Average Total Nitrogen Removal Rate Research Articles

Revealing sulfur-iron coupling mechanism for enhanced autotrophic denitrification in ecological floating beds

A sulfur-iron coupled ecological floating bed (EFB-SFe) was developed to enhance the denitrification capability of sulfur-based ecological floating beds (EFB-S). The denitrification performance, kinetic process and microbial community composition were explored. Results showed that sulfur-iron coupling effectively enhanced the denitrification performance of EFB, surpassing the sum of their individual effects. The average total nitrogen removal rate ranged from 1.56 to 4.56 g·m−2·d-1, with a removal efficiency of 22–84 %. The k value for the S + Fe group increased from 0.04 to 0.18 d-1 to 0.40–0.46 d-1 relative to the S group. The sulfur-iron coupling promoted the enrichment of denitrifying bacteria (Thiobacillus and Ferritrophicum). The denitrification genes in EFB-SFe were upregulated, being 12–22 times more abundant than in EFB-S. Sulfur and iron autotrophic denitrification were identified as the main nitrogen removal processes in EFB-SFe. Overall, sulfur-iron coupling showed the potential to enhance the denitrification capacity of EFB-S for treating low-pollution water.

Defense mechanism of Fe(III)-assisted anammox under salt stress: Performance and microbial community dynamics

Anammox process has attracted attention due to its excellent nitrogen removal properties in nitrogen-rich wastewater treatment. However, there were some obstacles for the application of anammox to treat high saline wastewater due to its sensitivity to salinity. In this study, Fe(III) addition strategy was developed to assist anammox to adapt high saline surroundings, with the defense mechanism involved in Fe(III)-assisted anammox emphasized. Nitrogen removal performance of anammox was deteriorated at 3.5% salinity, with the average total nitrogen removal rate of 0.85 kg/(m3·d) observed. The continuous addition of Fe(III) could significantly assist anammox to resist high salinity through facilitating the enrichment of anammox species. Candidatus Kuenenia was the main anammox species and outcompeted Candidatus Brocadia under high saline surrounding. The relative abundance of Candidatus Kuenenia increased with increased salinity and reached 41.04% under 3.5% salinity. The synthesis of key enzymes of anammox species were improved through Fe(III) addition and then facilitated the energy metabolism of anammox bacteria under 3.5% salinity. This study provides a new thought in Fe(III)-assisted anammox enhancement technologies and deepens the insight of anammox in high saline wastewater treatment.

Valorization of Dishwashing Scrubber as Biocarrier for the Enrichment of Anammox Bacteria Under Realistic Conditions

The hypersensitivity of anammox bacteria toward fluctuating temperature (seasonal) conditions significantly limits its real-world application. Biomass immobilization alleviates the impact of environmental shocks on the anammox process. In this study (291 d), a sequencing batch reactor engaging dishwashing scrubbers as model waste biocarriers and an amalgamation of activated, anaerobic, and anammox sludge (1:1:0.5 ratio) as inoculum (at influent pH 8.0) were deployed for the startup of the anammox process. Intriguingly, the SBR was run at ambient temperature (6–37 °C) at varying nitrogen loading rates (g N m−3 d−1) of 20, 30, 40, 46.4, 58, 60, 81.2, 92.8, and 116. Notably, anammox activation took place at ⁓247 d wherein the reactor performance improved and exhibited stable nitrogen removal (NH4 +–N, NO2 −–N and total nitrogen removals were 100, 99, and 72.04%, respectively). Additionally, post 279 days of reactor operation (280 – 291 d), the reactor demonstrated an average total nitrogen removal rate (g N m−3 d−1) of 88.2 at a maximum nitrogen loading rate (g N m−3 d−1) of 116. The 16S rRNA gene sequencing results revealed that Anammox bacteria predominated in the reactor, highlighting the fact that the reported increase in the percentage abundance of Candidatus Kuenenia at 266 d was exorbitantly higher (41.69%) than inoculum sludge (0.18%). Nitrospira (23.9%) and Nitrosomonas (4.32%), in addition to anammox, were found in high concentrations, suggesting presence of dissolved oxygen in the system.

