Microbial Nitrogen Removal Research Articles

Microbial nitrogen removal in synthetic aquaculture wastewater by fixed-bed baffled reactors packed with different biofilm carrier materials

Fixed-bed baffled reactors packed with carbon fiber (CFBR), polyurethane, or non-woven fabrics were developed to support microbial nitrification–denitrification reactions for nitrogen removal from synthetic aquaculture wastewater. The CFBR showed the best performance, with a short hydraulic retention time and low C/N ratio. Microbial communities in the reactor’s biofilms and deposited sludge were analyzed using high-throughput sequencing and quantitative polymerase chain reactions. The biofilms efficiently enriched the nitrifying and denitrifying bacteria in the CFBR. Moreover, bacteria capable of denitrification under aerobic conditions were detected in the aerobic chamber biofilm, showing positive correlations with the main nitrifiers and denitrifiers, which provides potential synergistic interactions for simultaneous nitrification–denitrification in the aerobic chamber. A network analysis revealed that the CFBR had more complex cooperative interactions than others. This study provides insights into the influence of different carrier materials on biofilm formation, proving that the CFBR has potential applications in aquaculture wastewater treatment.

Comparison of Oyster Aquaculture Methods and Their Potential to Enhance Microbial Nitrogen Removal From Coastal Ecosystems

Coastal ecosystems are impacted by excessive nutrient inputs that cause degradation of water quality and impairments of ecosystem functioning. Regulatory and management efforts to enhance nutrient export from coastal ecosystems include sustainable oyster aquaculture that removes nitrogen in the form of oyster biomass and increases particulate export to underlying sediments where increased organic material may enhance microbial denitrification. To better understand the impacts of oyster aquaculture on nitrogen removal, we examined bacterial processes in sediments underlying three of the most common aquaculture methods that vary in the proximity of oysters to the sediments. Sediment samples underlying sites managed with these different aquaculture methods were examined using the 16S rRNA gene to assess microbial community structure, gene expression analyses to examine nitrogen and sulfur cycling genes, and nitrogen gas flux measurements. All sites were located in the same hydrodynamic setting within Waquoit Bay, MA during 2018 and 2019. Although sediments under the different oyster farming practices showed similar communities, ordination analysis revealed discrete community groups formed along the sampling season. Measured N2 fluxes and expression of key genes involved in denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) increased during mid-summer and into fall in both years primarily under bottom cages. While all three oyster growing methods enhanced nitrogen removal relative to the control site, gene expression data indicate that the nitrogen retaining process of DNRA is particularly enhanced after end of July under bottom cages, and to a lesser extent, under suspended and floating bags. The choice of gear can also potentially increase processes that induce nitrogen retention in the form of ammonia in the underlying sediments over time, thus causing deviations from predicted nitrogen removal. If nitrogen removal is a primary objective, monitoring for these shifts is essential for making decisions about siting and size of aquaculture sites from year to year.

Community Composition and Spatial Distribution of N-Removing Microorganisms Optimized by Fe-Modified Biochar in a Constructed Wetland.

Microbial nitrogen (N) removal capability can be significantly enhanced in a horizontal subsurface flow constructed wetland (HSCW) amended by Fe-modified biochar (FeB). To further explore the microbiological mechanism of FeB enhancing N removal, nirS- and nirK-denitrifier community diversities, as well as spatial distributions of denitrifiers and anaerobic ammonium oxidation (anammox) bacteria, were investigated in HSCWs (C-HSCW: without biochar and FeB; B-HSCW: amended by biochar; FeB-HSCW: amended by FeB) treating tailwater from a wastewater treatment plant, with C-HSCW without biochar and FeB and B-HSCW amended by biochar as control. The community structures of nirS- and nirK-denitrifiers in FeB-HSCW were significantly optimized for improved N removal compared with the two other HSCWs, although no significant differences in their richness and diversity were detected among the HSCWs. The spatial distributions of the relative abundance of genes involved in denitrification and anammox were more heterogeneous and complex in FeB-HSCW than those in other HSCWs. More and larger high-value patches were observed in FeB-HSCW. These revealed that FeB provides more appropriate habitats for N-removing microorganisms, which can prompt the bacteria to use the habitats more differentially, without competitive exclusion. Overall, the Fe-modified biochar enhancement of the microbial N-removal capability of HSCWs was a result of optimized microbial community structures, higher functional gene abundance, and improved spatial distribution of N-removing microorganisms.

