High Nitrate Removal Efficiency Research Articles

Performance and microbial communities of Mn(II)-based autotrophic denitrification in a Moving Bed Biofilm Reactor (MBBR)

In this study, Mn(II) as electron donor was tested for the effects on denitrification in the MBBR under the conditions of initial nitrate concentration (10mgL−1, 30mgL−1, 50mgL−1), pH (5, 6, 7) and hydraulic retention time (HRT) (4h, 8h, 12h) which conducted by response surface methodology (RSM), the results demonstrated that the highest nitrate removal efficiency was occurred under the conditions of initial nitrate concentration of 47.64mgL−1, HRT of 11.96h and pH 5.21. Analysis of SEM and flow cytometry suggested that microorganisms were immobilized on the Yu Long plastic carrier media successfully before the reactor began to operate. Furthermore, high-throughput sequencing was employed to characterize and compare the community compositions and structures of MBBR under the optimum conditions, the results showed that Pseudomonas sp. SZF15 was the dominant contributor for effective removal of nitrate in the MBBR.

Treatment of Nitrate-Rich Saline Effluent by Using Citrate-Rich Waste as Carbon Source and Electron Donor in a Single-Stage Activated Sludge Reactor

Disposing of nitrate-containing effluents from seawater-fed intensive aquacultural applications is a major environmental problem. A possible solution is to mix nitrate-rich effluents from marine recirculating aquaculture systems (RASs) with citrate-rich liquid wastes (CLW), a common by-product of the food industry. Where possible, such strategy can alleviate two environmental problems simultaneously, in a cost-effective fashion. However, concerns are often raised regarding secondary pollution stemming from the use of CLW, particularly related to phosphorus and heavy metals. This work showed that both phosphorus and heavy metal were completely absorbed by the bacterial sludge generated in the process, indicating low environmental risk associated with the disposal of the treated effluent to the environment. Operation of continuous stirred-tank reactor (CSTR) single-sludge denitrification reactor with CLW as electron and carbon donor resulted in high nitrate removal efficiency (>95 %) and denitrification rate of up to 1.6 g NO3-N L−1 reactor day−1 along with low bacterial biomass yield [0.23 g chemical oxygen demand (COD) new cells g−1 COD citrate]. Moreover, the use of CLW was found to be environmentally safe and equally efficient to the use of traditional, costly carbon sources such as methanol and acetic acid, rendering this alternative attractive for treatment of nitrate-rich saline effluents.

Bioelectrochemical denitrification using carbon felt/multiwall carbon nanotube

The aim of this work was to enhance the efficiency of a bioelectrochemical denitrification process using a biocathode of carbon felt (CF)/multiwall carbon nanotube (MWCNT) composite. The efficiency of the bioelectrochemical denitrification was assessed as the function of various operational parameters, such as ORP, pH, current density, retention time and nitrate concentrations. Scanning electron microscope (SEM) images of the biocathode surfaces revealed a homogeneous distribution of the MWCNT on the CF matrix. Optimum ORP, pH, current density and retention time were −100 mV, 7.0, 15 mA/cm2 and 6 h, respectively. The highest nitrate removal efficiency at the optimum condition was 92.7% for CF/MWCNT. The reduction time for achieving the nitrate standard using CF/MWCNT was 4 h. It is proposed that the prepared nanocomposite will have the best biocathode properties in the bioelectrochemistry denitrification experiments.

