Unisense new H2S sensor allows users to track hydrogen sulphide

The new industry grade wastewater sensor from Unisense measures dissolved hydrogen sulphide directly in the sewer system

A new sensor from Unisense makes it possible to measure instantly and directly hydrogen sulphide (H2S) dissolved in wastewater, allowing utilities and consultants to find the root cause of hydrogen sulphide odour problems in sewer networks.

“Hydrogen sulphide has the characteristic smell of rotten eggs. It is quite common in sewer networks – especially, when wastewater is pumped over long distances,” Ebbe Kruse Vestergaard, Technical Business Developer at Unisense, said. “Warm climate and long retention times is also a dangerous cocktail that often leads to both odour nuisances and downstream corrosion issues.”

With more precise and cost-effective root-cause analysis of sulphide problems, more effective mitigation initiatives can be used, saving significant cost for chemicals.

“Utilities and consultants face severe difficulties identifying the real source of hydrogen sulphide in their sewer network. They find that their current practice of grab samples and gas detectors at the location of odour complaints is clearly insufficient,” Vestergaard continued. “Consequently, they end up over-treating and spending tons of chemicals on a large upstream sewer network where most branches may be leading to no or very little sulphide related problems.”

Able to communicate with computers and SCADA systems, the sensor is also a key tool in preventing over treatment.

“Utilities and consultants can easily make measurements in the different sewer branches leading to the location of the symptoms,” Vestergaard explained. “This way, they can find the exact source containing dissolved sulphide and look for the right mitigation strategy for that branch. Often this is a dedicated dosage of chemicals.”

Odour complaints from citizens are, however, not the only reason to optimise hydrogen sulphide in the sewer lines. According to Vestergaard, high concentrations of the gas can also cause severe corrosion of concrete pipes, pump stations and pumps.

“If a normal sewer pipe with a lifespan of 50-100 years is exposed to high concentration of hydrogen sulphide, then the concrete walls can be degraded to the point of breakage in less than 10 years,” Vestergaard continued. “Replacing and repairing sewers is one of the biggest operational costs of utilities, and with the sensor’s ability to map out the sulphide concentrations throughout the network, new approaches to asset management may be seen in the future.”