Nitrogen Removal Capacity Research Articles

Attaining superior nitrogen removal from integrated mature landfill leachate and kitchen waste digestion liquid via a two-stage partial nitrification/anammox (PN/A) process

The advanced nitrogen removal of mature landfill leachate (MLL) with low carbon to nitrogen ratio (C/N) is a topic worthy of further research. A two-stage partial nitrification/anammox (PN/A) system for integrated MLL and kitchen waste digestion liquid (KWDL) treatment was established in this study. The nitrogen removal efficiency (NRE) of this process was 98.1 ± 1.3 %, with an effluent TIN concentration of 15.2 ± 1.8 mg/L. In the partial nitrification-sequencing batch reactor (PN-SBR), aerobic hydraulic retention time (HRT) accounted for just 36.4 % of the whole process with dissolved oxygen (DO) < 0.3 mg/L, which significantly reduced energy consumption. Furthermore, the introduction of KWDL heightened anoxic denitrification and aerobic simultaneous nitrification and denitrification (SND) processes, contributing to 74.2 ± 4.3 % and 25.8 ± 4.3 % of the total NRE, respectively. This greatly strengthened the nitrogen removal capacity of PN-SBR. Batch tests indicated that the capacity of KWDL as a carbon source to drive the process of partial denitrification coupled with anammox (PDA) was equal to that of sodium acetate. Adding KWDL in the later phase of each cycle in the anammox-sequencing batch reactor (A-SBR) facilitated achieving stable PDA and advanced nitrogen removal. The nitrate accumulation problem in the traditional two-stage PN/A process has been resolved without the addition of carbon sources. Nitrosomonas (3.7 %→7.9 %), Thauera (0.04 %→40.7 %) and a salt-tolerant AnAOB microbe, unclassified_f_Brocadiaceae (0 %→5.3 %) were dominant in the combined system. This study revealed a pioneering avenue for efficient high-strength wastewater treatment.

Achieving ultra-high nitrogen and phosphorus removal from real municipal wastewater in a novel continuous-flow anaerobic/aerobic/anoxic process via partial nitrification, endogenous denitrification and nitrite-type denitrifying phosphorus removal

Achieving economic and efficient removal of nutrients in mainstream wastewater treatment plants (WWTPs) continues to be a challenging research topic. In this study, a continuous-flow anaerobic/aerobic/anoxic system with sludge double recirculation (AOA-SDR), which integrated partial nitrification (PN), endogenous denitrification (ED) and nitrite-type denitrifying phosphorus removal (nDNPR), was constructed to treat real carbon-limited municipal wastewater. The average effluent concentrations of total inorganic nitrogen (TIN) and PO43−-P during the stable operation period were 1.8 and 0.3 mg/L, respectively. PN was achieved with an average nitrite accumulation ratio of 90.4 % by combined strategies. Adequate storage of polyhydroxyalkanoates and glycogen in the anaerobic zone promoted the subsequent nitrogen removal capacity. In the anoxic zone, nitrite served as the main electron acceptor for the denitrifying phosphorus removal process. Mass balance analysis revealed that nDNPR contributed to 23.6 % of TIN removal and 44.7 % of PO43−-P removal. The enrichment of Nitrosomonas (0.45 %) and Ellin 6067 (1.31 %), along with the washout of Nitrospira (0.15 %) provided the bacterial basis for the successful implementation of PN. Other dominant endogenous heterotrophic bacteria, such as Dechlormonas (10.81 %) and Candidatus Accumulibacter (2.96 %), ensured simultaneous nitrogen and phosphorus removal performance. The successful validation of integrating PN, ED and nDNPR for advanced nutrient removal in the AOA-SDR process provides a transformative technology for WWTPs.

