering the water body, exhausted dissolved oxygen, and
produced anaerobic conditions that accompanied by the offensive orders of
hydrogen sulfide and other putrid matter)
During mid-nineteenth century, a period known as the Great Sanitary
Awakening, Sir Edwin Chadwick led a crusade to build sewage treatment
facilities: construction of interceptor sewers that could drain to sewage
treatment plants.
In 1964, many cities in US have combine sewages
Waste water treatment
Primary waste treatment consists of removing the suspended solid
materials by screening, sedimentation, and floatation; requires 103
hours;
the solid materials form a sludge that is treated in digesters where the
organic material undergoes anaerobic decomposition;
outputs:
1.
a liquid effluent that still contains more than half of the dissolved
and suspended organic material from the raw waste; and
2.
the solid waste from the sludge digesters.
In Boston, the primary effluent is chlorinated to kill the pathogenic
bacteria and then released to the harbor through a system of offshore
outfall pipes. Sludge disposal is a relatively expensive part of waste
treatment. So, sometimes, it is dumped into the harbor.
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1. Preliminary treatment: Upon arrival via the sewer system, the
wastewater is sent through a bar screen, which removes large solid
objects such as sticks and rags. Leaving the bar screen, the wastewater
flow is slowed down entering the grit tank. This allows sand, gravel, and
other heavy material that was small enough not to be caught by the bar
screen to settle to the bottom. All the collected debris from the grit tank
and bar screen is disposed of at a sanitary landfill or recycled.
• 2. Primary treatment: the physical separation of solids and greases from
the wastewater. The screened wastewater flows into a primary settling
tank where it is held for several hours. This allows solid particles to settle
to the bottom of the tank and oils and greases to float to the top.
• 3. Secondary treatment: a biological treatment process that removes
dissolved organic material from wastewater. The partially treated
wastewater from the settling tank flows by gravity into an aeration tank.
Here it is mixed with solids containing micro-organisms that use oxygen
to consume the remaining organic matter in the wastewater as their food
supply. The aeration tank uses air bubbles to provide the mixing and the
oxygen, both of which are needed for the micro-organisms to multiply.
From here the liquid mixture, composed of solids with micro-organisms and
water, is sent to the final clarifier. Here the solids settle to the bottom
where some of the material is sent to the solids handling process, and
some is re-circulated to replenish the population of micro-organisms in
the aeration tank to treat incoming wastewater.
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4. Final treatment: Wastewater that remains is disinfected to kill harmful microorganisms before being released into receiving waters. Although there are many
methods available to kill these micro-organisms, chlorine and ultraviolet
disinfection are the most widely used.
De-chlorination occurs in the final wastewater treatment step. A solution of
sodium bisulfite is added to the chlorinated effluent to remove residual chlorine.
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Following disinfection and de-chlorination, the treated wastewater (now called
final effluent) can be returned to the receiving waters from which it came. The
flow is conveyed to an outfall and discharged through a series of diffusers into a
surface water body or stream.
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5. Solids processing
Primary solids from the primary settling tank and secondary solids from the
clarifier are sent to the digester. During this process, micro-organisms use the
organic material present in the solids as a food source and convert it to byproducts such as methane gas and water. Digestion results in a 90% reduction
in pathogens and the production of a wet soil-like material called “biosolids” that
contain 95-97% water. To remove some of this water and reduce the volume,
mechanical equipment such as filter presses or centrifuges are used to squeeze
water from the biosolids. The biosolids are then sent to landfills, incinerated, or
beneficially used as a fertilizer or soil amendment.
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More complete waste water treatment is available now
consists of 4 steps
http://www.regulatorystaff.sc.gov/ORSContent.asp?pageID=654
Anaerobic digestion component of Lübeck
mechanical biological treatment plant in Germany,
2007
Ground water pollution (Super Fund)
Is difficult and expensive to cleanup:
1. Contaminants are not diluted and dispersed effectively
2. Low concentration of dissolved oxygen and smaller
populations of decomposing bacteria, and cold
temperature, slow down chemical reactions that
decomposes wastes.
45% of municipal groundwater in US has been
contaminated by one or more chemicals; 76,000
underground tanks storing gasoline, diesel fuel, home
heating oil, and toxic solvents were leaking their content into
groundwater in the U.S in 2002.
