High Nitrogen Removal Rate Research Articles

Nitrogen processing by treatment wetlands in a tropical catchment dominated by agricultural landuse

Agriculture is a major contributor to marine nitrogen pollution, and treatment wetlands can be a strategy to reduce it. However, few studies have assessed the potential of treatment wetlands to mitigate nitrogen pollution in tropical regions. We quantify the nitrogen removal rates of four recently constructed treatment wetlands in tropical Australia. We measured denitrification potential (Dt), the inflow-outflow of nutrients, and tested whether the environment in these tropical catchments is favourable for nitrogen removal. Dt was detected in three of the four systems with rates between 2.0 and 12.0 mg m-2 h−1; the highest rates were measured in anoxic soils (ORP −100 to 300 mV) that were rich in carbon and nitrogen (>2% and >0.2%, respectively). The highest nitrogen removal rates were measured when NO3−-N concentrations were >0.4 mg L−1 and when water flows were slow. Treatment wetlands in tropical regions can deliver high removal rates of nitrogen and other pollutants when adequately managed. This strategy can reduce nutrient loads and their impacts on sensitive coastal zones such as the Great Barrier Reef.

Mechanism involved in the treatment of sulfamethoxazole in wastewater using a constructed wetland microbial fuel cell system

A constructed wetland (CW) and a constructed wetland microbial fuel cell (CW-MFC) were used for 70 d to remove sulfamethoxazole from wastewater. The amount of sulfamethoxazole removed, extracellular polymer content, microbial community evolution, and changes in the abundances of genes related to antibiotic resistance were assessed. The total nitrogen, ammonia nitrogen, and sulfamethoxazole removal efficiencies were significantly (P < 0.05) higher (6.87%, 21.07%, and 11.05% higher, respectively) for the CW-MFC than the CW. Good removal efficiencies and the power generation performance indicated that the CW-MFC was more stable than the CW in the presence of sulfamethoxazole. The extracellular polymer content was lower for the CW-MFC than the CW. The phylum Proteobacteria was dominant in the CW-MFC. High Pseudomonas concentrations in the CW would have caused organic matter decomposition but not electricity generation. The Methylotenera content was 4.5 times higher in the CW-MFC anode than the CW anode. Methylotenera are able to perform denitrification and could have caused the high nitrogen removal rate for the CW-MFC. The sulfamethoxazole resistance gene copy number was much higher for the CW than the CW-MFC, indicating a higher risk of antibiotic resistance genes spreading in the CW than the CW-MFC. The results indicated that the CW-MFC is a promising technique for removing sulfamethoxazole from wastewater that offers environmental and economic benefits over alternative methods.

Efficiency of hybrid systems enhanced with different sludge ratios in improving resistance to short-term low temperatures

Complete autotrophic nitrogen removal over nitrite (CANON) is used in wastewater treatment. However, the performance of the CANON system significantly decreases at low temperatures; thus, a new strategy to improve the resistance of the CANON system is required. To investigate the impact of sludge ratio control (high-granule, equivalent, and high-floc systems) on the resistance of CANON to low temperatures, and their recovery after restoring to normal temperature, the nitrogen removal performance of hybrid systems with different ratios was evaluated. The equivalent system had the lowest nitrite accumulation rate and highest nitrogen removal rate. Anaerobic ammonia oxidation was the rate-limiting step of each system, and hzs was the rate-limiting gene. The higher anaerobic ammonium oxidizing bacteria (AAOB) abundance and hzs expression levels resulted in an equivalent system with better resistance and recovery to short-term low temperatures at the gene level.

Behavior of Nitrogen in GH4169 Superalloy Melt during Vacuum Induction Melting Using Returned Materials

The nitrogen behavior of superalloy melt GH4169 during the vacuum induction melting (VIM) process was clarified by using different proportions of returned materials including block-shaped returned material, chip-shaped returned material, and pure materials to produce a high–purity superalloy melt and provide guidance for the purification of the superalloy melt. For the nitrogen removal during the VIM process, the denitrification rate in the refining period reached 10 ppm per hour on average, which is significantly higher than 1 ppm per hour on average in the melting period. The denitrification reaction of superalloy melt GH4169 under extremely low vacuum pressure is controlled by both the mass transfer of nitrogen in the melt and the chemical reaction of the liquid–gas interface. The nitrogen removal of superalloy melts during VIM occurs through the two methods of gasification denitrification and nitride floatation because the nitrides begin to precipitate in the liquid phase at 1550 °C. A higher nitrogen removal rate can be obtained by increasing the proportion of chip-shaped material or decreasing the proportion of block-shaped material.

