Waste Water Treatment - Science, Class 7 Video Lecture

have you ever wondered where all the
rainwater goes or the snow once it melts
or the water in your sink table or
toilet after you've used it this
wastewater flows through the underground
sewer system to a treatment plant the
plant removes most of the pollutants
then releases the water into a lake or
river the underground sewer network
feeds into a regional interceptor which
is a kind of sewer highway that runs to
the treatment plant the action begins at
the plants pumping station it doesn't
look much from above but the building
extends some 15 stories below ground
right through solid rock
the waste water collects in huge
underground wells it's not a pretty
sight it's full of dirt rubbish and Wow
you know the rest it also contains high
levels of phosphorous a poisonous
element in the nitrogen family harmful
to waterways because it promotes the
growth of algae the water flows from the
wells to giant pumps that force it to
the surface the plant has backup
generators to keep the pumps working in
case of a blackout and devices to
prevent water from backing up should a
pump have to be shut down for servicing
once the wastewater reaches the surface
it flows through the pumping station
down discharge channels leading to the
treatment building along the way it
sprayed with either aluminium sulfate or
ferric chloride to chemical coagulants
they gradually transform phosphorus in
the water from liquid to solid so it can
be removed later on once the water
reaches the treatment building it flows
through screens this preliminary
filtration removes any solids larger
than 2.5 centimeters in diameter such
things as stones paper and plastic
giant presses compact this rubbish
squeezing out the excess water trucks
then hold the stuff to a landfill where
it's buried the wastewater meanwhile
flows into large tanks called grit
chambers grit refers to the particles in
the water such as gravel that are
inorganic meaning they don't decompose
or burn these particles some as tiny as
a grain of sand gradually settle to the
bottom then they're pumped out and
trucked to the landfill to remove
organic particles mainly phosphorus they
add a polymer a type of chemical
compound this demonstration shows what
happens remember as the waste water left
the pumping station it was sprayed with
a coagulant that transformed the
phosphorus in the water into solid
particles the polymer solution completes
the process it binds those particles
forming what are called flocs masses of
phosphorus that look like snowflakes
they're heavier than water so they sink
to the bottom
and that's exactly what occurs in the
plant clarify tanks it takes about two
hours for the flocks to settle at the
bottom forming a layer of sediment
called sludge a system of rakes and
pumps collects it and transfers it to
the sludge treatment building unless
testing shows a need for additional
treatment the clarified fully treated
wastewater now flows to what's called
the outfall a series of channels that
discharge into the river in the sludge
treatment building they spray the wet
sludge with another type of polymer this
further solidifies it so that the filter
presses can more easily squeeze out the
water most of the sludge goes into giant
incinerators to be burned the ashes go
into a landfill the gas that the
incinerators admit powers several
machines that dry and transform the
remaining sludge into pellets these
pellets are sold as organic fertilizer
when it arrived at the plant the
wastewater was full of contaminants that
can harm life now after treatment
it contains 80% fewer suspended solids
and 75% less phosphorus and it also
smells a lot better