Rapid establishment of municipal sewage partial denitrification-anammox for nitrogen removal through inoculation with side-stream anammox biofilm without domestication.

Mainstream partial denitrification anammox was achieved through inoculation of side-stream mature partial nitritation anammox biofilm without domestication. The contribution of anammox to nitrogen removal was 29.4 %. Moreover, prolonging anoxic hydraulic retention time and introducing side-stream nitrite under different carbon/nitrogen ratios enriched anammox bacteria. The abundance of anammox bacteria increased by âˆ¼ 10 times ((2.19 ± 0.17) × 1012 copies gene / g dry sludge) with a total relative abundance of 18.51 %. During 258 days of operation, the contribution of anammox to nitrogen removal gradually increased to 68.8 %. The total nitrogen in the effluent decreased to 8.84 mg/L with a total nitrogen removal efficiency of 76.4 % under a carbon/nitrogen ratio of 3. This paper proposes a novel way to rapidly achieve mainstream partial denitrification anammox via inoculation with side-stream mature partial nitritation anammox biofilm. This method achieves advanced nitrogen removal from municipal wastewater, even under low carbon/nitrogen ratios.

Linking morphological features to anammox communities in a partial nitritation and anammox (PN/A) biofilm reactor.

Partial nitritation/anammox (PN/A) has been recognized as a cost-efficient process for wastewater nitrogen removal. The addition of carriers could help achieve biomass retention and enhance the treatment efficiency by forming the dense biofilm. However, accurately determining the abundance of anammox bacteria (AnAOB) to evaluate the biofilm development still remains challenging in practice without access to specialized facilities and experimental skills. In this study, we explored the feasibility of utilizing the morphological features of anammox biofilm as an indication of the biofilm development progression, and its correlation with microbial communities was also revealed. The time-series biofilms from an integrated fixed-film activated sludge (IFAS) system with stable PN/A performance were sampled representing the different biofilm development stages. The biofilm morphological features including color and texture were respectively quantified by red (R) coordinate and Local binary pattern (LBP) descriptor via image processing. Hierarchy clustering analysis proved that the extracted morphological descriptors could well distinguish the different stages (colonization, succession, and maturation) of biofilm development. The microbial community dynamics of time-series anammox biofilms were investigated using the amplicon sequence variant (ASV) analysis. Candidatus Brocadia, as the typical AnAOB, dominated in the whole communities of 16.3%-20.0%, moreover, the biofilm development was found to be driven by distinct Brocadia species. Linear regression evidenced that the Brocadia abundance could be directly correlated to the value of R and LBP, and the total variation of microbial communities could be significantly explained by the morphological features via redundancy analysis. This study demonstrates a new way to monitor the biofilm development by extracting the visible features of anammox aggregates, which can help facilitate the automated control of anammox-based bioprocess.

Advanced nutrient removal and external sludge reduction: Demonstration in a pilot-scale sequencing batch reactor.

Although the addition of excess sludge fermentation products to improve nutrient removal from sewage is cost-effective, its application has rarely been demonstrated. In this study, the external sludge was first collected and fermented under a sludge retention time of 10 days, then introduced into SBR with a 1:15 sewage ratio. The results revealed a gradual increase in the nitrite accumulation ratio to 34.7% in the SBR at the end of the oxic stage after 64 days of adding fermented sludge products. In addition, the average effluent total nitrogen and phosphorous decreased to 7.3 and 0.5 mg/L, corresponding to removal efficiencies of 86.7% and 95.5%, respectively. On the other hand, the use of the fermented sludge products as external organic carbon sources in the SBR increased the external sludge reduction ratio to 42.5%. High-throughput sequencing demonstrated that the increase in the endogenous denitrifier community, polyphosphate-accumulating organisms, and fermentation bacteria were the main factors contributing to the increase in nutrient removal and excess sludge reduction. The economic evaluation indicated that the operational cost of the pilot-scale system saves 0.011$/m3 of sewage treated. PRACTITIONER POINTS: Fermented sludge addition effectively enhanced nutrient removal in pilot-scale SBR. Average effluent TN and PO4 3- -P decreased to 7.3 and 0.5 mg/L, respectively. Highest external sludge reduction rate was 42.5% in pilot-scale reactor. Sewage treatment cost can save 0.011$/m3 under advanced nutrient removal.

Successful Application of Anammox Using the Hybrid Autotrophic-Heterotrophic Denitrification Process for Low-Strength Wastewater Treatment.

