Groundwater Denitrification Research Articles

Groundwater quality in alluvial and prolluvial areas under the influence of irrigated agriculture activities

ABSTRACTThe aim of this study was to investigate the groundwater pollution from alluvial aquifers lying under surface agriculture activities in two geologically different areas: alluvial and prolluvial. The groundwater in investigated areas is neutral to alkaline (pH 7.05–8.45), and the major dissolved ions are bicarbonate and calcium. Groundwater samples from the alluvial area are characterized by nitrate concentration above the national maximum concentration limit (MCL) at 20.5% of samples [mean value (Me) 6.31 mg/L], arsenic concentrations greater than national MCL at 35.6% of investigated samples (Me 12.12 µg/L) and elevated concentrations of iron (Me 202.37 µg/L) and manganese (Me 355.22 µg/L) at 22.7% and 81% of investigated samples, respectively. Groundwater samples from the prolluvial area did not show significantly elevated concentrations of heavy metals, but the concentration of nitrate was considerably higher (Me 65.06 mg/L). Factor analysis positively correlates As with Mn and Fe, suggesting its natural origin. Nitrate was found in positive correlation with SO42− and Ni but in negative with NH4+, suggesting its anthropogenic origin and the relationship of these ions in the process of denitrification. The t-test analysis showed a significant difference between nitrate pollution of groundwater from alluvial and prolluvial areas. According to the chemical composition of groundwater, the process of denitrification is considered to be the main reason for the reduced presence of nitrate in the groundwater lying under alluvial deposits represented by chalk and sandstones. Denitrification in groundwater lying under prolluvial deposits represented by magmatic and metamorphic rock formations was not observed.

The impact of an underground cut-off wall on nutrient dynamics in groundwater in the lower Wang River watershed, China

ABSTRACTUnderground cut-off walls in coastal regions are mainly used to prevent saltwater intrusion, but their impact on nutrient dynamics in groundwater is not clear. In this study, a combined analysis of multiple isotopes () and nitrogen and phosphorus concentrations is used in order to assess the impact of the underground cut-off walls on the nutrient dynamics in groundwater in the lower Wang River watershed, China. Compared with the nitrogen and phosphorus concentrations in groundwater downstream of the underground cut-off walls, high and total dissolved nitrogen concentrations and similar concentration levels of and total dissolved phosphorus are found in groundwater upstream of the underground cut-off walls. The isotopic data indicated the probable occurrence of denitrification and nitrification processes in groundwater upstream, whereas the fingerprint of these processes was not shown in groundwater downstream. The management of fertilizer application is critical to control nitrogen concentrations in groundwater restricted by the underground cut-off walls.

Denitrification of synthetic nitrate-contaminated groundwater combined with rice washing drainage treatment

This research used an upflow zeolite-based biofilm reactor (UZBR) with rice washing drainage (RWD) as carbon source to improve denitrification efficiency and simultaneously treat RWD in the process. Removal performance in two UZBRs inoculated with and without activated sludge was investigated at different ratios of RWD to synthetic nitrate-contaminated groundwater (1/3 (v/v), 1/5.5 (v/v), 1/8 (v/v)). At optimum conditions (1/5.5 (v/v)), nitrate removal efficiencies reached 97.0%±2.0% with activated sludge and 98.2%±1.1% without activated sludge, and TOC concentration in RWD decreased by 80.6%±1.1% and 88.6%±3.9%, respectively. Illumina sequencing analysis revealed that the microbial community structures in the reactor with activated sludge differed with the reactor without the activated sludge. RWD itself generated polyphosphate accumulating organisms (PAOs) without the breeding of glycogen accumulating organisms (GAOs). Further, the read counts of denitrifiers were more at the bottom and middle of the reactor than at the top. It has been suggested that RWD could provide electron donors and denitrifiers for denitrification and simultaneously treat RWD on-site in a reactor.

