Nitrate Removal Rate Research Articles

Combining electro-bioremediation of nitrate in saline groundwater with concomitant chlorine production

Groundwater pollution and salinization have increased steadily over the years. As the balance between water demand and availability has reached a critical level in many world regions, a sustainable approach for the management (including recovery) of saline water resources has become essential. A 3-compartment cell configuration was tested for a new application based on the simultaneous denitrification and desalination of nitrate-contaminated saline groundwater and the recovery of value-added chemicals. The cells were initially operated in potentiostatic mode to promote autotrophic denitrification at the bio-cathode, and then switched to galvanostatic mode to improve the desalination of groundwater in the central compartment. The average nitrate removal rate achieved was 39±1 mgNO3−-N L−1 d−1, and no intermediates (i.e., nitrite and nitrous oxide) were observed in the effluent. Groundwater salinity was considerably reduced (average chloride removal was 63±5%). Within a circular economy approach, part of the removed chloride was recovered in the anodic compartment and converted into chlorine, which reached a concentration of 26.8±3.4 mgCl2 L−1. The accumulated chlorine represents a value-added product, which could also be dosed for disinfection in water treatment plants. With this cell configuration, WHO and European legislation threshold limits for nitrate (11.3 mgNO3−-N L−1) and salinity (2.5 mS cm−1) in drinking water were met, with low specific power consumptions (0.13±0.01 kWh g−1NO3−-Nremoved). These results are promising and pave the ground for successfully developing a sustainable technology to tackle an urgent environmental issue.

Characterization of a novel aciduric and halotolerant aerobic denitrifying fungus Fusarium solani DS3 isolated from coastal seawater

A novel aerobic denitrifying fungus strain was isolated from coastal seawater and identified as Fusarium solani strain DS3, which was capable of aerobic nitrogen removal and exhibited tolerance to low pH and high salinity. The removal rates of nitrate, nitrite and ammonium were 3.33, 2.56 and 5.19 mg·L−1·h−1, respectively. Detection of N2O and CO2 in headspace gas samples indicates its capability for aerobic denitrification using nitrite as electron acceptor (but not nitrate). The unabated total nitrogen in nitrate treatments in nitrogen balance revealed that nitrate was incompetent to trigger aerobic denitrification. We measured 22.02% and 11.84% of total nitrogen converted to gaseous nitrogen using around 80 mg·L−1 of nitrite and ammonium as nitrogen source, respectively. Nitrite reductase activity assay revealed that dissimilatory and assimilatory nitrite reductases worked together in nitrite reduction. The present study indicates that fungal strain DS3 is a promising candidate for nitrogen removal, especially for saline wastewater.

Inhibition characteristics of the electrokinetic removal of inorganic contaminants from soil due to evolution of the acidic and alkaline fronts

This study comprehensively investigates the inhibition characteristics of the electrokinetic removal (EKR) of inorganic pollutants from soil due to evolution of the acidic and alkaline fronts (EAAF). The effects of EAAF on the ion strength of the soil pore fluid, potential distribution, soil colloids, clay minerals, and soil microstructure are systematically examined, in addition to the control effects of non-target charged species on the removal of target pollutants. The results show that the transport of target species near the anode region is mainly inhibited by potential flattening, soil colloid aggregation, and the closure of soil pores. Migration near the cathode region is mainly inhibited by the immobile chemical states of metals, potential flattening, soil dehydration, and a high soil adsorption ability owing to the relatively developed pores. This results also show that H+, OH-, and soluble Al have a significantly control effect on the macroscopic dynamics of EKR of the target contaminants. The injection of acidic solution near the cathode alleviates the potential jump and prevents the formation of metal hydroxides to some extent. The average removal rates of nitrate, Pb, and Cd after EKR improved from 85.5%, 11.1%, and 21.8–98.5%, 35.8% and 47.7%, respectively.