High nitrogen removal performance of anaerobically treated fish processing wastewater by one-stage partial nitritation and anammox process with hydroxyapatite (HAP)-based syntrophic granules and granule structure

The one-stage partial nitritation and anammox process with the hydroxyapatite (HAP)-based syntrophic granules was studied for the ammonium nitrogen removal from the effluents of a self-agitated anaerobic baffled reactor treating the fish processing wastewater. When the ammonium in the influent was 1140 mg N·L-1, a high nitrogen removal rate and nitrogen removal efficiency of 1.51 ± 0.10 kg N·m−3·d-1 and 88.2% were obtained, respectively. Anammox bacteria of Candidatus Kuenenia stuttgartiensis and ammonium oxidizing bacteria of Nitrosomonas were the two most predominant bacteria, while nitrite oxidizing bacteria activity was low and could be neglected during the treatment. The inorganic element properties of the sludge were analyzed by several methods to confirm the existence of HAP granules. Optical microscopic observation and scanning electron microscopy analysis revealed the structure of the granular sludge.This study supports the feasibility and potential of this process for high-efficiency nitrogen removal from fish processing wastewater.

High-rate nitrogen removal in a continuous biofilter anammox reactor for treating low-concentration nitrogen wastewater at moderate temperature

The high-rate nitrogen removal in a continuous biofilter anammox reactor (CBAR) was investigated to treat low-concentration nitrogen wastewater. Shortening hydraulic retention time (HRT) gradually could restart CBAR and accumulate anammox bacteria effectively in the reactor, where the carmine anammox granular sludge and biofilm were coexisted well. It spent 21 days to restart CBAR completely after it had been idle for 116 days. Meanwhile, the total nitrogen removal rate remained stable at 86.42% accompanied with a total biomass concentration of 26.02 g-SS/L in 0 ~ 20 cm zone under nitrogen loading rate of 4.25 ± 0.10 kg-N/(m3·day), HRT of 20 min and 25 ℃. In addition, the specific anammox activity of biomass exceeded 0.28 g-N/(g-VSS·day) in 0 ~ 20 cm zone, which was related with a high relative abundance of Candidatus Brocadia (>30%) in the same zone. Thus, it is a feasible approach to adopt CBAR to treat low-concentration nitrogen wastewater efficiently.

Nitrogen removal performance using anaerobic ammonium oxidation considering variable conditions.

The anaerobic nitrogen removal performance of anammox at 30°C, 25°C, and 16°C were studied by using the UASB (Up flow Anaerobic Sludge Blanket) reactor and the influent concentration of NH4+-N and NO2--N were 16.9 and 20.6 mg L-1 respectively. Experimental results showed that high-efficiency anammox nitrogen removal could be achieved at 30°C, when hydraulic retention time (HRT) was 0.14 h, the nitrogen removal rate (NRR) was 5.73 kg N m-3 d-1. The anammox reactor operated stably for more than 80 days under the condition of 16°C-20°C, and the high NRR of 2.78 kg N m-3 d-1 was obtained. In this experiment, DO had little effect on the activity of anammox granular sludge, and the nitrogen removal performance could be quickly recovered in a short period of time after being affected by DO. Moreover, the stoichiometric ratio of NO2--N and NH4+-N consumption (ΔNO2--N/ΔNH4+-N) and the stoichiometric ratio of NO3--N production and NH4+-N conversion (ΔNO3--N/ΔNH4+-N) were 1.21 ± 0.11and 0.25 ± 0.06 respectively at 30°C, which were very close to the theoretical value, it indicated that anammox bacteria were the dominant bacteria at 30°C.