Molecular analysis of microbial nitrogen transformation and removal potential in mangrove wetlands under anthropogenic nitrogen input

Mangrove ecosystems are natural nitrogen removal systems that are primarily mediated by nitrogen cycle microorganisms, but their relative contributions to nitrogen transformation and removal in mangrove sediments under anthropogenic nitrogen input needs further resolution and characterization. Here, we investigated the responses and the relative contributions of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), anaerobic ammonium oxidizing (anammox) bacteria and denitrifying bacteria after spiking urea into mangrove sediments incubated in a laboratory microcosm experiment for four weeks. During incubation, the diversity, abundances and transcription levels of the hzo genes for anammox bacteria, amoA genes for AOA and AOB, and nirS genes for denitrifying bacteria were monitored using targeted gene clone library analyses and quantitative PCR assays at the DNA and RNA levels. The results showed that mangrove sediments harbour habitat-specific anammox bacteria which related to Candidatus Scalindua and Candidatus Kuenenia clades. Mangrove specific AOA related to deep branched clades within Candidatus Nitrososphaera and Candidatus Nitrosotalea, and AOB related to Nitrosomonas and Nitrosospira were also detected in the collected sediment samples. Growth and activity of AOA were detected at all levels of amendment of nitrogen input, whereas AOB growth was detectable only at the high-level nitrogen input (1.5 mg urea per gram of dry sediment) with no amoA transcripts and lower abundance than AOA. The abundance and transcription levels of the nirS gene were higher (~1000 times) than those of the hzo gene in all groups. Pearson correlation analysis demonstrated that the abundance of both AOA and AOB amoA genes had a significant positive correlation with the nirS gene (p < 0.01). These results indicated that nitrification (primarily mediated by the AOA)-denitrification process played the most important role in nitrogen removal from the amendment of nitrogen short-term input in the mangrove sediments.

Effect of biomass immobilization and reduced graphene oxide on the microbial community changes and nitrogen removal at low temperatures

The slow growth rate and high optimal temperatures for the anaerobic ammonium oxidation (anammox) bacteria are significant limitations of the anammox processes application in the treatment of mainstream of wastewater entering wastewater treatment plant (WWTP). In this study, we investigate the nitrogen removal and microbial community changes in sodium alginate (SA) and sodium alginate–reduced graphene oxide (SA-RGO) carriers, depending on the process temperature, with a particular emphasis on the temperature close to the mainstream of wastewater entering the WWTP. The RGO addition to the SA matrix causes suppression of the beads swelling, which intern modifies the mechanical properties of the gel beads. The effect of the temperature drop on the nitrogen removal rate was reduced for biomass entrapped in SA and SA-RGO gel beads in comparison to non-immobilized biomass, this suggests a ‘‘protective” effect caused by immobilization. However, analyses performed using next-generation sequencing (NGS) and qPCR revealed that the microbial community composition and relative gene abundance changed significantly, after the implementation of the new process conditions. The microbial community inside the gel beads was completely remodelled, in comparison with inoculum, and denitrification contributed to the nitrogen transformation inside the beads.

Effect of microplastics on ecosystem functioning: Microbial nitrogen removal mediated by benthic invertebrates

While ecotoxicological impacts of microplastics on aquatic organisms have started to be investigated recently, impacts on ecosystem functions mediated by benthic biota remain largely unknown. We investigated the effect of microplastics on nitrogen removal in freshwater sediments where microorganisms and benthic invertebrates (i.e., chironomid larvae) co-existed. Using microcosm experiments, sediments with and without invertebrate chironomid larvae were exposed to microplastics (polyethylene) at concentrations of 0, 0.1, and 1 wt%. After 28 days of exposure, the addition of microplastics or chironomid larvae promoted the growth of denitrifying and anammox bacteria, leading to increased total nitrogen removal, in both cases. However, in microcosms with chironomid larvae and microplastics co-existing, nitrogen removal was less than the sum of their individual effects, especially at microplastics concentration of 1 wt%, indicating an adverse effect on microbial nitrogen removal mediated by macroinvertebrates. This study reveals that the increasing concentration of microplastics entangled the nitrogen cycling mediated by benthic invertebrates in freshwater ecosystems. These findings highlight the pursuit of a comprehensive understanding of the impacts of microplastics on the functioning in freshwater ecosystems.

