Enhanced Nitrogen Removal Research Articles

Hematite-facilitated microbial ammoxidation for enhanced nitrogen removal in constructed wetlands

Hematite-facilitated microbial ammoxidation for enhanced nitrogen removal in constructed wetlands

Enhancing anammox process with granular activated carbon: A study on Microbial Extracellular Secretions (MESs)

Granular activated carbon (GAC), a porous carbon-based material, provides increased attachment space for functional microorganisms and enhances nitrogen removal by facilitating extracellular electron transfer in the anammox process. This study investigates the effects of GAC on the biosynthesis of microbial extracellular secretions (MESs) and explores the roles of these secretions in anammox activities. Four lab-scale reactors were operated: two downstream UASB reactors (D1 and D2) receiving effluents from the upstream UASB reactors (U1: no-GAC, U2: yes-GAC). Our results indicate that MESs were enhanced with the addition of GAC. The effluent from U2 exhibited a 59.62 % higher amino acid content than that from U1. These secretions contributed to an increase in the nitrogen loading rate (NLR) in the downstream reactors. Specifically, NLR in D1 increased from 130.5 to 142.7 g N/m3/day, and in D2, it escalated from 137.5 to 202.8 g N/m3/day, likely through acting as cross-feeding substrates or vital nutrients. D2 also showed increased anammox bacterial activity, enriched Ca. Brocadia population and hao gene abundance. Furthermore, this study revealed that D2 sludge has significantly higher extracellular polymeric substances (EPS) (48.71 mg/g VSS) and a larger average granule size (1.201 ± 0.119 mm) compared to D1 sludge. Overall, GAC-stimulated MESs may have contributed to the enhanced performance of the anammox process.

Constructed wetland – Microbial fuel cell (CW-MFC) packed with suspended fillers to enhance denitrification with Acorus calamus biomass addition

There is an urgent need to meet strict nitrogen discharge limitation for secondary effluent from wastewater treatment plants, but the nitrogen removal is restricted due to the lack of carbon sources. To address the issues, high-density polyethylene (HDPE) was utilized in the constructed wetland-microbial fuel cell (CW-MFC) for the treatment of low carbon wastewater. Meanwhile, wetland plant biomass was efficiently reclaimed, leading to higher nitrogen removal and bioelectricity generation. CW-MFC with biomass added in the anode attained the maximum total nitrogen (TN) removal of 97.55 % and power density of 2.22 mW/m2 with hydraulic retention time (HRT) of 2d, which were much better than those in CW, CW-MFC with no biomass and CW-MFC with biomass added in the cathode. Owing to the HDPE fillers and Acorus calamus biomass addition in CW-MFC, more than 88 % chemical oxygen demand (COD) and 70 % TN were removed with HRT of 1.5d. In addition, metabolisms related to glycolysis, cellulose degradation and nitrogen were increased in CW-MFC, contributing to the enrichment of denitrifying, electroactive and heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria. This study verifies the feasibility of application of HDPE as the biocarriers in CW-MFC and provides mechanistic insights for the enhancement of nitrogen removal in low carbon wastewater treatment with plant biomass addition.

The Effect of Electricity Generation on the Performance of Microbial Fuel Cells for Anammox

The Anammox anaerobic fluidized bed microbial fuel cell (Anammox AFB-MFC) exhibits exceptional performance in both nitrogen removal and electricity generation, effectively eliminating ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2−-N) pollutants. This technology offers the advantages of high efficiency in nitrogen removal and low electricity consumption. By coupling an AFB with an MFC, the Anammox AFB-MFC was developed through the introduction of anaerobic ammonia-oxidizing bacteria (AnAOB) into MFC. Anammox AFB-MFC’s nitrogen removal ability was found to be superior at an influent COD concentration of 200 mg/L, as determined by a study conducted under unchanged conditions. Subsequently, an open and closed-circuit experiment was performed on the Anammox AFB-MFC system while maintaining a COD concentration of 200 mg/L in the influent. Remarkably, the reactor exhibited significantly enhanced nitrogen removal performance when electricity generation occurred. Throughout the entire experimental process, the reactor consistently maintained high nitrogen removal efficiency and electricity production performance. Under optimal experimental conditions, the reactor achieved a remarkable nitrogen removal rate of 91.8% and an impressive output voltage of 439.1 mV. Additionally, the generation of Anammox bioparticles in MFC significantly contributed to efficient pollutant removal. This study elucidates the impact of organic matter on both the nitrogen removal and electricity generation capabilities of Anammox AFB-MFC, as well as highlights the synergistic effect between MFC electricity generation and nitrogen removal in the reactor.

