A novel single-stage process integrating simultaneous COD oxidation, partial nitritation-denitritation and anammox (SCONDA) for treating ammonia-rich organic wastewater

Municipal solid waste leachate treatment by three-stage membrane aeration biofilm reactor system

A combined process of coagulation pretreatment and three-stage membrane aeration biofilm reactor (MABR) system was successfully applied for the first time to treat actual municipal solid waste leachate (MSWL), which was characterized by high concentrations of toxic hard-to-degrade organics and salinity. The results showed that 9.8%-21.3% of organics could be removed from actual MSWL by coagulation with polymeric aluminum chloride (PAC). Three-stage MABR contributed 95.6% of the chemical oxygen demand (COD) removal, with the influent COD concentration ranging from 6000 to 7000 mg/L. At the same time, the removal efficiencies of total nitrogen (TN) and ammonia (NH4+-N) could reach to 84.3% and 79.9% without the addition of external carbon source, respectively. The nitrifying/denitrifying bacteria were enriched in the biofilm including Thiobacillus, Azoarcus and Methyloversatilis, which supported the MABR with high nitrogen removal efficiency and significantly toxic tolerance. Principal component analysis (PCA) and the Pearson correlation coefficients (r) illustrated that aeration pressure is a crucial operational parameter, exhibiting a strong correlation between the MABR performance and microbial communities. This work demonstrates that MABR is an effective and low-energy option for simultaneous removal of carbon and nitrogen in the treatment of MSWL.

Characterizing algal-bacterial symbiotic biofilms: Insights into coexistence of algae and anaerobic microorganisms

This study constructed an integrated algae/partial nitrification/anammox biofilm system and operated it for 240 days. The total nitrogen removal efficiency exceeded 90 %. The structure, compositions, and function of this symbiotic biofilm, which played a pivotal role in the system, were analyzed in detail. Microscope photos and fluorescence in situ hybridization both showed that bacteria and algae were well integrated. The dissolved oxygen gradient further confirmed that different functional microorganisms grew at varying depths within biofilm. Algae formed an oxygen-producing zone (0-0.48 mm), followed by ammonia oxidizing bacteria (AOB) consuming oxygen to form an oxygen-consuming zone (0.48-0.86 mm), and anaerobic ammonia oxidizing bacteria (AnAOB) removed nitrogen in anaerobic zone (>0.86 mm). Chlorella, Nitrosomonas and Candidatus_Kuenenia were identified as the dominant algae, AOB and AnAOB, with relative abundances of 11.80 %, 19.77 % and 3.07 %, respectively. This layered biofilm benefitted providing a suitable environment for various microorganisms to survive within a complex biofilm.

Efficient nitrogen removal from ammonia rich wastewater using aerobic granular sludge (AGS) reactor: Selection and enrichment of effective microbial community

Anaerobically digested sludge supernatant, characterized by its high ammonia and low biodegradable chemical oxygen demand (COD) content, has raised concerns when returned to mainstream treatment lines due to potential impacts on effluent quality. Addressing this, an aerobic granular sludge (AGS) reactor adopted nitritation/denitritation with external COD addition was utilized and achieved a considerable nitrogen treatment capacity of 4.2 kg N/m3/d, reaching over 90% removal efficiencies for both ammonia and total inorganic nitrogen. This study applied progressively increased nitrogen loading to select for a microbial community that exhibited high nitrogen oxidation and reduction rates, demonstrating peak rates of 0.5 g N/g VSS/d and 3 g N/g VSS/d, respectively. The enrichment of highly efficient microbial community was achieved along with the increased biomass density peaked at 17 g/L MLVSS, with the system retaining small-sized granular sludge at 0.5 mm. The primary ammonia oxidizing bacteria was Nitrosomonas, while Thauera was the dominated denitrifiers. Quantitative polymerase chain reaction analyses reinforced the enhanced nitrogen removal capacity based on the progressively increased abundance of nitrogen cycling functional genes. The high nitrogen treatment capacity, synergistic attributes of high specific microbial activities and the substantial biomass retention, suggest the AGS's efficacy and capacity in ammonia rich wastewater treatment.

Modeling Free Nitrous Acid Inhibition on the Removal of Nitrogen and Atenolol during Sidestream Partial Nitritation Processes

Sidestream serves as an important reservoir collecting pharmaceuticals from sludge. However, the knowledge on sidestream pharmaceutical removal is still insufficient. In this work, atenolol biodegradation during sidestream partial nitritation (PN) processes characterized by high free nitrous acid (FNA) accumulation was modeled. To describe the FNA inhibition on ammonia oxidation and atenolol removal, Vadivelu-type and Hellinga-type inhibition kinetics were introduced into the model framework. Four inhibitory parameters along with four biodegradation kinetic parameters were calibrated and validated separately with eight sets of batch experimental data and 60 days' PN reactor operational data. The developed model could accurately reproduce the dynamics of nitrogen and atenolol. The model prediction further revealed that atenolol biodegradation efficiencies by ammonia-oxidizing bacteria (AOB)-induced cometabolism, AOB-induced metabolism, and heterotrophic bacteria-induced biodegradation were 0, ∼ 60, and ∼35% in the absence of ammonium and FNA; ∼ 14, ∼ 29, and ∼28% at 0.03 mg-N L-1 FNA; and 7, 15, and 5% at 0.19 mg-N L-1 FNA. Model simulation showed that the nitritation efficiency of ∼99% and atenolol removal efficiency of 57.5% in the PN process could be achieved simultaneously by controlling pH at 8.5, while 89.2% total nitrogen and 57.1% atenolol were removed to the maximum at pH of 7.0 in PN coupling with the anammox process. The pH-based operational strategy to regulate FNA levels was mathematically demonstrated to be effective for achieving the simultaneous removal of nitrogen and atenolol in PN-based sidestream processes.

Stimulating extracellular polymeric substances production in integrated fixed-film activated sludge reactor for advanced nitrogen removal from mature landfill leachate via one-stage double anammox

Introducing carbon sources to achieve nitrogen removal from mature landfill leachate not only increases the costs and carbon emissions but also inhibits the activity of autotrophic bacteria. Thus, this study constructed a double anammox system that combines partial nitrification-anammox (PNA) and endogenous partial denitrification-anammox (EPDA) within an integrated fixed-film activated sludge (IFAS) reactor. In this system, PNA primarily contributes to nitrogen removal pathways, achieving a nitrite accumulation rate of 98.23%. The production of extracellular polymer substances (EPS) in the IFAS reactor is stimulated by introducing co-fermentation liquid. Through the utilization of EPS, the system effectively achieves EPDA with the nitrite transformation rate of 97.20%. Under the intermittent aeration operation strategy, EPDA combined with PNA and anammox in the oxic and anoxic stages enhanced the nitrogen removal efficiency of the system to 99.70 ± 0.12%. The functional genus Candidatus kuenenia became enriched in biofilm sludge, while Thauera and Nitrosomonas predominated in floc sludge.

Control strategies for microplastic pollution in groundwater

Groundwater is the primary source of water that occurs below the earth's surface. However, the advancement in technology and the increasing population, which lead to the discharge of contaminants such as microplastics (MPs), have an adverse impact on the quality of groundwater. MPs are ubiquitous pollutants that are widely found throughout the world. The maximum abundance of MPs is 4 items/L and 15.2 items/L in groundwater at the specific location of China and USA. Various factors can affect the migration of MPs from soil to groundwater. The occurrence of MPs in water causes serious health issues. Therefore, taking appropriate strategies to control MP contamination in groundwater is urgent and important. This review summarizes the current literature on the migration process of MPs from soil to groundwater along with possible methods for the remediation of MP-polluted groundwater. The main objective of the review is to summarize the technical parameters, process, mechanism, and characteristics of various remediation methods and to analyze strategies for controlling MP pollution in groundwater, providing a reference for future research. Possible control strategies for MP pollution in groundwater include two aspects: i) prevention of MPs from entering groundwater; ii) remediation of polluted groundwater with MPs (ectopic remediation and in-situ remediation). Formulating legislative measures, strengthening public awareness and producing more environment-friendly alternatives can be helpful to reduce the production of MPs from the source. Manage plastic waste reasonably is also a good strategy and the most important part of the management is recycling. The shortcomings of the current study and the direction of future research are also highlighted in the review.