Nitrogen metabolism potential in biofilm microbial communities: potential applications in the mariculture wastewater treatment

Marine aquaculture wastewater is one of the major sources of nitrogen pollution in coastal areas, and excessive discharge poses a threat to human health and the marine ecosystem. In order to investigate the nitrogen metabolism potential of microorganisms in marine aquaculture water, metagenomic sequencing was conducted, and microbial communities involved in nitrogen metabolism on composite filler biofilms and their contributions to nitrogen metabolism functions were analyzed based on KEGG annotation. Metagenomic analysis revealed that nitrogen metabolism microorganisms were primarily composed of Proteobacteria, Planctomycetota, Bacteroidota, and Firmicutes. KEGG results indicated the presence of complete nitrogen metabolism pathways within the biofilm. Analysis of nitrogen metabolism modules and relative enzyme abundance showed that the nitrification module was much less abundant compared to denitrification. Denitrification, dissimilatory nitrate reduction, and ammonia conversion to amino acids were the major modules of nitrogen metabolism in the biofilm, reflecting the main nitrogen transformation pathways. The study systematically revealed key driving taxa in the nitrogen cycle within the biofilm. Proteobacteria, Planctomycetota, Bacteroidota, and Verrucomicrobia were identified as the major executors of nitrogen metabolism pathway modules and enzyme functions in the biofilm. This research underscores the diverse microbial communities cooperate to maintain the potential nitrogen removal capacity of the biofilm. This study provide new insights into the critical driving factors of nitrogen cycling in marine aquaculture wastewater, which can serve as a scientific basis for the efficient purification of aquaculture wastewater.

Isolation and characterization of a cold-tolerant heterotrophic nitrification–aerobic denitrification bacterium and evaluation of its nitrogen-removal efficiency

With a view toward addressing the poor efficiency with which nitrogen is removed from wastewater below 10 °C, in this study, we isolated a novel cold-tolerant heterotrophic nitrification–aerobic denitrification (HN-AD) bacterium from a wetland and characterized its nitrogen removal performance and nitrogen metabolic pathway. On the basis of 16S rRNA gene sequencing, this strain was identified as a species of Janthinobacterium, designated J1-1. At 8 °C, strain J1-1 showed excellent removal efficiencies of 89.18% and 68.18% for single-source NH4+-N and NO3−-N, respectively, and removal efficiencies of 96.23% and 79.64% for NH4+-N and NO3−-N, respectively, when supplied with mixed-source nitrogen. Whole-genome sequence analysis and successful amplification of the amoA, napA, and nirK functional genes related to nitrogen metabolism provided further evidence in support of the HN-AD capacity of strain J1-1. The deduced HN-AD metabolic pathway of the strain was NH4+-N→NH2OH→NO2−-N→NO3−-N→NO2−-N→NO→N2O. In addition, assessments of NH4+-N removal under different conditions revealed the following conditions to be optimal for efficient removal: a temperature of 20 °C, pH of 7, shaking speed of 150 rpm, sodium succinate as a carbon source, and a C/N mass ratio of 16. Given its efficient nitrogen removal capacity at 8 °C, the J1-1 strain characterized in this study has considerable application potential in the treatment of low-temperature wastewater.

Storm characteristics influence nitrogen removal in an urban estuarine environment

Abstract. Sustaining water quality is an important component of coastal resilience. Floodwaters deliver reactive nitrogen (including NOx) to sensitive aquatic systems and can diminish water quality. Coastal habitats in flooded areas can be effective at removing reactive nitrogen through denitrification (DNF). However, less is known about this biogeochemical process in urbanized environments. This study assessed the nitrogen removal capabilities of flooded habitats along an urban estuarine coastline in the upper Neuse River estuary, NC, USA, under two nitrate concentrations (16.8 and 52.3 µM NOx, respectively). We also determined how storm characteristics (e.g., precipitation and wind) affect water column NOx concentrations and consequently DNF by flooded habitats. Continuous flow sediment core incubation experiments quantified gas and nutrient fluxes across the sediment–water interface in marsh, swamp forest, undeveloped open space, stormwater pond, and shallow subtidal sediments. All habitats exhibited net DNF. Additionally, all habitats increased DNF rates under elevated nitrate conditions compared to low nitrate. Structured habitats with high-sediment organic matter had higher nitrogen removal capacity than unstructured, low-sediment organic matter habitats. High-precipitation–high-wind-storm events produced NOx concentrations significantly lower than other types of storms (e.g., low-precipitation–high-wind, high-wind–low-precipitation, low-wind–low-precipitation), which likely results in relatively low DNF rates by flooded habitats and low removal percentages of total dissolved nitrogen loads. These results demonstrate the importance of natural systems to water quality in urbanized coastal areas subject to flooding.

