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, Vasiliki 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
Dates:
DateEvent
15 July 2019Accepted
3 August 2019Published Online
Uncontrolled Keywords: Free-water surface constructed wetlands;Longitudinal mixing;Vegetation ageing;Agricultural runoff;Flow rate variation;Residence time distribution curves;Decay plant period
Subjects: CAH02 - subjects allied to medicine > CAH02-05 - medical sciences > CAH02-05-04 - anatomy, physiology and pathology
CAH02 - subjects allied to medicine > CAH02-02 - pharmacology, toxicology and pharmacy > CAH02-02-01 - pharmacology
CAH03 - biological and sport sciences > CAH03-01 - biosciences > CAH03-01-02 - biology (non-specific)
CAH03 - biological and sport sciences > CAH03-01 - biosciences > CAH03-01-10 - others in biosciences
CAH06 - agriculture, food and related studies > CAH06-01 - agriculture, food and related studies > CAH06-01-03 - agriculture
CAH07 - physical sciences > CAH07-02 - chemistry > CAH07-02-01 - chemistry
CAH26 - geography, earth and environmental studies > CAH26-01 - geography, earth and environmental studies > CAH26-01-02 - physical geographical sciences
CAH10 - engineering and technology > CAH10-01 - engineering > CAH10-01-07 - civil engineering
CAH10 - engineering and technology > CAH10-01 - engineering > CAH10-01-10 - others in engineering
CAH10 - engineering and technology > CAH10-03 - materials and technology > CAH10-03-02 - materials technology
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
Depositing User: Vasiliki Ioannidou
Date Deposited: 09 Oct 2019 07:45
Last Modified: 03 Mar 2022 15:49
URI: https://www.open-access.bcu.ac.uk/id/eprint/8126

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