Systematic investigation of simultaneous copper biosorption and nitrogen removal from wastewater by an aerobic denitrifying bacterium of auto-aggregation

Finding effective methods for simultaneous removal of eutrophic nutrients and heavy metals has attracted increasing concerns for the environmental remediation. Herein, a novel auto-aggregating aerobic denitrifying strain (Aeromonas veronii YL-41) was isolated with capacities for copper tolerance and biosorption. The denitrification efficiency and nitrogen removal pathway of the strain were investigated by nitrogen balance analysis and amplification of key denitrification functional genes. Moreover, the changes in the auto-aggregation properties of the strain caused by extracellular polymeric substances (EPS) production were focused on. The biosorption capacity and mechanisms of copper tolerance during denitrification were further explored by measuring changes in copper tolerance and adsorption indices, as well as by variations in extracellular functional groups. The strain showed extremely strong total nitrogen removal ability, with 67.5%, 82.08% and 78.48% of total nitrogen removal when NH4+-N, NO2--N, and NO3--N were used as the only initial nitrogen source, respectively. The successful amplification of napA, nirK, norR, and nosZ genes further demonstrated that the strain accomplished nitrate removal through a complete aerobic denitrification pathway. The production of protein-rich EPS of up to 23.31 mg/g and an auto-aggregation index of up to 76.42% may confer a strong biofilm-forming potential to the strain. Under the stress of 20 mg/L copper ions, the removal of nitrate-nitrogen was still as high as 71.4%. In addition, the strain could achieve an efficient removal of 96.9% of copper ions at an initial concentration of 80 mg/L. Scanning electron microscopy and deconvolution analysis of characteristic peaks confirmed that the strains encapsulate heavy metals by secreting EPS and, meanwhile, form strong hydrogen bonding structures to enhance intermolecular forces to resist copper ion stress. This study provides an innovative and effective biological approach for the synergistic bioaugmentation removal of eutrophic substances and heavy metals from aquatic environments.

Increasing specific biomass nitrogen load facilitated nitrite accumulation in mainstream wastewater treatment

By regulating influent nitrogen loading rate (NLR) and solids retention time (SRT), the effect of specific biomass nitrogen load (BNL) on the start-up of mainstream partial nitrification (PN) was investigated in five parallel sequencing batch reactors inoculated with ordinary nitrification sludge. The results showed that increasing BNL by both methods could achieve nitrite accumulation. Moreover, a high initial activity of ammonium oxidizing bacteria (AOB) accelerated nitrite accumulation. Increasing influent NLR (ammonium: 55-70 mg N/L) achieved only 30%-40% of nitrite accumulation ratio (NAR) and gradually decreased with reactor operation. By increasing BNL via controlling SRT (30 days), desirable PN with an average NAR of 81.7 ± 4.4% (effluent nitrite: ∼10 mg N/L) was obtained. Nitrite oxidizing bacteria (NOB) were effectively inhibited, and the AOB to NOB activity ratio increased from 1.5 to 7.8, promoting efficient nitrite accumulation. Overall, increasing BNL by regulating SRT was a potential method for start-up of mainstream PN.

Intensifying single-stage denitrogen by a dissolved oxygen-differentiated airlift internal circulation reactor under organic matter stress: Nitrogen removal pathways and microbial interactions

Current research focuses on efficient single-stage nitrogen removal from organic matter wastewater using the partial nitritation-anammox (PNA) process. In this study, we constructed a single-stage partial nitritation-anammox and denitrification (SPNAD) system using a dissolved oxygen-differentiated airlift internal circulation reactor. The system was operated continuously for 364 days at 250 mg/L NH₄⁺-N. During the operation, the COD/NH₄⁺-N ratio (C/N) was increased from 0.5 to 4 (0.5, 1, 2, 3, and 4), and the aeration rate (AR) gradually increased. The results showed that the SPNAD system maintained efficient and stable operation at C/N = 1-2 and AR = 1.4-1.6 L/min, with an average total nitrogen removal efficiency of 87.2%. The removal pathways of pollutants in the system and the interactions between microbes were revealed by analyzing the changes in sludge characteristics and microbial community structure at different phases. As the influent C/N increased, the relative abundance of Nitrosomonas and Candidatus Brocadia decreased, and that of denitrifying bacteria, such as Denitratisoma, increased to 44%. The nitrogen removal pathway of the system gradually changed from autotrophic nitrogen removal to nitrification-denitrification. At the optimum C/N, the SPNAD system synergistically removed nitrogen through PNA and nitrification-denitrification. Overall, the unique reactor configuration facilitated the formation of dissolved oxygen compartments, providing a suitable environment for different microbes. An appropriate organic matter concentration maintained the dynamic stability of microbial growth and interactions. These enhance microbial synergy and enable efficient single-stage nitrogen removal.

A review on the emerging conversion technology of cellulose, starch, lignin, protein and other organics from vegetable-fruit-based waste

A large amount of vegetable-fruit-based waste (VFBW) belonging to agricultural waste is produced around the world every year, imposing a huge burden on the environment and sustainable development. VFBW contains a lot of water and useful organic compounds (e.g., cellulose, minerals, starch, proteins, organic acids, lipids, and soluble sugars). Taking into account the composition characteristics and circular economy of VFBW, many new emerging conversion technologies for the treatment of VFBW (such as hydrothermal gasification, ultrasound-assisted extraction, and synthesis of bioplastics) have been developed. This review summarizes the current literature discussing the technical parameters, process, mechanism, and characteristics of various emerging conversion methods, as well as analyzing the application, environmental impact, and bio-economy of by-products from the conversion process, to facilitate solutions to the key problems of engineering cases using these methods. The shortcomings of the current study and the direction of future research are also highlighted in the review.

Decoding the Role of Extracellular Polymeric Substances in Enhancing Nitrogen Removal from High-Ammonia and Low-C/N Wastewater in a Sequencing Batch Packed-Bed Biofilm Reactor

Although the role of extracellular polymeric substances (EPSs) as a viscous high-molecular polymer in biological wastewater treatment has been recognized, in-depth knowledge of how EPSs affect nitrogen removal remains limited in biofilm-based reactors. Herein, we explored EPS characteristics associated with nitrogen removal from high-ammonia (NH₄⁺-N: 300 mg/L) and low carbon-to-nitrogen ratio (C/N: 2-3) wastewater in a sequencing batch packed-bed biofilm reactor (SBPBBR) under four different operating scenarios for a total of 112 cycles. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared (FTIR) analysis revealed that the distinct physicochemical properties, interface microstructure, and chemical composition of the bio-carrier were conducive to biofilm formation and microbial immobilization and enrichment. Under the optimal conditions (C/N: 3, dissolved oxygen: 1.3 mg/L, and cycle time: 12 h), 88.9% ammonia removal efficiency (ARE) and 81.9% nitrogen removal efficiency (NRE) could be achieved in the SBPBBR. Based on visual and SEM observations of the bio-carriers, biofilm development, biomass concentration, and microbial morphology were closely linked with nitrogen removal performance. Moreover, FTIR and three-dimensional excitation-emission matrix (3D-EEM) spectroscopy demonstrated that tightly bound EPSs (TB-EPSs) play a more important role in maintaining the stability of the biofilm. Significant shifts in the number, intensity, and position of fluorescence peaks of EPSs determined different nitrogen removal. More importantly, the high presence of tryptophan proteins and humic acids might promote advanced nitrogen removal. These findings uncover intrinsic correlations between EPSs and nitrogen removal for better controlling and optimizing biofilm reactors.

