GROSS SOLIDS TRANSPORT AND DEGRADATION

The paper describes the first stages of a study of the origin, transpo rt, 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 gros s solids has confirmed general existing field observations that many s anitary solids undergo little degradation, whereas toilet paper and fa eces are readily degraded. A study of solid advection and deposition i n 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, in troducing the retarding effect of the pipe wall at the soffit, have te nded to reduce solid velocities especially for floating solids. Genera lly the advective velocity of artificial solids of the same material a nd shape has not varied significantly with solid size. However size ha s had a clearer influence on deposition: with decreasing size, solids of the same density have been deposited at lower values of depth and v elocity. (C) 1998 IAWQ. Published by Elsevier Science Ltd.