Bioremediation of benzene from groundwater by calcium peroxide (CaO2) nanoparticles encapsulated in sodium alginate

Design of a two functional permeable reactive barrier for synergistic enzymatic and microbial bioremediation of phenol-contaminated waters: laboratory column evaluation : Enzymatic and microbial bioremediation of phenol in a bilayer permeable reactive barrier

The present study aimed to develop a system using a combination of enzymatic and microbial degradation techniques for removing phenol from contaminated water. In our prior research, the HRP enzyme extracted from horseradish roots was utilized within a core-shell microcapsule to reduce phenolic shock, serving as a monolayer column. To complete the phenol removal process, a second column containing degrading microorganisms was added to the last column in this research. Phenol-degrading bacteria were isolated from different microbial sources on a phenolic base medium. Additionally, encapsulated calcium peroxide nanoparticles were used to provide dissolved oxygen for the microbial population. Results showed that the both isolated strains, WC1 and CC1, were able to completely remove phenol from the contaminated influent water the range within 5 to 7 days, respectively. Molecular identification showed 99.8% similarity for WC1 isolate to Stenotrophomonas rizophila strain e-p10 and 99.9% similarity for CC1 isolate to Bacillus cereus strain IAM 12,605. The results also indicated that columns using activated sludge as a microbial source had the highest removal rate, with the microbial biofilm completely removing 100% of the 100 mg/L phenol concentration in contaminated influent water after 40 days. Finally, the concurrent use of core-shell microcapsules containing enzymes and capsules containing Stenotrophomonas sp. WC1 strain in two continuous column reactors was able to completely remove phenol from polluted water with a concentration of 500 mg/L for a period of 20 days. The results suggest that a combination of enzymatic and microbial degrading systems can be used as a new system to remove phenol from polluted streams with higher concentrations of phenol by eliminating the shock of phenol on the microbial population.

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

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.

Facilitated transport of toluene and naphthalene with humic acid in high- and low-permeability systems: Role of ionic strength and cationic type

The occurrence of colloids on pollutants transport in groundwater has attracted more attention. However, the research on the regulation mechanism of colloids on combined pollutants transport in heterogeneous aquifers is limited. In this study, a series of tank experiments were conducted to systematically investigate the effects of ionic strength, and cation type on humic acid (HA) facilitated transport of toluene (TOL), and naphthalene (NAP) in high- and low-permeability systems. The results showed that HA facilitated pollutants transport in low Na+ solution. In Ca2+ solution, the presence of HA hindered pollutants transport, and the inhibition increased with the increase of ionic strength. Both in Na+ solution and low Ca2+ solution, the influence of heterogeneous structure on pollutant transport played a dominant role, and TOL and NAP had a greater transport potential in the high permeability zone (HPZ) due to the preferential flow. Whereas, deposition of HA aggregates, and electrostatic attractive interaction had negative effects on transport than groundwater flow in high Ca2+ solution. Pollutants were prone to accumulate at the bottom of the HPZ, and the top of the low permeability zone (LPZ). These new findings provide insights into the mechanism of colloids influence on the pollutants transport in heterogenous aquifer.

Genome-resolved analyses of oligotrophic groundwater microbial communities along phenol pollution in a continuous-flow biodegradation model system

Groundwater pollution is one of the major environmental concerns. The entrance of pollutants into the oligotrophic groundwater ecosystems alters native microbial community structure and metabolism. This study investigated the application of innovative Small Bioreactor Chambers and CaO2 nanoparticles for phenol removal within continuous-flow sand-packed columns for 6 months. Scanning electron microscopy and confocal laser scanning microscopy analysis were conducted to indicate the impact of attached biofilm on sand surfaces in bioremediation columns. Then, the influence of each method on the microbial biodiversity of the column’s groundwater was investigated by next-generation sequencing of the 16S rRNA gene. The results indicated that the simultaneous application of biostimulation and bioaugmentation completely eliminated phenol during the first 42 days. However, 80.2% of phenol remained in the natural bioremediation column at the end of the experiment. Microbial diversity was decreased by CaO2 injection while order-level groups known for phenol degradation such as Rhodobacterales and Xanthomonadales dominated in biostimulation columns. Genome-resolved comparative analyses of oligotrophic groundwater prokaryotic communities revealed that Burkholderiales, Micrococcales, and Cytophagales were the dominant members of the pristine groundwater. Six-month exposure of groundwater to phenol shifted the microbial population towards increasing the heterotrophic members of Desulfobacterales, Pseudomonadales, and Xanthomonadales with the degradation potential of phenol and other hydrocarbons.

