Nitrate Remediation Research Articles

Hydrogen Donors for Reduction of RDX, 2,4-DNT, and Nitrate in Groundwater

The Pueblo Chemical Depot, located east of Pueblo, CO, is typical of a number of U.S. facilities that were involved in weapons manufacturing, training and testing, or demilitarization in which the soil and groundwater became highly contaminated with explosives residues and are needing remediation. In this study, soil amendments of Hydrogen Release Compound® (HRC®), sodium lactate and corn syrup were evaluated in bench-scale batch reactors, mimicking in situ treatment, to determine the effectiveness of hydrogen donors on the remediation of soil contaminated with primarily RDX, but also 2,4-DNT, and excessive nitrate. Bench-scale batch reactors made from 55-gallon drums were designed to simulate aquifer conditions with site soil and contaminated groundwater. HRC® and corn syrup achieved the groundwater cleanup levels of 0.25 μ g/L for RDX by day 25 of the study, 0.0885 μ g/L for 2,4-DNT by day 7, and 1.0 mg/L for nitrate by day 7, reducing their average concentrations from 10.48 ± 0.48 μ g/L, 0.34 ± 0.15 μ g/L, and 99.7 ± 11.5 mg/L, respectively. The sodium lactate groups did not reach the groundwater cleanup goals for RDX, 2,4-DNT, or nitrate before returning to an oxidizing state. This indicates that HRC® and corn syrup are suitable electron donors for bioremediation, while sodium lactate may not be the best option for the remediation of RDX, 2,4-DNT, and nitrate.

Coupled acidification and ultrasound with iron enhances nitrate reduction

Contaminated soils, especially when pollutant concentrations are high, pose potentially serious threats to surface and groundwater quality, when there are spills, discharges, or leaking storage tanks. For in situ remediation of nitrate in groundwater, the use of zero-valent iron (Fe 0) is suggested. The formation of passivating scales on Fe 0 over time may limit the long-term reduction potential of Fe 0. The aim of this study was to investigate the effect of ultrasound and pH on the destruction of passive oxide film. Batch tests were conducted in a specially designed protocol using ultrasound, and changing iron (commercial iron powder of micro-scale grain size) loading and pH. The results showed deactivation of the degradation process by Fe 0 with combined ultrasound/iron system and with ultrasound alone. However, the degradation rate increases with decrease in pH. The degradation rate was 45% for pH 2 and 20% for pH 4. The combination of iron, acidification, and ultrasound showed excellent degradation efficiency, and the degradation rate was 99%. Acidification could destroy passive oxide film and activate iron, thus, hastening the reaction between Fe 0 and nitrate. Ultrasound was helpful in destroying or preventing the formation of passive oxide film under acidification.

A REVIEW OF REMEDIATION AND CONTROL SYSTEMS FOR THE TREATMENT OF AGRICULTURAL WASTE WATER IN IRELAND TO SATISFY THE REQUIREMENTS OF THE WATER FRAMEWORK DIRECTIVE

In Ireland agricultural activities have been identified as major sources of nutrient input to receiving waters, and it has been estimated that these activities contribute 75.3% of the N and 33.4% of the P found in these waters. The strategy at European level focuses on the prevention of nutrient loss by improved farm management. However, it does not focus on nutrient remediation or incidental nutrient loss from farmyard manures to surface water and groundwater. This review describes the impact of agriculture on the environment in Ireland and examines emerging technologies for agricultural waste-water treatment. An integrated approach at pretreatment and field stages for nitrate (NO 3 ) remediation and P control is recommended.

Removal of added nitrate in the single, binary, and ternary systems of cotton burr compost, zerovalent iron, and sediment: Implications for groundwater nitrate remediation using permeable reactive barriers