Electrostatic self-assembly to form unique LiNbO3/ZnS core-shell structure for photocatalytic nitrate reduction enhancement

Photocatalytic NO3– reduction in water has been regarded as a promising route due to its high efficiency and green feature. Several limiting factors, such as lack of catalytic sites, insufficient light collection, and spatial charge separation capacity photocatalytic denitrification, still need to be overcome for the practical applications. Herein, an innovative LiNbO3/ZnS heterojunction with a unilateral opening core–shell structure was constructed. ZnS was tightly anchored on the surface of LiNbO3 by modified electrostatic self-assembly method. High nitrate removal rate (98.84%) and N2 selectivity (98.92%) were achieved with a molar ratio of LiNbO3 and ZnS of 1:5 (1:5L-ZS) using formic acid as a hole scavenge. The LiNbO3/ZnS degradation kinetics of NO3– was corresponding to the first-order kinetics equation. The nitrate removal rate and N2 selectivity remained stable after three cycles in such photocatalytic NO3– reduction. The outstanding photocatalyst performance can be ascribed to the improved surface active sites, the well-matched band structure, and the unique core–shell structure. It provides an effective strategy for controllable fabrication of core–shell photocatalyst with strong light-harvesting ability and charge separation efficiency to enhance the removal rate of nitrate in water.

Inhibition of ferrous iron (Fe2+) to sulfur-driven autotrophic denitrification: Insight into microbial community and functional genes

The effect of Fe2+ on the performance of sulfur-driven autotrophic denitrification (SDAD) using S0 as electron donor was evaluated. The experimental results showed that as initial Fe2+ concentration increased, nitrate (NO3–) removal rate significantly decreased. Fe2+ ion (0.1 mM and 1 Mm) inhibited SDAD rate (approximately 10% and 50%) and resulted in an accumulation of nitrite (NO2–) and nitrous oxide (N2O). The relative abundance of Thiobacillus was positively correlated with NO3– removal rate, whereas negatively correlated with Fe2+ concentration, suggesting that Fe2+ inhibited the sulfur-oxidizing denitrifying bacteria. Moreover, the abundance of bacterial 16S rRNA, denitrifying genes (narG, nirS, nirK and nosZ) and sulfur-oxidizing genes (soxB and dsrA) decreased with the increase of Fe2+ concentration, among them nosZ and soxB were the most sensitive genes to Fe2+, and nosZ/narG, soxB/(bacterial 16S rRNA) and soxB/nirK had influence on NO3– removal rate, while nosZ/(bacterial 16S rRNA) affected N2O accumulation rate.

Enhanced Denitrification of Integrated Sewage Treatment System by Supplementing Denitrifying Carbon Source.

Integrated sewage treatment system (ISTY) is a new technology for rural domestic sewage treatment. In the ISTY, the carbon source in the denitrification stage is often insufficient, affecting the denitrification efficiency. In order to improve the denitrification efficiency, several commonly available agricultural wastes, peanut shell (PS), sawdust (SD), peat (PT), and their mixtures (MT), were selected as supplementary carbon sources in the denitrification stage of ISTY to study the denitrification efficiency. Results show that PS exhibited a high carbon release capacity. PS released an enormous amount of carbon in 144 h, and the cumulative total organic carbon was 41.99 ± 0.7 mg/(g·L). The optimum carbon source dosage was 3 g/L, the nitrate removal rates of PS exceeded 95% after 48 h, and the denitrification rates were 9.35 mg/(g·L), which were 63.92% higher than that of the control group. After running the ISTY for 120 h, and with PS as supplementary carbon sources, the removal rate of TN increased from 29.76% to 83.86%. At the genus level, the dominant denitrifying bacteria in ISTY, after adding PS, were Pseudomonas and Cupriavidus, accounting for 78.68%, an increase of 72.90% compared with the control group. This evidence suggested that PS can obviously enhance the denitrification efficiency of the ISTY as a supplementary carbon source.

