Oxygen Release Compound Research Articles

Enhanced aerobic bioremediation of an aquifer heavily contaminated with a mixture of chlorobenzenes and hexachlorocyclohexanes at the Sardas landfill (Spain)

The groundwater at the Sardas landfill in Huesca, Spain, is contaminated with benzene, chlorobenzenes, and hexachlorocyclohexane (HCH) isomers due to illegal waste dumping from a former lindane factory. In this study, microcosms using field-derived groundwater to evaluate in situ bioremediation were constructed. Anaerobic biostimulation with lactate successfully transformed α-, β-, δ-, and γ-HCH within two weeks, but failed to degrade benzene and less chlorinated benzenes, even with nutrient addition. In contrast, aerobic biostimulation led to rapid degradation of benzene, chlorobenzenes, and α-, δ-, and γ-HCH. Notably, adding a phosphorus source significantly increased the degradation rates. Following these laboratory results, an in situ pilot test using the oxygen-releasing compound CaO2 was conducted at two site injection wells. The field results mirrored those from the microcosms, showing a marked reduction in contaminants at both the injection wells and surrounding wells. Bacterial community analysis based on the 16S rRNA genes in samples derived from aerobic microcosms and groundwater before and after the biostimulation test revealed a marked increase in the genus Pseudomonas, suggesting its potential role as biodegrading agent. This study illustrates the effectiveness of biostimulation as a viable strategy for treating groundwater contaminated with HCH isomers, benzene, and chlorobenzenes.

Unlocking the efficacy of cement-shell encapsulation for microbial self-healing process of concrete cracks

Oxygen supply and bacterial viability are crucial for efficient calcium carbonate precipitation in concrete crack healing processes. However, the open deliverance of oxygen-releasing compounds (ORCs) and bacterial spores during concrete mixing and casting poses a threat to spore viability and limits oxygen availability. To address these challenges, we developed an innovative approach integrating an oxygen self-supply strategy with bacterial strain B6. As such, B6 spores, along with Ca(OH)2 and CaO2 as oxygen sources and essential nutrients, were embedded within cement-shell microcapsules to build a microbial self-healing system. The result shows that in the presence of oxygen source and nutrients, B6 group (BPN) exhibits successful crack repair, achieving a repair ratio of approximately 100% after 30 days, while other control groups show less effective repair rates (20–60%). Moreover, water permeability significantly improves in the BPN specimens after crack repair, reaching 0 ml/cm−2·min, highlighting the efficacy of the developed self-healing system. Encapsulating the healing agent within cement shell effectively mitigates the reactivity between ORCs (CaO2) and water, thereby facilitating stable oxygen supply and safe delivery of microbial agents during crack healing. Furthermore, in-situ micromorphology and composition identification of crack repair materials affirm the presence of calcium carbonate precipitation to seal the concrete cracks. The encapsulation of healing material within cement shell stands out as an innovative approach, demonstrating an efficient self-healing process of concrete cracks. These findings might unveil new possibilities for bio-concrete to be used in sustainable and resilient construction practices, particularly in environments prone to cracking and water ingress.

Enhanced phenanthrene biodegradation in river sediments by harnessing calcium peroxide nanoparticles and minerals in Sphingomonas sp. DSM 7526 cultivation

ABSTRACT Coupling chemical oxidation and biodegradation to remediate polycyclic aromatic hydrocarbon (PAH)-contaminated sediment has recently gained significant attention. In this study, calcium peroxide nanoparticles (nCaO2) were utilized as an innovative oxygen-releasing compound for in-situ chemical oxidation. The study investigates the bioremediation of phenanthrene (PHE)-contaminated sediment inoculated with Sphingomonas sp. DSM 7526 bacteria and treated with either aeration or nCaO2. Using three different culture media, the biodegradation efficiencies of PHE-contaminated anoxic sediment, aerobic sediment, and sediment treated with 0.2% w/w nCaO2 ranged from 57.45% to 63.52%, 69.87% to 71.00%, and 92.80% to 94.67%, respectively. These values were significantly higher compared to those observed in non-inoculated sediments. Additionally, the type of culture medium had a prominent effect on the amount of PHE removal. The presence of minerals in the culture medium increased the percentage of PHE removal compared to distilled water by about 2–10%. On the other hand, although the application of CaO2 nanoparticles negatively impacted the abundance of sediment bacteria, resulting in a 30–42% decrease in colony-forming units after 30 days of treatment, the highest PHE removal was obtained when coupling biodegradation and chemical oxidation. These findings demonstrate the successful application of bioaugmentation and chemical oxidation processes for treating PAH-contaminated sediment.

