Moisture Sensing Methods for Biofilters Treating Exhaust Air from Livestock Buildings

Abstract

Biofilters using media of crop residue materials have been shown effective in removingodorants from air exhausted from livestock buildings, especially swine facilities. Adequate mediamoisture is critical in maintaining biological growth in filters, and most biofilter installations use eitherportable or permanently installed equipment for adding water to the media. A reliable method isneeded for continuously evaluating media moisture, to determine when water should be added to thefilter to replenish moisture levels deep within the filter.<br><br>This project tested five different types of moisture meters in a typical biofilter medium: LincolnIrrigation soil moisture meter, Farmex HMT-3 digital hay moisture meter, Campbell ScientificHydrosense digital soil moisture meter, Vaisala Hummiter50Y relative humidity probe, and a site-builtradio-frequency large-area capacitive plate sensor.<br><br>None of the soil and hay moisture meters performed adequately in predicting biofilter media moisturecontent. The relative humidity probe did, however, produce a calibration curve with a viablesensitivity in the media moisture range of interest, and was subsequently tested for a period of months in a field application. The large-area capacitive plate sensor showed nearly linear responseof system capacitance with moisture content on laboratory tests at media moisture contents of 10 to70% (wet basis) over energized frequencies of 300 kHz to 15 MHz.