Recent research has shown that carbonaceous solid materials and zerovalent iron (Fe(0)) may potentially be used as media in permeable reactive barriers (PRBs) to degrade groundwater nitrate via heterotrophic denitrification in the solid carbon system, and via abiotic reduction and autotrophic denitrification in the Fe(0) system. Questions arise as whether the more expensive Fe(0) is more effective than the less expensive carbonaceous solid materials for groundwater nitrate remediation, and whether there is any synergistic effect of mixing the two different types of materials. We carried out batch tests to study the nature and rates of removal of added nitrate in the suspensions of single, binary, and ternary systems of cotton burr compost, Peerless Fe(0), and a sediment low in organic carbon. Cotton burr compost acted as both organic carbon source and supporting material for the growth of indigenous denitrifiers. Batch tests showed that cotton burr compost alone removed added nitrate at a greater rate than did Peerless Fe(0) alone on an equal mass basis with a pseudo-first-order rate constant k=0.0830+/-0.0031 h(-1) for cotton burr compost and a k=0.00223+/-0.00022 h(-1) for Peerless Fe(0); cotton burr compost also removed added nitrate at a faster rate than did cotton burr compost mixed with Peerless Fe(0) and/or the sediment. Furthermore, there was no substantial accumulation of ammonium ions in the cotton burr compost system, in contrast to the systems containing Peerless Fe(0) in which ammonium ions persisted as major products of nitrate reduction. It is concluded that cotton burr compost alone may be used as an excellent denitrification medium in a PRB for groundwater nitrate removal. Further study is needed to evaluate performance of its field applications.

論文 酸化的浅層地下水における硝酸性窒素の原位置浄化

硝酸性窒素汚染地下水の浄化対策として有効であると考えられる生物化学的浄化法を用い,自然浄化(脱窒)が期待できない酸化的条件下である筑波台地のローム層を研究対象地域とし,硝酸性窒素汚染地下水の原位置浄化を試みた.その結果,浄化壁の上流に位置する観測井で37.5mg/Lあった硝酸イオンが浄化壁内部で0.1mg/Lまでに低下した.また,一般的に脱窒反応の条件として,有機物の存在と還元的な環境があげられるが,豊富な有機物が条件として満たされると,有機物の分解に伴う微生物の代謝により還元的な環境が形成されるので,脱窒反応の最も重要な制限要因は電子供与体としての有機物の存在であることが示唆された.

Removal of added nitrate in cotton burr compost, mulch compost, and peat: Mechanisms and potential use for groundwater nitrate remediation

We conducted batch tests on the nature of removal of added nitrate in cotton burr compost, mulch compost, and sphagnum peat that may be potentially used in a permeable reactive barrier (PRB) for groundwater nitrate remediation. A rigorous steam autoclaving protocol (121 °C for 2 h each day for three consecutive days) for the cotton burr compost and autoclaving of all labware and the nitrate working solutions resulted in drastically different results compared to the non-autoclaved treatment. In the non-autoclaved cotton burr compost, added nitrate at 20 mg N l −1 decreased rapidly and was not detected after 3 d; whereas, the autoclaved cotton burr compost showed persistent nitrate above 15.5 mg N l −1 even after 10 d, which is comparable with nitrate concentrations above 17.6 mg N l −1 in a treatment using NaN 3 at 1000 mg l −1. Dewaxed cotton burr compost showed decreased nitrate reduction compared to the pristine cotton burr compost. No nitrate reduction was detected in the dewaxed sphagnum peat. It is concluded that nitrate removal in the organic media is controlled by microbiologically mediated processes. The use of readily available cotton burr and mulch composts may offer a cost-effective method of nitrate removal from contaminated groundwater.

Chloride Interactions with Iron Surfaces: Implications for Perchlorate and Nitrate Remediation Using Permeable Reactive Barriers

Perchlorate (Cl O4− ) can be reduced by iron surfaces, suggesting that permeable reactive barriers may represent a useful groundwater remediation strategy. However, chloride produced by the reaction inhibits further perchlorate removal. Adsorption of chloride on iron filings was investigated as a potential mechanism of chloride interference. The effect of chloride on the removal of nitrate, another oxyanion reactive at iron surfaces, was also investigated to draw more general conclusions about anion competition when target compounds adsorb electrostatically. A triple layer adsorption model was used to describe chloride sorption isotherms on the iron filings using magnetite as the model surface and defining a single type of surface hydroxyl sorption site. The model considered electrostatic attraction, specific sorption, and the effect of adsorbed Fe2+ on chloride sorption. Experimental and modeling results indicate that chloride competition is probably not of concern for nitrate reduction in permeable reac...

