Microbial community response to influent shift and lowering temperature in a two-stage mainstream deammonification process

Elucidating prioritized factor for mainstream partial nitritation between C/N ratio and dissolved oxygen: Response surface methodology and microbial community shifts

Recently, C/N ratio is suggested as a promising control factor with dissolved oxygen (DO) achieving mainstream partial nitritation (PN); however, their combined effects on mainstream PN are still limited. This study evaluated the mainstream PN with respect to the combined factors, and investigated the prioritized factor affecting the community of aerobic functional microbes competing with NOB. Response surface methodology was performed to assess the combined effects of C/N ratio and DO on the activity of functional microbes. Aerobic heterotrophic bacteria (AHB) played the greatest role in oxygen competition among functional microbes, which resulted in relative inhibition of nitrite-oxidizing bacteria (NOB). The combination of high C/N ratio and low DO had a positive role in the relative inhibition of NOB. In bioreactor operation, the PN was successfully achieved at ≥ 1.5 of C/N ratio for 0.5-2.0 mg/L DO conditions. Interestingly, aerobic functional microbes outcompeting NOB were shifted with C/N ratio rather than DO, suggesting C/N ratio is more prioritized factor achieving mainstream PN. These findings will provide insights into how combined aerobic conditions contribute to achieve mainstream PN.

Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (A_med) and 15 ± 3 °C (A_low). Results showed that anammox was successful after 138 d for A_low, only 7 d longer than A_med. Stable operation to 194 d in A_low, the nitrogen loading rate (NLR) increased to 1.01 kg m^-3·d^-1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of A_med (90%). More extracellular polymeric substance (EPS) was produced by the microbes of A_low compared to A_med, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in A_med with relative abundance 7.4%, while the "cold-tolerant" Candidatus Kuenenia with 4% was the dominant anammox bacteria in A_low. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Integrating conventional nitrogen removal with anammox in wastewater treatment systems: Microbial metabolism, sustainability and challenges

The various forms of nitrogen (N), including ammonium (NH₄⁺), nitrite (NO₂^-), and nitrate (NO₃^-), present in wastewaters can create critical biotic stress and can lead to hazardous phenomena that cause imbalances in biological diversity. Thus, biological nitrogen removal (BNR) from wastewaters is considered to be imperatively urgent. Therefore, anammox-based systems, i.e. partial nitrification and anaerobic ammonium oxidation (PN/anammox) and partial denitrification and anammox (PD/anammox) have been universally acknowledged to consider as alternatives, promising and cost-effective technologies for sustainable N removal from wastewaters compared to nitrification-denitrification processes. This review comprehensively presents and discusses the latest advances in BNR technologies, including traditional nitrification-denitrification and anammox-based systems. To a deep understanding of a better-controlled combining anammox with traditional processes, the microbial community diversity and metabolism, as well as, biomass morphological characteristics were clearly reviewed in the anammox-based systems. Explaining simultaneous microbial competition and control of crucial operation parameters in single-stage anammox-based processes in terms of optimization and economic benefits makes this contribution a different vision from available review papers. The most important sustainability indicators, including global warming potential (GWP), carbon footprint (CF) and energy behaviours were explored to evaluate the sustainability of BNR processes in wastewater treatment. Additionally, the challenges and solutions for BNR processes are extensively discussed. In summary, this review helps facilitate a critical understanding of N removal technologies. It is confirmed that sustainability and saving energy would be achieved by anammox-based systems, thereby could be encouraged future outcomes for a sustainable N removal economy.

Advanced nitrogen removal from municipal sewage via partial nitrification-anammox process under two typical operation modes and seasonal ambient temperatures

A novel two-stage partial nitrification-anammox (PN-A) process was developed, achieving nitrogen removal from low carbon/nitrogen ratio municipal sewage under two typical operational modes and seasonal ambient temperatures. When complete nitritation-anammox was performed at temperatures greater than 19.4 °C, the effluent concentration of total inorganic nitrogen (TIN) was 4.1 mg/L, corresponding to a nitrogen removal efficiency (NRE) of 94.3 %. In contrast, when partial nitritation-anammox was performed at temperatures below 19.4 °C, the effluent TIN was 12.3 mg/L, corresponding to a NRE of 83.6 %. The relative abundance of Nitrosomonas and Nitrosomonadaceae increased from 0.02 % to 0.28 %, while Ca. Brocadia decreased from 1.85 % to 1.30 %, with the contribution of anammox to nitrogen removal being highest under low temperatures (19.4℃ to 13.8℃), at 59.0 %. This novel two-stage PN-A process provides a new approach for the stable operation of wastewater treatment plants (WWTPs) under low ambient temperatures.

