Transport of Wipes in Sewers

The inappropriate disposal of wipes has caused severe sewer blockages in many cities, especially during the COVID-19 pandemic. To understand the transport mechanism of wipes in sewers, systematic experiments were conducted in a circular pipe using non-flushable wipes. The critical flow velocity for the incipient motion of wipes was found to increase with the decrease of the relative wipe size, starting from the value of 0.05 m/s. Non-dimensional equations were developed for characterizing the incipient motion using two commonly used parameters for particles: the critical Shield number and particle Froude number. The mean wipe velocity and the cross-sectional mean ambient velocity had a linear relationship. Different movement modes of wipes were observed and classified by using the transport stage number T*. The movement of the wipe started from the sliding mode. The rolling/saltation mode started at T* = 2.5, and the suspension mode started at T* = 12.6.