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New Sensor System Could Soon Help Isolate and Expose Polluters

Criminal machinations could be challenging to prove—for example, when those involved stealthily discharge dangerous wastewater into sewers.

Sensor ring for use in wastewater treatment plants. (Image credit: Volker Mai)

Fraunhofer scientists and their collaborators have designed and built a new sensor system that could soon assist safety agencies to find such offenses: when positioned within a sewage canal, it senses relevant substances and helps segregate and reveal polluters.

There is always one rotten apple, and the industry is no exception. Although most of the companies eliminate their wastewater properly, some intend to evade the related costs, so they covertly and silently discharge their dangerous wastewater into the sewage canals.

In general, at present, safety agencies lack the techniques to detect this type of environmental crime on a larger scale—carrying this out would significantly exceed their work-force potential. However, this unlawful sewage poses significant problems for wastewater treatment facility operators and can even lead to turnover of the affected wastewater treatment ponds.

Detecting Pollutants in Wastewater

Soon, an innovative sensor system could render it easier for safety agencies to unravel these types of offenses. The technology was created by scientists from the Fraunhofer Institutes for Integrated Circuits IIS and for Reliability and Microintegration IZM, along with their collaborators in the EU microMole project.

The sensor system is designed to detect certain substances that are typically found in affected wastewater. It comprises two sensor components—physical sensors and a chemical sensor—as well as an energy management system, a control and communication system and a sampling system.

Dr Matthias Völker, Group Manager, Fraunhofer IIS

If hazardous wastewater often poses issues at wastewater treatment plants, safety agencies could investigate the sewage system at specific points and, by making a number of measurements, slowly close in on and eventually reveal the perpetrator.

A robot makes the measurements by placing three rings in the sewage pipe. The first ring is directly placed in front of the suspect company’s inlet and the second directly behind it. Both rings are fitted with a physical sensor to measure different parameters, like pH, temperature, and water conductivity.

The two rings wirelessly communicate with one another and compare the measurement data from their sensors. The difference in measurements could be caused by the discharge of tainted wastewater from the building in question.

The third ring, placed slightly further back in the sewage canal, is fitted with a sampling system and a chemical sensor. In case a special signal is transmitted by the second ring, these systems “wake up.” A few microliters of the wastewater is withdrawn by a micropump, which then dilutes it and transfers it to the chemical sensor. The chemical sensor includes six electrodes, each coated with a unique polymer coating.

The distinctive feature of this system is that the polymer layers include a number of gaps that are each ideally sized to house specific pollutants—very similar to pieces of a puzzle. Upon binding to the polymer layer, there is a change in the electrical capacity of these pollutants. Therefore, when the electrodes sense the change, it is indicated that the wastewater includes specific pollutants.

Yet, since this cannot be used as evidence in a court of law, the system also collects a small sample of the wastewater that can be subsequently tested thoroughly by hand in the lab. A cleaning solution allows the chemical sensor to be used for several measurements by flushing out the attached molecules again following every measurement.

The sensor system was developed in a joint effort between various research institutions and other collaborators. The Fraunhofer IIS scientists created the electronics, the signal acquisition and evaluation of the sensor module, and the system energy supply.

Their collaborators at Fraunhofer IZM developed the BUS system on the metal ring and designed the waterproof plug contacts for the individual components and the chemical-proof and waterproof casing. In addition, they miniaturized the physical sensors.

Large-Scale Test Run Planned

At first, the components were individually tested in the labs of the project partners; then, they were tested together with real wastewater in an artificial wastewater system. Thirdly, tests of different components were performed in a real sewage pipe.

Initial outcomes of the study look promising: “The system detected suspect sewage and triggered a corresponding alarm,” concluded Harald Pötter, department head at Fraunhofer IZM. During a follow-up project, the scientists from Fraunhofer IZM now intend to perform a large-scale test run of the physical sensors of the system with collaborators in five European cities.


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