Analysis of clogging in constructed wetlands using magnetic resonance

Morris, Robert H.; Newton, Michael I.; Knowles, Paul; Bencsik, Martin; Davies, Philip A.; Griffin, Paul F.; McHale, Glen

doi:10.1039/c0an00986e

Cited by 17 publications

(17 citation statements)

References 18 publications

(26 reference statements)

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“…This study was conducted using sensors in a Helmholtz style configuration, very similar to a design previously presented [10]. Two N42 neodymium magnets (height = 20.0 mm, radius = 17.5 mm; HKCM Gmbh, Germany) were arranged with parallel magnetisation and spaced by 20 mm, generating a magnetic field in the magnet aperture (center field strength = 0.2468 T at 292 K), as shown in Fig.…”

Section: Mr Sensor Designmentioning

confidence: 99%

“…A repetition time of 15 s was used to ensure the system fully returned to equilibrium before the next experiment. T1 measurements were taken using a variable repetition time method (uneven intervals between 25 ms and 15 000 ms) as performed in previous work [10], [13], [14]. When taking readings at the wetland 128 echoes were summed to provide a greater signal intensity.…”

Section: Mr Measurement Protocolmentioning

confidence: 99%

“…Determining the clog state of both model systems and wetland samples have been extensively investigated in the laboratory setting using relaxation measurements [10], [11], [12], [13], [14]. The parameter T2 eff has been previously used to successfully characterize clogging in a model system where a highly homogeneous magnetic field has been used for MR measurements [11], [12], however this was not possible with the inhomogeneous magnetic field of a low-cost permanent magnet system such as the type used in this work [14].…”

Section: Introductionmentioning

confidence: 99%

“…The parameter T2 eff has been previously used to successfully characterize clogging in a model system where a highly homogeneous magnetic field has been used for MR measurements [11], [12], however this was not possible with the inhomogeneous magnetic field of a low-cost permanent magnet system such as the type used in this work [14]. Therefore this work focusses on T1 relaxation measurements which have also been used to determine the clog state with a similar sensor in the past [10], [13], [14].…”

Section: Introductionmentioning

confidence: 99%

“…In this work we use a 'Helmholtz-style' sensor (shown in Fig. 2) and sensors of a similar design to this have been presented elsewhere [10]. A probe of a comparable design was used to collect a set of preliminary measurements exploring the temperature effects [23] however the design and construction technique has been refined since then.…”

Section: Introductionmentioning

confidence: 99%

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Temperature dependence of magnetic resonance probes for use as embedded sensors in constructed wetlands

Hughes‐Riley

Dye

Anderez

et al. 2016

Sensors and Actuators A: Physical

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Constructed wetlands are now accepted as an environmentally friendly means of wastewater treatment however, their effectiveness can be limited by excessive clogging of the pores within the gravel matrix, making this an important parameter to monitor. It has previously been shown that the clog state can be characterised using magnetic resonance (MR) relaxation parameters with permanent magnet based sensors. One challenge with taking MR measurements over a time scale on the order of years is that seasonal temperature fluctuations will alter both the way that the sensor operates as well as the relaxation times recorded. Without an understanding of how the sensor will behave under different temperature conditions, meaningful information about the clog state cannot be successfully extracted from a wetland. This work reports the effect of temperature on a permanent magnet based MR sensor to determine if the received signal intensity is significantly compromised as a result of large temperature changes, and whether meaningful relaxation data can be extracted over the temperature range of interest. To do this, the central magnetic field of the sensor was monitored as a function of temperature, showing an expected linear relationship. Signal intensity was measured over a range of temperatures (5 °C to 44 °C) for which deterioration at high and low temperatures compared to room temperature was observed. The sensor was still operable at the extremes of this range and the reason for the signal loss has been studied and explained. Spin-lattice relaxation time measurements using the sensor at different temperatures have also been taken on a water sample and seem to agree with literature values. Further to this, measurements have been taken in an operational wetland over the course of 203 days and have shown a linear dependence with temperature as would be expected. This work concluded that the sensor can perform the task of measuring the spin-lattice relaxation time over the required temperature range making it suitable for long-term application in constructed wetlands.

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Section: Mr Sensor Designmentioning

confidence: 99%

Section: Mr Measurement Protocolmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Temperature dependence of magnetic resonance probes for use as embedded sensors in constructed wetlands

Hughes‐Riley

Dye

Anderez

et al. 2016

Sensors and Actuators A: Physical

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A mechanistic model (BCC‐PSSICO) to predict changes in the hydraulic properties for bio‐amended variably saturated soils

Brangarí

Sánchez-Vila

Freixa

et al. 2017

Water Resources Research

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This is the peer reviewed version of the following article: [Carles Brangarí, A., X. Sanchez-Vila, A. Freixa, A. M. Romaní, S. Rubol, and D. Fernàndez-Garcia (2017), A mechanistic model (BCC-PSSICO) to predict changes in the hydraulic properties for bio-amended variably saturated soils, Water Resour. Res., 53, 93–109, doi:10.1002/2015WR018517], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/2015WR018517/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The accumulation of biofilms in porous media is likely to influence the overall hydraulic properties and, consequently, a sound understanding of the process is required for the proper design and management of many technological applications. In order to bring some light into this phenomenon we present a mechanistic model to study the variably saturated hydraulic properties of bio-amended soils. Special emphasis is laid on the distribution of phases at pore-scale and the mechanisms to retain and let water flow through, providing valuable insights into phenomena behind bioclogging. Our approach consists in modeling the porous media as an ensemble of capillary tubes, obtained from the biofilm-free water retention curve. This methodology is extended by the incorporation of a biofilm composed of bacterial cells and extracellular polymeric substances (EPS). Moreover, such a microbial consortium displays a channeled geometry that shrinks/swells with suction. Analytical equations for the volumetric water content and the relative permeability can then be derived by assuming that biomass reshapes the pore space following specific geometrical patterns. The model is discussed by using data from laboratory studies and other approaches already existing in the literature. It can reproduce (i) displacements of the retention curve toward higher saturations and (ii) permeability reductions of distinct orders of magnitude. Our findings also illustrate how even very small amounts of biofilm may lead to significant changes in the hydraulic properties. We, therefore, state the importance of accounting for the hydraulic characteristics of biofilms and for a complex/more realistic geometry of colonies at the pore-scale.Peer ReviewedPostprint (author's final draft

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