Nitrogen Removal Rate Research Articles

Effect of biochar on the SPNA system at ambient temperatures

Biochar has been extensively studied in wastewater treatment systems. However, the role of biochar in the single-stage partial nitritation anammox (SPNA) system remains not fully understood. This study explored the impact of biochar on the SPNA at ambient temperatures (20 °C and 15 °C). The nitrogen removal rate of the system raised from 0.43 to 0.50 g N/(L·d) as the biochar addition was raised from 2 to 4 g/L. Metagenomic analysis revealed that gene abundances of amino sugar metabolism and nucleotide sugar metabolism, amino acid metabolism, and quorum sensing were decreased after the addition of biochar. However, the gene abundance of enzymes synthesizing NADH and trehalose increased, indicating that biochar could stimulate electron transfer reactions in microbial metabolism and assist microorganisms in maintaining a steady state at lower temperatures. The findings of this study provide valuable insights into the mechanism behind the improved nitrogen removal facilitated by biochar in the single-stage partial nitritation anammox system.

Effect of hydrofluoric acid-modified Co3O4/Y-type molecular sieves on MFC performance

Microbial fuel cell (MFC) is a green technology that facilitates resource utilization of wastewater by generating electricity while degrading organic and ammonia nitrogen pollutants. The anode plays a crucial role in the MFC performance, demanding excellent electrochemical performance and high stability. In this paper, a new high-performance anode of Co3O4 composite Y molecular sieve (Co3O4/Y) was prepared, and the effect of the Co3O4 ratio and hydrofluoric acid (HF) modification on the Co3O4/Y performance was also investigated. The results showed that the Co3O4/Y, synthesized through the hydrothermal method with 30 wt% loading of Co3O4 followed by 10 % HF treatment, demonstrated superior electrochemical performance, which had the highest redox peak current density, the largest current response area, and the maximum exchange current density of 0.038 mA/cm2. Four anode catalysts of MFC, namely, blank carbon cloth (CC), Co3O4-CC, Co3O4/Y-CC, and H-Co3O4/Y-CC were prepared, and four groups of MFCs were constructed for the treatment of mixed wastewater consisting of the aged landfill leachate and shale gas fracturing wastewater. Notably, the H-Co3O4/Y-CC group showed the best performance in power generation, achieving a maximum stabilized output voltage (448 mV), a maximum power density (1179 mW/m2), and a minimum apparent internal resistance (466 Ω). Additionally, the removal rate of ammonia nitrogen exceeded 40 % in the mixed wastewater of the 4 groups of MFCs. This study provided a viable strategy for fabricating high-performance MFC anode materials and offered insights into the simultaneous disposal of domestic and industrial wastewater in MFCs.

FAST START-UP MARINE ANAMMOX PROCESS USING INTENSIVE SHRIMP POND SOLID WASTE AS INOCULUM IN FILTER BIOREACTOR

Intensive shrimp culture waste contains high nitrogen, which can reduce water quality and environmental-carrying capacity. Anaerobic ammonium oxidation (anammox) is a potential and economical nitrogen removal process. However, limited information is available on the application of anammox process in aquaculture. The purpose of this study was to start up an anammox process in two filter bioreactors (FtBR) based on different inoculums. Run 1 used intensive shrimp solid waste, and Run 2 used intensive shrimp solid waste and granular of fresh anammox bacteria belonging to Candidatus Brocadia fulgida. Ammonium and nitrite concentrations of 70-100 mg N L-1 each were added to filtered and sterilized seawater as synthetic wastewater and flowed to the reactor with HRT 24-hour. After 120 days, the maximum ammonium conversion efficiency (ACE), nitrogen removal efficiency (NRE), and nitrogen removal rate (NRR) for Run 1 and 2 were 82.48%, 72.58%, 0.12 kg N (m3·d)-1 and 83.06%, 63.59%, 0.10 kg N (m3·d)-1, respectively. Experiment nitrogen stoichiometric ratios of NH4+:NO2-:NO3- were 1:1.40:0.12 and 1:1.13:0.14, which were close to the stoichiometry of the anammox process. Fast start-up of anammox process was achieved using intensive shrimp solid waste as inoculum. Anammox can be a new method for developing intensive shrimp culture wastewater treatment.

Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by Fe(Ⅲ)

The rapid enrichment of anammox bacteria and its fragile resistance to adverse environment are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation, nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III) (R5). These enhanced pathways were crucial to energy generation, nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Ca. Brocadia and facilitating their resistance to adverse environments. Microbial community analysis showed that the proportion of Ca. Brocadia in R5 also increased to 64.42 %. Hence, R5 could adapt rapidly to the increased nitrogen loading rate and increase the nitrogen removal rate by 108 % compared to the system without Fe(III) addition. However, the addition of 10 and 20 mg/L Fe(III) showed inhibitory effects on the growth and activity of anammox bacteria, which exhibited the lower relative abundance of Ca. Brocadia and unstable or even collapsed nitrogen removal performance. This study not only clarified the concentration range of Fe(III) that promoted and inhibited the enrichment of anammox bacteria, but also deepened our understanding of the functional and metabolic mechanisms underlying enhanced enrichment of anammox bacteria by Fe(III), providing a potential strategy to hasten the start-up of anammox from conventional activated sludge.

Novel anammox granules formation from conventional activated sludge for municipal wastewater treatment through flocs management

The direct integration of anammox process into municipal wastewater treatment has caused widespread concern, but the lack of anammox seeds limited its real application. This study successfully cultivated anammox granules (322.0 μm) from conventional activated sludge treating municipal wastewater. Through ultra-low floc sludge retention times of 8d, nitrifiers on flocs were eliminated and partial nitrification was realized. Furthermore, highly bacteria-enriched granules were initially formed, with Nitrosomonas and Ca. Competibacter 4-fold higher than that of flocs. Specific staining results revealed the microbial interaction with Ca. Brocadia, considering that Ca. Competibacter and Nitrosomonas correspondingly identified in the inner and outer layers of granules. The percentage of Ca. Brocadia present on the granules increased substantially from 0.0 % to 3.0 %, accompanied by a nitrogen removal rate of 0.3 kg·m−3·d−1. Our findings revealed a valuable reference for the anammox bacteria in-situ enrichment under mainstream conditions, which provides theoretical guidance for anammox-based processes practical application.

A new model to estimate shallow lake nitrogen removal rate based on satellite derived variables

Lake nitrogen (N) removal, mainly resulting from bacterial denitrification that converts nitrate (NO3 −) to gaseous N (N2), is important for lake water quality and eutrophication control. However, quantifying lake N removal is challenging due to the high background atmosphere N2 concentration and the heavy burden of field surveys, leading to a decoupling of watershed N management and water quality improvement. Here, we developed and validated an innovative nonlinear model for lake N removal rate estimation by linking the N removal rates with remote sensing-derived variables (chlorophyll-a, chromophoric dissolved organic matter, and lake surface water temperature). The model was validated in shallow eutrophic Lake Taihu in the Yangtze River basin and at the global scale. Based on the new N removal model, we estimated that an annual average of 3.21 × 104 t N yr‒1 was removed in Lake Taihu from 2011 to 2020, accounting for 53%–66% of the total lake N loading. The remaining N loading after denitrification removal in Lake Taihu would be approximately 2.37 mg N l‒1, and 0.79 × 104 t N y‒1 of lake N loading still needs to be removed to meet the target of class IV water quality (1.5 mg N l‒1). This is the first study linking lake N removal in sediment microcosm incubations with reach-scale remote sensing derived variables, providing timely-much insights into lake N removal. This approach can be easily applied in other lakes with satellite derived data, to better understand lake N budget, drivers of eutrophication control, and watershed N management.

