High Nitrate Removal Efficiency Research Articles

A new Method for the Removal of Ammonium from Drinking Water Using Hybrid Method of Modified Zeolites / Catalytic Ozonation

Introduction: Ammonia in form of ammonium ions is toxic and could decrease the dissolved oxygen in water and endanger the aquatic life. The aim of this study is the removal of ammonium using oxidation and adsorption by catalytic ozonation and clinoptilolite zeolite, respectively. Methods: The research method is Experimental. First, optimal pH of ammonium adsorption on carbon catalyst (5 g/L), Garmsar and Firoozkooh zeolites and oxidation were determine. Then, in catalytic ozonation process, the effect of other variables on ammonium removal efficiency such as the concentration of carbonic catalyst (0.5- 50 g/L) and the reaction time were investigated. Then the effect of retention time and adsorbent concentration on adsorption of the remaining ammonium and nitrate produced by the oxidation process using zeolites and their modifications were determined. Resuts: The results showed that optimum pH for the ammonium adsorption process by carbon catalyst, catalytic ozonation and zeolite was 8, 9 and 8, respectively. However, the optimum pH 4 was determined for nitrate removal. The highest ammonium absorption capacity was related to natural Firoozookh zeolite and 18.5 mg/g, and the effect of ligand and acid modification decreased 12 and 14% of absorbed capacity, respectively. It is also, the highest nitrate removal efficiency was related to Garmsar ligand modified zeolite (98%) and an absorption capacity of 11.2 mg/g. In the COP/absorption process the concentration of ammonium was decreased to 0.6 m /L. Conclusion: This method effectively eliminates ammonium, and the modification of zeolite with cationic surfactant increases the efficiency of nitrate removal and the concentrates of all pollutants are brought below standards.

Substrate competition and microbial function in sulfate-reducing internal circulation anaerobic reactor in the presence of nitrate

Nitrate and sulfate often coexist in organic wastewater. In this study, an internal circulation anaerobic reactor was conducted to investigate the impact of nitrate on sulfate reduction. The results showed that sulfate reduction rate dropped from 78.4% to 41.4% at NO3- /SO42- ratios ranging from 0 to 1.03, largely attributed to the inactivity of acetate-utilizing sulfate-reducing bacteria (SRB) and preferential usage of nitrate of propionate-utilizing SRB. Meanwhile, high nitrate removal efficiency was maintained and COD removal efficiency increased with nitrate addition. Enhancement of propionate and butyrate degradation based on Modified Gompertz model and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) analysis. Moreover, nitrate triggered the shift of microbial community and function. Twelve genera affiliated to Firmicutes, Bacteroidetes and Proteobacteria were identified as keystone genera via network analysis, which kept functional stability of the bacterial community responding to nitrate stress. Increased nitrate inhibited Desulfovibrio, but promoted the growth of Desulforhabdus. Both the predicted functional genes associated with assimilatory sulfate reduction pathway (cysC and cysNC) and dissimilatory sulfate reduction pathway (aprA, aprB, dsrA and dsrB) exhibited negative relationship with nitrate addition.

Woodchip bioreactors provide sustained denitrification of brine from groundwater desalination plants

Woodchip bioreactors are widely known as a best management practice to reduce excess nitrate loads that are discharged with agricultural leachates. The aim of this study was to evaluate the performance of citrus woodchip bioreactors for denitrification of brine (electrical conductivity ≈ 17 mS cm−1) from groundwater desalination plants with high nitrate content (NO3−-N ≈ 48 mg L−1) in the Campo de Cartagena agricultural watershed, one of the main providers of horticultural products in Europe. The performance was evaluated relative to seasonal changes in temperature, dissolved organic carbon (DOC) provided by woodchips, hydraulic residence time (HRT) and woodchip aging. Bioreactors (capacity 1 m3) operated for 2.5 years (121 weeks) in batch mode (24 h HRT) with three batches per week. Denitrification efficiency was modulated by DOC concentration, temperature, hydraulic residence time and the drying-rewetting cycles. High salinity of brine did not prevent nitrate removal from occurring. The high DOC availability (>25 mg C L−1) during the first ≈48 weeks resulted in high nitrate removal rate (>75%) and nitrate removal efficiency (until ≈ 25 g N m−3 d−1) regardless of temperature. Moreover, the high DOC contents in the effluents during this period may present environmental drawbacks. Denitrification was still high after 2.5 years (reaching ≈9.3 g N m−3 d−1 in week 121), but dependence on warm temperature became more apparent with woodchips aging from week ≈49 onwards. Nitrate removal efficiency was highest on the first weekly batch, immediately after woodchips had been unsaturated for four days. It was attributable to a flush of DOC produced by aerobic microbial metabolism during drying that stimulated denitrification following re-saturation. Hence, alternance of drying-rewetting cycles is an operation practice that increase bioreactors nitrate removal performance.