Low-concentration methanol effect on the microorganisms, nitrogen removal, and recovery of the completely autotrophic nitrogen removal over nitrite.

Methanol has a significant effect on the performance of the completely autotrophic nitrogen removal over the nitrite (CANON) process. In this research, the effect of low-concentration methanol on the functional microorganisms and nitrogen removal and recovery in the CANON system is investigated. The result shows that the anaerobic ammonium-oxidizing bacteria (AnAOB) was suppressed with low-concentration methanol addition, and the phylum Planctomycetes was hidden. The genus Candidatus Brocadia was restrained, and the relative abundances reduced from 25.5 to 15.0% in the upper biofilm and from 20.3 to 14.3% in the bottom biofilm, respectively. However, low-concentration methanol promoted the nitrifying oxidizing bacteria (NOB) activity. This phenomenon reduced the average ammonium nitrogen removal rate from 95.0 to 70.7%, and the average total nitrogen removal rate decreased from 81.3 to 43.6%, respectively. The results demonstrated that the low-concentration methanol as an organic carbon matter harmed the CANON process. Fortunately, the CANON system had an excellent self-healing ability when the methanol was stopped, with the average ammonium nitrogen removal rate and total nitrogen removal rate returning to 95.5 and 80.9%, respectively. This research supplies a reference for practical engineering design and application by improving the understanding of the effects of low-concentration methanol on CANON process performance.

Modeling and simulation of the biological process for treating wastewater with a low COD:N ratio under different dissolved oxygen conditions using an extended ASM2d model

Studies are currently lacking on the reaction mechanism of bacterial biopolymers (extracellular polymeric substances (EPS) and soluble microbial products (SMP)) for biological nutrient removal (BNR) in the activated sludge model No. 2d (ASM2d). Meanwhile, the relationship between biopolymers and BNR under different dissolved oxygen (DO) conditions is not completely clear. Thus, this work presented a modified ASM2d model that combines EPS and SMP (E-S-ASM2d), described in detail the interaction between the different bacteria and biopolymer dynamics in an anaerobic, anoxic, microaerobic and oxic (AAMO) reactor, and simulated the influences of DO on BNR process in low COD:N wastewater and on bacterial biopolymers. In addition, 16S rRNA gene analysis was used to characterize the microbial community dynamics in the AAMO reactor under different DO conditions, thus verifying the necessity of introducing microbial interactions to the E-S-ASM2d model. According to the measurements, the average total nitrogen removal rate of effluent increased 19.4 %, and the average EPS content increased 15.5 % under low DO. According to sensitivity analysis, high sensitivity parameters vary under different DO concentrations (namely 3 mg L−1 and 0.5 mg L−1 DO), which demonstrates the need to determine and separately calibrate these parameters according to DO. Finally, compared with traditional ASM2d model, the correlation likelihood values of E-S-ASM2d model for COD, ammonia nitrogen, total nitrogen and total phosphorus of AAMO effluent increased from 0.622, 0.704, 0.639 and 0.329 to 0.850, 0.894, 0.909 and 0.897, respectively, indicating E-S-ASM2d can significantly improve the simulation of nutrient removal under low influent COD:N.