Microbial community structure and nitrogen removal responses of an aerobic denitrification biofilm system exposed to tetracycline

We investigated the compositional shift of the microbial community and the denitrification performance of an aerobic denitrification system after exposure to tetracycline (TC), an antibiotic widely used to treat aquaculture organisms showing clinical signs of disease. TC substantially affected the microbial denitrifying community and its diversity. Microbial community richness reached maximum values at 50 μg/L, however with minimum diversity. Proteobacteria was the dominant phylum and was enriched with increasing TC concentration. Marinobacter and Halomonas were the dominant genera in the reactor without TC, but Winogradskyella, Muricauda and Simplicispira were relatively abundant at higher antibiotic concentrations. Nitrate-N removal rates appeared substantially unchanged at 2 μg/L TC, but significantly decreased (p < .05) at 5 and 20 μg/L, and recovery of nitrate removal effectiveness was observed at 50 μg/L TC.

Achieving single-stage autotrophic nitrogen removal by composite membrane aerated biofilm with gel under two microbial entrapping patterns: experimental and modeling aspects.

Single-stage autotrophic nitrogen removal offers advantages of low energy and carbon consumptions. Based on previous work about a novel composite membrane aerated biofilm (CMAB), two microbial entrapping patterns (mixed and stratified patterns) were evaluated for their applicability to artificially regulate the spatial distribution of distinct microbial aggregates for single-stage autotrophic nitrogen removal. Experimental results showed that the stratified pattern caused little accumulation of NO2- and NO3-, which leads to a superior nitrogen removal performance compared with the mixed pattern. Candidatus Kuenenia was found to be the major anammox bacterium in the gel film of the mixed pattern and the outer film of the stratified pattern. In contrast, Nitrosomonas, as a representative genus of ammonia-oxidizing bacteria, was substantially enriched in the inner film of the stratified pattern and the gel film of the mixed pattern. Finally, modeling results further confirmed the advantages of the stratified pattern with respect to the formation of rational microbial and nutrient profiles in gel films. The ratio of partial nitrification and anammox film thicknesses should remain below 3:2 to obtain a high fraction of anammox bacteria and to avoid NO2- accumulation. Increasing O2 surface loading does not affect microbial profiles, but can greatly promote the TN removal performance only in the stratified pattern. Overall, the stratified pattern should be employed to achieve optimal microbial profiles and nitrogen removal efficiency.

Fe-modified biochar enhances microbial nitrogen removal capability of constructed wetland

To improve the nitrogen removal capability of constructed wetlands, the biochar, produced from bamboo, activated with HCl and coated with Fe (FeCl3·6H2O), and then was added as a substrate into the systems. Three horizontal subsurface flow constructed wetlands (HSCWs) was established to treat the low C/N tailwater from the wastewater treatment plant: C-HSCW (quartz sand + soil), B-HSCW (quartz sand + soil + unmodified biochar), and FeB-HSCW (quartz sand + soil + Fe-modified biochar). Under different combinations of hydraulic retention time and nitrogen loading, the FeB-HSCW revealed extremely effective nitrogen removal, compared to the C-HSCW and B-HSCW. The highest removal efficiencies of NO3−-N (95.30%), TN (86.68%), NH4+-N (86.33%), NO2−-N (79.35%) and COD (63.36%) were obtained in FeB-HSCW with the hydraulic retention time of 96 h. and low influent nitrogen loading (C/N of 2.5). Nitrogen mass balance analysis showed that microbial processes played the most important role of nitrogen removal in HSCWs and the Fe-modified biochar significantly enhanced the microbial nitrogen removal. A total of 128.40 g nitrogen was removed by microorganisms in FeB-HSCW (average removal rate of 2.52 g N/(m3·d1)), much higher than that in other two HSCWs. The contributions of microorganisms, substrate storage and plant uptake on the total amount of nitrogen removal in the FeB-HSCW was 92.69%, 2.97% and 4.34%, respectively. Moreover, FeB significantly increased the abundances of genes involved in nitrogen removal. The copy numbers of bacterial 16S rRNA and amx, as well as of genes nirS, nirK, nosZ-I, nosZ-II, and hzsA were 1.3- to 27.8-fold higher in the FeB-HSCW than that in the other two HSCWs. Thus, Fe-modified biochar provides a feasible and effective amendment for constructed wetlands to improve the nitrogen removal, particularly nitrate-N, for low C/N wastewaters by enhancing the microbial nitrogen removal capacity (mainly of the denitrification).