Remedial trial of sequential anoxic/oxic chemico-biological treatment for decontamination of extreme hexachlorocyclohexane concentrations in polluted soil.

During production of γ-hexachlorocyclohexane (γ-HCH), thousands of tons of other isomers were synthesized as byproducts, and after dumping represent sources of contamination for the environment. Several microbes have the potential for aerobic and anaerobic degradation of HCHs, and zero-valent iron is an effective remediation agent for abiotic dechlorination of HCHs, whereas the combination of the processes has not yet been explored. In this study, a sequence of anoxic/oxic chemico-biological treatments for the degradation of HCHs in a real extremely contaminated soil (10-30g/kg) was applied. Approximately 1500kg of the soil was employed, and various combinations of reducing and oxygen-releasing chemicals were used for setting up the aerobic and anaerobic phases. The best results were obtained with mZVI/nZVI, grass cuttings, and oxygen-releasing compounds. In this case, 80 % removal of HCHs was achieved in 129 days, and 98 % degradation was achieved after 1106 days. The analysis of HCHs and their transformation products proved active degradation when slight accumulation of the transformation product during the anaerobic phase was followed by aerobic degradation. The results document that switching between aerobic and anaerobic phases, together with the addition of grass, also created suitable conditions for the biodegradation of HCHs and monochlorobenzene/benzene by microbes.

Mitigating translocation of arsenic from rice field to soil pore solution by manipulating the redox conditions

Arsenic (As) is uptaken more readily by rice over wheat and barley. The exposure of As to humans being in the rice-consuming regions is a serious issue. Thus, an effective practice to reduce the translocation of As from soil to rice grain should be implemented. During a flooding period, the water layer greatly limits the transport of oxygen from atmosphere to soil, which provides favorable conditions for reduction of oxygen. The reduction of Fe in the soil during the flooding condition is closely related to the As mobility, which expedites the release of As to the soil pore solution and increases As uptake by rice plants. Therefore, the performance of oxygen releasing compounds (ORCs) was evaluated to lower the translocation of As from soil to soil solution. Specifically, in the simple system containing ORCs and water, the oxygen releasing capacity of ORCs was scrutinized. In addition, ORCs was applied to sea sand and arsenic bearing ferrihydrite to identify the contribution of ORCs to As and iron mobility. Especially, ORCs were introduced to the closed (completely mixed system) and open (static) systems to simulate the paddy soil environment. Introducing ORCs increased the DO in the aqueous phase, and CaO2 was more effective in increasing DO than MgO2. In the static system simulating a rice field, the dissolution of ORCs was inhibited. The pH increased due to the formation of hydroxide, but the increase was not significant in the soil due to the buffering capacity of the soil. Finally, the As concentration in the soil solution was lowered to 25–50% of that of the control system by application of ORCs in the static paddy soil system. All experimental findings signify that the application of ORCs can be an effective practice to lower the translocation of As from soil to pore solution.