Purification effect of bioretention with improved filler on runoff pollution under low temperature conditions

In recent years, there have been a number of studies on bioretention during hot summer, with only few studies reported during low-temperature winters. The application of bioretention in cold areas still lacks effective guidance. In this study, runoff simulation experiments were conducted to explore the influence of wood chips filler and water treatment residue on the removal of runoff pollutants under different packing gradations and low temperature conditions. Under low temperature, nitrate nitrogen removal rate of wood chips filler decreased from 70% to 90% in autumn to −23%- 35% in winter, the total nitrogen removal rate decreased from 75 to 90% in autumn to 20%–50% in winter, the removal rate of ammonia nitrogen and total phosphorus exceeded 70% during the entire experiment. Water treatment residue filler maintained a high ammonia nitrogen and total phosphorus removal rate during the experiment, with the total phosphorus removal rate above 90% and ammonia nitrogen removal rate above 80%. The bioretention effluent concentration of nitrate and total nitrogen was higher than 7.3 mg/L and 8.5 mg/L, respectively, most of the time. However, at low temperature, the COD removal rate of the two fillers was 25%–50%, which was very poor. Therefore, wood chips filler was observed to be better suited for the removal of nitrate and total nitrogen from the runoff, while water treatment residue had a better effect on the removal of ammonia nitrogen and total phosphorus in winter. Thus, for the application of bioretention in northern China, appropriate fillers should be selected considering the water quality characteristics of the area.

Optimization of the step feeding ratio for nitrogen removal by SBR using technique for order preference by similarity to ideal solution (TOPSIS)

The performance of nitrogen (N) removal was investigated by altering the influent step feeding in a sequencing batch reactor (SBR). The optimum condition for influent step feeding was analyzed using Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) with entropy weight method, considering the C/N ratio range 1.5 to 4.5. The results showed that the SBR with the multi-step-feeding system achieved a high nitrogen removal rate of 92.7% at the three-step influent feeding mode. Nitrogen removal was significantly improved due to the multi-step influent feeding, which provided the required carbon source in the anoxic phase for the removal of nitrate that enhanced the denitrification process. The highest nitrogen removal rate at real-time operation was observed at the three-step feeding mode with 60% primary feeding, 30% secondary feeding, and 10% tertiary feeding, respectively. TOPSIS analysis results also showed that the optimum step feeding ratio was identical to the real-time operation of the SBR.

Novel one-stage reactor configuration for deammonification process: Hydrodynamic evaluation and fast start-up of NITRAMMOX® reactor

This study brings an alternative to treat high ammonium-containing wastewater, presenting a new approach exclusively developed to operate one-stage deammonification process called NITRAMMOX®. The reactor was developed to reduce costs and simplify the operation, promising to be favorable to ANAMMOX and AOB. The correlation between reactor configuration and process efficiency were evaluated using the hydrodynamic characterization, flow anomalies identification, oxygen mass transfer efficiency and reactor start-up. NITRAMMOX® quickly acclimated bacteria after inoculation, presenting a 12-day start-up using 6 h-θ, 25 °C. The hydrodynamic results obtained at different superficial gas velocity (0.40 to 31.8 cm min−1) showed a quick oxygen mass transfer and movement, due to the adequate geometric proportion and reactor design. Deviations from ideality do not compromise the ability of the tracer distribution throughout the NITRAMMOX®, indicating great fluid longitudinal dispersion with no dead zones (θr≥θt), no short circuits (Ψ≤0.3) and good hydraulic efficiency (λ > 0.75), approaching the behavior of a complete mixing reactor. The treatment concept by NITRAMMOX® was shown to be suitable for biomass retention and to establish and favor ANAMMOX bacteria, which can achieve high nitrogen removal rates. The reactor can be applied as a new technology for field application in wastewater treatment systems with low C/N ratio.

