Promoting nitrification by using functional gel as immobilizing medium under different temperature stimulation patterns

Nitrification with nitrifiers immobilized by temperature stimuli-responsive N-isopropylacrylamide-Chlorophyll (NIPA-CH) gel was investigated under several patterns of temperature stimulation, compared with that at constant temperature. The results show that in response to a cyclic temperature stimulus of 32-36°C or 32-34°C with a period of 4 or 2 h, respectively, the gel swelled and shrank reversibly and promoted biological nitrification. But in the case of a cyclic temperature change of 32-36°C with a stimulation cycle of 2 h, nitrite oxidization declined. The results suggested that adequate stimulus facilitated substrate transfer into gels that promoted nitrification in the reactor, but quite frequent swelling and shrinking of the gel squeezed nitrifier out of the gel resulting in washing nitrifier out and declining nitrification. When gels that undergone cyclic temperature stimuli began to swell at 32°C, oxygen consumption of nitrifiers in the gels was more than that of nitrifiers in the gels at constant temperature of 32°C all the time, but when gels of two reactors shrank at 36°C, their oxygen consumption reduced and there was almost no difference between them regardless of their undergone temperature stimuli once or not. Practical application of nitrifier immobilized by NIPA-CH gel in wastewater treatment was also discussed.