The “Technische Betriebe Wilhelmshaven” (TBW) waste management service is responsible for the drainage and treatment of wastewater in the towns of Wilhelmshaven and Schortens. It operates a 520 kilometer underground canal system as well as two primary and 65 auxiliary pumping stations, which convey the wastewater to the central wastewater treatment plant via pressure pipelines. The TBW's urban drainage system treats around 20,000 cubic meters of wastewater every day.
The TBW is continuously optimizing its systems. As part of the modernization of the wastewater treatment plant, four clarifiers, the grit channel, pumping stations, and digestion towers were fitted with a wireless system from Phoenix Contact in order to cost-effectively transmit signals and data to the control center.
Integration of quantity measurement into the control system
Approximately 300 meters away from the primary pumping station, on the other side of the Ems-Jade canal, quantity measurements are taken in the pressure pipeline. The analog measuring signal could not be connected to the PLC in the primary pumping station by cable as it proved too difficult to channel beneath the Ems-Jade canal.
Frank Jakobs, responsible for automating the sewage treatment plant and pumping stations, reports, “When searching for a solution to this problem I discovered wireless technology from Phoenix Contact.” Two Bluetooth converters, which integrate the sensor signal directly into the PROFIBUS system of the primary pumping station, are now used in place of cables. “This has turned out to be a very economical solution”, concludes Frank Jakobs.
Immediate notification if the fill level is exceeded
Coarse solids are removed from the wastewater in the raking and sand trap system. Solids such as sand and road grit are deposited on the floor of the ventilated sand trap. They are then pumped away and conveyed to a grit washing system. The pump is located in a shaft that used to overflow frequently without anyone noticing.
Thanks to the Wireless-MUX system this problem is now a thing of the past; if the water in the pump shaft rises above a certain fill level, the wireless modules emit a signal that shuts down all pumps in the sand trap scraper.
When the water level drops, an evaluation unit with a fill level sensor reactivates the pumps. The Wireless-MUX system has been working without interruption for several years. “Based on our positive experience, we are now using wireless systems from Phoenix Contact in several other areas”, reports Frank Jakobs.
Cost-effective alternative to sliding contacts
Another field of application for industrial wireless technology is secondary clarification; in each of the four clarifiers a process probe from Hach Lange measures the sludge level using an optical process. The probes are located on the scraper bridges revolving around the clarifiers. The measured values are transmitted to the respective controller and then forwarded to the control room in the factory building via PROFIBUS.
Since transmission via traditional transmission media such as sliding contacts proved maintenance-intensive and prone to faults, a wireless solution was chosen for this particular application.
A Bluetooth converter was installed on each of the four scraper bridges and connected to the corresponding PROFIBUS controller. The probes then transmit the data via Bluetooth to a central station between the scrapers, which in turn is connected to the PROFIBUS master in the factory building via FO converter.