Effect of Temperature on ANAMMOX Process in Sequencing Batch Biofilm Reactors: Nitrogen Removal Performance and Bacterial Community

For the ambient and low-temperature operation of the anaerobic ammonium oxidation (ANAMMOX) process, sequence batch biofilm reactors (SBBR) with non-woven fabric and modified polyurethane foam as carriers, respectively, were used to treat nitrogenous wastewater. Nitrogen removal performances of both reactors were investigated while the temperature decreased from 35℃ to 15℃. When the nitrogen loading rate (NLR) was 110 mg·(L·d)-1, the average total nitrogen (TN) removal rate of the non-woven fabric reactor increased from 71.16% (35℃) to 76.19% (30℃) and then decreased to 61.11% (15℃). The average TN removal rate of the modified polyurethane foam reactor increased from 78.71% (35℃) to 81.75% (20℃) and then decreased to 75.68% (15℃). Compared with the non-woven fabric, the modified polyurethane foam provided a more stable nitrogen removal performance and could be used as the preferred carrier. High-throughput sequencing of the modified polyurethane foam biofilm indicated that Candidatus Kuenenia was the dominant ANAMMOX genus, with relative abundances of 8% (35℃), 5% (25℃), and 16% (15℃). Candidatus Kuenenia still grew and enriched at low temperatures. The decrease in temperature significantly affected the biofilm microbial community structure.

A Novel Constructed Wetland Combined with Microbial Desalination Cells and its Application.

Wastewater recycling can alleviate the shortage of water resources. Saline water is seldom treated with biological processes, and its recycling rate is low. Constructed wetland (CW) is a safe, economical, and ecological water treatment method. However, the saline water treatment performance of CW is not good. Microbial desalination cells (MDC) utilizing a bioelectrochemical approach achieve functions of desalination and power generation. In this study, MDC was used to strengthen CW to form a composite system, MDC-CW. Through optimization of design parameters, MDC-CW was applied in the treatment of salt-containing water. The average total nitrogen removal rate in MDC-CW-P1 reached 87.33% and the average COD removal rate was 92.79%. The average desalination rate of MDC-CW-P1 was 55.78% and the average voltage of MDC-CW-P1 reached 0.40mV. Planting Canna indica in the MDC-CW was conducive to the functions of desalination and power generation. The above results were also verified by the microbial analysis results of gravels in the substrate, plant rhizosphere, and electrodes. In addition, the decontamination of the device mainly depended on the function of the bacteria commonly used in water treatment, such as Proteobacteria and Bacteroidetes, whereas the generation of power depended on the function of Geobacter. Salt ions moved spontaneously to the cathode and anode under the influence of current generation so that the desalination function was realized under the selective isolation function of exchange membranes. The device design and laboratory applications of MDC-CW experimentally achieved the electrochemical function and broadened the treatment scale of CW.

Enhancing the in-situ enrichment of anammox bacteria in aerobic granules to achieve high-rate CANON at low temperatures

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH4+ <0.15) and selective washing-out of NOB-preferred smaller particles at short hydraulic retention time (HRT, 25-15 min) contributed to the NOB repression. Then the stepwise down-regulating DO concentrations from 2.8 to 1.2 mg/L enhanced the enrichment of anammox bacteria in the aerobic granules. The enriched anammox species was dominated by Ca. Brocadia sapporoensis with the estimated growth rate of 0.008–0.013 d−1 at 15 °C. Chloroflexi and Chlorobi-affiliated bacteria were also significantly enriched in the granules, which may benefit the anammox bacteria activity and growth. At the end of this study, the average total nitrogen removal rate and efficiency of the granular CANON process respectively reached 1.26 kg N·m−3·d−1 and 68% treating low-strength ammonium (∼50 mg N·L−1) wastewater under such aggressive conditions (DO = 0.8–1.5 mg/L, HRT< 1.0 h, and T = 15 °C). Overall, the aerobic granules provided a habitable niche for the proliferation and almost complete retention of the anammox bacteria. This study provides a roadmap for in-situ starting up of high-rate CANON process for mainstream wastewater treatment with aerobic granules as inoculum.

