Impedance-based moisture content sensor assessment for gas-phase biofilter media

A woodchip-based gas-phase biofilter is capable of mitigating livestock airborne ammonia efficiently with low cost. Control of the moisture content (MC) of biofilter media is critical for ammonia mitigation and limiting nitrous oxide generation. It is important to monitor the real-time biofilter MC to maintain biofilter performance. The objectives of this study were to further develop and evaluate impedance-based MC measurement and to improve methodologies to monitor the MC of gas-phase biofilters. A sensor consisting of a sensing unit (three perforated parallel plates) and a circuit generating DC voltage output was used to measure MC. The sensor readings changed significantly with stepwise MC increases, particle size distribution, and nitrogen (ammonia-nitrogen, nitrate-nitrogen) concentrations in biofilter media. A mathematical model was developed for the relationship between the sensor reading and MC. A statistical model was established to predict the MC in biofilter media based on the sensor reading, ammonia-nitrogen concentration, and nitrate-nitrogen concentration.