Total Nitrogen Removal Rate Research Articles

Chlorella potential to purify domestic garbage leachate for biomass production and community structure responses of wastewater-borne bacteria

The microalgae growth, accumulation of high value-added substances of Chlorella sp. HQ and its water purification potential during cultivation in diluted domestic garbage leachate (DGL) were investigated and changes in the structure of wastewater-borne bacteria community were also analyzed. Results showed that the highest density of Chlorella (1.70 × 108 cells/mL) was obtained in DGL diluted 5 times with rural sewage, the contents of protein and sugar in microalgae cells were 36.0 % and 45.6 %, Moreover, energy volumetric yield reached 48.54 kJ/L. After 15 d of microalgae treatment, the removal rates of total nitrogen (TN), ammonia nitrogen (NH4+-N), chemical oxygen demand (COD), total phosphorus (TP) of diluted DGL were 88.2 %, 97.3 %, 94.9 %, and 95.2 %, respectively, with the fluorescence peaks of humic-like organic matter shifting to longer wavelengths. Moreover, high-throughput sequencing of wastewater-borne bacteria showed that microalgae growth could promote the enrichment of denitrifying polyphosphate accumulating bacteria, which suggests that wastewater-borne bacteria and Chlorella may form a cooperative mode to achieve water purification.

Application of low-intensity ultrasound to enhance simultaneous nitrification/iron-based autotrophic denitrification.

Intermittent ultrasound with an intensity of 0.2W/ml was applied during simultaneous nitrification/iron-based autotrophic denitrification to evaluate its impacts on total nitrogen (TN) removal efficiency and microbial characteristics during low carbon/nitrogen ratio (C/N) wastewater treatment. At an optimal dissolved oxygen (DO) concentration of 1.2mg/L, the TN removal rate was 91 ± 4%, and the TN concentration in the effluent decreased by 31% owing to the ultrasound treatment. In addition, the number of iron-compounds that formed in the sludge and wastewater increased by 55% and 37%, respectively. Low-intensity ultrasound caused a substantial increase in ammonia monooxygenase activity. Moreover, when the DO concentration increased to 1.2mg/L, the activities of nitrate reductase and nitrite reductase, both of which are associated with denitrification, were effectively maintained. High-throughput sequencing indicated that low-intensity ultrasound enriched ammonium oxidising bacteria (Nitrosomonas) and suppressed the growth of heterotrophic denitrifying bacteria (Zoogloea and Simplicispira). These changes benefited simultaneous nitrification and autotrophic denitrification. Thus, low-intensity ultrasound promoted the simultaneous nitrification/iron-based autotrophic denitrification process during low C/N wastewater treatment.

Enhancing nitrogen removal from domestic sewage with low C/N ratio using a biological aerated filter system with internal reflux-coupled intermittent aeration

Biological aerated filter (BAF) systems with internal reflux-coupled intermittent aeration enhance the removal of nitrogen pollutants from low-C/N ratio domestic sewage. Two experimental systems with the same specifications, a BAF system with internal reflux-coupled intermittent aeration (system A) and a traditional BAF system (system B) was constructed to explore the efficiency of nitrogen removal. Overall, the nitrification in system B was higher than that in system A due to the influence of aeration model. Conversely, the system A can use the alternating anoxic (DO<0.5 mg·L−1) and aerobic (DO around 1 mg·L−1) environment to obtain better Total Nitrogen (TN) removal rate of 21.56 mg·(kg·h)−1 in the bottom of 30–70 cm zone of the reactor by combining reflux nitrate with influent COD. This section had a low specific oxygen uptake rate but high triphenyl tetrazolium chloride-dehydrogenase activity, indicating that the system enhanced nitrogen removal by denitrification in this section. The 16 S rDNA high-throughput sequencing analysis showed that the diversity index of system A was higher than that of system B. The abundance of microorganisms involved in denitrification was higher in the 30–50 cm zone of system A, mainly in the phylum (10.63%) and the phylum Bacillus (32.05%), indicating that system A was used for denitrification through nitrate reflux and intermittent aeration.

