A low-cost novel optical sensor for water quality monitoring

With increasing environmental pressure due to global climate change, increases in global
population and the need for sustainable obtained resources, water resources management
is critical. In-situ sensors are fundamental to the management of water systems by providing
early warning, forecasting and baseline data to stakeholders. To be fit-for-purpose,
monitoring using in-situ sensors has to be carried out in a cost effective way and allow
implementation at larger spatial scales. If networks of sensors are to become not only a
reality but common place, it is necessary to produce reliable, inexpensive, rugged sensors
integrated with data analytics.

In this context, the aim of this project was to design and develop a low cost, robust and
reliable optical sensor which capable of continuous measurement of chemical and physical
parameters in aquatic environments. An iterative engineering design method cycling
between sensor design, prototyping and testing was used for the realisation and optimisation
of the sensor. The sensor can provide absorption, scatter, and fluorescence readings over a
broad spectral range (280nm to 850nm) and temperature readings in real-time using a suite
of optical sensors (CMOS Spectrometers and photodiode detector), custom designed LED
array light source and a digital temperature probe. Custom electronics and firmware were
developed to control the sensor and facilitate data transmission to an external network.
Sensor electronics are housed in a marine grade watertight housing; the optical components
are mounted inside a custom designed 3D-printed optical head which joins with the sensor
housing. The sensor is capable of measuring a range of optical parameters and temperature
in a single measurement cycle. Sensor analytical performance was demonstrated in the
laboratory, for detection and quantification of turbidity using analytical standards and in the
field by comparison with a commercially available multi- parameter probe (YSI, EXO 2).
The laboratory and field trials demonstrate that the sensor is fit-for-purpose and an excellent
tool for early warning monitoring by providing high frequency time-series data, operate
unattended in-situ for extended periods of times and capture pollution events.

Acknowledgement - This research is carried out with the support of Project Ireland’s 2040’s
Disruptive Technologies Innovation Fund.