Real-time, low-maintenance DOC monitoring using the Proteus

excitation emission matrix with CDOM peak highlighted

Proteus Instruments have launched the new Proteus range of sensors that enable the accurate real-time measurement of parameters that were previously difficult measure at high frequency, including dissolved organic carbon (DOC), Biochemical Oxygen Demand (BOD) and refined oils and chlorophyll a, alongside traditional water quality parameters.


DOC is operationally defined as the amount of organic carbon compounds that will pass through a 0.45 um filter. In natural river systems, DOC quantity is of interest to river basin managers as shifts in concentration can alter the nutrient supply, pH, light absorbance and photochemistry. In addition, high DOC concentration has implications for drinking water treatment by affecting coagulant demand, filter backwashes and runtime, disinfectant dose and the formation of disinfectant by-products (Trihalomethanes – THMs). Trihalomethanes may have long-term effects on health and they should be considered when chlorinating drinking water high in DOC. However, to date real-time DOC measurement has required expensive monitoring cabinets with high reagent costs and maintenance requirements. Hence, many industrial and environmental monitoring regimes have consisted of sporadic grab samples with subsequent laboratory analysis.

The real-time measurement solution

relationship between CDOM and laboratory measured DOCFluorescence spectroscopy is a selective and sensitive optical technique enabling in-situ, real-time measurement of dissolved organic matter. Molecules absorb light of a specific wavelength and orbiting electrons are excited to a higher energy state. The electrons then emit light of a specific wavelength to return to the base state. The use of fluorescence spectroscopy as a technique for the rapid assessment of organic matter quantity, particularly DOC, has been widely used by academic researchers. A subset of the coloured dissolved organic matter (CDOM) pool is fluorescent (FDOM) has a distinct fluorescence signal (Fig. 1). This peak is associated with humic and fluvic acids; the by-products of microbial degradation of vascular plant material. The intensity of the FDOM fluorescence signal is strongly related to DOC concentration (Fig. 2).

The CDOM/FDOM peak is generally associated with excitation at ~365nm and emission at ~470nm, see the red box on excitation emission matrix (Fig 1). However, analysis of CDOM has until recently required sample collection and transport to a laboratory for analysis on expensive, large, power hungry spectrofluorometers.

Over the last 3 years RS Hydro have developed and rigorously testing the Proteus DOC; a fluorescence based real-time DOC monitoring platform. By combining a miniaturised LED based CDOM sensor, thermistor and turbidity sensor the Proteus DOC is able to provide users with a highly accurate and reliable real-time indication of DOC.

proteus and tablet

The Proteus DOC is unique as it has a strong scientific under pinning with a research article in a leading international scientific journal (e.g. Khamis et al., 2017 ). In addition, the sensor is embedded with robust correction algorithms to account for signal interference associated with temperature and turbidity variability providing unrivalled accuracy and repeatability. The Proteus DOC also comes equipped with a standard factory DOC calibration derived from installations across a diverse range of applications, which can then be tweaked for specific monitoring sites for optimal accuracy. RS Hydro provide consultation on all aspects of installation and calibration and strive to provide the optimal solution for all clients. Furthermore, the Proteus DOC also has an integrated wiper for cleaning all optical windows to eradicate fouling in demanding environments, thus reducing the need for user intervention and ensuring a stable baseline for long term deployments.

Applications graph showing relationship between proteus DOC and labratory DOC

The Proteus DOC has been deployed for extended periods in urban river systems with wastewater drainage problems (i.e. CSOs and cross-connections). In these systems, the Proteus DOC is able to measure DOC very accurately during base flow and storm flow conditions (see Figs 4 and 5). laboratories. The sensor has to be corrected for temperature quenching (reduction in the signal) and turbidity to obtain strong relationships with laboratory DOC but once this is established excellent continuous records of DOC can be obtained (Fig. 5). Note the sensor is sensitive enough to pick up daily oscillation of DOC associated with photodegradation, production and uptake cycles.

In addition to urban applications the Proteus DOC has been used on an inlet to a water treatment works with excellent correlations between CDOM and TOC (Total Organic Carbon) obtained. A number of research organisations have also purchased the sensor package and are using it to improve understanding of reactive organic matter dynamics. The Birmingham Institute of Forest Research (BIFOR) purchased two units for a long-term monitoring project and are extremely happy with the sensor stability and accuracy: Dr. Phillip Blaen BIFOR Research Fellow “The low maintenance requirements due to the integrated wiper and infrequent calibration requirements make the Proteus ideal for long term monitoring of organic matter”.

graph showing concentration for an urban river system Added benefits of the Proteus DOC
  • Real-time data - easy link up to telemetry and SCADA for alarms/alerts of specified
  • Easily deployable – wide range of environments (inc. inlets, effluents, reservoirs or boreholes)
  • Versatile - modular design enables a wide range of additional parameters to be recorded concurrently (e.g. Temperature, turbidity, pH, conductivity, optical DO, chlorophyll a, ORP, ammonia)
  • Portable - blue-tooth option available
  • Sensitive - can detect very low concentrations for use in clean water systems
  • Low maintenance - self-cleaning with automatic wiper and simple calibration only every 6 – 12 months
  • graph showing in-situ proteus measurements and laboratory TOC
  • Numerous applications
    • Monitoring effluents for compliance
    • Environmental monitoring
    • Monitoring inflow to water treatment works
    • Research tool for academia

1Lee E-J, Yoo G-Y, Jeong Y, Kim K-U, Park J-H, Oh N-H. 2015. Comparison of UV–VIS and FDOM sensors for in situ monitoring of stream DOC concentrations. Biogeosciences 12: 3109–3118.DOI: 10.5194/bg-12-3109-2015

2Khamis K, Bradley C, Stevens R, Hannah DM. 2017. Continuous field estimation of dissolved organic carbon concentration and biochemical oxygen demand using dual-wavelength fluorescence, turbidity and temperature. Hydrological Processes 31: 540–555.DOI: 10.1002/hyp.11040