Adsorption and oxidation of ciprofloxacin by a novel layered double hydroxides modified sludge biochar

In this study, biochar derived from municipal sludge (SBC) was modified by CoFe-Layered double hydroxides (CoFe-LDH), and used as adsorbent and oxidant for the removal of ciprofloxacin (CIP) for the first time. Under the optimal conditions, the CIP removal rate is increased by 24% compared with the single SBC, while the removal rates of total organic carbon and total nitrogen in the modified one are increased by 24% and 27%, respectively. Mechanism investigation suggested that the specific surface area and adsorption sites of modified biochar increased, and more CIP was adsorbed to the composite surface and then oxidized by more environmental persistent free radicals contained in the CoFe-LDH@SBC, when the adsorbed CIP molecules was oxidized and degraded, the adsorption sites can be freed and thus new CIP could be adsorbed to the CoFe-LDH@SBC. In addition, the plausible degradation pathways of CIP were proposed according to high-performance liquid chromatography-mass spectrometry and density functional theory calculation. It not only reveals that CoFe-LDH@SBC has the high ability of adsorption and oxidation for CIP removal but also sheds novel insight into the application of biochar.

Performance and mechanism of Chlorella in swine wastewater treatment: Roles of nitrogen-phosphorus ratio adjustment and indigenous bacteria

The effects of adjusting the nitrogen-phosphorus (N/P) ratio of wastewater and indigenous bacteria on swine wastewater treatment by Chlorella sp. HL were investigated. The optimal N/P ratio of Chlorella in swine wastewater was 20 by adjusting the phosphorus concentration. The participation of indigenous bacteria increased total extracellular polymeric substances content, which was beneficial to maintain the stability of the algal-bacterial consortium, and improved the algal density and the removal rate of total nitrogen, total phosphorus, and chemical oxygen demand by 47.8%, 24.0%, 30.7%, and 326.7%, respectively. Proteobacteria was the dominant phylum with the relative abundance of 71.58% in the algal-bacterial system at optimal N/P ratio, and Brevundimonas, Chryseobacterium, and Pseudomonas played positive roles in the establishment of symbiotic systems at the genus level. These results provide a theoretical basis for the construction of an efficient algal-bacterial symbiotic system in swine wastewater treatment and support for commercial scale-up.

Study on Water Purification Effect and Operation Parameters of Various Units of Wastewater Circulation

The discharge of wastewater from aquaculture ponds causes a certain degree of damage to the environment. It is necessary to continuously improve the treatment efficiency of wastewater treatment devices. The purpose of this study is to obtain an optimal ratio of wastewater circulation devices in order to obtain the best operating parameters and to reduce the discharge of polluted water. We constructed an experimental wastewater circulation device consisting of three units. The primary unit contained modified attapulgite (Al@TCAP-N), volcanic stone, and activated carbon for precipitation. The secondary and tertiary units used biological methods to enhance removal rates of nitrogen and phosphorus. Water quality indicators of total phosphorus (TP), total nitrogen (TN), ammonia (NH3-N), permanganate (CODMn), and total suspended solids (TSS) were detected. Water quality was tested under different matching ratios for three units of different hydraulic retention time (HRT) and load Results showed that the removal rate of TP, TN, NH3-N, and TSS reached 20–60%, 20%, 30–70%, and 10–80%, respectively. The average reduction efficiencies of secondary module chlorella and filler on TP, TN, NH3-N, CODMn, and TSS were 56.88%, 30.09%, 0.43%, 46.15%, and 53.70%, respectively. The best removal rate can be achieved when the matching ratio of each unit becomes 2:1:1 and the hydraulic retention time is maintained within 2 h in the high-concentration load. Finally, the average removal rates of TP, TN, NH3-N, and TSS reached 58.87%, 15.96%, 33.99%, and 28.89%, respectively. The second unit obtained the enhanced removal effect in this wastewater treatment system when adding microorganisms and activated sludge.

An Eco-Friendly Conversion of Aquaculture Suspended Solid Wastes Into High-Quality Fish Food by Improving Poly-β-Hydroxybutyrate Production

The aquaculture industry is vital in providing a valuable protein food source for humans, but generates a huge amount of solid and dissolved wastes that pose great risks to the environment and aquaculture sustainability. Suspended solids (in short SS), one of the aquaculture wastes, are very difficult to be treated due to their high organic contents. The bioconversion from wastewater, food effluents, and activated sludge into poly-β-hydroxybutyrate (PHB) is a sustainable alternative to generate an additional income and could be highly attractive to the agricultural and environmental management firms. However, little is known about its potential application in aquaculture wastes. In the present study, we first determined that 7.2% of SS was PHB. Then, the production of PHB was increased two-fold by the optimal fermentation conditions of wheat bran and microbial cocktails at a C/N ratio of 12. Also, the PHB-enriched SS showed a higher total ammonia nitrogen removal rate. Importantly, we further demonstrated that the PHB-enriched SS as a feed could promote fish growth and up-regulate the expression of the immune-related genes. Our study developed an eco-friendly and simple approach to transforming problematic SS wastes into PHB-enriched high-quality food for omnivorous fish, which will increase the usage efficiency of SS and provide a cheaper diet for aquatic animals.

