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Renewing Old Sewers The Example of London
By Jefferson Coultas
(0518053)
How Old Is London’s Sewer System?• Combined sewer system designed by Sir Joseph
Bazalgette in 1858 • Completed in 1865
Why have changes to the original system been necessary?
Population growth and the expansion of London
Mogden Treatment Plant – West of London
Riverside and LongReach.- East of London
Riverside
LongReach
Development of new treatment technologies
The original STWs
Inlet from sewers
Liming Station
Precipitation Channels
Settlement Channels
Discharge
(into Thames)
Storage Tanks
Shipped out to sea for dumping
Solids
Consolidated sludge
20th century developments to STWs
Inlet from sewers
Coarse screens
Fine screens
Constant velocity channel
Primary sedimentation tank
Aeration tank
Final settlement tank
BOD/AmmN measurement
Discharge
R.A.S.
S.A.S.
Cleansing
Landfill
Shipped out to sea for dumping
Rebuilding, repair and maintenance to sewer pipes
• London’s sewers are periodically inspected using CCTV or by human inspection
• Cleaning and removal of grease and fat is carried out periodically
• Repairs are carried out when necessary by; repointing of masonry interceptor sewers, cement mortar spray lining and cured in place pipe linings (CIPPs)
• When the sewer is in danger of collapse a full rebuild may be required
Introduction of new legislation
Set higher effluent standards and banned the dumping of sewage sludge out at sea
The Urban Waste Water Treatment Directive, UWWTD
Introduced by the European Commission in 1998
At Beckton and Crossness
The sludge is thickened before being incinerated in order to generate power
The sludge at Riverside is currently pumped to Beckton for incineration.
At Mogden and Longreach
The sludge undergoes thickening processes before being passed through an anaerobic digester.
The digestion process emits methane (Biogas)
This is used to power part of the site
The digested sludge is recycled as agricultural fertilizer.
Changes to the sewage sludge disposal procedure
Climate changeOver the past 100 years the intensity of UK precipitation has increased
Over the last 40 years the total precipitation has also increased
Urbanization Covering up once permeable surfaces with impermeable materials, such as concrete and tarmac.
This prevents rainfall percolating into the ground.
London’s population in 1958 (when Bazalgette designed the system) was approximately 2.5 million
Bazalgette designed the system for a future population of 4 million.
London’s population is now approaching 8 million and rising
Population Growth
What are the challenges faced by London’s sewer in the 21st Century?
What happens when the sewers reach full capacity?
Excess content (which is a mixture of sewage and surface runoff) is discharge directly into the Thames via 57 combined sewer overflows, CSOs
However, if this doesn’t happen quickly enough localised flooding in basement properties of low lying catchments can occur
Local Flooding
£346m investment by 2015 to protect 2,500 properties from flooding.
• Counters Creek
• Chelsea and Kensington
• Newham.
Short term solution - Installation of FLIP devices
A small pump with a non return valve for low gradient connections
Long term solution – Construction of storm relief sewers
A storm relief sewer diverts the flow from bottleneck zones and provides extra capacity during periods of intense rainfall
Are combined sewer overflows acceptable?
• 39m tonnes of raw sewage is discharged into the Thames each year
• Discharges occur once a week
• Triggered by as little as 2mm of rain
The UWWTD states that pollution from CSOs must be limited
The Water Framework Directive, WFD (new)
Requires member states to achieve “good ecological” status by 2015
Good ecological status refers to river bodies that have only slightly differing ecological properties to a similar river that has not been subject to human activity
Failure to comply with the UWWTD or WFD will result in EU fines typically of the order of £100m per annum
Thames tideway strategic study
Study undertaken by the Thames Tideway Group
The EA classified the 57 CSOs by their environmental impact
34 polluting CSOs were identified
Conclusion
To meet the standards set by the UWWTD and WFD…
The 34 CSOs must be intercepted
The treatment standards must also be improved at Crossness, Longreach and Riverside
The Thames & Lee tunnels
Thames Tunnel (£3.6bn)
• 7.2m diameter
• 22km long
• Up to 75m deep
• 2020 Completion
Lee Tunnel (£635m)
• 7 m diameter
• 6.9 km long
• 2014 Completion
Technical detailsExcess fluid is diverted to the tunnel just upstream of the CSO
If the tunnel reaches full capacity the excess fluid will overflow via the existing CSOs
The project will intercept 96% of the fluid discharge to the Thames
Main challenge is the site selection for the drop sites due to;
• Their central location,
• Visual impact and
• Ocassional foul odours
Draindown and pumping operation
Full height walls with isolating penstock will be installed at various locations along the tunnel to enable sequential rapid draindown of tunnel sections
At Beckton, a pumping station will be built consisting of 6 pumps (4 operational and 2 standby) with a running power of 3.5 Mw per pump
Sewer treatment plant upgrades
Higher treatment standards and increased capacity will be achieved by upgrading the existing treatment works
The upgrades at each treatment plant will involve renewing the existing equipment and the installation of additional treatment streams
Treatment Works
Current Proposed
Flow (Ml/d) BOD (mg/l) AmmN (mg/l) Flow (Ml/d) BOD (mg/l) AmmN (mg/l)
Beckton 1420 6 1 2336 8 1
Crossness 982 10 7 1118 8 1
Mogden 810 11 1 1064 11 1
Longreach 311 20 25 328 10 3
Riverside 200 15 20 206 8 1
The odour impact at each site will be mitigated by enclosing many of the treatment processes in buildings and treating the air before extraction
Total cost will be £675m
2014 completion
2012 completion
Renewable energy generationBeckton, Crossness and Riverside
Biogas ProductionInlet from sewers
Coarse screens
Fine screens
Constant velocity channel
Primary sedimentation tank
Aeration tank
Final settlement tank
BOD/AmmN measurement
Discharge
R.A.S.