Nanoscale zero-valent iron (nZVI) encapsulated within tubular nitride carbon for highly selective and stable electrocatalytic denitrification

Nanoscale zero-valent iron (nZVI) encapsulated within tubular nitride carbon for highly selective and stable electrocatalytic denitrification. • Tubular NC encapsulated nZVI regulated selective NO 3 − reduction to N 2 . • N 2 selectivity reached 98% with rapid NO 3 − removal in eutrophic water. • Hydrophilic NC with high surface area and porosity promoted NO 3 − adsorption. • Electrons and [H] rejuvenated Fe(III) to Fe (II) for sustained NO 3 − reduction. • Tubular NC layer protected active Fe for high stability and acid-base tolerance. Denitrification of nitrate (NO 3 − ) to dinitrogen (N 2 ) is of fundamental importance in water pollution control and environmental remediation. Conventional catalytic denitrification requires the use of expensive and often toxic metal such as Pd and Cu. Nitrate also can be rapidly reduced by environment-friendly nanoscale Zero-Valent Iron (nZVI), unfortunately the end product is mostly ammonia. Herein, nZVI is reconstructed with nitrogen-doping, dispersed and encapsulated within a tubular nitride carbon (nZVI@NC) as an electrocatalyst, regulating the multi-electron transfer reaction. The tubular iron structure is about 400–450 nm in length, has a diameter around 70–100 nm and wall thicknesses about 20–25 nm, surface area at 1445 m 2 /g. The nZVI@NC exhibits high nitrate removal efficiency (92%) and N 2 selectivity (97%), and maintains consistent performance in the pH range of 5–11. With nitrate selectively adsorbing on the highly porous and hydrophilic NC layer, the N-O bond is efficiently cleaved by gaining electrons from nZVI and activated hydrogen [H] to produce benign N 2 . Meanwhile, the intermediate product NH 4 + can be oxidized to N 2 by the HClO generated on the anode. This study points to promising prospects of modified nZVI for applications in denitrification and environmental remediation.

Pd–In bimetallic nanoparticles supported on chelating resin for nitrate removal from water: high efficiency and low NH4+ selectivity

The supported Cu/Pd bimetallic catalyst could prestore hydrogen and no additional reducing agent is required during the nitrate reduction process. High nitrate removal efficiency (96%) and low NH4+ selectivity (<2%) were achieved.

Evaluation of South African Sand/Zero-Valent Iron Combinations for the Treatment of Nitrate-Contaminated Water: Kinetic and Effect of Competitive Ions

This study aimed to define the optimum weight ratio between Berea Red sand (BRS)/zero-valent iron (ZVI) combinations to be used in the treatment of nitrate contaminated water. The effect of competing ions (phosphate and sulfate) on the nitrate removal efficiency of the best performing BRS-ZVI w/w ratio was also assessed. To achieve this objective, batch tests were performed under anoxic and acidic conditions (pHi = 4.5), using two combinations: 50%BRS-50%ZVI (w/w) and 25%BRS-75%ZVI (w/w), as well as 100%ZVI as a control. BRS and ZVI had 1 to 2-mm grain size. pH and nitrogen species were tested during these batch tests. Kinetic analysis was also carried out. While the removal efficiencies of 100%ZVI and 25%BRS-75%ZVI (w/w) were 70.2% and 83.1%, respectively, the experimental results showed that the combination of 50%BRS-50%ZVI (w/w) had the highest nitrate removal efficiency (99.5%), implying a synergistic effect between BRS and ZVI. Likewise, the kinetic analysis showed that the nitrate removal rate (k) increased as the BRS mass in the BRS-ZVI combination increased. Furthermore, the presence of phosphate and sulfate negatively affected the nitrate removal performance of the 50%BRS-50%ZVI combination, which was the best performing weight ratio. However, this weight ratio still showed high nitrate removal capacities in the presence of phosphate and sulfate, respectively. The 50%BRS-50%ZVI combination demonstrated to be the optimum among the used ones. However, further investigation in a large-scale reactor on this combination is recommended for further optimization of its performance.