Advanced Treatment of Tail Water Using Pilot-scale Horizontal and Vertical Subsurface Flow Constructed Wetlands in Low-temperature Seasons

There were significant differences in the working efficiency and mechanism of constructed wetlands between low temperature and suitable temperature conditions. This study designed a horizontal subsurface flow constructed wetland (HFCW) and a vertical subsurface flow constructed wetland (VFCW) to explore their performance differences in advanced treatment of sewage based on contaminant degradation analysis including the removal of organic matters, total nitrogen (TN), and total phosphorus (TP), as well as the analysis of microbial community structure. The results showed that when the COD concentration of influent was between 37.50 to 80.00 mg·L-1, the concentration of total nitrogen and total phosphorus were within the first level A criteria specified in the discharge standard of pollutants for municipal wastewater treatment plant at the continuous flow of 2 m3·d-1:①Both HFCW and VFCW showed stable degradation ability of organic matter in influent and good resistance to high organic load. ②Supplementation of the carbon source significantly improved the nitrogen removal efficiency of two subsurface flow constructed wetlands. HFCW achieved the average removal rate of TN at 76.01%, and the average removal rate of TN by VFCW reached 71.69% after the carbon addition. In contrast, dosage of an external carbon source showed limited effect on phosphorus removal. Furthermore, it worked more effectively for performance improvement of HFCW than that of VFCW. ③The analysis of microbial community structure in wetland substrate and plant rhizosphere samples revealed that Proteobacteria, Firmicutes, and Verrucomicrobia were the dominant phylum in two series of wetland samples. For the dominant microbiota at the genus level, there were more significant differences in microbial community structure in wetland substrate samples than that in plant rhizosphere samples. Hydrogenophaga, Erysipelothrix, and Devosia contributed the most to the differences between the microbial communities of HFCW and VFCW. Overall, the species diversity and abundance of microbial samples from VFCW was higher than those from HFCW.

Start-up of CANON Process and Short-cut Nitrification in a Pilot-scale MBBR Reactor

Using a 150 L moving bed biofilm reactor (MBBR), with the temperature controlled at 28℃ and high NH4+-N concentration (average concentration 350 mg·L-1), inorganic wastewater was used as an influent to start the completely autotrophic nitrogen removal over nitrite (CANON) process. Meanwhile, the flocculent sludge was taken into a 5 L sequencing batch reactor, and the influent NH4+-N concentration was maintained at 90-200 mg·L-1 for the recovery of short-cut nitrification. The results showed that in the MBBR reactor, when the average hydraulic retention time (HRT) was 12 h, short-cut nitrification and total nitrogen (TN) removal rate were mutually constrained, the average TN removal rate was 38.2%, and the average δNO3--N/TN value was 0.274; when the HRT dropped to 6 h, the δNO3--N/TN value decreased from 0.347 to 0.146. The sequencing batch reactor (SBR) maintained aeration and anoxic time for 30 min and 20 min, respectively, by intermittent aeration, while the dissolved oxygen concentration during the aerobic process was 0.5 mg·L-1 to 0.6 mg·L-1, the free nitrous acid concentration was higher than 0.18 mg·L-1 at the end of each cycle, NAR increased from 0 to 99.2% after 12 days, NUR decreased to 0 from an initial 24.8 mg·(g·h)-1, and the TN removal rate decreased from 13% to 3%; the system successfully converted to short-range nitrification. High-throughput sequencing results showed that the abundance of Candidatus Kuenenia in the flocculent sludge and biofilm in the MBBR reactor were 7.91% and 17.38% respectively, Nitrosomonas accounted for 27.43% and 2.55%, respectively, while Nitrospira accounted for 0.30% and 0.28%, respectively. After the recovery of short-cut nitrification in the SBR, the abundance of ammonia-oxidizing bacteria and anaerobic ammonia oxidation decreased to 1.18% and 0.01%, respectively, and the abundance of Nitrospira increased to 1.39%.