Multidrug-resistant plasmid RP4 inhibits the nitrogen removal capacity of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and comammox in activated sludge

In wastewater treatment plants (WWTPs), ammonia oxidation is primarily carried out by three types of ammonia oxidation microorganisms (AOMs): ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and comammox (CMX). Antibiotic resistance genes (ARGs), which pose an important public health concern, have been identified at every stage of wastewater treatment. However, few studies have focused on the impact of ARGs on ammonia removal performance. Therefore, our study sought to investigate the effect of the representative multidrug-resistant plasmid RP4 on the functional microorganisms involved in ammonia oxidation. Using an inhibitor-based method, we first evaluated the contributions of AOA, AOB, and CMX to ammonia oxidation in activated sludge, which were determined to be 13.7%, 41.1%, and 39.1%, respectively. The inhibitory effects of C2H2, C8H14, and 3,4-dimethylpyrazole phosphate (DMPP) were then validated by qPCR. After adding donor strains to the sludge, fluorescence in situ hybridization (FISH) imaging analysis demonstrated the co-localization of RP4 plasmids and all three AOMs, thus confirming the horizontal gene transfer (HGT) of the RP4 plasmid among these microorganisms. Significant inhibitory effects of the RP4 plasmid on the ammonia nitrogen consumption of AOA, AOB, and CMX were also observed, with inhibition rates of 39.7%, 36.2%, and 49.7%, respectively. Moreover, amoA expression in AOB and CMX was variably inhibited by the RP4 plasmid, whereas AOA amoA expression was not inhibited. These results demonstrate the adverse environmental effects of the RP4 plasmid and provide indirect evidence supporting plasmid-mediated conjugation transfer from bacteria to archaea.

Optimizing SRT for improved biomass production and nutrient removal from wastewater secondary effluent in a continuous mode MPBR system with Monoraphidium sp.: An experimental and growth kinetics model approach

This study aimed to evaluate the impacts of solids retention time (SRT) and influent nutrient concentration on the specific growth rate and nutrient removal efficacy of Monoraphidium sp. in a continuous mode membrane photobioreactor (MPBR). At SRT of 1 d, maximum biomass productivity of 421 mg·L−1·d−1 and nutrient removal rates of 59.9 % and 79.8 % for total nitrogen (TN) and total phosphorus (TP) were achieved. After reducing the influent nutrient concentration, Monoraphidium sp. maintained high biomass productivity of 385 mg·L−1·d−1 and nutrient removal rates of >95 % for TN and TP. The most important factor in Monoraphidium sp. growth assessment was intracellular nitrogen concentration (QN) rather than extracellular nutrient concentration. Flynn modified Droop model showed a better fit when the dimensionless parameter (Kq) was 0.235 for the relationship between the specific growth rate (μ) and QN. The model also revealed that even at low nitrogen concentrations (0.1 mg·L−1), the nitrogen removal capacity of Monoraphidium sp. was equal to its maximum removal capacity. Even at different extracellular nutrient concentrations, the Flynn model showed a linear relationship between μ and light irradiance per unit algae biomass (Iavp), when Iavp was below 18 μmol·g−1·s−1. This study highlights the promising potential of Monoraphidium sp. in MPBR. It demonstrates that considering QN and Iavp is essential for optimizing MPBR to achieve high biomass production and inorganic nutrient removal from secondary wastewater effluent.

Performance and bacterial community analysis of multi-stage A/O biofilm system for nitrogen removal of rural domestic sewage