The r/K selection theory and its application in biological wastewater treatment processes

Understanding the characteristics of functional organisms is the key to managing and updating biological processes for wastewater treatment. This review, for the first time, systematically characterized two typical types of strategists in wastewater treatment ecosystems via the r/K selection theory and provided novel strategies for selectively enriching microbial community. Functional organisms involved in nitrification (e.g., Nitrosomonas and Nitrosococcus), anammox (Candidatus Brocadia), and methanogenesis (Methanosarcinaceae) are identified as r-strategists with fast growth capacities and low substrate affinities. These r-strategists can achieve high pollutant removal loading rates. On the other hand, other organisms such as Nitrosospira spp., Candidatus Kuenenia, and Methanosaetaceae, are characterized as K-strategists with slow growth rates but high substrate affinities, which can decrease the pollutant concentration to low levels. More importantly, K-strategists may play crucial roles in the biodegradation of recalcitrant organic pollutants. The food-to-microorganism ratio, mass transfer, cell size, and biomass morphology are the key factors determining the selection of r-/K-strategists. These factors can be related with operating parameters (e.g., solids and hydraulic retention time), biomass morphology (biofilm or granules), and operating modes (continuous-flow or sequencing batch), etc., to achieve the efficient acclimation of targeted r-/K-strategists. For practical applications, the concept of substrate flux was put forward to further benefit the selective enrichment of r-/K-strategists, fulfilling effective management and improvement of engineered pollution control bioprocesses. Finally, the future perspectives regarding the development of the r/K selection theory in wastewater treatment processes were discussed.

Challenges, solutions and prospects of mainstream anammox-based process for municipal wastewater treatment

Anaerobic ammonia oxidation (anammox) process has a promising application prospect for the mainstream deammonification of municipal wastewater due to its high efficiency and low energy consumption. In this paper, challenges and solutions of mainstream anammox-based process are summarized by analyzing the literature of recent ten years. Slow growth rate of anammox bacteria is a main challenge for mainstream anammox-based process, and enhancement of bacteria retention has been recognized to be necessary. Compared with directly increasing sludge retention time (SRT) with membrane bioreactors or sequencing batch reactors, culturing anammox bacteria in the form of biofilm or granule sludge is more promising for its feasibility of eliminating nitrite oxidizing bacteria (NOB). Besides, adding external electron donors or conductive materials and enriching the concentration of ammonia with absorption materials have also been proved helpful to improve the activity of anammox bacteria. Other challenges include the elimination of NOB and achieving ideal ratio of NH₄⁺ and NO₂^-. To solve these problems and achieve stable partial nitrification, composite control strategies based on low SRT and limited aeration are needed based on the special characteristics of ammonia oxidizing bacteria (AOB) and NOB. When treating actual wastewater, interference of low temperature and components in the influent is another problem. Relatively high activity of anammox bacteria has been realized after artificial acclimation at low temperature and the mechanism was also preliminary explored. Different pre-treatment sections have been designed to reduce the concentration of COD and S^2- from the influent. As for the nitrate produced by the anammox reaction, coupling processes are useful to reduce the concentration of nitrate in the effluent. In brief, suitable reactor and coupling process should be selected according to the temperature, influent quality and discharge targets of different regions. The future prospects of the mainstream anammox-based process are also put forward.

Achieving high-rate partial nitritation with aerobic granular sludge at low temperatures

