Highest Total Nitrogen Removal Efficiency Research Articles

Enhancing simultaneous nitrification and denitrification in a plant-scale integrated fixed-film activated sludge system: Focusing on the cooperation between activated sludge and biofilm

To further remove nutrients through simultaneous nitrification and denitrification (SND), the integrated fixed-film activated sludge (IFAS) system has become one of the most efficient pathways for modifying the existing wastewater treatment plants. This study investigated the cooperation between suspended activated sludge and carrier-attached biofilm for promoting SND in different seasons in a plant-scale IFAS system. The results showed that the involvement of biofilm could stimulate SND, removing 23.9 % of influent total nitrogen (TN) in the aerobic IFAS system. The nitrification rate and the SND ratio were much influenced by the temperature, resulting in higher TN removal efficiency in summer (90.3 %) than that in winter (86.4 %). The highest SND ratio of 67 % could be achieved at the temperature of 23 °C. Additionally, the SND ratio also depended on a variety of operational parameters (such as dissolved oxygen (DO), COD/NH4+-N, and mixed liquor suspended solids (MLSS)). High-throughput sequencing technology further confirmed that the composition of the functional bacterial communities in activated sludge significantly differed from that in biofilm. Nitrifying bacteria were mostly detected in biofilm samples, while more denitrifying bacteria existed in activated sludge, thus resulting in the enhancement of synergic nitrogen removal via SND in the IFAS system.

Optimizing nitrogen removal in constructed wetlands for low C/N ratio wastewater treatment: Insights from fermentation liquid utilization

The inefficient nitrogen removal in constructed wetlands (CWs) can be attributed to insufficient carbon sources for low carbon-to-nitrogen (C/N) ratio wastewater. In this study, sugarcane bagasse fermentation liquid (SBFL) was used as a supplemental carbon source in intermittently aerated CWs to enhance nitrogen removal. The impact of different regulated influent C/N ratios on nitrogen removal and greenhouse gas (GHG) emissions was investigated. Results demonstrated that SBFL addition significantly enhanced the denitrification capacity, resulting in faster NO3--N removal compared to sucrose. Moreover, intermittently aerated CWs significantly improved NH4+-N removal efficiency compared to non-aerated CWs. The highest total nitrogen removal efficiency (98.3 %) was achieved at an influent C/N ratio of 5 in intermittently aerated CWs with SBFL addition. The addition of SBFL resulted in a reduction of N2O emissions by 17.8 %–43.7 % compared to sucrose. All CWs exhibited low CH4 emissions, with SBFL addition (0.035–0.066 mg·m-2h-1) resulting in lower emissions compared to sucrose. Additionally, higher abundance of denitrification (nirK, nirS and nosZ) genes as well as more abundant denitrifying bacteria were shown in CWs of SBFL inputs. The results of this study provide a feasible strategy for applying SBFL as a carbon source to improve nitrogen removal efficiency and mitigate GHG emissions in CWs.

Enhance PD/A biofilm formation via a novel biochar/tourmaline modified-biocarriers to treat low-strength contaminated surface water: Initial adhesion and high-substrate microenvironment

In this work, a novel polyurethane carrier modified with biochar and tourmaline/zeolite powder at ratio of 1:1 and 1:2 was developed to promote the formation of biofilms and the synergy of overall bacterial activity for Partial Denitrification/Anammox to treat low-nitrogen contaminated surface water. Based on the batch experiment, the modified biocarrier, BTP2 (biochar: tourmaline = 2: 1), exhibited the highest total nitrogen removal efficiency (83.63%) under influent total nitrogen of 15 mg/L and COD/NO3− of 3. The dense biofilm was formed in inner side of biocarrier owing to the increased surface roughness and various functional groups suggested by scanning electron microscopy and Fourier-transform infrared analysis. The EPS content increased from 200.15 to 220.26 mg/g VSS in BTP2 system. Besides, the rapid NH4+ capture and organics release of the modified carrier fueled the growth of anammox and denitrification bacteria, with the activity of 2.13 ± 0.52 mg N/gVSS/h and 6.70 ± 0.52 mg N/gVSS/h (BTP2). High-throughput sequencing unraveled the increased abundances of Candidatus_Competibacter (0.82%), Thauera (0.60%) and Candidatus_Brocadia (0.55%) which was responsible for the synergy of incomplete reduction of NO3− to NO2− and NH4+ oxidation. Overall, this study provided a valid and simple-control guide for biofilm formation towards rapid enrichment and great collaboration of Anammox and denitrification bacteria.