Exploiting refractory organic matter for advanced nitrogen removal from mature landfill leachate via anammox in an expanded granular sludge bed reactor

Anammox is an efficient low-carbon nitrogen removal technology for mature landfill leachate (MLL). However, it produces 11 % nitrate theoretically, which needs further removal. In this study, the mechanisms of exploiting refractory organic matter (ROM) from an MLL as an inner carbon source for advanced nitrogen removal via anammox were systematically analyzed, and the effects of hydraulic retention time on nitrogen and ROM removal/utilization were investigated. Without any external carbon source, a total nitrogen and organic carbon removal efficiency of 94.50 % and 27.12 %, respectively, were achieved, with a nitrogen loading rate of 2.4 kg N/(m³·d). The abundances of norank_f_norank_o_SBR1031, OLB13, and norank_f_A4b, which had the capacity to degrade ROM, increased from 21.63 % to 49.21 %. This study reveals that the ROM in an MLL can be exploited for synchronous advanced nitrogen and organic matter removal.

Advancements of sequencing batch biofilm reactor for slaughterhouse wastewater assisted with response surface methodology

Slaughterhouse wastewater (SWW) contains a significant volume of highly polluted organic wastes. These include blood, fat, soluble proteins, colloidal particles, suspended materials, meat particles, and intestinal undigested food that consists of higher concentrations of organics such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrogen and phosphorus hence an efficient treatment is required before discharging into the water bodies. The effluent concentrations and performance of simultaneous sequential batch biofilm reactor (SBBR) with recycled plastic carrier media support are better than the local single-stage sequential batch reactor (SBR), which is lacking in the literature in terms of COD, NH₃, NO₃, and PO₄ treatment efficiency. The present study reports a novel strategy to remove the above mentioned contaminants using an intermittently aerated SBBR with recycled plastic carrier media support along with simultaneous nitrification and denitrification. The central composite design was evaluated to optimize the treatment performance of seven different process variables including; different alternating conditions (Oxic/anoxic) for aeration cycles (3/2 h in a 6 h cycle, 6/5 h in a 12 h cycle and 9/8 h in an 18 h cycle) and hydraulic retention time (6, 12 and 18 h). The average removal efficiencies are 94.5% for NH₃, 93% for NO₃ and 90.1% for PO₄, and 99% for COD. The study reveals that the denitrification in the post-anoxic phase was more efficient than the pre-anoxic phase for pollutant removal and maintaining higher quality effluent. The effluent concentrations and performance of simultaneous SBBR with recycled polyethylene carrier support media were better than local SBR system in terms of COD, NH₃, NO₃ and PO₄ treatment efficiency. Results stipulated the suitability of SBBR for wastewater treatment and reusability as a sustainable approach for wastewater management under optimum conditions.

Mature landfill leachate treatment using granular sludge-based reactor (GSR) via nitritation/denitritation: Process startup and optimization

Mature landfill leachate wastewater (LLW) was characterized by high ammonia, refractory chemical oxygen demand (COD) and heavy metal contents, which limits the nitrogen removal in conventional activated sludge systems. Granular sludge is known to be more resistant to toxic compounds because of its dense structure and diverse microbial community. Here, granular sludge-based reactor (GSR) was applied with nitritation/denitritation (Nit/DNit) process for effective ammonia-rich mature LLW treatment at 20 °C. After a short startup period, the efficiencies of ammonia removal and total inorganic nitrogen removal stabilized at 99 % and 93 %, respectively, under a hydraulic retention time (HRT) of 6 h. High ammonia oxidation rate (~ 0.64 g N/g VSS/d) was achieved, with ~93 % ammonia conversing to nitrite before being reduced to nitrogen gas. Microbial analysis results revealed that Nitrosomonas (ammonia oxidizing bacteria) and Thauera (denitrifiers) were the dominant bacteria with key functional genes involved in the Nit/DNit. With an increase in the LLW loading, increased ammonia oxidation rates and biomass retention were also observed. This study demonstrated that granular sludge-based technology is feasible for mature LLW treatment.

Insights into deterioration and reactivation of a mainstream anammox biofilm reactor response to C/N ratio

In-depth knowledge of the deterioration and reactivation of the anaerobic ammonium oxidation (anammox) induced by carbon-to-nitrogen (C/N) is still lacking. Herein, the anammox performance was investigated in an anaerobic sequence biofilm batch reactor fed with low-strength partial nitration effluent in the range of C/N ratio from 0.5 to 3. The anammox was hardly deteriorated at C/N lower than 1.5, while became worsen if C/N was above 2.0. The specific anammox activity (SAA) experiments showed an 85% decrease of SAA at C/N of 3.0 compared with the maximum value (C/N:0). However, anammox capacity was rapidly recovered once influent C/N was adjusted back to zero. Moreover, C/N also highly affected the composition, structure and function of extracellular polymeric substance of the anammox biofilm. High-throughput sequencing revealed a close correlation between C/N change and microbial structure shift. Finally, the potential inhibition and restoration mechanism of the C/N-dependent anammox were proposed based on metagenomic analysis. This research provides some insights into the reinstatement of a mainstream anammox biofilm process after it is interrupted by high C/N influent.

Efficient nitrate removal of immobilized mixed aerobic denitrifying bacteria and community dynamics response to temperature and low carbon/nitrogen polluted water

The denitrification performance of immobilized mixed aerobic denitrifying bacteria (IMADB) was investigated. IMADB displayed strong temperature adaptability under low Carbon/Nitrogen conditions. At 5, 15, and 25 °C, the nitrate removal efficiencies of volcanic rock and polyester fiber sponge immobilized system reached 83.95%-98.25% and 89.71%-98.14%, respectively. The nitrate content removed by the carrier accounted for 41.18%-82.47% of the nitrate content removed by the immobilized system at different temperature, and played a major role in nitrate removal. The lower the temperature, the greater the role of the carrier. At the same temperature, carrier had a relatively higher richness, diversity, and evenness. Network analysis revealed that carrier species, which were positively correlated with nitrate removal efficiency, had the largest OTUs and abundance. Meanwhile, carrier had the widest niche. The total nitrogen removal efficiency of IMADB reached 56.10%-62.31% in the natural water system, highlighting a promising application prospect.

Deciphering the concurrence of comammox, partial denitrification and anammox in a single low-oxygen mainstream nitrogen removal reactor

One-stage anammox-based autotrophic nitrogen removal technology has attracted increasing interest to sustainable biological nitrogen removal for future wastewater treatment. However, its application in mainstream municipal wastewater treatment is still challenging due to low nitrogen and high organics of raw wastewater. Herein, a novel Simultaneous Carbon Oxidation, partial Comammox, Denitratation and Anammox (SCOCDA) was firstly developed in a single sequencing batch biofilm reactor operated at a dissolved oxygen concentration of ∼0.5 mg/L for treating synthetic municipal wastewater (50 mg/L NH₄⁺-N and 100-250 mg/L COD). The long-term operation showed that almost complete COD and nitrogen removal performance could be achieved at a carbon/nitrogen ratio (COD/NH₄⁺-N) of 3-5 with the corresponding effluent total nitrogen (TN)＜5 mg/L. Microbial community and amoA-targeting amplicon sequencing analysis further verified that comammox Nitrospira spp., denitrifier Thauera and other aerobic/facultative heterotrophs could work synergistically with anammox bacteria, Candidatus Kuenenia. Moreover, nitrogen metabolic and inorganic carbon fixation pathways through the interaction between comammox and anammox were also revealed with the aid of Kyoto Encyclopedia of Genes and Genomes (KEGG). Lastly, potential application of proposed SCOCDA process was illustrated. This research sheds new light on advanced nitrogen removal towards limit of technology via the synergy of comammox and anammox.