Partial nitritation is necessary for the implementation of the mainstream anammox (anaerobic ammonium oxidation) process in wastewater treatment plants. However, the difficulty in outcompeting nitrite-oxidizing bacteria (NOB) at mainstream conditions hinders the performance of partial nitritation. The present work aimed to develop a high-rate partial nitritation process for low-ammonium wastewater treatment at low temperatures by seeding aerobic granules. Experimental results suggested that both stratified structure of nitrifiers developed in the granules and sufficient residual ammonium concentration (18-35 mg N L^-1) in the bulk liquid contributed to efficient NOB repression. With the hydraulic retention time progressively shortened from 1.0 to 0.17 h, the influent nitrogen loading rate of the partial nitritation process reached 6.8 ± 0.4 kg N m^-3 d^-1 even at 10-15 °C. The high concentration (7.5 gVSS L^-1) and activity (0.48 g N g^-1 VSS d^-1 at 11 °C) of granular sludge made the reactor possess an overcapacity evaluated by the ratio between the actual ammonium oxidation rate of the granules and their maximum potential. The overcapacity helped the reactor to face the adverse effect of decreasing temperatures. Overall, this work indicated the great potential of applying aerobic granules to achieve high-rate partial nitritation at mainstream conditions. Moreover, anammox bacteria with a relative abundance of 2.8% was also identified in the partial nitritation granules at the end of this study, suggesting that the granules provided a habitable niche for anammox bacteria growth. Note that these results cannot fully relate to the treatment of real domestic/municipal wastewater, they are a source of important information increasing the knowledge about low temperature partial nitrification.

Water diversion induces more changes in bacterial and archaeal communities of river sediments than seasonality

Previous studies have demonstrated that seasonal variation is often the most important factor affecting aquatic bacterial assemblages. Whether anthropogenic activities can dominate community dynamics remains unknown. Based on 16S rRNA high-throughput sequencing technology, this study revealed and compared the relative influence of water diversions and seasonality on bacterial and archaeal communities in river sediments from a region with obvious seasonality. The results indicate that the influence of water diversion on bacteria and archaea in water-receiving river sediments exceeded the influence of seasonal variation. Water diversion affected microbes by increasing EC, salinity, water flow rate, and organic matter carbon and nitrogen contents. Seasonal variations affected microbes by altering water temperature. Diversion responders but no season responders were classified by statistical methods in the microbial community. Diversion responder numbers were related to nitrogen concentrations, complex organic carbon contents and EC values, which were mainly affected by water diversion. With the joint impact of water diversion and seasonality, the correlations of bacterial and archaeal numbers with environmental factors were obviously weakened due to the increases in the ecological niche breadths of microorganisms. Natural seasonal changes in bacterial and archaeal communities were totally altered by changes in salinity, nutrients, and hydrological conditions induced by anthropogenic water diversions. These results highlight that human activity may be a stronger driver than natural seasonality in the alteration of bacterial and archaeal communities.

Enhancing the in-situ enrichment of anammox bacteria in aerobic granules to achieve high-rate CANON at low temperatures

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH₄⁺ <0.15) and selective washing-out of NOB-preferred smaller particles at short hydraulic retention time (HRT, 25-15 min) contributed to the NOB repression. Then the stepwise down-regulating DO concentrations from 2.8 to 1.2 mg/L enhanced the enrichment of anammox bacteria in the aerobic granules. The enriched anammox species was dominated by Ca. Brocadia sapporoensis with the estimated growth rate of 0.008-0.013 d^-1 at 15 °C. Chloroflexi and Chlorobi-affiliated bacteria were also significantly enriched in the granules, which may benefit the anammox bacteria activity and growth. At the end of this study, the average total nitrogen removal rate and efficiency of the granular CANON process respectively reached 1.26 kg N·m^-3·d^-1 and 68% treating low-strength ammonium (∼50 mg N·L^-1) wastewater under such aggressive conditions (DO = 0.8-1.5 mg/L, HRT< 1.0 h, and T = 15 °C). Overall, the aerobic granules provided a habitable niche for the proliferation and almost complete retention of the anammox bacteria. This study provides a roadmap for in-situ starting up of high-rate CANON process for mainstream wastewater treatment with aerobic granules as inoculum.

Adaptation of flocculent anammox culture to low temperature by cold shock: long-term response of the microbial population

Partial nitritation-anammox (PN/A) process will substantially reduce the costs for the removal of nitrogen in the mainstream of municipal sewage. However, one of the mainstream PN/A challenges is to reduce the time necessary for the adaptation of anammox bacteria to lower temperatures in mild climates. In this study, we exposed anammox flocculent culture to cold shocks [35°C → 5°C (8 h) → 15°C] and evaluated long-term cold shock response. Over a post-shock period of 40 d at 15°C, the nitrogen removal rates in the shocked culture were significantly higher compared to control, with maximum rates up to 0.082 and 0.033 kg-N/kg-VSS/d or 0.164 and 0.076 kg-N/m3/d, for shocked culture and control, respectively. In the corresponding semi-batch cycles, the shocked culture was on average 136 ± 101% more active than the control, due to the negative effect of cold shock on side populations and more active anammox cells. Per FISH, Ca. Brocadia anammoxidans and Ca. Scalindua survived the shock and remained present throughout. Thus, both anammox microorganisms seem to respond favourably to cold shocks. In sum, we provide further evidence that cold shocks accelerate the adaptation of anammox to the mainstream of municipal WWTPs. Further, for the first time, we report the long-term adaptive response of anammox to cold shocks.

