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Water and Wastewater Plant Directory
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Swindon, Wiltshire, England
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Swindon Sewage Treatment Works
Swindon STW,
Barnfield Road
Swindon, Wiltshire, SN2 2DP
England
Contact Information:
Contact:
Email:
Telephone: 0845 9200 800
Fax: N/A
Plant Operation: Municipal
Processing: Wastewater
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Web site:
http://www.thames-water.com
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Plant/Process Description:
Swindon STW was the first site within Thames
Water to have Acid Phase Digestion.
A 17 million Pound project to upgrade Swindon
Sewage
Treatment Works has received a major award from
the Institution of Chemical Engineers.
The plant has been upgraded to meet new treatment
standards which will be introduced by the
Environment Agency, and the capacity of the works
has been increased by 25 per cent, to meet
population growth in the area.
Improvements have also boosted the quality of
water discharged into the River Ray and the
sludge recycled from the works as soil
conditioner for local farms.
Engineers also installed a process
called “biological nutrient removal” which has
substantially reduced the amount of phosphates,
commonly found in detergents, released into the
river.
The improvements were carried out without the
need to expand on to the surrounding land, which
Thames Water has made into a wildlife
sanctuary.
Thames Water Project Manager Nigel McClatchey
said: “The award recognises our commitment to
improving the quality of water discharged into
the River Ray and meeting the needs of the
growing population in Swindon and
Wroughton.”
Swindon wastewater treatment works serves a
growing population of 200,000. Water used in
Residential, Commercial and Industrial is classed
as dirty water. Before it can be put back into
the river, it has to be cleaned or treated. There
are harmful Chemicals and Bacteria in the water,
which can harm the Environment, Wildlife, and
Humans.
The water goes through many processes. There are
four main categories:
· Preliminary
· Primary
· Biological
· Final treatment
Wastewater comes into the works via the main
gravity pipeline and two main pump stations, one
at ‘Barnfield Road’ and the other at ‘Nine Elms’
Sewage pumping stations are used to assist
gravity in getting raw sewage from its places of
Origin to Swindon’s Treatment Works for
treatment.
Sewage can only travel down hill so far before it
has to be lifted back to a higher level to start
its downhill run again.
Sewage pumping stations exist all around the
sewage network and have stand alone controls
which keep these unmanned stations operational or
warn Thames Water Operators by Telemetry via
Waste Control Centre when something goes wrong.
The average flow per day at Swindon Treatment
Works is 49,000M3
Preliminary treatment at Swindon starts with the
flow being measured if the flow is greater then 6
X Dry Weather it overflows into our storm
tank.
The flow passes thru the ‘Coarse Bars’ these
protect the works from any large objects which
could damage the ‘Screens’.
The ‘ 6mm Perforated Screens’ are designed for
the removal of rags, plastic, wood and any other
floating material known as ‘Screenings’
The ‘Screenings’ are discharged into launder
channels and ‘Wash Water’ helps deliver
the ‘screenings’ to the ‘WashPactors’
The ‘Washpactors’ creates turbulence, which
breaks down the faecal matter within the
screenings. This cleans the screenings and they
overspill into a screw compactor, which acts like
a sieve to drain of the dirty water, at this
point clean water is sprayed over the screenings
to rinse and eliminate any residue.
Washed ‘Screenings’ are forced by backpressure up
the shoot and into the skip to wait landfill.
Meanwhile the main flow continues and is measured
by the 3 X Dry Weather Overflow.
Anything greater will be sent to the ‘Storm
Tank’
The next stage is ‘Grit Removal’ for this process
it is important to slow the flow down to 0.3m/l
so that the grit (Road chippings, metal
fragments, sand, material from damaged sewers
etc) settles.
The flow is reduced with help from the Dorr
Oliver Detroiter.
The Rotating Detroiter pushes the grit towards
the ‘Grit Donkey’.
The ‘Grit Donkey’ acts like a conveyor belt in
respect to the way it removes the grit.
To prevent Organic materials being removed, an
Organics pump has been installed, this will
create a gentle current, which will send Organics
back into the main flow.