A partial siphon operational strategy strengthens nitrogen removal performance in partially saturated vertical flow constructed wetlands

The carbon‒oxygen balance has always been problematic in constructed wetlands (CWs), putting pressure on stable and efficient nitrogen removal. In this study, a novel partial siphon operational strategy was developed to further optimize the carbon and oxygen distributions of a partially saturated vertical flow CW (SVFCW) to enhance nitrogen removal. The removal performances of the partial siphon SVFCW (S-SVFCW) were monitored and compared with those of the SVFCWs at different partial siphon depths (15 cm, 25 cm and 35 cm) in both the warm and cold seasons. The results showed that the partial siphon operating strategy significantly facilitated the removal of ammonia and total nitrogen (TN) in both the warm and cold seasons. When the partial siphon depth was 25 cm, the S-SVFCWs had the highest TN removal efficiency in both the warm (71%) and cold (56%) seasons, with an average improvement of 46% and 52%, respectively, compared with those of the SVFCWs. The oxidation‒reduction potential (ORP) results indicated that richer OPR environments and longer hydraulic detention times were obtained in the S-SVFCWs, which enriched the denitrification bacteria. Microbial analysis revealed greater nitrification and denitrification potentials in the unsaturated zone with enriched functional genes (e.g., amo_AOA, amo_AOB, nxrA and nirK), which are related to nitrification and denitrification processes. Moreover, the strengthening mechanism was the intensified oxygen supply and carbon utilization efficiency based on the cyclic nitrogen profile analysis. This study provides a novel partial siphon operational strategy for enhancing the nitrogen removal capacity of SVFCWs without additional energy or land requirements.

Adaptation of anammox process for nitrogen removal from acidic nitritation effluent in a low pH moving bed biofilm reactor.

Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4-5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH=4.6±0.2), the pH of an anammox reactor was self-sustained in the range of pH 5-6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7±3.9mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments.

Pilot Study of Oxic–Anoxic Process under Low Dissolved Oxygen for Nitrogen Removal from Low COD/N Tropical Wastewater

Conventionally, nitrification in biological nitrogen removal (BNR) requires high dissolved oxygen (DO) concentrations (>2 mg L−1), making the process energy intensive. Recent studies have shown that efficient ammonium removal and energy reduction can be realized by operating the nitrification at low DO concentrations (<1 mg L−1). In this study, the low-DO oxic anoxic (low-DO OA) process was operated in a pilot-scale sequencing batch reactor (SBR) over 218 days to evaluate the feasibility of nitrogen removal from low chemical oxygen demand-to-nitrogen ratio (COD/N) tropical municipal wastewater. The results revealed that the low-DO OA process attained high removal efficiency for ammonium (97%) and total nitrogen (TN) (80%) under an average DO concentration of 0.6 mg L−1. The effective TN removal efficiency is attributed to the occurrence of simultaneous nitrification–denitrification (SND) under low DO conditions. Further batch tests revealed that slowly biodegradable COD (sbCOD) in tropical wastewater can support denitrification in the post-anoxic phase, resulting in a high TN removal rate. Compared with high DO concentrations (2 mg L−1), low DO conditions achieved 10% higher TN removal efficiency, with similar ammonium and COD removal efficiency. This study is crucial in promoting the energy efficiency and sustainability of wastewater treatment plants treating low COD/N wastewater.

Microbial community dynamics and performance of simultaneous anammox and denitrification (SAD) process at varying substrate loadings during long-term operation

The simultaneous anammox and denitrification (SAD) process has attracted more and more attention due to its low energy consumption and high-efficiency, but its optimal operating conditions and the interspecies interactions between the main functional microorganisms anaerobic ammonia oxidation bacteria (AnAOB) and denitrifying bacteria (DNB) have not been fully elucidated. In this study, SAD was achieved by enriching DNB through the addition of sodium acetate to anammox granular sludge. Furthermore, the pollutant removal effect and the composition of the main functional microbial community under different organic loads were investigated by manipulating the influent C/N ratio. The results indicated that the reactor achieved the highest total nitrogen removal efficiency of 89.05% at a C/N ratio of 1 and the activity of AnAOB was inhibited on a higher C/N ratio, leading to the deterioration of effluent quality. Candidatus_Brocadia was the dominant genus of AnAOB, reaching a maximum relative abundance of 0.49% at a C/N ratio of 1. DNB was also significantly enriched after the addition of sodium acetate, and the synergistic effect of the two functional bacteria contributed the simultaneous nitrogen and carbon removal of the SAD process.

