Microbial distribution of Accumulibacter spp. and Competibacter spp. in aerobic granules from a lab-scale biological nutrient removal system

Granular sludge for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was generated and studied in a lab-scale sequencing batch reactor (SBR). The SBR was monitored for 450 days during which the biomass was transformed from flocs to granules, which persisted for the last 130 days of operation. Short sludge settling time was employed to successfully generate the granules, with the 10th and 90th percentiles of diameter being 0.7 and 1.6 mm respectively. Good phosphorus removal and nitrification occurred throughout the SBR operation but only when granules were generated were denitrification and full nutrient removal complete. Fluorescence in situ hybridization and oxygen microsensors were used to study the granules at a microscale. Accumulibacter spp. (a polyphosphate-accumulating organism, PAO) and Competibacter spp. (a glycogen non-polyphosphate-accumulating organism, GAO) were the most abundant microbial community members (together 74% of all Bacteria) and both are capable of denitrification. In the aerobic period of the SBR operation, the oxygen penetrated 250 mu m into the granules leaving large anoxic zones in the centre part where denitrification can occur. In granules > 500 mu m in diameter, Accumulibacter spp. was dominant in the outermost 200 mu m region of the granule while Competibacter spp. dominated in the granule central zone. The stratification of these two populations between the outer aerobic and inner anoxic part of the granule was highly significant (P < 0.003). We concluded that the GAO Competibacter spp., and not the PAO Accumulibacter spp., was responsible for denitrification in this SBR. This is undesirable for SNDPR as savings in carbon demand cannot be fulfilled with phosphorus removal and denitrification being achieved by different groups of bacteria.

在实验室规模的序批式反应器（SBR）中产生并研究了用于同步硝化、反硝化和除磷（SNDPR）的颗粒污泥。对该SBR进行了450天的监测，在此期间生物质从絮体转变为颗粒，这种颗粒在运行的最后130天一直存在。采用较短的污泥沉降时间成功地产生了颗粒，其直径的第10和第90百分位数分别为0.7毫米和1.6毫米。在整个SBR运行过程中都有良好的除磷和硝化作用，但只有当产生颗粒时，反硝化和完全的营养物去除才得以完成。利用荧光原位杂交和氧微传感器在微观尺度上对颗粒进行了研究。聚磷菌属（一种聚磷积累生物，PAO）和竞争杆菌属（一种非聚磷积累糖原生物，GAO）是最丰富的微生物群落成员（共占所有细菌的74%），并且两者都能够进行反硝化。在SBR运行的好氧阶段，氧气渗透到颗粒内250微米处，在中心部分留下较大的缺氧区域，反硝化可在此处发生。在直径>500微米的颗粒中，聚磷菌属在颗粒最外层200微米区域占主导地位，而竞争杆菌属在颗粒中心区域占主导地位。这两种菌群在颗粒的外好氧层和内缺氧层之间的分层非常显著（P<0.003）。我们得出结论，在这个SBR中，是GAO竞争杆菌属而非PAO聚磷菌属负责反硝化。这对于SNDPR是不利的，因为如果除磷和反硝化由不同的细菌群完成，就无法满足对碳需求的节省。