Effect of applying calcium peroxide on the accumulation of arsenic in rice plants grown in arsenic-elevated paddy soils

Water management such as drainage for creating aerobic conditions is considered to be an adequate method for reducing the accumulation of arsenic (As) in rice grains; however, it is difficult to conduct drainage operations in some areas that experience a lengthy rainy season as well as in soils with poor drainage. In this regard, application of oxygen-releasing compounds (ORCs) may be an alternative method for maintaining aerobic conditions even under flooding in paddy soils. Therefore, a pot experiment was conducted to investigate the effects of application of an ORC, calcium peroxide (CaO2), on the growth and accumulation of As in rice plants grown in As-contaminated paddy soils. The rice plants were grown in two soils with different characteristics and As levels, and all of the tested soils were treated with 0, 5, 10, and 20 g CaO2 kg−1. Results revealed that the concentration of As and the distribution of arsenite in the pore water of all tested soils was reduced by CaO2 application. In addition, the grain yields increased and the concentration of inorganic As in brown rice decreased by 25–45% upon CaO2 treatment of low-As-level soils (<16 mg kg−1). However, the effect of CaO2 application on the accumulation of inorganic As in brown rice in As-enriched soils (>78 mg kg−1) could not found in this study, due to the rice plant suffered from serious As phytotoxicity. It suggests that CaO2 amendment may be suitable for reducing the As concentration of rice grains grown in low-As-level paddy soils, but for As-enriched soils, the proposed CaO2 application method is not feasible.

Oxygen-releasing manganese clay hybrid complex triggers p53-mediated cancer cell death in hypoxia

Hypoxia in tumor microenvironment is responsible for resistance to conventional modes of cancer therapeutics. A manganese-clay hybrid compound MHC was shown to generate molecular oxygen in aqueous solution. In this study we have shown that MHC, in hypoxia, causes cancer cell death, through release of molecular oxygen and via p53-dependent apoptosis. MHC treatment of cells results in depletion of mitochondrial membrane potential and inhibition of ROS production, in a cell-specific manner. In hypoxia, the oxygen from MHC releases cells from S-phase arrest thus causing p53-dependent apoptosis. The induction of apoptosis by MHC is higher in p53 Wt/Wt cells when it is compared with p53 Mt/Mt cells. The released oxygen from MHC triggers apoptosis via p53 activation through its enhanced homo-oligomerization, post-translational modifications and nuclear localization. Thus MHC as a cellular oxygen-releasing compound has high potential as a drug for hypoxic tumor regression.

A novel magnesium-based oxygen releasing compound for eutrophic water remediation

Eutrophication of surface water bodies is a global problem in recent years. Dosing polluted water with oxygen releasing compounds (ORCs), especially those that can remove excessive nutrients simultaneously is regarded as one of the most economical and eco-friendly methods of treating eutrophic waters. In this study, a novel Mg-based ORC was synthesized and characterized as a magnesium hydroxide and hydrogen peroxide complex (MHHPC) with Mg to H2O2 ratio of 2:1. Oxygen-releasing, pH-adjusting and nutrient-removal potentials of MHHPC were evaluated in nano-pure and eutrophic water. The overall performance of MHHPC in preventing the eutrophic water from turning black and odorous was compared with the performance of other ORCs namely, MgO2, CaO2 and the combination of MgCl2 and H2O2. The results showed that MHHPC was capable of constantly releasing oxygen to aqueous phase over a period of one week. Phosphate and ammonia nitrogen in synthetic buffered water can were removed as struvite and other precipitates from the aqueous phase. In the synthetic eutrophic water, all the ORCs tested were able to reduce aqueous ammonia nitrogen below 0.5 mM, while only CaO2 and MHHPC successfully removed the aqueous phosphate. However, CaO2 and MgCl2+H2O2 significantly inhibited microbial activity.

A Remediation Study of Contaminated Marine Sediment through Application of Naturally Developed Oxygen Releasing Compound