Effects of exposure to polyether sulfone microplastic on the nitrifying process and microbial community structure in aerobic granular sludge

The effects of polyether sulfone (PES) microplastic concentration on the nitrifying process of aerobic granular sludge (AGS) were investigated together with the microbial community structure of AGS. The PES microplastic concentration inhibited the removal of ammonia nitrogen only to a small extent. The average total nitrogen removal rate increased by 5.6% after PES addition. On the 30th day, the addition of 0.5 g/L PES inhibited the specific nitrate reduction rate (SNRR) by 38.84 mg N/(g MLSS·h). Nitrite oxidase (NOR) performance of the AGS were inhibited with addition the PES. According to the high-throughput sequencing results, in the presence of PES, the abundance of Bacillales_Incertae Sedis XII reduced, while the abundance of Anaerolineaceaen increased in the AGS. According to the clusters of orthologous groups (COG) and kyoto encyclopedia of genes and genomes (KEGG), the content of cytochrome c-containing reduced and the Amino Acid Metabolism increased with addition 0.5 g/L PES microplastic.

Correlations of nitrogen removal and core functional genera in full-scale wastewater treatment plants: Influences of different treatment processes and influent characteristics

The denitrification process is crucial for biological nitrogen removal in wastewater treatment plants (WWTPs). In this study, the nitrogen removal efficiency in full-scale WWTPs with different treatment processes and influent characteristics was investigated. The results indicated that the average total nitrogen removal rate (NRR) and denitrification rate in the A/O or A2/O systems were 67.5% and 2.08 mg N h−1 gMLVSS−1, respectively. However, cyclic activated sludge systems (CASSs) showed more efficient nitrogen removal with an average NRR and denitrification rate of 79.6% and 9.89 mg N h−1 gMLVSS−1, respectively. The microbial communities in WWTPs with similar influent compositions were similar and mainly shaped by BOD5. Candidatus Competibacter, Caldilineaceae and Anaerolineaceae were the functional genera closely associated with nitrogen removal based on high-throughput sequencing and correlation analysis. This study provides new insights into the regulation and amelioration of full-scale WWTPs to meet the increasingly stringent nitrogen discharge standard.

High-rate Nitrogen Removal in a Two-stage Partial Nitritation-ANAMMOX Process Under Mainstream Conditions

A two-stage partial nitritation (PN)-ANAMMOX process was successfully carried out for low-strength NH4+-N (50 mg·L-1) wastewater treatment at ambient/low temperatures. The results show that an average total nitrogen removal rate and removal efficiency above 0.6 kg·(m3·d)-1and 80% could be maintained, respectively, at temperatures between 20℃ and 14℃. The two-stage PN-ANAMMOX process was successful both under NO2--N-limited and NH4+-N-limited conditions. When the two-stage PN-ANAMMOX process was operated under NH4+-N-limited conditions, the "limit of technology" for nitrogen removal (TN<3 mg·L-1) could be easily achieved by following anoxic denitrification. Lowering the temperature to 12℃ resulted in the reduction of the total nitrogen removal rate to~0.5 kg·(m3·d)-1. Due to the low temperature, the anammox reaction became the rate-limiting step for nitrogen removal, while the PN reaction was not impacted. In the temperature range of 10-20℃, the activity-temperature coefficients (θ) of the PN granules and ANAMMOX sludge were 1.056 and 1.172, respectively, suggesting that the anammox bacteria have a higher temperature sensitivity than the ammonium oxidizing bacteria (AOB). Overall, the results clearly indicate that the nitrogen removal loading rate of the two-stage PN-ANAMMOX process is mainly controlled by the activity and quantity of anammox biomass. In contrast, the process nitrogen removal efficiency mainly depends on the performance of the first-stage PN (i.e., effluent NO2--N/NH4+-N ratio and NO3--N concentration) under a constant nitrogen removal loading rate (no overload). Based on these results, a hierarchically separate control strategy was proposed to obtain a high-rate nitrogen removal during the two-stage mainstream PN-ANAMMOX process.

Shortcut Biological Nitrogen Removal from Coal Gasification Wastewater in Three-Stage MBBRs.