Directly integrating anammox into sewage treatment is attractive, but anammox bacteria (AnAOB) enrichment is complex due to vicious competition from heterotrophic bacteria (HB). A novel strategy of optimal organics management using a preanaerobic stage and subsequent limited-oxygen conditions (0.32 ± 0.15 mg-O2/L) is applied, and a hybrid autotrophic-heterotrophic denitrification process is developed to treat sewage-like wastewater with a COD/N ratio of 3.1 for 420 days. The stable process was achieved, and a high total nitrogen removal rate of 0.53 kg-N/(m3·d) was obtained compared to conventional nitrification/denitrification. The 16S rRNA high-throughput sequencing analysis suggested that the relative abundance of the nonendogenous HB (Denitratisoma and Thauera) was drastically reduced (P ≤ 0.001), whereas the endogenous denitrifying HB (Candidatus (Ca.) Competibacter) was significantly enriched in the anammox granules (9.98%, P ≤ 0.001). Moreover, Ca. Competibacter as an inner core and Nitrospira and Ca. Brocadia as an outside coating of the anammox granules indicated the cooperation of AnAOB with HB as revealed by laser-scanning confocal microscopy and qPCR. In situ tests further confirmed nitrite from two pathways (partial nitritation and endogenous partial denitritation) that favored AnAOB enrichment. Optimal organics management can mitigate the competition of HB with AnAOB by redirecting the metabolic pathways and microbial community, which is critical to directly integrating anammox into sewage treatment.

Biofilm phenotypes and internal community succession determines distinct growth of anammox bacteria in functional anammox biofilms.

In this study, time-series anammox functional biofilms were obtained in a lab-scale simultaneous partial nitritation/anammox process for treating high-strength ammonium. The variations in the biofilm phenotypes, community succession, and anammox bacteria abundance over time were evaluated using optical microscopy, 16S rRNA gene sequencing, and qPCR. The result revealed that biofilm has three distinct stages of the community development trajectory across a 182-day temporal scale. Anammox bacteria growth rates were 0.035 d-1, 0.0015 d-1, and 0.011 d-1, respectively. The diversity and network analysis suggested that the positive priority effect of ammonia oxidizing bacteria was the primary factor for the rapid proliferation of anammox bacteria, and the species replacement triggering priority effect forfeiture and substituted functional recruitment were reasons for the slow proliferation and stable proliferation of anammox bacteria, respectively. Taken together, the higher microbial diversity and stable community composite were key prerequisites for the proliferation of the anammox bacteria.

Distinct granulation pathways of anammox granular sludge under biofilm enhancement.

The simultaneous partial nitrification and anammox (PN/A) granular sludge process in a plug-flow reactor has been difficult to achieve. This study provides a novel way to enhance granulation using biofilm detachment. In a plug-flow reactor, a fixed carrier was added to the activated sludge, and a PN/A biofilm gradually formed during the operation. Mature biofilm detachment appeared and caused the emergence of micro-granule. Then the fixed carriers were removed from the reactor, but the nitrogen removal rate (NRR) of the reactor was barely affected. This result suggests granular sludge is a feasible replacement for biofilm. Moreover, the particle size of the granule increased from 212 to 425 µm, and the NRR was 1.63 kg N/(m3·d), with a maximum nitrogen removal efficiency of 86.5%. Overall, this study implies that it is feasible to maintain granular sludge in a plug-flow PN/A reactor, and biofilm detachment significantly favors the granulation process.

A Dynamic Risk Appraisal Model and Its Application in VTS Based on a Cellular Automata Simulation Prediction.

The successful implementation of Vessel Traffic Services (VTS) relies heavily on human decisions. With the increasing development of maritime traffic, there is an urgent need to provide a sound support for dynamic risk appraisals and decision support. This research introduces a cellular automata (CA) simulation-based modelling approach the objective of which is to analyze and evaluate real-time maritime traffic risks in port environments. The first component is the design of a CA model to monitor ships' behavior and maritime fairway traffic. The second component is the refinement of the modelling approach by combining a cloud model with expert knowledge. The third component establishes a risk assessment model based on a fuzzy comprehensive evaluation. A typical scenario was experimentally implemented to validate the model's efficiency and operationality.

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.

Rapid achieving partial nitrification in domestic wastewater: Controlling aeration time to selectively enrich ammonium oxidizing bacteria (AOB) after simultaneously eliminating AOB and nitrite oxidizing bacteria (NOB).

