their large-scale deployment. It has to be noted, however, that the production
volumes of these devices are low, typically in the hundreds or at most a few thousand
per year. Therefore, these are all specialty products, which are intrinsically less costeffective to produce than mass products. With ongoing miniaturisation of components and increasing demand (e.g. in situ UV/Vis spectrometer sales volumes have
been increasing steadily for the last 15 years), prices can be expected to decrease in
the future.
Perhaps the biggest challenge to wider use of these instruments is the data
interpretation. This is less of technological challenge than a conceptual one. Most
spectroscopic methods, as described previously, do not provide information on
specific compounds but on the general state of the sample and/or on substance
groups. In the water industry, however, a substance specific look at water quality
is deeply ingrained. Spectrometer devices are traditionally compared against laboratory methods and are in many cases found to be less sensitive and less specific and
therefore disregarded. However, they provide a different type of information: continuous insight into water composition and a much broader coverage and descriptive
power on the state and state changes of a medium than can be achieved with the
traditional grab-sampling and laboratory approach. The complementary nature of the
online approach is of prime importance; the online methods are not likely to replace
the laboratory altogether, but they provide another level of information. It is especially this real-time information that allows the direct monitoring of water systems
and allows for operational and control applications. Furthermore, the continuous
monitoring of the state of the water and changes therein provides useful inputs for
smart water systems, especially when combined with other data sources.
Although all the methods described have the potential to produce results
(near) real-time, each methodology provides a different type of information. The
established methodologies primarily provide information on classes of chemicals
and a small number of selected substances. The techniques that so far remain in
limited use or have only been demonstrated to have potential in academic research
are either more generic offering a generic chemical status indicator (refractive index)
and generic microbiological status indicator (image analysis) or are highly specific
for molecules (Raman) or elements (LIBS). Table 2 provides a short overview of the
different methods and their strengths and weaknesses.
The primary application of the technologies described is found in process control
and early detection of incidents or process failures. These are applications where a
rapid response is essential. This is where the current generation of online systems
comes into its own. The possibility to monitor processes and, through better understanding, optimise operation and control means a positive return on investment can
be achieved. The case for quality monitoring, e.g. for drinking water, is often more
difficult to make as it primarily provides more insight but not necessarily any gains
in operational efficiency or reduction in costs. Online monitoring of wastewater
effluent for compliance purposes is, however, in some cases being applied as it can
be used to determine the total contaminant load discharged as well as failure of the
treatment. Monitoring for legislative purposes on individual substances remains
Spectroscopic Methods for Online Water Quality Monitoring
309
volumes of these devices are low, typically in the hundreds or at most a few thousand
per year. Therefore, these are all specialty products, which are intrinsically less costeffective to produce than mass products. With ongoing miniaturisation of components and increasing demand (e.g. in situ UV/Vis spectrometer sales volumes have
been increasing steadily for the last 15 years), prices can be expected to decrease in
the future.
Perhaps the biggest challenge to wider use of these instruments is the data
interpretation. This is less of technological challenge than a conceptual one. Most
spectroscopic methods, as described previously, do not provide information on
specific compounds but on the general state of the sample and/or on substance
groups. In the water industry, however, a substance specific look at water quality
is deeply ingrained. Spectrometer devices are traditionally compared against laboratory methods and are in many cases found to be less sensitive and less specific and
therefore disregarded. However, they provide a different type of information: continuous insight into water composition and a much broader coverage and descriptive
power on the state and state changes of a medium than can be achieved with the
traditional grab-sampling and laboratory approach. The complementary nature of the
online approach is of prime importance; the online methods are not likely to replace
the laboratory altogether, but they provide another level of information. It is especially this real-time information that allows the direct monitoring of water systems
and allows for operational and control applications. Furthermore, the continuous
monitoring of the state of the water and changes therein provides useful inputs for
smart water systems, especially when combined with other data sources.
Although all the methods described have the potential to produce results
(near) real-time, each methodology provides a different type of information. The
established methodologies primarily provide information on classes of chemicals
and a small number of selected substances. The techniques that so far remain in
limited use or have only been demonstrated to have potential in academic research
are either more generic offering a generic chemical status indicator (refractive index)
and generic microbiological status indicator (image analysis) or are highly specific
for molecules (Raman) or elements (LIBS). Table 2 provides a short overview of the
different methods and their strengths and weaknesses.
The primary application of the technologies described is found in process control
and early detection of incidents or process failures. These are applications where a
rapid response is essential. This is where the current generation of online systems
comes into its own. The possibility to monitor processes and, through better understanding, optimise operation and control means a positive return on investment can
be achieved. The case for quality monitoring, e.g. for drinking water, is often more
difficult to make as it primarily provides more insight but not necessarily any gains
in operational efficiency or reduction in costs. Online monitoring of wastewater
effluent for compliance purposes is, however, in some cases being applied as it can
be used to determine the total contaminant load discharged as well as failure of the
treatment. Monitoring for legislative purposes on individual substances remains
Spectroscopic Methods for Online Water Quality Monitoring
309