Combined Sewage Outflow Monitoring

What is combined sewer overflow?

Combined sewer overflow (CSO) is the discharge of a combination of storm water and domestic sewage waste water caused by sewer capacity being exceeded during heavy storms.  When waste water exceeds the sewage system's capacity, storm and sewage water is directed into CSOs which flow into streams, rivers and the sea, through outfall pipes. CSOs provide a failsafe during heavy storms to stop household domestic sewage waste and storm water backing up through the system and flooding peoples' homes and streets.

The CTG  BACTI-Wader and the BOD-Wader enable  in situ r eal-time reporting of Bacteria within natural water systems and are effective tools for monitoring transitional and coastal waters to detect outflow events from waste water treatment works (such as Combined Sewage Overflows) and farm slurry.

The sensors detects fluorescent proteins that are inherent within sewage and slurry.  The principle behind the measurement is the excitation of Tryptophan-like fluorescence within UV wavelength band, which is highly sensitive and has been shown to correlate with bacterial contamination. 

The National Water Quality Instrumentation Service (NWQIS) has been working with local environment officers and Chelsea Technologies deploying and trialing the Chelsea BACTI-Wader  to help detect high levels of sewage pollution in bathing waters off the UK coast. 

Combined Sewage Outflow


Applications for the BACTI-Wader & BOD-Wader include:

  • Combined Sewage Overflow (CSO) event detection
  • Bathing water quality monitoring
  • Faecal Indicator (FI) monitoring
  • Assessment of bathing & shellfish waters
  • River pollution surveillance and investigative monitoring
  • Point source pollution surveys

Contact Us:

55 Central Avenue
West Molesey

Tel: +44 (0)20 8481 9000
Fax: +44 (0)20 8941 9319

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