Total Nitrogen Removal Percentage Research Articles

Rapid start-up of an innovative pilot-scale staged PN/A continuous process for enhanced nitrogen removal from mature landfill leachate via robust NOB elimination and efficient biomass retention

The start-up and stable operation of partial nitritation-anammox (PN/A) treatment of mature landfill leachate (MLL) still face challenges. This study developed an innovative staged pilot-scale PN/A system to enhance nitrogen removal from MLL. The staged process included a PN unit, an anammox upflow enhanced internal circulation biofilm (UEICB) reactor, and a post-biofilm unit. Rapid start-up of the continuous flow PN process (full-concentration MLL) was achieved within 35 days by controlling dissolved oxygen and leveraging free ammonia and free nitrous acid to selectively suppress nitrite-oxidizing bacteria (NOB). The UEICB was equipped with an annular flow agitator combined with the enhanced internal circulation device of the guide tube, which achieved an efficient enrichment of Candidatus Kuenenia in the biofilm (relative abundance of 33.4 %). The nitrogen removal alliance formed by the salt-tolerant anammox bacterium (Candidatus Kuenenia) and denitrifying bacteria (unclassified SBR1031 and Denitratisoma) achieved efficient nitrogen removal of UEICB (total nitrogen removal percentage: 90.8 %) and at the same time effective treatment of the refractory organic matter (ROM). The dual membrane process of UEICB fixed biofilm combined with post-biofilm is effective in sludge retention, and can stably control the effluent suspended solids (SS) at a level of less than 5 mg/L. The post-biofilm unit ensured that effluent total nitrogen (TN) remained below the 40 mg/L discharge standard (98.5 % removal efficiency). Compared with conventional nitrification-denitrification systems, the staged PN/A process substantially reduced oxygen consumption, sludge production, CO2 emissions and carbon consumption by 22.8 %, 67.1 %, 87.1 % and 87.1 %, respectively. The 195-day stable operation marks the effective implementation of the innovative pilot-scale PN/A process in treating actual MLL. This study provides insights into strategies for rapid start-up, robust NOB suppression, and anammox biomass retention to advance the application of PN/A in high-ammonia low-carbon wastewater.

The Interaction Effects of Aeration and Plant on the Purification Performance of Horizontal Subsurface Flow Constructed Wetland.

Aeration and plants exhibit influence on the water purification performance in constructed wetlands (CWs). However, the interaction between aeration and plants on enhancing performance of domestic sewage treatment is unclear. Our study aims to optimize the combination of aeration position and plant species, promoting the extensive and effective application of CWs. Herein, six horizontal subsurface flow (HSSF) CWs small scale plots were established and divided into two groups according to the plant (i.e., Canna indica and Iris sibirica). To adjust the distribution of dissolved oxygen (DO) in CWs, each group had three plots of HSSF CWs. One plot was aerated at the bottom of the first quarter of the filtration chamber, one plot was aerated at the bottom of the inflow chamber, and the remaining plot was not aerated as a control. Results showed that aeration at the bottom of the first quarter filtration chamber could contribute to the highest removal efficiency of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) and total nitrogen (TN). The COD, NH4+-N, and TN removal percentages decreased with the drop in temperature. However, the plot aerated at the bottom of the first quarter filtration chamber with I. sibirica exhibited the best average CODCr, NH4+-N and TN removal percentages in both the warm season (83.6%, 82.7% and 76.8%) and the cool season (66.3%, 44.1% and 43.8%). Therefore, this study indicated that the combination of aerating at the bottom of the first quarter filtration chamber and planting with I. sibirica in the HSSF CWs would be a promising way forward for wastewater treatment, especially in low temperature seasons.

Start-up of anammox systems with different feeding patterns: System performance, microbial community and potential microbial interactions

Successful start-up of the anaerobic ammonium oxidization (anammox) system is the main challenge for its application. Two anammox biofilm systems with pulse feeding pattern (AN-P) and constant feeding pattern (AN-C) were operated, and the performance of nitrogen removal and microbial interactions among anammox bacteria, heterotrophs, and other microorganisms were investigated. The total nitrogen removal percentage reached 82% (AN-P) and 82.4% (AN-C) in 13 days and 32 days, respectively. AN-P could start up and reach steady state quicker than AN-C. Candidatus Kuenenia was the dominant functional microorganism in both reactors. Heterotrophs (Pseudomonas and Hyphomicrobium) might play important roles in nitrogen and carbon metabolisms. N-decanoyl-DL-homoserine lactone and N-dodecanoyl-DL-homoserine lactone were detected, and acyl homoserine lactone-based quorum sensing system existed in the anammox system. Complex microbial interactions, including competition, cooperation and cross-feeding co-existed in the anammox system and affected system performance.