Simultaneous enhanced biological phosphorus removal and semi-nitritation (EBPR-SN) followed by anammox process treating municipal wastewater at seasonal temperatures: From summer to winter

This work investigated the feasibility of a novel simultaneous enhanced biological phosphorus removal and semi-nitritation (EBPR-SN) plus anammox process treating real municipal wastewater from summer to winter (28.1- 15.3 °C). Two lab-scale sequential reactors were used in this study, namely EBPR-SN and Anammox sequencing batch reactors (SBRs). Long-term operation suggested that ammonium oxidizing bacteria abundance decreased from 1.67% to 0.89% whereas nitrite oxidizing bacteria decreased to nearly undetected in the EBPR-SN SBR, maintaining the stable nitritation (nitrite accumulation ratio: 98.3 ± 1.0%). Lowering airflow rate was effective to retain nitritation with temperature decrease. Reliable nutrient removal was still maintained in winter (16.4 ± 0.7 °C), i.e. the removal efficiencies for nitrogen and phosphorus were 80.0 ± 3.5% and 95.4 ± 5.2%, respectively, with short aerobic HRT (6.4 h) and low dissolved oxygen (0.2-1.5 mg/L). The percentage of anammox contribution to nitrogen-removal increased with temperature decrease, although Candidatus Brocadia abundance decreased. Additionally, the protection of extracellular polymeric substances was important to the successful performance.

Microbial invasions in sludge anaerobic digesters

Among processes that control microbial community assembly, microbial invasion has received little attention until recently, especially in the field of anaerobic digestion. However, knowledge of the principles regulating the taxonomic and functional stability of microbial communities is key to truly develop better predictive models and effective management strategies for the anaerobic digestion process. To date, available studies focus on microbial invasions in digesters feed with activated sludge from municipal wastewater treatment plants. Herein, this review summarizes the importance of invasions for anaerobic digestion management, the ecological theories about microbial invasions, the traits of activated sludge microorganisms entering the digesters, and the resident communities of anaerobic reactors that are relevant for invasions and the current knowledge about the success and impacts of invasions, and discusses the research needs on this topic. The initial data indicate that the impact of invasions is low and only a small percentage of the mostly aerobic microorganisms present in the activated sludge feed are able to become stablished in the anaerobic digesters. However, there are still numerous unknowns about microbial invasions in anaerobic digestion including the influence of anaerobic feedstocks or process perturbances that new approaches on microbial ecology could unveil. KEY POINTS: • Microbial invasions are key processes to develop better strategies for digesters management. • Knowledge on pathogen invasions can improve anaerobic digestion microbial safety. • To date, the number of successful invasions on anaerobic digesters from activated sludge organisms is low. • Feed organisms detected in digesters are mostly inactive residual populations. • Need to expand the range of invaders and operational scenarios studied.

Comparing nitrite-limited and ammonium-limited anammox processes treating low-strength wastewater: Functional and population heterogeneity

Biomass segregation between granules/biofilm and flocs is widespread in anammox-based processes. The segregation of biomass allows for easy control of processes stability. The goal of this study is to understand the biomass segregation in two anoxic anammox reactors respectively operated in nitrite-limited (R_NO2) and ammonium-limited (R_NH4) modes treating low-strength wastewater at 20 °C. Results showed that size-based biomass segregation was developed in both reactors. But the functional and population heterogeneity was more significant in the ammonium-limited anammox reactor. The activity and abundance of anammox bacteria in large granules were significantly higher than that in flocs under the ammonium-limited conditions. The large granules played a major role in nitrogen removal in R_NH4. By contrast, both large granules and small flocs contributed significantly to the nitrogen loss in the nitrite-limited anammox reactor, since a large number of anammox bacteria existed in both granules and flocs. Besides, a number of Nitrospira-like NOB were also detected in both anoxic anammox reactors, which primarily inhabited in flocs seemingly droved by the availability of oxygen. But the abundance of Nitrospira in R_NH4 was much higher than that in R_NO2. All these results suggested that selective flocs removal would be necessary for R_NH4 to improve its anammox performance but non-essential for R_NO2. The two anammox reactors shared the predominant anammox species with the closest relative to Ca. Brocadia sp. 40 (98%). Unexpectedly, the anammox species grew faster in R_NH4. But the microbial diversity and evenness was much greater in R_NO2, suggesting its higher functional stability.

