Indigenous bacteria are essential for the performance of bio-filters for drinking water treatment. Yet it is slow and difficult to develop biofilm in a granular activated carbon (GAC) filter with low nutritional levels in the influent, especially during winter. In this study, the biofilm development in three laboratory-scale GAC columns with different types of influent was investigated in southeast China during winter. The results indicated that nitrogen was the limiting factor for biofilm development in GAC columns for this source water. The biomass density in the column with ammonia nitrogen addition was much higher than those of the other two filters, while its microbial diversity and biological activity were lower. Moreover, the ammonia-feeding column also showed the highest removal of organic contaminants during the stable operating periods, i.e. chemical oxygen demand (CODMn), assimilable organic carbon as well as biodegradable dissolved organic carbon. Therefore, nitrogen amendment favors the formation of biofilm. It could shorten the start-up time of a GAC filter and enhance the bio-stability of its effluent. This might add some new insights towards the operation of GAC filters with low nutritional levels in the influent during winter.

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