Analyzing the effect of organic carbon on partial nitrification-anammox process based on metagenomics and quorum sensing.

The effects of adding organic carbon on the performance of different partial nitrification-anammox (PNA) process (the activated sludge process and biofilm process) were studied, especially nitrogen removal, functional microbial activity, and microbial community structure. The potential influences of quorum sensing (QS) on the nitrogen metabolism were also analyzed. The results showed that the addition of organic carbon in biofilm systems could reduce total nitrogen (TN) removal percentages, while in activated systems it could increase TN removal percentages. The TN removal percentages in SBBR-CN (the biofilm system with addition of organic carbon) and SBR-CN (the activated sludge system with addition of organic carbon) were 15% and 45%, respectively, and those in SBBR-N (the biofilm system without addition of organic carbon) and SBR-N (the activated sludge system without addition of organic carbon) were 75% and 21%, respectively. Batch experiments have proved that organic carbon inhibited the activities of nitrite-oxidizing bacteria (NOB) and anaerobic ammonia oxidation (anammox) bacteria, and organic carbon could promote the activity of denitrifying bacteria in activated sludge systems. Compared with activated sludge systems, biofilm systems could protect the activity of anammox bacteria. The relative abundances of ammonia oxidizing bacteria (AOB) and anammox bacteria were decreased, while the relative abundances of denitrifying bacteria (Thauera) were increased with the addition of organic carbon. The biofilm systems were more conducive to the growth of anammox bacteria. Metagenomics revealed that the same bacteria might be involved in different nitrogen metabolism, and nitrogen metabolism was achieved through the complex cooperation among functional bacteria. Besides, functional bacteria involving in the nitrogen metabolism had genes related to QS, indicating that QS might affect the nitrogen metabolism by regulating the functional bacteria activity. PRACTITIONER POINTS: PNA was achieved through SBBR and complete nitrification was achieved through SBR under the low ammonia nitrogen concentration condition. The effect of organic carbon on biofilm and activated sludge PNA process was different under the low ammonia nitrogen concentration condition. QS and QQ may affect the nitrogen removal performance by regulating the expression of nitrogen metabolism-related genes.

Successful startup of one-stage partial nitritation and anammox system through cascade oxygen supply and potential ecological network analysis

It is challenge for the stable operation of the anaerobic ammonium oxidation (Anammox) based wastewater treatment processes. The feasibility for the startup of the partial nitritation and Anammox (PNA) process was demonstrated with cascade oxygen supply by controlling anoxic/aerobic durations. Under steady state conditions, total nitrogen removal percentages of 63.2% (pulse feeding) and 88.0% (constant feeding) were obtained with the anoxic/aerobic duration of 5 min/7 min at 26 °C, and PNA was successfully achieved. The microbial community analysis revealed that Candidatus Kuenenia and Nitrosomonas were dominant genera of Anammox bacteria and ammonia oxidizing bacteria, respectively. Microbial interactions were examined through acyl-homoserine lactones-based quorum sensing (AHLs-QS) and metagenomics analyses. N-octanoyl-homoserine lactone, N-decanoyl homoserine lactone and N-dodecanoyl homoserine lactone had obvious relationships with the abundance of the Anammox bacteria. The AHLs-QS system could control microbial interactions among Anammox bacteria, nitrifiers and heterotrophs, especially for their balances in the PNA system.