Comparative nitrogen removal via microbial ecology between soil and green sorption media in a rapid infiltration basin for co-disposal of stormwater and wastewater

In this study, a rapid infiltration basin (RIB) designed as green infrastructure for co-disposal of wastewater effluent and stormwater runoff was retrofitted for sustainable groundwater recharge after nitrogen removal. For comparison of nitrogen removal efficiency via different filtration media, the RIB was divided into two sub-basins for different filtration processes. One sub-basin was filled with a native sandy soil with about 2–4% clay (Control RIB), and the other sub-basin was modified with Biosorption Activated Media (BAM) (BAM RIB), for the enhancement of microbial nitrogen removal. The two sub-basins accept an equal amount of excess reclaimed wastewater in non-storm periods, and stormwater during periodic storm events. The infiltrate in both the BAM RIB and the Control RIB eventually reaches the Upper Floridan Aquifer. The seven microbial species involved in this microbial ecology study are nitrite oxidizing bacteria (NOB), ammonia oxidizing bacteria (AOB), anaerobic oxidation of ammonium (anammox) bacteria, complete ammonia oxidizer (Comammox) bacteria, denitrifiers, dissimilatory nitrate reduction to ammonium (DNRA) and ammonia-oxidizing archaea (AOA). The population dynamics study was conducted with the aid of the quantitative polymerase chain reaction (qPCR) for the quantification of the microbial gene population in support of microbial ecology discovery. The qPCR results demonstrated the competition effect between AOA, AOB, and Comammox, the inhibition effect between NOB and DNRA with the presence of anammox, and the complementary effect due to an abundance of NOB and AOB in the microbial ecology. Although, competition between denitrifiers and DNRA was expected to impact population dynamics, both microbial species were found to be the most predominant in both control and BAM RIBs. Research findings indicate that the use of BAM RIB achieves significantly efficient nitrogen removal driven by complementary effects in the microbial ecology.

Microbial community similarity and dissimilarity inside and across full-scale activated sludge processes for simultaneous nitrification and denitrification.

Simultaneous nitrification and denitrification under low dissolved oxygen conditions is an energy-saving modification of the activated sludge process to achieve efficient nitrogen removal. Geographically distinct full-scale treatment plants are excellent platforms to address the links of microbial community with operating parameters. Mixed liquor samples were collected from a sequencing batch reactor plant, oxidation ditch plant, and step-feed activated sludge plant. Next-Generation Sequencing of the samples showed that the microbial communities were similar at the phylum level among the plants, being dominated by Proteobacteria. Microbial composition of functional groups was similar between the react fill and react phases of the sequencing batch reactors, among four sequencing batch reactors, and among four oxidation ditches. Nitrospira was the only identified genus of autotropic nitrifying bacteria with a relative abundance of 2.2-2.5% in the oxidation ditches and 0.4-0.7% at the other plants. Heterotrophic nitrifying-aerobic denitrifying bacteria were dominated by Dechloromonas with a relative abundance of 0.4-1.0%. Microbial community composition and nitrogen removal mechanisms were related to overall level and local zonation of dissolved oxygen, mixed liquor suspended solids concentration, nitrogen and organic loadings, and solids retention time. Low dissolved oxygen and low organic and nitrogen loadings favored growth of Nitrospira.

Impact of static biocarriers on the microbial community, nitrogen removal and membrane fouling in submerged membrane bioreactor at different COD:N ratios

The polyvinyl formal (PVFM) biocarrier addition in a membrane bioreactor (MBR) was evaluated at high and low carbon/nitrogen (C/N) ratio of 20.0 and 6.7. Results indicated that static biocarrier addition could enrich nitrification and denitrification bacteria, dominating by Tauera, Amaricoccus and Nitrosospira at the genus level and slightly improved the total nitrogen removal even at a low C/N ratio. The bulk sludge characteristics (such as bigger particle size, lower SMP, lower SMP P/C) were also significantly changed in the hybrid MBR (HMBR), leading to a more sustainable membrane operation. The biocarrier addition also reduced the relative abundance of Sphingobacterials_unclassified, Ohtaekwangia and Rhodocyclaceae_unclassified at the genus level, indicating less membrane fouling in the HMBR. Consequently, HMBR with static PVFM addition could partially overcome the drawback of low C/N ratio for total nitrogen removal and membrane fouling control, providing a more resilient MBR to the undesirable environment such as low C/N ratio.

