抄録
Thermosensitive polymers are soluble in water at low temperature, but are insoluble above the intrinsic temperature of the polymer because of the transition to the hydrophobicity. Poly(N-isopropylacrylamide) (poly(NIPAM)) is a representative nonionic thermosensitive polymer, with a transition temperature of about 32°C. In this work, a novel dewatering method of activated sludge utilizing the hydrophilic/ hydrophobic transition of thermosensitive polymers was examined. Cationic thermosensitive copolymers of NIPAM and N,N-dimethylaminopropylacrylamide (DMAPAA) synthesized with various DMAPAA contents were used. The activated sludge and the polymer solution were mixed well at room temperature. The mixture was heated to the desired temperature, and then the constant pressure filtration and expression were carried out. The temperature of the filtration/expression apparatus was kept at the desired one during the dewatering, i.e., the filtration and expression processes. When the dewatering was carried out at the room temperature, the moisture content of the dewatered cake increased with increasing the polymer dosage, because the sludge covered sufficiently with the adsorbed hydrophilic polymer molecules is dispersed stably. On the other hand, by dewatering above the transition temperature of the polymer, which depended on the content of DMAPAA in the polymer, the moisture content of the dewatered cake decreased remarkably with increasing the polymer dosage. The dewatering performance depended on the temperature and the content of DMAPAA in the copolymer. Such a high dewatering performance with thermosensitive polymers are attributed to the hydrophobic interaction of thermo- sensitive polymer molecules adsorbed on the sludge.