C/N ratios inform sustainable aerobic denitrification for nitrogen pollution control: Insights into the key parameter from a view of metabolic division

Aerobic denitrification is a feasible and sustainable process for nitrogen removal in environmental protection. The C/N ratio was the vital one that has a significant impact on the performance. However, comprehension of the C/N ratio effect on this bioprocess was not well clarified. In this study, the response of an aerobic denitrifier (Pseudomonas balearica strain RAD-17) to the C/N ratio was investigated from a view of metabolism. It was found that a high total nitrogen (TN) removal efficiency of about 95% was achieved with the dosing C/N ratio of 7.5, while only a slight increase when the dosing C/N ratios were further increased to a high range of 10–30. The carbon validity was out of sync with TN removal and a balance between the two was realizable at a dosing C/N ratio of 7.5 based on the economic consideration. Moreover, weakened assimilation while enhanced respiration along with the increased C/N ratios was revealed, evidenced by the decreased net intracellular nitrogen and increased nitrogenous gas proportions in nitrogen balance analysis. The growth characteristics in terms of cell number and OD600 showed a division for the high flux of nitrate and organics directed to assimilation and respiration, respectively. The expression levels of carbon and nitrate metabolism-related function genes in P. balearica supported the results above. The C/N ratio of 5.0–7.5 was supposed to be the turning region for the metabolism division between assimilation and respiration in aerobic denitrifying. The results are expected to offer a guideline for the decision made for organics supply for the aerobic denitrification process and support its sustainable application.

Enhancing anammox nitrogen removal by static magnetic field exposure: Performance, microbial community and symbiotic relationship analysis

Anammox batch reactors were operated with different static magnetic field (SMF) intensities (0 mT, 40 mT, and 100 mT). The impacts of SMF and the influent nitrogen concentration on nitrogen removal were analyzed. Sludge characteristics, microbial community structure, and metabolism pathways were explored. The results show that a high nitrogen load greatly decreased the nitrogen removal efficiency. Still, applying SMF with appropriate intensity enhanced the nitrogen removal performance, especially under high nitrogen loading conditions. Systems with 40 mT SMF at normal nitrogen loading conditions had the highest total nitrogen removal efficiency. In contrast, a higher SMF intensity was conducive to the anammox process with a high nitrogen load. Candidatus Kuenenia was fast enriched under high nitrogen loading conditions in the control systems. However, Candidatus Brocadia was more abundant than Ca. Kuenenia in the systems with SMF application. SMF was the main factor affecting the microbial metabolism, enhancing the metabolic pathways related to bacterial growth and resistance to environmental stress. The metabolic interactions between the anammox bacteria and other bacteria were enhanced by applying SMF to the anammox process, especially for the cross-feeding of cofactors and vitamins in the anammox consortia.

Simultaneous Organic Matter and Nitrogen Removal from Piggery Slaughterhouse Wastewater Using Bioaugmented Gaslift Membrane Bioreactor

AbstractA single bioaugmentation reactor and a side‐stream gaslift membrane bioreactor combined with bioaugmentation are conducted to treat real wastewater from a centralized piggery slaughterhouse in Vietnam. The bioaugmented reactor is inoculated with heterotrophic microorganisms (Bacillus sp.) isolated from piggery slaughterhouse wastewater. The results of a single bioaugmentation experiment show high removal efficiency of chemical oxygen demand (COD) (84.8%–97.5%) and total nitrogen (TN) (69.9%–87.2%) at loading rates of 1.28–3.89 and 0.14–0.37 kg m−3 d−1, respectively. The combined system demonstrates a significantly higher TN removal efficiency (89.0%–96.1%) (p < 0.001), more stable flux (36.0–38.4 L m−2 h−1), and transmembrane pressure (0.95–1.05 bar), and better capacity of separation of solid–liquid phases compared to the single bioaugmentation. High COD and TN removal efficiency is possibly due to assimilation and simultaneous nitrification and denitrification processes. The results of this study also indicate the feasibility and propitious efficiency of the bioaugmented gaslift membrane bioreactor for piggery slaughterhouse wastewater treatment.