Enhancing nitrogen removal efficiency for anammox granular sludge at low temperature by fulvic acids from different sources

The stable and efficient operation of the anaerobic ammonia oxidation (anammox) process in mainstream wastewater treatment at low temperatures still faces significant challenges. In this study, the effect of mineral fulvic acid (MFA) and biochemical fulvic acid (BFA) on the nitrogen removal efficiency of the anammox reactor at low temperature (20 °C) was investigated. The results demonstrated that both MFA and BFA could improve the nitrogen removal performance of the anammox reactor, with MFA exhibiting a more pronounced promotional effect than BFA. At concentrations of 30 mg total organic carbon (TOC)/L for both MFA and BFA, the nitrogen removal rate (NRR) increased by 26.68 % and 21.93 %, respectively. MFA and BFA stimulated the secretion of extracellular polymeric substances (EPS), preventing the disintegration of granular sludge at low temperatures, with a notable increase in the particle size of granular sludge, especially at high concentrations of MFA. Moreover, serving as electron shuttles, MFA demonstrated superior electron transfer ability compared to BFA, significantly enhancing the metabolic activity of anammox bacteria (AnAOB) under low temperatures. In addition, compared with BFA, MFA exhibited the potential to promote the growth of Candidatus_Kuenenia, offering a beneficial contribution to improving the nitrogen removal performance of the anammox reactor at low temperatures.

Enhancing nitrogen removal in constructed wetlands: The role of influent substrate concentrations in integrated vertical-flow systems

Recent advancements in constructed wetlands (CWs) have highlighted the imperative of enhancing nitrogen (N) removal efficiency. However, the variability in influent substrate concentrations presents a challenge in optimizing N removal strategies due to its impact on removal efficiency and mechanisms. Here we show the interplay between influent substrate concentration and N removal processes within integrated vertical-flow constructed wetlands (IVFCWs), using wastewaters enriched with NO3−-N and NH4+-N at varying carbon to nitrogen (C/N) ratios (1, 3, and 6). In the NO3−-N enriched systems, a positive correlation was observed between the C/N ratio and total nitrogen (TN) removal efficiency, which markedly increased from 13.46 ± 2.23% to 87.00 ± 2.37% as the C/N ratio escalated from 1 to 6. Conversely, in NH4+-N enriched systems, TN removal efficiencies in the A-6 setup (33.69 ± 4.83%) were marginally 1.25 to 1.29 times higher than those in A-3 and A-1 systems, attributed to constraints in dissolved oxygen (DO) levels and alkalinity. Microbial community analysis and metabolic pathway assessment revealed that anaerobic denitrification, microbial N assimilation, and dissimilatory nitrate reduction to ammonium (DNRA) predominated in NO3−-N systems with higher C/N ratios (C/N ≥ 3). In contrast, aerobic denitrification and microbial N assimilation were the primary pathways in NH4+-N systems and low C/N NO3−-N systems. A mass balance approach indicated denitrification and microbial N assimilation contributed 4.12–47.12% and 8.51–38.96% in NO3−-N systems, respectively, and 0.55–17.35% and 7.83–33.55% in NH4+-N systems to TN removal. To enhance N removal, strategies for NO3−-N dominated systems should address carbon source limitations and electron competition between denitrification and DNRA processes, while NH4+-N dominated systems require optimization of carbon utilization pathways, and ensuring adequate DO and alkalinity supply.

