A systematic insight into a single-stage deammonification process operated in granular sludge reactor with high-loaded reject-water: characterization and quantification of microbiological community

Autofluorescent characteristics of Candidatus Brocadia fulgida and the consequences for FISH and microscopic detection

An enrichment culture of Candidatus Brocadia fulgida was identified by three independent methods: analysis of autofluorescence using different microscope filter blocks and a fluorescence spectrometer, fluorescence in situ hybridization (FISH) with anammox-specific probes and partial sequencing of the 16S rDNA, hydrazine synthase hzsA and hydrazine oxidoreductase hzo. The filter block BV-2A (400-440, 470 LP, Nikon) was suitable for preliminary detection of Ca. B. fulgida. An excitation-emission matrix revealed three pairs of excitation-emission maxima: 288-330 nm, 288-478 nm and 417-478 nm. Several autofluorescent cell clusters could not be stained with DAPI or by FISH, suggesting empty but intact cells (ghost cells) or inhibited permeability. Successful staining of autofluorescent cells with the FISH probes Ban162 and Bfu613, even at higher formamide concentrations, suggested insufficient specificity of Ban162. Under certain conditions, Ca. B. fulgida lost its autofluorescence, which reduced the reliability of autofluorescence for identification and detection. Non-fluorescent Ca. Brocadia cells could not be stained with Ban162, but with Bfu613 at higher formamide concentrations, suggesting a dependency between both parameters. The phylogenetic analysis showed only good taxonomical clustering of the 16S rDNA and hzsA. In conclusion, careful consideration of autofluorescent characteristics is recommended when analysing and presenting FISH observations of Ca. B. fulgida to avoid misinterpretations and misidentifications.

Role of extracellular polymeric substance in determining the high aggregation ability of anammox sludge

The high aggregation ability of anammox sludge has been extensively observed, but the cause for their aggregation is challenging. Here the structure and composition of extracellular polymeric substance (EPS) excreted from anammox sludge were systematically investigated to interpret the high aggregation ability. We combine results of contact angle, zeta potential and surface thermodynamics analysis as well as the following DLVO theory to address this issue. The results show that hydrophobic interaction is the main force determining the aggregation of anammox sludge. To go insight into inherent mechanism, Fourier transform infrared (FTIR) and x-ray photoelectron (XPS) spectroscopy were conducted and demonstrated there were comparatively few hydrophilic functional groups in the EPS of anammox sludge, compared to that of activated sludge, nitrifying and denitrifying sludge. Further, amino acid composition and secondary structure analyses of protein indicated that large amounts of hydrophobic amino acids and high level of protein loose structure for exposing inner hydrophobic groups of protein in EPS significantly contributed to the hydrophobic interaction and further to the high aggregation ability of anammox sludge, which is the critical finding of this work. This investigation is useful for understanding anammox bacteria and then for accelerating the application of the anammox process in wastewater treatment.

Successful application of nitritation/anammox to wastewater with elevated organic carbon to ammonia ratios

The nitritation/anammox process has been mainly applied to high-strength nitrogenous wastewaters with very low biodegradable organic carbon content (<0.5 g COD∙g N(-1)). However, several wastewaters have biodegradable organic carbon to nitrogen (COD/N) ratios between 0.5 and 1.7 g COD∙g N(-1) and thus, contain elevated amounts of organic carbon but not enough for heterotrophic denitrification. In this study, the influence of elevated COD/N ratios was studied on a nitritation/anammox process with suspended sludge. In a step-wise manner, the influent COD/N ratio was increased to 1.4 g COD∙g N(-1) by supplementing digester supernatant with acetate. The increasing availability of COD led to an increase of the nitrogen removal efficiency from around 85% with pure digester supernatant to >95% with added acetate while the nitrogen elimination rate stayed constant (275 ± 40 mg N∙L(-1)∙d(-1)). Anammox activity and abundance of anammox bacteria (AMX) were strongly correlated, and with increasing influent COD/N ratio both decreased steadily. At the same time, heterotrophic denitrification with nitrite and the activity of ammonia oxidising bacteria (AOB) gradually increased. Simultaneously, the sludge retention time (SRT) decreased significantly with increasing COD loading to about 15 d and reached critical values for the slowly growing AMX. When the SRT was increased by reducing biomass loss with the effluent, AMX activity and abundance started to rise again, while the AOB activity remained unaltered. Fluorescent in-situ hybridisation (FISH) showed that the initial AMX community shifted within only 40 d from a mixed AMX community to "Candidatus Brocadia fulgida" as the dominant AMX type with an influent COD/N ratio of 0.8 g COD∙g N(-1) and higher. "Ca. Brocadia fulgida" is known to oxidise acetate, and its ability to outcompete other types of AMX indicates that AMX participated in acetate oxidation. In a later phase, glucose was added to the influent instead of acetate. The new substrate composition did not significantly influence the nitrogen removal nor the AMX activity, and "Ca. Brocadia fulgida" remained the dominant type of AMX. Overall, this study showed that AMX can coexist with heterotrophic bacteria at elevated influent COD/N ratios if a sufficiently high SRT is maintained.