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Printer Friendly VersionSelected Information - Completed Research

CP367  The Effect of Reduced Water Usage on Sewer Solid Movement in Small Pipes Sewerage
Project Appreciation and Objectives

Reducing water consumption, for example, as detailed in the Code for Sustainable Homes (CSH), will result in less wastewater being passed to sewer. Previous investigations have shown that considerable savings can be made through the use of low flush WCs. However, other research has suggested WC flushes are the main vehicle for moving sewer solids in small pipes with intermittent flows leading from houses. There is therefore a risk that reduced water use could inadvertently lead to problems with the movement of sewer solids; potentially increasing the likelihood of blockages and property flooding/environmental pollution incidents.

This project provided a practical investigation to better understand the link between reduced water usage and increasing problems with solid movement in small pipes. This work will forewarn sewerage undertakers and regulators as to the type and scale of problems that may be expected with reduced water usage.

The experimental programme was designed in collaboration with Prof David Butler of the Centre for Water Systems at the University of Exeter.

Benefits to Clients

Improved understanding of the link between reduced water usage and potential problems with solid movements in low flows, will establish whether:

  • Installing water saving devices in properties with drains built to current standards will have an impact on drain serviceability.
  • The widespread use of water saving devices in an area (e.g. a new development) will have an impact on the serviceability of sewers built to current design standards.
  • There is a need to change existing design standards for drains and sewers to reflect lower water usage.

Work Programme

    Collation of existing information on: sewer solid movement and intermittent flows in small diameter pipes; and, reduced water usage.

  1. Development of a testing schedule.
  2. Rig scale testing.
  3. Assessment of the test results, including interim meeting.
  4. Limited further testing.
  5. Project reporting and dissemination meeting.

Project Output

  • Interim and final report, including the full test results.

  • Charts showing 'safe operating envelopes' for different combinations of:

    • water reduction/WC flush; and,
    • solids/flushable and disposable products.

Related WRc Work

  • Postgraduate Training Partnership Project - Small Bore Sewers, 1996-2000.
  • Various research regarding sewer solid movement in small diameter pipes over the last 10 years.
  • Flushability of Disposable Products, CP311, 2006-2008.
  • "Less Water to Waste" Environment Agency, 2007

WRc's Portfolio Programme
Summary of the £1.5 million per annum research programme

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