Start-up and optimization of a one-stage partial nitrification-anammox (PN-A) process treating low ammonium concentration wastewater: experimental results and modeling investigation.

Although the partial nitrification-anammox process (PN-A) has achieved great success in nitrogen removal for the high ammonium concentration wastewater, its application is still limited in low ammonium concentration wastewater treatment due to its instability and low nitrogen removal efficiency. In this study, a sequencing batch reactor (SBR) with continuous aeration was employed to enrich ammonia oxidation bacteria (AOB) and suppress nitrite oxidation bacteria (NOB) first; then, the SBR was operated intermittently aerated SBR (IASBR), to which the anammox granular sludge (AMX) was added to achieve complete autotrophic nitrogen removal under low influent ammonium concentration of 100mg/L. A mathematical model was used to optimize the IASBR aeration strategy to achieve sub-optimal nitrogen removal. The experimental results showed that high nitrite accumulation efficiency (above 80%) in the SBR and a fast start-up within 100days and a stable TN (total nitrogen) removal efficiency of 70% were achieved in the IASBR. Meanwhile, the simulation results indicated that keeping aeration duration at 4h, kLa (oxygen transfer coefficient) at 50day-1, or aeration duration at 2.5h, kLa at 80day-1 could obtain a higher total nitrogen removal efficiency (TNR) (TNR > 80%), and the TN removal could also be improved by increasing hydraulic retention time (HRT) under the optimal oxygen supply rate.

Deciphering the coupling of partial nitrification/anammox and sulfur autotrophic denitrification: Microbial metabolism and antibiotic resistance genes propagation

Partial nitrification/anaerobic ammonium oxidation (anammox) (PN/A) was considered as an economically beneficial and environmentally friendly biological nitrogen removal process. The elimination of nitrate produced by PN/A system was the key to improving the total nitrogen removal efficiency (TNRE) of the system under mainstream conditions. In this study, the feasibility of the coupling S(0)-driven autotrophic denitrification (SAD) with PN/A in a single sequencing moving bed biofilm reactor (SMBBR) at room temperature was explored. Additionally, biological treatment process is ideal environments for the emerge and spread of emerging pollutants antibiotic resistance genes (ARGs), therefore, the shifts of ARGs in the system were investigated. After the coupling of PN/A and SAD, SMBBR was steadily operated with high TNRE. Nitrite-oxidizing bacteria (Nitrospira and Candidatus Nitrotoga) and nitrite oxidoreductase enzyme were inhibited by SAD process. And anammox bacteria were enriched, especially oligotype GAGTTTAAT of Ca. Brocadia. Sulfurimonas became the predominant autotrophic denitrifier. Heterotrophic denitrifiers Thauera and Dechloromonas were elutriated out from the system during the coupling of PN/A and SAD process, and they might be potential hosts for ARGs, leading to the decrease of ARGs. Overall, this study proposed a new strategy that SAD could promote the TNRE of PN/A and cut the risks of ARGs propagation, and PN/A-SAD coupling system was a biological nitrogen removal technology with promising applications under mainstream conditions.

Nitrogen removal and microbial mechanisms in a novel tubular bioreactor-enhanced floating treatment wetland for the treatment of high nitrate river water.

