Remediation Of Nitrate-contaminated Groundwater Research Articles

Synergistic effect of LDHs/loofah composites for in-situ remediation of nitrate in contaminated groundwater

Permeable reaction barrier (PRB) is an innovative technology for in-situ remediation of nitrate-contaminated groundwater. In this study, layered double hydroxides (LDHs)/loofah composites were prepared and used as active fillers for PRB to facilitate nitrate removal from groundwater. Under the conditions of initial nitrate concentration of 5 mg/L, a hydraulic retention time (HRT) of 4 h, and without additional carbon source, the nitrate removal rates of the natural loofah, MgAl-LDHs, and CaMgAl-LDHs composite were 69.31 %, 85.35 %, and 97.82 %, respectively. The CaMgAl-LDHs composite exhibits the highest denitrification capacity, attributed to the presence of Ca2+and Mg2+. Ca2+ and Mg2+is an essential element for the structural integrity of microbial cells, which demonstrated that Ca2+ reduces the surface charge of bacteria, leading to hydrophobicity and facilitating biofilm formation. Electrochemical tests demonstrate that LDHs with distinctive two-dimensional layered structure, contribute to the augmentation of electron transfer during denitrification. LDHs can also promote the formation of highly active biofilms and the secretion of extracellular polymeric substances (EPS) on the surface of loofah, thereby enhancing the metabolic activity of microorganisms. Metagenomic analysis revealed that LDHs enhance the enrichment of denitrifying bacteria and the activity of key enzymes involved in denitrification. Therefore, the adsorption-biological coupled degradation of the LDHs/loofah composites have great potential to enhance the efficiency of biological denitrification, making it promising filling materials for PRB technology applied in groundwater remediation.

Development of a mathematical model for a microbial denitrification co-culture system comprising acetogenic bacterium Sporomusa ovata and denitrifying bacterium Pseudomonas stutzeri.

Previous study has shown that co-culturing acetogenic bacterium Sporomusa ovata (SO), with denitrifying bacterium Pseudomonas stutzeri (PS), is a promising strategy to enhance the microbial denitrification for nitrate-contaminated groundwater remediation. However, the mutual effects and reaction kinetics of these two bacteria in the co-culture system are poorly understood. In this study, a mathematical model for this co-culture system was established to fill this knowledge gap. Model simulation demonstrated that SO had a significant effect on the kinetics of denitrification by PS, while PS slightly affected the kinetics of acetate production by SO. The optimal initial HCO3-/NO3- ratio and SO/PS inoculation ratio were 0.77-1.48 and 67 for the co-culture system to achieve satisfied denitrification performance with less acetate accumulation. Finally, the minimum hydrogen supply was recommended when the initial bicarbonate and nitrate concentrations were assigned in the range of 2-20 mM and 2-4 mM for simulating the natural nitrate-contaminated groundwater treatment. These findings could provide useful insights to guide the operation and optimization of the denitrification co-culture system.

Stimulating Nitrate Removal with Significant Conversion to Nitrogen Gas Using Biochar-Based Nanoscale Zerovalent Iron Composites

For efficient and environmentally friendly removal of nitrate from groundwater, biochar-based nanoscale zerovalent iron composites were prepared, where biochar was derived from pine sawdust at 4 different pyrolysis temperatures. The results show that biochar with different pyrolysis temperatures played a great role in both nitrate removal efficiency and nitrate conversion rate to nitrogen gas for the prepared composites. Specifically, the composite with biochar pyrolyzed at 500 °C, ZB12-500, showed the best performance in both nitrate removal and conversion to nitrogen gas. With an initial solution pH from 5 to 10, ZB12-500 maintained high removal efficiencies varying from 97.29% to 89.04%. Moreover, the conversion of nitrate to nitrogen gas increased with the initial nitrate concentration, and it reached 31.66% with an initial nitrate concentration of 100 mg/L. Kinetics analysis showed that the nitrate removal process fit well with a two-compartment first-order kinetic model. Meanwhile, the test of nitrate removal by ZB12-500 in synthetic groundwater showed that HCO3− and SO42− limited nitrate removal but improved nitrate conversion to nitrogen gas. Furthermore, the nitrate removal mechanism suggested that biochar could facilitate electron transfer from zero valent iron to nitrate, which led to high nitrate removal efficiency. In addition, the interaction of ferrous ions and the quinone group of biochar could increase the nitrate conversion to nitrogen gas. Therefore, this study suggests that ZB12-500 is a promising alternative for the remediation of nitrate-contaminated groundwater.

