Gas-phase biofiltration for livestock building ammonia emission mitigation

This study aims to improve the basic biofilter engineering designs (media selection, airflow resistance measurement), ammonia removal efficiency, and also to examine the effect of moisture on nitrous oxide generation. Besides that, a moisture sensor was developed to control the moisture content in biofilter media in order to achieve high ammonia removal efficiency and low nitrous oxide generation.;Biofilter media selection and pressure drop management affect the affordability of biofilters. In this study, physical, chemical properties and airflow resistances of eleven commonly used biofilter media, including ten organic and one inorganic materials, were characterized. The density, porosity, particle size distribution, pH, total C, total N, and organic matter content of each material were analyzed using standard methods. The airflow resistance property was tested on a large chamber (LxWxH: 1.0mx0.6mx0.6m) with cross-section airflow rate of 0-0.15 m3.m-2.s-1. Airflow resistance driving factors, including moisture content, particle size distribution, bed thickness and compaction, were experimentally evaluated. The testing results were fitted into Hukill and Ives (1955) equation, and then two equation constants, a and b, were calculated for comparison and also used as an initial database for future biofilter designs. Based on the observations of moisture, bed thickness and compaction effects on air flow resistance, an empirical modification implementing derating factors was suggested to improve the Hukill and Ives equation.;In order to evaluate the function of biofilters, a baseline test was carried out to examine ammonia removal efficiency and nitrification kinetics at extreme conditions where a high ammonia loading without pre-humidifying was introduced and a high pH value was maintained in the biofilter media. Two bench-scale biofilters were built for this study and the test was composed of an N-enriching step, an N-depleting step, and a second N-enriching step. The results showed that 90-94% ammonia removal efficiencies were observed for about ten days and then decreased in the first N-enriching step.;To examine the role of moisture content in biofilter application, a four-month test was conducted on four bench-scale biofilters. The moisture contents in the treatment biofilters were manipulated from 35% to 55%, then to 63%, with a final step of 55%; while the moisture content in control biofilters were managed at 35% and then kept constantly at 55%. It was found that ammonia removal efficiency was improved when media moisture content was increased from 35% to 55%; but further increasing moisture content to 63% did not enhance ammonia mitigation much. In contrast, little increase of nitrous oxide (0.10?0.15 ppm) was observed when moisture content was increased from 35% to 55%, but further increasing moisture content to 63% caused a peak of nitrous oxide generation.;Based on the previous study results of moisture effects on biofilter performance, it becomes necessary to manage the moisture content in the biofilter media. To achieve this goal, a moisture sensor based on media impedance measurement was developed. The sensor is composed of a sensing unit and a circuit that returns dc voltages. In a validation test, the sensor was used to measure moisture contents in two woodchips and one compost with moisture contents of 5-65%. The results fitted theoretical predictions quite well, showing that impedance can be a reliable indicator of moisture content. Besides that, temperature and compaction effects on impedance measurement were explored. It was found that increasing temperature from 22° to 27° and further to 32° did not change impedance of media (which is closely related to sensor reading) while compaction for eight days did. Applying the sensors in two bench-scale ammonia mitigation biofilters for one month showed that the sensors were sensitive to moisture changes. Incorporated with a water pump control strategy, the media moisture contents were successfully managed within a desired range of 44-47% according to the sensor readings. (Abstract shortened by UMI.).