Analysis of the nitrifying bacterial community in BioCube sponge media using fluorescent in situ hybridization (FISH) and microelectrodes

Carrier type induces anammox biofilm structure and the nitrogen removal pathway: Demonstration in a full-scale partial nitritation/anammox process

In this study, two typical carrier types, microporous and macroporous carriers, were collected from a full-scale partial nitritation/anammox reactor for analysis and comparison of the biofilm structure characteristics, performance and removal nitrogen pathway. For microporous carriers, a thicker biofilm (>5 mm) was obtained with higher biomass and abundance of anammox bacteria as well as a higher nitrogen removal efficiency due to the integration of denitrifying and anammox bacteria. In addition, higher microbial community stability can be expected under varying environmental conditions. In comparison, macroporous carrier biofilm exhibited a lower thickness (0.4-2.3 mm) and lower microbial richness, with a strong network correlation among genera. Analysis showed that the mainly positive correlation between anammox bacteria and ammonium oxidizing bacteria, enhancing coupling partial nitritation and anammox. These findings help further our understanding of the mechanisms of anammox biofilm nitrogen removal and provide a baseline for optimization of the design of carrier structures.

Impacts of ammonia loading and biofilm age on the prevalence of nitrogen-cycling microorganisms in a full-scale submerged attached-growth reactor

This study reports the impacts of seasonal ammonia load changes and biofilm age on the quantity of biomass and on the prevalence of ammonia- and nitrite-metabolizing organisms within a submerged attached-growth reactor (SAGR™) following lagoon treatment. Ammonia (NH₃ ) loadings (0.12-3.17 kg/d) in the primary SAGR were measured over 223 days from May to December in 2017. Adjustment of the wastewater flow path on September 1 successfully increased NH₃ loading to the primary SAGR, which subsequently caused reactor biomass to increase. The NH₃ removal rate in October (0.5 kg/d) was greater than rates in June and July (0.3 and 0.2 kg/d) despite a water temperature decrease from >24 to 15.6°C. This elevated removal rate in October, and the sustained removal rate in December (0.4 kg/d, 5.3°C) were associated with a measured increase in microbial biomass. The relative abundance of the anammox organism C. Brocadia was 5 times greater in the mature biofilm after 686 days of growth, and the genus Pseudomonas increased sevenfold. The presence of Pseudomonas, which contains denitrifying species, and anammox suggests a high potential for removal of total nitrogen in SAGRs. PRACTITIONER POINTS: Pseudomonas prevalence and the presence of anammox suggest a high potential for total nitrogen removal in mature SAGR biofilms. The abundance of the anammox microorganism C. Brocadia was greater after 686 days of biofilm growth compared with 33 days. Simple operational changes can increase biomass in the SAGR to maintain, or even increase, NH₃ transformation rates during cold weather.

Autotrophic nitrogen removal in an integrated fixed-biofilm activated sludge (IFAS) reactor: Anammox bacteria enriched in the flocs have been overlooked

In this study, an autotrophic nitrogen removal process was established using an integrated fixed-biofilm activated sludge (IFAS) reactor treated with high ammonium wastewater. A nitrogen removal rate (NRR) of 2.78 kg N/(m³·d) was obtained during the 206-day operation. Moreover, during the stable period, the large flocs (D > 0.2 mm) had a significantly higher abundance of anammox bacteria than the small flocs (D < 0.2 mm) and biofilm, resulting in 51% of the anammox bacteria being located in the flocs. The result indicates that anammox bacteria can be enriched in the flocs and in the biofilm, which has been rarely reported for IFAS reactors. In addition, the large flocs are likely formed through biofilm detachment since the microbial community was similar for the two kinds of biomass. Overall, the role of flocs in IFAS reactors are complicated and their contribution to the anammox reaction have been overlooked thus far.

Linking nitrification characteristic and microbial community structures in integrated fixed film activated sludge reactor by high-throughput sequencing

The primary goal of this study is to investigate ammonia removal, abundance of nitrifying bacteria and microbial community structures in a laboratory-scale integrated fixed film activated sludge (IFAS) reactor. The results of Illumina MiSeq sequencing based on 16S rRNA genes showed Proteobacteria and Bacteroidetes were the dominant phyla in both biofilm and suspended sludge samples in the IFAS reactor. The dominant ammonia-oxidizing bacteria (AOB) species was Nitrosomonas and the dominant nitrite-oxidizing bacteria species was Nitrospira. The contribution of biofilm to ammonia removal increased from 4.0 ± 0.9% to 37.0 ± 2% when the temperature decreased from 25 °C to 10 °C. The real-time polymerase chain reaction (PCR) result showed the abundance of AOB in suspended sludge was higher than that in biofilm at the same time. However, nitrification is more dependent on attached growth than on suspended growth in the IFAS reactor at 15 °C and 10 °C and the abundance of AOB in biofilm was also higher than that in suspended sludge. The more robust ammonia removal rate at low temperatures by biofilm contributed to the relatively stable ammonia removal, and biofilm attached on carriers in the IFAS reactor is advantageous for nitrification in low-temperature environment.

