Sampling systems for gas measurement in wastewater applications.
Mar 04 2020
Water and wastewater organisations have for many years struggled with measuring gases and vapours in sewers over long periods of time. The physical nature of the application creates high levels of corrosive gases, heat, water and high humidity which negatively impact all sensors including catalytic, electrochemical and photo ionisation.
In recent years, PID technology has advanced but the sensor is still directly affected by humidity creating inaccurate readings in this application. There have been many attempts to create filters within the sensor housing, or externally, but most of these have proven ineffective.
The need for sampling in sewer applications has increased over the years, with the desire to use gas sampling as a method to track and trace polluters. By measuring low VOC concentrations, regulatory bodies can determine when an offender has discharged chemicals or solvents into the sewer. PID technology is perfect for this application but the sensor is not useful unless the humidity and water vapour are eliminated from the sampling stream.
Several utilities have been on the forefront in attempting to find a solution. The key is having a system which can eliminate the particulate, reduce humidity and water to a level which sensors can withstand, which will allow accurate measurement and long-term sensor life.
Designed as a sampling system, the GSCS can incorporate single or multiple sensor detection, suited to monitor gas and vapour atmospheres from extreme environments containing temperature, humidity, particulate and pressure challenges. Any sensor technology or manufacturer can be incorporated into the GSCS.
A powerful air aspirator pulls samples from up to 50 metres in distance (longer if required) which is then filtered and conditioned before being passed across one or multiple sensors. System integrity is always maintained using flow fail monitoring devices which provide dry contacts that activate if the sample line becomes blocked, damaged or interrupted. On board communication systems provide information to key personnel.
The system can be designed to accommodate any number of sensors or can be a transportable sampling system which can be used with portable handheld instruments. For applications where a liquid sample is required at the time of high gas exposure, a second pump will be activated drawing up the liquid sample and storing it in a locked compartment of the sampling system. This provides real time liquid sample and gas measurement even when the regulatory team aren’t nearby. Each system is designed for the specific customer requirements. With over 7 years of experience is water/wastewater applications the GSCS is a proven solution to challenging monitoring applications.
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