This study developed a novel strategy for rapidly achieving partial nitrification (PN) without additional chemical agents, and infrastructure costs, only by controlling aeration time to selectively enrich ammonium oxidizing bacteria (AOB) after simultaneously eliminating AOB and nitrite oxidizing bacteria (NOB). Shorter aeration time and sludge retention time (10 days) were implemented to simultaneously eliminate AOB and NOB, the bioactivities drastically decreased to 13 and 0%, respectively. Subsequently, a gradually prolonged aeration time selectively enriched AOB and resulted in PN. The amoA abundances increased to 1.9 × 1010 copies gVSS-1, whereas Nitrospira and Nitrobacter abundances remained stable (3.2 × 109 and 3.1 × 109 copies gVSS-1). A nitrite accumulation rate above 96% was achieved and maintained for 205 days over the entire temperature range (28.5-17.9 °C). The effluent contained 1.9 mg N L-1 of ammonium, 25.3 mg N L-1 of nitrite, and less than 1.0 mg N L-1 of nitrate, facilitating mainstream wastewater anammox.

Rapid enrichment of anammox bacteria linked to floc aggregates in a single-stage partial nitritation-anammox process: Providing the initial carrier and anaerobic microenvironment.

Rapid enrichment of anaerobic ammonia oxidation bacteria (AnAOB) is highly associated with the granulation process; however, the interactive mechanism remains unclear, especially for the initial granulation process. A single-stage partial nitritation-anammox (PN/A) bioreactor combined with granular/floc sludge was operated for 400 days. During the experimental period, the nitrogen removal rate increased from 0.60 to 1.21 kg N m-3d-1, and the nitrogen removal capability improved primarily during a transition period (days 200-250), which was accompanied by a particle size increase and AnAOB proliferation (4.9 ± 1.7 days). Moreover, as observed by the biomass physio-morphology, the size distribution, and the microbial community shift, small flocs (< 200 µm) aggregated due to the addition of excess sodium acetate. The emerging floc aggregates represented an early form of granules, providing the initial biological carrier and necessary anaerobic microenvironment for the growth of attached AnAOB, resulting in a high AnAOB growth-rate. These results are the first direct evidence that floc aggregates are essential to AnAOB enrichment, and that they can be affected by operational conditions. This study provides an in-depth understanding of the link between floc aggregations and AnAOB enrichment and broadens the feasibility of optimizing PN/A applications.

A Ship Trajectory Prediction Framework Based on a Recurrent Neural Network.

Ship trajectory prediction is a key requisite for maritime navigation early warning and safety, but accuracy and computation efficiency are major issues still to be resolved. The research presented in this paper introduces a deep learning framework and a Gate Recurrent Unit (GRU) model to predict vessel trajectories. First, series of trajectories are extracted from Automatic Identification System (AIS) ship data (i.e., longitude, latitude, speed, and course). Secondly, main trajectories are derived by applying the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm. Next, a trajectory information correction algorithm is applied based on a symmetric segmented-path distance to eliminate the influence of a large number of redundant data and to optimize incoming trajectories. A recurrent neural network is applied to predict real-time ship trajectories and is successively trained. Ground truth data from AIS raw data in the port of Zhangzhou, China were used to train and verify the validity of the proposed model. Further comparison was made with the Long Short-Term Memory (LSTM) network. The experiments showed that the ship's trajectory prediction method can improve computational time efficiency even though the prediction accuracy is similar to that of LSTM.

Improving Efficiency and Stability of Anammox through Sequentially Coupling Nitritation and Denitritation in a Single-Stage Bioreactor.

This study developed an innovative process for the treatment of low-ammonium wastewater in a single-stage bioreactor over 250 days. Partial nitritation-anammox and partial denitritation-anammox (PN/A-PDN/A) processes were combined under aerobic/anoxic operation, and a high nitrogen removal efficiency (94.6%) was obtained at a nitrogen removal rate of 0.54 kg N m-3 d-1 and a chemical oxygen demand to total inorganic nitrogen (COD/TIN) ratio of 0.28. Mass balance analysis identified anammox as the dominant nitrogen removal pathway, achieving 88.3% nitrogen loss. The abundance of anammox bacteria and their bioactivity rapidly increased and were effectively maintained, as indicated by qPCR and bioactivity tests. The PN/A-PDN/A process provided two pathways of nitrite production for anammox, which favored the enrichment of anammox bacteria and stable processing. In addition, the enrichment of anammox bacteria was promoted by selective floc discharge since anammox bacteria are mainly located in granules (relative abundance of 29.64 ± 7.89%). Competitive organisms (including heterotrophic bacteria and nitrite oxidizing bacteria), enriched in flocs, were washed out. Overall, these findings confirmed anammox, sequentially combined with PN and PDN via aerobic/anoxic strategy, as a promising alternative for mainstream anammox.

Insight into the impacts of organics on anammox and their potential linking to system performance of sewage partial nitrification-anammox (PN/A): A critical review.

