A woodchips-based gas-phase biofilter is capable of mitigating airborne ammonia efficiently. The moisture content (MC) of the biofilter media is important to determine ammonia mitigation and nitrous oxide generation. It is critical to monitor real-time moisture content of the biofilter media for maintaining biofilter performance. The objectives of this research are to obtain a deep insight into the impedance-based moisture content measurement and to improve methodologies to monitor the moisture content of gas-phase biofilters. A sensor consisting of a sensing unit (three parallel plates) and a circuit generating DC voltage outputs was used in this study to measure moisture content. The sensor readings changed with step-wise increase of moisture content as well as different particle size distribution and nitrogen (ammonia-nitrogen, nitrate-nitrogen) concentrations of biofilter media. The results show that both particle size distribution and nitrogen concentrations significantly affected impedance-based moisture sensing. A mathematical model was formulated, which was able to demonstrate the relationship between the sensor reading and moisture content of the biofilter media. A model was established to predict the moisture content of the biofilter media based on sensor reading, ammonia-nitrogen concentration and nitrate-nitrogen concentration