Nitrate removal and secondary effects of a woodchip bioreactor for the treatment of subsurface drainage with dynamic flows under pastoral agriculture

While enabling economically viable use of poorly drained soils, artificial subsurface drainage has also been found to be a significant pathway for nutrient transfers from agricultural land to surface waters. Thus, mitigating the impacts of agriculture on surface water quality needs to address nutrient transfers via subsurface drainage. Woodchip bioreactors are a promising mitigation option as demonstrated under arable agriculture in the mid-west of the USA. However, research is needed to ascertain their efficiency in removing nutrients from very flashy drainage flows common in New Zealand (NZ) pastoral agriculture and any possible pollution swapping (e.g. reduction of leaching losses vs. greenhouse gas emissions). Accordingly, a lined 78-m3 woodchip bioreactor was constructed on a dairy farm in the Hauraki Plains (Waikato, NZ) with a drainage area of 0.65 ha. Rainfall, flow, hydrochemistry and dissolved gases in the inflow and outflow were monitored for two drainage seasons (part of 2017, 2018). Based on the nitrate-N fluxes, the estimated nitrate removal efficiency of the bioreactor was 99 and 48% in 2017 and 2018, respectively. The higher removal efficiency in 2017 could be attributed to two reasons. Firstly, the substantially longer hydraulic residence time (HRT) of the water in the bioreactor (mean = 21.1 days vs 4.7 days in 2018) provided more opportunity for microorganisms to reduce the nitrate. A strong positive relationship between HRT and removal efficiency was also observed within the 2018 drainage season. Secondly, denitrification was supported in 2017 by greater electron donor availability. Evidence of this was the higher mass of DOC discharge from the bioreactor (318 mg C L−1 of bioreactor volume vs 165 mg C L−1 in 2018). Removal rates in the bioreactor varied from 0.67–1.60 g N m−3 day−1 and were positively correlated with inflow nitrate loads. Pollution swapping was observed during the start-up phase of the bioreactor in both years (DOC, and DRP only in 2017) and during periods with very long HRTs (hydrogen sulphide (H2S) and methane (CH4) production). Substantially elevated discharges of DOC and DRP, as compared to inlet conditions, occurred during the initial start-up phase of the bioreactor in 2017 (3 to 3.5 pore volumes of the bioreactor), but only slightly elevated DOC and decreased DRP discharges were observed when drainage flow resumed at the start of the 2018 drainage season. Unexpectedly, cumulative DRP removal during the 2018 drainage season amounted to 89% of the DRP inflow into the bioreactor. Long HRTs (>5 days) enabled high nitrate removal efficiency (≥59%) and promoted complete reduction of nitrate to harmless dinitrogen gas but also promoted strongly reduced conditions, resulting in the production of H2S and CH4. On the other hand, short HRTs (<4 days) only allowed for moderate nitrate removal efficiency (≤43%) and constrained complete reduction of nitrate resulting in higher nitrous oxide concentrations in the outflow as compared to the inflow. Thus, nitrate removals above 50% were not able to be achieved without inducing H2S and CH4 generation. However, it may be achievable when the microbial community is provided with an additional source of readily available carbon during the critical periods when hydraulic flow and concomitant N load peaks occur.

