Determining Water Content in Waste Sludge Cake by Time-Domain NMR

The application of low-field time-domain nuclear magnetic resonance (TD-NMR) to measure water content and assess the distribution of water fractions in sludge samples has been investigated. The results of TD-NMR measurements on 26 dewatered sludge samples revealed a strong correlation between sludge water content and key features of the T₂ distribution curves, including the maximum relaxation time and peak area, demonstrating the potential of the TD-NMR method for estimating sludge moisture content. We have not observed a direct relationship between the peaks in T2 relaxation distribution curves obtained by Inverse Laplace Transform (ILT) and the expected water fraction ratios, apparently because sludge structure is highly variable from sample to sample. Despite the bio-complexity of sludge samples, the direct correspondence between key features of the T₂ relaxation curves and moisture content demonstrates the high potential of TD-NMR as a tool for controlling sludge moisture content, even in an online device configuration.