Succession of microbial communities reveals the inevitability of anammox core in the development of anammox processes

The lack of anammox seeds is regarded as the bottleneck of anammox-based processes. Although the interactions in anammox consortia have attracted increasing attention, little is known about the influence of inoculated sludge populations on the growth of anammox bacteria. In this study, four sludge of distinct communities mixed with anammox sludge (the relative abundance of Ca. Kuenenia was 1.96 %) were used as the seeds, respectively for the start-up of anammox processes. Notably, all these mixed microbial communities tend to form a similar microbial community, defined as the anammox core, containing anammox-bacteria (22.9 ± 5.9 %), ammonia-oxidizing-bacteria (0.8 ± 0.7 %), nitrite-oxidizing-bacteria (0.2 ± 0.2 %), Chloroflexi-bacteria (0.7 ± 0.4 %), and heterotrophic-denitrification-bacteria (0.3 ± 0.2 %). It also elucidated that the communities of Nitrosomonas-dominated sludge were the closest to the anammox core, and achieved the highest nitrogen-removal rate of 0.73 kg-N m^-3 d^-1. This study sheds light on the solution to the shortage of anammox seeds in the full-scale wastewater treatment application.

Nitrogen contribution and microbial community of size-fractionated anammox sludge in continuous stirred-tank reactors

In this study, the microbial diversity of size-fractionated anammox sludge in a well-mixed system and their contribution to nitrogen transformation were investigated. Results showed that small granules (0.2-1.0 mm) contributed to the major part of the nitrogen removal rate (56 %) due to its largest mixed liquor volatile suspended solids (1240 ± 80 mg·L^-1). However, large granules (>1.0 mm) possessed the highest relative abundances of Ca. Kuenenia stuttgartiensis and specific anammox activity, representing 49.34 % and 24.45 ± 0.01 mg-N·g^-1-mixed liquor volatile suspended solids·h^-1, respectively. The microbial diversity decreased as the increase of granular size, resulting in microbial community shifting to a simpler model. Metagenomic analysis showed that fine sludge might be the potential major for NO/N₂O production in the mature well-mixed system under inorganic conditions. This study provides guidance for the evaluation of nitrogen contribution by anammox size-fractionated sludge and the inhibition of the potential NO/N₂O emission in anammox processes.

Microbial commensalism-assisted fast acclimation of HAP-anammox granules to dewatered liquid of dry methane fermentation

The treatment of a dewatered liquid of dry fermentation via the anammox process was investigated in the present study. Fast acclimation was established: within 2-months of operation, nitrogen removal rate reached 5 times (5.5 g-N/L/d) higher than it was at startup, which was achieved by inoculation with cold-stored HAP-anammox granules and inhibition control. The specific anammox activity of the dewatered liquid was highly improved and quite comparable to that of synthetic wastewater. Ca. Kuenenia with the relative abundance of 31.1% was revealed to be the only anammox genre and maintained its dominance throughout the operation. Simultaneously, Ca. D. denitrificans was proliferated, with its relative abundance increasing from 1.5% to 14.9%. The microbial co-occurrence network of HAP-anammox granules developed during the treatment of the dewatered liquid of dry fermentation. The experience of this work provides valuable strategies facilitating fast acclimation of the anammox process for the treatment of high-strength wastewater.

Effects of temperature on anammox performance and community structure

A lab-scale anammox up-flow anaerobic sludge blanket (UASB) reactor was run to investigate the influence of temperature on anammox performance and community structure. The anammox system had a higher substrate tolerance at 13 °C than at 18 °C. The adverse effects caused by the use of a lower temperature (8 °C) could be restored. The nitrogen removal rate (NRR) decreased with decreasing in situ specific anammox activity (SAA). Interestingly, the ex situ SAA acclimated at 23 °C, when exposed to ex situ temperatures of 33 and 28 °C, was higher than for those acclimated at 33 and 28 °C. No shift was observed in the optimum temperature for ex situ SAA in the whole lowering process of anammox UASB. More extracellular polymeric substances were produced in response to cooler conditions (18 °C and 13 °C). Ca. Kuenenia became much more abundant (55.18% of the microbial community) and had a competitive advantage over other anammox bacteria (AnAOB) at 13 °C.

Nitrogen removal performance and loading capacity of a novel single-stage nitritation-anammox system with syntrophic micro-granules

The operation performance of a novel micro-granule based syntrophic system of nitritation and anammox was studied by controlling the oxygen concentration and maintaining a constant temperature of 25°C. With the oxygen concentration of around 0.11 (<0.15)mg/L, the single-stage nitritation-anammox system was startup successfully at a nitrogen loading rate (NLR) of 1.5kgN/m³/d. The reactor was successfully operated at volumetric N loadings ranging from 0.5 to 2.5kgN/m³/d with a high nitrogen removal of 82%. The microbial community was composed by ammonia oxidizing bacteria (AOB) and anammox bacteria forming micro-granules with an average diameter of 0.8mm and good settleability. Results from pyrosequencing analysis revealed that Ca. Kuenenia and Nitrosomonas were selected and enriched in the community over the startup period, and these were identified as the dominant anammox bacteria and AOB species, respectively.