The Development of a Simulated Sediment Dosing Apparatus for Deposition Research in Wastewater Collection Systems

Abstract

Water conservation initiatives promote installation of water efficient and low-flow appliances in waste water collection systems. This has resulted in lower flow rates in those systems than the intended design loading, causing solid deposition and sedimentation in some areas. A joint UKWIR/EPSRC CASE grant (14440031) has funded the work described in this paper which investigates sedimentation and solid deposition in building drainage system pipes. The purpose of this paper is to detail the design, calibration and operation of a sediment dosing apparatus to simulate sedimentation rates and explore possible solutions to this issue with a full scale laboratory model based on real site data. The methodology adopted is an experimental approach, where tests have been conducted on the sediment dosing apparatus based on calculations and observations to determine an appropriate sediment dosing regime representative of typical systems. Further tests were conducted with the addition of everyday household products to investigate their effects on sedimentation. The results indicated that a suitable dosing rate was approximately 12% weight-to-volume (w/v) of a fine sand with a known particle size distribution, diluted 1:5 in a clean water base flow. It was also shown that the addition of the household products added to the problem of sedimentation within drainage systems. The results give excellent correlation to real site data, with deposition depth and distribution comparable to measured site data to within 10%. The deposition was achieved within three hours, which approximated six weeks deposition in the live site used in the study. This straightforward investigation details the design, construction and testing of a device to cause accelerated sedimentation in a full scale model of a building drainage system. This is the first step in the process of updating research underpinning our understanding of the behaviour of these systems under conditions of low flow rates caused by water conservation, sedimentation, and the use of common household additives. It will be used to improve simulation of water flow and solid transport in sediment-laden systems. Specifically, the results will be used to determine refinements required to a specific drainage simulation model (DRAINET), which currently has an unquantified sedimentation component. This work is part of a larger body of current research funded by two joint EPSRK/UKWIR grants.