Remediation of nitrate-contaminated groundwater by a combined treatment method of novel Mass Bio System and solid organic carbon sources: In-depth study

In recent years, one of the most pervasive groundwater (GW) contaminants worldwide is nitrate. Traditional technologies for the remediation of nitrate-contaminated GW are usually expensive, lengthy, and often only partly effective. Of the emerging technologies for nitrate remediation, biological denitrification technologies are more economical, timely, and more efficient means of reducing nitrate contamination to standard levels. The present study investigates the roles of combined treatment method of novel Mass Bio System (MBS), an advanced nontoxic immobilized biologically activated water purification product and solid organic carbon sources (SOCS) for the removal of nitrate from GW to meet the drinking water standards. Natural organic rice straws and commercially available paper plates rich in cellulose were used as SOCS. Effects of various parameters such as nitrate nitrogen concentration, hydraulic retention time, pH and temperature on denitrification process were studied. In the present study, four batch tests are conducted to evaluate two common solid organic carbons and their combination with MBS for nitrate removal from GW. Overall, the reactor with MBS particles and SOCS exhibited clear advantages over reactor inoculated with activated sludge and SOCS with respect to better denitrification, stable operation, strong environmental adaptability and complete nitrate removal. At last, the concentrations of nitrate and nitrite were lowest in the combined system. Kinetic analysis by Monod model showed good agreement with the experimental results. MBS particles are responsible for the main denitrification and the reaction kinetic model conforms to Monod equation of double substrate. Static carbon release test and degradation mechanism of solid carbon sources were carried out. It showed the slow-release carbon source by their own hydrolysis and contain easily soluble organic matter that can be quickly dissolved into water, which substantiated the analysis of the results further. All the results demonstrate that this combined method is a potentially nontoxic, cleaner and sustainable technology for remediation of nitrate-contaminated GW.

Enhanced self-powered system with graphene oxide modified electrode for simultaneous remediation of nitrate-contaminated groundwater and river sediment

Simultaneous in situ remediation of malodorous organic sediment and nitrate-contaminated groundwater was achieved with a novel, enhanced, self-driven three-chamber bio-electrochemical system with Graphene Oxide (GO) modified electrodes. It has been successfully improving the electron transfer efficiency and self-purification ability by the special configuration combining surface water, sediment with underground water. The upper part can be regarded as a Sediment Microbial Fuel Cell (SMFC). The organic sediment serves as available carbon source to provide electrons for the microbes coated on the anode instead of potential pollutants. The lower part is the Biofilm Electrode Reactor (BER). Electrons were synchronously obtained from the loaded biofilm to reduce nitrate. The electricity generated from the upper part was applied directly to the lower part as electrical stimulation to enhance bacterial denitrification of the system. The electron conduction efficiency was further improved by graphene oxide modifying. With a maximum power density of 14.21 W/m2, as well as the voltage outputs ranging from 700 mV to 900 mV, nitrate removal was accelerated with less accumulation of intermediates compared with the controls without graphene oxide. The maximum output power was increased by 1.5 times and the nitrate removal efficiency (in 10 h) was increased from 89.13 ± 1.4% to 99.9 ± 0.1% after the modification. The organic matter in the sediment decreased by 78% after 270 days simultaneously. Sequencing of the microbial community showed that Geobacter and Anaerolinina were enriched in the anode. And theα-proteobacteria were enriched in the four experimental groups and had a good effect on nitrate removal especially in the C-GO-SSG system (Carbon felt anode-Graphene Oxide Modified cathode equipped Surface-water Sediment and Groundwater System) after 270 days operation. These results demonstrate that the C-GO-SSG system can be further used to remediation of sediment and groundwater with improved efficiency.