Insight into the role of microbial community interactions on nitrogen removal facilitated by a bioelectrochemical system in an osmotic membrane bioreactor

Insufficient nitrogen removal is a key challenge for the application of an osmotic membrane bioreactor (OMBR). The integration of a bioelectrochemical system (BES) and an OMBR was constructed to enhance nitrogen removal.To optimize the operation, five aeration intensities and three draw solutes (DSs) were applied in the proposed system. The results showed that the proposed system obtained the highest nitrogen removal efficiency of 77.36 ± 3.55 % with an aeration intensity of 0.6 L/min, and it was further increased to 94.99 ± 2.83 % and 99.92 ± 0.14 %with the NaOAc DS and the glucose DS, respectively.The analysis ofmetabolic pathways implied that species interactions existed,andthe following different mechanisms of enhanced nitrogen removal for the two organic DSs were proposed. The growth of denitrifying bacteria was enhanced by using reverse-fluxed organic NaOAc DS as a carbon source;glucoseDS stimulated electron transfer system activity to accelerate denitrification.

A novel electrochemical sensor based on autotropic and heterotrophic nitrifying biofilm for trichloroacetic acid toxicity monitoring

Trichloroacetic acid (TCA), a toxic substance produced in the disinfection process of wastewater treatment plants, will accumulate in the receiving water. The detection of TCA in the water can achieve the purpose of early warning. However, currently there are few reports on microbial sensors used for TCA detection, and the characteristics of their microbial communities are still unclear. In this work, a toxicity monitoring microbial system (TMMS) with nitrifying biofilm as a sensing element and cathode oxygen reduction as a current signal was successfully constructed for TCA detection. The current and nitrification rate showed a linear relationship with low TCA concentration from 0 to 50 μg/L (R²_current = 0.9892, R²_{nitrification} = 0.9860), and high concentration range from 50 to 5000 μg/L (R²_current = 0.9883, R²_{nitrification} = 0.9721). High-throughput sequencing revealed that the TMMS was composed of autotrophic/heterotrophic nitrifying and denitrifying microorganisms. Further analysis via symbiotic relationship network demonstrated that Arenimonas and Hyphomicrobium were the core nodes for maintaining interaction between autotropic and heterotrophic nitrifying bacteria. Kyoto Encyclopedia of Genes and Genomes analysis showed that after adding TCA to TMMS, the carbon metabolism and the abundance of the tricarboxylic acid cycle pathway were reduced, and the activity of microorganisms was inhibited. TCA stress caused a low abundance of nitrifying and denitrifying functional enzymes, resulting in low oxygen consumption in the nitrification process, but more oxygen supply for cathode oxygen reduction. This work explored a novel sensor combined with electrochemistry and autotrophic/heterotrophic nitrification, which provided a new insight into the development of microbial monitoring of toxic substances.

Simultaneously enhanced removal of PAHs and nitrogen driven by Fe2+/Fe3+ cycle in constructed wetland through automatic tidal operation

The lack of dissolved oxygen and weak substrate removal capacity in constructed wetlands (CW) leads to terrible removal of nitrogen and polycyclic aromatic hydrocarbons (PAHs). In this study, automatic tidal flow CW microcosms were constructed by improving the oxygen environment (siphon and air-duct) and substrate (magnetite) to enhance purification performance and the mechanism was explored. The results showed that the addition of air-duct could improve the oxygen collection and thus improved the NH₄⁺ removal efficiency. Additionally, nitrogen removal was improved greatly due to the simultaneous nitrification and denitrification in aerobic layer with the addition of magnetite. Mass balance indicated the microbial degradation dominated (32-62%) the removal of PAHs. Metagenomic analysis proved the existence of magnetite enhanced the number of PAHs-degrading bacteria, functional groups and metabolic pathways and thus greatly improved the microbial degradation of PAHs. Furthermore, Fe²⁺/Fe³⁺ cycle played an important role in promoting the anaerobic degradation of PAHs, which might be served as an electron conduit to establish the direct interspecies electron transfer between iron-reducing bacteria (e.g. Deltaproteobacteria bacterium) and Anaerolineae bacterium to degrade PAHs efficiently. This study provided better understanding of the simultaneous removal of PAHs and nitrogen in tidal flow CWs.

Accelerating anammox nitrogen removal in low intensity ultrasound-assisted ASBBR: Performance optimization, EPS characterization and microbial community analysis

Efficient enrichment of slow-growing anammox species is essential for rapid start-up and stable operation of high-rate anammox reactors. Herein, a low intensity ultrasound (LIU) was introduced into anaerobic sequencing batch biofilm reactors (ASBBRs) to enhance anammox nitrogen removal from nitrogen-rich wastewater. Operation results demonstrated that the maximum total nitrogen (TN) removal efficiency of 91.5% were achieved under the optimal ultrasonic parameters (32.7 °C water temperature, 0.18 W/cm² ultrasonic intensity and 25.7 min ultrasonication time). Moreover, significant increases of extracellular polymeric substances (EPS) components and contents were observed via the ultrasonication stimulation. A close correlation between nitrogen removal and shifts in transformation and intensity of spectrum peaks was also verified by three-dimensional excitation-emission matrix spectroscopy (3D-EEM) analysis. High-throughput sequencing revealed that the relative abundance of Candidatus Kuenenia as the key anammox consortium significantly increased after applying optimal ultrasonication condition. Furthermore, enhancement mechanisms and future prospect of the LIU-assisted anammox process was elucidated and discussed. This research provides a viable and promising acceleration strategy for anammox-based process in practice.

Seasonal temperatures impact on the mass flows in the innovative integrated process of anaerobic membrane bioreactor and one-stage partial nitritation-anammox for the treatment of municipal wastewater

A pilot-scale anaerobic membrane bioreactor (AnMBR) integrated with a one-stage partial nitritation-anammox (PN/A) reactor was operated for the treatment of municipal wastewater (MWW) at seasonal temperatures of 15-25 °C. The removal efficiencies of COD and total nitrogen (TN) were always > 90% and > 75% respectively. The methanogenesis and PN/A were identified as the primary removal pathways of COD and TN, respectively, and were suppressed at low temperatures. With the temperature dropped from 25 °C to 20 °C to 15 °C, the methane-accounted COD decreased from 63.1% to 59.6% to 48.4%, and the PN/A-accounted TN decreased from 58.1% to 51.7% to 45.3%. The AnMBR and PN/A mutually complement each other in this combined process, as the AnMBR removed 8.5%-16.1% of TN by sludge entrainment and the PN/A reactor removed 2.6%-3.4% of COD by denitrification and aerobic oxidation. These results highlighted the strong feasibility of applying the AnMBR-PN/A process to the treatment of MWW in temperate climate.

