| Aerobic granules composed of various kinds of bacteria including aerobic, anaerobic and facultative bacteria, and they are feactured with outstanding settleability, large volume of biomass and simultaneous nitrogen and phosphorus removal. This technology has found its application in municipal wastewater, toxic wastewater, heavy metal wastewater treatment. However, researches on aerobic granular sludge were mainly limited to theoretical study with lab scale due to of its instability and energy intensive consumption. Our previous study showed that aerobic granules could be successfully cultivated all the seasons in a temperature-controlled room, however, it was rather unstable with water-bath temperate controlled reactors but the room temperature was varied in summer. This study was carried out in order to identify the reasons for the difficulty to cultivate the aerobic granules at high room temperature in summer.In this experiment, the seed sludge was taken from a wastewater treatment plant with oxidation ditch process, and three geometrically identical sequencing batch reactors(SBRs) were employed, which were placed in a room with room temperature varied in the range of 27-31℃. Reactor R1 and raw wastwater had no temperature control, and the temperature of R1 was the range of 25-28℃; the raw wastewater temperature for reactor R2 varied with room temperature, the temperature of R2 was controlled under 23±2℃using water bath; reactor R3 and its raw wastewater was controlled to 23±2℃using water bath. All the temperatures were recorded using a paperless datalog. The instability of aerobic granular sludge was analysized in terms of water quality parameters, granular morphology, settleability of granular, filamentous bacteria. Results showed that:(1) Aerobic granules occurred in the three reactors and in the later period of this study filamentous bacteria were predominated. The average size in R1, R2, R3 was 1152.2-2385.5μm,467.0-1361.1μm,444.7-1326.0μm, respectively. The roundness of R1, R2, R3 less than 3 accounted for 43.29%,90.25%,66.26% of total volume, respectively. Slightly higher temperature in the reactor (R1) discouraged the formation of regular granules, however, the high temperature of feeding wastewater encouraged the formation of regular granules (R2).(2) The temperature of reactor affected formation and stability of granules more significantly than that of feeding did; and the relatively high temperature of air during summer accounted for the difficulty of granule formation and stability.(3) When the temperature of air pumped into the reactor was lower than the biomass in the reactor, it would eliminate the unbalanced growth for the microorganisms on the surface and the inside of granules and favor to stability of granules. However, when the temperature of air pumped into the reactor was higher than the biomass in the reactor, it would enhance the unbalanced growth, which may result in more voids inside granules, and consequently led to instability of granules.(4) The difference between temperatures of air pumped into the reactor and the temperature of granules surface, the temperature of feeding in R1 changed sharply, which led to some bacterium difficult to adapt. However, filamentous bacterium could take advantage of the changes and finally overgrew.(5) With the high room temperature, the temperature influenced nitrifiers firstly. The remove rate of NH4+-N is much less than in winter (under the same conditions). Until the system was failure to operation, the temperature slightly affect the activities of heterotrophic bacteria, and lots of filamentous bacteria did not necessary lead to the increase of the effluent COD. |
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