A lab-scale aerobic-anoxic-aerobic (AE1-AN-AE2) MBBR system was tested for the removal of COD, <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm01.gif"/>, SCN-, phenols, and nitrogen from coal gasification wastewater, using a shortcut biological nitrogen removal process. Dissolved oxygen concentration in AE1 was maintained at 1.0 to 2.0 mg/L to ensure stable <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm12.gif"/> accumulation. Adding methanol wastewater to AN guaranteed denitrification efficiency. AE2 ensured high removal rates of <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm23.gif"/>, SCN-, and phenols. The effects of influent pollutant concentration and hydraulic retention time (HRT) on nitrogen removal were studied. Improving the dissolved oxygen concentration in AE1 eliminated the negative effect of increased organic loading on nitrification, but it affected the stability of nitrosation. Shortening the HRT had negative effects on the performance of the system and performance recovered after it was extended. The average total nitrogen removal rate was 82.6% with a CODmethanol/<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm34.gif"/> ratio of 3.5. Biomass and activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were measured to understand the evolution of nitrification.

Further contributions to the understanding of nitrogen removal in waste stabilization ponds.

A set of experiments were conducted in Brazil in a pilot-scale waste stabilization pond (WSP) system (a four-maturation-pond series) treating an upflow anaerobic sludge blanket (UASB) reactor effluent. Over a year and a half the pond series was monitored under two flow rate conditions, hence also different hydraulic retention times and surface loading rates. On-site and laboratory trials were carried out to assess: (i) ammonia losses by volatilization using acrylic capture chambers placed at the surface of the ponds; (ii) organic nitrogen sedimentation rates using metal buckets placed at the bottom of the ponds for collecting settled particulate matter; (iii) nitrogen removal by algal uptake based on the nitrogen content of the suspended particulate matter in samples from the ponds' water column. In addition, nitrification and denitrification rates were measured in laboratory-based experiments using pond water and sediment samples. The pond system achieved high nitrogen removal (69% total nitrogen and 92% ammonia removal). The average total nitrogen removal rates varied from 10,098 to 3,849 g N/ha·d in the first and the last ponds, respectively, with the following fractions associated with the various removal pathways: (i) 23.5-45.6% sedimentation of organic nitrogen; (ii) 13.1-27.8% algal uptake; (iii) 1.2-3.1% ammonia volatilization; and (iv) 0.15-0.34% nitrification-denitrification.

Start-up of Combined Floc-granule CANON Process and the Effects of SRT on Reactor Performance

To shorten the start-up time of CANON process and guide the sludge dischargement in the practical project, the start-up of CANNON process and influence of different flocs SRT were studied by inoculation ANAMMOX granules of different proportions in two same specifications of SBR reactor. During the experiment, the temperature was controlled at 30℃±1℃ and pH was 7-8. The results showed that it was not good for CANON process rapid start-up when the two reactors were inoculated with 5% and 10% ANAMMOX granules respectively and the initial FA concentration exceeded 44 mg·L-1. When the two reactors were inoculated with 5% and 10% ANAMMOX granular sludge, the reactors were started-up successfully on Day 46 and Day 35, respectively. When the flocs SRT was maintained at 30 d, 90 d and un-initiative discharge respectively, the average total nitrogen removal rate could reach 0.35 kg·(m3·d)-1 stably. The quantitative PCR results of the three different flocs SRT showed that with increasing flocs SRT, the abundance of AOB was relatively stable, the abundance of ANAMMOX increased slightly, while the abundance of NOB significant increased. Therefore, it is necessary to elutriate flocs from reactor for decreasing the quantity of NOB and long-term stable operation of the CANON process.