The performance of simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) method in the treatment of digested effluent of fish processing wastewater

The simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) method was successfully carried out in an air-lift moving bed biofilm reactor (AL-MBBR) with cylinders carriers for the treatment of digested fish processing wastewater (FPW). Synthetic wastewater was used as substrate at stage 1. It changed into the digested FPW with dilution variation in order to increase the nitrogen and COD loading rates. With influent concentration of NH₄⁺-N of 909 ± 101 mg-N/L and COD of 731 ± 26 mg/L, the nitrogen removal efficiency was 86.8% (nitrogen loading rate of 1.21 g-TN/L/d) and the COD removal efficiency was 50.5% (COD loading rate at 0.98 g-COD/L/d). This study showed that the process has the advantages in treating the real high ammonia concentration of digested wastewater containing organic compounds. The nitritation and anammox route was predominant in nitrogen removal, while COD oxidation and microbe proliferation played the main role in COD removal.

Simultaneous Partial Nitrification and Denitrification Maintained in Membrane Bioreactor for Nitrogen Removal and Hydrogen Autotrophic Denitrification for Further Treatment

Low C/N wastewater results from a wide range of factors that significantly harm the environment. They include insufficient carbon sources, low denitrification efficiency, and NH4+-N concentrations in low C/N wastewater that are too high to be treated. In this research, the membrane biofilm reactor and hydrogen-based membrane biofilm reactor (MBR-MBfR) were optimized and regulated under different operating parameters: the simulated domestic sewage with low C/N was domesticated and the domestic sewage was then denitrified. The results of the MBR-MBfR experiments indicated that a C/N ratio of two was suitable for NH4+-N, NO2−-N, NO3−-N, and chemical oxygen demand (COD) removal in partial nitrification-denitrification (PN-D) and hydrogen autotrophic denitrification for further treatment. The steady state for domestic wastewater was reached when the MBR-MBfR in the experimental conditions of HRT = 15 h, SRT = 20 d, 0.04 Mpa for H₂ pressure in MBfR, 0.4–0.8 mg/L DO in MBR, MLSS = 2500 mg/L(MBR) and 2800 mg/L(MBfR), and effluent concentrations of NH4+-N, NO3−-N, and NO2−-N were 4.3 ± 0.5, 1.95 ± 0.04, and 2.05 ± 0.15 mg/L, respectively. High-throughput sequencing results revealed the following: (1) The genus Nitrosomonas as the ammonia oxidizing bacteria (AOB) and Denitratisoma as potential denitrifiers were simultaneously enriched in the MBR; (2) at the genus level, Meiothermus,Lentimicrobium, Thauera,Hydrogenophaga, and Desulfotomaculum played a dominant role in leading to NO3−-N and NO2−-N removal in the MBfR.

The existence, spread, and strategies for environmental monitoring and control of SARS-CoV-2 in environmental media

Coronavirus disease 2019 (COVID-19) is the most influential infectious disease to emerge in the early 21st century. The outbreak of COVID-19 has caused a great many deaths and has had a negative impact on the world's economic development. The etiological agent of COVID-19 is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2, which is highly infectious and variable, can be transmitted through different environmental media (gaseous, liquid, and solid). There are many unanswered questions surrounding this virus. This review summarizes the current knowledge on the latest global COVID-19 epidemic situation, SARS-CoV-2 variants, the progress in SARS-CoV-2 vaccine use, and the existence and spread of SARS-CoV-2 in gaseous, liquid, and solid media, with particular emphasis on the prevention and control of further spread of the disease. This review aims to help people worldwide to become more familiar with the transmission characteristics of SARS-CoV-2 in environmental media, so as targeted measures to fight the epidemic, reduce deaths, and restore the economy can be implemented under the pressure of global SARS-CoV-2 vaccine shortages.

An effective strategy for in situ start-up of mainstream anammox process treating domestic sewage

The feasibility of in situ start-up of mainstream anammox process was investigated in three parallel sequencing batch biofilm reactors (SBBRs) inoculated with nitrification sludge, partial nitrification sludge, and denitrifying phosphorus removal sludge, respectively. The SBBRs were operated under alternate anaerobic/aerobic/anoxic pattern at ambient temperature (16.5-26.8 °C). The influent organic and nitrogen loading rates were increased stepwise. Anammox bacteria grew exponentially with relative abundance and overall bacterial activity increasing from 0 to 0.004% to 0.29-0.40% and 'not detected' to 6-7 mg N/L/h, respectively. Desirable nitrogen removal efficiency of about 86% was obtained in 3-4 months for the influent nitrogen of 40.5-73.6 mg N/L. Anammox was the primary nitrogen transformation pathway. For the anammox bacterial enrichment, biofilm, alternate anaerobic/aerobic/anoxic pattern, and limited aeration played important roles. Seed sludge with high ammonium oxidizing bacterial activity further promoted the start-up of anammox process. The in situ start-up strategy could promote the full-scale application of mainstream anammox.

Adaptation of anammox granules in swine wastewater treatment to low temperatures at a full-scale simultaneous partial nitrification, anammox, and denitrification plant

In the anammox process, maintaining a high anammox activity at low water temperatures for stable nitrogen removal is a challenge. In this study, to verify the adaptability of anammox to low water temperatures, we investigated effects of annual temperature fluctuations on nitrogen removal in a full-scale swine wastewater treatment plant, where anammox bacteria accumulated. Annual quarters were defined as L-1 (November-January), L-2 (February-April), H-1 (April-July), and H-2 (July-October). The total nitrogen removal rate was stable at 0.08-0.11 kg-N/m³/d, even during temperature fluctuations. Removal efficiencies of biochemical oxygen demand and total nitrogen were consistently high at 95-99% and 69-81%, respectively. The anammox activity and abundance of anammox bacteria were highest in granule L-1 and lowest in granule H-2. The optimal temperature for anammox activity shifted from 35 °C in granules H-1 and H-2 to 30 °C in granules L-1 and L-2, while the latter maintained a moderate activity compared to the former at low temperature. Candidatus Jettenia asiatica was predominant, especially in granule L-2, accounting for up to 54% of the microbial community composition at the genus level. The high specific anammox activity in granule L-2 was considered to be due to the abundance of anammox bacteria and the adaptation of Ca. Jettenia asiatica to low temperature. The anammox granules adapted well to low temperatures and demonstrated high efficiency in the simultaneous partial nitrification anammox and denitrification process without heating. Thus, constructing an energy-saving and cost-effective nitrogen removal system can be considered.

Efficiency and microbial diversity of aeration solid-phase denitrification process bioaugmented with HN-AD bacteria for the treatment of low C/N wastewater

To evaluate the simultaneous nitrification and denitrification (SND) performance of the aeration solid-phase denitrification (SPD) process and improve the operating efficiency, aeration SPD process using polybutanediol succinate as carbon source was optimized and the process was bioaugmented with heterotrophic nitrification-aerobic denitrification bacteria for the treatment of real wastewater. The results showed that after bioaugmentation, the total nitrogen removal efficiency of the aeration SPD process increased by 50.46 % under condition of dissolved oxygen (DO) 3 mg/L. According to Illumina MiSeq sequencing and correlation analyses, the microbial community can perform SND under the conditions of DO 5 mg and HRT 6 h, but is susceptible to DO. Bioaugmentation mainly affected the carbon source metabolic network with heterotrophic bacteria Methyloversatilis, Thiothrix, and norank_Lentimicrobiaceae as nodes to change the community structure, thereby improving the performance of the functional microbial community. Kyoto Encyclopedia of Genes and Genomes analysis suggested that narB, narG, narH, nirK and narI were the key genes involved in the response to bioaugmentation. This work provides new insights for the application of the SPD process in wastewater treatment.