Nitrogen removal performance and bacterial flora analysis of a partial nitrification-anaerobic ammonium oxidation-denitrification system treating rare earth element tailings wastewater

In this study, the start of partial nitrification (activated sludge)-anaerobic ammonia oxidation (immobilized fillers)-denitrification (immobilized fillers) and stable nitrogen removal in the treatment of rare earth element tailings wastewater were explored. The results showed that, at 25–30 °C, partial nitrification could be rapidly established by controlling the combination of average free ammonia concentration (25.4–60.2 mg/L) and dissolved oxygen concentration (0.5 mg/L). Adopting the stepwise substrate (three stages) and shortening hydraulic retention time (HRT) methods, the total nitrogen removal rate of anaerobic ammonia oxidation (anammox) immobilized fillers reached up to 0.99 kg N•(m3•d)−1. Adopting the C/N ratio of 4.5:1 and shorter HRT methods, the total nitrogen removal rate of denitrification immobilized fillers reached up to 1.07 kg N•(m3•d)−1. The activities of the anammox and denitrification immobilized fillers were increased by 8.39 and 4.46 times, respectively. At steady state operation, the average effluent ammonia nitrogen concentration was 3.01 mg/L, with an average effluent total nitrogen concentration of 5.11 mg/L, which met the requirements of the "Emission Standard for Pollutants from Rare Earth Industry" GB 26451–2011. High-throughput sequencing technology showed that the relative abundance ratios of Nitrosomonas and Nitrospira changed from 0.36:1–108.05:1. The dominant bacterial genera of the anammox immobilized fillers was Candidatus Kuenenia, and that of denitrification immobilized fillers were Pseudomonas and Thauera. This process provides a new technical approach for rare earth element tailings wastewater treatment, with high significance in engineering.

Enhancing Algal Yield and Nutrient Removal from Anaerobic Digestion Piggery Effluent by an Integrated Process-Optimization Strategy of Fungal Decolorization and Microalgae Cultivation

The dark brown anaerobic digestion piggery effluent (ADPE) with a large amount of ammonium generally needs high dilution before microalgae cultivation due to its inhibiting effects on algal growth. Due to the strong decolorization of fungi by degrading organic compounds in wastewater, the process-optimization integrated strategy of fungal decolorization of ADPE and subsequent microalgae cultivation with ammonium-tolerant strain may be a more reliable procedure to reduce the dilution ratio and enhance algal biomass production, and nutrient removal from ADPE. This study determined a suitable fungal strain for ADPE decolorization, which was isolated and screened from a local biogas plant, and identified using 26s rRNA gene sequence analysis. Subsequently, ADPE was pretreated by fungal decolorization to make low-diluted ADPE suitable for the algal growth, and conditions of microalgae cultivation were optimized to achieve maximum algal yield and nutrient removal from the pretreated ADPE. The results showed one promising locally isolated fungal strain, Nanchang University-27, which was selected out of three candidates and identified as Lichtheimia ornata, presenting a high decolorization to ADPE through fungal pretreatment. Five-fold low-diluted ADPE pretreated by L. ornata was the most suitable medium for the algal growth at an initial concentration of ammonium nitrogen of 380 mg L−1 in all dilution treatments. Initial optical density of 0.3 and pH of 9.0 were optimal culture conditions for the algal strain to provide the maximum algal yield (optical density = 2.1) and nutrient removal (88%, 58%, 65%, and 77% for the removal rates of ammonium nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand, respectively) from the pretreated ADPE. This study demonstrated that fungal decolorization and subsequent microalgae cultivation could be a promising approach to algal biomass production and nutrient removal from ADPE.