Preparation and application of microfiltration porous coal gangue–loess‐based ceramic membrane

AbstractThe ceramic membrane is widely used in the field of domestic sewage treatment due to its high flexural strength, acid and alkali corrosion resistance, easy cleaning, and other advantages. This article uses coal gangue and loess as the main raw material (coal gangue:loess = 8:2), calcium carbonate as the pore‐forming agent, and carboxymethyl cellulose as the binder. The ceramic membrane was prepared by extrusion molding method and solid particle sintering method. The effects of pore‐forming agent content and sintering temperature on the physical and chemical properties of the ceramic membrane, such as flexural strength, microstructure, pure water flux, and acid‐base corrosion rate, were investigated. The results show that when the sintering temperature is 1000°C and the pore‐forming agent content is 10wt%, the pure water flux exceeds 1434L/h m2 MPa, the flexural strength exceeds 25.4 MPa, the porosity exceeds 46.9%, and the acid‐alkali corrosion rate of the ceramic membrane below 1.6%/0.15%. At this time, the treatment efficiency of domestic sewage is excellent, the removal rate of COD, suspended solids and ammonia nitrogen exceeds 27.66%, 99.9%, and 26.77%, respectively. This work has trend‐setting significance for the fabrication and application of low‐cost ceramic membranes.

Formation of autotrophic nitrogen removal granular sludge driven by the dual-partition airlift internal circulation: Insights from performance assessment, community succession, and metabolic mechanism

Granular sludge has been recognized as an effective method for the application and industrialization of the anammox-based process due to its good biomass retention capacity and environmental tolerance. In this study, a one-stage autotrophic nitrogen removal (ANR) dual-partition system with airlift internal circulation was implemented for 320 days. A high nitrogen removal efficiency of 84.6% was obtained, while the nitrogen removal rate reached 1.28 g-N/L/d. ANR granular sludge dominated by Nitrosomonas and Candidatus Brocadia was successfully cultivated. Results showed that activity and abundance of functional flora first increased with granulation process, but eventually declined slightly when particle size exceeded the optimal range. Total anammox activity was observed to be significantly correlated with protein content (R2 = 0.9623) and nitrogen removal performance (R2 = 0.8796). Correlation network revealed that AnAOB had complex interactions with other bacteria, both synergy for nitrogen removal and competition for substrate. Changes in abundances of genes encoding the Carbohydrate Metabolism, Energy Metabolism, and Membrane Transport suggested energy production and material transfer were possibly blocked with further sludge granulation. Formation of ANR granular sludge promoted the interactions and metabolism of functional microorganisms, and the complex nitrogen metabolic pathways improved the performance stability. These results validated the feasibility of granule formation in the airlift dual-partition system and revealed the response of the ANR system to sludge granulation.

Functional differentiation of size-fractionated biomass in the mixotrophic mainstream UASB-anammox process

The soluble organic matter in sewage is one of the major obstacles to the stable operation of mainstream anammox, which would induce the excessive proliferation of heterotrophic bacteria. Given its excellent volumetric nitrogen removal rate (>2.0 kg N m−3 d−1) in mainstream treatment at 15 °C, the physicochemical properties and microbial ecology of size-fractionated aggregates in mixotrophic anammox-UASB system were investigated to develop strategies for population management. The presence of glucose or acetate (COD/N = 1.0) decreased the contribution of anammox by approximately 30 %, thereby causing the increase of effluent TN concentrations to over 12 mg N L−1, in which NH4+-N accounted for ∼85 %. Interestingly, the relative abundance of anammox bacteria were increased from 1.0 % in flocs (<0.2 mm) to 34.9 % in big granules (>0.8 mm) of the acetate-fed reactor, while the abundance of denitrifying bacteria was decreased from 74.0 % in flocs to 12.0 % in big granules. Similar trend was also observed for the glucose-fed reactor. As a result, the expressions of anammox functional genes, specific anammox activity, extracellular polymeric substances and heme c contents were all increased with the increase of particle sizes. Notably, in contrast to the glucose-fed biomass, the acetate-fed biomass showed significant potential of denitratation. Accordingly, the screen with a size of around 0.2 mm may be an effective tool to uncouple the retention times of denitrifying bacteria and anammox bacteria. These results provided direct evidences for functional differentiation of size-fractionated biomass and would guide us to balance their functions for a satisfactory effluent quality.