Denitrification of groundwater using PHBV blends in packed bed reactors and the microbial diversity

In the present study, three kinds of biopolymers, PHBV, PHBV/starch and PHBV/bamboo powder (BP) blends were used as carbon source and biofilm carriers for denitrification in packed bed reactors to remove nitrate from groundwater. Results showed that a fast start-up was obtained in bioreactors filled with both PHBV/Starch and PHBV/BP blends without external inocula and it took more than 3 month for PHBV reactor to reach the same loading rate. The PHBV/BP packed reactor exhibited a better nitrate removal efficiency (87.4 ± 7.0%) and less adverse effects in nitrite accumulation and DOC release (below 0.5 mg NO2N L−1 and 10.5 mg DOC L−1 in the effluent) during stable operation. Pyrosequencing analysis demonstrated that bacteria belonging to genus Clostridium in phylum Firmicus, which play the primary role in degrading the biopolymers, are the most dominant (33–15% of the sequences). The predominant species in all samples is related to Clostridium crotonatovorans. All the identified 11 genera of denitrifying bacteria affiliated with phylum Proteobacteria and constituted 30–55% in the representative sequences. The PHBV/BP blend is economically attractive carbon source with good denitrification performance.

Bioelectrochemical denitrification on biocathode buried in simulated aquifer saturated with nitrate-contaminated groundwater.

Nitrate contamination in aquifers has posed human health under high risk because people still rely on groundwater withdrawn from aquifers as drinking water and running water sources. These days, bioelectrochemical technologies have shown a great number of benefits for nitrate remediation via autotrophic denitrification in groundwater. This study tested the working possibility of a denitrifying biocathode when installed into a simulated aquifer. The reactors were filled with sand and synthetic groundwater at various ratios (10, 50, and 100%) to clarify the effect of various biocathode states (not-buried, half-buried, and fully buried) on nitrate reduction rate and microbial communities. Decreases in specific nitrate reduction rates were found to be correlated with increases in sand/medium ratios. A specific nitrate reduction rate of 322.6mgm(-2)day(-1) was obtained when the biocathode was fully buried in an aquifer. Microbial community analysis revealed slight differences in the microbial communities of biocathodes at various sand/medium ratios. Various coccus- and rod-shaped bacteria were found to contribute to bioelectrochemical denitrification including Thiobacillus spp. and Paracoccus spp. This study demonstrated that the denitrifying biocathode could work effectively in a saturated aquifer and confirmed the feasibility of in situ application of microbial electrochemical denitrification technology.

Ti nano electrode fabrication for electrochemical denitrification using Box–Behnken design

In this study, a novel Ti nano cathode was produced for electrochemical denitrification of groundwater. The factors that influence the production of Ti nano electrodes were optimized by response surface methodology (RSM). Efficient reduction of the nitrate electrode was achieved. A Box–Behnken design can be used to develop mathematical models that predict the best geometry for electrochemical nitrate removal. The interaction between parameters can be identified in this typical electrochemical removal process. A correlation coefficient R2>0.90 for the present mathematical model indicates a high correlation between observed and predicted values. The best conditions for preparation of the Ti nano electrode are as follows: 0.03wt% hydrofluoric acid and 5.00V oxidation voltage, without addition of acetic acid. Under these conditions, the nitrate reduction efficiency was 154% higher than that from an untreated electrode and the energy consumption was 5.97×10−4kWh.

Quantifying the fate of agricultural nitrogen in an unconfined aquifer: Stream‐based observations at three measurement scales