Annealing enhancement in stability and performance of copper modified boron-doped diamond (Cu-BDD) electrode for electrochemical nitrate reduction

Nitrate contamination in groundwater requires efficient remediation to prevent adverse environmental impacts. This study illustrates the improvement in nitrate reduction process using copper modified BDD (Cu-BDD) with higher stability after annealing treatment. The highest values for nitrate reduction and the selectivity of nitrogen gas were about 71% and 45%, respectively, which were obtained using annealed Cu-BDD electrode. Annealing process promoted the homogeneity of copper oxides that consolidated the electrodeposited copper oxides on the surface of Cu-BDD to enhance the stability of electrode. Meanwhile, annealed Cu-BDD exhibited higher conductivity to facilitate nitrate reduction initiating at a more positive potential. Furthermore, cuprous ions and metallic Cu were formed during the annealing treatment, and had active chemical reaction with nitrate and excellent catalytic capability for the reaction, which efficiently enhanced either the nitrate reduction efficiency or the selectivity of nitrogen gas. The findings advance the current understanding on the enhancement of electrochemical stability and nitrate reduction performance using Cu-BDD after the annealing treatment, and also offer a promising technology for remediation of nitrate-contaminated groundwater.

Remediation of nitrate-contaminated groundwater in a denitrifying bioelectrochemical system

Remediation of nitrate-contaminated groundwater in a denitrifying bioelectrochemical system

Impregnated calcium-alginate beads as floating reactors for the remediation of nitrate-contaminated groundwater

In this study, calcium-alginate beads impregnated with nano zero valent iron (NZVI), magnetite nanoparticles (MNP), and powdered activated carbon (PAC) were synthesized, as they were mixed with calcium carbonate powders in sodium alginate solution and reacted with calcium chloride and citric acid. Optical and scanning electron microscopy (SEM) images showed that the nanoparticles were uniformly embedded, and gas bubbles formed, in the polymeric beads. Comparative experiments were carried out as the nanoparticles were dosed, in original (bare) or immobilized form (embedded in the beads), into 100 mg/L nitrate-nitrogen (NO3-N) solutions at 5, 10, and 15 g/L. In 48 h, each gram of immobilized NZVI in the beads were found to reduce 4.3–9.6 mg NO3-N to ammoniacal-nitrogen (NH4-N). Up to 47.8% NH4-N resulted from NO3-N reduction was immobilized by PAC in the beads. These results demonstrated the effectiveness of using the beads for in-situ removal of nitrate, potentially producing an alternative technique to treat nitrate contaminated waters under anaerobic condition.

Horizontal Well Test for Simulating the In Situ Remediation of Nitrate Contaminated Groundwater by Microbial Denitrification

An in situ horizontal well (IHW) fan-shaped test tank was constructed in the laboratory. And nitrate removal rates were analyzed under different hydraulic loads. When the initial concentration of groundwater nitrate-N was 25 mg/L and the hydraulic load increased from 0.78 to 3.90 m3/(m2 day), the results show that the nitrate-N concentration was less than 1.25 mg/L after the denitrification process stabilized. Additionally, the nitrate-N removal rate was over 95%. The concentration of nitrite-N was still below 1 mg/L, and the level of ammonia-N was between 0.5 and 1.00 mg/L. No increase in nitrite-N and ammonia-N concentration occurred during the test. The hydraulic conductivity of the medium in the horizontal well showed little variation, ranging from 34.09 to 31.64 m/day, indicating that there was no blockage caused by microbial growth in the IHW during the test. In addition, no ethanol was detected in the test tank except for the horizontal well, revealing that ethanol did not diffuse into the surrounding aquifer. Therefore, when the concentration of groundwater nitrate contamination is 25 mg/L, the hydraulic load under the IHW test tank condition is 3.90 m3/(m2 day). The IHW test tank had a stable and good biological denitrification effect, and it can provide certain reference significance for in situ remediation of nitrate-contaminated groundwater.

A three chamber bioelectrochemical system appropriate for in-situ remediation of nitrate-contaminated groundwater and its reaction mechanisms

