Changes

A precondition for Solids-Free Sewer networks is efficient pre-treatment at the household level. The interceptor, septic or settling tank removes settleable particles that could clog small pipes. A grease trap should also be added. Because there is little risk of clogging, the sewers do not have to be self-cleaning (i.e. no minimum flow velocity) and can therefore be laid at shallow depths, can have fewer inspection points (manholes), can follow the topography more closely and have inflective gradients (i.e. negative slope). When the sewer roughly follows the ground contours, the flow in the sewer is allowed to vary between open channel flow and pressure (full-bore) flow. However, care should be taken with negative slopes as they may lead to surging above the ground level during peak flows. Inspection points should be provided at major connection points or when the size of the pipe changes.

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