Purification mechanism of city tail water by constructed wetland substrate with NaOH-modified corn straw biochar

The pollution of corn straw to the environment had attracted much attention. The preparation and alkali modification of corn straw biochar as the constructed wetland (CW) substrate was conducive to solving the environment pollution caused by straw and improving the purification effect of CW. The NaOH modification mechanism of corn straw biochar was analyzed by measuring the surface morphology, element content, specific surface area (SSA), pore volume, crystal structure, surface functional groups and CO2 adsorption. Biochar prepared under relatively optimal NaOH-modified conditions was used as the vertical flow CW substrate to treat city tail water. The results showed that controlling the modification condition of NaOH (< 1.0 mol·L−1, ≤ 24 h) was conducive to prevent the biochar structure destruction and C element reduction. The SSA and pore volume of NaOH (0.1 mol·L−1) modified biochar are 360 m2·g−1 and 0.109 cm3·g−1, respectively. The biochar adsorption for CO2 conformed to the Langmuir and Freundlich isothermal adsorption theoretical model (R2 > 0.9). The maximum adsorption capacity of CO2 by modified biochar with NaOH (0.1 mol·L−1) was 64.516 cm3·g−1 and increased by 10.3%. The city tail water treated by CW with plants showed that the removal rates of ammonia nitrogen, total nitrogen and nitrate nitrogen reached about 90%. The research results improved the utilization value of straw, realized straw carbon sequestration and promoted the progress of CW technology.

Comparison of single and mixed plant artificial floating islands for domestic sewage treatment

The artificial floating island is an ecological restoration technology of water environment based on the principle of ecological hydraulics aiming at solving the problem of eutrophic water by degrading chemical oxygen demand, total nitrogen, and total phosphorus. It has good social benefits, environmental benefits, and broad application prospects. Against the backdrop of domestic wastewater treatment, the mixed plant-type artificial floating island, which include pickerel weed, Scirpus tabernaemontani, and bog rushes, was put into a test environment. Through the analysis of the adsorption and the absorption effect of various plants, the purifying effect of the mixed type of plant artificial floating island was thus determined and summarized based on the known total nitrogen, total phosphorus, and chemical oxygen demand values. According to the test results, it can be concluded that the effect of the mixed type of plant artificial floating island system in treating domestic wastewater is significant. The removal rate of total nitrogen and total phosphorus reached 55.12 % and 37.59 %, respectively, and the removal rate of chemical oxygen demand reached 47.85 %. The mixed type of plant artificial floating island can effectively dispose the nitrogen and phosphorus in the water.

Use of sponge iron dosing in baffled subsurface-flow constructed wetlands for treatment of wastewater treatment plant effluents during autumn and winter

Sponge iron (SI) is widely used in water treatment. As effluents from wastewater treatment plant (WWTP) require advanced treatment methodology, three forms of constructed wetlands (CWs): wetlands with sponge iron (SI), copper sulfate modified sponge iron (Cu/SI), and sponge iron coupled with solid carbon sources (C/SI), have been investigated in this paper for the removal effects of organic matter and nutrients in WWTP effluents, and the corresponding mechanisms have been analyzed. The results showed the effect of baffled subsurface-flow constructed wetland (BSFCW) with SI dosing to purify the WWTP effluents after the stable operation. The water flow of this BSFCW is the repeated combination of upward flow and downward flow, which can provide a longer treatment pathway and microbial exposure time. The average removal rates of total inorganic nitrogen (TIN) were 27.80%, 30.17%, and 44.83%, and the average removal rates of chemical oxygen demand (COD) were 19.96%, 23.73%, and 18.38%. The average removal rates of total phosphorus (TP) were 85.94%, 82.14%, and 83.95%. Cu/SI improved the dissolution of iron, C/SI improved denitrification, and a winter indoor temperature retention measure was adopted to increase the effectiveness of wetland treatment during the winter months. After comprehensively analyzing X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and two-dimensional numerical simulation diagrams, a plausible conjecture that microbes use electrons from SI for autotrophic denitrification is presented. Moreover, the stress effect of wetlands dosed with SI on plants decreased stepwise along the course since C/SI used on wetlands had less impact on plant stress.

Novel strategy for rapid start-up and stable operation of anammox: Negative pressure coupled with the direct-current electric field

An application challenge of anaerobic ammonia oxidation (anammox) is the slow proliferation rate of anaerobic ammonium oxidation bacteria (AnAOB). This study adopted negative pressure coupled with the direct-current electric field (NP–DCEF) to evaluate system nitrogen removal performance. Results showed that the total nitrogen removal rate (TNRR) of the NP–DCEF system was stable at 88.6% after seven days. Compared with that of the ordinary operating system (45.4%), the relative abundance of Candidatus–kuenenia considerably increased from 51.9% to 57.6%. Under transient and long-term influent fluctuation, the NP–DCEF system showed high nitrogen removal performance. The specific activity of AnAOB (SAA) reached 11.0 mg N∙g Vss−1 h−1 under load fluctuation, and it was 8.7 mg N∙g Vss−1 h−1 under ordinary operational conditions. In addition, the specific activities of hydrazine dehydrogenase (HDH) and hydrazine synthetase (HZS) reached 32.66 and 92.95 U∙L−1, which are considerably higher than those under the ordinary operating conditions (18.41 and 63.20 U∙L−1). These results indicated that the novel operation strategy has specific feasibility and potential for the start-up and long-term operation of anammox.