Application of a new type of Si–Al porous clay material as a solid phase support for immobilizing Acidovorax sp. PM3 to treat domestic sewage

A novel Si–Al porous clay material W (reprocessed from ceramic waste) was used for Acidovorax sp. strain PM3 immobilization to promote the growth of strains and improve nitrogen and phosphorus removal performance in water treatment systems. The porous clay material W was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy indicating that porous clay material W was a type of mullite with 63.52 m2/g specific surface area. After immobilization, the maximum biomass increased 2.7 times the specific growth rate and the removal rates of chemical oxygen demand (COD), ammonia (NH4+–N), and total phosphorus (TP) by the immobilized PM3 were 42.99, 29.19, and 11.76% higher than the free strain after 24 h. The Monod equation showed that the growth rate and processing speed of immobilized PM3 increased. The maximum adsorption capacities of COD and NH4+–N onto porous clay material W were 2.33 and 0.32 mg/g on the basis of Langmuir isotherm. The removal capacities of COD, NH4+–N, and TP by the immobilized PM3 were 588.24, 20.37, and 5.06 mg/l, respectively, as shown by kinetic studies. These results demonstrated that porous clay material W could improve the efficiency of microbial nitrogen and phosphorus removal, and the immobilized microorganism system could effectively treat domestic sewage. The adsorption isotherms can well describe the adsorption process. The maximum adsorption capacity of COD and NH4+–N on porous clay material W is 2.33 and 0.32 mg/g, respectively. Kinetic studies showed that the removal capacity of immobilized PM3 to COD, NH4+–N, and TP was 58.824, 20.37, and 5.06 mg/l, respectively.

Bend-induced sediment redistribution regulates deterministic processes and stimulates microbial nitrogen removal in coarse sediment regions of river

Understanding the differences of biogeochemical processes between straight and bent channel is important for weighting them in urban river planning and reconstruction. Shifts in the assembly of the sediment microbial community of bent channels are key, but understudied, component of bend-induced increases in biogeochemical reaction rates. Here, the assembly of microbial community and its feedback to nitrogen transformation in urban river bends were firstly studied by coupling ecological theory, aqueous biogeochemistry, DNA sequencing, and hydrodynamic profiling. It was found that the sediment particle size was the main driving force for producing the significant difference of microbial community structure in river bends. Homogeneous selection, quantified by β-nearest taxon index (βNTI), emerged in the urban river bends and accounted for 79.2% of all ecological processes. Moreover, a significant positive relationship between βNTI and the sediment particle size indicated that shifts in particle size were associated with shifts in deterministic selective pressures, which govern the composition of the microbial community. The significant correlation between the βNTI and changes in nitrate concentration also indicated that nitrate leads to deterministic processes, which select microbial taxa. These microbial taxa which are governed by deterministic processes show specific nitrogen transformation traits, and react on the nitrate concentration. A multiphase transport model allowed the separation of the effects of deterministic processes on nitrogen concentration from measured concentration influenced by complex biogeochemical processes. The results indicated that both the ammonia transformation and microbial nitrogen removal were stimulated in coarse sediment regions of the river bends, and were confirmed by abundant differences of microbial taxa that could promote ammoxidation and denitrification. The coarse sediment benefits microbial nitrogen removal in urban river bends, a discovery that should inform urban river reconstruction designs and the efforts to assess the environmental water capacity of urban rivers.

