In-situ monitoring of BOD and DOC using fluorescence sensors

Kieran Khamis, Chris Bradley, David Hannah, Rob Stevens

k.khamis@bham.ac.uk / kieran.khamis@rshydro.co.uk

Dissolved Organic Matter (DOM) in urban catchments

• Urbanization will increase significantly by 2030 - implications for water quality Seto et al. (2012) PNAS 109, 16083

• Understanding of DOM pollution dynamics in urban river systems are still

limited due to:

heterogeneous source and transport pathways Hosen et al. (2014) Env. Sci. Tech. 48, 7817

temporal variability (e.g. diel STW release / seasonal dynamics) McElmurry et al. (2014) Env. Sci. Tech. 48, 45

flashy hydrology - event pulses important but easy to miss Gurnell et al. (2007) Geog. Compass 1/5, 1118

• Hence, there is a need to re-evaluate monitoring techniques, particularly given legislative requirements (WFD).

•Fluorescence: a form of luminescence which occurs over short time scales at the molecular/atomic level.

What is Fluorescence?

•Fluorescence: a form of luminescence which occurs over short time scales at the molecular/atomic level.

Sjoback et al. (1995) Spec. Acta A 51, 7-21

What is Fluorescence?

Fluorescence for DOM characterisation • Fluorescence (EEM) characterisation can

provide information on DOM: - source - redox state - reactivity • Rapid and precise technique • Correlations: Biochemical oxygen demand (BOD) - Tpeak Dissolved organic carbon (DOC) – Cpeak

However…… • Temporally intensive sampling necessary to characterise

DOM pollution dynamics in urban systems not feasible

Excitation wavelength

Emis

sio

n w

avel

engt

h

Submersible fluorometers

Temperature quenching

Khamis et al. (2015) Env. Sci. : Process and Impacts

Khamis et al. (2015) Env. Sci. : Process and Impacts

Turbidity compensation

Study aim

To validate and refine a multi-wavelength fluorescence

monitoring system for the in-situ quantification of BOD and DOC

Sensor specification

Multi wavelength monitoring – • Tryptophan like fluorescence (TLF) = proteinaceous material • Humic like fluorescence (HLF) = aromatic material of vascular plant orgin • Turbidity = a surrogate for particle load

Study location

Hydro-meteorological data

Flashy hydrology

Diurnal dynamics

First flush turbidity spikes

v

Relationship with BOD and DOC

Relationship with BOD and DOC

v v

Outliers due to high turbidity >150 NTU

Multi-wavelength models

Multi parameter regression models –

BOD (R2 = 0.93) DOC (R2 = 0.93)

Turbidity HLF

TLF TLF

Continuous data

Continuous data

Rapid flush of reactive organic matter from/through engineered system

Delayed flush of less reactive organic matter from natural environment

DOC

BOD

Temperature correction

DOC

BOD

Over estimation of flux without compensation

Temperature correction

DOC

BOD

Important to account for- particularly when longer term monitoring for restoration/ infra structure development

Conclusions and implications

Multi-wavelength fluorescence (+turbidity and temperature)

offers a robust proxy for in-situ measurement of DOC and BOD.

In-situ fluorescence monitoring - a cost effective monitoring solution.

Important to adequately compensate for thermal quenching

and turbidity interference (incorporate into regression model) .

In-situ fluorescence can provide new insights into OM process/water quality dynamics at higher resolution than hitherto.

Conclusions and implications

Two conceptual organic matter sources - fast (engineered

environment) and slow (natural environment). The sensor/approach can easily be adopted by a range of end-

users : (i) Academics - improve understanding of catchment hydrology and OM dynamics; (ii) Utilities / industry - improve process control and effluent monitoring; (iii) Monitoring bodies – increase resolution of BOD monitoring for legislative purposes.

Acknowledgments

Richard Johnson and Mel Bickerton (University of Birmingham) James Sorenson and Pete Williams (BGS) Phil Blaen (University of Birmingham) James Chapman (RS Hydro)