Deciphering the role of hydraulic retention time (HRT) in integrated fixed-film activated sludge (IFAS) system under aniline stress: Effects on microbial succession and communication

Integrated fixed-film activated sludge (IFAS) system offered an energy-efficient option for nitrogen removal from aniline wastewater. The regulation of hydraulic retention time (HRT) has been reported to affect the fate of functional microbial communities with different generation cycles, but the role of HRT in IFAS under aniline stress has not been sufficiently revealed. Herein, it was observed that shortening the HRT altered the mechanisms underlying the adaptation of a continuous flow micro-aerated IFAS system to aniline stress, thereby negligibly impacting the removal of aniline. The total nitrogen removal rate in Y2 (HRT = 0.5 day) was 40.28 % higher than Y1 (1 day), and 23.7 % higher than Y3 (0.25 day). This could be attributed to Y2 having an ample supply of electron donors for denitrification compared to Y1, as well as showing weaker stress to inhibit nitrification compared to Y3. Furthermore, with the progressive intensification of stress induced by HRT reduction, microorganisms gradually enhanced their adaptation to aniline. This led to an increased migration of microorganisms towards the inner layers of the biofilm, resulting in enhanced functional complementarity between the sludge and biofilm in Y2. Also, there was a distinct development of autotrophic denitrification, with arenimonas predominant in Y1, and Thauera predominant in Y2 and Y3. Moreover, Y2 possessed a high abundance of functional genes related to the production and reception of quorum sensing signal molecules, which may enhance the electron transport-dependent nitrogen metabolism reaction.

Diversity of Anammox Bacteria from Landfill Treatment Plant Sludge in Tropical Area

The anaerobic ammonium oxidation (anammox) process is known as the warm process. Tropical areas have an advantage due to their consistent temperature throughout the year. This study analyzed the diversity of anammox bacteria in the tropical area using leachate sludge from a landfill as an inoculum in a filter bioreactor (FtBR) and observed nitrogen removal performance. Ammonium and nitrite concentrations of 70, 150, and 200 mg-N/L were delivered into the reactor continuously with hydraulic retention time (HRT) of 24 h and 12 h and run for 131 days at ambient tropical temperature (25–28 °C). High performance achieved with nitrogen removal rate (NRR), nitrogen removal efficiency (NRE), and ammonium conversion efficiency (ACE) were 0.866 kg-N/m3.d, 99.19%, and 98.90%, respectively. The cultivated leachate sludge could perform an anammox process with four anammox species, Candidatus Brocadia fulgida, Candidatus Brocadia sapporoensis, Candidatus Brocadia sp uncultured, Candidatus Jettenia sp with abundance 6.52%, 13.82%, 0.77%, and 0.69%, respectively. These findings contribute to the advancement of biotechnology in wastewater treatment, particularly in tropical countries, and highlight the potential for highly cost-effective technology.

Treatment of nitrogen and phosphorus from sewage tailwater in paddy rice wetlands: concept and environmental benefits.

Domestic sewage tailwater (DSTW) reuse for crop irrigation is considered a promising practice to reduce water demand, mitigate water pollution, and substitute chemical fertilization. The level of the above environmental benefits of this water reuse strategy, especially when applied to paddy wetlands, remains unclear. In this study, soil column experiments were conducted to investigate the nitrogen and phosphorus fate in paddy wetlands subjected to different tailwater irrigation and drainage strategies, specifically, (i) TW1 and TW2 for regular or enhanced irrigation-drainage without N fertilization, (ii) TW3 and TW4 for regular irrigation with base or tillering N fertilizer, (iii) conventional fertilization N210, and (iv) no-fertilization controls N0. The results showed that the total nitrogen (TN), nitrate (NO3-), and total phosphorus (TP) removal rates from the paddies irrigated by DSTW ranged between 51.92 and 59.34%, 68.1 and 83.42%, and 85.69 and 86.98% respectively. Ammonia emissions from the DSTW-irrigated treatments were reduced by 14.6~47.2% compared to those paddies subjected to conventional fertilization (N210), similarly for TN emissions, with the exception of the TW2 treatment. Overall, it is established that the paddy wetland could effectively remove residual N and P from surface water runoffs, while the partial substitution of chemical fertilization by DSTW could be confirmed. The outcome of this study demonstrates that DSTW irrigation is a promising strategy for sustainable rice production with a minimized environmental impact.