Spatial distribution and viability of nitrifying, denitrifying and ANAMMOX bacteria in biofilms of sponge media retrieved from a full-scale biological nutrient removal plant

The spatial distribution and activities of nitrifying and denitrifying bacteria in sponge media were investigated using diverse tools, because understanding of in situ microbial condition of sponge phase is critical for the successful design and operation of sponge media process. The bacterial consortia within the media was composed of diverse groups including a 14.5% Nitrosomonas spp.-like ammonia oxidizing bacteria (AOB), 12.5% Nitrobacter spp.-like nitrite oxidizing bacteria (NOB), 2.0% anaerobic ammonium-oxidizing (ANAMMOX) bacteria and 71.0% other bacteria. The biofilm appeared to be most dense in the relatively outer region of the media and gradually decreased with depth, but bacterial viabilities showed space-independent feature. The fluorescent in situ hybridization results revealed that AOB and NOB co-existed in similar quantities on the side fragments of the media, which was reasonably supported by the microelectrode measurements showing the concomitant oxidation of NH(4) (+) and production of NO(3) (-) in this zone. However, a significantly higher fraction of AOB was observed in the center than side fragment. As with the overall biofilm density profile, the denitrifying bacteria were also more abundant on the side than in the center fragments. ANAMMOX bacteria detected throughout the entire depth offer another advantage for the removal of nitrogen by simultaneously converting NH(4) (+) and NO(2) (-) to nitrogen gas.

Nitrogen removal from wastewater and bacterial diversity in activated sludge at different COD/N ratios and dissolved oxygen concentrations

The impact of the organic carbon to nitrogen ratio (chemical oxygen demand (COD)/N) in wastewater and dissolved oxygen (DO) concentration on carbon and nitrogen removal efficiency, and total bacteria and ammonia-oxidizing bacteria (AOB) communities in activated sludge in constantly aerated sequencing batch reactors (SBRs) was determined. At DO of 0.5 and 1.5 mg O2/L during the aeration phase, the efficiency of ammonia oxidation exceeded 90%, with nitrates as the main product. Nitrification and denitrification achieved under the same operating conditions suggested the simultaneous course of these processes. The most effective nitrogen elimination (above 50%) was obtained at the COD/N ratio of 6.8 and DO of 0.5 mg O2/L. Total bacterial diversity was similar in all experimental series, however, for both COD/N ratios of 6.8 and 0.7, higher values were observed at DO of 0.5 mg O2/L. The diversity and abundance of AOB were higher in the reactors with the COD/N ratio of 0.7 in comparison with the reactors with the COD/N of 6.8. For both COD/N ratios applied, the AOB population was not affected by oxygen concentration. Amplicons with sequences indicating membership of the genus Nitrosospira were the determinants of variable technological conditions.

Macroscale and microscale analysis of Anammox in anaerobic rotating biological contactor

Inoculated with conventional anaerobic activated sludge, the Anammox process was successfully developed in an anaerobic rotating biological contactor (AnRBC) fed with a low ratio of C/N synthetic wastewater. Operated in a single point feed mode, the AnRBC removed 92.1% (n = 126) of the influent N at the highest surface load of 12 g/(m2 x day). The biomass increased by 25% and 17.1 g/(m2 x day) of maximum N removal surface load was achieved by elevating flow rate with another feed point. Fluorescence in situ hybridization and polymerase chain reaction analysis indicated that the Anammox genus Candidatus Kuenenia stuttgartiensis dominated the community. Both Anammox and denitrifying activity were detected in biofilm by the application of microelectrodes. In the outer layer of the biofilm (0-2500 microm), nitrite and ammonium consumed simultaneously in a ratio of 1.12/1, revealing the occurrence of Anammox. In the inner layer (> 2500 microm), a decrease of nitrate was caused by denitrification in the absence of nitrite and ammonium.