Wastewater Treatment using the "Sulfate Reduction, DenitrificationAnammox and Partial Nitrification (SRDAPN)" Process

Although nitrogen removal from wastewater is essential to prevent eutrophication, the biological processes employed to this end are characterized by several disadvantages, including high energy consumption and the production of large quantities of sludge. Thus, in this study, the organic matter and nitrogen removal efficiencies of the new sulfate reduction, denitrification/anammox and partial nitrification (SRDAPN) process were examined using an anaerobic-anoxic-oxic biofilter reactor. The results showed that the organic matter removal efficiency of the new process at loading rate 1.0 kg COD/m³ per day was 97%. With a circulation flow from the oxic to the anoxic column that was 3 times influent, the nitrogen removal efficiency of the sulfur denitrification and nitrification (SRDN) process without anammox, was 66%, while that of the SRDAPN process with anammox was 76%. Additionally, nitrogen consumption by the anammox reaction in the anoxic column was 13.8% for nitrite-nitrogen and 10.5% for ammonium-nitrogen, and the withdrawal of excess sludge was not required throughout the 170 days of operation. Microbial community analysis showed that acetogenic sulfate reducing bacteria and acetoclastic methanogens coexisted in the anaerobic column, and in the anoxic column, the total relative abundance of anammox bacteria, including Candidatus Brocadia, which coexisted with heterotrophic denitrifying bacteria and sulfur denitrifying bacteria, was 17-18%. Thus, this study established the SRDAPN process as an energy saving and high removal efficiency process.

Process performance and anammox community diversity in a deammonification reactor under progressive nitrogen loading rates for swine wastewater treatment

The performance of a deammonification reactor fed with increasing nitrogen loading rates (NLR) was evaluated. The digestate from a continuous stirred tank reactor (CSTR) treating sludge from a swine production unit was diluted to provide different ammonia concentrations. The biomass samples from the end of each experimental phase were analyzed for microorganism community evaluation. The results proved that deammonification system supported a NLR up to 3.27 ± 0.13 g N L^-1 d^-1 with nitrogen removal efficiency of 83%. The specific ammonia consumption rate (µ_NH3-N) did not decrease up to this NLR proving the stability of reactor performance. Anammox bacteria genus shifted along the experiment and at the end the predominant anammox bacteria found in the reactor was candidatus Brocadia. Finally, it was proved that a deammonification reactor for nitrogen removal from CSTR digestate could be easily controlled only by monitoring pH and dissolved oxygen.

Performance and microbial community analysis of two sludge type reactors in achieving mainstream deammonification with hydrazine addition

The deammonification process is a promising and energy efficient nitrogen removal technology. Since deammonification process has succeeded in high-strength ammonia nitrogen wastewater treatment (sidestream deammonification) but its application in treating low-strength ammonium nitrogen wastewater (mainstream deammonification) remains a great challenge. In this study, mainstream deammonification process in two reactors maintained stability with hydrazine (N₂H₄) addition. The two reactors consisted of a deammonification granular reactor and a mixed ammonia oxidizing bacteria (AOB) flocculent with anaerobic ammonia oxidizing bacteria (AnAOB) granular reactor. Deammonification granular reactor had a more efficient total nitrogen removal efficiency (TNRE, 80.5 ± 5.8%) and nitrogen removal rate (NRR, 0.33 ± 0.04 g/(L·day)). The advantage of retain biomass in granular sludge reactor lead to a more balanced ex-situ activity between AOB (0.37 mg N/(g VSS·h)) and AnAOB (0.43 mg N/(g VSS·h)). Candidatus Brocadia and Nitraspira were detected the dominant genus responsible for the observed AnAOB and nitrite oxidizing bacteria (NOB), respectively. The more obvious effect of N₂H₄ on enhancing AnAOB and suppressing NOB both in ex-situ activity and genus abundances in mixed sludge reactor were also founded may due to loose spatial distribution among species.