Simultaneous removal of nitrate and aniline from groundwater by cooperating heterotrophic denitrification with anaerobic ammonium oxidation

To investigate the performance of cooperating heterotrophic denitrification (HD) with anaerobic ammonium oxidation (ANAMMOX) in removing nitrate and aniline simultaneously from organic limitation combined contamination groundwater, batch cultures, and flow column experiments were constructed. The two experimental results showed that it was feasible to remove nitrogen and carbon simultaneously by indigenous HD and ANAMMOX bacteria existing ubiquitously in groundwater aquifer medium, and the cooperation effect was significant. Batch cultures results demonstrated that high nitrate, aniline, and COD removal efficiency (over 79.0, 96.6, and 69.6%) were achieved at selected C/N of 0.3, 0.46, and 0.91 conditions, and the maximum activities of HD and ANAMMOX reached to 25.22 mg/(d·l), 5.54 mg/(d·l), and 7.06 mg/(d·l) after 150 days inoculation. As such, nitrate, aniline, and COD removal efficiency were equal to 99.8, 99.9, and 89.5% in continuous flow column with nitrate 1,000 mg L−1 and aniline 50 mg L−1. The variations of NO2--N, NH4+-N, pH, and EC could indicate HD and ANAMMOX coupling characteristics accurately. Moreover, carbon source utilization efficiency was dramatically improved by the synergetic effect of HD and ANAMMOX, as ANAMMOX could use CO2 and other inorganic carbon produced by HD process, which confirmed its great potential and feasibility to develop energy-saving and high efficiency in situ technology in the remediation of complex polluted groundwater.

Nitrate removal from groundwater by cooperating heterotrophic with autotrophic denitrification in a biofilm–electrode reactor

An intensified biofilm–electrode reactor (IBER) combining heterotrophic and autotrophic denitrification was developed for treatment of nitrate contaminated groundwater. The reactor was evaluated with synthetic groundwater (NO 3 −–N50 mg L −1) under different hydraulic retention times (HRTs), carbon to nitrogen ratios (C/N) and electric currents ( I). The experimental results demonstrate that high nitrate and nitrite removal efficiency (100%) were achieved at C/N = 1, HRT = 8 h, and I = 10 mA. C/N ratios were reduced from 1 to 0.5 and the applied electric current was changed from 10 to 100 mA, showing that the optimum running condition was C/N = 0.75 and I = 40 mA, under which over 97% of NO 3 −–N was removed and organic carbon (methanol) was completely consumed in treated water. Simultaneously, the denitrification mechanism in this system was analyzed through pH variation in effluent. The CO 2 produced from the anode acted as a good pH buffer, automatically controlling pH in the reaction zone. The intensified biofilm–electrode reactor developed in the study was effective for the treatment of groundwater polluted by nitrate.

Nitrate removal from aqueous solutions by nanofiltration

Due to excessive usage of nitrate fertilizers in agricultural sectors and dumping of domestic wastewaters, nitrate levels of water resources are increased in aqueous environments. Increased nitrate-containing compounds in the water resources, could lead to serious problems including eutrophication, and cause potential hazards for human and animal health. The aim of the present study was to investigate the effectiveness of nitrate removal from aqueous environments using nanofiltration (NF) membranes. In this study, the effect of different factors such as initial nitrate concentration, flow rate and associated cation and co-existing anions on the retention of nitrate by NF was examined. The results showed that with increased initial concentration of nitrate, flow rate and associated anions, the removal efficiency of nitrate decreased. The experiment indicated that many of negative charge groups on the membrane surface are covered by cations. The divalent cations covered membrane charge more effectively than monovalent cations. The result showed with high removal of sulfate ion, many nitrates are forced to pass through the membrane. The highest nitrate removal efficiency was 80.5%. According to the findings of this study, NF membrane usage could be recommended as an effective and reliable method for removing nitrates from aqueous environments.