AbstractWe compared three stream‐based sampling methods to study the fate of nitrate in groundwater in a coastal plain watershed: point measurements beneath the streambed, seepage blankets (novel seepage‐meter design), and reach mass‐balance. The methods gave similar mean groundwater seepage rates into the stream (0.3–0.6 m/d) during two 3–4 day field campaigns despite an order of magnitude difference in stream discharge between the campaigns. At low flow, estimates of flow‐weighted mean nitrate concentrations in groundwater discharge ([ ]FWM) and nitrate flux from groundwater to the stream decreased with increasing degree of channel influence and measurement scale, i.e., [ ]FWM was 654, 561, and 451 µM for point, blanket, and reach mass‐balance sampling, respectively. At high flow the trend was reversed, likely because reach mass‐balance captured inputs from shallow transient high‐nitrate flow paths while point and blanket measurements did not. Point sampling may be better suited to estimating aquifer discharge of nitrate, while reach mass‐balance reflects full nitrate inputs into the channel (which at high flow may be more than aquifer discharge due to transient flow paths, and at low flow may be less than aquifer discharge due to channel‐based nitrate removal). Modeling dissolved N2 from streambed samples suggested (1) about half of groundwater nitrate was denitrified prior to discharge from the aquifer, and (2) both extent of denitrification and initial nitrate concentration in groundwater (700–1300 µM) were related to land use, suggesting these forms of streambed sampling for groundwater can reveal watershed spatial relations relevant to nitrate contamination and fate in the aquifer.

Electrolytic denitrification with an ion-exchange membrane in groundwater

Nitrate contamination of groundwater is an important issue in rural areas. In this study, an electrolytic method for the denitrification of groundwater was investigated in a laboratory reactor. We used an ion-exchange membrane, employing a titanium oxide anode and five kinds of cathode for the investigation. The nitrate removal efficiencies with Cu, Pb, Ti/Ir/Ru, Ti/Ir/Ta, and Zn cathodes were 30.0%, 59.9%, 73.8%, 23.3%, and 80.6%, respectively. A cation-selective membrane was employed to separate the electrode compartments, and only the proton produced in the anode side was permitted to the cathode side in order to avoid reversible reactions. In terms of the nitrate removal, good experimental results were obtained by using the membrane reactor equipped with the Zn cathode. The nitrate concentration level dropped from 30 to 6 mg/L, which is below the limit for drinking water. The pH was not affected significantly by the current density and it increased up to 9.0 at 100 mA/cm2. The nitrate removal efficiency showed the highest value with 1 mM of NaCl as an electrolyte. The impression was that membrane electrolysis made it possible to avoid the re-oxidation problem. It appears clear that electrolytic denitrification with an ion-exchange membrane is a very effective process with a mean energy consumption of only between 26.9 and 112.9 kWh/kg-NO3.

Continuous treatments of synthetic groundwater by an in situ denitrification and oxidation process with injection of electrolytic hydrogen and oxygen

Long-term continuous treatments of synthetic groundwater containing 15.06 ± 0.55 mg-N/L nitrate were conducted using an in situ denitrification and oxidation process under different operating conditions. In the experiments, electrolytic hydrogen and oxygen were injected upstream and downstream in a laboratory-scale aquifer, respectively, and measurements were made for nitrate, nitrite, pH, dissolved oxygen, dissolved hydrogen, total organic carbon (TOC), turbidity, and chromaticity. Experimental results demonstrated that steady-state denitrification and oxygenation of groundwater were achieved over 820 days. During the initial phase of the experiments, nitrite was accumulated at a level of several mg-N/L in a hydrogen-injected zone, but it was almost completely oxidized to nitrate in a downstream oxygen-injected zone. In subsequent experiments, nitrite accumulation was not observed in effluent, and satisfactory treatments were achieved. Effluent concentrations of total nitrate and nitrite, TOC, turbidity, and chromaticity were generally below World Health Organization guidelines for drinking water (11.3 mg-N/L). It should be mentioned that water quality parameters such as TOC, turbidity, and chromaticity were lower in effluent than influent, and no clogging problem was observed. From these results, we concluded that the present in situ process has superior properties in terms of long-term performance and stability.

Biological denitrification in simulated groundwater using polybutylene succinate or polylactic acid-based composites as carbon source

Two novel multiple component carbon sources, mainly polybutylene succinate (PBS) and polylactic acid, were prepared by twin-screw extrusion to treat simulated groundwater. Both of the composites also contained high-density polyethylene and walnut shell (WS) to adjust the denitrification rate. The composites could release soluble organic carbon and be carriers for bacteria. The addition of foaming agent in the composite enriched the porous channels which increased the surface area for biofilm loading. The results indicated that the average N-NO3- removal efficiency in reactor 1 (filled with WS/PBS) was 83%. When the inflow concentration of nitrate changed from 50 to 55 mg L−1, the reactor 1 had an acclimation time of 13 d to accept the high concentration. However, the N-NO3- removal efficiency in reactor 2 (filled with WS/PLA) decreased from 86 to 78% because of the propagation of blue-green algae which also led to a high COD value in effluent. WS/PBS was a stable carbon source releaser and could adapt to the environmental change easily. Therefore, it has the potential of using as carbon source of biological denitrification of groundwater.

