Level Measurement & Control


Level monitoring in wastewater applications

August 2014 Level Measurement & Control

Any water that has been used is classified as wastewater and will at some time enter the recovery system. Generally, wastewater flows through the network to treatment plants to recondition it and to allow safe return to the natural resources such as rivers, streams and the ocean. In many of the treatment stages, level monitoring is required.

Level measurement and pump control

As wastewater moves through the sewage collection network, it often needs to be stored and pumped to higher levels in so called lift or pump stations. These stations often use submersible pressure transmitters for level monitoring and pump control.

Any component used in raw sewage will gradually become encased in fatty deposits and a level transmitter is no exception. However, unlike floats which will sink when deposits build up, submersible hydrostatic level transmitters will continue to provide accurate level monitoring. As long as these fat deposits are not allowed to dry up, the hydrostatic pressure is still accurately transmitted to the diaphragm. Hydrostatic level transmitters are also unaffected by the internal structures of tanks and lift stations, such as internal bars supporting pumps, which can cause reflections and disrupt ultrasonic or radar-based level detectors.

When wastewater arrives at the treatment plant, it will flow to the various tanks of the treatment process where level monitoring is critical for control and automation. Submersible pressure transmitters will be used to regulate and control the pumps moving the sewage around the wastewater treatment plant.

Primary and secondary stages

Primary treatments such as settlement tanks will allow human wastes and other organic solid matter to sink to the bottom. The solids, often called sludge, are removed for further processing. Fat and grease will rise to the surface and be scraped off. When the sludge height reaches a defined level it will be recovered and processed through either drying systems or large hydraulic filter presses, controlled by pressure transmitters. The fresh water above the sludge level and from the filter process then flows to the secondary treatment stages, such as aeration tanks or microbial reactors.

Secondary treatment such as aeration encourages natural helpful bacteria to multiply and break down hazardous bacteria. Alternatively membrane bioreactors are becoming popular and work as an extremely fine bio-filter to remove hazardous bacteria. Both systems require level monitoring of wastewater to work most efficiently and level transmitters are then used to monitor the clean recovered water. The water may then pass into further settlement tanks from where it is returned to the natural resources.

At all stages through the wastewater network and treatment, level monitoring using hydrostatic and submersible pressure transmitters provides essential control and feedback on the process.



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