Rural domestic sewage was difficult to collect, and there was a lack of skilled professionals for its treatment. This study constructed a high-efficiency anaerobic- aerobic (A/O) biofilm reactor with multi-stage free combination, simple operation, and low consumption. The nitrogen removal capacity of the system was enhanced by changing the number of A/O stages, influent, and hydraulic retention times (HRT). The most economical system with the required total nitrogen (TN) removal loading is tertiary A/O with a step-feed ratio of 1:1:1 and HRT = 36 h. At this time, the TN removal rate could reach 71.29 %. Realizes high-efficiency nitrogen removal with low consumption and unattended operation. Increasing the influent carbon to nitrogen (C/N) ratio could effectively enhance the nitrogen removal capacity. In addition, chemical oxygen demand (COD) removal was better under various operating conditions. Pseudomonas was the dominant genera in the anaerobic zone, contributing to organic pollutant removal and denitrification. The aerobic zone was enriched with Nitrospira, related to the nitrification and denitrification process. The anoxic zone contained more heterotrophic denitrifying bacteria genera such as Denitratisoma. The system had excellent performance with the synergistic effect of the above microorganisms. The efficient and low-consumption biofilm system developed in this study suits engineering applications in poor rural areas.

POLLUTION REMOVAL CAPACITIES OF AQUATIC PLANT SPECIES IN THE DATONG WETLAND PARK IN NORTH CHINA

The purification effect of a natural wetland landscape is often low when the focus is placed on the landscape effect. The effective combination of constructed wetland technology with landscape construction is challenging. Taking the Yuhe Wetland Park in Datong, Shanxi Province, China, as an example, the COD, phosphorus, and nitrogen removal capacities of aquatic plant species were determined, as well as the effects of the soil and the microbial communities. The highest COD and P removal capacity was observed for Typha orientalis Presl. which the purification rate reached 76.9% and 76.6%, and the highest N removal capacities were found for Scirpus validus Vahl., the rate of purification was 83.4%. Gram-negative bacteria were dominant.

Promoting aerobic denitrification in reservoir water with iron-activated carbon: Enhanced nitrogen and organics removal efficiency, and biological mechanisms

Carbon scarcity limits denitrification in micropolluted water, especially in drinking water reservoirs. Therefore, a Fe-activated carbon (AC) carrier was used in this study to enhance the nitrogen removal capacity of aboriginal denitrification in drinking water reservoirs under aerobic conditions. Following carrier addition, total nitrogen (TN) and permanganate index (CODMn) removal efficiencies reached 81.89% and 72.66%, respectively, and were enhanced by 40.45% and 39.65%. Nitrogen balance analysis indicated that 77.86% of the initial TN was converted into gaseous nitrogen. Biolog analysis suggested that the metabolic activity of denitrifying bacteria was substantially enhanced. 16S rRNA gene sequencing indicated that organic degradation bacteria, hydrogen-consuming, Fe-oxidizing, and Fe-reducing denitrifying bacteria (e.g., Arenimonas, Hydrogenophaga, Zoogloea, Methylibium, and Piscinibacter) evolved into the dominant species. Additionally, napA, nirS, nirK, and nosZ genes were enriched by 3.17, 6.68, 0.40, and 6.70 folds, respectively, which is conducive to complete denitrification. These results provide a novel pathway for the use of Fe-AC to promote aerobic denitrification in micropolluted drinking water reservoirs.

Remoción de nitrógeno y fósforo acoplada a la fijación de CO2 de dos microalgas verdes, Chlorella sp. y Quadrigula sp., nativas de la costa de Chiapas, México

Microalgae remove nitrogen and phosphorus from water for their growth and biomass production, wich has several biotechnological applications. This study evaluated the growth, NO3−, NO2−, NH4+, urea, PO43− and total nitrogen removal capacity, as well as the biomass production and the CO2 fixation of two new microalgae isolates, Chlorella sp. and Quadrigula sp., from the coast of Chiapas, México. Chlorella sp. had a higher specific growth rate (0.74/day) and a shorter doubling time (0.92 days) than Quadrigula sp. Removal per unit volume (mg/L) of NO3−, NH4+ and total nitrogen by Chlorella sp. was higher (26.88%, 10.58% and 16.63%, respectively) than removal by Quadrigula sp. On the other hand, daily removal (mg/L/d) of NO3−; NH4+; NO2−; urea and total nitrogen by Chlorella sp. was also higher (88%, 33%, 89%,15% and 50%, respectively) than daily removal by Quadrigula sp. The biomass productivity (mg/L/d) and the CO2 fixation rate (mg/L/d) were similar among both microalgae. The results of this study suggest that Chlorella sp. and Quadrigula sp. have potential for nutrient removal, biomass production and CO2 fixation.