Enhanced nitrogen removal via partial nitrification/denitrification coupled Anammox using three stage anoxic/oxic biofilm process with intermittent aeration

Pre-capturing organics in municipal wastewater for biogas production, combined with Anammox-based nitrogen removal process, improves the sustainability of sewage treatment. Thus, enhancing nitrogen removal via Anammox in mainstream wastewater treatment becomes very crucial. In present study, a three-stage anoxic/oxic (AO) biofilm process with intermittent aeration was designed to strengthen partial nitrification/denitrification coupling Anammox (PNA/PDA) in treatment of low C/N wastewater, which contained chemical oxygen demand (COD) of 79.8 mg/L and total inorganic nitrogen (TIN) of 58.9 mg/L. With a hydraulic retention time of 8.0 h, the process successfully reduced TIN to 10.6 mg/L, achieving a nitrogen removal efficiency of 83.3 %. The 1st anoxic zone accounted for 32.0 % TIN removal, with 10.3 % by denitrification and 21.7 % by PDA, meanwhile, the 2nd and 3rd anoxic zones contributed 19.4 % and 4.5 % of TIN removal, primarily achieved through PDA (including endogenous PD coupling Anammox). The 1st and 2nd intermittent zones accounted for 27.2 % and 17.0 % of TIN removal, respectively, with 13.7 %-21.3 % by PNA and 3.2 %-5.3 % by PDA. Although this process did not pursue nitrite accumulation in any zone (< 1.5 mg-N/L), PNA and PDA accounted for 35.1 % and 52.1 % of TIN removal, respectively. Only 0.21 % of removed TIN was released as nitrous oxide. The AnAOB of Candidatus Brocadia was enriched in each zone, with a relative abundance of 0.66 %-2.29 %. In intermittent zones, NOB had been partially suppressed (AOB/NOB = 0.73–0.88), mainly due to intermittent aeration and effective nitrite utilization by AnAOB since its population size was much greater than NOB. Present study indicated that the three-stage AO biofilm process with intermittent aeration could enhance nitrogen removal via PNA and PDA with a low N2O emission factor.

Interactions and coupling mechanisms between Anammox, partial denitrification (PD) and hydroxyapatite (HAP) biomineralization in a PD/A-HAP system

In this study, hydroxyapatite (HAP) crystallization was introduced into a partial denitrification/Anammox (PD/A) process to develop PD/A-HAP granules and achieve simultaneous removal of nitrogen and phosphorus from wastewater. During the formation of PD/A-HAP granules, an unbalanced relationship between the biomass growth and phosphorus crystallization was observed, which resulted in a mass transfer inhibition inside the system. PD and Anammox activities were both impacted by the impeded nutrient contact, and PD process was revealed to be more susceptible to inhibition. Through the regulation of COD and NO3–-N, a dynamic balance between microbial proliferation and phosphorus crystallization was achieved. As a result, high nitrogen removal efficiency (NRE) was attained at 97.8±1.2 % in the final stage of operation, accompanied by a phosphorus removal efficiency (PRE) of 59.4±2.9 %. Furthermore, the recovered phosphorus was transformed into HAP crystals and encapsulated by the PD/A biomass to form granules, which greatly promoted the settling performance of the sludge. This study underlines the importance of reconciling biomass and HAP growth for a strengthened PD/A granular sludge and an enhanced nitrogen removal system. The constructed PD/A-HAP process will expand the application of PD/A with its ability to remove phosphorus while efficiently removing nitrogen.

Insight into performance of nitrogen removal enhanced by adding lactic acid-rich food waste fermentation liquid as carbon source in municipal wastewater treatment

Lactic acid-rich fermentation liquid (LAFL) of food waste is found to act as a promising alternative carbon source for nitrogen removal in wastewater treatment. Here, LAFL was employed to investigate its impacts on nitrogen removal during raw municipal wastewater treatment with a comparison to sodium acetate (NaAc). Results indicated that nitrogen removals were comparable when incorporated with LAFL and NaAc (92.89 % v.s. 91.23 %). Unlike the utilization of NaAc, using LAFL could avoid suppressing the relative abundance of the nitrification genes and thus pose a negative risk to nitrogen removal during prolonged operation. The introduction of LAFL increased the stability and robustness of the functional microbial community and effectively reduced excess activated sludge (AS) generation by 109 % compared to NaAc addition, consequently enhancing nitrogen removal but diminishing the treatment cost. In general, LAFL exhibits prospective engineering application potentials and economic advantages in improving nitrogen removal by AS process.