Treatment of wastewater with high carbon-to-nitrogen ratio using a waterfall aeration biofilm reactor combined with sequencing batch reactor: Microbial community structure and metabolism analysis

A low-cost and high-efficiency waterfall aeration biofilm reactor (WABR) combined with a sequencing batch reactor (SBR) was established to treat wastewater with a C/N ratio of 50. Three WABR-SBR systems with different fillers were used. In the stable operation phase, the removal efficiency of chemical oxygen demand was R1 (approximately 99%), R2 (97-99%), and R3 (96-99%); the effluent concentration of NH₄⁺-N was 0.5 mg/L without nitrite or nitrate accumulation. High-throughput 16S rRNA sequencing revealed that the dominant phyla in the microbial community structure were Proteobacteria, Bacteroidetes, and Planctomycetes. Quantitative PCR was used to quantify the nitrification and denitrification gene expressions (Nitrobacter, nirS, and nirK) to evaluate the simultaneous nitrification and denitrification processes. Both anammox and denitrifying bacteria were abundant. Metagenomic annotation of genes that revealed the metabolic pathways of carbohydrates, amino acids, and the two dominant enzymes (GH and GT) provide valuable information for microbial ecology analysis.

Ecological Linkages between a Biofilm Ecosystem and Reactor Performance: The Specificity of Biofilm Development Phases

In biofilm-based engineered ecosystems, the reactor performance was closely linked to interspecies interactions within a biofilm ecosystem, whereas the ecological processes underpinning such linkage were still unenlightened. Herein, the principles of community succession and assembly were integrated to capture the ecological laws of biofilm development by molecular ecological networks and assembly model analysis based on the 16S rRNA sequencing analysis and metagenomics in a well-controlled moving bed biofilm reactor. At the initial colonization phase (days 0-2, driven by initial colonizers), interspecific cooperation (74.18%) facilitated initial biofilm formation, whereas some pioneers, and keystone species disappeared at later phases. At the accumulation phase (days 3-30, rapid biofilm development), interspecific cooperation (81.41 ± 5.07%) contributed to rapid biofilm development and keystone species were mainly involved in quorum sensing or positively correlated with extracellular polymeric substance production. At the maturation phase (days 31-106, a well-adapted quasi-equilibrium state), increased interspecific competition (32.74 ± 4.77%) and higher small-world property facilitated the rapid information transportation and pollutant treatment, and keystone species were positively correlated with the removal of COD and NH₄⁺-N. Homogenizing dispersal diminished the contemporary community dissimilarities, while turnover but rather nestedness governed the temporal variations in the biofilm succession period. This study highlighted the specificity of ecological processes at distinct biofilm development phases, which would advance our understanding on the development-to-function linkages in biofilm-based treatment processes.

Identification of optimal parameters for treatment of high-strength ammonium leachate by mixed communities of heterotrophic nitrifying/aerobic denitrifying bacteria

Heterotrophic nitrifying and aerobic denitrifying bacteria (HNADB) are important for partial nitrification treatment of high strength ammonium leachate. However, conditions for their optimal performance in mixed reactor systems have yet to be determined. In this study, optimal parameters were identified and included free ammonia (FA) concentrations below 40 mg/L, a dissolved oxygen concentration of 1.2 mg/L, a carbon to nitrogen ratio of 5 and a reflux ratio of 4. These conditions were applied to a continuous anoxic/oxic membrane moving biofilm reactor treating raw incineration leachate with high total ammonium nitrogen (TAN = 1400 mg/L). Ammonium conversion and nitrogen removal efficiencies of 99% and 86% were achieved. Autotrophic ammonia oxidizing bacteria were inhibited at FA concentrations above 25 mg/L. HNADB, particularly Paracoccus species, contributed to ammonium conversion at high FA (25-40 mg/L). These results show that leachate with high TAN and FA can be treated using parameters that support the growth of HNADB.

Simultaneous nitrogen and phosphorus removal from simulated digested piggery wastewater in a single-stage biofilm process coupling anammox and intracellular carbon metabolism

A Single-stage biofilm process coupling Anammox and Intracellular Carbon metabolism (SAIC) was constructed for treating simulated digested piggery wastewater with low carbon/nitrogen ratio (C/N) in this study. TN removal in SAIC system increased by more than 12.77% compared to the reference, and the maximum total phosphorus (TP) removal efficiency reached to 83.70% (C/N = 1.5). Denitrification driven by intracellular carbon, mainly poly-β-hydroxybutyrate (PHB, 78.57%), contributed 32.60% of TN elimination at most, and at least 67.40% should be attributed to anammox. Phosphorus was thought to be mainly removed through biological route, while chemical precipitation also explained around 10% of removed TP. Furthermore, commensalism of glycogen accumulating organisms (GAOs), phosphate accumulating organisms (PAOs), nitrifiers and anammox bacteria was revealed by combining 16S rRNA amplicon sequencing and metagenomics. As a result, multiple metabolic pathways including anammox, (partial) nitrification, endogenous (partial) denitrification and biological P-removal played synergistic effect in SAIC system.

A novel inhibition mechanism of aniline on nitrification: Aniline degradation competes dissolved oxygen with nitrification

Aniline is a toxic aromatic amine and an inhibitor of nitrification. This study explored the inhibition effect and underlying mechanism. After sludge acclimation, 540 mg/L aniline was removed in 24 h and almost all ammonia released from aniline was oxidized to nitrate. However, nitrification never started until no aniline left. The cellular adenosine triphosphate (cATP) concentration of acclimated sludge reduced only by 2% after aniline exposure. Neither transmembrane transport of ammonia nor ammonia monooxygenase (AMO) activity was affected by aniline. Growing initial aniline concentration did not deteriorate the specific nitrification rate (NR). These all revealed that the toxicity of aniline only play a minor role in inhibition. Competition for dissolved oxygen (DO) was proposed to be another possible inhibition mechanism. The oxygen affinity constant (Ks) of aniline degraders and ammonia-oxidizing bacteria (AOB) was calculated to be 0.894 mg/L and 1.274 mg/L respectively, suggesting the former possessed much stronger oxygen affinity (P < 0.01). With aniline and ammonium as initial substrates, increasing aeration intensity advanced nitrification and increased the NR. Max NR of 0.63 mgN/(gMLSS·h) was achieved at the highest aeration intensity of 1000 mL/min. This study brings one step closer to better removal of aniline and derived nitrogen pollutants.

A novel single-stage ceramic membrane moving bed biofilm reactor coupled with reverse osmosis for reclamation of municipal wastewater to NEWater-like product water

In this study, a single-stage ceramic membrane moving bed biofilm reactor (CMMBBR) was developed for simultaneous COD and nitrogen removal, while its effluent was further reclaimed to ultra-clean water by a coupled reverse osmosis (RO) unit. Results showed that approximately 97% of COD and 93% of total nitrogen (TN) removal were obtained in CMMBBR, with the effluent COD and TN concentrations being 8.15 mg/L and 2.31 mg/L, respectively. The excellent performance of CMMBBR was achieved at a constant permeate flux of 30 L/m²/h (LMH), with the average dTMP/dt of 0.05 bar/d due to the low suspended sludge concentration (i.e. 75 mg VSS/L) and the effective membrane scouring by fluidized biocarriers. The excellent permeate quality of CMMBBR could lead to a very low RO fouling rate of 0.029 bar/d, with the product water quality meeting typical NEWater standards in major ions concerned. In addition, the energy and cost analyses further indicated that the proposed CMMBBR-RO process could reduce 43.8% of energy consumption and 23.5% of operating cost compared to the current NEWater production process. It is expected that the integrated CMMBBR-RO process could provide a promising alternative for municipal wastewater reclamation to high-grade product water towards minimized sludge production and energy-efficient operation.

