User Manual
Table Of Contents
output August 19, 2019 8:28 Page 16
SPECIFICATIONS
OPERATING PRINCIPLES OF THE SENSOR
Electrochemical measurements of hydrogen sulfide
The SulfiLogger
™
sensor contains multiple individual sensing el-
ements which are all based on Unisense core microsensor technol-
ogy. For further information on the technology, visit: www.sulfilogger.com
The electrochemical microsensors in the SulfiLogger
™
sensor mea-
sures dissolved H
2
S which is one of the three forms of dissolved
sulfide in equilibrium in the water phase, H
2
S, HS
-
, and S
2-
. For
all practical purposes in sewer applications, only the first two of
these are of interest. The
p
Ka
value for deprotonation of H
2
S is
around
pH = 7
, which is approximately the same as typical domes-
tic wastewater. For this reason, wastewater will typically contain
both H
2
S and
HS
−
, and a separate measurement of the
pH
-value
of the wastewater is necessary to calculate the total amount of
dissolved sulfides in the wastewater. Please contact Unisense if
you need guidance on how to find the concentration of total dis-
solved sulfide from the SulfiLogger
™
sensor signal (only dissolved
H
2
S). For many purposes however, the dissolved H
2
S measured by
the SulfiLogger
™
sensor is indeed the parameter of interest, since
the concentration of dissolved H
2
S is directly linked to the emis-
sion of gas phase H
2
S which gives rise to the well-known odour
and corrosion problems in the sewer. Measuring the concentra-
tion of H
2
S in the liquid instead of in the gas phase gives a more
reliable signal since the measurement is independent of the daily
variations in ventilation conditions in the head space of the sewer,
and it is independent of the exact mounting position of the sen-
sor (in the liquid, the sulfide concentration is fairly homogeneous,
whereas very large differences in gas phase concentration has
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