Iron-carbon micro-electrolysis facilitates autotrophic denitrification and Feammox in tidal flow constructed wetlands for enhanced nitrogen removal and reduced N2O emissions

This study focused on developing a tidal flow constructed wetland (CW) with an iron-carbon (Fe-C) substrate to enhance nitrogen removal efficiency. The results demonstrated significant improvements in the removal of NH4+-N and TN in the iron-carbon tidal flow constructed wetland (IC-TFCW) compared to traditional gravel CW. IC-TFCW achieved a 23.82 % and 31.01 % more effective removal, resulting in reductions of 82.45 % and 74.13 %, respectively. The large specific surface area and electron transfer effect of the Fe-C substrate facilitated pollutant retention and proliferation of denitrifying microorganisms. However, the Fe-C substrate inhibited plant growth and rhizosphere microorganisms, reducing plant nitrogen uptake by 2.69-fold. Galvanic cell reaction in the Fe-C substrate facilitated the release of iron and its oxides and promoted iron cycling under the alternating aerobic-anoxic conditions induced by tidal flow. This led to the enrichment of autotrophic denitrifying and Fe-reducing bacteria by 14.89 and 1.1 times, and increase in the relative abundance of denitrification genes nar (narG, narH, narI) and nap (napA, napB) by 60.94 %. The Fe2+ released during the galvanic cell reaction contributed electrons to denitrification, while the reduction of Fe3+ facilitated the Anammox process, resulting in the Feammox reaction. This created an autotrophic denitrification pathway (autotrophic denitrification and Feammox), synergizing with the heterotrophic denitrification pathway and the iron cycling process to significantly increase TN removal and reduce N2O emissions per unit of TN removed by up to 36.99 %. These findings elucidate the various denitrification pathways present in CW and provide insights into improving denitrification efficiency.

Enhancing nitrogen removal from wastewater via photoelectrocatalytic oxidation over a Ru/TiO2 system

Water pollution is a significant global environmental concern that threatens the sustainable progress of humanity. In this study, the concepts of photocatalytic oxidation in the cathodic zone (NH4+-N adsorption-NH3-N conversion) and electrochemical oxidation in the anodic zone (NH4+-N direct oxidation + chlorination) were proposed to remove ammoniacal nitrogen, and experimental studies were conducted. The stirring of the test solution during the reaction process enhanced the ammoniacal nitrogen removal efficiency by ∼9% after 90 min of reaction. The removal efficiency of ammoniacal nitrogen was comparatively high at low concentrations. After 60 min of reaction in the presence of 15 mg·L−1 ammonium chloride, the removal efficiency exceeded 95%; the removal efficiency of ionized ammonia increased with increasing current density. After 60 min, the removal efficiency of ammoniacal nitrogen exceeded 80%. Under the same ammoniacal nitrogen concentration conditions, the ammoniacal nitrogen removal efficiency in the test solution increased with the increase in the chlorine ion concentration, and in the absence of chlorine ions, ammoniacal nitrogen removal in the electrochemical reaction environment was insignificant. Under the same power and light conditions, the photoelectrochemical reaction exhibited a ∼15% higher ammoniacal nitrogen removal efficiency than electrochemical oxidation.

Bidirectional Enhancement of Nitrogen Removal by Indigenous Synergetic Microalgal-Bacterial Consortia in Harsh Low-C/N Wastewater.

