harmful (industrial) contaminations, which can cause failure of the biological
treatment resulting in costs for plant recovery and economic damages due to
noncompliance of the discharged effluent.
5.1.8 Remote Sensing
A recent addition to the field of UV/Vis spectroscopy for water monitoring is remote
sensing. Remote sensing is primarily used to determine levels of chlorophyll,
suspended solids and chromatic dissolved organic matter (CDOM) in lakes and
seas. It uses either long-range satellite-based optical sensors; close-range sensors that
can be hand-held, fixed or mounted on drones; or a combination of both. The sensors
are radiometers, i.e. they measure reflected natural light. Satellites are used to map
the water quality over large areas, whereas smaller land-based systems provide
higher-resolution measurements and have the advantage that they can also be
operated under cloud cover. These are used independently as well as for validation
of optical satellite data. The big advantages of remote sensors are the fact that they
work from a distance, removing the need to physically access a location, and their
ability to cover a large area where in situ sensors only provide spot sampling.
5.2 Fluorescence Spectroscopy
Another method widely used for water quality monitoring is fluorescence spectroscopy. Light absorbed by a molecule excites it to a higher energy state. Generally,
molecules fall back from this higher energy state to their equilibrium energy state
through various non-radiative mechanisms (Fig. 2). With fluorescent materials,
however, part of the energy is emitted through the emission of a photon. This photon
has a longer wavelength (i.e. lower energy) than the excitation energy. The intensity
of the light at the emitted wavelength (known as fluorescence) is a measure for the
concentration of the fluorescent molecules.
A fluorescence spectrometer is an instrument consisting of the following main
components: a light source, a measurement compartment and a detector. The light
source sends a beam of light at a wavelength tuned to the molecules of interest
through the sample in the measurement compartment. The detector measures the
intensity of the fluorescence generated. Generally, a wavelength filter is placed in
front of the detector, allowing only the fluorescence to fall on the detector. This filter
makes the measurement specific and reduces interference from natural light. Different types of online fluorescence spectrometer instruments are available:
• Single excitation – emission pair (excitation at a specific wavelength, emission
measured at a specific wavelength). Often the excitation and/or emission wavelengths can be changed, by the user or the manufacturer, via the selection of
different filters and/or different LEDs.
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treatment resulting in costs for plant recovery and economic damages due to
noncompliance of the discharged effluent.
5.1.8 Remote Sensing
A recent addition to the field of UV/Vis spectroscopy for water monitoring is remote
sensing. Remote sensing is primarily used to determine levels of chlorophyll,
suspended solids and chromatic dissolved organic matter (CDOM) in lakes and
seas. It uses either long-range satellite-based optical sensors; close-range sensors that
can be hand-held, fixed or mounted on drones; or a combination of both. The sensors
are radiometers, i.e. they measure reflected natural light. Satellites are used to map
the water quality over large areas, whereas smaller land-based systems provide
higher-resolution measurements and have the advantage that they can also be
operated under cloud cover. These are used independently as well as for validation
of optical satellite data. The big advantages of remote sensors are the fact that they
work from a distance, removing the need to physically access a location, and their
ability to cover a large area where in situ sensors only provide spot sampling.
5.2 Fluorescence Spectroscopy
Another method widely used for water quality monitoring is fluorescence spectroscopy. Light absorbed by a molecule excites it to a higher energy state. Generally,
molecules fall back from this higher energy state to their equilibrium energy state
through various non-radiative mechanisms (Fig. 2). With fluorescent materials,
however, part of the energy is emitted through the emission of a photon. This photon
has a longer wavelength (i.e. lower energy) than the excitation energy. The intensity
of the light at the emitted wavelength (known as fluorescence) is a measure for the
concentration of the fluorescent molecules.
A fluorescence spectrometer is an instrument consisting of the following main
components: a light source, a measurement compartment and a detector. The light
source sends a beam of light at a wavelength tuned to the molecules of interest
through the sample in the measurement compartment. The detector measures the
intensity of the fluorescence generated. Generally, a wavelength filter is placed in
front of the detector, allowing only the fluorescence to fall on the detector. This filter
makes the measurement specific and reduces interference from natural light. Different types of online fluorescence spectrometer instruments are available:
• Single excitation – emission pair (excitation at a specific wavelength, emission
measured at a specific wavelength). Often the excitation and/or emission wavelengths can be changed, by the user or the manufacturer, via the selection of
different filters and/or different LEDs.
Spectroscopic Methods for Online Water Quality Monitoring
299