Electrocatalytic reduction of nitrate in water using Cu/Pd modified Ni foam cathode: High nitrate removal efficiency and N2-selectivity

Electrocatalytic reduction of nitrate is a promising technology for nitrate removal from groundwater or surface water to eliminate the negative influence on human. The activity of an electrode usually depends on many factors such as catalytic metal, accessible active centers and electrode geometry. In this work, we prepared Cu/Pd modified nickel foam electrode (NF-Cu/Pd) according to two-step electrodeposition method using nickel foam (NF) as substrate. Cu/Pd particles with a grape-cluster-like shape with pores around 100 nm between clusters were formed on the NF surface according to the field emission scanning electron microscope with energy dispersive spectroscopy (FESEM-EDS) results. The crystal structure and the valence state of the prepared NF-Cu/Pd electrode were analyzed by using powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) technology. Linear sweep voltammetry (LSV) tests indicated that the prepared NF-Cu/Pd electrode had high electrocatalytic activity for nitrate reduction either using Na2SO4 as electrolyte or using NaCl as electrolyte. According to the dynamic experiment, 97% of the initial 100 mg/L NO3–-N were removed with a N2-selectivity of 99% at the cathode potential of −1.2 V vs. Ag/AgCl (sat. KCl) when using 0.05 M Na2SO4 as electrolyte. Using NaCl as electrolyte could improve the N2-selectivity of the nitrate electrocatalytic reaction under general conditions. The cathode potential and the current density affects the reaction pathways of nitrate reduction. In the microenvironment around the active sites, the mole ratio of NO2– and Had dominated the main product of NO3– reduction. Long time cyclic voltammetry test indicated that the prepared NF-Cu/Pd electrode has a good long-term electroactive stability for nitrate reduction from water solution. And the prepared NF-Cu/Pd showed high nitrate removal efficiency (96.4%) and N2-selectivity (65.4%) from the municipal wastewater treatment plant (WWTP) effluent.

Nitrate removal from tile drainage water: The performance of denitrifying woodchip bioreactors amended with activated carbon and flaxseed cake

The performance of three (1.0 m3 volume each) pilot-scale bioreactors, with one filled with woodchips only and the other two amended (10% v/v) with activated C and flaxseed cake, respectively, was tested under field conditions for nitrate removal from tile drainage water in Lithuania. The bioreactors were monitored for a period of 1.5 y, during which the flow rate, hydraulic retention time, water T, pH, dissolved O, nitrate, nitrite, ammonium, sulfate, and chemical O demand concentrations were measured. The results showed that the average nitrate removal efficiency in the bioreactor with no additives was 40.3%, and it was 44.1% in the bioreactor with activated C additives. In the bioreactor with flaxseed cake additives, 41.2% of the N was removed. During the cold seasonal period when the inflow T varied between +1.8 °C and +10.0 °C, activated C-amended woodchips showed higher efficiency and supported higher nitrate removal rates compared to those of other fillers. The highest nitrate removal efficiency was achieved at a pH of 7.0–7.5.The experiment demonstrated the potential for the enhancement of nitrate removal through the incorporation of activated C in denitrifying bioreactors. The addition of activated C substantially reduced the organic C losses while maintaining denitrification. Woodchips amended with flaxseed cake showed no significant difference in nitrates removal compared to the woodchips only treatment. A much higher release of organic C with no added effect on nitrate removal indicated that flaxseed cake as an external C source was more biodegradable than woodchips, but the benefit of its addition to woodchips was not proved.

Effect of Cu, Ni and Zn on Fe(II)-driven autotrophic denitrification

Fe(II)-mediated autotrophic denitrification in the presence of copper (Cu), nickel (Ni) and zinc (Zn) with four different microbial cultures was investigated in batch bioassays. In the absence of metals, complete nitrate removal and Fe(II) oxidation were achieved with a Thiobacillus-dominated mixed culture and Pseudogulbenkiania sp. 2002 after 7 d. A nitrate removal of 96 and 91% was observed with a pure culture of T. denitrificans and an activated sludge enrichment, respectively, after 10 d of incubation. Cu, Ni and Zn were then supplemented at an initial concentration of 5, 10, 20 and 40 mg Me/L. A decrease of approximately 50% of the soluble metal concentrations occurred in the first 4 d of denitrification, due to metal precipitation, co-precipitation, sorption onto iron (hydr)oxides, and probably sorption onto biomass. A higher sensitivity to metal toxicity was observed for the microbial pure cultures. Pseudogulbenkiania sp. 2002 was the least tolerant among the biomasses tested, resulting in only 6, 8 and 6% nitrate removal for the highest Cu, Ni and Zn concentrations, respectively. In contrast, the highest nitrate removal efficiency and specific rates were achieved with the Thiobacillus-dominated mixed culture, which better tolerated the presence of metals. Averagely, Cu resulted in the highest inhibition of nitrate removal, followed by Zn and Ni.