Bioaugmentation potential evaluation of a bacterial consortium composed of isolated Pseudomonas and Rhodococcus for degrading benzene, toluene and styrene in sludge and sewage

Bioaugmentation was conducted using a bacterial consortium of Pseudomonas putida SW-3 and Rhodococcus ruber SS-4, to test their ability to degrade benzene, toluene, and styrene (BTS). SW-3 and SS-4 were isolated from domestic sludge and sewage samples to establish a synthetic consortium with an optimized ratio of 2:1 to reach a degradation efficiency of 82.5-89.8% of BTS. The bacterial consortium was inoculated with sludge and sewage samples at a ratio of 2:1, resulting in a degradation efficiency of 97.9% and 92.7%, respectively, at a BTS concentration of 1800 mg·L^-1. Analysis of bacterial community structure following bioaugmentation indicated an increase in abundance of BTS-degrading bacteria, particularly Acinetobacter and Pseudoxanthomonas in sludge and Pseudomonas in sewage, enhancing the collective BTS degradation ability of the bacterial community. Principal component analysis demonstrated that a more balanced bacterial community structure was established following intervention. This indicated that the selected bacteria are excellent candidates for bioaugmentation.

Development of aerobic methane oxidation, denitrification coupled to methanogenesis (AMODM) in a microaerophilic expanded granular sludge blanket biofilm reactor

The issue of enhancing nitrogen removal and managing dissolved methane emission in anaerobic treatment systems is a major bottleneck in its wider application to treat high-strength organic wastewater with nitrate. Herein, a novel aerobic methane oxidation, denitrification coupled to methanogenesis (AMODM) process was developed in a glucose-fed microaerobic expanded granular sludge blanket biofilm reactor (EGSBBR) through in-situ utilization of produced methane for nitrogen removal. The 162-day operation demonstrated that long-term treatment performance under the decreased COD/NO₃^--N (C/N) ratio from 66.7 to 10 and the optimal C/N ratio for completing AMODM was found to be 16.7. Microbial community analysis further evidenced that Methanothrix as key methanogen predominated in the sludge bed, while Methlogaea as aerobic methane oxidizer was mainly detected in the packing bed of the hybrid system. Meanwhile, some facultative heterotrophic and dissimilated nitrate-reduction (DNRA) genera also co-existed. The profiling of key functional genes further proved concurrent occurrence of methanogenesis, aerobic methane oxidation and denitrification. Furthermore, possible microbial mechanism on AMODM process was elucidated from the prospective of targeted species interaction within the reactor. This research provides a robust and environment-friendly alternative process treating nitrate-containing organic wastewater towards efficient nitrogen removal, low resource consumption, bioenergy recovery and greenhouse gas reduction.

Unclassified Anammox bacterium responds to robust nitrogen removal in a sequencing batch reactor fed with landfill leachate

Treatment of landfill leachate was conducted in a lab-scale sequencing batch reactor (SBR). The SBR was started through inoculating activated sludge with controlling dissolved oxygen of 0.5-1.0 mg/L. Anammox reaction took place within around three months. The SBR established robust nitrogen removal with incremental NLRs of 0.25-2.17 kg N/m³/d. At the final phase, it achieved elevated nitrogen removals of 1.68-1.91 kg N/m³/d. 16S rRNA gene amplicon sequencing analysis revealed Nitrosomonas, unclassified Anammox bacterium, and diverse denitrifying populations coexisted and accounted for 4.02%, 20.05% and 34.69%, respectively. Phylogenic analysis and average nucleotide identity comparison jointly suggested the unclassified Anammox bacterium potentially pertained to a novel Anammox lineage. The functional profiles' prediction suggested sulfate reduction, arsenate reduction and eliminations of antibiotics and drugs likely occurred in the SBR. The finding from this study suggests contribution of unclassified Anammox bacteria in influencing nitrogen budget in natural and engineering systems is currently being underestimated.

Functional microorganisms and enzymes related nitrogen cycle in the biofilm performing simultaneous nitrification and denitrification

Simultaneous nitrification and denitrification (SND) is a potential energy-saving process in wastewater treatment while the nitrogen removal mechanism is still unclear due to the lack of information about the functional microbes and enzymes. Sequencing batch biofilm reactors were implemented to achieve efficient SND. Eight nitrogen removal related microorganisms out of the top abundant 20 microbial community and reference species were used to construct a phylogenetic tree. Functional enzymes and modules analysis were investigated to reveal the SND pathway: in the aerobic part of the biofilm, ammonia oxidation was catalyzed by complete ammonia oxidizers while in the inner anoxic part, denitrification, dissimilatory nitrate reduction (DNRA) and nitrogen fixation (NF) cooperated to stimulate nitrate removal. These results provide a practical aeration control strategy to achieve SND and indicate that DNRA and NF are important nitrogen removal pathways that should not be ignored in the SND mechanism.

Insight into using up-flow anaerobic sludge blanket-anammox to remove nitrogen from an anaerobic membrane reactor during mainstream wastewater treatment

A partial nitritation/anammox system treating the effluent of an anaerobic membrane bioreactor was investigated in this study with emphases on the nitrogen conversion and microbial dynamics along the up-flow anaerobic sludge blanket. An average total nitrogen concentration of 12.3 mg/L was achieved in effluent, which resulted in a total nitrogen removal efficiency of 75.9% ± 0.6%, in which the contribution of anammox was over 98%, and mainly occurred at the bottom of the up-flow anaerobic sludge blanket. Furthermore, external nitrite produced from nitrate reduction enhanced the nitrogen removal efficiency. Ca. Brocadia was the dominant anammox bacteria and was enriched at the bottom; Dokdonella and Thermomonas were identified as the denitrifiers for nitrite production and existed in the whole reactor. Findings of this study can be used in a practical model for the future development of integrating anaerobic digestion with partial nitritation/anammox in mainstream wastewater treatment.

Unravelling nitrogen removal and nitrous oxide emission from mainstream integrated nitrification-partial denitrification-anammox for low carbon/nitrogen domestic wastewater

Stable supply of nitrite is often a major obstacle for achieving mainstream anammox due to washout failure of nitrite oxidizers (NOB) at low influent ammonia of municipal wastewater. In this study, an integrated nitrification, partial denitrification and anammox (INPDA) as a one-stage mainstream nitrogen removal alternative was established in a low-oxygen sequencing batch biofilm reactor treating synthetic sewage. The overall nitrogen removal and nitrous oxide (N₂O) emission were mainly investigated at 50 mg/L NH₄⁺-N influent with a low carbon/nitrogen (C/N) of 2.5. Continuous operation demonstrated that as high as 98.8% NH₄⁺-N and 94.1% TN were removed in SBBR system. Cyclic experiment verified sequential completion of nitrification, partial denitrification and anammox were responsible for high-rate TN removal. During one typical cycle, the trend of N₂O emission was characterized by firstly rapid rise, then fluctuant decrease followed by rapid decrease and finally slow disappearance. The maximum N₂O emission rate reached up to 6.7 μg/(L·min) occurred at 75 min. High-throughput sequencing revealed the co-existence of nitrifying, denitrifying and anammox species and large detection of key functional genes (Hzs, Hdh, Hao, Nor) in an oxygen-limited SBBR, thereby highly correlating nitrogen removal and N₂O emission characteristics. Nitrogen metabolic pathways analysis further suggest denitratation(NO₃^--N to NO₂^--N)-based anammox is a main route for mainstream nitrogen removal. Moreover, N₂O might be generated by both hydroxylamine oxidation step in nitrification and also heterotrophic denitrification pathway. The research findings provide more deep understandings of enhanced nitrogen removal and mitigated N₂O footprint from a single mainstream anammox-based system.