Study of the effect of pyrite and alkali-modified rice husk substrates on enhancing nitrogen and phosphorus removals in constructed wetlands.

The combined effects and respective advantages of using pyrite and alkali-modified rice husk (RH) were studied as substrates for nitrogen and phosphorus removal from constructed wetlands, and the effects of the carbon to nitrogen (C/N) ratio and the tidal flow mode on system performance were explored. The results showed that alkali-modified RH, which enhances heterotrophic denitrification, had far more advantages than pyrite, which enhances autotrophic denitrification, and alkali-modified RH can be used for the treatment of sewage containing low C/N ratios. At a C/N ratio of 1.5, the total nitrogen (TN) removal rates exceeded 95%. However, the removal efficiency of the system with only pyrite only reached 76.90% when the influent C/N ratio was 6. Pyrite achieved a total phosphorus (TP) removal 10-20% higher than that of the control group. The tidal flow CWs showed enhanced nitrification, and the NH4+-N removal rates increased by approximately 10%, but the increase in dissolved oxygen (DO) was still insufficient to meet the needs of the systems, leading to limited TP removal. The combination of pyrite and alkali-modified RH was optimal for improving the ability of constructed wetlands to treat wastewaters, simultaneously removing nitrogen and phosphorus from sewage containing low C/N ratios. Combined with the tidal flow mode strategy, the use of pyrite and alkali-modified RH as substrates showed substantial advantages for improving water quality.

Purification of Micro-Polluted Lake Water by Biofortification of Vertical Subsurface Flow Constructed Wetlands in Low-Temperature Season

In this study, a novel lab-scale biofortification-combination system (BCS) of Oenanthe javanica and Bacillus series was developed to improve the treatment ability of vertical subsurface flow constructed wetlands (VSFCW) at low temperatures (0–10 °C). The results showed that BCS-VSFCW overcame the adverse effects of low temperature and achieved the deep removal of nutrients. In addition, the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) by BCS-VSFCW were 38.65%, 28.20%, 18.82%, and 14.57% higher than those of blank control, respectively. During the experiment, Oenanthe javanica and low temperature tolerant Bacillus complemented each other in terms of microbial activity and plant uptake. Therefore, VSFCW combined with Oenanthe javanica and low temperature tolerant Bacillus has a promising future in low temperature (&lt;10 °C) areas of northern China.

Exerting applied voltage promotes microbial activity of marine anammox bacteria for nitrogen removal in saline wastewater treatment

To date, the application of marine anammox bacteria (MAB) is still a challenge in saline wastewater treatment due to the low growth rate and high sensitivity. Herein, bioelectrochemical system with applied voltage was exerted for the first time to promote the activity of MAB for removing nitrogen from saline wastewater. At the optimal voltage of 1.5 V, the mean total nitrogen removal rate (TNRR) reached the maximum of 0.65 kg/m3•d, which was 27.45% higher than that without applied voltage. Besides, applied voltage reduced the microbial diversity of MAB-based consortia, but the relative abundance of Candidatus Scalindua increased by 4.63% at 1.5 V compared with that without applied voltage. Also, proper applied voltage promoted the secretion of EPS and heme c, which resulted in the enhancement of MAB activity. Based on the remodified Logistic model analysis, the lag time of the nitrogen removal process was shortened by 0.72 h at the voltage of 1.5 V. Furthermore, it was found that higher voltage (> 2.0 V) had a negative effect on the MAB activity for low TNRR of 0.33 kg/m3•d (2.5 V). However, TNRR increased back to 0.61 kg/m3•d after removing the high applied voltage, which implied that the bioactivity was recoverable after being inhibited. These findings demonstrated that external electrical stimulation is an effective strategy to promote nitrogen removal and MAB activity for treating saline wastewater.

