Lecture Eight

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17 Dec 2010
Lecture 8
Urban Ecosystems, Pollution
Urban Ecosystem Analysis
During the last 15 years new understandings of cities as complex ecosystems
Cities are now seen as complex organisms with their own metabolic processes
They have huge inputs and outputs that are structured by metabolic processes of
production, delivery, consumption and waste emission
Inputs and outputs can be measured and where necessary can be influenced by public
It is critical to the understand the nature of inputs and outputs
To be able to reduce waste u need to know what is going on in a city- u cannot influence
until u know what is happening. Need to understand nature of inputs and outputs
Water inputs and outputs
Water is one of the most important urban inputs
Ensuring quality water supply is important for health
Polluted water is one of the main urban outputs
One of the key achievements of 19 century sanitary revolution was the development of
public water supply and waste water removal infrastructure
Initially just pipes to dump water downstream, later primary treatment secondary
treatment, tertiary treatment systems were added
Polluted water dumped somewhere else which is fine if u dump downstream and u r near
a lake, the problem is downstream people will get sick
Primary waste treatment was streams, let water and small particulates keep flowing,
secondary system= settling ponds , putting bacteria and aerating the water, bacteria
metabolized most of the organic matter and the other junk was filtered out ( rubber, paper
clips, that doesnt dissolve) so water is actually quite clean. Tertiary systems= take out not
just organic stuff but actually toxic material, example heavy metals that goes into sewer
systems, organic solvents. Now people are developing ways of cleaning toxic waste out of the
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system. There has been a progression of figuring out how to deal with more complicated
stuff thats in the waste water stream
Current Water Challenges
Arise partly from dominant sewer technology
Combined sanitary and storm water sewer systems used one set of pipes for all waste water
in cities
Works well in dry weather, but heavy rain events routinely overloaded the system and water
released into streams, rivers, lakes
Billions of gallons of untreated waste into water bodies
Gradually cities were rebuilding systems to separate sanitary and storm sewers
Storage for storm water surges
Problem of combined sewer system is that it only works when it is not raining. The problem
is when u have rain, almost all combined sewer systems ever built cannot handle storm
water surges so they dump untreated billions of gallons in nearby river and lake. One of the
solutions is separating the systems, trying to divert he storm water so it s=doesnt go into
the sewerage plan, building double sets of pipes. Storm water retention ponds. In new
suburbs the requirement in Ontario is that if u build a subdivision u have to keep storm
water on site, the parks are low lying areas. If u have huge heavy rain, there is an incentive
system to take water from roof and take it into garden so it will leak into the ground.
Enormous tunnel underground which holds certain cubic meters if water is for storm water
retention. When u have a surge of water it gets diverted fills up the tunnel and next day
after rain has stopped they start pumping it back out,
Current water challenges-2
Point source and non point source
Point sources are those where there is a clear point of discharge e.g. factories, sewers etc
with a pipe that discharges liquid wastes
These are relatively easy to monitor, and considerable progress in cleanup
Non point source pollution is everything else including pesticides and fertilizers on lawns,
dog feces and pollution on roads (anti freeze, gasoline, and tire rubber)
Things that dont have a single location. In a lot of cities dog shit is a big source. Non point
source is target for tertiary treatment system. Chemicals on the surface of the roads are
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