Dewatering of inorganic sludge using dual ionic thermosensitive polymers

The dewatering of inorganic sludge by a novel method based on the hydrophilic/hydrophobic transition of ionic thermosensitive polymers was investigated. As an inorganic sludge, the drinking water treatment sludge was used. Cationic thermosensitive polymers, poly(NIPAM-co-DMAPAA), which were synthesized by copolymerizing N,N-dimethylaminopropylacrylamide (DMAPAA) as the cationic component with N-isopropylacrylamide (NIPAM) as the thermosensitive component, were effective in dewatering the sludge. When the dewatering was performed at room temperature, the optimum polymer dosage for the dewatering rate was observed similar to the conventional hydrophilic polymeric flocculants. On the other hand, when the dewatering was carried out above the lower critical solution temperature (LCST) of poly(NIPAM-co-DMAPAA), the dewatering rate increased remarkably as the polymer dosage increased. Such high dewatering rates can be attributed to the hydrophobic interaction among the thermosensitive polymer molecules adsorbed on the sludge. However, the LCST of poly(NIPAM-co-DMAPAA) increased considerably as the DMAPAA content increased. In order to solve this problem, the use of dual ionic thermosensitive polymers was investigated. By using the anionic thermosensitive polymer, poly(NIPAM-co-AAC), which was synthesized by copolymerizing acrylic acid (AAC) with NIPAM, in combination with cationic poly(NIPAM-co-DMAPAA), the dewatering rate was remarkably increased at relatively low temperatures. This increase was attributed to the formation of a polymer complex that decreased the LCST of the polymer molecules adsorbed on the sludge.

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► The dewatering method based on the hydrophilic/hydrophobic transition of thermosensitive polymer was effective.
► The dewatering rate increased remarkably by using the dual ionic thermosensitive polymers.
► The increase was attributed to the formation of a polymer complex that decreased the LCST of the polymer.