Magnetite-mediated electrically connected community for shortening startup of methane-dependent denitrification in a membrane biofilm reactor

Denitrifying anaerobic methane oxidation (DAMO) not only mitigates methane emission from wastewater treatment, but compensates for the deficiency of current nitrogen removal process. However, the doubling time of DAMO microbes is usually more than two weeks, resulting in a long-period startup of a methane-dependent denitrification reactor especially with anaerobic sludge as inoculum. The study presented here found that, in the presence of magnetite, the nitrate removal rate reached 17.6 ± 0.4 mgNO3−-N/L/d after the 120-day experiments, which was approximately 2.4 folds higher than that in the absence of magnetite (7.3 ± 0.1 mgNO3−-N/L/d). The nitrate removal rate in the presence of magnetite reached 7–8 mgNO3−-N/L/d at day 80–85, which shortened the startup periods of approximately 35–40 days. Microbial morphology based on scanning electron microscope and transmission electron microscope showed that, the surface of cells was deposited by magnetite and they might be connected via magnetite. Further investigations via cyclic voltammetry and electrochemical impedance spectroscopy showed that magnetite mediated an electrically connected community with a higher capacitance and lower resistance than that in the absence of magnetite. Microbial community analysis showed that, in the presence of magnetite, the potential DAMO bacteria (Methylacidimicrobium and Methylotetracoccus species), methanogens (Methanothrix species) as well as nitrate-reducing bacteria (Bellilinea and Dechloromonas species) were enriched. They might participate in direct interspecies electron transfer (DIET) via magnetite substituting for c-type cytochromes as the electrical connection components, since methane oxidation in the presence of magnetite was insensitive to the external addition of potential intermediates, such as hydrogen.

Effects of different carbon sources on the efficiency of sulfur-oxidizing denitrifying microorganisms

This study aims to compare the effects of different carbon sources on sulfur-oxidizing denitrifying microorganisms by using glucose, ethanol, and acetate as carbon sources. Under the same chemical oxygen demand Cr (CODCr), nitrate, and sulfide concentrations, the removal rate of nitrate and total organic carbon, and the yield of elemental sulfur in a static experiment and a continuous flow reactor with glucose as the carbon source were lower than those with ethanol and acetic acid as the carbon source. The core sulfur-oxidizing denitrifying bacteria that use glucose as the carbon source were Azoarcus, Geoalkalibacter, and Mangroviflexus; those that use ethanol as the carbon source were Arcobacter, Pseudomonas, and Thauera; those that use acetate as the carbon source were Pseudomonas and Azoarcus. The metabolic activity of microorganisms that use different carbon sources was explained by functional gene detection. The fluctuation of gltA, a functional gene indicating heterotrophic metabolism of microorganisms, was small in three reactors, but that of the sulfur oxidation gene, Sqr, in the reactor with acetic acid as the carbon source was larger. Our results suggest that acetate is a more suitable carbon source for denitrification-desulfurization systems.

Biofilm carrier type affects biogenic sulfur-driven denitrification performance and microbial community dynamics in moving-bed biofilm reactors

Autotrophic denitrification with biosulfur (ADBIOS) provides a sustainable technological solution for biological nitrogen removal from wastewater driven by biogenic S0, derived from biogas desulfurization. In this study, the effect of different biofilm carriers (conventional AnoxK™ 1 and Z-200 with a pre-defined maximum biofilm thickness) on ADBIOS performance and microbiomics was investigated in duplicate moving bed-biofilm reactors (MBBRs). The MBBRs were operated parallelly in continuous mode for 309 days, whilst gradually decreasing the hydraulic retention time (HRT) from 72 to 21 h, and biosulfur was either pumped in suspension (days 92–223) or supplied in powder form. Highest nitrate removal rates were approximately 225 (±11) mg/L·d and 180 (±7) mg NO3−-N/L·d in the MBBRs operated with K1 and Z-200 carriers, respectively. Despite having the same protected surface area for biofilm development in each MBBR, the biomass attached onto the K1 carrier was 4.8-fold more than that on the Z-200 carrier, with part of the biogenic S0 kept in the biofilm. The microbial communities of K1 and Z-200 biofilms could also be considered similar at cDNA level in terms of abundance (R = 0.953 with p = 0.042). A relatively stable microbial community was formed on K1 carriers, while the active portion of the microbial community varied significantly over time in the MBBRs using Z-200 carriers.