Directed regulation of anammox communities based on exogenous siderophores for highly efficient nitrogen removal.

It is expected that the quicker domestication of anaerobic ammonia oxidation (anammox) communities and the enhancement of their nitrogen transformation capability can be achieved through targeted regulation of anammox communities. Iron cast a vital role in the growth and metabolism of anammox bacteria. Specific siderophores offer promising prospects for the targeted regulation of anammox communities by facilitating the efficient utilization of iron. Two siderophores-enterobactin and putrebactin-exclusively for Ca. Brocadia and Ca. Kuenenia were developed to specifically regulate anammox communities towards different directions, respectively. Anammox communities in the reactors evoluted targetedly towards Ca. Brocadia-dominated communities and Ca. Kuenenia-dominated communities, respectively, leading to a maximum increase in community nitrogen removal capacity by 84.64±0.55% and 210.26±0.57%, respectively, under different nitrogen concentrations. It was indicated that siderophores could regulate anammox communities by redistributing iron resources in a targeted manner based on the analyses of transcriptome and proteome. This study provides novel insights into the rational selection and utilization of exogenous siderophores as an effective implement to manipulate anammox communities and create communities with high nitrogen removal ability fleetly.

Pseudomonas fluorescens 2P24: A root beneficial bacterium with an excellent ability to remove multiple nitrogen sources

The nitrogen removal capacity of the root-associated beneficial bacterium Pseudomonas fluorescens 2P24 was investigated in synthetic wastewater and actual wastewater. The results revealed that strain 2P24 removed 97.63 % of ammonium and 100 % of nitrate and nitrite within 48 h when ammonium, nitrate, or nitrite served as the sole nitrogen source (initial concentrations of 100 mg/L). At an ammonium to nitrate to nitrite ratio of 1:1:1, ammonium, nitrate, and nitrite were all removed with efficiencies exceeding 98 %. In addition, strain 2P24 exhibited high nitrogen removal performance in actual wastewater, removing 79.52 % of ammonium and 100 % of nitrate from unsterilized domestic sewage in 10 h. Moreover, regardless of whether the strain was grown in the presence of a sole nitrogen source or mixed nitrogen sources, there was no hazardous nitrite accumulation after 48 h of cultivation. Collectively, the findings indicated that strain 2P24 has potential applications as a standby bacterium for the biological treatment of wastewater.

Salt marsh expansion into estuarine mangrove mudflats reduces nitrogen removal capacity

Salt marsh (Spartina alterniflora) has been rapidly encroaching into mangrove wetlands worldwide. However, the potential effects of salt marsh expansion on coastal nitrogen cycling and ecosystem function remain unclear. In this study, sediment cores were seasonally collected from mangroves, salt marshes and mudflats from 2020 to 2021 to assess their nitrogen cycling. Nitrogen transformation rates of mineralization, immobilization, nitrification, denitrification, anaerobic ammonium oxidization (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) were determined using 15N isotope tracer techniques. Rate measurements were paired with analysis of physicochemical properties, carbon isotopes, and nitrogen functional genes. The results showed that compared to mangrove sediments, salt marsh sediments mostly exhibited lower mineralization and denitrification rates but higher nitrification rates. Mudflat sediments had the lowest mineralization and denitrification rates among the studied habitats, while the nitrification rates were close to those of salt marshes. The differences in carbon quantity and source, nitrogen gene abundances, and carbon and nitrogen substrate availabilities controlled the variations in nitrogen transformation rates. The balance of these rates was used to indicate the net nitrogen retention or removal capacity of the three habitats. On an annual scale, salt marshes exhibited ammonium (NH4+-N) removal while mangroves had net NH4+-N retention. Nitrate (NO3--N) was removed both in salt marsh and mangrove sediments with larger removal capacity in mangroves. Salt marsh sediments had lower NH4+-N removal but higher NO3--N removal levels than mudflat sediments. In summary, salt marsh invasion decreased the overall nitrogen removal levels in the mangrove-mudflat wetland. The future scenarios of increasing salt marsh coverage suggest a decreased removal of nitrogen loads, which has important implications for mitigating coastal eutrophication.