Blocking the influx of nutrients from contaminated sediment and reducing terrigenous loads are essential to control eutrophication in coastal water areas. In this study, the use of an oyster-shell-based ORC (oxygen-releasing compound) was investigated with respect to nutrients such as nitrogen, phosphorous, and sulfur compounds in the sediment environment. The ORC, which was produced by pyrolyzing oyster shell powder, was found to be overoxidized and consisted of calcium peroxide. A series of experiments simulating a typical overlying water-sediment system were carried out in open-lid cylindrical columns over the fifteen-day experimental period. The elution and distribution of crucial contaminating species within that system are discussed. T-N, NH4 +-N, T-P, and Pi propagated with time toward the overlying water from the sediment through diffusive migration, showing a constrained increase over distance at the sediment-water interface. The nitrate levels decreased with time, possibly due to local denitrification. Partial oxidation in a homogenized mixture of sediment and oxidized oyster shell powder resulted in an increased DO level within the experimental time frame, which in turn caused T-N, NH4 +-N, T-P, and Pi to propagate at a lower rate than sediment without any ORC. Analyses for sulfates and sulfides in the sediment mixed with ORC confirmed that the chemical environment changed into a more oxidized state in fifteen days. Diffusive migration, along with chemical reactions and/or adsorption, successfully explained the propagation and distribution of the concerned nutrient species resulting from the use of oyster shell powders.

The effect of calcium peroxide originating from oyster shell powder on control of phosphorus compounds in oceanic sediment

This study evaluated the water quality above the marine sediment by inputting oxygen releasing compound (ORC) processed from calcined oyster shells. Presumed vital parameters such as DO, pH, ORP, chlorophyll-a and classified phosphorous compounds were monitored for 20 d. ORP decreased with time in the control bed, while it increased to a positive value as a result of the ORC effect. DO kept showing a relatively high concentration in ORC treated column. We observed an increase of chlorophyll-a and a decrease of dissolved inorganic phosphate (DIP) simultaneously, which meant the released inorganic phosphorus would convert to an organic form in the overlying water. TP rises were the lowest in the ORC column (79%), meanwhile in the control column those went up to 0.304 mg/L (85%). Also, phosphorus fractions were measured in the sediment: Fe-P decreased in control while Fe-P and Ca-P soared greatly in the ORC column. This implies that in more oxidized environment inorganic phosphate bound to Ca-species would be eliminated as solidified precipitates in the sediment pore water, and it consequently suppressed the release of phosphates to the overlying water. The results indicate that the release of phosphorus and resulting eutrophication could be effectively controlled via the local environment improved by calcined ORC.

The impact of calcium peroxide on groundwater bacterial diversity during naphthalene removal by permeable reactive barrier (PRB).

Oxygen-releasing compounds (ORCs) have recently gained much attention in contaminated groundwater remediation. We investigated the impact of calcium peroxide nanoparticles on the groundwater indigenous bacteria in a bioremediation process by permeable reactive barrier (PRB). Three sand-packed columns were applied, including (1) control column (fresh groundwater), (2) natural remediation column (contaminated groundwater), and (3) biostimulation column (contaminated groundwater amended with CaO2). Actinobacteria and Proteobacteria constituted the main phyla among the identified isolates. According to the results of next-generation sequencing, Proteobacteria was the dominant phylum (81% relative abundance) in the natural remediation condition. But, it was declined to 38.1% in the biostimulation column. Meanwhile, the abundance of Actinobacteria and Bacteroidetes were increased to 25.9% and 15.4%, respectively, by exposing the groundwater microbial structure to CaO2 nanoparticles. Furthermore, orders Chlamydiales, Nitrospirales, and Oceanospirillales existing in the control column were detected in the presence of naphthalene. Shannon index was 4.32 for the control column samples, while it was reduced to 2.73 and 2.00 in the natural and biostimulation columns, respectively. Therefore, the present study provides a considerable insight into the impact of ORCs on the groundwater microbial community during the bioremediation process.

Changes in Phosphorus and Sediment Oxygen Demand in Coastal Sediments Promoted by Functionalized Oyster Shell Powder as an Oxygen Release Compound