Evolution of microbial dynamics with the introduction of real seawater portions in a low-strength feeding anammox process

The salinity effect on anammox bacteria has been widely reported; however, rare studies describe the microbial dynamics of anammox-based process response to the introduction of real seawater at mainstream conditions. In this study, an anammox process at mainstream conditions without pre-enriching anammox bacteria was shifted to the feeds of a synthetic wastewater with a portion of seawater mixture. It achieved over 0.180 kg-N/(m³ day) of nitrogen removal rate with an additional seawater proportion of 20% in the influent. The bacterial biodiversity was significantly increased with the increase of seawater proportions. High relative abundance of anammox bacteria (34.24–39.92%) related to Ca. Brocadia was enriched and acclimated to the saline environment. However, the introduction of seawater caused the enrichment of nitrite-oxidizing Ca. Nitrospira, which was responsible for the deterioration of nitrogen removal efficiency. Possible adaptation metabolisms in anammox bacteria and other nitrogen transforming bacteria are discussed. These results highlight the importance of microbial diversity for anammox process under the saline environments of 20% and 40% seawater composition.

Towards more efficient nitrogen removal and phosphorus recovery from digestion effluent: Latest developments in the anammox-based process from the application perspective

Over the past forty years, anammox-based processes have been extensively researched and applied to some extent. However, some of the long-standing problems present serious impediments to wide application of these processes, and knowledge gap between lab-scale research and full-scale operations is still considerable. In recent years, anammox-based research has developed rapidly and some emerging concepts have been proposed. The focus of this review is on the critical problems facing actual application of anammox processes. The latest developments in anammox-based processes are summarized, and particular consideration is given to the following aspects: (1) the evolution of the chemical stoichiometry of anammox reaction; (2) the status of several main anammox-based processes; (3) the critical problems and countermeasures; (4) the emerging anammox-based processes; and (5) the suggested optimal process integrating partial nitritation, anammox, hydroxyapatite crystallization and denitratation for digestion effluent treatment towards more efficient nitrogen removal and phosphorus recovery in the future.

Granules abrasion cause deterioration of nitritation in a mainstream granular sludge reactor with high loading rate

Biomass detachment generally occurred in granular sludge systems. However, little is known about the influence of biomass detachment on the granules performing nitritation. Here, a granular sludge reactor with high loading rates (6.8 ± 0.4 kg N·m^-3·d^-1) was achieved at mainstream conditions. Though the low ratio control strategy was maintained, the deterioration of nitritation performance was observed after the further increase of air supply rates to 3.4 ± 0.2 L min^-1. In parallel with that, the loss of AOB and the proliferation of NOB was observed. Additionally, with the decrease of granules size and biomass concentration, the incomplete stratification of nitrifiers in the granules was confirmed by batch tests. All these results suggested that granules abrasion under the high shear stress conditions caused the detachment of external AOB and hence resulted in the deteriorated stratified structure of nitrifiers, which subsequently contributed to the proliferation of the internal NOB and the deterioration of nitritation. These findings highlight that the granules abrasion should be well controlled in the development of high-rate nitritation process with granular sludge.

Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.

An improved start-up strategy for mainstream anammox process through inoculating ordinary nitrification sludge and a small amount of anammox sludge

The difficulties in enriching anammox bacteria and maintaining stable partial nitrification during start-up phase limit the application of mainstream anammox process. In this study, the feasibility of starting up simultaneous partial nitrification, anammox and denitrification (SNAD) reactor treating municipal wastewater by inoculating ordinary nitrification sludge (96.2%) and a small amount of anammox sludge (3.8%) was investigated. A sequencing batch reactor with intermittent aeration was used for the SNAD process. The SNAD reactor was started up in 75 days with a nitrogen removal efficiency of 85.4% at ambient temperature. The nitrogen removal performance maintained stable despite the fluctuating inflow. Anammox bacterial activity exponentially increased although nitrite oxidizing bacteria (NOB) activity in seeding sludge was high. The enhanced ammonium oxidizing bacterial activity and partial denitrification provided sufficient nitrite for anammox bacteria. Moreover, NOB was inhibited by intermittent aeration, anammox bacteria had competitive advantage on nitrite. The improved particle size and settleability of activated sludge also favored the anammox bacterial enrichment. This study provided an improved and easily-implemented start-up strategy for mainstream anammox. The seeding sludge was easily obtained and the operation strategy was simple. These findings were meaningful to the engineering application of mainstream anammox.