A novel thermosensitive persulfate controlled-release hydrogel based on agarose/silica composite for sustained nitrobenzene degradation from groundwater

The increasing risk of organic contamination of groundwater poses a serious threat to the environment and human health, causing an urgent need to develop long-lasting and adaptable remediation materials. Controlled-release materials (CRMs) are capable of encapsulating oxidants to achieve long-lasting release properties in aquifers and considered to be effective strategies in groundwater remediation. In this study, novel hydrogels (ASGs) with thermosensitive properties were prepared based on agarose and silica to achieve controlled persulfate (PS) release. By adjusting the composition ratio, the gelation time and internal pore structure of the hydrogels were regulated for groundwater application, which in turn affected the PS encapsulated amount and release properties. The hydrogels exhibited significant temperature responsiveness, with 6.8 times faster gelation rates and 2.8 times longer controlled release ability at 10 ℃ than at 30 ℃. The ASGs were further combined with zero-valent iron to achieve long-lasting degradation of the typical nitrobenzene compound 2,4-dinitrotoluene (2,4-DNT), and the degradation performance was maintained at 50 % within 14 PV, which was significantly improved compared with that of the PS/ZVI system. This study provided new concepts for the design of controlled-release materials and theoretical support for the remediation of organic contamination.

Control of arsenic release from paddy soils using alginate encapsulated calcium peroxide

The mobilization of As in paddy soils is affected by iron redox cycles. In this regard, calcium peroxide (CaO₂) can be used as an alternative to maintaining oxidizing conditions by liberating oxygen under flooding environments. Nevertheless, the problem of increase in pH by CaO₂ dissolution remains unresolved. In this study, the encapsulation of CaO₂ using alginate is proposed. Encapsulated CaO₂ (CaO₂-b) using 1% sodium alginate was applied to As-contaminated soil to evaluate the ability of pH control and As mobility during flooding conditions. The pH increased rapidly from 6.8 to 9.0 in unencapsulated CaO₂ (CaO₂-p) within 1 day, while CaO₂-b increased slowly to 8.6 over 91 days. CaO₂ created an oxidizing condition in the soil by providing oxygen, thus effectively prevented the reductive dissolution of iron. The mobility of As decreased by 50% (CaO₂-p) and 83% (CaO₂-b) compared with that of the control soil. Furthermore, the As in pore water was three times lower than CaO₂-p because CaO₂-b released 1.8 times more Ca²⁺ to form Ca-As complexes than CaO₂-p. Consequently, the encapsulated CaO₂ reduced the negative effects of CaO₂ treatment on increasing pH of the soil and furnished a better environmental condition for inhibiting As mobility.

An optimized CaO2-functionalized alginate bead for simultaneous and efficient removal of phosphorous and harmful cyanobacteria