In this study, we performed a sediment elution experiment to evaluate water quality in terms of phosphorus, as influenced by the dissolved oxygen consumed by sediments. Three separate model column treatments, namely, raw, calcined, and sonicated oyster shell powders, were used in this experiment. Essential phosphorus fractions were examined to verify their roles in nutrient release from sediment based on correlation analyses. When treated with calcined or sonicated oyster shell powder, the sediment-water interface became “less anaerobic,” thereby producing conditions conducive to partial oxidation and activities of aerobic bacteria. Sediment Oxygen Demand (SOD) was found to be closely correlated with the growth of algae, which confirmed an intermittent input of organic biomass at the sediment surface. SOD was positively correlated with exchangeable and loosely adsorbed phosphorus and organic phosphorus, owing to the accumulation of unbound algal biomass-derived phosphates in sediment, whereas it was negatively correlated with ferric iron-bound phosphorus or calcium fluorapatite-bound phosphorus, which were present in the form of insoluble complexes, thereby facilitating the free migration of sulfate-reducing bacteria or limiting the release from complexes, depending on applied local conditions. PCR-denaturing gradient gel electrophoresis revealed that iron-reducing bacteria were the dominant species in control and non-calcined oyster shell columns, whereas certain sulfur-oxidizing bacteria were identified in the column treated with calcined oyster powder.

Properties of Concrete Prepared with Recycled Aggregates Treated by Bio-Deposition Adding Oxygen Release Compound.

Recycled aggregates have high water absorption and crushing index. In order to improve the properties of recycled aggregates in concrete production, various treatments were used to modify the aggregates. In recent years, bio-deposition as a new treatment method of recycled aggregates was environmentally friendly. An improved method of bio-deposition was implemented to modify the properties of recycled mortar aggregates (RMA). O-bio-deposition is based on aerobic bacteria induced CaCO3 precipitation by respiration by varying the distance between the RMA and the bottom of the container and by adding an oxygen release compound to the culture solution that contains bacteria to promote the induction of CaCO3. First, the physical properties, including water absorption, crushing value, and apparent density, of the coarse RMA under different treatment methods were determined, and an o-bio-deposition treatment method was obtained. The fine RMA was treated and compared with the untreated RMA. Concretes were then prepared from the treated coarse RMA, and compressive strength and slump were determined. In addition, the effect of the o-bio-deposition treatment on the RMA surface and the micro-cracks of concretes were observed by scanning electron microscopy (SEM). It was found that the water absorption and crushing index of the coarse RMA treated by o-bio-deposition were reduced by 40.38 and 19.76% compared with untreated RMA, respectively. Regarding the concrete, the slump and the compressive strength (28 d) of concrete were increased by 115% and 25.3%, respectively compared with the untreated concrete.

Integrated electrokinetic processes for the remediation of phthalate esters in river sediments: A mini-review

Concerning the contamination of phthalate esters (PAEs) in river sediments, this mini-review introduces four recently reported novel “integrated electrokinetic (EK) processes” for the remediation purpose, namely two combined technologies of the EK process and advanced oxidation process (EK-AOP Processes) and two combined technologies of the EK process and biological process (EK-BIO Processes). The following is a comprehensive summary for these remediation processes: (1) the EK process coupled with nano-Fe3O4/S2O82− oxidation process – Test results have shown that nanoscale Fe3O4 played a significant role in activating persulfate oxidation. Even a recalcitrant compound like di(2‑ethylhexyl)phthalate (DEHP), its concentration in test sediment was reduced to 1.97 mg kg−1, far below the regulatory levels set by Taiwan EPA; (2) the EK process integrated with a novel Fenton-like process catalyzed by nanoscale schwertmannite (nano-SHM) – Test results have revealed that simultaneous injection of nano-SHM slurry and H2O2 into the anode reservoir and sediment compartment is a good practice. 70–99% in removal efficiency was obtained for various target PAEs; (3) enhanced in situ bioremediation coupled with the EK process for promoting the growth of intrinsic microorganisms by adding H2O2 as an oxygen release compound (ORC) – Test results have demonstrated that an intermittent mode of injecting lab-prepared ORC directly into the contaminant zone would be beneficial to the growth of intrinsic microorganisms in test sediment for in situ bioremediation of target PAEs; and (4) coupling of a second-generation ORC (designated 2G-ORC) with the EK-biological process – Test results have proved that 2G-ORC is long-lasting and can be directly utilized as the carbon source and oxygen source for microbial growth resulting in an enhanced biodegradation of PAEs. Except DEHP having a residual concentration of 4 μg kg−1, all other target PAEs in test sediment were totally removed by this novel combined remediation process.

