The benefits of using refractive index for water quality monitoring in distribution networks A comparison of Optiqua EventLab and traditional water quality parameters

To monitor the dynamics in water quality in drinking water distribution networks, and to facilitate a quick and timely response to quality incidents and pro-active network operations, real-time water quality information is vital. Measurement devices with a sufficiently low operational footprint to allow implementation in distribution networks are only available for a small range of chemical and physical parameters, such as pH, ORP, conductivity, dissolved oxygen, UV absorption and fluorescence. The use of sensors for these traditional water quality parameters has serious limitations, both in terms of detection capabilities as well as operational aspects. Each of these sensors measures only a limited sub-set of all possible constituents of the water matrix, and therefore a multitude of sensors is required to obtain substantial coverage. Nevertheless, even using a combination of the traditional sensors, there remains a significant gap in detection capabilities, with a blind spot that includes most non-aromatic organic molecules. The response from these systems is further complicated by intrinsic characteristics of the technologies used, and include inconsistent sensitivity for different types of substances, matrix cross-interference and non-linear response. Furthermore, using a combination of sensors, which all require maintenance, is not beneficial for the robustness of the monitoring set-up, and will result in a high maintenance load. This is especially the case when electrochemical sensors are used, for example for pH, ORP and ion selective electrodes, as they demand frequent maintenance and calibration. Optiqua has developed a generic optical sensor concept, EventLab, that can be deployed online throughout a distribution network, and that meets the four key operational requirements of such an water quality event monitoring system: (i) continuous real-time detection, (ii) generic: one sensor covering the full spectrum of possible chemical contaminants, (iii) high sensitivity, and (iv) low cost and low maintenance. EventLab measures minute refractive index (RI) changes in water. RI is a useful generic indicator of water quality as any substance, when dissolved in water, will change the refractive index of the water matrix. Intrinsic advantages include consistent sensitivity for all substances, response linear with concentration and high resistance to matrix interference. Results from installations have confirmed the added value of EventLab. Systems installed in various distribution networks have monitored variations in baseline water quality and detected water quality events all of which were not detected by traditional sensor systems installed at the same sites. As expected on the basis of the differences in measurement principles EventLab picks up water quality variations that remain invisible to traditional sensors. These results obtained under operational conditions in distribution network applications validate the true added value of refractive index measurements. EventLab can be used as a stand-alone water quality monitoring solution, providing consistent coverage to detect any water quality variation due to dissolved substances. Alternatively, EventLab can be used as the basis for a multi-sensor monitoring strategy. A combination with other sensors can be used to further expand the range of events that can be detected, e.g. to include particles, or provide the capability for a global classification of the detected quality change. 1: Optiqua Technologies, Hengelosestraat 705, 7521 PA, Enschede, The Netherlands The benefits of using refractive index for water quality monitoring in distribution networks Page 2 of 1