Effect evaluation of remediation in three typical rivers with Vallisneria natans under different pollution and spatial characterization of functional microorganisms

Submerged plants can improve water quality, but the evaluation of practical engineering applications and the research on the characterization of functional microorganisms in the ecosystem are still insufficient. Three typical rivers (gradient pollution, persistent point pollution, and non external pollution) planted with Vallisneria natans in Guangzhou, China, were selected for monitoring to evaluate the restoration effect by measuring ralated environmental parameters and pollutant indexes, while microbial sequencing was used to analyze the spatial characterization of functional microbial composition. The results showed that Haizhu wetland phase III had a higher pH (9–10) and Xinshichong had a relatively lower concentration of dissolved oxygen (0.23–6.29 mg/L) varied with the intensity of light. Nitrogen pollution level followed the order of Xinshichong > Haizhu wetland phase I > Haizhu wetland phase III generally. The nitrate removal rate in Haizhu wetland phase I reached over 88%. 16S rRNA sequencing analysis showed that the sediment, leaves, and water bodies had different microbial community structures and Proteobacteria were abundant in all samples. Cyanobacteria attached to the leaves of Vallisneria natans, thereby inhibiting the growth in the water and sediment. Sulfur and iron circulation functional bacteria were mainly found in the sediment, while iron-oxidizing bacteria also presented on the leaves. The sediment from Xinshichong also contained abundant methane-related functional bacteria. The distributions of nitrogen cycling-related functional bacteria in the sediment and water, and on the leaves varied according to the different pollution levels at the sites. Therefore, Vallisneria natans can regulate DO environment, improve water quality, and work as an important attachment site for functional microorganisms in the ecosystem to prevent the waterbodies from black and odor. Additional work will be necessary to explore the process on the production of black and odor and the synergistic mechanism of microorganisms.

Nitrogeniibacter mangrovi gen. nov., sp. nov., a novel anaerobic and aerobic denitrifying betaproteobacterium and reclassification of Azoarcus pumilus as Aromatoleum pumilum comb. nov.

Denitrification is a vital link in the global bio-nitrogen cycle. Here, we isolated a strain (M9-3-2T) that is a novel benzo[a]pyrene (BaP)-tolerant, anaerobic and aerobic denitrifying bacterium from a continuous BaP-enrichment cultured mangrove sediment. In silico comparative genomics and taxonomic analysis clearly revealed that strain M9-3-2T (=MCCC 1K03313T=JCM 32045T) represents a novel species of a novel genus named as Nitrogeniibacter mangrovi gen. nov., sp. nov., belonging to family Zoogloeaceae, order Rhodocyclales. In addition, the species Azoarcus pumilus is transferred into genus Aromatoleum and named Aromatoleum pumilum comb. nov. The predominant respiratory quinone of strain M9-3-2T was ubiquinone-8 and the major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, three unidentified phospholipids and three unidentified aminophospholipids. In this study, the capacity of strain M9-3-2T to eliminate nitrate was detected under anaerobic and aerobic conditions, and the removal rates of nitrate were 6.1×10-6 µg N/l/h/cell and 3×10-7 µg N/l/h/cell, respectively. Our results suggested that strain M9-3-2T could play an important role in the nitrogen removal regardless of the presence of oxygen in natural or/and man-made ecosystems.

Nitrogen behavior during artificial groundwater recharge through ponds: A case study in Xiong’an New Area

The Xiong'an New Area (XA) was established as a development hub in China. Excessive exploitation of groundwater has caused a series of environmental and geological problems, restricting further development of XA. The widely distributed ponds in this area have been targeted as convenient and efficient sites of artificial groundwater recharge. However, nitrogen accumulation in the shallow vadose zone associated with agricultural activities may pose environmental risks to groundwater during the recharge and infiltration process. Therefore, this study investigated the effects, transfer, and transformation of nitrogen during artificial groundwater recharge. The aeration zone is thick and the medium comprises fine particles, with total nitrogen and nitrate accumulation mainly in the shallow aeration zone. In indoor experiments, the nitrate removal rate reached 83.5% when organic carbon in the source water was increased by 10mg/L. For Baigou diversion river water(BW) with slightly higher (14.46mg/L) and lower (5.04mg/L) nitrate contents, the nitrate content decreased by 26.0% (10.70mg/L) and 26.8% (3.69mg/L), respectively, after 150days. When the water head was increased by 20cm to increase the recharge rate, the time required for nitrate and ammonium to reach the maximum and equilibrium concentration was reduced by 50%. These findings indicate that nitrogen concentration in the source water, aeration zone media, and groundwater should be considered in pond replenishment. It is also necessary to control the concentration of organic carbon and the rate of recharge, which would provide guidance for other similar projects.

