Fundamental studies of municipal waste, (2)

The state of water molecules in sludges has been studied by taking NMR spectra. By changing the water content of sludges such as activated sludge, aluminum hydroxide and fine silica particles, NMR spectra of the samples were measured with 100 M Hz high resolution NMR at room temperature. The amount of bound water molecules in aluminum hydroxide, activated sludge and fine silica particles were estimated to be 1.4, 3.0 and 2.3 g/g-dry solid, respectively, on the basis of relationships between water content and H-NMR line width. From the results it was supposed that the amount of free water would be very small in the mechanically dewatered sludge and degree of dewatering difficulty depends on the ratio of free water volume to the total water volume, i.e. sum of free and bound water volume. After aluminum hydroxide and activated sludge has been frozen and then defrosted, the mobility of water in the former increased significantly while that in the latter remained almost unchanged. So the difference of characteristics of water molecules in activated sludge and in aluminum hydroxide has become apparent in terms of the mobility of water molecules and the conformation of water in the sludge. After being heated to 900C and cooled down to room temperature, the mobility of water in these two samples showed similar tendencies due to the difference of water structure in the sludges. Through the studies of sludge water characterization, NMR method has been proved to be a useful tool in the dewatering control process. (author)