Partial nitrification-anammox (PN/A) is an energy-efficient process for nitrogen removal from sewage. The influent organics of sewage is usually pre-removed, reducing the risk for enriching anammox bacteria (AnAOB). However, recent studies demonstrate that optimum influent organics could improve nitrogen removal and operational stability of PN/A. Thus, the impact of organics on PN/A-based process should not be overlooked. In this review, the complicated impacts of organics-containing influent on anammox and their linking to apply PN/A are discussed. Firstly, the effect of organics on AnAOB metabolism and the competition relationship between AnAOB and heterotrophic bacteria are summarized. Secondly, the combined effects of influent organics and operational strategies on PN/A-based process were reviewed. Thirdly, how to control influent organics in the real application of PN/A were discussed. Lastly, recent development of the PN/A-based process combined with denitrification were reviewed. Overall, influent organics could be an essential factor for successful application of sewage PN/A.

Full-scale partial nitritation/anammox (PN/A) process for treating sludge dewatering liquor from anaerobic digestion after thermal hydrolysis.

In this study, a full-scale partial nitritation/anammox (PN/A) process was successfully established to treat dewatering liquor (filtrate) from the activated sludge after thermal hydrolysis (THP) - anaerobic digestion (AD). The filtrate had an average ammonium of 1407 mg/L with a COD/N ratio of 1.43 ±â€¯0.3. Under limited anammox biofilm inoculation, PN/A was started-up in an integrated fixed - biofilm activated sludge (IFAS) reactor. During the stable period, 2500 m3 of THP - AD sludge filtrate was treated daily and an average nitrogen removal rate of 0.21 kg N/(m3·d) was maintained with a removal efficiency over 85%. The application of PN/A reduced mainstream total inorganic nitrogen in effluent by 4.4 mg/L, saving $3.5 million in operational costs annually due to the reduction of organics addition. Overall, IFAS - PN/A process can be an efficient and economical method to treat THP - AD sludge filtrate and improve mainstream nitrogen removal performance.

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.

NOB suppression in partial nitritation-anammox (PNA) process by discharging aged flocs: Performance and microbial community dynamics.

The partial nitritation-anammox (PNA) process is the most promising technique to treat municipal sewage; however, nitrite oxidizing bacteria (NOB) are a hindrance to achieve PNA. This study investigated the effects of selectively discharging flocs (<200 µm) to washout NOB in a sequencing batch reactor (SBR) over 200 d. The experiment was divided into three phases with different floc sludge retention times (SRTs; 30, 20 and 30 d). When the SRT of the flocs was reduced from 30 to 20 d to washout NOB, a significant reduction of ammonia oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing (anammox) bacteria in the flocs was found. This indicates that a low floc SRT (20 d) leads to the loss of AOB and anammox bacteria in the flocs (<200 µm) and destroys PNA. Activity tests and qPCR analysis revealed the variations of functional bacteria in the granules and flocs, indicating that the enrichment of AOB, NOB, anammox bacteria in the granules is caused by the long-term discharging of flocs. High-throughput sequencing analysis revealed that the microbial shift of Tetrasphaera was significant in the flocs and may be connected to the enrichment of anammox bacteria and the stability of the PNA requires further research. All the obtained NOB sequences were affiliated with the genera Nitrospira and could further influence the PNA system. Overall, this study provides an in-depth understanding of the impact of discharging flocs to washout NOB and promotes the application of combing granules/floc PNA in sewage treatment.

Enhancing the digestion of waste activated sludge through nitrite addition: insight on mechanism through profiles of extracellular polymeric substances (EPS) and microbial communities.

Extracellular nitrite has been used to improve the digestion of waste activated sludge (WAS). However, the underlying mechanism remains largely unknown. In this study, WAS was treated with 0.2 gNO2--N/gVSS for 7 days and its performance was compared to that of aerobic and anaerobic treatments. The addition of nitrite had a distinct effect on the reduction of VSS/SS and the accumulation of soluble organics compared to the control reactors. As evident by the variations of extracellular polymeric substances (EPS), nitrite addition had a positive effect on decreasing protein. In particular, the decrease of protein mainly occurred in tightly bound EPS (TB-EPS), which caused sludge disintegration and enhanced sludge reduction. Additionally, the decrease of microbial diversity with nitrite addition was significant compared to the control reactors, accompany with a decrease of live/dead cells ratio and an increase of supernatant DNA concentration. This suggests that nitrite could cause cell death and lysis, resulting in sludge degradation. Thus, nitrite addition enhanced sludge treatment through the combined effect of TB-EPS disintegration and cell lysis. These findings will be useful for the optimization of sludge treatment process based on nitrite addition.