Three-dimensional electro-Fenton system with iron foam as particle electrode for folic acid wastewater pretreatment

At the very first time, a three-dimensional (3D) iron foam was used as the particle electrode for folic acid (FA) wastewater pretreatment in the electro-Fenton (EF) process. In this work, the effects of key operating parameters, including the initial COD concentration, applied current, initial pH and iron foam dosage were optimized regarding the chemical oxygen demand (COD) and total nitrogen (TN). COD and TN removal percentage of FA wastewater reached 43.5% and 70.4%, respectively during 6 h electrolysis under the following optimal conditions: initial COD concentration of 10,000 mg/L, applied current of 300 mA, initial pH of 3 and iron foam dosage of 4 g. Regarding the main oxidant species in the proposed EF with iron foam particle electrode, OH and active chlorine were responsible for FA mineralization, confirming by the electron paramagnetic resonance (EPR) spectra of DMPO−OH. The kinetic analysis and mechanism study suggested that both electro-oxidation and electro-coagulation exited in the system. A possible FA degradation pathway based on the identification of by-products was proposed according to Liquid chromatography/time-of-flight/mass spectrometry results. In addition, BOD5/COD ratio improved from 0.22 to 0.44 after EF treatment coupled with toxicity reduction. In a word, EF with iron foam particle electrode was a feasible process for FA pretreatment.

The effect of fermented superphosphate pretreatment and step-feed mode on biological denitrification of piggery wastewater

Chemical pretreatment can reduce NH3-N levels in piggery wastewater to a certain extent, but the lack of a carbon source for subsequent biological treatment leads to a low denitrification efficiency and poor total nitrogen (TN) removal percentage. Taking superphosphate (SP) pretreatment (SP/Pretreatment) as the control, this research studies the influence of fermented superphosphate (FSP; SP plus a carbon source) pretreatment (FSP/Pretreatment) on biological denitrification in a subsequent biological treatment step. Furthermore, the removal of pollutants under different influent modes is also evaluated. The experimental results show that with the addition of the SP pretreatment, the removal percentage of NH3-N was 52%, and the chemical oxygen demand (COD)/TN ratio increased from 0.36 to 0.71. However, with the addition of the FSP pretreatment, the removal percentage of NH3-N reached 64%, and the COD/TN ratio increased to 2.28. The combination of the FSP pretreatment and a subsequent sequencing batch reactor (SBR) step in the step-feed influent mode resulted in the best denitrification, with a TN removal percentage of 57%. This result was 51% higher than that of the SP/Pretreatment-SBR system, indicating that the addition of the FSP pretreatment improves the biological denitrification of piggery wastewater. After the full treatment process for piggery wastewater, the effluent COD was 57.33 mg·L−1, the NH3-N was 66.32 mg·L−1, and the total phosphorus (TP) was 1.17 mg·L−1, all of which meet the emission standards of the “Fouling Standards for Pollutants in the Livestock Breeding Industry” (GB 18596–2001) (400 mg·L−1 COD, 80 mg·L−1 NH3-N, 8 mg·L−1 TP).

Comprehensive assessment of system performance in a full-scale wastewater treatment plant with an anaerobic/anoxic/aerobic membrane bioreactor combined with the ozonation process.

The system performance, economic cost and environmental impact of a full-scale anaerobic/anoxic/aerobic/membrane bioreactor (3AMBR) combined with the ozonation process were evaluated. The 3AMBR/ozonation process removed biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, NH4-N and total phosphorus efficiently, with removal percentages above 94%, while the total nitrogen removal percentage was only 70%. The multiple linear regression analysis showed that hydraulic retention time (HRT) had a significant effect on nitrogen removal. A low HRT benefited nitrogen removal. Ferrous sulfate dosage close to the optimal value and a high mixed liquid suspended solid could enhance the phosphorus removal. The electricity cost accounted for 88% of the total economic costs. Greenhouse gas (GHG) emissions from the BOD oxidation and endogenous decay accounted for more than 50% of total emissions. The second largest GHG emission source was electricity consumption, accounting for 41%. The key to reduce the eutrophication was to enhance nitrogen removal. The composite cost of the 3AMBR/ozonation process was 251 CNY/t CODeq removed, among which economic cost accounted for 82.5%, while environmental impact cost accounted for a small proportion.

Characteristics of Biological Nitrogen Removal in a Multiple Anoxic and Aerobic Biological Nutrient Removal Process.

Two sequencing batch reactors, one with the conventional anoxic and aerobic (AO) process and the other with the multiple AO process, were operated to examine characteristics of biological nitrogen removal, especially of the multiple AO process. The long-term operation showed that the total nitrogen removal percentage of the multiple AO reactor was 38.7% higher than that of the AO reactor. In the multiple AO reactor, at the initial SBR cycle stage, due to the occurrence of simultaneous nitrification and denitrification, no nitrite and/or nitrate were accumulated. In the multiple AO reactor, activities of nitrite oxidizing bacteria were inhibited due to the multiple AO operating mode applied, resulting in the partial nitrification. Denitrifiers in the multiple AO reactor mainly utilized internal organic carbon for denitrification, and their activities were lower than those of denitrifiers in the AO reactor utilizing external organic carbon.