A novel laboratory experiment of three chamber bioelectrochemical (surface water-sediment-groundwater, SSG) system was established in this study, which combined a sediment microbial fuel cell (SMFC) reactor and biofilm electrode reactor (BER) and was self-driven. Simulated groundwater was firstly used to explore the reaction mechanisms of this system. The simulated groundwater conditions were static and the surface water and the groundwater systems were isolated. The results showed that the SMFC continuously supplied a stable voltage of 622 mV ± 20 mV, driving the BER and the related nitrate removal process. Compared to the control systems, the SSG system had higher nitrate removal with a denitrification rate of 3.87 mg N/(L·h). In addition, the sediment organic matter in the SMFC reactor decreased by 66.2%. Based on the electrochemical analysis and microbial community analysis, the SMFC reactor and BER worked synergistically to enhance the performance of both reactors in this system. The presence of microorganisms accelerated the electron transfer efficiency throughout the system, and the microcurrent helped a more fixed community structure to develop and stimulated the growth of denitrifying bacteria. The dominant genera detected in the mature biofilm samples were all microorganisms common in soil and groundwater, indicating that this system may be environmentally friendly. The nitrate removal efficiency for actual groundwater was higher than that for the simulated groundwater, indicating that the elements in the actual groundwater promote the nitrate removal efficiency. These results indicate that the SSG system has the potential for in-situ nitrate bioremediation, with minimal maintenance and health risk.

Performance of a field-scale biological permeable reactive barrier for in-situ remediation of nitrate-contaminated groundwater

We report the performance of a field-scale permeable reactive barrier (PRB) for the biological treatment of nitrate-contaminated groundwater. The reactive material of the PRB consisted of a mixture of gravel and mulch as a carbon source for denitrifying bacteria. The PRB was equipped with a delivery system that allowed injecting NO3− at controlled rates from the surface directly into the up-gradient layer of the PRB. This way, NO3− concentration entering the PRB was varied (from 1 to 530 mg/L) with the purpose of evaluating the ultimate efficiency of the PRB under different NO3− loadings. The PRB was successful at removing NO3− from groundwater at inlet concentrations up to 280 mg/L (with NO3− removal percentages ≥97%). Monitoring of groundwater at different depths within the PRB provided evidence that NO3− underwent denitrification preferably at the deepest part of the PRB, where more favourable reducing conditions were achieved. Among the shortcomings of the PRB were the fluctuations of groundwater fluxes caused by intense rainfalls during the study period, although they generally did not pose concern for the denitrification capacity of the PRB. Emission fluxes of gases (CO2, CH4 and N2O) from the PRB to the atmosphere were also measured. The results are finally compared with the few others reported existing PRBs for nitrate-contaminated groundwater worldwide.

Sulfur autotrophic denitrification (SAD) driven by homogeneous composite particles containing CaCO3-type kitchen waste for groundwater remediation

This study first developed homogeneous sulfur/buffer composite particles to obtain an alkalinity-uniform and cost-effective sulfur autotrophic denitrification (SAD) technology. As single solid-phase material, the composites performed better in enrichment of microorganisms and stabilization of S/C ratio throughout the reaction. Natural CaCO3-type kitchen waste, used as a buffer in the developed composites, was conducive to providing rich metal nutrients (K, Na, Mg, Al, and Ca) for the metabolism of microorganisms. Maximum denitrification efficiency of 96.4%, 96.8% and 96.8% were obtained by the 1.25:1 PSL, 1.72:1 PSE and 1.25:1 PSS composites, respectively, and nitrate removal rates of >0.6 mg-N/L-h and stable pH between 6.20 and 8.00 were achieved. The S0-eggshell microcosms showed more significant accumulations of ammonium-N and sulfate, reaching ∼1.2 mg-N/L and 405.99 ± 9.47 mg/L, respectively. When dealing with nitrate in real groundwater, the composites showed a great advantage over the dispersed materials at a denitrification efficiency of more than 99.7% and rate of 0.40 mg-N/L-h. No ammonium was observed by PSE and PSS throughout the batch. This study confirmed the potential of waste composites to enhance SAD performance in nitrate-contaminated groundwater remediation.

Enhanced nitrate removal and high selectivity towards dinitrogen for groundwater remediation using biochar-supported nano zero-valent iron