Selective reduction of nitrate to ammonium over charcoal electrode derived from natural wood

Electrocatalytic nitrate reduction has been regarded as an efficient alternative route for ammonia production. Developing efficient, economical and environment-friendly cathodes is a significant concern for the practical applications of this method. Herein, we report a charcoal electrode fabricated by carbonizing natural wood for efficient nitrate reduction. It displays high overpotential for hydrogen evolution, moderate sp3 C structure and oxygen-containing surface groups. Benefiting from these features, the charcoal cathode exhibits high nitrate removal rate (91.2%), outstanding selectivity (98.5%) and fast production rate (0.570 mmol L−1 h−1 cm−2) for ammonium. Both removal rate and selectivity are superior to other carbon materials and comparable to metal-containing cathodes. These results exhibit the possibility of using charcoal as cathodes for denitrification and ammonia recovery from wastewater.

Post-Treatment of the Effluent from Anaerobic Digestion of the Leachate in Two-Stage SBR System Using Alternative Carbon Sources

Although anaerobic digestion (AD) enables biogas production and facilitates renewable electricity production, its effluent must be post-treated before discarding it into the environment. However, during AD designing, the post-treatment step is often overlooked. This paper presents the kinetics and efficiency of nitrogen removal from effluent after AD of leachate from the aerobic stabilization of the organic fraction of municipal solid waste. A two-stage SBR system was used. An ammonium oxidation rate of 15.5 mg N-NH4/(L·h) ensured a 98% nitrification efficiency (I stage). For denitrification (II stage), alternative carbon sources (ACS) (molasses, crude glycerine, or distillery stillage) were used. Two volumetric exchange rates (n) were tested: 0.35 1/d (COD/N-NO3 ratio of 8) and 0.5 1/d (COD/N-NO3 of 7). With all ACS and COD/N-NO3 ratios, almost 100% of nitrate was denitrified; at the COD/N-NO3 of 8, biodegradable organics remained in the effluents. At the COD/N-NO3 of 7, the denitrification removal rates were lower (29.6-45.1 mg N-NOx/(L·h)) than at the ratio of 8 (72.1–159.5 mg N-NOx/(L·h)), because of temporal nitrite accumulation. The highest nitrate removal rates were obtained with molasses, the lowest with a distillery stillage. Considering the nitrate removal rate and the effluent COD concentration, molasses was recommended as the most effective carbon source for AD effluent treatment at the COD/N-NO3 of 7.

Sarcocornia neei: A novel halophyte species for bioremediation of marine aquaculture wastewater and production diversification in integrated systems

The integration of bioremediation systems is one of the most promising techniques to mitigate the environmental impact of aquaculture effluents. Also, it allows nutrient recycling, production diversification, and the creation of high-value by-products. In marine aquaculture, where the implementation of salt-tolerant extractive species is essential, halophyte plants have demonstrated to be optimal candidates for bioremediation of saline aquaculture wastewater.This study aimed to evaluate for the first time the efficiency of Sarcocornia neei (Lag.), a halophyte plant with high adaptability, salinity tolerance and growth potential when irrigated with seawater, in removing nutrients from marine fish aquaculture wastewater and artificial effluents. Two experiments were carried out. In the first one, the growth rate, removal of inorganic nutrients, and accumulation of organic compounds in deep-water hydroponics and sand-substrate systems were evaluated in artificial effluents with different nitrogen and phosphate loads during 70 days. In the second, due to the better performance achieved by S. neei in deep-water systems, its nitrogen removal efficiency and productivity rates were evaluated in deep-water aquaponics with marine aquaculture wastewater and artificial effluents at higher nitrogen loads during 61 days.The highest productivity rates achieved by S. neei (14.41 ± 0.78 kg m−2) were obtained in deep-water culture units, reaching 100% plant survival, suggesting that this species is more suitable for its implementation in this type of system. Significant total ammonia nitrogen removal rates were obtained by the plants, achieving a maximum in sand-substrate systems (0.68 ± 0.41 g m−2 day−1). The results of nitrate removal rates obtained by S. neei (11.25 ± 31.38 g m−2 day−1) make this species an ideal potential candidate for the removal of this compound present in marine RAS effluents. Accumulation of organic compounds was corroborated by obtaining a significant increase (p < 0.05) in organic N (31.2 ± 0.1 mg g dry weight−1) and organic P (4.0 ± 0.6 mg g dry weight−1) content in plant biomass at the end of the trials.These results indicated that S. neei is a good candidate for its use as a biofilter for marine aquaculture wastewater. Further investigations should be done to analyze possible influences on growth rates and nutrient removal efficiency by adding essential micronutrients, adjusting effluent salinity, and implementing different plant densities. Also, further studies could be interesting to determine the feasibility of long-term integration of a bioremediation system with S. neei associated with marine aquaculture effluents, approaching its application to industrial-scale production systems.