A sign that the Organics pump is not working is
Sweet corn in the Grit Skip.
Now that the Preliminary treatment is complete,
the sewage flows by gravity to the Inlet Wet
Well.
From here it is pumped to the P.S.T Main
Distribution Chamber.
The Raw sewage is distributed into the
12 ‘Primary Settlement Tanks’
In most Waste Water Treatment Works, gravity
takes the raw sewage to these tanks. However here
at Swindon Treatment Works the primary tanks are
elevated so a pump is needed.
The Raw sewage is distributed into the
12 ‘Primary Settlement Tanks’ All of the primary
tanks have a half bridge scraper. The Wastewater
stays in the primary tanks for 2-4 hours
depending on flow, allowing roughly 50 to 70% of
the suspended solids to settle, 65% of oil and
grease are removed here. The liquid contains
about 10 million bacteria per litre.
The half bridge scraper travels round the primary
tank and scrapes the sludge from the bottom of
the tank into the centre of the tank. This
organic waste or 'sludge' is then pumped away to
the Primary Raw Sludge Sump.
‘Settled Sewage’ overflows…
The ‘Settled Sewage’ now passes to biological
treatment Aeration Lanes 1 - 5
Biological Nutrient Removal (BNR) is a method of
removing Nitrogen and Phosphorus at the same
time. High phosphorus levels in rivers encourage
algae to grow and an excess of algae can also
kill fish due to a lack of oxygen in the water.
Ammonia and Phosphorus levels are regulated by
the Environment Agency.
Phosphorus comes from human waste, industrial
trade waste, detergents and household cleaning
products we remove Phosphorus chemically by the
use of ferric chloride, which is dosed directly
into the aeration lanes…
There are 3 main parts to the Aeration lanes…
*Anoxic Zone*
No diffusers in anoxic zone.
Return activated sludge rich in nitrate mixes
with wastewater.
Biological breakdown of nitrate to nitrogen gas
De Nitrification takes place.
*Anaerobic Zone*
No Oxygen Present
Microorganisms require food in the form of
Volatile Fatty Acids (VFA’s)
Microorganisms exchange VFAs for internal
phosphate
Phosphate released into wastewater
In the presence of oxygen, phosphate starved
microorganisms take up excessive amounts of
phosphate from the wastewater. This is called
LUXURY ‘P’ UPTAKE.
This reduces the total phosphate in the
effluent.
*Aerobic Zone-Nitrification*
In the presence of oxygen in the aerobic zone,
microorganisms convert ammonia to nitrate
This nitrate is recycled back through the RAS
back to the start of the process in the anoxic
zone.
Factors that will affect BNR performance:
· Upstream processes
· PST operation /sludge thickening
process
· Sludge age
· Oxygen distribution
· FST Operation.
Biological treatment processes vary but the 2
most common are Bio filters or Activated sludge,
the effluent is now distributed to the ‘Final
Settlement Tanks’
This is where any remaining suspended solids are
removed. The sludge collected in these final
tanks is returned back into the inlet of the
aeration lanes, this is known as R.A.S (Return
Activated Sludge) depending on the position of
the Boll Mouth the flow of R.A.S being returned
to the Aeration lanes can be increased or
decreased.
Activated Sludge is taken to the top of the lanes
via big Archimedes screws instead of pumps this
is so the Activated Sludge is not damaged.
We remove excess Activated Sludge…
If we fail to Surplus, the sludge blankets in the
F.S.T’s would continue to rise and spill causing
serious environmental issues.
We monitor the mixed liquors and blanket levels
to determine how much Return Activated Sludge we
need to surplus.
The Final effluent spills over the Final
Settlement Tanks…
The Final Effluent passes through the ‘Wash Water
Chamber’.
This chamber contains 4 pumps. Water is pumped
back to the works to be used as Wash Water. There
is a Penstock here, which will close
automatically in the event of a Blanket
spill
Ammonia is a contaminant in sewage and must be
reduced to a consented level before it is
discharged into the River.