We prepared nano zero-valent iron/biochar composites (nZVI/BC) to remove nitrate from groundwater with harmless products. Results show nZVI/BCs derived from different mass ratios of Fe(0) to biochar exhibited different nitrate removal efficiencies, and the mass ratio of 1:2 developed the nZVI/BC with optimum nitrate removal. The nZVI/BC maintained preferable nitrate removal (75.0%–97.0%) over a wide pH range 2–12. Nitrate removal amount declined due to serious corrosion and clogging of nZVI/BC’s surface when initial nitrate concentration exceeded 40 mg/L. The nitrate removal process followed a first-order kinetic reaction. As regards real groundwater, the nZVI/BC removed more nitrate than both pure Fe(0) nanoparticles and biochar. Reaction product analysis revealed 60.1% of removed nitrate selectively became dinitrogen. X-ray photoelectron spectroscopy measurements suggested that nitrate-oxidized Fe(0) resulted in significant increase of magnetite on the surface of nZVI/BC. The redox potential and pH of long duration in reaction changed around −210 mV and 8–9, respectively. These changes facilitated the selective reduction of nitrate to dinitrogen. We also proposed that biochar may provide favorable circumstances for nitrate reduction by directly mediating redox potential, pH and electron transfer, which establishes a possible mechanism for the enhanced removal and selective reduction of nitrate. Our study suggests that nZVI/BC would be a promising alternative for the remediation of nitrate-contaminated groundwater.

Enhancement of rice bran as carbon and microbial sources on the nitrate removal from groundwater

The use of rice bran as carbon and microbial sources has the potential to enhance the groundwater denitrification performance. This research investigated the effects of rice bran dosage, filling modes and biofilm carriers’ types on the nitrate-contaminated groundwater remediation through batch and a series of column studies. NO3− removal rate increased as the rice bran increase in batch studies; however, the highest total nitrogen removal efficiency of 96.2% was achieved at 7 d with 1.50 g rice bran. Microorganism analysis indicated that bio-degradation (Massilia, Sphingomonas, Chryseobacterium and Sorangium) and bio-denitrification (Pseudomonas, Flavobacterium, Delftia and Comamonadace-ae) microorganisms were coexisted in rice bran denitrification system. Moreover, rice bran-gauze segmented (RGS) column had the lowest and most stable average effluent NO3− with low accumulations of NO2− and NH4+. The highest NO3− removal rate of 262.20 g·(m3·d)−1 was obtained when hydraulic retention time (HRT) was12 h. The results indicate that rice bran was an effective carbon and microbial sources for denitrification in NO3−-contaminated groundwater.

Remediation of nitrate-contaminated groundwater by PRB-Electrokinetic integrated process

Activated carbon is used as a reactive media in Permeable Reactive Barrier (PRB) for the removal of inorganic contaminants such as nitrate from groundwater. Since removal rate by this media decreases by time and due to the high costs of excavation and replacement of new media, the usage of activated carbon as an adsorbent in PRB is limited. The present study aimed to solve this defect by integrating electrokinetic process and PRB, using in-situ regeneration of activated carbon. This research was carried out on a laboratory scale using synthetically contaminated water and modified activated carbon as a reactive media in PRB. The effects of pH, nitrate concentration, carbon to sand ratio, and also electric gradient on the performance of the process were evaluated, and optimal conditions were determined, to increase the system longevity. According to the results, by applying an electric gradient of 1.25 V cm−1 to the PRB alone process in optimum operating condition (135 mg L−1 initial nitrate concentration, flow rate of 2.3 L min−1, pH = 6.8, and carbon to sand ratios of 1:1) the adsorbent capacity increased by 90%. Under these conditions, the integrated process could keep nitrate concentration in the effluent below the standard limit for about 111 h, while the PRB alone process could do the same job for about 59 h. Also, SEM analysis showed that by applying electrokinetic process, activated carbon was regenerated. Integration of electrokinetic process and PRB was also caused nitrate to transfer from activated carbon media into the soil layer above the system. This nitrate-rich soil has the potential for reuse in agricultural activities.

Use of Cotton as a Carbon Source for Denitrification in Biofilters for Groundwater Remediation

This study is part of a comprehensive research aimed at the development and application of the “Water Sensitive Cities” idea in Israel. This is a sustainable concept, incorporating among others the harvesting, treatment, and reuse of storm-water. The use of engineered biofiltration systems for the harvesting and treatment of storm-water in Israel is complicated due to the prolonged dry climate period, spanning 7–8 months of the year. Therefore, the tactic suggested is to use a hybrid biofiltration system for both storm-water harvesting/polishing during winter, and for remediation of nitrate-contaminated groundwater during summer. This paper focuses on the summer design (denitrification) configuration. In preliminary experiments, it was found that crude cotton could serve as an effective carbon source for denitrification. Further results are reported herein regarding the design and operation of biofilter columns applied for the treatment of synthetic mixtures simulating nitrate-contaminated groundwater. The columns were composed of crude cotton wool and polyethylene beads, which prevented the effect of cotton compression. This application was shown to enable controlled removal of nitrate to low levels, while emitting very low concentrations of total organic carbon (TOC) and nitrite. It was also concluded that a biofilter requires judicious design and operation, since complete removal of nitrogen oxides might lead to the formation of undesired compounds such as sulfides due to the development of anaerobic conditions.