Effects of sulfamethoxazole on nitrogen removal and molecular ecological network in integrated vertical-flow constructed wetland

Response of nitrogen removal efficiency and microbial interactions to organic pollution has been a major issue in wastewater treatment system. However, the nitrogen removal efficiency and interactions among microbial community under antibiotics press is still unclear. Thus, the effect of sulfamethoxazole (SMX) on nitrogen removal and microbial responses of IVCWs was investigated through recorded the nitrogen removal efficiency before and after adding SMX and random matrix theory (RMT)-based network analysis. Results showed that better NH4+-N removal (>90%) after a long period of operation were achieved in IVCWs, but NO3--N was accumulated. However, nitrate removal rates were significantly increased after long-term exposure (60 d) to 100 μgL−1 SMX (from 27.35% to 35.57%) with relatively high SMX removal (53.50%). Surprisingly, the ammonia nitrogen removal rate (90.07−92.70%) were not significantly affected by SMX in IVCWs. Moreover, the bacterial richness was decreased and the bacterial community structures were altered by the presence of SMX, especially those of nitrogen-transforming microorganisms. Molecular ecological network analysis suggested that SMX had positive influences on denitrifying bacteria interactions but reduced the network complexity and microbial interactions on whole molecular network, and among-module connections were weakened obviously at SMX.

Effect of different C/N ratios and hydraulic retention times on denitrification in saline, recirculating aquaculture system effluents

Data on operation and performance of cost-effective solutions for end-of-pipe removal of nitrate from land-based saltwater recirculating aquaculture systems (RAS) are scarce but increasingly requested by the aquaculture industry. This study investigated the performance of a (semi)commercial-scale fixed-bed denitrification unit using single sludge for treating effluent from a commercial, saltwater RAS used for production of Atlantic salmon (Salmo salar). A fixed-bed denitrification reactor was fed continuously with 3-days hydrolyzed sludge from the commercial RAS, and was operated at different hydraulic retention times (HRTs; 1.82, 3.64, 5.46, or 7.28 h) or influent C/N ratios (3, 5, 7, or 10). Twenty-four h pooled samples were collected from the inflowing RAS water and the hydrolyzed sludge as well as from the denitrification reactor outlet, and samples were analyzed for nutrients and organic matter content.Nitrate removal rates increased consistently with decreasing HRT (from 64.3 ± 5.2–162.7 ± 22.0 g NO3-N/m3/d within the HRTs tested) at non-limiting C/N ratios, while nitrate removal efficiencies decreased (from 99.6 ± 0.3–58.2 ± 8.9 %). With increasing influent C/N ratios at constant HRT (3.64 h), nitrate removal rates increased until the removal efficiency was close to 100 % and nitrate concentration in the denitrification reactor became rate-limiting. A maximum nitrate removal rate of 162.7 ± 2.0 g NO3-N/m3/d was achieved at a HRT of 1.82 h and an influent C/N of 6.6 ± 0.5, while the most efficient use of hydrolyzed sludge (0.19 ± 0.02 g NO3-N removed/g sCOD supplied) was obtained with a HRT of 3.64 h and a C/N ratio of 2.9. Removal rates of organic matter significantly and consistently increased with decreasing HRT and increasing C/N ratio. In addition, reducing HRT and increasing C/N ratios significantly improved removal of total phosphorus (TP) and PO4-P.In conclusion, optimal management of the operating parameters (HRT and C/N ratio) in a single-sludge denitrification process can significantly reduce the discharge of nitrogen, organic matter, and phosphorous from land-based saltwater RAS and thus contribute to increased sustainability.