Conventional microalgal-bacterial consortia have limited capacity to treat low-C/N wastewater due to carbon limitation and single nitrogen (N) removal mode. In this work, indigenous synergetic microalgal-bacterial consortia with high N removal performance and bidirectional interaction were successful in treating rare earth tailing wastewaters with low-C/N. Ammonia removal reached 0.89 mg N L-1 h-1, 1.84-fold more efficient than a common microalgal-bacterial system. Metagenomics-based metabolic reconstruction revealed bidirectional microalgal-bacterial interactions. The presence of microalgae increased the abundance of bacterial N-related genes by 1.5- to 57-fold. Similarly, the presence of bacteria increased the abundance of microalgal N assimilation by 2.5- to 15.8-fold. Furthermore, nine bacterial species were isolated, and the bidirectional promotion of N removal by the microalgal-bacterial system was verified. The mechanism of microalgal N assimilation enhanced by indole-3-acetic acid was revealed. In addition, the bidirectional mode of the system ensured the scavenging of toxic byproducts from nitrate metabolism to maintain the stability of the system. Collectively, the bidirectional enhancement system of synergetic microalgae-bacteria was established as an effective N removal strategy to broaden the stable application of this system for the effective treatment of low C/N ratio wastewater.

Novel Biochar/Fe-Modified Biocarriers Assisted Tidal-Flow Constructed Wetlands for Enhanced Nitrogen Removal from Eutrophic Water under Low Temperatures

Novel Biochar/Fe-Modified Biocarriers Assisted Tidal-Flow Constructed Wetlands for Enhanced Nitrogen Removal from Eutrophic Water under Low Temperatures

Temperature-resilient superior performances by coupling partial nitritation/anammox and iron-based denitrification with granular formation

Partial nitritation-anammox (PN/A), an energy-neutral process, is widely employed in the treatment of nitrogen-rich wastewater. However, the intrinsic nitrate accumulation limits the total nitrogen (TN) removal, and the practical application of PN/A continues to face a significant challenge at low temperatures (<15 °C). Here, an integrated partial nitritation-anammox and iron-based denitrification (PNAID) system was developed to address the concern. Two up-flow bioreactors were set up and operated for 400 days, with one as the control group and the other as the experiment group with the addition of Fe0. In comparison to the control group, the experiment group with the Fe0 supplement showed better nitrogen removal during the entire course of the experiment at different temperature levels. Specifically, the TN removal efficiency of the control group decreased from 82.9 % to 53.9 % when the temperature decreased from 30 to 12 °C, while in stark contrast, the experiment group consistently achieved 80 % of TN removal in the same condition. Apart from the enhanced nitrogen removal, the experiment group also exhibited better phosphorus removal (10.6 % versus 74.1 %) and organics removal (49.5 % versus 65.1 %). The enhanced and resilient nutrient removal performance of the proposed integrated process under low temperatures appeared to be attributed to the compact structure of granules and the increased microbial metabolism with Fe0 supplement, elucidated by a comprehensive analysis including microbial-specific activity, apparent activation energy, characteristics of granular sludge, and metagenomic sequencing. These results clearly confirmed that Fe0 supplement not only improved nitrogen removal of PN/A process, but also conferred a certain degree of robustness to the system in the face of temperature fluctuations.

Ferric and sulfate coupled ammonium oxidation enhanced nitrogen removal in two-stage partial nitrification - Anammox/denitrification process for food waste liquid digestate treatment

Liquid digestate of food waste is an ammonium-, ferric- and sulfate-laden leachate produced during digestate dewatering, where the carbon source is insufficient for nitrogen removal. A two-stage partial nitrification-anammox/denitrification process was established for nitrogen removal of liquid digestate without pre-treatment (>300 d), through which nitrogen (95 %), biodegradable organics (100 %), sulfate (78 %) and iron (100 %) were efficiently removed. Additional ammonium conversion (20 %N) might be coupled with ferric and sulfate reduction, while produced nitrite could be further converted to di-nitrogen gas through anammox (75 %) and denitrification (25 %). Notably, since increasingly contribution of hydroxylamine producing nitrous oxide, and up-regulated expression of electron transfer and cytochrome c protein, the enhanced ammonium oxidation was probably conducted through extracellular polymeric substances-mediated electron transfer between sulfate/ferric-reducers and aerobic ammonium oxidizers. Thus, the established partial nitrification-anammox/denitrification process might be a cost-efficient nitrogen removal technology for liquid digestate, benefitting to domestic waste recycling and carbon neutralization.