Biodegradable organic matter-containing ammonium wastewater treatment through simultaneous partial nitritation, anammox, denitrification and COD oxidization process

For both nitrogen and COD removal from biodegradable organic matter (BOM)-containing ammonium wastewater, the simultaneous partial nitritation, anammox, denitrification and COD oxidization (SNADCO) process is a promising solution. In this study, with the stable influent ammonium concentration of 250.0 mg/L (nitrogen loading rate of 0.5 kg/m³/d) and the variation of influent COD/NH₄⁺-N (C/N) ratio from 0.0 to 1.6, the performance of the SNADCO process in a one-stage carrier-packing airlift reactor with continuous mode was investigated for the first time. The results showed that until the C/N ratio of 0.8, both the well nitrogen and COD removal targets could be reached. Mass balance calculations indicated that the average nitrogen removal efficiency (NRE) of 80.9% achieved at the C/N ratio of 0.8 were due to both the anammox and denitrification pathways. Correspondingly, the achieved average COD removal efficiency of 94.6% was attributed to both the denitrification and COD oxidization pathways. Based on the specific sludge activity tests and Fluorescence in Situ Hybridization observation, anammox and denitrification bacteria were mainly distributed in the biofilm sludge, while ammonium oxidizing bacteria and ordinary heterotrophic organisms were mainly in the suspended sludge. At the C/N ratio of 1.6, the washout of suspended sludge became serious while the biofilm sludge was well retained, resulting in inefficient nitritation and a subsequent decrease in NRE. The microbial interaction analysis provided a clear explanation of the performance change of the SNADCO process under different C/N ratios. This research enriches the knowledge of the SNADCO process in BOM-containing ammonium wastewater treatment.

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.

Performance and microbial community in a single-stage simultaneous carbon oxidation, partial nitritation, denitritation and anammox system treating synthetic coking wastewater under the stress of phenol

As a highly toxic pollutant, phenol is typically present in some high-strength nitrogenous wastewater. In this study, a synthetic coking wastewater with 400 mg L^-1 ammonia-nitrogen and 50-250 mg L^-1 phenol was treated. Results showed that simultaneous carbon oxidation, partial nitritation, denitritation and anammox (SCONDA) was successfully achieved by step-wise phenol addition. At 200 mg L^-1 phenol, 99.8% phenol, 97.5% COD and 89.8% nitrogen could be together removed. However, further increase in phenol concentration caused significant deterioration of the short-terms nitrogen removal efficiency. High-throughput sequencing revealed remarkable evolution in microbial biodiversity, community composition, especially functional species at different phenol concentrations. When the phenol addition was increased from 200 to 250 mg L^-1, the relative abundance of Candidatus Kuenenia as predominant anammox species decreased by 87.1%, while phenol-degrading bacteria was increasingly abundant. Furthermore, the removal mechanism of phenol and nitrogen was elucidated by the collaboration among different key functional microbial consortia.

Optimization of nitrogen removal performance in a single-stage SBR based on partial nitritation and ANAMMOX

A partial nitritation (PN)/anaerobic ammonium oxidation (ANAMMOX) process in sequencing batch reactor (SBR) was successfully developed to treat high-strength ammonium wastewater. The feed distribution in the SBR cycle and sub-cycles was considered as the main operating strategy, and was optimized using a response surface methodology (RSM)-based optimization technique. In the SBR cycle, the maximum nitrogen removal rate (NRR) of 0.79 ± 0.01 kg m^-3 d^-1 was achieved by applying a feed distribution strategy that considered the kinetic characteristics of ANAMMOX and ammonia oxidizing bacteria (AOB). However, this strategy negatively affected the nitrogen removal efficiency (NRE) due to alkalinity loss. Therefore, the feed distribution in the SBR sub-cycles with respect to the NRE and the NRR was further studied. The nitrogen removal performance was optimized in the optimum region and an NRE of 88% and an NRR of 0.84 kg m^-3 d^-1 were achieved. The optimized model was verified in confirmation test. The RSM-based optimization results provide insights into the feed distribution strategy for achieving single-stage PN/ANAMMOX SBR operation.

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.

Toxicity assessment of artificially added zinc, selenium, and strontium in water

The present research was to study the toxicology of artificially added Zn, Se and Sr in water. Specifically, we investigated the mortality and liver toxicity in zebrafish (Danio rerio), caused by different water concentrations of zinc sulfate (ZnSO₄), sodium selenite (Na₂SeO₃), and strontium chloride hexahydrate (6H₂O·SrCl₂). Adult and embryo-larval zebrafish were used in the experiment. Analysis was performed of mortality, liver area and impermeability, delayed absorption area of the yolk sac, and liver tissue structure. The concentration change of sodium selenite exerted the most significant effect on the mortality of adult zebrafish, followed by that of strontium chloride hexahydrate, and zinc sulfate. Elevated strontium chloride hexahydrate concentration was associated with liver toxicity in zebrafish in the preliminary experiment. However, embryo-larval zebrafish were observed to die when the concentration of Zn²⁺ or Se⁴⁺ increased to a certain extent, without obvious liver toxicity. Our results indicated strontium chloride hexahydrate was hepatotoxic to embryo-larval zebrafish, which was manifested mainly as hepatomegaly and delayed absorption of the yolk sac. In addition, the artificially added strontium chloride hexahydrate destroyed liver tissue structure, resulting in hepatocyte enlargement, cell nucleus enlargement, blurred cytoplasmic boundaries, and formation of a vacuolar liver. These findings suggest the amount of strontium chloride hexahydrate added in soft drinks should be limited to certain levels.

Enhanced simultaneous nitrification and denitrification in treating low carbon-to-nitrogen ratio wastewater: Treatment performance and nitrogen removal pathway

Simultaneous nitrification and denitrification (SND) is an energy-saving wastewater treatment process, however, the nitrogen removal pathways are not clear. An enhanced SND sequencing batch biofilm reactor with a SND ratio above 97.3% was built to treat low carbon to nitrogen ratio wastewater. When traditional nitrification was inhibited, ammonia removal efficiency still reached 45% in 8 h while the NO₃^- and NO₂^- concentration was less than 3 mg/L and 0.01 mg/L during the complete process, respectively. The pathways that could not be suppressed by the inhibitors (ATU and ClO₃^-) were stimulated by heterotrophic nitrifiers and aerobic denitrifiers with periplasmic nitrate reductase and contributed 55% of the total removed NH₄⁺ and produced 51% of the emitted N₂O. The contributions of different nitrogen removal pathways indicate that the unconventional pathways are important in wastewater treatment system and inhibitors should be carefully used in nitrogen removal pathway assays.

Start-up and performance of partial nitritation process using short-term starvation

Partial nitritation is a key step toward cost-effective shortcut biological nitrogen removal and anammox process. The current study presents a novel method for achieving partial nitritation at influent ammonium nitrogen concentration of 100 mgNL^-1 using short-term starvation and low air flow rate. Mixed activated sludge was introduced into sequencing batch reactor (SBR) under aerobic/anaerobic condition. Variations in the reactor performance, nitrifying bacteria activities, and bacterial community structures were investigated. The results showed that partial nitritation was rapidly achieved, and an average nitrite accumulation rate (NAR) of 878 gNm^-3d^-1 was observed. The short-term starvation stress on nitrite oxidation bacteria (NOB) activity was relatively higher than that on aerobic ammonium oxidation bacteria (AerAOB) activity. The dominant species of general AerAOB were Nitrosomonas and Nitrosomonadaceae_uncultured, which had better self-adaption to short-term starvation. The moderate starvation could be utilized to achieve nitrite accumulation and nitritation.