Dynamic model extension for the design of full-scale artificial free superficial flow wetland systems

Addressing the low total nitrogen removal percentages observed during the sewage treatment in free superficial flow wetland systems is crucial to the design of full-scale facilities. A well-controlled pilot-scale experiment with two parallel shallow basins, one planted with Typha latifolia and the other without, enabled the development of a mathematical model, following the activated sludge model framework. The pilot unit was operated so as to achieve both organic matter and nitrogen removal. The key processes accounted for were ammonification, heterotrophic growth, nitrification, algal growth and plant transpiration. The dynamic model developed predicts the plant mass and evapotranspiration rate throughout the year. The predictive ability of the model was tested with a free water surface constructed wetland serving a population of 400, with the sole modification being the need to account for oxygen limitation in the rate of nitrification. The required inputs include the inflow characteristics and rainfall and air temperature climatic data, directly influencing the plant evapotranspiration rate. The seasonal dependence of the water temperature was determined through an energy balance.

Air-lift internal loop biofilm reactor for realized simultaneous nitrification and denitrification

Simultaneous nitrification and denitrification (SND) was realized by means of a novel air-lift internal loop biofilm reactor, in which aeration was set in middle of the reactor. During operation, the aeration was adjusted to get appropriate dissolve oxygen (DO) in bulk solution and let aerobic and anoxic zone coexist in one reactor. When aeration was at 0.6 and 0.2L/min, corresponding to DO of 5.8 and 2.5mg/L in bulk solution, ammonia nitrogen removal percentage reached about 80 and 90%, but total nitrogen removal percentage was lower than 25%. While the aeration was reduced to 0.1L/min, aerobic and anoxic zones existed simultaneously in one reactor to get 75% of ammonia nitrogen and 50% of total nitrogen removal percentage. Biofilms were, respectively, taken from aerobic and anoxic zone to verify their function of nitrification and denitrification in two flasks, in which ammonia nitrogen was transferred into nitrate completely by aerobic biofilm, and nitrate was removed more than 80% by anoxic biofilm. Microelectrode was used to measure the DO distribution inside biofilms in anoxic zone corresponding to different aerations. When aeration was at 0.6 and 0.2L/min, DO inside biofilm was more than 1.5mg/L, but the DO inside biofilm decreased to anoxic status with depth of biofilm increasing corresponding to aeration of 0.1L/min. The experimental results indicated that SND could be realized because of simultaneous existence of aerobic and anoxic biofilms in one reactor.

Treatment of Domestic Sewage in an Anaerobic–Aerobic Fixed‐bed Reactor with Recirculation of the Liquid Phase

AbstractThis study reports the performance of a combined anaerobic–aerobic packed‐bed reactor that can be used to treat domestic sewage. Initially, a bench‐scale reactor was operated in three experimental phases. In the first phase, the anaerobic reactor was operated with an average organic matter removal efficiency of 77% for a hydraulic retention time (HRT) of 10 h. In the second phase, the reactor was operated with an anaerobic stage followed by an aerobic zone, resulting in a mean value of 91% efficiency. In the third and final phase, the anaerobic–aerobic reactor was operated with recirculation of the effluent of the reactor through the anaerobic zone. The system yielded mean total nitrogen removal percentages of 65 and 75% for recycle ratios (r) of 0.5 and 1.5, respectively, and the chemical oxygen demand (COD) removal efficiencies were higher than 90%. When the pilot‐scale reactor was operated with an HRT of 12 h and r values of 1.5 and 3.0, its performance was similar to that observed in the bench‐scale unit (92% COD removal for r = 3.0). However, the nitrogen removal was lower (55% N removal for r = 3.0) due to problems with the hydrodynamics in the aerobic zone. The anaerobic–aerobic fixed‐bed reactor with recirculation of the liquid phase allows for concomitant carbon and nitrogen removal without adding an exogenous source of electron donors and without requiring any additional alkalinity supplementation.