Study on the Effect of Flow Velocity on the Denitrification of Groundwater

Using the mixed filling reaction column, this article examines that the influence of different inlet flow rate on the removal of nitrate nitrogen in groundwater, respectively by 90mL/h, 150 mL/h, 210mL/h velocity, under 30 °C each run five days, comparativly studies the influence of velocity on denitrification. The results show that the flow rate has an important effect on the denitrification of water, when the water inlet velocity decreased from 150mL/h to 90mL/h, the concentration of nitrate nitrogen reaction column effluent decreased gradually, and the denitrification of nitrite nitrogen accumulation system has been in a low level, but the ammonia nitrogen accumulation only in the flow rate of 90mL/h, began when the flow rate decreased significantly; also increased from 90mL/h to 210mL/h, the effluent nitrate nitrogen concentration, nitrite nitrogen concentration and ammonia nitrogen concentration increased significantly.

Denitrification of nitrate-contaminated groundwater in an anoxic rotating biological contactor: a case study

In this study, denitrification of Tehran (Iran) oil refinery groundwater in an anoxic rotating biological contactor (ARBC) was investigated. Influence of different parameters such as hydraulic retention time (HRT), Carbon/Nitrogen ratio, and nitrate loading in the influent, on the nitrate, nitrite, ammonium, alkalinity, and chemical oxygen demand concentration of effluent were evaluated. Acetate was used as a carbon source in a heterotrophic process. Nitrate concentration of treated water in all experiments was far below the standard limitation and nitrate removal efficiency reached over 97% in optimum value of Carbon/Nitrogen = 1.25 and HRT = 8 h. Nitrite accumulation wasn’t observed up to nitrate loading of 105 mg/L. Based on the results of this experiment, ARBC reactor could be an adequate and convenient method in denitrification of groundwater.

Structure and mass transportation model of slow-release organic carbon-source material for groundwater in situ denitrification

Based on the theories of organic polymer and chemical kinetics, the structure and mass transportation model of slow-release organic carbon-source (SOC) material was developed in this study to reveal and predict the carbon release mechanisms of polymer carbon source, which was feasible for in situ denitrification in nitrate-contaminated groundwater. Composed of polyvinyl alcohol (PVA) and starch, the SOC material formed the interlocking/disperse-phase structure. PVA performed as continuous phase and skeleton, whereas the starch or cellulose behaved as release component. Carbon release process was identified in two stages: solid-phase (inner) and interface (gel layer) diffusion. Solid-phase diffusion was affected by material porous medium parameters, for example, distance between the crosslinking points and starch free energy. The interface diffusion depended mostly on the groundwater dynamics and interface energy distribution. The interface diffusion was found as the limiting step of carbon release process, and the carbon release coefficient corresponded to kD,I as static coefficient and kC,I as dynamic coefficient. As the key indicator to evaluate carbon release capacity, kD,I and kC,I represented appropriate boundary conditions and interface properties. Sensitivity analysis showed that the key parameters of the carbon release model were the distance between the crosslinking points and the free energy of polymer, influenced by regulation of preparation technique, raw material composition and additive dosage.

Denitrification of groundwater using a sulfur-oxidizing autotrophic denitrifying anaerobic fluidized-bed MBR: performance and bacterial community structure.