Influence of the carbon source concentration on the nitrate removal rate in groundwater

ABSTRACT At present, groundwater nitrate pollution in China is serious. The use of microorganisms for biological denitrification has been widely applied, and it is a universal and efficient in situ groundwater remediation technique, but this approach is influenced by many factors. In this study, glucose was adopted as the carbon source, four different concentrations of 0, 2, 5 and 10 g/L were considered, and natural groundwater with a nitrate concentration of 300.8 mg/L was employed as the experimental solution. The effect of the carbon source concentration on the nitrate removal rate in groundwater was examined through heterotrophic anaerobic denitrification experiments. The results showed that the nitrate removal rate could be improved by the addition of an external carbon source in the process of biological denitrification, and an optimal concentration was observed. At a glucose concentration of 2 g/L, the denitrification effect was the best.

Exploration and verification of the feasibility of sulfur-based autotrophic denitrification process coupled with vibration method in a modified anaerobic baffled reactor for wastewater treatment

As an effective nitrate removal process with lower sludge production, sulfur-based autotrophic denitrification (SAD) has attracted extensive attention in recent years. This study investigated a modified anaerobic baffled reactor coupled with a vibration frame (MV-ABR) for the SAD process to treat nitrate contaminated water. The nitrate removal rate (NRR) of 0.34 kg NO3−-N·m−3·d−1 was obtained under an ambient temperature. With adding oyster shells in two steps, the maximum NRR can be further increased from 0.34 kg NO3−-N·m−3·d−1 to 0.37 kg NO3−-N·m−3·d−1. The MV-ABR also achieved a strong impact resistance and robustness nitrogen removal performance under transient shocks. In addition, coupling the anaerobic baffled reactor (ABR) with the vibration method demonstrated that vibration could improve the denitrification performance, even under low temperatures (10 °C–15 °C). Under a suitable intermittent vibration intensity (level 1 (5–60)), the average NRR increased from 0.26 kg NO3−-N·m−3·d−1 to 0.35 kg NO3−-N·m−3·d−1, which suggests this is an economic and effective method for the SAD process. Overall, these results suggest that the MV-ABR could boost the SAD treatment performance, and present a stable nitrate removal performance even under a lower temperature environment (<15 °C) or transient shocks.

Nitrate removal by quaternized mesoporous silica gel in ternary anion solutions: Flow-through column experiments and artificial neural network modeling

The aim of this study was to examine nitrate removal by quaternized silica gel (q-SG) in ternary solutions of nitrate, phosphate, and sulfate under flow-through column conditions. q-SG was synthesized by grafting dimethyloctyl[3-(trimethoxysilyl)propyl] ammonium chloride on silica gel. Fixed-bed column experimental conditions (N = 15) were designed using central composite design to examine dynamic removal behaviors of competing anions in columns containing q-SG. During the experiments, influent solution containing ternary anions of nitrate, phosphate, and sulfate was injected into flow-through columns. In the effluent, the ternary anions along with chloride were monitored to obtain competitive breakthrough curves. Column experiments demonstrated the dynamic and competitive removal behaviors of anions during adsorption and leaching in the columns. Artificial neural network (ANN) model was developed based on the column experimental data to predict the removal rates of anions in the column experiments. In the model development, influent concentrations of nitrate, phosphate, and sulfate were selected as three variables in the input layer, whereas removal rates of nitrate, phosphate, and sulfate were chosen as three variables in the output layer. The developed ANN model with topology 3:8:9:3 (three input variables, eight neurons in the first hidden layer, nine neurons in the second hidden layer, and three output variables) could simultaneously predict the removal rates of anions in column experiments.