In-situ biological denitrification using pretreated maize stalks as carbon source for nitrate-contaminated groundwater remediation

A simulation apparatus of in-situ groundwater remediation (SAIR) that used maize stalks pretreated with sodium hydroxide (MSSH) as a carbon source was designed for nitrate-contaminated groundwater treatment. Two experiments, RA and RB, were constructed in this SAIR. The removal performance of SAIR fed with real nitrate contaminated water was investigated under static and dynamic conditions. In the static remediation experiment, good removal efficiency (>95% for nitrate, 89% for total nitrogen) was observed in both experiments. However, nitrate removal efficiency did not differ greatly between RA and RB at a hydraulic retention time (HRT) of 15 d. Overall, these results indicate that MSSH has potential for use as an alternative carbon source for denitrification.

Pyrite-based autotrophic denitrification for remediation of nitrate contaminated groundwater

In this study, pyrite-based denitrification using untreated pyrite (UP) and acid-pretreated pyrite (AP) was evaluated as an alternative to elemental sulfur based denitrification. Pyrite-based denitrification resulted in a favorable nitrate removal rate constant (0.95d−1), sulfate production of 388.00mg/L, and a stable pH. The pretreatment of pyrite with acid led to a further increase in the nitrate removal rate constant (1.03d−1) and reduction in initial sulfate concentration (224.25±7.50mg/L). By analyzing the microbial community structure using Denaturing Gradient Gel Electrophoresis, it was confirmed that Sulfurimonas denitrificans (S. denitrificans) could utilize pyrite as an electron donor. A stable pH was observed over the entire experimental period, indicating that the use of a pH buffer reagent would not be necessary for pyrite-based denitrification. Therefore, pyrite could effectively replace elemental sulfur as an electron donor in autotrophic denitrification for nitrate-contaminated groundwater remediation.

Erratum to: Nitrate-contaminated groundwater remediation by combined autotrophic and heterotrophic denitrification for sulfate and pH control: batch tests

Erratum to: Nitrate-contaminated groundwater remediation by combined autotrophic and heterotrophic denitrification for sulfate and pH control: batch tests

An anaerobic two-layer permeable reactive biobarrier for the remediation of nitrate-contaminated groundwater

In this paper, an anaerobic two-layer permeable reactive biobarrier system consisting of an oxygen-capturing layer followed by a biodegradation layer was designed firstly for evaluating the remediation effectiveness of nitrate-contaminated groundwater. The first layer filling with granular oxygen-capturing materials is used to capture dissolved oxygen (DO) in groundwater in order to create an anaerobic condition for the microbial denitrification. Furthermore, it can also provide nutrition, such as carbon and phosphorus, for the normal metabolism of immobilized denitrifying bacteria filled in the second layer. The second layer using granular activated carbon as microbial carrier is able to biodegrade nitrate entering the barrier system. Batch experiments were conducted to identify the effect of DO on microbial denitrification, oxygen-capturing performance of zero valent iron (ZVI) powder and the characteristics of the prepared oxygen-capturing materials used to stimulate growth of denitrifying bacteria. A laboratory-scale experiment using two continuous upflow stainless-steel columns was then performed to evaluate the feasibility of this designed system. The first column was filled with granular oxygen-capturing materials prepared by ZVI powder, sodium citrate as well as other inorganic salts, etc. The second column was filled with activated carbon immobilizing denitrifying microbial consortium. Simulated nitrate-contaminated groundwater (40 mg NO3–N/L, pH 7.0) with 6 mg/L of DO content was pumped into this system at a flow rate of 235 mL/d. Samples from the second column were analyzed for nitrate and its major degradation byproduct. Results showed that nitrate could be removed more than 94%, and its metabolic intermediate, nitrite, could also be biodegraded further in this passive system. Further study is necessary in order to evaluate performance of its field application.