The final effluent passes this Ammonia Monitor
seen below it works by reacting the ammonia with
chemicals reagents which release ammonia as a gas
which then produces an electric signal at the
probe.
However these Ammonia Monitors require regular
maintenance to ensure accurate readings. The
information sent from this Ammonia Monitor to our
S.C.A.D.A system is not reliable so a manual
sample must be taken regularly.
The Sludge Stream at Swindon Continued....
From the Primary Sludge Sump, The Raw sludge is
pumped into the Raw Sludge Buffer Tank which is a
holding tank to eliminate Lag.
Feed pumps, pump the Raw sludge from the Buffer
Tank into the Drum Thickeners.
A Drum Thickener is a rotary screen used to
thicken sludge. The main frame is constructed
with stainless steel. Mounted on the frame of the
drum thickener is a wire cylindrical drum, chain
driven. Under speed is monitored by a rotation
sensor.
Un-thickened sludge is fed in at the drive end,
through a launder pan, which distributes the
liquor inside the drum. VFA's drain through the
drum into the under pan to the filtrate discharge
pumps.
The VFA’s are pumped from the tank back to the
Aeration Lanes 1-5 via these pumps.
The thickened sludge is discharged at the non-
driven end into the sludge hopper, which feeds
the sludge pump. Probes are located in the hopper
to control the sludge pump and stop the drum
thickener in the event of excessive high
levels.
Located on the feed pipe is an injecting and
mixing device. It injects Polyelectrolyte into
the sludge line.
Polyelectrolyte is a dewatering agent. It is a
flocculent which helps the sludge particles stick
together.
The Poly is delivered in a powder form in 800kg
bags, The Powder Poly fills a hopper which will
give an alarm signal if the powder level becomes
low.
The blower mounted under the hopper blows the
Polymer into the mixing tank. The Polymer is
mixed together with water; the solution is
stirred for approx one hour before it is ready to
be injected via the poly dosing pumps.
This Thickened Primary Sludge is pumped from the
Hopper of the Drum Thickener to the ‘Blending
Tank.
The Surplus Activated Sludge is fed from the ‘SAS
Holding Tank’ into the ‘SAS House’.
The Suspended Solids in the Surplus Activated
Sludge form coagulated flocks and are separated
from liquid by adding Polymer flocculent.
The coagulated sludge is fed onto the Porous SAS
belts allowing the liquid to pass through as
filtrate. And the larger flocks larger then the
porous belt remain on the belt as concentrated
sludge.
The filtrate is discharged into the Bottom
Drainage Reservoir where it is pumped back to the
head of the aeration lanes.
The solids are carried to the end of the belt and
dropped into a hopper.
The thickened secondary sludge is collected in a
Hopper where it is pumped to the Blending Tank
where it mixes with the thickened Primary sludge
from the ‘Drum Thickeners'.
The next stage for the Primary Thickened Sludge
and the Secondary Thickened Sludge, which have
been mixed together in the Blending Tank, is Acid
Phase Digestion (APD)
The APD process is the start of the digestion
process.
The function of this APD is to provide optimum
conditions for growth of bacteria to break down
the sludge before its transfer to the Digestion
stage, which coverts the VFA into gas.
The APD improves the overall E.coli reduction in
the final product due to the acid condition in
the APD tank.
This APD was designed and constructed as part of
the AMP3 improvement at Swindon STW.
The main aims of the installation of the APD were
to improve the quality of the final product in
terms of compliance.
The APD has also been known to increase digester
gas production and reduce final product quantity
for disposal.
The APD also provides extra digestion capacity
for Swindon’s growing population.
The retention time of the APD is 1-3
days.
To Be Continued..............
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Owner:
Thames Water
Web site:
http://www.thames-water.com
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Operating Company:
Thames Water
Web site:
http://www.thames-water.com
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Directions:
Swindon West, Next to the main Bus Depot!
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Disclaimer:
Water and Wastewater.com provides the information on
this page for reference purposes only. We do not certify
the accuracy of the information provided by third-party
individuals for this listing.
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