Metagenomic analysis of the biotoxicity of titanium dioxide nanoparticles to microbial nitrogen transformation in constructed wetlands

Extensive use of titanium dioxide nanoparticles (TiO2 NPs) in various products has increased the release of these particles into wastewater, posing potential environmental risks. As an ecological wastewater treatment facility, constructed wetland (CW) is an important sink of NPs. However, little is known about the effects of NPs on microbial nitrogen transformation and related genes in CWs. In this study, short-term (5 days) and long-term (60 days) exposure experiments were conducted to investigate the effect of TiO2 NPs (0, 1, and 50 mg/L) on microbial nitrogen removal in CWs. The results showed that nitrogen removal efficiency was decreased by 35%–51% after long-term exposure to TiO2 NPs. Metagenomic analysis further confirmed that TiO2 NPs declined the relative abundance of functional genes and those enzyme encoding genes involved in the nitrogen metabolism pathway and glycolysis metabolism process. Furthermore, our data proved that the indigent glycolysis metabolism process resulted in the shortage of electron (NADH) and energy sources (ATP), causing inefficient nitrogen removal. Overall, these results revealed that the accumulation of TiO2 NPs altered the genetic expression of biofilm in CWs, which had significant impacts on biological nitrogen transformation.

Complex microbial nitrogen-cycling networks in three distinct anammox-inoculated wastewater treatment systems

Microbial nitrogen removal mediated by anaerobic ammonium oxidation (anammox) are cost-effective, yet it is time-consuming to accumulate the slow-growing anammox bacteria in conventional wastewater treatment plants (WWTPs). Inoculation of anammox enriched pellets is an effective way to establish anammox and achieve shortcut nitrogen removal in full-scale WWTPs. However, little is known about the complex microbial nitrogen-cycling networks in these anammox-inoculated WWTPs. Here, we applied metagenomic and metatranscriptomic tools to study the microbial nitrogen removal in three conventional WWTPs, which have been inoculated exogenous anammox pellets, representing partial-nitrification anammox (PNA) and nitrification-denitrification nitrogen removal processes. In the PNA system of Bali (BL), ammonia was partially oxidized by ammonia-oxidizing bacteria (AOB) Nitrosomonas and the oxidized nitrite and the remaining ammonium were directly converted to N2 by anammox bacteria Ca. Brocadia and Ca. Kuenenia. In the nitrification-denitrification system of Wenshan (WS), ammonia-oxidizing archaea (AOA) Thaumarchaeota unexpectedly dominated the nitrifying community in the presence of AOB Nitrosomonas. Meanwhile, the biomass yield of Ca. Brocadia was likely inhibited by the high biodegradable organic compound input and limited by substrate competitions from AOA, AOB, complete ammonia oxidizers (comammox) Nitrospira, nitrite-oxidizing bacteria (NOB) Nitrospira, and heterotrophic denitrifiers. Unexpectedly, comammox Nitrospira was the predominant nitrifier in the presence of AOB Nitrosomonas in the organic carbon-rich nitrification-denitrification system of Linkou (LK). These results clearly showed that distinct active groups were working in concert for an effective nitrogen removal in different WWTPs. This study confirmed the feasibility of anammox application in ammonium-rich systems by direct inoculation of the exogenous anammox pellets and improved our understanding of microbial nitrogen cycling in anammox-driven conventional WWTPs from both physiochemical and omics perspectives.

Insight into the Process of Mn-ANAMMOX in Soils of Agricultural Drainage Ditches

Anaerobic ammonium oxidation mediated by MnO2 (termed Mn-ANAMMOX) is a newly discovered microbial nitrogen removal pathway. However, few studies have reported on the Mn-ANAMMOX process and related microbial communities in agricultural drainage ditches. In this study, Mn(Ⅳ)-reducing bacteria (MnBR) enrichment cultivation was carried out for 340 days and an isotope tracing technique and high-throughput sequencing technology were used to provide convincing evidence of the occurrence of Mn-ANAMMOX. The results showed that simultaneous NH4+ oxidation and MnO2 reduction occurred during the reaction, and the production of NO2-, NO3-, 30N2, and Mn2+ was detected. Additionally, the average Mn-ANAMMOX rate, ammonium removal rate, and total nitrogen removal rate were 2.88 mg·(kg·d)-1, 20%, and 15%, respectively. Moreover, high-throughput sequencing results showed that after 340 d in the enrichment cultivation experiments, the abundance of MnBR increased from 27% to 70% at the phylum level, and the major genera of MnBR were determined as Acinetobacter and Geothrix, with relative abundances of 26.63% and 4.07%, respectively. Overall, the occurrence of Mn-ANAMMOX was directly proven during the MnBR enrichment cultivation experiments, and it might play an essential role in the pathway of microbial nitrogen removal.

