The population dynamics of nitrifiers in ammonium-rich systems

Filamentous bacteria in the nitrifying activated sludge

Filamentous bacteria in addition to wastewater treatment are responsible for the shape of flocs and sedimentation properties of activated sludge. Their dynamics in activated sludge influences the performance of the whole sewage treatment plant. Therefore the composition of activated sludge biocenosis and its dynamics in the nitrification process were investigated. Four laboratory-scale activated sludge membrane bioreactors fed with wastewater highly concentrated with ammonium (synthetic wastewater imitating landfill leachate) were operated to obtain a high rate of nitrification. The sludge age was 8, 12, 24 and 32 days. An additional fifth reactor was conventionally ammonium loaded at 12-day sludge age and served as the reference. A shift in filamentous bacteria population was observed in all operated reactors. There was no influence of sludge age on composition or abundance of filamentous biocenosis. In high ammonium loaded activated sludge Nostocoida limicola, Haliscomenobacter hydrossis and also Type 021N were the most abundant filamentous bacteria. In the reference reactor Type 021N and Sphaerotilus natans dominated the activated sludge.

Assessing bacterial diversity in a seawater-processing wastewater treatment plant by 454-pyrosequencing of the 16S rRNA and amoA genes

The bacterial community composition of activated sludge from a wastewater treatment plant (Almería, Spain) with the particularity of using seawater was investigated by applying 454-pyrosequencing. The results showed that Deinococcus-Thermus, Proteobacteria, Chloroflexi and Bacteroidetes were the most abundant retrieved sequences, while other groups, such as Actinobacteria, Chlorobi, Deferribacteres, Firmicutes, Planctomycetes, Spirochaetes and Verrumicrobia were reported at lower proportions. Rarefaction analysis showed that very likely the diversity is higher than what could be described despite most of the unknown microorganisms probably correspond to rare diversity. Furthermore, the majority of taxa could not be classified at the genus level and likely represent novel members of these groups. Additionally, the nitrifiers in the sludge were characterized by pyrosequencing the amoA gene. In contrast, the nitrifying bacterial community, dominated by the genera Nitrosomonas, showed a low diversity and rarefaction curves exhibited saturation. These results suggest that only a few populations of low abundant but specialized bacteria are responsible for removal of ammonia in these saline wastewater systems.