Application of encapsulated magnesium peroxide (MgO2) nanoparticles in permeable reactive barrier (PRB) for naphthalene and toluene bioremediation from groundwater

One of the challenges in the petroleum hydrocarbon contaminated groundwater remediation by oxygen releasing compounds (ORCs) is to identify the remediation mechanism and determine the impact of ORCs on the environment and the intrinsic groundwater microorganisms. In this research, the application of encapsulated magnesium peroxide (MgO2) nanoparticles in the permeable reactive barrier (PRB) for bioremediation of the groundwater contaminated by toluene and naphthalene was studied in the continuous flow sand-packed plexiglass columns within 50 d experiments. For the biodiversity studies, next generation sequencing (NGS) of the 16S rRNA gene was applied. The results showed that naphthalene was metabolized (within 20 days) faster than toluene (after 30 days) by microorganisms of the aqueous phase. By comparing the contaminant removal in the biotic (which resulted in the complete contaminant removal) and abiotic (around 32% removal for naphthalene and 36% for toluene after 50 d) conditions, the significant role of microorganisms on the decontamination process was proved. Furthermore, the attached microbial communities on the porous media were visualized by scanning electron microscopy (SEM). Microbial community structure analysis by NGS technique revealed that the microbial species which were able to degrade toluene and naphthalene such as P. putida and P. mendocina respectively were stimulated by addition of MgO2 nanoparticles. The presented study resulted in a momentous insight into the application of MgO2 nanoparticles in the hydrocarbon compounds removal from groundwater.

Synthesis and characterization of stabilized oxygen-releasing CaO2 nanoparticles for bioremediation

Bioremediation is one of the general methods to treat pollutants in soil, sediment, and groundwater. However, the low concentration and restricted dispersion of dissolved oxygen (DO) in these areas have limited the efficiency of remediation especially for microorganisms that require oxygen to grow. Calcium peroxide (CaO2) is one of the oxygen-releasing compounds and has been applied to magnify the remediation efficacy of polluting areas. In this study, CaO2 nanoparticles (NPs) were synthesized and evaluated by wet chemistry methods as well as dry and wet grinding processes. The characteristics of CaO2 particles and NPs were analyzed and compared by dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and X-ray powder diffraction. Our results showed that wet-grinded CaO2 NPs had an average particle size of around 110 nm and were more stable compared to other particles from aggregation and sedimentation tests. In addition, we also observed that CaO2 NPs had better DO characteristics and patterns; these NPs generated higher DO levels than their non-grinded form. Accordingly, our results suggested that wet-grinding CaO2 particles to nanoscale could benefit their usage in bioremediation.

A novel approach to accelerate bacterially induced calcium carbonate precipitation using oxygen releasing compounds (ORCs)

Abstract In the present study, a mixture of oxygen releasing compounds (ORCs) was designed in an attempt to continuously supply dissolved oxygen (DO) in the oxygen-limiting conditions and evaluate bacterially induced calcium carbonate (CaCO3) production. The biomineralization of CaCO3 was adversely affected in the presence of calcium peroxide (CP) and zinc peroxide (ZP), whereas urea-hydrogen peroxide (UP) and magnesium peroxide (MP) were found to be significant on enhancing the biosynthesis of CaCO3. The optimal values for UP and MP obtained from central composite face-centered (CCF) were 1800 mg/L and 8.3 mg/L, respectively. As compared to the control samples, the bacterially induced CaCO3 precipitation was not only enhanced but also accelerated when the optimum concentrations of ORCs were supplemented in the fermentation media. Moreover, the morphology of the precipitated CaCO3 was affected in the presence of ZP, while no such effect was observed when the media were supplemented with CP, UP or MP. The results of this study can be used in many natural and engineered applications such as the constructional purposes for designing a more efficient bio self-healing concrete. The other applications of this innovative technology are the removal of heavy metals, radionuclides and calcium ions contaminants from the environment.

