Radar sensors in wastewater processing

In a country where water has to be treated as a precious resource, it is perhaps no surprise that the Australian water industry is leading the world in adopting technology to maximise the re-use of every possible drop.

One man who appreciates this from the sharp end of the business is John Leadbetter, Managing Director of sensor specialist VEGA Australia.

The water industry is a major target for VEGA worldwide, with a market-leading portfolio of level sensors, together with a complementary range of pressure sensors. And VEGA Australia is punching above its weight: it ranks second worldwide among VEGA companies for sales to the water industry on a per-head-of-population basis.

The treatment of wastewater is a particular area where Australia leads the world, a point borne out, says Leadbetter, by the security levels employed at even the most humble sewage treatment plant. “It’s all about protecting resources,” he says.

“There is no doubt that the authorities are much more mindful of the value of water than they were 20 years ago,” adds Leadbetter, pointing to the work of the Environmental Protection Agency in monitoring of wastewater flows from commercial premises as further evidence.

Radar technology

So, what are the technologies that are enabling this improved monitoring? It all comes down to radar, and the dramatic reduction in the cost of the technology in recent years.

For example, one of the critical stages early in the sewage processing chain is to ensure that there is a steady flow of sewage to the treatment works. The continuous level measurement of wastewater in the sink enables pumps to be switched in only when required.

Traditionally this level measurement has been performed using a submerged probe, which would inevitably become clogged with all manner of rags and other solids in the sewage flow, and so the maintenance required was both time-consuming and hazardous (given the nature of the sewage).

This has become a perfect case for radar level measurement, and VEGA’s solution is its Vegapuls WL 61 radar sensor, a low-cost unit that includes Bluetooth communications as standard. So, not only does the radar sensor not come into direct contact with the sewage, wireless communications allow it to be set up and calibrated without human contact as well.

Additionally, the radar sensor is not fooled by the foam that can often occur in such applications. It measures the level of the fluid, not the foam.

Another “standard” measurement required in wastewater processing is the flow rate in an open channel – whether it be an inflow to a treatment plant or an outflow from a commercial process.

A knowledge of the exact rate of inflow to the plant is crucial to control of the complex system, and discharge level measurement is mandated for environmental compliance in commercial operations.

Both cases call for continuous level measurement to ensure that the total flows are recorded accurately.

Here, again, the Vegapuls WL 61 sensor is now the preferred option. Easily mounted above any open channel, the sensor provides highly accurate level measurement, from which the flow rate can be calculated, typically using standard VEGA signal-conditioning hardware such as the Vegamet 391.

This measurement solution is immune to the effects of temperature fluctuations, air movement or foam on the surface of the liquid. And the sensor remains out of the wastewater, avoiding the risks of soiling from any solids in the flow.

Monitoring methane

One of the biggest changes to sewage processing in recent years concerns the mitigation of gas emissions caused by the breakdown of the organic matter – most notably methane.

According to the Global Methane Initiative, in 2010 methane emissions from municipal wastewater treatment plants accounted for around 7% of total global

methane emissions. And methane is considered a more destructive greenhouse gas than carbon dioxide.

The trend is now for the use of anaerobic digesters to process the wastewater biosolids, collecting the methane (and other gases) for use as fuel – either to cover the plant’s power requirements or even to sell on as commercial fuel.

This has led to a further measurement task well suited to radar technology: measuring the sludge level in the digestion tower. However, the digestion process often also leads to the production of high levels of foam – which cannot be allowed to spill over into the gas plant.

The solution here involves a combination of technologies. The Vegapuls 68 radar level sensor will reliably detect the surface level of the sludge, regardless of the gas concentration in the digester. And as it approved for Ex areas, it is safe for use in the flammable atmosphere.

The second technology involves the use of a capacitive sensor, the Vegacap 64, to detect rising foam levels and stop the foam from entering the gas system.

Chemical compatibility

A further wastewater processing application that takes a dual-sensor approach is in the monitoring of the chemicals used in the process, most of which are subject to legislation covering substances that are hazardous to water.

Here, the Vegapuls 61 provides noncontact measurement of storage tank levels. This particular radar sensor has a plastic-encapsulated antenna, which gives it increased levels of chemical resistance.

The full assurance of overspill protection is provided using a Vegaswing 63 vibrating level switch that can be specified in a variety of materials to match the corrosiveness of the media being monitored. Options include stainless steel, Hastelloy and plastic or enamel coatings.

With radar sensors deployed at so many stages of the wastewater processing chain, the technology has become inextricably embedded in the process. It could also explain exactly why there is such high security at Australia’s wastewater treatment plants.

And for John Leadbetter and VEGA Australia, it certainly reinforces the old adage that where there’s muck there’s money.

VEGA Australia
1800 817 135

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