The effects of flow rate variation and vegetation ageing on the longitudinal mixing and Residence Time Distribution (RTD) in a full-scale constructed wetland

IOANNIDOU, V.G and Pearson, J.M (2019) The effects of flow rate variation and vegetation ageing on the longitudinal mixing and Residence Time Distribution (RTD) in a full-scale constructed wetland. Ecological Engineering, 138 (Nov-19). pp. 248-263. ISSN 0925-8574

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Abstract

A field-based experimental study has been undertaken within a full-scale constructed wetland, designed to treat runoff from agricultural land in Knapwell, Cambridgeshire, UK. The effects of flow rate variation and natural vegetation ageing on the mixing characteristics are investigated over a eight month period. Detailed fluorometric measurements were made to examine the longitudinal spreading of a solute within the wetland. Between a UK November winter period, and June summer period, 125 tracer tests were undertaken for a range of dry weather and storm flow conditions, using an automated daily injection tracer system. The longitudinal dispersion results show that the dispersion is influenced by the flow rate for low discharge conditions, however, for higher discharges, the longitudinal dispersion becomes independent of discharge. Residence Time Distribution (RTD) curves are examined through a series of flow conditions for each testing month, ranging from transitional (Re~2000) to turbulent (Re~7000) flow conditions. For the conditions measured, differing flow rates produce changes in the RTD, demonstrating that higher flow rates induce shorter mean residence times, generating predominantly an advective flow regime. The effects of plant age are prominent on the mixing pattern. Towards the end of the plant annual cycle, in February/March, mixing pattern approaches complete mixing, longitudinal mixing increases significantly due to long tails on the RTDs, and mean flow velocity is retarded. This indicates that the dormant plant period, which normally takes 5-6 months (October to March), alters progressively the mixing pattern in the system in such a way that it is significantly different from the mixing pattern during the growing plant season.

Item Type: Article
Identification Number: https://doi.org/10.1016/j.ecoleng.2019.07.014
Date: 3 August 2019
Uncontrolled Keywords: Free-water surface constructed wetlands;Longitudinal mixing;Vegetation ageing;Agricultural runoff;Flow rate variation;Residence time distribution curves;Decay plant period
Subjects: B200 Pharmacology, Toxicology and Pharmacy
C100 Biology
C900 Others in Biological Sciences
D400 Agriculture
F100 Chemistry
F800 Physical and Terrestrial Geographical and Environmental Sciences
H200 Civil Engineering
H900 Others in Engineering
J200 Metallurgy
Divisions: Faculty of Computing, Engineering and the Built Environment
Faculty of Computing, Engineering and the Built Environment > School of Computing and Digital Technology
Faculty of Computing, Engineering and the Built Environment > School of Computing and Digital Technology > Enterprise Systems
Faculty of Computing, Engineering and the Built Environment > School of Engineering and the Built Environment
Faculty of Computing, Engineering and the Built Environment > School of Engineering and the Built Environment > Advanced Systems Engineering
Faculty of Computing, Engineering and the Built Environment > School of Engineering and the Built Environment > Resilient Environments
REF UoA Output Collections > REF2021 UoA13: Architecture, Built Environment and Planning
Depositing User: Vasiliki Ioannidou
Date Deposited: 09 Oct 2019 07:45
Last Modified: 29 Jun 2020 12:46
URI: http://www.open-access.bcu.ac.uk/id/eprint/8126

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