This paper investigates a novel sulfur-oxidizing autotrophic denitrifying anaerobic fluidized bed membrane bioreactor (AnFB-MBR) that has the potential to overcome the limitations of conventional sulfur-oxidizing autotrophic denitrification systems. The AnFB-MBR produced consistent high-quality product water when fed by a synthetic groundwater with NO3 (-)-N ranging 25-80 mg/L and operated at hydraulic retention times of 0.5-5.0 h. A nitrate removal rate of up to 4.0 g NO3 (-)-N/Lreactord was attained by the bioreactor, which exceeded any reported removal capacity. The flux of AnFB-MBR was maintained in the range of 1.5-15 L m(-2) h(-1). Successful membrane cleaning was practiced with cleaning cycles of 35-81 days, which had no obvious effect on the AnFB-MBR performance. The (15) N-tracer analyses elucidated that nitrogen was converted into (15) N2-N and (15) N-biomass accounting for 88.1-93.1 % and 6.4-11.6 % of the total nitrogen produced, respectively. Only 0.3-0.5 % of removed nitrogen was in form of (15)N2O-N in sulfur-oxidizing autotrophic denitrification process, reducing potential risks of a significant amount of N2O emissions. The sulfur-oxidizing autotrophic denitrifying bacterial consortium was composed mainly of bacteria from Proteobacteria, Chlorobi, and Chloroflexi phyla, with genera Thiobacillus, Sulfurimonas, and Ignavibacteriales dominating the consortium. The pyrosequencing assays also suggested that the stable microbial communities corresponded to the elevated performance of the AnFB-MBR. Overall, this research described relatively high nitrate removal, acceptable flux, indicating future potential for the technology in practice.

Using cassava distiller's dried grains as carbon and microbe sources to enhance denitrification of nitrate-contaminated groundwater.

Nitrate removal from synthetic and real groundwater was investigated by using cassava distiller's dried grains (CDDG), which served as sole carbon source as well as the only microbe seed. It was found that remarkably higher total nitrogen removal efficiency (96.8 ± 0.6 %) could be reached; the accumulation of nitrite and the releases of organic compounds, meanwhile, were insignificant in the denitrification process. Scanning electron microscope (SEM) analysis showed that CDDG were degraded during the denitrification process. Further investigation showed that CDDG were anaerobically hydrolyzed and acidified to butyric acid, acetic acid, and carbohydrate, which could be utilized directly as the reducing equivalent providers for denitrification by the microorganisms separated from CDDG. Microbial community analysis revealed that the fungi and bacteria present in the original CDDG functioned as the denitrifiers, which mainly consisted of Aspergillus (69.8 %) and Rhizomucor (15.9 %) in the fungi community and Burkholderia (20.6 %) and Rhizobium (15.9 %) in the bacteria community, respectively. Finally, the use of CDDG as both carbon and microbial sources for real groundwater denitrification was testified to be feasible and safe with a total nitrogen removal efficiency of around 100 %.

Innovative slow-release organic carbon-source material for groundwater in situ denitrification

Slow-release organic carbon-source (SOC) material, a new kind of electron donor for in situ groundwater denitrification, was prepared and evaluated in this study. With starch as a biologically utilized carbon source and polyvinyl alcohol (PVA) as a frame, this material performed controllable carbon release rates and demonstrated stable behaviour during the simulated denitrification process. Raman spectrum analysis showed that the PVA skeleton formed cross-linking network structures for hydrogen-bonded water molecules reset in low temperatures, and the starchy molecules filled in the interspace of the skeleton to form a two-phase interlocking/disperse phase structure. In a static system, carbon release processes followed the Fickian law with (1.294–6.560) × 10−3 mg g−1 s−1/2 as the release coefficient. Under domestication and in situ groundwater simulation conditions, SOC material played a favourable role during denitrification, with 1.049 ± 0.165 as an average carbon–nitrogen ratio. The denitrification process followed the law of zero-order kinetics, while the dynamics parameter kN was 0.563–8.753 gN m−3 d−1. Generally, SOC material was suggested to be a potential carbon source (electron donor) suitable for in situ groundwater denitrification.