Simultaneous removal of phosphorus (P) and algae is important to mitigate eutrophication, however, it is rather challenging in remediation of harmful algal blooms (HABs)-contaminated water. In this study, a wet alginate bead functionalized by CaO₂ particle formed layer by layer was prepared with an in-situ method and optimized to remove phosphorous and inhibit algae growth. The stable H₂O₂ release with a concentration level of 0.06 mM was observed for a period of 26 d. The content of peroxy groups (-O-O-) in the optimal bead was 0.44 mmol·g^-1 through permanganate-based titration study. For solution with an initial phosphorous concentration of 10 mg·L^-1, the removal was around 97% in pH 3.0-10.0. XRD, SEM, and XPS studies and kinetic modelings showed that removal of phosphorus was mainly due to formation of insoluble Ca-P compounds in the bead. The CaO₂-functionalized bead inhibited algae growth with an effect lasting over 170 d, which was much better than liquid H₂O₂ and Ca(OH)₂ bead; the phosphorous removal with an efficiency of about 70% was simultaneously obtained. Furthermore, the bead demonstrated to be effective in removing algae in the realistic water from a reservoir. In summary, this study shows that the CaO₂-functionalized material is promising for simultaneous removal of phosphorous and management of HABs.

Bubble-Assisted HIFU Ablation Enabled by Calcium Peroxide

High intensity focused ultrasound (HIFU), as one of the most advanced and preferred cancer treatment modes, has shown great promise due to its minimal invasiveness and irradiation-free feature. However, a...

Solid Peroxy Compounds as Additives to Organic Waste for Reclamation of Post-Industrial Contaminated Soils

Solid peroxy compounds have been increasingly applied for the removal of organic pollution from contaminated groundwater and soil due to their ability to release oxygen and hydrogen peroxide. The influence of two solid peroxy compounds (sodium percarbonate, 2Na₂CO₃·3H₂O₂ and calcium peroxide, CaO₂) with poultry manure (PM) added to contaminated soil on the growth of the tested plants (Sinapis alba, Lepidium sativum L. and Sorghum bicolor L. Moench) and the quality of soil water leachates was investigated. A series of experiments involving the addition of CaO₂ and 2Na₂CO₃·3H₂O₂ at the dose of 0.075 g/g PM improved the growth of tested plants. The conducted study indicated that the use of peroxy compounds not only removed pathogens from livestock waste, but also improved the quality of plant growth. The calculated factors for the growth of roots (GFR) and growth of shoots (GFS) in soils treated with a mixture of peroxy compounds and PM were higher than in soils treated only with PM. The physicochemical analysis of soil water leachates indicated that solid peroxy compounds may be a promising alternative compared to the currently used hygienizing agent such as calcium hydroxide (Ca(OH)₂). Solid peroxy compounds increased the bioavailability of components necessary for proper seed germination and plant growth (N, P, K, Ca, Mg and S). In most of the studied cases, the obtained plant shoot and root growth rates were higher for soil mixtures containing organic waste deactivated by biocidal compounds, compared to soils that contained only poultry manure.

Efficient hexabromocyclododecane-biodegrading microorganisms isolated in Taiwan

The potential toxicity of hexabromocyclododecane (HBCD), its persistence in the environment, and its high bioaccumulation characteristics pose a need to remediate HBCD in the environment. Bacillus cereus and B. subtilis species complexes we isolated from Taiwan soil are capable of degrading HBCD. B. cereus can degrade HBCD with a half-life only 0.911 days. The highest efficiency of HBCD degradation by B. cereus was achieved at pH 7.0, 35 °C, and 0.10 ppm HBCD. The removal mechanism of HBCD by B. cereus is debromination and its pathway was proposed. The addition of surfactant Tween 60 improved HBCD removal but the addition of CaO₂, slow-releasing oxygen, did not. These findings can facilitate the bioremediation of HBCD in the environment.