Changes in the Bacterial Community Structure under Different DO Concentrations with New Method for Nitrate Removal

This study focused on the change of bacterial communities from a new denitrificatin technology where corncob was used as carbon source and the only physical support for microorganisms, under different dissolved oxygen (DO) conditions. The polymerase chain reaction (PCR) and denaturting gradient gel electrophoresis (DGGE) technique was used for extracting DNA from biofilm samples which collected from corncobs. The sequences of several 16S rDNA DGGE fragments were determined, and the dominant bacterial species that were present in each sample were proposed after comparing the results with data of the NCBI Gene Bank. The results indicated that PCR-DGGE technique was successfully used in this study. Clear relationship was found between DO condition and dominant bacterial communities during the experiment. Facultative anaerobic microorganism such as Bacteroidetes and Clostridium were found as dominant bacteria when DO was lower than 1mg/L. And aerobic microorganism such as Bacillus became the dominant bacteria when DO in the water was high than 2mg/L. These bacterial species mentioned above are all main types of denitrifying bacteria reported in other researches. And the results are helpful to explain the phenomenon why high nitrate removal efficiency was always found when DO condition changed. In addition, the results provided some valuable references for studing bacterial communities under different DO conditions.

Salt Inhibition Effects on Simultaneous Heterotrophic/Autotrophic Denitrification of High Nitrate Wastewater

Denitrification of high- nitrate high- salinity wastewater is difficult due to plasmolysis and inactivation of denitrifiers at high salinity conditions. In this study, the effects of salinity and empty bed contact time (EBCT) on simultaneous heterotrophic and sulfur based autotrophic denitrification of synthetic wastewater were evaluated in an up flow packed bed reactor .The reactor was filled with granular elemental sulfur particles with diameters of 2.8-5.6 mm and porosity of 40%. The initial culture was prepared from sludge of Shahrak-e- ghods domestic wastewater treatment plant. The influent nitrate concentration and EBCT were 600 mg NO3-N/lit and 16 h respectively. First, the stoichiometric fraction of nitrate removed by heterotrophic denitrification (with methanol as organic carbon source) supplied enough alkalinity to compensate the autotrophic alkalinity consumption, was determined 60%. Then, salt concentration was gradually increased with NaCl from 0% in the feed. The Process kept high nitrate removal efficiency (>99%) even at 3.5 % NaCl. During these changes the alkalinity variations were insignificant which showed the microbial population ratio of acclimated autotrophic to heterotrophic denitrifiers had no any significant changes with NaCl concentrations up to 3.5% in the feed. At 4 and 5% NaCl, the efficiency drastically decreased to 78% and 48%, respectively. Similar behavior was also observed for methanol removal efficiency, effluent turbidity as an indirect determinant of biological mass and sulfate production. The effects of flow rates on denitrification of synthetic high nitrate high salinity wastewater with 3.5 %NaCl under mixotrophic condition were also investigated by increasing the flow rate from 7.06 lit/day to 70.6 lit/day with corresponding EBCT 20 to 2 h. Denitrification efficiency was close to 100% at EBCT of 20 to 8 hr, but decreased to 79% and 39% when the EBCT was 4 and 2 h, respectively. The decrease in effluent sulfate concentration (as an indicator for autotrophic denitrification) and the increase in effluent alkalinity (as an indicator for heterotrophic denitrification) and pH at EBCT of 4 and 2 h were considerable correspondingly. These results imply that the population ratio of autotrophic to heterotrophic denitrifiers depends on EBCT.

Biological Denitrification Using Corncobs as a Carbon Source and Biofilm Carrier

In this research, agricultural waste--in particular, comcobs--was investigated for use as the sole carbon source and biofilm carrier to remove nitrate from wastewater in up-flow laboratory reactors. An artificial wastewater with a temperature range of 27 to 33 degrees C was used. Fast startup of the reactor and a high nitrate removal efficiency were observed. The highest denitrification rate of 0.203kg/(m3 x d) was achieved when flow rate and nitrate concentration were 153 L/d and 25.3 mgN/L, respectively. The accumulation of nitrite was not observed in this process. Moreover, flow rate and nitrate concentration of the influent were observed to have a significant effect on nitrate removal efficiency. A sharp decline of nitrate removal efficiency was observed when the flow rate was greater than 50 L/d. The reactor had the ability to accommodate a wide range of pH levels (6.5 to 8.5) and dissolved oxygen (1.5 mg/L to 4 mg/L). A time-dependent decrease in nitrate removal efficiency was observed after 67 days of operation. The addition of fresh corncobs brought about a rapid increase of nitrate removal efficiency. Results showed that corncobs could be used as an economical and effective carbon source for denitrification.