Aerobic and anoxic utilization of organic matter for flexible nitrite supply in nutrient conversion pathways based on anaerobic ammonium oxidation: Microbial interactive mechanism

This study investigated nutrient conversion pathways and corresponding interactive mechanisms in a mainstream partial-nitritation (PN)/anaerobic ammonium oxidation (anammox)/partial-denitrification-(PD)-enhanced biological phosphorus-removal (EBPR) (PN/A/PD-EBPR) process. A laboratory-scale sequencing batch reactor was operated for 301 days under different operational strategies. Mainstream PN/A/PD-EBPR was successfully operated with aerobic and anoxic utilization of organic matter. Aerobic utilization of organic matter was an effective strategy for conversion to denitrifying polyphosphate-accumulating organism-based phosphorus removal, referring to a biological reaction that outperformed nitrite-oxidizing bacteria. Aerobically adsorbed organic matter could be used as a carbon source for PD, which further enhanced nitrogen removal by PN/A. Ultimately, the interaction between complex nutrient conversion pathways served to achieve stable performance. High-throughput sequencing results elucidated the core microbe functioning in the mainstream PN/A/PD-EBPR process with respect to various nutrients. The outcomes of this study will be beneficial to those attempting to implement mainstream PN/A/PD-EBPR.

Mechanism of Nitrogen Removal Enhancement in Low Carbon/Nitrogen Municipal Sewage by AAO Process with Activated Sludge-Biofilm Composite System

Mechanism of Nitrogen Removal Enhancement in Low Carbon/Nitrogen Municipal Sewage by AAO Process with Activated Sludge-Biofilm Composite System

Enhancement of immobilized biochar/FeS on nitrogen removal in constructed wetland at low temperature

Constructed wetland (CW) is an eco-friendly and economically treatment for the deep nitrogen removal. Microbial denitrification, a key process in CW, is temperature-sensitive, with decreased nitrogen removal efficiency at low temperature. To enhance the nitrogen removal efficiency at low temperature, this study explored the use of functional substrates, focusing on iron sulfide (FeS) nanoparticles and biochar (BC). The results showed that immobilized BC/FeS significantly improved nitrate (NO3-N) and total nitrogen (TN) removal in CW at low temperature (8–13 °C), which reached 93.59 ± 2.07 and 80.06 ± 3.00 %, respectively, with 30 % immobilized BC/FeS. Increasing the dosage of immobilized BC/FeS accelerated denitrification rate and reduced nitrite (NO2-N) accumulation. Autotrophic denitrification was the primary pathway, with the contribution of autotrophic denitrification increasing from 64.06 % (10 % immobilized BC/FeS) to 83.25 % (30 % immobilized BC/FeS). Sulfurimonas was the dominant denitrifying bacteria identified as a cold-tolerant denitrifying bacteria. The study underlines the potential of composite electron donor substrates to enhance nitrogen removal in CW, providing a sustainable solution to nitrogen pollution in cold climates.

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.

Enhanced nitrogen removal through aerobic denitrifying bacteria in horizontal subsurface flow constructed wetlands: Influencing factors and microbial community structure

Variation in the demand for dissolved oxygen during nitrification and denitrification processes is one of the main constraints for nitrogen removal performance in conventional constructed wetlands. This study aimed to enhance the performance of horizontal submerged flow constructed wetland (HSCW) systems through aerobic denitrification (AD). The effects of different operating conditions on the performance and microbial community structure of the system were investigated using three experimental systems including a non-aerated HSCW without bacterial inoculation (CWC), a non-aerated HSCW with bacterial inoculation (CWM) and an intermittently aerated HSCW with bacterial inoculation (CWMA). Results showed that C/N ratio of 10 and aeration rate of 0.2 L/(min·L) were the optimum conditions for CWMA, which showed 29.01 % and 12.17 % higher COD and TN removals than CWC, even at an average temperature of 8.80℃. Microbial community analysis revealed that the addition of Pseudomonas stutzeri significantly increased the microbial diversity and abundance within the HSCWs. This study provides a new idea for the treatment of nitrogenous wastewater and the AD-CW system has a promising application in low-temperature areas.