Exploring the nitrogen removal capacity of Klebsiella aerogenes B23 isolated from shrimp farm wastewater: heterotrophic nitrification and aerobic denitrification

Exploring the nitrogen removal capacity of Klebsiella aerogenes B23 isolated from shrimp farm wastewater: heterotrophic nitrification and aerobic denitrification

Improved simultaneous nitrification–denitrification in fixed-bed baffled bioreactors treating mariculture wastewater: Performance and microbial community behaviors

As mariculture develops, wastewater treatment becomes crucial. In this study, fixed-bed baffled reactors (FBRs) packed with carbon fiber (CFBR) or polyurethane (PFBR) as biofilm carriers were used for mariculture wastewater treatment. Under salinity shocks between 0.10 and 30.00 g/L, the reactors showed efficient and stable nitrogen removal capacities, and the maximum NH4+-N removal rates were 107.31 and 105.42 mg/(L·d) for CFBR and PFBR, respectively, with an initial NH4+-N concentration of 120.00 mg/L. Further, in the independent aerobic chambers of the FBRs for nitrogen removal, taxa enrichment varied depending on the biofilm carrier, and the assembly process was more deterministic in CFBR than in PFBR. Two distinct clusters representing the spatial distribution of the adhering and deposited sludge in CFBR and the front and rear compartments in PFBR were noted. Furthermore, microbial interactions were more numerous and stable in CFBR. These findings improve the application prospects of FBRs in mariculture wastewater treatment.

Partial nitritation-anammox for treatment of saline wastewater: Hydrazine-assisted salinity adaptation and nitrate control

In biological wastewater treatment, salinity can significantly restrict bacterial activity, and a long adaptation period to the saline condition is needed. This study investigated the feasibility of using partial nitritation-anammox (PNA) in an integrated fixed-film activated sludge (IFAS) reactor for enhanced biological nitrogen removal from saline municipal wastewater. The experimental results show that the salinity increase in the influent seriously affected the activity of anammox bacteria and disrupted the PNA process for autotrophic nitrogen removal when seawater was added to a 20% proportion with a resultant salinity of around 6.5‰. However, the addition of N2H4 (dosage: 5 mg/L for 3 weeks), an exogenous enhancer of both ammonia-oxidizing bacteria and anammox bacteria, effectively facilitated the rapid recovery and adaptation of PNA to salinity stress with a negligible additional cost for long-term operation. The PNA-IFAS reactor achieved a nitrogen removal capacity of 83.4 ± 5.9 mg N/(L‧d) in treating the saline municipal wastewater containing 40% seawater and an ammonia-N concentration of around 60 mg N/L. Salinity in the influent advantageously suppressed the activity and growth of the co-existing nitrite-oxidizing bacteria (NOB). The relative abundances of NOB in the suspended sludge (0.15%) and biofilms (0.33%) were kept at low levels, maintaining a low nitrate yield of 6.6 ± 1.5% in the bioreactor. The result suggests that salinity in the influent may offer potential benefits for reducing the risk of nitrate build-up and increasing the robustness of the PNA process for sustainable wastewater treatment.

Nitrogen removal by a novel strain Priestia aryabhattai KX-3 from East Antarctica under alkaline pH and low-temperature conditions

To boost the poor nitrogen removal capacity of microorganisms under alkaline and low-temperature conditions, a new strain Priestia aryabhattai KX-3 able to heterotrophically nitrify and aerobically denitrify (HN-AD) was isolated from the Larsemann Hills in East Antarctica. The unique HN-AD function described herein has never been reported previously. At 10 ℃ and pH 10.0, strain KX-3 can remove 96.0% of nitrate–N (40 mg/L), 92.5% of ammonium–N (40 mg/L), and 56.7% of nitrite–N (40 mg/L). In addition, functional genes (amoA, hao, napA, nirS, and nosZ) and three key enzymes related to nitrogen reduction (NIR, NR and HAO) were detected, confirming the HN-AD abilities of strain KX-3. Finally, transcriptomics data confirmed the up-regulation of genes associated with the GDH22GDH: Glutamate dehydrogenase pathway, such as gln A and gltBD. In addition, the genes for the cold-resistant ABC transporters and Na+/H+ antiporters (MnhACDEFG, NhaCD, and TrkAH) were expressed highly. Strain KX-3 has a strong potential for nitrogen removal under low temperature and alkaline conditions. Moreover, it also provides reference value for research on microbial tolerance to extreme conditions in East Antarctica.