Unraveling potential mechanism of different metal ions effect on anammox through big data analysis, molecular docking and molecular dynamics simulation

Heavy metals (HMs) have been widely reported to pose an adverse effect on anaerobic ammonia oxidation (anammox) bacteria, yet the underlying mechanisms remain unclear. This study provides new insights into the potential mechanisms of interaction between HMs and functional enzymes through big date analysis, molecular docking and molecular dynamics simulation. The statistical analysis indicated that 10 mg/L Cu(II) and Cd(II) reduced nitrogen removal rate (NRR) by 85% and 43%, while 5 mg/L Fe(II) enhanced NRR by 29%. Additionally, the results of molecular simulations provided a microscopic interpretation for these macroscopic data. Molecular docking revealed that Hg(II) formed a distinctive binding site on ferritin, while other HMs resided at iron oxidation sites. Furthermore, HMs exhibited distinct binding sites on hydrazine dehydrogenase. Concurrently, the molecular dynamics simulation results further substantiated their capacity to form complexes. Cu(II) displayed the strongest binding affinity with ferritin for −1576 ± 79 kJ/mol in binding free energy calculation. Moreover, Cd(II) bound to ferritin and HDH for −1052.67 ± 58.49 kJ/mol, −290.02 ± 49.68 kJ/mol, respectively. This research addressed a crucial knowledge gap, shedding light on potential applications for remediating heavy metal-laden industrial wastewater.

Cattle wastewater treatment using green microalga Coelastrella sp. KNUA068 as a promising bioenergy feedstock with enhanced biodiesel quality.

Global water scarcity increased the demand for clean water, leading to attention on microalgae-based biological treatment for wastewater due to economic feasibility and sustainable biomass applications. This study isolated indigenous microalga Coelastrella sp. KNUA068 from a wastewater treatment plant, observed its admissible growth rate in diluted cattle wastewater (DCW), and used it for wastewater treatment analysis. The microalga showed high growth rates in indoor and outdoor cultivation with 100% DCW. In addition, the ammonia nitrogen and nitrate nitrogen removal rates of the microalga were 69.97 and 60.35%, respectively, in indoor cultivation, and 50.63 and 67.20%, respectively, in outdoor cultivation. Carotenoid content analysis revealed lutein as the highest productivity carotenoid, and zeaxanthin production was higher in outdoor cultivation. The biomass exhibited suitable biodiesel quality with a cetane number of 50.8 for high-quality biodiesel production. Coelastrella sp. KNUA068 demonstrates potential for bioenergy feedstock, carotenoid production, and wastewater treatment.

Layered double hydroxide@zeolite composite modified sponge: A versatile biocarrier for enhancing nitrogen removal in biofilters

Conventional denitrification filters exhibit limited nitrogen removal efficiency in micropolluted surface waters with high dissolved oxygen levels (6 ∼ 8 mg/L). In this study, an innovative denitrification biofilter with a novel modified sponge biocarrier, composed of a layered double hydroxide@zeolite composite (LZMC) was employed to enhance the removal of nitrogen from surface waters. Based on the response surface methodology, an LZMC with high nitrogen adsorption performance was prepared. The greatest enhancement in the denitrification efficiency in the LZMC reactor was 30.62 % compared with the control reactor, and the total nitrogen removal rate reached 91.39 % under optimal conditions. Improving the carrier surface characteristics effectively boosted biofilm formation , increased biomass accumulation, and the abundance of dominant denitrifying bacteria. Additionally, the LZMC effectively accelerated electron transfer due to its high conductivity, which promoted related gene expression and enzyme activity. In conclusion, this study presents a viable route to facilitate nitrogen removal in micropolluted surface waters.

