Smart sewers: development of wireless in-situ sensors for dissolved gases in liquid waste

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Liquid Waste Service (LWS) infrastructures, such as those at Metro Vancouver (MV), encompass a vast network of sewer pipes, pumping stations and treatment facilities to accommodate large volumes of waste. However, the sewer environment provides ideal conditions for particular bacteria species. As a byproduct of their metabolic processes various nuisance gases are produced, including hydrogen sulfide, ammonia, carbon dioxide, methane, and nitrous oxide. These target gases are responsible for corrosion, offensive fugitive odours, and greenhouse gas emissions. Biogenic acid corrosion is of particular concern; biological processes can create strong acids from hydrogen sulfide which drastically reduce the lifespan of the LWS infrastructure and increase the risk of sewer pipe collapse. A variety of mitigation treatments are used to control and prevent the production of nuisance gases and their related consequences. However, the chemicals used for these treatments are expensive and require targeting specific "hotspots" of biogenic gas to increase cost-effectiveness. Since gas production occurs within the liquid-phase of sewer pipes, there has been an expressed need for a detector capable of being situated along the pipeline over extended periods. This industry problem will be addressed in the following research objectives: (1) Develop a gas sensor using a sensitive metal oxide semiconductor coupled with a selective microfluidic diffusion channel. (2) Integrate the sensor with support systems for sample extraction, filtration, sample delivery, sensor recovery and cleansing. (3) Develop a microcontroller and data collection components to operate all the systems of the detector and to transmit data for analysis on portable devices. (4) Construct a robust platform to integrate the sensor and supporting systems and provide durability in the turbid sewer environment. (5) Conduct field tests to optimize the device and address identified issues. This device will provide real-time data to LWS personnel to better inform their biogenic gas mitigation strategies. Ultimately, the developed technology will help extend LWS infrastructure service life, reduce the carbon footprint of LWS, and mitigate nuisance odours to surrounding communities.