Enhanced Simultaneous Nitrogen and Phosphorus Removal Performance of the AGS-SBR Reactor Based on the Effects of the C/N Ratio and Microbial Community Change

In recent years, the development of AGS technology will likely lead to a new direction in wastewater treatment development in the future. Traditional sewage treatment technology has been unable to meet the increasingly strict quality standards of wastewater treatment and limited land requirements. AGS technology may be a new method to replace traditional sewage treatment technology. However, the stable operation of AGS technology is a major obstacle to the popularization and development of this technology. The C/N ratio is an important parameter affecting the stability and simultaneous nitrogen and phosphorus removal of AGS technology. In order to enhance the nitrogen and phosphorus removal capacity of a low-load aerobic granular sludge SBR (AGS-SBR) system, changes in the morphology, EPS, and simultaneous removal of organic matter, nitrogen, and phosphorus in the AGS system were studied by regulating different C/N ratios (20, 15, 10, 5). The changes in the microbial community in the system were deeply analyzed by high-throughput sequencing technology. The results showed that different C/N ratios have a significant effect on the nitrogen removal rate of AGS but have little effect on the removal rate of organic matter and phosphorus. When the C/N ratio was reduced to 10, it was conducive to the stability of the low-load AGS-SBR system. An effective C/N ratio promoted the secretion of EPS by microorganisms, and the increase in the PN value contributed to the stability of the granular sludge, which became smooth and compact. The main functional genus in the system were norank_f__Saprospiraceae, Tetrasphaera, Ellin6067, and Pseudomonas. In addition, the simultaneous nitrogen removal performance of the system was significantly improved.

Quantifying the Nitrogen-Removal Performance of a Constructed Wetland Dominated by Diffuse Agricultural Groundwater Inflows Using a Linked Catchment–Wetland Model

Nitrogen loading from diffuse agricultural sources is a major water-quality problem worldwide. Constructed wetlands have been increasingly used to treat runoff and drainage from agricultural lands. However, the diffuse nature of nitrogen loading from farmlands often makes it challenging to trace flow pathways and measure the direct input loading to wetlands, and assess their nutrient-reduction performance. The Owl Farm wetland, Cambridge, New Zealand, receives inputs mainly from a subsurface drain and groundwater seepage. As it was not possible to directly measure wetland inflows, we used the Soil and Water Assessment Tool (SWAT) to estimate and partition the wetland inflow and nitrogen loading from the drain and seepage. A dynamic first-order tanks-in-series wetland model was linked with SWAT to evaluate the wetland capacity for nitrogen removal over a four-year period. The linked catchment–wetland model could simulate flow and nitrate load at the wetland outlet reasonably well with a Nash–Sutcliffe efficiency (NSE) of 0.7 and 0.76, respectively, suggesting that it provides a good representation of the hydrological and nitrogen processes in the upland catchment and the constructed wetland. We used two approaches, a mixed measurement-and-modelling-based approach and a process-based modelling approach to estimate the wetland efficiency of nitrogen removal. In both approaches, we found that the percentage load removal for nitrate-N and total N was related exponentially to the wetland outflow rate. Based on the process-based model estimates, the Owl Farm constructed wetland is very effective in removing nitrate-N with annual estimates of 55–80% (average 61%) removal. However, this capacity is very dynamic depending on the inflow from the catchment. The removal efficiency is very high at low flow and reduces when flow increases but is still maintained at around 20–40% during higher-flow periods. However, actual nitrogen-load removal in the wetland is greatest during high-flow periods when input loads are elevated. This study illustrates how a linked catchment–wetland modelling approach can be used to partition and quantify diffuse nitrogen input loads into wetlands from different types of runoff and to evaluate their subsequent reduction rates. The tool is particularly useful for situations where diffuse groundwater inflows, which are difficult to measure, are important nutrient sources.