Communication mediated interaction between bacteria and microalgae advances photogranulation

Recently, photogranules composed of bacteria and microalgae for carbon-negative nitrogen removal receive extensive attention worldwide, yet which type of bacteria is helpful for rapid formation of photogranules and whether they depend on signaling communication remain elusive. Varied signaling communication was analyzed using metagenomic method among bacteria and microalgae in via of two types of experimentally verified signaling molecule from bacteria to microalgae, which include indole-3-acetic acid (IAA) and N-acyl homoserine lactones (AHLs) during the operation of photo-bioreactors. Signaling communication is helpful for the adaptability of bacteria to survive with algae. Compared with non-signaling bacteria, signaling bacteria more easily adapt to the varied conditions, evidenced by the increased abundance in the operated reactors. Signaling bacteria are easier to enter the phycosphere, and they dominate the interactions between bacteria and algae rather than non-signaling bacteria. The co-abundance groups (CAGs) with signaling bacteria possess higher abundance than that without signaling bacteria (22.27 % and 6.67 %). Importantly, signaling bacteria accessibly interact with microalgae, which possess higher degree centralities and 32.50 % of them are keystone nodes in the network, in contrast to only 18.66 % of non-signaling bacteria. Thauera carrying both IAA and AHLs synthase genes are highly enriched and positively correlated with nitrogen removal rate. Our work not only highlights the essential roles of signaling communication between microalgae and bacteria in the development of photogranules, but also enriches our understanding of microbial sociobiology.

Mitigation of fouling problem and optimization of treatment effect in the polyvinylidene fluoride (PVDF) based electrochemical membrane bioreactor (EMBR)

The hydrophobic polyvinylidene fluoride (PVDF) membrane is one of the most widely used membrane material in the treatment of domestic sewage, while it still endures the fouling problem. Many studies have focused on the fouling control, among which the electrochemical membrane bioreactor (EMBR) is promising because of its chemical-free nature, but the specific influence of applied electric field on the mitigation of membrane fouling and the treatment effect are unclear and need further exploration. In this work, the influence and interaction of operation parameters (operation voltage, electrode spacing, power-on mode, and hydraulic retention time) on fouling development and pollutants removals in a PVDF based EMBR were carefully explored for the optimal operating conditions. Results showed that the run time of EMBR system under optimal conditions was 23.4 % longer than that of the MBR system without a weak electric field, indicating that the membrane fouling problem was well alleviated. In addition, the effluent quality of EMBR was also improved than that treated by the MBR system. The removal rates of chemical oxygen demand, ammonia nitrogen, total phosphorus, and total nitrogen were increased by 2.25 %, 2.64 %, 9.02 %, and 12.1 %, respectively, revealing the improvement of this EMBR system in sewage treatment. This work shows that introduction of a weak electric field in MBR system not only effectively controls membrane fouling, but also increases the effluent quality, and thus endows EMBR as a candidate for sustainable and green technique in sewage treatment.

Integration of hydrothermal liquefaction of Cyanophyta and supercritical water oxidation of its aqueous phase products: Biocrude production and nutrient removal

