Helping Water Industries to Protect Our Waterways

The Wastewater industry is growing and diversifying at a rapid rate and the regulations supporting it are immense.

Water treatment plants do not just clean water, they also use their own bio-product to generate energy for the plant itself, provide processed remains as fertilisers for farming communities and recycle water back into the natural waterways. The industry is multifaceted and becoming what is now termed a circular economy and is an ideal example of recycling to make the best use of waste products whilst also protecting the environment.

Bearing this in mind Delta Mobrey were asked to assist with some of the measurement and reporting in the final settlement tanks of a water company based in the south of England.  It is imperative to know what is happening within the treatment plant, and more importantly to know immediately if something is not working as it should.  The crucial factor for this company was to categorically know and be confident that sludge did not overflow from the final settlement tanks into the local waterway. The penalties for the company would be high and the environmental problems would be felt for some time. They did have a solution, but it was far from effective. There were a great many tanks and under their previous workflow while they might have known there was a problem, they could not have known with which tank and therefore needed manual inspection before they were able to act. Their real challenge therefore was to detect and identify a rising sludge level remotely before it could become a hazard.

During the wastewater treatment process, water settles in various tanks and gravity allows the heavier elements contained within the water to drop to the bottom of the tank, whilst the lighter filter to the top.  The sludge blanket is really the top layer of the settled solids. For the best possible outcome, the sludge blanket should be maintained as a minimum 0.6m or 2ft.  That is deep enough to ensure that the bio-products are held at the bottom whilst ensuring that lighter aspects, i.e. cleaner water rises to the top. The substance above the sludge blanket is called the supernatant.  It is imperative that a good sludge blanket system is maintained so knowing the depth is essential.  Wastewater cannot be allowed to mix with our waterways until it meets all the recognised criteria set by Ofwatt, the Environment Agency, the Health Protection Agency, DEFRA – Department for Environment, Food and Rural Affairs.

Delta Mobrey’s customer needed to make sure that the sludge blanket layer would not rise to a level where it would overflow to the surrounding weir and then be discharged into the waterways.  The recommendation to meet this customer’s challenge was to use a gap sensor and a control unit that was fitted onto a rotating bridge in each of the Final Settlement Tanks. A sensor was placed within the supernatant, giving continuous feedback to a control unit positioned above on the rotating arm. The ultrasonic signal from the sensors passes easily through the clean water, but gets interrupted, or attenuated by sludge.  The control unit detects this change in the received signal and switches a relay to indicate an alarm condition.  The offending tank is identified by the plant’s control system, and the problem can be quickly sorted.  By identifying the problem and the location early, untreated water can be prevented from entering the clean water system.  A lot of financial and administration time was saved, and the legal and social responsibility of the company is maintained.


The solution was a combination of The Delta Mobrey Undissolved Solids Sensor, the 433SD, designed specifically for sludge level detection in tanks, combined with the Delta Mobrey Control Unit, the MCU200 series. Together they provide a simple and cost-effective electronics system with LED indicators and outputs for alarm status: ie Normal, Alarm and Fault, including continuous cable health check.  We chose this solution as the Ultrasonic gap sensors have proved to be trouble free controls for practical applications where alternative technologies require regular attention. This system therefore provides an ideal solution to detect increasing sludge levels, trigger alarms and to ensure preventative action can be taken to safeguard the environment.

The customer was able to focus on other areas of the business, confidently knowing that the Delta Mobrey solution would not allow contaminated water to flow into the natural waterways.

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Delta Mobrey Limited is a global specialist in the design and manufacture of temperature, pressure and flow process control instrumentation, with particular expertise in hazardous areas. With a proud history spanning over 100 years, Delta Mobrey Limited is a globally recognised specialist in the design & manufacture of process instrumentation. Trusted ...