Trichloroethylene degradation by PVA-coated calcium peroxide nanoparticles in Fe(II)-based catalytic systems: enhanced performance by citric acid and nanoscale iron sulfide

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative study was performed with optimum usages of chemical reagents in both PVA@nCP/Fe(II)/CA and PVA@nCP/Fe(II)/nFeS systems. Further, the probe compounds tests and electron paramagnetic resonance (EPR) analysis confirmed the generation of reactive oxygen species. The scavenging experiments elucidated the dominant role of HO• to TCE degradation, particularly in PVA@nCP/Fe(II)/nFeS system. Both CA and nFeS strengthened PVA@nCP/Fe(II) system, but displayed completely different mechanisms in the enhancement of active radicals generation; hence, their different contribution to TCE degradation. The acidic environment was favorable for TCE degradation, and a high concentration of HCO₃^- inhibited TCE removal in both systems. Conclusively, compared to PVA@nCP/Fe(II)/nFeS system, PVA@nCP/Fe(II)/CA system resulted in encouraging TCE degradation outcomes in actual groundwater, showing great potential for prolonged benefits in the remediation of TCE polluted groundwater. Graphical abstract.

The performance of nCaO2 for BTEX removal: Hydroxyl radical generation pattern and the influences of co-existing environmental pollutants

In this study, nano-CaO₂ (nCaO₂ ) was successfully synthesized and constituted the nCaO₂ /Fe(II) system applying to remediate BTEX, which are typical mixed pollutants in contaminated groundwater. The particle size of the synthesized nCaO₂ was 108.91 nm, and it displayed better BTEX remediation performance than that of commercial CaO₂ . The innovative generation pattern of hydroxyl radicals ( HO · ) in the nCaO₂ /Fe(II) system has been investigated using benzoic acid as the HO · probe, and the proper molar ratio of nCaO₂ /Fe(II) was optimized as 1/1. Over 90% of BTEX was removed in 180 min with the nCaO₂ /Fe(II)/BTEX molar ratio of 40/40/1. Further experiments evaluated the influence of co-existence of mixed pollutants chlorinated hydrocarbon compounds (CHCs) or surfactant constituents on BTEX remediation performance. The experimental results suggested that CHCs have limited influence on BTEX removal rate and surfactants have negative effects on BTEX remediation performance in the experimental conditions. In conclusion, the findings in this study could give some inspirations to apply the nCaO₂ /Fe(II) process in remediating co-existing pollutants in contaminated groundwater. PRACTITIONER POINTS: nCaO₂ /Fe(II) system applied to remediate mixed contaminants. HO · generation pattern of the nCaO₂ /Fe(II) system has been investigated. The influence of chloride hydrocarbon compounds have been studied. The effects of surfactants were evaluated.

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.

Bioremediation of benzene-contaminated groundwater by calcium peroxide (CaO2) nanoparticles: Continuous-flow and biodiversity studies

Calcium peroxide (CaO₂) nanoparticles have been extensively applied in treatment of contaminated groundwater through bioremediation or modified Fenton (MF) processes. In the present study utilization of CaO₂ in bioremediation and MF (CaO₂+FeSO₄) reaction is investigated for benzene (50 mg/L) removal in continuous flow sand-packed columns. The results indicated that MF produced OH radicals markedly increased benzene remediation at first 30 days (up to 93%). But, OH generation rate was gradually declined when the pH was increased and finally 75% of initial benzene removed after 100d. In bioremediation column, because of supplying adequate oxygen by CaO₂, the number of planktonic bacteria logarithmically increased to more than 5 × 10⁶ CFU/mL (two orders of magnitude) and consequently 100% benzene removal was achieved by the end of experiment. Scanning electron microscopy analysis visualized the attached biofilm growth on sand surfaces in CaO₂ injected columns indicating their key role in the remediation process. The impact of each process on the microbial biodiversity of groundwater was investigated by next generation sequencing (NGS) of the 16S rRNA gene. The alpha and beta analysis indicated that microbial diversity is decreased by CaO₂ injection while benzene-degrading species such as Silanimonas, Arthrobacter and Pseudomonas spp. were dominated in remediation column.