Construction and optimization of an iron particle–zeolite packing electrochemical–adsorption system for the simultaneous removal of nitrate and by-products

Abstract In this study, an electrochemical–adsorption (ECA) system was constructed by packing iron particles and zeolites between electrodes to simultaneously remove nitrate and its by-products without excessive active chloride accumulation. Response surface methodology (RSM) with Box–Behnken design (BBD) was applied to investigate the effects of independent variables (iron particle, zeolite and current density) and their interaction on the system performance, also determining its optimum working state. The optimal conditions for the amount of iron particles (19.74 g) and zeolites (28.19 g) as well as the current density (18.72 mA/cm2) resulted in a high nitrate removal efficiency of 95% and merely a little ammonia accumulation. Polarized iron particles could provide more reactive sites and increase mass transfer efficiency, thus promoted nitrate reduction and decreased energy consumption. Synergistic effects of electrolysis and zeolite adsorption accelerated ammonium removal by increasing the rate of ion directional migration. The system having low operation costs and no secondary pollution appeared to be an advisable enhancing strategy for removing nitrate and by-products.

Treatment of nitrate-contaminated groundwater by heterotrophic denitrification coupled with electro-autotrophic denitrifying packed bed reactor

A mixotrophic system consisting of heterotrophic and autotrophic denitrification (HAD) is a reliable system to enhance the denitrification performance of individual systems. In this study, a novel heterotrophic denitrification coupled with an electro-autotrophic denitrifying packed bed reactor (HEAD-PBR) was developed for the treatment of nitrate-contaminated groundwater. Because of the combination of electrochemical and biological denitrification processes in series, electrochemical inhibition of microorganisms was eliminated, and sufficient hydrogen was supplied safely. The efficiency of HEAD-PBR was evaluated using synthetic groundwater (containing 50 and 25 mg N/L of NO3−) at different hydraulic retention times. A high nitrate removal efficiency (∼99%) was achieved, the electrolysis, heterotrophic denitrification, and autotrophic denitrification were responsible for 15.6%–23.4%, 44.6%–68.4% and 15.7%–31.7% of nitrate removal, respectively. This effective material conversion can be attributed to microbial ecological interactions such as sufficient utilization of sawdust and proper consumption of hydrogen, oxygen, and ammonia. The HEAD-PBR was found to be an efficient reactor system with high treatment capacity, but without accumulation of byproduct in effluent. Thus, HEAD-PBR is a promising reactor configuration for nitrate removal and implementation of HAD technology.

Fe/Cu Composite Electrode Prepared by Electrodeposition and Its Excellent Behavior in Nitrate Electrochemical Removal

The Fe/Cu electrode, prepared via a cathodic electro-deposition method, was applied as cathode material for electrochemical denitrification and achieved an enhanced NO3−-N removal efficiency. The Fe/Cu electrode was characterized by SEM and EDS. The results showed that nano-Fe particles were evenly distributed on the surface of Cu foam. Compared with Cu foam (24.3%) and Fe (76.0%), the Fe/Cu electrode reached a much higher nitrate removal efficiency (98.6%) within 90 min. Influencing factors of electrolysis such as initial NO3−-N concentration, current density, pH and temperature were further studied, showing that high current density and temperature were conductive to NO3−-N removal. What's more, effect of Cl− on decreasing NH4+-N generation and promoting TN removal was investigated thoroughly. Result presented that addition of 1.0 g L−1 Cl− greatly decreased NH4+-N generation, leading to a 98.2% TN removal efficiency after 3 h treatment. Based on the analysis experimental results, a possible pathway of nitrate electro-reduction was proposed. Additionally, the Fe/Cu composite electrode maintained excellent efficiency and qualified iron leaching, demonstrating its potential application in the treatment of nitrate contaminated water.