Hydroponic Farm Wastewater Treatment Using an Indigenous Consortium

Hydroponic farms produce wastewater that need to be treated before being released into the environment. A three-step screening process (microplate, batch, and semi-continuous flasks experiments) initially designed to select an efficient microalgae strain allowed the isolation of a consortium that naturally developed in the hydroponic farm wastewater. During the non-optimized semi-continuous experiments, the best performing microalgae strain, Scenedesmus obliquus UTEX393 and the wastewater-born consortium cultures achieved good average linear growth rate (0.186 and 0.198/d, respectively) and high average nitrogen removal rates (23.5 mgN/L/d and 21.9 mgN/L/d, respectively). Phosphorus removal was very high probably due to precipitation. An integrated process was designed to treat the hydroponic farm wastewater using the wastewater-born consortium. Despite relatively low coagulation efficiencies in the preliminary tests, when integrated in a continuous process, chitosan was efficient to harvest the naturally wastewater-born consortium. The process was also efficient for removing nitrate and phosphate in less than seven days (average removal of 98.2 and 87.1% for nitrate and phosphate, respectively). These very promising results will help to define a pre-industrial pilot process.

Utilization of Elemental Sulfur in Constructed Wetlands Amended with Granular Activated Carbon for High-Rate Nitrogen Removal

To investigate the role of granular activated carbon (GAC) on nitrogen removal performance of elemental sulfur-based constructed wetlands (S0-based CWs), three systems were constructed according to the different configurations in the functional layer, namely S-CW (S0 added in the functional layer), CSC-CW (GAC, S0 and GAC placed in layers in the functional layer) and SC-CW (S0 and GAC mixed evenly in the functional layer). In CSC-CW and SC-CW, the volumetric ratio of S0:GAC was 9:1. Three CWs were operated under four different hydraulic retention times (HRTs) ranged from 48 h to 6 h. Over the experiment, total inorganic nitrogen (TIN) removal rates of the three CWs were 3.1 – 23.6 g m−2 d−1, 3.5 – 24.1 g m−2 d−1 and 3.4 – 11.5 g m−2 d−1, respectively; CSC-CW remained high TIN removal efficiency (from 74.7 ± 20.2 % to 93.4 ± 1.9 %) while SC-CW had significant lower values when HRT = 6 h (29.8 ± 30.1 %). Mass balance and high-throughput sequencing analysis revealed that mixotrophic denitrification at the sulfur layer and simultaneous nitrification-denitrification (SND) at the rhizosphere played the major role in N removal from CSC-CW (> 95 %). GAC addition facilitated the growth of Iris pseudacorus with the final fresh weight increased from 33.9 gFW ind−1 to 82.3 gFW ind−1 in CSC-CW and 82.7 gFW ind−1 in SC-CW. This study optimizes the practical application of S0-based CWs amended with GAC for N removal from carbon-limited wastewater.

An innovative integrated process for helium and NGL recovery and nitrogen removal

Raw natural gas is composed of several hydrocarbons, incombustible gases, such as nitrogen and helium, and impurities. While all the impurities are typically rejected at the beginning of the process, the removals of the two inert gases are postponed to last steps, where almost all the hydrocarbons except methane are already produced in an NGL recovery unit. Hence, NGL recovery, nitrogen removal and helium extraction steps are counted the most downstream units of the entire gas processing plant. This study investigates an integrated design and optimization of the three processes. In this paper, a novel process configuration, for co-production of sales gas, NGL and crude helium, is introduced. For this purpose, first we investigate and propose an efficient design to embed the helium extraction unit into a single-column nitrogen removal process. The proposed configuration is extended to an integrated process structure which combines nitrogen removal, NGL recovery and helium extraction units. The design reduces significantly the quantity of equipment as eliminating the need for the open refrigeration cycle and propane pre-cooling systems in NGL plants. High ethane and helium recovery, high nitrogen removal rate for different ranges of nitrogen, as well as the crude helium with high purity, are the outstanding potentials of the novel process. We finally optimize the key process parameters using the particle swarm optimization method to guarantee the minimum required work and present the economic evaluation of the new developed process.

Nitrogen Removal Efficiency for Pharmaceutical Wastewater with a Single-Stage Anaerobic Ammonium Oxidation Process.

