The paper describes the first stages of a study of the origin, transport, and fate of sewer gross solids. The background to the project, its overall plan, and relevant previous studies are outlined. Progress to-date is described. A laboratory study of physical degradation of gross solids has confirmed general existing field observations that many sanitary solids undergo little degradation, whereas toilet paper and faeces are readily degraded. A study of solid advection and deposition in a laboratory pipe system has covered a wide variety of sanitary and artificial solids. The velocity at which sanitary solids are advected with the flow has been observed to be similar for most solids in spite of a considerable range of shapes and sizes. Pipe-full conditions, introducing the retarding effect of the pipe wall at the soffit, have tended to reduce solid velocities especially for floating solids. Generally the advective velocity of artificial solids of the same material and shape has not varied significantly with solid size. However size has had a clearer influence on deposition: with decreasing size, solids of the same density have been deposited at lower values of depth and velocity.

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