Purification efficiency of nitrogen and phosphorus in Ottelia acuminata on four kinds of simulated sewage

Erhai Lake is mainly composed of low-pollution river water, farmland return water, village farmland mixed sewage, and village ditch water. The study of whether Ottelia can adapt to these four types of sewage and clean the water not only can clarify the resistance of Ottelia to contamination but also has good application value. Ottelia was experimentally cultivated in simulated sewage through artificial water distribution according to the characteristics of nitrogen and phosphorus in the four kinds of sewage. The changes in the nitrogen and phosphorus contents in water and Ottelia were determined. The adaptation of Ottelia to these four kinds of sewage, as well as the nitrogen and phosphorus purification efficiencies, was studied. Results showed that Ottelia could survive in simulated farmland return water, low-pollution river water (Yongan River) and village farmland mixed sewage. The nutrients in water influenced the flowering behavior of Ottelia. The maximum average total phosphorus and ammonia nitrogen removal rates of 29.88% and 32.4%, respectively, in Ottelia were found in the low-pollution river group. The average total nitrogen removal rate in the farmland return water group was the highest at 31.29%. Considering the removal rate, total removed volume, and Ottelia growth, the efficiency of applying Ottelia in the treatment of farmland return water around Erhai Lake was the highest. Moreover, the optimal hydraulic retention time should be 4 days when Ottelia is applied for the treatment of farmland return water from constructed wetlands.

Removal of nitrogenous compounds from polluted river water by floating constructed wetlands using rice straw and ceramsite as substrates under low temperature conditions

To reduce the loading of nitrogenous compounds under low temperature conditions (4.3–9.2°C), we used two floating constructed wetlands (FCWs), assembled from either rice straw (FCW-RS) or light ceramsite (FCW-LC) as a substrate for microorganisms and macrophytes. Under batch conditions, the concentrations of total nitrogen (TN), ammonium nitrogen (NH4+N), nitrate nitrogen (NO3−N) and nitrite nitrogen (NO2−N) in raw water were 1.32–2.97, 0.50–1.32, 0.41–1.10, and 0.18–1.24mg/L. The average removal rates of TN, NO3−N and NH4+N after 7d using FCW-RS and FCW-LC were 78.2%, 62.1%, 81.2% and 65.5%, 42,2%, 71.6%, respectively. Both the FCW-RS and FCW-LC systems proved to be proficient in nitrogenous compounds removal, and FCW-RS showed less NO2−N accumulation.

Effects of Alternating Oxic-Anoxic Model on Nitrite Accumulation in Biological Nitrogen Removal System

The effects of chemical oxygen demand (COD), ammonia nitrogen, total nitrogen removal rates and nitrite accumulation are investigated under alternating oxic-anoxic model in biological nitrogen removal system——sequencing batch reactor (SBR). The system operational effect was studied by analyzing pollutants removal and nitrite accumulation changes. The results showed that the ammonium nitrogen removal rate increased gradually and reached 60% at last. The average removal rate of ammonia nitrogen was 50.2%. The average total nitrogen removal rate was 31.0% due to the low ammonia nitrogen removal and the low carbon in the inflow. The average COD removal rate was 41.7%, finally the COD removal rate reached near 60%. The average nitrite accumulation rate was 68.71%. The alternating oxic-anoxic model reached stable nitrite accumulation.

Nitrogen Removal along Vertical direction by Plant Biological Membrane System

Based on the equipment of integrated constructed wetlands (ICWs) with independent intellectual property rights. Plant biological membrane system (PBMS) was constructed to purify nitrogen of sanitary sewage. PBMS includes palm silk, non-woven and floating plant (Trifolium repens L.). Total nitrogen (TN), ammonia nitrogen (NH3-N) was investigated to evaluate the effects of the layered purification and resistance to the outside impact. The results showed that layered purification occurred along the flowing vertical direction. The average removal rate of TN, NH3-N and total dissolved solids was 65.6%, 60.7% and 38.7%, respectively. The TN and NH3-N removal load of the lower, middle and upper layer were 1.0, 0.8, 0.7g/ (m2.d) and 0.8, 0.8, 0.3g/ (m2.d), respectively. The higher concentration of inflow the stronger resists impact load capability. The TN and NH3-N average removal load of the lower, middle and upper layer were 4.1, 1.88, 1.57 times and 3.13, 1.25, 1 time than those of the stable phase, respectively.