A single-stage anaerobic ammonium oxidation (ANAMMOX) process with an integrated biofilm–activated sludge system was carried out in a laboratory-scale flow-through reactor (volume = 57.6 L) to treat pharmaceutical wastewater containing chlortetracycline. Partial nitrification was successfully achieved after 48 days of treatment with a nitrite accumulation of 70%. The activity of ammonia oxidizing bacteria (AOB) decreased when the chemical oxygen demand (COD) concentration of the influent was 3000 mg/L. When switching to the single-stage ANAMMOX operation, (T = 32–34 °C, DO = 0.4–0.8 mg/L, pH = 8.0–8.5), the total nitrogen (TN) removal loading rate and efficiency were 1.0 kg/m3/d and 75.2%, respectively, when the ammonium concentration of the influent was 287 ± 146 mg/L for 73 days. The findings of this study imply that single-stage ANAMMOX can achieve high nitrogen removal rates and effectively treat pharmaceutical wastewater with high concentrations of COD (1000 mg/L) and ammonium.

Application of down-flow hanging sponge – Upflow sludge blanket system for nitrogen removal in Epinephelus bruneus closed recirculating aquaculture system

A high-rate nitrogen removal process is required to maintain the water quality in aquaculture tanks used to produce high-density fish populations in recirculating aquaculture systems. In this study, a combined pilot-scale system of down-flow hanging sponge (DHS) reactors and upflow sludge blanket (USB) reactors was applied as a nitrogen removal system for a longtooth grouper Epinephelus bruneus recirculating aquaculture system. The DHS reactors demonstrated high total ammonium nitrogen (TAN) removal efficiencies and the TAN concentration in the aquaculture tank was maintained at 0.32 ± 0.12 mg-N·L−1. The USB reactor fed with sodium acetate acted as a denitrification unit and adjusted the pH through denitrification reaction. All E. bruneus survived the entire experimental period and the daily weight gain rate of 0.6%·day−1 was comparable to that in marine aquaculture. This result shows that the DHS-USB system to be a novel applicable system for nitrogen removal processes in recirculating aquaculture systems and further study at a large scale should be recommended.

Effect of oxic/anoxic conditions on the removal of organic micropollutants in the activated sludge process

Among the emerging issues in the field of wastewater treatments, reducing energy consumption and removal of new organic pollutants have become of primary concern. With respect to the first goal, alternating oxic/anoxic conditions in the bioreactor has demonstrated to be a feasible way to ensure the required efficiency of carbon and nitrogen removal along with energy saving. The aim of the present study was to investigate if these alternating oxic/anoxic conditions are also capable of boosting organic micropollutants degradation, by stimulating the appropriate enzymes. Three different aeration frequencies were tested in a laboratory scale activated sludge reactor and the effects evaluated in terms of removal of carbon, nitrogen and a mixture of OMPs (Sulfamethoxazole, Sulfadiazine, Lincomycin, Carbamazepine, Pyrazole, Naproxen, Atrazine and Sucralose). It was also evaluated if these aeration strategies could change the microbial community composition with respect to the control test conducted under continuous air supply. Among the tested strategies, the longest and shortest durations of anoxic conditions promoted the best removal for the majority of OMPs. This enhancement was statistically well correlated to the activity increase of Lignin Peroxidase and Cellulase enzymes whereas the microbial speciation did not change statistically. The same durations were also capable of maintaining high carbon and nitrogen removal rates within the same biological reactor.

Integration of Algae to Improve Nitrogenous Waste Management in Recirculating Aquaculture Systems: A Review.

This review investigates the performance and the feasibility of the integration of an algal reactor in recirculating aquaculture systems (RAS). The number of studies related to this topic is limited, despite the apparent benefit of algae that can assimilate part of the inorganic waste in RAS. We identified two major challenges related to algal integration in RAS: first, the practical feasibility for improving nitrogen removal performance by algae in RAS; second, the economic feasibility of integrating an algal reactor in RAS. The main factors that determine high algal nitrogen removal rates are light and hydraulic retention time (HRT). Besides these factors, nitrogen-loading rates and RAS configuration could be important to ensure algal performance in nitrogen removal. Since nitrogen removal rate by algae is determined by HRT, this will affect the size (area or volume) of the algal reactor due to the time required for nutrient uptake by algae and large surface area needed to capture enough light. Constraints related to design, space, light capture, and reactor management could incur additional cost for aquaculture production. However, the increased purification of RAS wastewater could reduce the cost of water discharge in places where this is subject to levees. We believe that an improved understanding of how to manage the algal reactor and technological advancement of culturing algae, such as improved algal reactor design and low-cost artificial light, will increase the practical and economic feasibility of algal integration in RAS, thus improving the potential of mass cultivation of algae in RAS.