A novel tubular bioreactor-enhanced floating treatment wetland (TB-EFTW) was developed for the in situ treatment of high nitrate river water. When compared with the enhanced floating treatment wetland (EFTW), the TB-EFTW system achieved 30% higher total nitrogen removal efficiency. Further, the average TN level of the TB-EFTW effluent was below the Grade IV requirement (1.5mg/L) specified in Chinese standard (GB3838-2002). Microbial analysis revealed that both aerobic and anoxic denitrifying bacteria coexisted in the new system. The relative abundance of aerobic and anoxic denitrifiers were 42.69% and 22% at the middle and end of the tubular bioreactor (TB), respectively. It is reasonable to assume that effective nitrogen removal can mainly be attributed to the addition of solid carbon source and the spatial difference in DO distribution (oxic-anoxic areas in sequence) inside the TB. The initial investment cost and operating costs associated with the TB-EFTW system are approximately 14,000 and 3500 yuan per 1000 m3 river water, respectively. Considering its low cost, minimal maintenance requirements, and effective nitrogen removal, this newly developed system can be regarded as a promising technology for treating high nitrate river water. PRACTITIONER POINTS: A novel TB-EFTW system was developed to upgrade traditional in situ treatment techniques. The TB-EFTW could achieve 30% higher nitrogen removal efficiency than EFTWs. Both aerobic and anoxic denitrifying bacteria coexisted in the system. The system shows better technical and economic performance compared with routine techniques.

Integrating electrochemical pretreatment (EPT) and side-stream sulfidogenesis with conventional activated sludge process: Performance, microbial community and sludge reduction mechanisms

• Coupling EPT and sulfidogenic side-stream reactor (ESSR) with CAS process was studied. • EPT at 15 V/5min with 125 mg S/L of SO 4 2− dosage improved sludge reduction. • The ESSR could be designed with a very short SRT of 2.5 days. • The integrated process (ESSR-CAS) was operated over 200 d with good performance. • Possible reasons for fast sludge hydrolysis in ESSR-CAS were discussed. Recently, inserting an anaerobic side-stream reactor into a conventional activated sludge (CAS) process for upgrading biological wastewater treatment plants with in-situ sludge reduction function has been extensively studied. A typical example is an oxic-settling anaerobic (OSA) process, which can achieve efficient sludge reduction, but requires ample space, limiting its application potential. Optimizing the conventional OSA process towards compact and energy-efficient is necessary. This paper studied a new method by integrating electrochemical pretreatment (EPT) and sulfidogenesis-enhanced anaerobic treatment with a conventional OSA process to achieve considerable in-situ sludge reduction with a limited side-stream size requirement (i.e. short sludge retention time (SRT)). The proposed idea was verified experimentally – first, batch experiments were conducted to determine the effective sulfate concentration for the EPT and sulfidogenic side-stream reactor (ESSR); then, the ESSR-CAS process (upgrading CAS with a new ESSR) and a stand-alone CAS process (control) were operated in parallel for 200 days. The experimental results showed that: The new ESSR, with approximately 125 mg S/L of sulfate dosed and 5 min electrochemical sludge pretreatment at 15 V, can successfully accelerate anaerobic reactions, resulting in a short SRT of 2.5 days. The ESSR-CAS process can reduce sludge production by 61%, with high soluble chemical oxygen demand (SCOD) and total nitrogen (TN) removal efficiencies of 96% and 70% respectively. The possible mechanisms of ESSR for the augment of sludge hydrolysis (sludge floc disintegration, extracellular polymer destruction, and cell structure breakage) as well as the economic considerations of this new sulfur-cycle bioprocess are discussed.

Insights into a novel nitrogen removal process based on simultaneous anammox and denitrification (SAD) following nitritation with in-situ NOB elimination

Simultaneous anammox and denitrification (SAD) is an efficient approach to treat wastewater having a low C/N ratio; however, few studies have investigated a combination of SAD and partial nitritation (PN). In this study, a lab-scale up-flow blanket filter (UBF) and zeolite sequence batch reactor (ZSBR) were continuously operated to implement SAD and PN advantages, respectively. The UBF achieved a high total nitrogen (TN) removal efficiency of over 70% during the start-up stage (days 1–50), and reached a TN removal efficiency of 96% in the following 90 days (days 51–140) at COD/NH4+-N ratio of 2.5. The absolute abundance of anammox bateria increased to the highest value of 1.58 × 107 copies/µL DNA; Comamonadaceae was predominant in the UBF at the optimal ratio. Meanwhile, ZSBR was initiated on day 115 as fast nitritation process to satisfy the influent requirement for the UBF. The combined process was started on day 140 and then lasted for 30 days, during the combined process, between the two reactors, the UBF was the main contributor for TN (66.5% ± 4.5%) and COD (71.8% ± 4.9%) removal. These results demonstrated that strong SAD occurred in the UBF when following a ZSBR with in-situ NOB elimination. This research presents insights into a novel biological nitrogen removal process for low C/N ratio wastewater treatment.