S.A.S.
Cleansing
Landfill Incineration
Picket fence
thickening
Belt thickening
Thermal Hydrolysis Pre heating
Anaerobic digestion
Methane (biogas)
Sludge cake (used as fertilizer)
Wind turbines at Beckton & Crossness
Impact on user’s bills
Average bills are expected to rise by over £1 per week by 2018
Summary
Improvements have been made to London’s sewer system to;
• Allow for the expansion of the city • Treat the effluent to higher standards, • Avoid the collapse or leaking of sewer pipes• Dispose sludge sustainably • Prevent surcharging of the sewers• Minimise the untreated discharges of the
combined sewage overflows
Thank you for listening!
Any questions?
References• Slide 1• Jason Hawke, Aerial photographer Jason Hawkes. News. Retrieved 01/03/2011 from http://news.jasonhawkes.com/2007/09/• Slide 2• London evening standard, Bazalgette and his successor: The men with tunnel vision. Retrieved 01/03/2011 from
http://www.thisislondon.co.uk/lifestyle/article-23792076-bazalgette-and-his-successor-the-men-with-tunnel-vision.do• Floating down the river. Retrieved 02/03/2011 from http://www.the-river-thames.co.uk/environ.htm• Slide 3• Jacobs Babtie, Office of water services, 2006. Retrieved 01/03/2011 from http://www.thameswater.co.uk/cps/rde/xbcr/corp/ofwat-independant-review.pdf• Slide 4• English Heritage, 2009, Chimney to Beckton Sewage Works, East Ham . Retrieved 5 January 2011 from
http://www.britishlistedbuildings.co.uk/en-506196-chimney-to-beckton-sewage-works-east-ham• Thames Water, 2006, Solutions Working Group Report, Volume 2 – Treatment : Table 3.1, p8. Retrieved 5 January 2011 from
http://www.thameswater.co.uk/cps/rde/xbcr/corp/working-group-report-solutions-vol-2.pdf• Slide 5• REINFORCED plastics, 2004, Composites renovate deteriorating sewers. Retrieved 05/03/2011 from
http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VMX-4CNCSN5-V-9&_cdi=6162&_user=585204&_pii=S0034361704003388&_origin=gateway&_coverDate=06/30/2004&_sk=999519993&view=c&wchp=dGLbVzW-zSkWb&_valck=1&md5=6984f1c3bbc18b1d27cbc2a7e182be5d&ie=/sdarticle.pdf
• UKSTT, United Kingdom Society for Trenchless Technology. Retrieved 05/03/2011 from http://www.ukstt.org.uk/trenchless_technology/localised_repair/• Slide 6• Defra, 2006, Sewage Sludge. Retrieved 6 January 2011 from http://www.defra.gov.uk/evidence/statistics/environment/waste/wrsewage.htm• Slide 7• Thames Water, 2006, Solutions Working Group Report, Volume 2 – Treatment : Table 3.1, p8. Retrieved 5 January 2011 from
http://www.thameswater.co.uk/cps/rde/xbcr/corp/working-group-report-solutions-vol-2.pdf• Slide 8• Thames Water, 2007, London’s Victorian sewer system. Retrieved 6 January 2011 from http://www.thameswater.co.uk/cps/rde/xchg/corp/hs.xsl/10092.htm• Slide 10• Thames Water, What we’re doing to combat sewer flooding. Retried 6 January 2011 from http://www.thameswater.co.uk/cps/rde/xchg/corp/hs.xsl/7497.htm • Thames Water, 2010, Counters Creek Strategic Sewer Flooding Alleviation. Retrieved 6 January 2011 from
http://www.thameswater.co.uk/cps/rde/xbcr/corp/counters-creek-methodology-statement-june-2010doc.pdf• Slide 11• European Commission, 2000, Directive 2000/60/EC of the European Parliament and of the Council . Retrieved 8 January 2011 from
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:2000L0060:20090625:EN:PDF• Slide 12• Thames Water, 2006, Solutions Working Group Report, Volume 1 – Tunnels and Shafts . Retrieved 8 January 2011 from
http://www.thameswater.co.uk/cps/rde/xbcr/corp/working-group-report-solutions-vol-1.pdf • Slide 13• Thames Water, 2011, View preferred Thames Tunnel route. Retrieved 12 January 2011 from http://www.thameswater.co.uk/cps/rde/xbcr/corp/thames-tunnel-route.pdf• Slide 14• Thames Water, 2010, Site Selection Background Technical Paper: Figure 3.1, p11. Retrieved 10 January 2011 from
