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Development of an in-situ detector for dissolved gases in liquid waste

University of British Columbia

Monitoring volatile compounds in sewer systems is highly important due to the toxic and corrosive nature of various nuisance chemicals generated, such as hydrogen sulfide (H₂S). Hotspot monitoring facilitates identification of the location of the generated H₂S, and thereby targeted treatment can be applied, which eventually minimizes the use of chemicals and lowers the environmental effect within the sewer system. In this thesis, we present a portable detector that is designed to extract volatile components from aqueous samples by vaporizing the sample and then exposing it to a microfluidic-based detector, fabricated by a selective microchannel embedded with a metal oxide semiconductor (MOS) sensor. The setup consists of an exposure and recovery chamber, heater, servo, and a peristaltic liquid pump. The entire device is controlled using a microcomputer that transmits sensor data and receives inputs from the user. A testing procedure is also established for the setup, which consists of 5 steps, including sample extraction, vaporization, exposure, recovery, and purging. Using a wide concentration ranges of H₂S and ammonia (NH₃) dissolved in water (i.e., two components which the MOS sensor has potential cross-selectivity), a database for classification and regression was developed: the device was capable of classifying between NH₃ and H₂S by a recall value of 100% and 96% in separate and also returned a recall value of 97% with H₂S classification and 96% with NH3 classification in mixture aqueous solutions. Regression precision for separate and mixture aqueous solutions was 84.6% and 88.77%, respectively. The developed setup was used in a field test (at Annacis Island (Delta, BC) wastewater treatment plant (AI-WWTP)) where various tasks such as sample extraction, evaporation, and data transmission were automatically performed. The results show that the device is capable of identifying and measuring the concentration of H₂S and NH₃ in raw influent with 83.48% precision. Overall, the results presented show the potential of the proposed automated wireless device in recognizing and measuring NH₃ and H₂S in sewer systems which can facilitate the detection of hotspots, reduction of treatment costs, increase of the lifespan of buried infrastructure, and minimization of the involvement of highly-skilled personnel.

Text

2021-04-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/77954

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/