Transport of deformable solids within building drainage networks

Water conservation will become a design requirement in the provision of new build in response to both demographics and climate change. Measures to reduce per-capita water usage in both domestic and commercial buildings will reduce disproportionately the flow available to remove waste solids flushed into branch drains within or close to the building. The reduced flow loading of the sewer network will of necessity represent a lower percentage change. There is therefore a need to understand fully the mechanisms of solid transport close to the head of the network where solid transport takes place within an attenuating discharge flow and to provide design guidance. Extensive laboratory research and a major study of faecal and waste solid transport in installed systems are presented as a basis for identifying a suitable model for deformable solid transport. The results of these programmes have been confirmed by simulation models developed independently that in turn provide the basis for predicting the capability of low flush volume and dual flush toilets to transport deformable solids over acceptable lengths of drain within or close to the building. These simulations are available as assessment tools to aid system design and the development of codes and regulations recognizing the importance of waste removal within a water conservation-conscious environment.