http://www.thameswater.co.uk/cps/rde/xbcr/corp/tideway-site-selection-technical-summary.pdf• Slide 15• Thames Water, 2006, Solutions Working Group Report, Volume 2 – Treatment : Table 3.1, p8. Retrieved 5 January 2011 from
http://www.thameswater.co.uk/cps/rde/xbcr/corp/working-group-report-solutions-vol-2.pdf• Slide 16• Greater London Authority, 2010, planning report PDU/2151a/01 Crossness Sewage Treatment Works . Retrieved 11 January 2011 from
http://static.london.gov.uk/mayor/planning_decisions/strategic_dev/2010/20101006/crossness_sewage_treatment_works_report.pdf• Neyens, E and Baeyens, J, 2003, A review of thermal sludge pre-treatment processes to improve dewaterability . Retrieved 12 January 2011 from http://www.sciencedirect.com/science?
_ob=ArticleURL&_udi=B6TGF-47XSXVX-2&_user=585204&_coverDate=03/17/2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1604970164&_rerunOrigin=google&_acct=C000029838&_version=1&_urlVersion=0&_userid=585204&md5=0ae91a4bd1b74e5bb76a3befb0e7ebf2&searchtype=a
• Thames Water, Crossness Sewage Treatment Works. Retrieved 12 January 2011 from http://www.thameswater.co.uk/cps/rde/xchg/corp/hs.xsl/10097.htm• Slide 17• Thames Water, Thames Tunnel. Retrieved 10 January 2011 from http://www.thameswater.co.uk/cps/rde/xchg/corp/hs.xsl/10115.htm
Aeration tankThe activated sludge process
• Invented by Arden and Locket in 1914
• Used in sewage treatment for the first time in 1932
• The process involves mixing the influent (following primary treatment) with a mass of micro-organisms in an aeration tank
• Oxygen is pumped into the tank for several hours which promotes the digestion of organic dissolved matter by the micro-organisms
• The process converts the dissolved solids into suspended solids which are removed in a final settlement tank
Counters Creek project
Replacing existing pipe
Online replacement – Replace the existing sewer in the same location
Offline replacement – Build another sewer section parallel to the existing sewer. May decide to keep the existing sewer in operation and reduce its capacity.
Cut and fill
Excavate down to the level of the existing sewer and replace the sewer where necessary. Causes a high degree of disruption.
Trenchless technologies
• Pipe Bursting – An expanding device is introduced into the existing pipe. This device shatters the existing pipe and brings in the new pipe behind it. Has been used on pipes up to 600mm diameter.
• Pipe Splitting – Same as pipe bursting but used
on steel, iron or polyethylene pipes.
• Pipe Eating – Microtunnelling technique wherein the existing pipe is
excavated with surrounding ground using a TBM with a rock-crushing tunnelling shield. The excavated ground and pipe remnants are extracted and the new segmental pipe is inserted in its place. Available for pipe diameters of 200 – 600mm.
Sewer repair and lining
• Repointing of masonry sewers
• Resin injection – Injection of an epoxy resin or mortar to seal cracks
• Robotic repair – One robot removes encrustations and smooths surface and a second report applies an epoxy mortar
• Cement mortar and epoxy spray linings – Sprayed onto the interior of pipe to protect against corrosion
• Thermosetting and UV setting in place pipe linings – Custom made adhesive sleeve is introduced into clean pipe and inflated with compressed air to fill the pipe. The lining is then cured using heat or ultraviolet light. A robot notes the locations of the connections and once the lining is cured returns to cut holes in the lining at connection points. Pipes up to 2.7m have been repaired in this way.
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