CO2 bubble-assisted in-situ construction of mesoporous Co-doped Cu2(OH)2CO3 nanosheets as advanced electrodes towards fast and highly efficient electrochemical reduction of nitrate to N2 in wastewater

The development of high-efficient and cost-effective electrocatalysts is crucial to remove nitrate pollutant in wastewater. Herein, we design and prepare mesoporous Co-doped Cu2(OH)2CO3 malachite nanosheets as an electrocatalyst toward highly efficient nitrate reduction using a facile CO2 bubble-assisted coprecipitation synthesis. The electrocatalytic performance is subject to the Co/Cu ratio of this malachite. Remarkably, compared with the pristine monometal Cu or Co-based electrocatalyst, the optimal electrocatalyst, 0.3Co@Cu2(OH)2CO3, displays fast and highly efficient removal capacity of nitrate with an impressive high total nitrogen (TN) removal of 8628.99 mg N g−1CoCu (398.79 mg N gcat−1 h−1), N2 selectivity of 97.11% as well as negligible nitrite product at 100 mg L−1 NO3--N and 2000 mg L−1 Cl- neutral electrolyte. Above all, high total nitrogen removal efficiency (81.92%) and chemical oxygen demand (73.74%) in actual wastewater. Its excellent electrocatalytic performance is achieved by regulating the electronic structure and the adsorption/desorption of the intermediate. This study discovers a new type of electrode materials for nitrate removal in wastewater.

Effects of different growth form submerged macrophyte assemblages on biomass accumulation and water purification

种植水生植物，尤其是沉水植物，是目前广泛应用于受损水体的最主要的生态修复方法之一. 研究不同生长型沉水植物组合对水体理化因子的影响及营养物质的去除效率可为受损水生生态系统修复提供重要的科学依据. 本研究以我国水体修复中常用的3种不同生长型沉水植物苦草(Vallisneria natans)、黑藻(Hydrilla verticillata)和穗状狐尾藻(Myriophyllum spicatum)为研究对象，采用1种生长型种植和2种生长型及3种生长型混种模式，研究不同生长型沉水植物组合及其不同生长阶段对实验系统水质指标及氮、磷等营养物质去除率的影响. 结果表明，所有植物组合处理均显著提高了系统中总氮、总磷和氨氮去除率; 在实验前中期总氮、总磷和氨氮去除率最高. 从本实验受试物种组合来看，1种和2种生长型组合比3种生长型组合具有更高的生物量累积量和总氮去除率. Pearson相关性分析显示，实验系统中的pH、DO浓度与植物总生物量呈显著正相关，总氮、总磷、氨氮浓度均与植物总生物量呈显著负相关. 建议在受损浅水水生态系统修复过程中，根据生态修复不同阶段考虑不同生活型、生长型和功能群的水生植物组合; 在生态修复过程中需加强管理，如水生植物收割等，才能达到最好的修复效果.;Aquatic plants are important components of freshwater ecosystems and constitute a dominant actor in many shallow lakes. Planting aquatic plant, especially for submerged macrophytes, is one of the most important ecological restoration methods widely used in damaged shallow freshwater bodies. However, previously studies have mainly focused on the effects of macrophyte richness on biomass and water quality. Little is known about the effect of different assemblages with various growth form submerged macrophyte on biomass accumulation and water purification. In this study, three different growth form submerged plants, Vallisneria natans, Hydrilla verticillata and Myriophyllum spicatum, which are commonly used in water ecological restoration in China, were selected to test the effect of different growth form submerged macrophyte assemblages on water quality and nutrients removal rate. Our results showed that all different growth form assemblages have obvious purification effects on total nitrogen, total phosphorus and ammonia nitrogen, and higher purification effects were observed in the early and middle stage of the experiment. From different combinations, one and two growth form combinations have higher biomass accumulation and higher total nitrogen removal efficiency than three growth form combinations. Pearson correlation analysis showed that the pH, and DO in the experimental system were significantly positively correlated with the total biomass, and the concentrations of total nitrogen, total phosphorus and ammonia nitrogen were significantly negatively correlated with the total biomass. Our results suggest that in order to get the best restoration results, we need to take various factors into consideration during the process of ecological restoration, including different life form and growth form aquatic plant assemblages, harvesting aquatic macrophytes, etc.