Prevention is the most effective way
Coastal Pollution
• 40% world population live on or within 100KM (62miles) of
the coast and 14 of the world 15 largest metropolitan
areas (10 million or above) are near coastal waters.
• 1/4 of people using coastal beaches in the US develop ear
infections, sore throats, eye irritations, respiratory disease,
or gastrointestinal disease
• Runoffs of sewage and agricultural wastes into coastal
waters introduce large quantities of nitrate and phosphate
plant nutrients, cause harmful algae growth (red, brown,
or green toxic tides). They release waterborne and
airborne toxins that damage fisheries, kill some fish-eating
birds, poison seafood.
Quality of drinking water
• In developed countries, surface water is stored in
reservoir for several days to improve clarity and
taste by increasing dissolved oxygen content and
allowing suspended matter to settle; then pumped
to a purification plant and treated to meet
government drinking water standards.
• In US bottle water is 240 times to 10,000 times
more expensive than tap water (about ¼ of its tap
water, but 1/3 of bacteria contamination). Home
water treatment systems are not worth the expense
and maintenance hassles (unless contamination is
identified).
Drinking water contaminants
1. arsenic: a semi-metal element in the periodic table, it is odorless and tasteless.
It occurs naturally in the environment and as a by-product of some agricultural
and industrial activities; enter through ground or as runoff into surface water
sources;
Health impact: cancer of the bladder, lungs, skin, kidneys, nasal passages, liver
and prostate. The new standard is 10ppb in drinking water. Shot term effects
occur within hours of days of exposure, long term over many years.
2. Lead and copper:
Health impact: stomach stress and brain damage, especially for children under 6
years old. And stomach stress. Enter water through pipes. If lead
concentrations exceed an action level of 15 ppb or copper
concentrations exceed an action level of 1.3 ppm in more than 10% of
customer taps sampled, the system must undertake a number of
additional actions to control corrosion.
3. Microbial and disinfection byproducts
Microbial pathogens include a few types of bacteria, viruses, protozoa, and
other organisms. Some pathogens are often found in water,
frequently as a result of:
(1) Fecal matter from sewage discharges;(2) Leaking septic tanks; (3)
Runoff from animal feedlots into bodies of water
Health impact: epidemics such as typhoid and cholera
4. MTBE (methyl-t-butyl ether): MTBE is a member of a group of chemicals
commonly known as fuel oxygenates. Oxygenates are added to fuel to
increase its oxygen content. MTBE is used in gasoline throughout the United
States to reduce carbon monoxide and ozone levels caused by auto
emissions.
Releases of MTBE to ground and surface water can occur through leaking
underground storage tanks and pipelines, spills, emissions from
marine engines into lakes and reservoirs, and to some extent from air
deposition.
5. Radionuclides: A nuclide is a general term applicable to all atomic forms of an
element. Nuclides are characterized by the number of protons and neutrons in
the nucleus, as well as by the amount of energy contained within the atom. A
radionuclide is an unstable form of a nuclide. They may occur naturally, but
can also be artificially produced.
(1) Combined radium-226/-228; Naturally occurs in some drinking water sources.
Some people who drink water containing radium –226 or -228 in excess
of the MCL over many years may have an increased risk of getting cancer.
(2) (Adjusted) Gross Alpha; Naturally occurs in some drinking water sources.
Some people who drink water containing alpha emitters in excess of the
MCL over many years may have an increased risk of getting cancer.
(3) Beta Particle and Photon Radioactivity; May occur due to contamination from
facilities using or producing radioactive materials; Some people who drink
water containing beta and photon emitters in excess of the MCL over many
years may have an increased risk of getting cancer.
(4) Uranium; Naturally occurs in some drinking water sources. Exposure to
uranium in drinking water may result in toxic effects to the kidney.
6. Radon: Radon is a naturally-occurring radioactive gas that may
cause cancer, and may be found in drinking water and indoor
air. Some people who are exposed to radon in drinking water
may have increased risk of getting cancer over the course of
their lifetime, especially lung cancer. Radon in soil under homes
is the biggest source of radon in indoor air, and presents a
greater risk of lung cancer than radon in drinking water.
Good drinking water:
Low BOD (biological oxygen deman)
Low coliform organisms
Low sediment load