Application of half-order kinetics to sulfur-utilizing autotrophic denitrification for groundwater remediation

The kinetics of sulfur-utilized autotrophic denitrification of groundwater was evaluated in batch tests to obtain kinetic parameters. Experiments were performed in media bottles containing varying NO3 −-N concentrations (20, 44, and 77 mg/L) with 4.0–4.75 mm-sized sulfur particles. Alkalinity was set as a constant in all experimental containers at 850 mg/L as CaCO3. The half-order kinetic model was found to adequately describe the process efficiently, yielding denitrification rate constants of 4.36, 5.51, and 6.91 mg-N1/2/L1/2 · h in the presence of NO3 −-N at 20, 44, and 77 mg/L, respectively. The rate of denitrification increased with the increasing initial NO3 −-N concentrations.

Effects of Solid Organic Carbon on Nitrate Remove in Groundwater

In groundwater, the lack of carbon source is a key problem of in-situ denitrification. It is very important to choose appropriate solid carbon-source materials. In this work, wheatstraw and sawdust were selected as potential carbon sources to evaluate the performance for in-situ biological denitrification in groundwater by column experiments. The results showed that sawdust was a suitable corbon source with less release of nitrogen compounds and relatively stable release of organic carbon, compared with wheatstraw, and was applicable for further use as a filling material in in-situ ground water bioremediation.

Ion exchange membrane textile bioreactor as a new alternative for drinking water denitrification

This work enters in the optics of the denitrification of a polluted water by two membrane techniques, the Donnan dialysis (DD) and the ion exchange membrane bioreactor (IEMB), using a conventional barrier, composed by an anion exchange membrane (AEM), and a hybrid barrier, where the AEM is combined to an anion exchange textile (AET). The effects of the hydrodynamic factor and the nature of the carbon source on the transfer and the reduction of nitrate ions were studied. The study results obtained through the DD showed the effectiveness of the hybrid barrier in the recovery and concentration of nitrate ions. This was also recorded during denitrification by the hybrid process, called the ion exchange membrane textile bioreactor (IEMTB), with a significant reduction of nitrates, compared to IEMB, due to the efficiency of the Pseudomonas aeruginosa biofilm formed at the surface of the AET. Here, the permselectivity of the membrane and the good bioreduction of the pollutants are no longer major conditions to the better performance of the process. The application of IEMTB in the denitrification of groundwater, having a nitrate concentration of 96.67ppm, shows a total reduction of nitrate ions without changing the quality of the water. Indeed, the analysis of the recovered water, or yet the treated water, shows the absence of the bacterium by-products and concentrations in the nitrates and nitrites which are, respectively, equal to 0.02±0.01 ppm, and inferiors to the detection limit (<0.02 ppm).

Shallow groundwater denitrification in riparian zones of a headwater agricultural landscape.

Riparian zones adjacent to cropped lands are effective at reducing nitrate (NO) loads to receiving water bodies primarily through plant assimilation and denitrification. Denitrification represents a permanent removal pathway and a greenhouse gas source, converting NO to inert N gas or nitrous oxide (NO), and has been the subject of many studies in agricultural landscapes. Despite the prevailing notion that riparian zones can be areas of enhanced denitrification, there is a lack of in situ denitrification measurements from these areas that buffer streams and rivers from NO originating in upland cropped soils, especially over time scales that capture seasonal dynamics. We measured in situ groundwater denitrification rates in two riparian zones of an intensive dairy farm located in the headwaters of the Susquehanna River. Denitrification rates determined monthly over a 1-yr period with the N-NO push-pull method ranged from 0 to 4177 μg N kg soil d (mean, 830 ± 193 μg N kg soil d). Denitrification showed a distinct seasonal pattern, with highest rates observed in the spring and summer, concomitant with warmer temperatures and decreasing dissolved oxygen. We estimate an annual N loss of 470 ± 116 kg yr ha of riparian zone via denitrification in the shallow saturated zone, with the potential for >20% of this amount occurring as NO. Total denitrification from shallow groundwater in the riparian zone was equivalent to 32% of manure N spread on the adjacent upland field, confirming the importance of riparian zones in agricultural landscapes at controlling N loads entering downstream waters.