Complementary methods to investigate the development of clogging within a horizontal sub-surface flow tertiary treatment wetland


A combination of experimental methods was applied at a clogged, horizontal subsurface flow (HSSF) municipal wastewater tertiary treatment wetland (TW) in the UK, to quantify the extent of surface and subsurface clogging which had resulted in undesirable surface flow. The three dimensional hydraulic conductivity profile was determined, using a purpose made device which recreates the constant head permeameter test in-situ. The hydrodynamic pathways were investigated by performing dye tracing tests with Rhodamine WT and a novel multi-channel, data-logging, flow through Fluorimeter which allows synchronous measurements to be taken from a matrix of sampling points. Hydraulic conductivity varied in all planes, with the lowest measurement of 0.1 md1 corresponding to the surface layer at the inlet, and the maximum measurement of 1550 md1 located at a 0.4m depth at the outlet. According to dye tracing results, the region where the overland flow ceased received five times the average flow, which then vertically short-circuited below the rhizosphere. The tracer break-through curve obtained from the outlet showed that this preferential flow-path accounted for approximately 80% of the flow overall and arrived 8 h before a distinctly separate secondary flow-path. The overall volumetric efficiencyof the clogged system was 71% and the hydrology was simulated using a dual-path, dead-zone storage model. It is concluded that uneven inlet distribution, continuous surface loading and high rhizosphere resistance is responsible for the clog formation observed in this system. The average inlet hydraulic conductivity was 2 md1, suggesting that current European design guidelines, which predict that the system will reach an equilibrium hydraulic conductivity of 86 md1, do not adequately describe the hydrology of mature systems.

Publication DOI:
Divisions: College of Engineering & Physical Sciences > School of Engineering and Technology > Mechanical, Biomedical & Design
College of Engineering & Physical Sciences > Sustainable environment research group
Additional Information: © 2009 Elsevier Ltd. Open access under CC BY-NC-ND license
Uncontrolled Keywords: treatment wetlands,horizontal sub-surface flow,hydraulic conductivity,clogging,tracer tests,hydrodynamics,Water Science and Technology,Waste Management and Disposal,Pollution,Ecological Modelling
Publication ISSN: 1879-2448
Last Modified: 17 Apr 2024 07:09
Date Deposited: 12 Dec 2011 13:00
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Related URLs: http://www.scop ... tnerID=8YFLogxK (Scopus URL)
https://www.sci ... 6113?via%3Dihub (Publisher URL)
PURE Output Type: Article
Published Date: 2010-01
Authors: Knowles, P.R.
Griffin, P.
Davies, Philip A. (ORCID Profile 0000-0003-4783-1234)

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