Rice husk as carbon source and biofilm carrier for water denitrification

In this research, rice husk, a lignocellulosic waste from agroindustry, was investigated as the sole carbon source as well as biofilm carrier in the biological denitrification of wastewater in up-flowlaboratory reactors.Anartificialwastewaterwitha temperature in the range of 27–33 ◦C was used. Fast startup of the reactor and a high nitrate removal efficiency was observed. The highest rates of denitrification about 0.096kg/m3 d were achieved when flow rate and nitrate concentration were 41.4 L/d and 25.0mg/L, respectively. Nitrite accumulation in treated water was practically zero during the experiments. Flow rate and nitrate concentration of the influent were observed to have a significant effect on nitrate removal efficiency. A very sharp decline was observed when the flow rate reached 30L/d. The reactor had the ability to accommodate awind rangeof pH (6.5–8.5) andDO (1.5–4). A time-dependent decrease in nitrate removal ratewas observed after 72 days of operation. And the addition of new rice husk brought about a rapid increase of the nitrate removal efficiency. The results showed that rice husk could be an economical and effective carbon source for the nitrate removal process.

Optimizing sequencing batch reactor (SBR) reactor operation for treatment of dairy wastewater with aerobic granular sludge

The biological wastewater treatment using aerobic granular sludge is a new and very promising method, which is predominantly used in SBR reactors which have higher volumetric conversion rates than methods with flocculent sludge. With suitable reactor operation, flocculent biomass will accumulate into globular aggregates, due to the creation of increased substrate gradients and high shearing power degrees. In the research project described in this paper dairy wastewater with a high particle load was treated with aerobic granular sludge in an SBR reactor. A dynamic mathematical model was developed describing COD and nitrogen removal as well as typical biofilm processes such as diffusion or substrate limitation in greater detail. The calibrated model was excellently able to reproduce the measuring data despite of strongly varying wastewater composition. In this paper scenario calculations with a calibrated biokinetic model were executed to evaluate the effect of different operation strategies for the granular SBR. Modeling results showed that the granules with an average diameter of 2.5 mm had an aerobic layer in between 65-95 microm. Density of the granules was 40 kgVSS/m3. Results revealed amongst others optimal operation conditions for nitrogen removal with oxygen concentrations below 5 gO2/m3. Lower oxygen concentrations led to thinner aerobic but thicker anoxic granular layers with higher nitrate removal efficiencies. Total SBR-cycle times should be in between 360-480 minutes. Reduction of the cycle time from 480 to 360 minutes with a 50% higher throughput resulted in an increase of peak nitrogen effluent concentrations by 40%. Considering biochemical processes the volumetric loading rate for dairy wastewater should be higher than 4.5 kgCOD/(m3*d). Higher COD input load with a COD-based volumetric loading rate of 9.0 kgCOD/(m3*d) nearly led to complete nitrogen removal. Under different operational conditions average nitrification rates up to 5 gNH/(m3*h) and denitrification rates up to 3.7 gNO/(m3*h) were achieved.

Spatial Variation in Denitrification and N2O Emission in Relation to Nitrate Removal Efficiency in a N-stressed Riparian Buffer Zone