Evaluation of deammonification reactor performance and microrganisms community during treatment of digestate from swine sludge CSTR biodigester

Digestate from anaerobic processes still contains relatively high amount of total organic carbon (TOC) that can inhibit deammonification. In this sense, the present study investigated the interference of TOC in a lab-scale expanded granular sludge bed (EGSB) deammonification reactor treating digestate from a continuous stirred tank reactor (CSTR) swine sludge biodigester. Additionally, the microorganisms community was analyzed when the process was submitted to different operational conditions. The study was divided into three phases according to the C/N ratio (0, 0.5 and 1 for phase I, phase II and phase III, respectively). At phase I the average nitrogen removal efficiency (NRE) was 65 ± 1.6%. With the increase of TOC in phase II (156 ± 8.15 mg L^-1) the average NRE was 61 ± 9.8% which is statically equivalent to phase I (p < 0.05). On the other hand, at phase III (TOC was increased to 255 ± 3.50 mg L^-1) the NRE decreased to 50 ± 3.9% which was 22% lower than in phase II. Stoichiometric coefficients of N₂ was close to theoretical values during all experimental phases, while stoichiometric coefficient of N-NO₃^- was lower than theoretical values specially during phase III. Ca. Jettenia was favored when the reactor was fed with digestate although its proportion decreased in phase III. Thus, at the conditions employed in the present study it is recommended to use a C/N ratio of 0.5 (TOC concentration around 156 mg L^-1) to treat digestate by deammonification process, in order to not diminish anammox microorganisms abundance. Thereby, the microorganisms community can be modulated based on carbon and nitrogen loading rates of a deammonification reactor for swine manure treatment purpose.

Patterns of bacterial and archaeal communities in sediments in response to dam construction and sewage discharge in Lhasa River

The increased anthropogenic activities in the Tibetan Plateau may threaten the river environmental safety. However, limited information is available on the Lhasa River in the Tibetan Plateau, which is known as the remaining pure land on Earth. Here, we firstly investigated the distribution patterns of bacterial and archaeal communities in sediments in response to dam construction and sewage discharge along the reaches of the Lhasa River. The total organic carbon, total Nitrogen (N), nitrate and ammonium contents and the relative abundance of bacteria and archaea significantly increased in reservoir sites in comparison with sites below dam, and they also gradually increased from upstream to downstream in sewage discharge sites. By contrast, the diversity of sediment bacteria and archaea in reservoir sites were significantly less than that in sites below dam and sewage discharge sites at Operational Taxonomic Units (OTUs) level. The dominant species were water-bloom cyanobacteria in the reservoir area of Zhikong Dam and Proteobacteria in the sewage discharge sites, which were significantly correlated with the nutrient concentration. The abundance of nitrogen functional genes significantly also increased in reservoir sites and the downstream of sewage discharge areas. These results suggested that dam construction and sewage discharge caused the increase of sediment bacterial communities and nutrient levels and potentially induced eutrophication in the Lhasa River.

High-efficient nitrogen removal from municipal wastewater via two-stage nitritation/anammox process: Long-term stability assessment and mechanism analysis

This study focused on the long-term stability of a novel two-stage partial-nitritation/anammox (PN/A) process treating municipal wastewater with fluctuated water quality. Specifically, two parallel sequencing batch reactors (SBRs) were used for removing organic matters and achieving complete nitritation, while the expanded granular sludge bed (ANA-EGSB) was used for anammox. With the influent ammonium concentration varying from 32 to 79 mg/L and the average hydraulic retention time of 3.39 h in this system, more than 93% of ammonium was removed and the effluent TIN was 4.8-11.8 mg/L. The partial denitrifying occurring in the anammox reactor could reduce nitrate to nitrite that was reused by anammox bacterium, enhancing the TIN removal efficiency. Further, the "overconsumption of ammonium" under anaerobic conditions was observed in ANA-EGSB. Microbial community analysis showed that Nitrosomonas (AOB) were the dominant nitrifying bacteria in the nitritation SBR and Candidatus_Brocadia with the relative abundance of 6-13% dominated in ANA-EGSB.