Measuring moisture content of biofilter media using capacitance

Abstract

A biofilter operates by passing contaminated air through a moist medium like woodchips, saw dust, soil or artificial material. Maintaining moisture content within this medium is critical for biofilter operation. To date, most biofilters use a timer system and sprinklers to apply water to the medium which may lead to under-watering or over-watering. The moisture content of the filter medium in small and in research biofilters has been controlled gravimetrically using load cells. However, for full scale application of biofilters, this technique would be overly expensive and impractical. Some research is being undertaken to develop capacitor plates to monitor moisture levels within the biofilter medium. This technique shows promise and needs further development. This project will reviews the literature on biofilters and biofilter control methods, and also on capacitance-based and other possible moisture measurement techniques. Based on this research, designs are developed for the measurement of the moisture content of the selected biofilter media such as wood chips and soil. It is concluded that the completion of this project has demonstrated the advantages of using the capacitive sensor as the basis for the design and proved the feasibility of the capacitive sensing system in determining the moisture content of the biofilter media.