Cyanophyta has the potential to produce biocrude via hydrothermal liquefaction (HTL). However, aqueous phase products (APs), as by-products of HTL, pose a risk of eutrophication for the high levels of carbon, nitrogen, and phosphorus. Supercritical water oxidation (SCWO) can efficiently convert organics into small molecules, offering a technique for the harmless treatment of APs. Effects of holding time, pressure, and moisture content on the biocrude yields from isothermal HTL (300 °C) and fast HTL (salt bath temperature of 500 °C) were comprehensively investigated. Biocrude properties were characterized by elemental analysis, FT-IR and GC–MS. Subsequently, the APs obtained under the conditions producing the highest biocrude yield were subjected to SCWO at 550 °C with different oxidation coefficients (n) from 0 to 2. Removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3−N), and total phosphorus (TP) were further explored. The results show that the highest biocrude yields from isothermal HTL and fast HTL were 24.2 wt% (300 °C, 1800 s, 25 MPa, and 80 wt% moisture content) and 21.9 wt% (500 °C, 40 s, 25 MPa, and 80 wt% moisture content), respectively. The biocrude primarily consisted of N-containing heterocyclic compounds, amides, and acids. SCWO effectively degraded the COD and TP in APs, while the NH3-N required further degradation. At n = 2, the highest removal rates of COD, NH3-N and TP were 98.5 %, 22.6 % and 89.1 %, respectively.

Submerged macrophyte promoted nitrogen removal function of biofilms in constructed wetland

Biofilm is one of the important factors affecting nitrogen removal in constructed wetlands (CWs). However, the impact of submerged macrophyte on nitrogen conversion of biofilms on leaf of submerged macrophyte and matrix remains poorly understood. In this study, the CWs with Vallisneria natans and with artificial plant were established to investigate the effects of submerged macrophyte on nitrogen conversion and the composition of nitrogen-converting bacteria in leaf and matrix biofilms under high ammonium nitrogen (NH4+-N) loading. The 16S rRNA sequencing method was employed to explore the changes in bacterial communities in biofilms in CWs. The results showed that average removal rates of total nitrogen and NH4+-N in CW with V. natans reached 71.38% and 82.08%, respectively, representing increases of 24.19% and 28.79% compared with the control with artificial plant. Scanning electron microscope images indicated that high NH4+-N damaged the leaf cells of V. natans, leading to the cellular content release and subsequent increases of aqueous total organic carbon. However, the specific surface area and carrier function of V. natans were unaffected within 25 days. As a natural source of organic matters, submerged macrophyte provided organic matters for bacterial growth in biofilms. Bacterial composition analysis revealed the predominance of phylum Proteobacteria in CW with V. natans. The numbers of nitrifiers and denitrifiers in leaf biofilms reached 1.66 × 105 cells/g and 1.05 × 107 cells/g, as well as 2.79 × 105 cells/g and 7.41 × 107 cells/g in matrix biofilms, respectively. Submerged macrophyte significantly increased the population of nitrogen-converting bacteria and enhanced the expressions of nitrification genes (amoA and hao) and denitrification genes (napA, nirS and nosZ) in both leaf and matrix biofilms. Therefore, our study emphasized the influence of submerged macrophyte on biofilm functions and provided a scientific basis for nitrogen removal of biofilms in CWs.

Adsorption Performance of Different Wetland Substrates for Ammonia Nitrogen: An Experimental Study

To investigate the adsorption performance of different substrates for ammonia nitrogen in wastewater, adsorption experiments are conducted on four substrates, namely, zeolite, quartz sand, volcanic rock, and biological ceramsite, and the experimental data are analyzed using adsorption isotherms and three kinetic models. The results show that with the increasing dosage of the substrates, the adsorption capacity gradually decreases, and the removal rate gradually increases. The removal rates all show a rapid increase in the early stage (the first 14 h) and gradually reach a stable state in the later stage (after more than 48 h). The higher the concentration of ammonia nitrogen in the NH4Cl solution, the greater the unit adsorption capacity of ammonia nitrogen by the substrate, the longer the adsorption time required to reach adsorption equilibrium, the lower the total removal rate of ammonia nitrogen, and the longer it takes for the concentration of ammonia nitrogen in the substrate and solution to reach equilibrium. The adsorption capacity of zeolite to ammonia nitrogen is much higher than that of quartz sand, biological ceramsite, and volcanic rock, so zeolite is suitable as the wetland substrate. The adsorption of ammonia nitrogen by the four substrates is principally multi-molecular layer adsorption, and the adsorption phase is heterogeneous.