Mainstream nitrogen removal in membrane aerated biofilm reactor at minimal lumen pressure

Nitrogen removal via anammox is a promising and sustainable solution in mainstream wastewater treatment. To maintain stable anammox process, competitors of anammox bacteria should be suppressed while cooperators need to be favoured. This study demonstrated a synchronous aerobic and anaerobic ammonium removal process in a membrane aerated biofilm reactor (MABR) under minimal lumen pressure. By adjusting the lumen pressure, aerobic and anaerobic ammonium oxidation rate can be synchronized to minimize interference of nitrite oxidizing bacteria (NOB) by limiting NOB's access to both oxygen and nitrite. Long-term performance indicated that PN/A in MABR could be achieved at zero positive aeration pressure. Furthermore, by connecting two MABRs in series, high total nitrogen (TN) removal efficiency of 71.1% ± 5.3% was attained with a TN removal rate of 30.1 ± 3.2 mg-N/L/d. The organic carbon present in the wastewater reduced the nitrate concentration in the effluent while not affecting the overall nitrogen removal efficiency and rate. Real-time qPCR analysis suggested that the abundance of amoA gene was relatively stable while K-strategist Nitrospira 16S rRNA gene did not surge in the long-term operation. High throughput sequencing showed that Candidatus Brocadia and uncultured anaerobic ammonium oxidizing bacteria from Chloroflexi were the most abundant anammox taxa. Denitrifiers, such as Denitratisoma may be responsible to reduce the nitrate in the effluent.

Effects of various antibiotics on aerobic nitrogen removal and antibiotic degradation performance: Mechanism, degradation pathways, and microbial community evolution

Little information about the selective stress of various antibiotics and how they influence different stages of aerobic nitrogen removal is available. A long-term aerobic nitrogen removal-moving bed biofilm reactor was established by the inoculation of Achromobacter sp. JL9, capable of heterotrophic nitrification and aerobic denitrification, and aerobic activated sludge. The nitrogen removal and antibiotic degradation performances of various antibiotics were then measured. High total nitrogen (91.83% and 91.51%) removal efficiencies were achieved with sulfamethoxazole or no antibiotics, and lower efficiencies were observed with other antibiotics (trimethoprim, teicoplanin, and ciprofloxacin). These results suggest that various antibiotics have different selective inhibitory effects on aerobic nitrogen removal. Additionally, all antibiotics were partly degraded; proposed degradation pathways according to the detected intermediates included ring-opening, S-N bond cleavage, amination, hydroxylation, and methylation. High-throughput sequencing indicated that aerobic denitrifying, recalcitrant pollutant degrading, and antibiotic-resistant bacteria dominate during the community evolution process.

Enhancing autotrophic nitrogen removal with a novel dissolved oxygen-differentiated airlift internal circulation reactor: Long-term operational performance and microbial characteristics

Autotrophic nitrogen removal (ANR) processes have not been widely applied in wastewater treatment due to their long start-up time and unstable performance. In this study, a novel dissolved oxygen-differentiated airlift internal circulation reactor was developed to enhance ANR from wastewater. During 200 days of continuous operation, the reactor start-up was achieved within 30 days; a high total nitrogen removal efficiency of 80% was achieved and stably maintained under an aeration rate of 0.90 L/min and hydraulic retention time of 6 h. Additionally, the color of sludge went from a light yellow to dark red, and the amount and size of the micro-granules increased obviously. Medium-sized (1.0–2.5 mm) micro-granules accounted for 72.4% on day 190. The specific anammox activity increased from 0.53 to 1.43 g-N/g-VSS/d, while the SNOA decreased from 0.93 to 0.08 g-N/g-VSS/d. Furthermore, the microbial analysis showed that the Nitrosomonas (4.2%) and Candidatus Brocadia (22.6%) were enriched and formed the micro-granules after the reactor's long-term operation. The results indicate that novel configuration realizes the partitioning of dissolved oxygen (DO), optimizes nitritation and anammox reactions, and accelerates biochemical reactions, thereby enhancing ANR performance. This study provides a practical alternative to enhance ANR performance and a scientific basis for the development and application of novel nitrogen removal reactors.