Study on the advanced nitrogen removal under low temperature by biofilm on weak magnetic carriers.

The advanced nitrogen removal under low temperature is inhibited because of reduction of the microbial activity. Packed bed reactors filled with different magnetic carriers (0, 0.3, 0.6, 0.9 mT) were constructed to enhance advanced denitrification under low temperature (5 ℃). Results showed that 0.3 and 0.9 mT carriers significantly improved denitrification, indicating the "window" effect. Total nitrogen removals were increased by 6.96% and 8.25%, and NO ₂ ^- accumulation decreased by 25.70% and 13.90% in 0.3 and 0.9 mT reactors, respectively. Analysis of enzyme activity and electron transport chain showed that 0.3 mT carrier mainly increased NIR activity by improving compound III and cytC abundance while 0.9 mT carrier mainly increased NAR activity by improving compound I and NADH abundance, indicating different pathways. Similar microbial community in 0.3 and 0.9 mT reactors were revealed. Overall, weak magnetic carriers can be used to enhance advanced nitrogen removal under low temperature.
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