Spatial variability in hydrological flowpaths and nitrate-removal processes complicates the overall assessment of riparian buffer zone functioning in terms of water quality improvement as well as enhancement of the greenhouse effect by N2O emissions. In this study, we evaluated denitrification and nitrous oxide emission in winter and summer along two groundwater flowpaths in a nitrate-loaded forested riparian buffer zone and related the variability in these processes to controlling soil factors. Denitrification and emissions of N2O were measured using flux chambers and incubation experiments. In winter, N2O emissions were significantly higher (12.4 mg N m−2 d−1) along the flowpath with high nitrate removal compared with the flowpath with low nitrate removal (2.58 mg N m−2 d−1). In summer a reverse pattern was observed, with higher N2O emissions (13.6 mg N m−2 d−1) from the flowpath with low nitrate-removal efficiencies. Distinct spatial patterns of denitrification and N2O emission were observed along the high nitrate-removal transect compared to no clear pattern along the low nitrate-removal transect, where denitrification activity was very low. Results from this study indicate that spots with high nitrate-removal efficiency also contribute significantly to an increased N2O emission from riparian zones. Furthermore, we conclude that high variability in N2O:N2 ratio and weak relationships with environmental conditions limit the value of this ratio as a proxy to evaluate the environmental consequences of riparian buffer zones.

Biological denitrification of drinking water using various natural organic solid substrates

Denitrification of drinking water was studied using various natural organic solid substrates (NOSS) such as poplar, hornbeam, pine shavings and wheat straw as a carbon source in a batch unit. The highest nitrate removal efficiency was observed with the wheat straw, so it was chosen as the carbon source for biodenitrification in an upflow laboratory reactor. In order to remove solid particles from the effluent water, a sand filter unit was placed after the denitrification reactor. The soluble DOC contents in the reactor affected the efficiency of nitrate elimination and nitrate concentration of the effluent water remained below acceptable values (50 mg/l NO3-). In order to remove colour, DOC and nitrate from the water, powdered activated carbon adsorption studies were performed in the batch unit.

Simultaneous biological removal of nitrogen, carbon and sulfur by denitrification

Refinery wastewaters may contain aromatic compounds and high concentrations of sulfide and ammonium which must be removed before discharging into water bodies. In this work, biological denitrification was used to eliminate carbon, nitrogen and sulfur in an anaerobic continuous stirred tank reactor of 1.3 L and a hydraulic retention time of 2 d. Acetate and nitrate at a C/N ratio of 1.45 were fed at loading rates of 0.29 kg C/m 3 d and 0.2 kg N/m 3 d, respectively. Under steady-state denitrifying conditions, the carbon and nitrogen removal efficiencies were higher than 90%. Also, under these conditions, sulfide (S 2−) was fed to the reactor at several sulfide loading rates (0.042–0.294 kg S 2−/m 3 d). The high nitrate removal efficiency of the denitrification process was maintained along the whole process, whereas the carbon removal was 65% even at sulfide loading rates of 0.294 kg S 2−/m 3 d. The sulfide removal increased up to ∼99% via partial oxidation to insoluble elemental sulfur (S 0) that accumulated inside the reactor. These results indicated that denitrification is a feasible process for the simultaneous removal of nitrogen, carbon and sulfur from effluents of the petroleum industry.

Denitrification and neutralization treatment by direct feeding of an acidic wastewater containing copper ion and high-strength nitrate to a bio-electrochemical reactor process

The feasibility of the direct denitrification treatment of copper metal pickling wastewater by using a bio-electrochemical reactor process was investigated experimentally. Carbon electrodes were installed in the reactor as the anode and cathode and denitrifying microorganisms were fixed on the surface of the cathode. The reactor was continuously operated by applying an electric current and feeding acetate. In this reactor, copper ion removal and denitrification proceeded simultaneously and the pH value of the treated water was increased almost to neutral. The electric current that passed through the cathode contributed to the removal of the copper ion and the generation of hydrogen gas. The generated hydrogen gas as well as the added acetate was effectively utilized for denitrification. A theoretical evaluation of pH in the effluent suggested that the pH increase was mainly caused by the generation of hydroxyl ion during denitrification. In addition, the inorganic carbon species generated during denitrification with acetate and by the electrochemical oxidation of anodic carbon acted as a buffer to minimize a further increase of pH at higher nitrate removal efficiencies. These results demonstrated that copper ion removal, denitrification and neutralization could be achieved simultaneously by using a single bioelectrochemical reactor.