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.