High-rate nitrogen removal from carbon limited wastewater using sulfur-based constructed wetland: Impact of sulfur sources

This study aims to explore the application of sulfur-based constructed wetlands (CWs) for effective nitrogen (N) removal from wastewater. Two solid sulfur sources namely elemental sulfur (S0) and pyrite (FeS2) were used as substrates in two CWs, i.e. S-CW and P-CW, respectively. The CWs were vegetated with a common wetland plant Iris pseudacorus, and were operated to investigate the effects of hydraulic retention time (HRT) and temperature on N removal. The use of S0 resulted in the highest denitrification rate (19.0 ± 7.5 g m−2 d−1), whereas up to 20 times slower total inorganic nitrogen (TIN) removal was observed with FeS2. Different sulfur sources had negligible effects on the growth of I. pseudacorus, but the element contents (e.g., N, S, and P) within the plant tissues were different. Iris roots in S-CW had higher S content compared with those in P-CW, which resulted in the difference in shoots colors. The characteristics of rhizospheric microbial communities were closely related to the sulfur and nitrogen sources. Briefly, denitrifying and sulfur-oxidizing genera (e.g., Denitratisoma, Sulfurimonas, Thiobacillus) were dominating in the S-CW, suggesting the occurrence of both autotrophic and heterotrophic denitrification processes in the wetland. On the other hand, nitrifying bacteria were more abundant (e.g. Nitrospira, Piscinibacter) in the P-CW. S0 layer and rhizosphere accounted for 99.3% of nitrogen removal and the former part most likely played important roles with a decrease in HRT. Low temperature strongly affected the rate and efficiency of denitrification but recovered to 49.2 ± 25.8% when added with 30 mg L−1 sodium acetate. This study broadens the applications of sulfur-based CWs and provides a promising management strategy for denitrification at low temperatures.

Spatial optimization of operating microalgae bioreactor for nitrogen removal and electricity saving

Various biological nitrogen removal processes have been developed for energy saving in the municipal wastewater treatment plant (MWTP). Recently, a nitrogen removal method using microalgae is emerging as an innovative method. This study has addressed how much of nitrogen was removed by microalgae and how much of electric energy was saved at the same time. For the verification purpose, a long term operation was carried out in a round shape reactor to identify an optimum condition of the highest energy saving rate along with the highest nitrogen removal rate, determined by adjusting time using a light emitting diode (LED) to activate photosynthesis reaction of microalgae and aeration time in a laboratory scale. As a result, it was found that 6.6% or up to 23.8% of energy was saved with biological reaction of microalgae, compared with the traditional nitrogen removal process based on nitrification–denitrification. This indicated that the operation can be flexibly conducted according to the specific operating conditions from each MWTP and its own target energy independence rate, and the findings can be used as a base data for applying such methods using microalgae to the actual treatment plant.

Development of granular sludge coupling n-DAMO and Anammox in membrane granular sludge reactor for high rate nitrogen removal

The integration of nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) provides sustainable solution to simultaneously remove nitrate, nitrite and ammonium. This study demonstrated the sludge granulation process coupling n-DAMO and Anammox from mixed inoculum including river sediment, return activated sludge and crushed anaerobic granule sludge in a novel membrane granular sludge reactor (MGSR). Flocculent biomass gradually turned into compact aggregates and retained as granular sludge with an average diameter of 2.2 mm in MGSR after 684 days’ operation. When steady state with a hydraulic retention time of 1.19 days was reached, the MGSR achieved a nitrogen removal rate of 1.77 g N L−1 d−1. Granules with density of 1.043 g mL−1, settling velocity of 72 m h−1 and sludge volume index of 22 mL g−1 leaded to excellent biomass retention (42 g VSS L−1). Pyrosequencing analysis revealed that two dominant microbial groups, n-DAMO archaea and Anammox bacteria, in the microbial community of the granule were enriched to 31.09% and 12.45%. Fluorescence in situ hybridization revealed a homogenous distribution of n-DAMO archaea and Anammox bacteria throughout the granule. The granular sludge coupling n-DAMO and Anammox microorganisms provides significant potential for high rate nitrogen removal from wastewater.