Effects of salinity and COD/N on denitrification and bacterial community in dicyclic-type electrode based biofilm reactor

A dicyclic-type electrode based biofilm electrode reactor (BER) was developed for advanced nitrate removal from saline municipal wastewater. The denitrification efficiency was evaluated with a synthetic feed (NO3−-N, 20 mg L−1) under different salinity and COD to nitrogen ratios (COD/N). As the salinity increased from 0% to 1.0%, the denitrification performance of both the traditional biofilm reactor (BR) and BER was inhibited; however, the BER showed better adaptation and ability to recover. The BER achieved a high nitrate removal efficiency (≥90%) at a salinity of 1.0% and a low COD/N of 2.5 (theoretical stoichiometric 2.86 ignoring microbial growth). The abundance of Methylotenera mobilis in BR and Clostridium sticklandii in BER was higher than in the initial sludge sample used as inoculum. Likewise, the abundance of napA, nirS and nosZ genes increased as the COD/N further decreased. Under high salinity stress, the BER had a higher denitrification efficiency and the consumption of the organic carbon source (i.e., methanol) was reduced compared to BR. The cooperation between heterotrophic and autotrophic denitrifiers in the BER system provides a more efficient and feasible solution for nitrate removal from saline municipal wastewater.

Investigation into the nitrate removal efficiency and microbial communities in a sequencing batch reactor treating reverse osmosis concentrate produced by a coking wastewater treatment plant

ABSTRACTIn this study, a biological denitrifying process using a sequencing batch reactor (SBR) was employed to treat reverse osmosis (RO) concentrate with high conductivity produced from a coking wastewater plant. From the results, the average removal efficiencies for chemical oxygen demand, total nitrogen, and nitrate were 79.5%, 90.5%, and 93.1%, respectively. Different microbial communities were identified after sequencing the V1–V3 region of the 16S rRNA gene using the MiSeq platform, and the major bacterial phyla in the SBR system were Proteobacteria and Bacteroidetes. The main microorganisms responsible for denitrification were from the genera Hyphomicrobium, Thauera, Methyloversatilis, and Rhodobacter. Quantitative real-time PCR was used to quantify the absolute levels of denitrifying genes, including narG, nirS, nirK, and nosZ, during the start-up and stable operation of the SBR. The abundances of narG, nirK, and nosZ were lower during stable operation than those in the start-up period. The abundance of nirS at a concentration of 104–105 copies/ng in DNA was much higher than that of nirK, making it the dominant functional gene responsible for nitrite reduction. The higher nitrate removal efficiency suggests that biological denitrification using SBR is an effective technique for treating RO concentrate produced from coking wastewater plants.

Well-dispersed Pd-Cu bimetals in TiO2 nanofiber matrix with enhanced activity and selectivity for nitrate catalytic reduction

The present development gives an insight into the effect of the distribution of bimetallic sites in denitrification. A highly-dispersed Pd-Cu bimetallic catalyst supported by titanium dioxide nanofibers (Pd-Cu/TiO2) was in situ fabricated by electrospinning and subsequent calcination and chemical reduction, and then applied in the catalytic reduction of water phase nitrate (NO3−) to nitrogen gas (N2). Compared with ex situ Pd-Cu impregnated catalyst, the in situ Pd-Cu/TiO2 nanofibers exhibited the high nitrate removal efficiency, selectivity and fast kinetics (about twice that of impregnated ones). These good catalytic performances are mainly benefited from increased active sites and raised ratio of nitrogen to hydrogen on them, which are brought about by the well-dispersed and closely connected Pd-Cu bimetallic nanoparticles in TiO2 nanofiber matrix. Moreover, the in situ nanofiber matrix provides a physical barrier to inhibit bimetallic nanoparticles movement, aggregation and leakage from the support into water, and hence significantly enhances the recyclability for nitrate reduction.