Enhanced treatment of low-temperature and low carbon/nitrogen ratio wastewater by corncob-based fixed bed bioreactor coupled sequencing batch reactor

In this study, a combined corncob-based fixed bed bioreactor and sequencing batch reactor system (CCF-SBR) was developed to treat low-temperature (3–12 °C) and low carbon/nitrogen ratio (C/N = 2) wastewater with a single SBR as the control. Results showed similarly low COD concentration of CCF-SBR (20.4 ± 3.7 mg·L−1) and control SBR (24.9 ± 6.7 mg·L−1) effluent. However, the total nitrogen (TN) removal rate of CCF-SBR was significantly higher than that of control SBR (29.6 ± 2.7% vs 8.6 ± 2.3%). According to the nitrification and denitrification activities and the analysis of microbial community, CCF mainly played the role of denitrification based on fermentation genera and denitrifying genera, and SBR mainly implemented nitrification with Nitrospira and Acinetobacter. This study explores a promising way for agricultural waste resource utilization and wastewater treatment under low-temperature and low C/N ratio.

Does rice straw addition and/or Vallisneria natans (Lour.) planting contribute to enhancement in nitrate nitrogen and phosphorus removal in constructed wetlands under low temperature?

It is a global concern that nitrogen and phosphorus removal performances of constructed wetlands (CWs) are limited during cold weather. This study analyzed nutrient removal efficiencies and mechanisms in six CWs including combinations between evergreen submerged vegetation planting and rice straw adding under low temperature. The results showed that both unvegetated and vegetated CWs achieved the highest removal rates of total nitrogen (TN) (85.1–86.6%) and NO3–-N (98.2–98.7%) with increases of approximately 56% and 68% by adding rice straw in water, respectively. Moreover, microbial denitrification accounted for reduction in over 70% of influent TN load. Planting vegetation, adding rice straw or their combination could all improve total phosphorus removal. Compared with adding rice straw in sediment, more diversifying bacterial community and higher abundances of some anaerobic fermentative species in the rice straw biofilm might have contributed to higher nitrogen removal in CWs with rice straw added in water.

Mainstream nitritation and denitritation in a pilot-scale multi-cycle sequencing batch reactor

Addition of external carbon sources for deep nitrogen removal highly increased the cost of municipal wastewater treatment. In this study, a carbon-saving nitritation and denitritation process was developed in a pilot-scale multi-cycle sequential batch reactor over 230 days. In the first three stages, the effluent total nitrogen (TN) concentration of the pilot plant without external carbon addition was similar to that of the on-site cyclic activated sludge system with external carbon addition. A highest nitrite accumulation rate (57.3%) and TN removal rate (85.1%) was observed, respectively, under conditions that temperature of 28.3 °C, dissolved oxygen concentrations of 2.0 mg/L and COD/N ratios of 4.5:1 as well as a short oxic phase (32.8 min). As the influent TN decreased after heavy rain, NOB could still be suppressed by shortening oxic phase and lowering DO (1.5 mg/L). In winter, slight nitrite accumulation was still obtained by adding glucose in stage IV. Nitrite competition between NOB and denitrifiers was indeed the key to NOB suppression. It should be a good choice for wastewater treatment plants to achieve high discharge standard and save carbon source using such a proposed process.

Impact of influent strengths on nitrous oxide emission and its molecular mechanism in constructed wetlands treating swine wastewater

Constructed wetlands (CWs) can remove nitrogen (N) through plant assimilation and microbial nitrification and denitrification, while it also releases large greenhouse gas nitrous oxide (N2O) into the atmosphere. However, N2O emissions and the underlying microbial mechanisms of CWs when treating high-strength wastewater have not been systematically surveyed. Here, the effect of three influent strengths on N2O emissions in a pilot-scale CW treatment of swine wastewater was determined and the underlying microbial mechanisms were explored. The results showed that the removal rates of ammonium (NH4+) and total nitrogen (TN) increased significantly with the increasing influent strengths, however, the ratio of N2O emission/TN removal rose by 1.5 times at the same time. Quantitation of microorganisms responsible for N-cycle in the sediment indicated that the abundance of ammonia-oxidizing bacteria (AOB) in high influent strengths (COD, 962.38 ± 3.05 mg/L; NH4+, 317.89 ± 4.24 mg/L) was 51.6-fold compared with that in low influent strengths (COD, 516.94 ± 4.18 mg/L; NH4+, 100.65 ± 2.65), and AOB gradually replaced ammonia-oxidizing archaea (AOA) to dominate ammonia oxidizers. Structural equation models demonstrated that NO2− accumulations promoted the ratio of AOB/AOA, which further led to an increase in the ratio of N2O emission/TN removal. It is worth noting both the N removal rates and N2O emissions increased with the increasing influent strength. To obtain reduced N2O emissions, pretreatment technology for strength reduction should be supplemented before high-strength wastewater enters the CWs. This study may shed new light on the sustainable operation and application of CWs.