Perchlorate and Nitrate Remediation Efficiency and Microbial Diversity in a Containerized Wetland Bioreactor

We have developed a method to remove perchlorate (14–27 μg/L) and nitrate (48 mg/L) from contaminated groundwater using a wetland bioreactor. The bioreactor has operated continuously in a remote field location for more than 2 yr with a stable ecosystem of indigenous organisms. This study assesses the bioreactor for long-term perchlorate and nitrate remediation by evaluating influent and effluent groundwater for oxidation-reduction conditions and nitrate and perchlorate concentrations. Total community DNA was extracted and purified from 10-g sediment samples retrieved from vertical coring of the bioreactor during winter. Analysis by denaturing gradient gel electrophoresis of short, 16S rDNA, polymerase-chain-reaction products was used to identify dominant microorganisms. Bacteria genera identified were closely affiliated with bacteria widely distributed in soils, mud layers, and fresh water. Of the 17 dominant bands sequenced, most were gram negative and capable of aerobic or anaerobic respiration with nitrate as the terminal electron acceptor (Pseudomonas, Acinetobacter, Halomonas, and Nitrospira). Several identified genera (Rhizobium, Acinetobactor, and Xanthomonas) are capable of fixing atmospheric nitrogen into a combined form (ammonia) usable by host plants. Isolates were identified from the Proteobacteria class, known for the ability to reduce perchlorate. Initial bacterial assessments of sediments confirm the prevalence of facultative anaerobic bacteria capable of reducing perchlorate and nitrate insitu.

Nitrate reduction by zerovalent iron: effects of formate, oxalate, citrate, chloride, sulfate, borate, and phosphate.

Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L(-1) (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 degrees C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h(-1), corresponding to surface area normalized rates ranging from 0.126 to 4.15 h(-1) m(-2) mL. Correlation analysis showed a negative linear relationship between the nitrate reduction rates for the ligands and the conditional stability constants for the soluble complexes of the ligands with Fe2+ (R2 = 0.701) or Fe3+ (R2 = 0.918) ions. This sequence of reactivity corresponds also to surface adsorption and complexation of the three organic ligands to iron oxides, which increase in the order formate < oxalate < citrate. The results are also consistent with the sequence of strength of surface complexation of the inorganic ligands to iron oxides, which increases in the order: chloride < sulfate < borate < phosphate. The blockage of reactive sites on the surface of Fe0 and its corrosion products by specific adsorption of the inner-sphere complex forming ligands (oxalate, citrate, sulfate, borate, and phosphate) may be responsible for the decreased nitrate reduction by Fe0 relative to the chloride system.

Long‐Term Performance of In Situ Reactive Barriers for Nitrate Remediation

AbstractNitrate is now recognized as a widespread ground water contaminant, which has led to increased efforts to control and mitigate its impacts. This study reports on the long‐term performance of four pilot‐scale field trials in which reactive porous barriers were used to provide passive in situ treatment of nitrate in ground water. At two of the sites (Killarney and Borden), the reactive barriers were installed as horizontal layers underneath septic system infiltration beds; at a third site (Long Point), a barrier was installed as a vertical wall intercepting a horizontally migrating septic system plume; and at the fourth site (North Campus), a barrier was installed as a containerized subsurface reactor treating farm field drainage water. The reactive media consisted of 15% to 100% by volume of waste cellulose solids (wood mulch, sawdust, leaf compost), which provided a carbon source for heterotrophic denitrification. The field trials have been in semicontinuous operation for six to seven years at hydraulic loading rates ranging from six to 2000 L/day. Trials have been successful in attenuating influent NO3‐ (or NO3‐+ NH4+ at Borden) concentrations averaging from 4.8 mg/L N at North Campus to 57 mg/L N at Killarney, by amounts averaging 80% at Killarney, 74% at Borden, 91 % at Long Point, and 58% at North Campus. Nitrate consumption rates were temperature dependent and ranged from 0.7 to 32 mg L N/day, but did not deteriorate over the monitoring period. Furthermore, mass‐balance calculations indicate that carbon consumption by heterotrophic denitrification has so far used only about 2% to 3% of the initial carbon mass in each case. Results suggest that such barriers should be capable of providing NO3‐ treatment for at least a decade or longer without carbon replenishment.Reactive barriers have now been used to treat nitrate contamination from a variety of sources including septic systems, agricultural runoff, landfill leachate, and industrial operations. This demonstration of successful long‐term operation should allow this technology to become more widely considered for nitrate remediation, particularly at sites where passive treatment requiring a minimum of maintenance is desired.