Identification of the autotrophic denitrifying community in nitrate removal reactors by DNA-stable isotope probing

Autotrophic denitrification has attracted increasing attention for wastewater with insufficient organic carbon sources. Nevertheless, in situ identification of autotrophic denitrifying communities in reactors remains challenging. Here, a process combining micro-electrolysis and autotrophic denitrification with high nitrate removal efficiency was presented. Two batch reactors were fed organic-free nitrate influent, with H13CO3− and H12CO3− as inorganic carbon sources. DNA-based stable-isotope probing (DNA-SIP) was used to obtain molecular evidence for autotrophic denitrifying communities. The results showed that the nirS gene was strongly labeled by H13CO3−, demonstrating that the inorganic carbon source was assimilated by autotrophic denitrifiers. High-throughput sequencing and clone library analysis identified Thiobacillus-like bacteria as the most dominant autotrophic denitrifiers. However, 88% of nirS genes cloned from the 13C-labeled “heavy” DNA fraction showed low similarity with all culturable denitrifiers. These findings provided functional and taxonomical identification of autotrophic denitrifying communities, facilitating application of autotrophic denitrification process for wastewater treatment.

Interaction of short-chain fatty acids carbon source on denitrification

ABSTRACTShort-chain fatty acids (SCFAs) could be obtained from organic waste anaerobic digestion. The ability and interaction of different SCFAs on denitrification were investigated in this study. Two kinds of SCFAs (acetate and propionate with 5 different ratios) and 4 kinds of SCFAs (acetate, propionate, butyrate and valerate with 10 different ratios) were evaluated. Using acetate (Ac) and propionate (Pr) as carbon sources, the highest nitrate removal efficiency of 97.5% was obtained. When using the mixture of acetate (Ac), propionate (Pr), butyrate (Bu) and valerate (Va) as the carbon source, the highest nitrate removal efficiency obtained was 92.0%. The denitrification performance was affected significantly by different kinds and proportions of SCFAs. In addition, nitrite accumulation and chemical oxygen demand consumption for different contents of SCFAs were also analyzed.

Ammonium removal in granular activated carbon up-flow submerged reactors containing native bacterial consortium

Free ammonium in industries wastewater could be one of the worst toxic contaminants of aquatic life if diluted in water. Biological nitrogen removal (BNR) is the most common method for removing ammonium and nitrate from wastewater. Attached growth and suspended growth are the main BNR systems. The aim of the present work was to study the treatment of petrochemical wastewater (ammonium and nitrate removal) using native bacterial consortium isolated from Kermanshah Wastewater Treatment Plant, Iran, in two laboratory-scale high performance, granular activated carbon up-flow submerged reactors (GAC-USRs). The average maximum removal efficiency of NH 4 -N and NO 3 -N was 97.46% and 97.58% at the nitrification rate (NR) and denitrification rate (DR) of 2.44 kg NH 4 -N/m 3 .day and 2.31 kg NO 3 -N/m 3 .day, respectively. It was confirmed that the immobilized native bacterium on GAC could achieve a high ammonium and nitrate removal efficiency. The results of this study showed that the Bio-GAC-USRs can be an efficient method for complete ammonium and nitrate removal from wastewater.

Application of light-weight filtration media in an anoxic biofilter for nitrate removal from micro-polluted surface water.

The research investigated nitrate removal from micro-polluted surface water by the single-stage process of anoxic biofilter using light-weight polystyrene beads as filtration media. In this study, sodium acetate was used as an external carbon source and the nitrate removal efficiency under different regimes of hydraulic loading rate (HLR), water temperature, and C/N ratio was studied. In addition, the effect of backwash on denitrification efficiency was investigated. The results show that the biofilter achieved a high nitrate removal efficiency in 2 weeks at water temperatures ranging between 22 and 25 °C at a C/N ratio (COD:NO3(-)-N) of 6:1. Besides, the average removal efficiency of nitrate at HLRs of 5.66, 7.07 and 8.49 m(3) m(-2) h(-1) were 87.5, 87.3 and 87.1%, respectively. The average removal efficiency of nitrate nitrogen was 13.9% at a HLR of 5.66 m(3) m(-2) h(-1) at water temperatures of 12-14 °C, then it increased to 93.7% when the C/N ratio increased to 10. It suggests that the optimal hydraulic retention time is at water temperatures of 8-10 °C. The water consumption rate of backwash was about 0.2-0.3%, and denitrification efficiency returned to the normal level in 12 h after backwash.