with 1 nm or better spectral resolution, however, it has been possible to obtain
concentrations of both ions individually [18]. Nitrate and nitrite monitoring is
primarily used to monitor and control nutrient removal processes in WWTPs and
to monitor the nutrient load in surface waters.
5.1.3 Colour
Online monitoring of colour is mainly of interest in drinking water treatment. Colour
in water is caused by the absorption of visible light by dissolved and colloidal
substances and by the scattering of light by suspended particles. Both organic
compounds, such as humic acids, and inorganic compounds, such as iron, copper
and manganese, can be responsible for colour in water. The colour of natural water is
typically yellow to brown. Although colour in itself does not constitute a health risk,
high colour is considered aesthetically displeasing, and therefore, limits are defined
for colour in drinking water regulations. The most commonly used standard method
expresses the colour intensity compared to a solution of a platinum-cobalt complex
using Pt-Co units, also referred to as Hazen [11]. A distinction is made between
“apparent colour” for samples which include suspended matter and “true colour” for
samples that do not include suspended matter (after filtration through a 0.45 μm
filter). Both can be determined using online spectrometer instruments, where the
apparent colour value is obtained after applying a turbidity correction on the raw
spectral data.
5.1.4 Turbidity and Suspended Solids
Non-dissolved matter and colloidal matter cause scattering of the light passing
through a water sample. This scattering is referred to as turbidity and is observed
as a cloudiness or haziness of the liquid. A number of standard methods have been
defined to measure turbidity in water. The most common methods are US EPA
method 180.1 and ISO 7027, which measure scattering of light at a 90
angle with a
white (tungsten) and infrared (860 nm) light source, respectively. Instead of 90
scattering, UV/Vis spectrometer devices measure the attenuation of light at 180
.
The extinction of the signal observed in this instrument layout is caused by the
combination of scattering, blocking and shading by particles as well as absorption by
dissolved and particulate matter. Because the effect of turbidity on the spectrum is
predictable [14] and as in natural water and domestic wastewater the particulates are
the prime absorbers at wavelengths longer than 450 nm, turbidity and total
suspended solids can be derived from the absorption in the visible range of the
spectrum. Turbidity is used to assess the treatability of water and as quality control in
drinking water. For example, an increase in turbidity in the distribution network can
be an indication of ingress of foreign water, e.g. wastewater, resuspension of
sediments or the release of biofilm from pipe walls. In water treatment it can be
used to monitor particle carry-over from (sand) filters, helping in the optimisation of
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concentrations of both ions individually [18]. Nitrate and nitrite monitoring is
primarily used to monitor and control nutrient removal processes in WWTPs and
to monitor the nutrient load in surface waters.
5.1.3 Colour
Online monitoring of colour is mainly of interest in drinking water treatment. Colour
in water is caused by the absorption of visible light by dissolved and colloidal
substances and by the scattering of light by suspended particles. Both organic
compounds, such as humic acids, and inorganic compounds, such as iron, copper
and manganese, can be responsible for colour in water. The colour of natural water is
typically yellow to brown. Although colour in itself does not constitute a health risk,
high colour is considered aesthetically displeasing, and therefore, limits are defined
for colour in drinking water regulations. The most commonly used standard method
expresses the colour intensity compared to a solution of a platinum-cobalt complex
using Pt-Co units, also referred to as Hazen [11]. A distinction is made between
“apparent colour” for samples which include suspended matter and “true colour” for
samples that do not include suspended matter (after filtration through a 0.45 μm
filter). Both can be determined using online spectrometer instruments, where the
apparent colour value is obtained after applying a turbidity correction on the raw
spectral data.
5.1.4 Turbidity and Suspended Solids
Non-dissolved matter and colloidal matter cause scattering of the light passing
through a water sample. This scattering is referred to as turbidity and is observed
as a cloudiness or haziness of the liquid. A number of standard methods have been
defined to measure turbidity in water. The most common methods are US EPA
method 180.1 and ISO 7027, which measure scattering of light at a 90
angle with a
white (tungsten) and infrared (860 nm) light source, respectively. Instead of 90
scattering, UV/Vis spectrometer devices measure the attenuation of light at 180
.
The extinction of the signal observed in this instrument layout is caused by the
combination of scattering, blocking and shading by particles as well as absorption by
dissolved and particulate matter. Because the effect of turbidity on the spectrum is
predictable [14] and as in natural water and domestic wastewater the particulates are
the prime absorbers at wavelengths longer than 450 nm, turbidity and total
suspended solids can be derived from the absorption in the visible range of the
spectrum. Turbidity is used to assess the treatability of water and as quality control in
drinking water. For example, an increase in turbidity in the distribution network can
be an indication of ingress of foreign water, e.g. wastewater, resuspension of
sediments or the release of biofilm from pipe walls. In water treatment it can be
used to monitor particle carry-over from (sand) filters, helping in the optimisation of
296
J. van den Broeke and T. Koster