Time domain reflectometry measured moisture content of sewage sludge compost across temperatures

Abstract

Time domain reflectometry (TDR) is a prospective measurement technology for moisture content of sewage sludge composting material; however, a significant dependence upon temperature has been observed. The objective of this study was to assess the impacts of temperature upon moisture content measurement and determine if TDR could be used to monitor moisture content in sewage sludge compost across a range of temperatures. We also investigated the combined effects of temperature and conductivity on moisture content measurement. The results revealed that the moisture content of composting material could be determined by TDR using coated probes, even when the measured material had a moisture content of 0.581cm3cm−3, temperature of 70°C and conductivity of 4.32mScm−1. TDR probes were calibrated as a function of dielectric properties that included temperature effects. When the bulk temperature varied from 20°C to 70°C, composting material with 0.10–0.70cm3cm−3 moisture content could be measured by TDR using coated probes, and calibrations based on different temperatures minimized the errors.