In situ moisture content measurement in MSW landfills with TDR

Moisture content has an important effect on biodegradation rates in landfills. In situ moisture measurement is, therefore, at the center of any scientific studies related to optimal operation of bioreactor landfills. Because of the material heterogeneity, there is no commonly accepted way for in situ moisture measurement in wastes. The goal of this paper is to develop the instrumentation and analytical procedures to measure in situ moisture content in MSW materials. The system is based on Time Domain Reflectrometry (TDR), which had to be improved for moisture measurement in wastes. In particular, TDR probes have to be calibrated for the specific materials, and the effect of varying leachate electrical conductivity has to be reduced. A series of experiments were conducted with different waste materials and mixtures. The materials and the liquid electrical conductivity (eC) were varied systematically. The results show that a fourth-degree polynomial calibration equation, albeit with slightly differing coefficients for different materials, provides excellent fit (r(2) values over 0.99). Further, the type of material can be substituted by the porosity of the material to select the appropriate calibration coefficients. The variation of leachate electrical conductivity was eliminated at high eC values and noticeably reduced at low eCs (0.03-0.95S/m) by coating the TDR probes. These results indicate that TDR is a viable instrument to measure the in situ moisture content in landfill.