Remediation of phthalates in river sediment by integrated enhanced bioremediation and electrokinetic process

The objective of this study was to evaluate the feasibility of enhanced bioremediation coupling with electrokinetic process for promoting the growth of intrinsic microorganisms and removing phthalate esters (PAEs) from river sediment by adding an oxygen releasing compound (ORC). Test results are given as follows: Enhanced removal of PAEs was obtained by electrokinetics, through which the electroosmotic flow would render desorption of organic pollutants from sediment particles yielding an increased bioavailability. It was also found that the ORC injected into the sediment compartment not only would alleviate the pH value variation due to acid front and base front, but would be directly utilized as the carbon source and oxygen source for microbial growth resulting in an enhanced degradation of organic pollutants. However, injection of the ORC into the anode compartment could yield a lower degree of microbial growth due to the loss of ORC during the transport by EK. Through the analysis of molecular biotechnology it was found that both addition of an ORC and application of an external electric field can be beneficial to the growth of intrinsic microbial and abundance of microflora. In addition, the sequencing result showed that PAEs could be degraded by the following four strains: Flavobacterium sp., Bacillus sp., Pseudomonas sp., and Rhodococcus sp. The above findings confirm that coupling of enhanced bioremediation and electrokinetic process could be a viable remediation technology to treat PAEs-contaminated river sediment.

Removal of ammonium-nitrogen from groundwater using a fully passive permeable reactive barrier with oxygen-releasing compound and clinoptilolite

A novel fully passive permeable reactive barrier (PRB) with oxygen-releasing compound (ORC) and clinoptilolite was proposed for the removal of ammonium-nitrogen from groundwater. The PRB involves a combination of oxygen release, biological nitrification, ion exchange, and bioregeneration. A pilot-scale performance comparison experiment was carried out employing three parallel columns to assess the proposed PRB. The results showed that the PRB achieved nearly complete NH4+-N depletion (>99%). NH4+-N of 5.23–10.88 mg/L was removed, and NO2−-N of <1.93 mg/L and NO3−-N of 2.03–19.67 mg/L were generated. Ion exchange and biological nitrification both contributed to NH4+-N removal, and the latter played a dominant role under the condition of sufficient oxygen. Biological nitrification favored a delay in sorption saturation and a release of exchange sites. The ORC could sufficiently, efficiently supply oxygen for approximately 120 pore volumes. The clinoptilolite ensured a robust NH4+-N removal in case of temporary insufficient biological activities. No external alkalinity sources had to be supplied and no inhibition of aerobic metabolism occurred. The ceramicite had a negligible effect on the biomass growth. Based on the research findings, a full-scale continuous wall PRB was installed in Shenyang, China in 2012.

Laboratory column study for evaluating a multimedia permeable reactive barrier for the remediation of ammonium contaminated groundwater

In order to remediate ammonium contaminated groundwater, an innovative multimedia permeable reactive barrier (M-PRB) was proposed, which consisted of sequential columns combining oxygen releasing compound (ORC), zeolite, spongy iron and pine bark in the laboratory scale. Results showed that both ammonium and nitrate could be reduced to levels below the regulatory discharge limits through ion exchange and microbial degradation (nitrification and denitrification) in different compartments of the M-PRB system. The concentration of dissolved oxygen (DO) increased from 2 to above 20 mg/L after the simulated groundwater flowed through the oxygen releasing column packed with ORC, demonstrating that ORC could supply sufficient oxygen for subsequent microbial nitrification. Ammonium was efficiently removed from about 10 to below 0.5 mg N/L in the aerobic reaction column which was filled with biological zeolite. After 54 operating days, more than 70% ammonium could be removed by microbial nitrification in the aerobic reaction column, indicating that the combined use of ion exchange and nitrification by biological zeolite could ensure high and sustainable ammonium removal efficiency. To avoid the second pollution of nitrate produced by the former nitrification, spongy iron and pine bark were used to remove oxygen and supply organic carbon for heterotrophic denitrification in the oxygen removal column and anaerobic reaction column separately. The concentration of nitrate decreased from 14 to below 5 mg N/L through spongy iron-based chemical reduction and microbial denitrification.