Insight into CaO2-based Fenton and Fenton-like systems: strategy for CaO2-based oxidation of organic contaminants

This study conducted a comparison of the CaO₂-based Fenton (CaO₂/Fe(II)) and Fenton-like (CaO₂/Fe(III)) systems on their benzene degradation performance. The H₂O₂, Fe(II), Fe(III), and HO^● variations were investigated during the benzene degradation. Although benzene has been totally removed in the two systems, the variation patterns of the investigated parameters were different, leading to the different benzene degradation patterns. In terms of the Fe(II)/Fe(III) conversion, the CaO₂/Fe(II) and CaO₂/Fe(III) systems were actually inseparable and had the inherent mechanism relationships. For the CaO₂/Fe(III) system, the initial Fe(III) must be converted to Fe(II), and then the consequent Fenton reaction could be later developed with the regenerated Fe(II). Moreover, some benzene degradation intermediates could have the ability to facilitate the transformation of the Fe(III) to Fe(II) without the classic H₂O₂-associated propagation reactions. By varying the Fe(II) dosing method, an effective degradation strategy has been developed to take advantage of the two CaO₂-based oxidation systems. The proposed strategy was further successfully tested in TCE degradation, therefore extending the potential for the application of this technique.

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.

Naphthalene remediation form groundwater by calcium peroxide (CaO2) nanoparticles in permeable reactive barrier (PRB)

This study investigated the applicability of synthesized calcium peroxide (CaO₂) nanoparticles for naphthalene bioremediation by permeable reactive barrier (PRB) from groundwater. According to the batch experiments the application of 400 mg/L of CaO₂ nanoparticles was the optimum concentration for naphthalene (20 mg/L) bioremediation. Furthermore, the effect of environmental conditions on the stability of nanoparticles showed the tremendous impacts of the initial pH and temperature on the stability and oxygen releasing potential of CaO₂. Therefore, raising the initial pH from 3 to 12 elevated the dissolved oxygen from 4 to 13.6 mg/L and the stability of nanoparticles was significantly improved around 70 d. Moreover, by increasing the temperature from 4 to 30 °C, the stability of CaO₂ declined from 120 to 30 d. The continuous-flow experiments revealed that the naphthalene-contaminated groundwater was completely bio-remediated in the presence of CaO₂ nanoparticles and microorganisms from the effluent of the column within 50 d. While, the natural remediation of the contaminant resulted in 19.7% removal at the end of the experiments (350 d). Additionally, the attached biofilm on the surface of the PRB zone was studied by scanning electron microscopy (SEM) which showed the higher biofilm formation on the pumice surfaces in the bioremediation column in comparison to the natural remediation column. The physic-chemical characteristics of the effluents from each column was also analyzed and indicated no negative impact of the bioremediation process on the groundwater. Consequently, the present paper provides a comprehensive study on the application of the CaO₂ nanoparticles in PAH-contaminated groundwater treatment.

Application of magnesium peroxide (MgO2) nanoparticles for toluene remediation from groundwater: batch and column studies

In the present study, magnesium peroxide (MgO₂) nanoparticles were synthesized by electro-deposition process and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The batch experiments were conducted to evaluate the MgO₂ half-life (600 mg/L) in groundwater under various temperatures (4, 15, and 30 °C) and initial pH (3, 7, and 12). The effect of Fe²⁺ ions (enhanced oxidation) on the toluene remediation by MgO₂ was also investigated. Nanoparticles were injected to sand-packed continuous-flow columns, and toluene removal (50 ppm) was studied within 50 days at 15 °C. The results indicated that the half-life of MgO₂ at pH 3 and 12 were 5 and 15 days, respectively, in comparison to 10 days at the initial pH 7 and 15 °C. The nanoparticles showed 20 and 7.5 days half-life at 4 and 30 °C temperatures, respectively. Injection of Fe²⁺ ions indicated an impressive effect on toluene removal by MgO₂, and the contaminant was completely removed after 5 and 10 days, in the batch and column experiments, respectively. Confocal laser scanning microscope (CLSM) analysis indicated that the attached biofilm had a significant role in the decontamination of groundwater. Comparison of bioremediation and enhanced oxidation resulted in a considerable insight into the application of magnesium peroxide in groundwater remediation. Graphical abstract ᅟ.