Denitrification performance and microbial versatility in response to different selection pressures

This study investigated functional dynamics of microbial community in response to different selection pressures, with a focus on denitrification. Suspended-biomass experiments demonstrated limited aerobic and relatively higher anoxic nitrate and nitrite reduction capabilities; the highest NO2-N and NO3-N removal rates were 1.3 ± 0.1 and 0.74 ± 0.01 in aerobic and 1.4 ± 0.05 and 3.4 ± 0.1 mg/L.h in anoxic media, respectively. Key potential denitrifiers were identified as: (i) complete aerobic denitrifiers: Dokdonella, Flavobacterium, and Ca. Accumulibacter; (ii) complete anoxic denitrifiers: Acinetobacter, Pseudomonas, Arcobacter, and Comamonas; (iii) incomplete nitrite denitrifier: Diaphorobacter (aerobic/anoxic), (iv): incomplete nitrate denitrifiers: Thauera (aerobic/anoxic) and Zoogloea (strictly-aerobic). Granular biomass removed 72 mg/L NH4-N with no NOx− accumulation. Heterotrophic nitrification and aerobic denitrification were proposed as the principal nitrogen removal pathway in granular reactors, potentially performed by two key organisms Thuaera and Flavobacterium. Biodiversity analysis suggested that the selection pressure of nourishment condition was the decisive factor for microbial selection and nitrogen removal mechanism.

An Integrated Approach to Lysis-Cryptic Growth (Sludge Ozonation) and Sequencing Batch Reactor Coupled to an Anaerobic Side-Stream Reactor (SBR-ASSR): Performance and Characteristics

ABSTRACTAnaerobic side-stream reactors (ASSR) have been suggested to reduce waste activated sludge volumes benefiting from relatively low capital/operation costs and design simplicity. In this study, an evaluation of the feasibility of combining the ASSR system with the lysis-cryptic growth (ozonation) process was made so that a part of the sludge which passed through the ASSR anaerobic tank would be then treated by ozonation before returned to the aeration tank. The main independent factor was the ozonation flowrate (OFR), which is defined as the percent of return sludge which passed through the both the anaerobic tank and the ozonation unit. Three systems were studied, an ASSR control without ozonation (OFR-0), a combined ASSR with ozonation designated as OFR-2.5 (anaerobic interchange rate [AIR] of 10% per day and 25% of the exchanged sludge being ozonated [ozone interchange rate or OIR]), and OFR-3.1 (AIR = 12.5%, OIR = 25%). The results revealed that the insertion of an ozonation step led to an enhanced total microbial activity, eukaryotic population, and nitrogen removal. The linear relationship between the observed yield and the specific oxygen uptake rate indicated that microbial predation was the major relevant mechanism for the enhanced sludge reduction. The results of measurements of particle size distribution, and sludge dewaterability rates suggest that additional studies are needed to better understand and optimize this system.

Study on Purification Technology of High-salt Nitrogenous Printing and Dyeing Wastewater

This paper reports the microbial nitrogen removal, flocculation and decolorization purification technology of high-salt nitrogenous printing and dyeing wastewater. The combined microbial flora was used to perform simultaneous nitrification and denitrification (SND) nitrogen removal for high-salt nitrogenous printing and dyeing wastewater. When the sodium acetate was the carbon source and C:N was set to 7.5:1, the concentration of -N was reduced from the initial 2000.0 mg/L to 18.0 mg/L and the nitrogen removal rate was 99.1% and the nitrogen removal efficiency was 16.5 mg·L−1·h−1 at 120 h. Poly aluminum chloride (PAC) was the suitable flocculant. Under the optimized conditions that the dosage of PAC was 0.5 g/L and the flocculation time was 10 min, the flocculation rate reached 96.5%. Among the four decolorization methods of ozone, 84 disinfectant, hydrogen peroxide and chlorine dioxide, the decolorization effect of ozone oxidation was superior. When the production of ozone was 167 mg/min and the reaction time was 4 min, the decolorization rates all of neutral red, acid green and methyl orange could reach over 94.0%. This study provides theoretical and technical support for the purification of high-salt nitrogenous printing and dyeing wastewater.