Phenanthrene degradation in soil by ozonation: Effect of morphological and physicochemical properties

Integrating metal-organic framework ZIF-8 with green modifier empowered bacteria with improved bioremediation

Suspended microorganisms often experience diminished efficacy in the bioremediation of polycyclic aromatic hydrocarbons (PAHs). In this study, the potential of zeolite imidazolate framework-8 (ZIF-8) and the eco-friendly modifier citric acid (CA) was harnessed to generate a biomimetic mineralized protective shell on the surface of Bacillus subtilis ZL09-26, resulting in an enhanced capability for PAH degradation. This investigation encompassed the integrated responses of B. subtilis ZL09-26 to ZIF-8 and ZIF-8-CA at both cellular and proteomic levels. The amalgamation of ZIF-8 and CA not only stimulated the growth and bolstered the cell viability of B. subtilis ZL09-26, but also counteracted the toxic effects of phenanthrene (PHE) stress. Remarkably, the bioremediation prowess of B. subtilis ZL09-26@ZIF-8-CA surpassed that of ZL09-26@ZIF-8 and ZL09-26, achieving a PHE removal rate of 94.14 % within 6 days. After undergoing five cycles, ZL09-26@ZIF-8-CA demonstrated an enduring PHE removal rate exceeding 83.31 %. A complex interplay of various metabolic pathways orchestrated cellular responses, enhancing PHE transport and degradation. These pathways encompassed direct PHE biodegradation, central carbon metabolism, oxidative phosphorylation, purine metabolism, and aminoacyl-tRNA biosynthesis. This study not only extends the potential applications of biomineralized organisms but also offers alternative strategies for effective contaminant management.

Effect of site-specific conditions and operating parameters on the removal efficiency of petroleum-originating pollutants by using ozonation

Soil contamination is a worldwide problem, mainly caused by a wide range of organic compounds: e.g., alkanes, aromatics, and polynuclear aromatics. Using ozone to help remediate contaminated soils is gaining interest due to its capability in oxidizing recalcitrant contaminants in short application time., although studies using ozonation for soil remediation are so far limited to the laboratory scale. This review attempts to summarize and discuss the state of the art in the treatment of soils contaminated with recalcitrant organic contaminants by using ozone, emphasizing the influence of operating conditions, such as the content and age of soil organic matter, grain size, moisture content, pH, and ozone dose. Special attention is given to the combination of ozonation and biodegradation. The main advantages in using ozonation as a remediation technique are its high oxidation potential applicable to a wide range of organic pollutants and its oxygen release after chemical decomposition that allow aerobic biodegradation. The review results show that ozonated soils can be reused after ozonation treatment, therefore ozonation can be considered an excellent remediation technique, even if combined with biodegradation, allowing removal percentages of 90% and more.

Environmental relevance of adsorption of doxycycline, enrofloxacin, and sulfamethoxypyridazine before and after the removal of organic matter from soils

In this work batch-type experiments were used to study the adsorption of the antibiotics doxycycline (DC), enrofloxacin (ENR), and sulfamethoxypyridazine (SMP) in cultivation soils, before and after the removal of soil organic matter. Organic matter removal by calcination resulted not only in C and N removal, but also in increased soil pH, exchangeable basic cations and surface area values. The results indicate a very different behavior depending on the type of antibiotic, showing the adsorption sequence DC > ENR > SMP. Specifically, DC adsorption was very high in untreated soil samples (with organic matter), and was still high (although decreased) after the removal of soil organic matter. Furthermore, the adsorption behavior of DC was clearly dependent on the pH of the medium. Regarding ENR, it also showed high adsorption, although to a lesser extent than DC. However, when soil organic matter was removed, ENR adsorption significantly decreased in all soil samples. As regards SMP, it was adsorbed to a much lesser extent, and the removal of soil organic matter caused an additional drastic decrease in adsorption, reaching negligible values in some samples. Desorption followed the reverse sequence of adsorption, specifically in the order DC < ENR < SMP. In the case of DC, desorption was negligible, both in samples with and without organic matter, while for ENR and SMP, desorption clearly increased for soil samples where organic matter was removed. These results may be of relevance as regards environmental quality and public health, especially to facilitate a correct use of soils and organic amendments in areas that receive the application of substances containing the investigated antibiotics.

Effect of the type of soil on dimethyl phthalate degradation by ozone

In the present study, ozone was applied for the removal of dimethyl phthalate (DMP) from soil. The effect of several experimental parameters was investigated considering, the initial DMP concentration, ozone flow, the type of soil (sand and agricultural soil) and the presence of α-FeOOH as a potential catalyst in the reaction system with sand. The elimination of DMP using ozone is significantly affected by the type of soil. In the case of sand, conventional ozonation was capable to degrade 74% of the initial DMP concentration (0.5 mg g^-1) after 8 h of the reaction, however, the mineralization degree was below 50%. Under the same experimental conditions, the complete elimination of DMP was achieved when calcined agricultural soil was present reaching a 70% of mineralization. The presence of metal oxides in calcined agricultural soil combined with ozone produced oxidants species which were responsible of incrementing the mineralization degree (around 20% in comparison with the sand). The toxicity tests on lettuce seed demonstrated lower toxicity of DMP byproducts after ozonation. The DMP high removal efficiencies and the lower toxicity of generated byproducts in soil prove the applicability of ozone treatment for soil remediation.

Ozone-encapsulated colloidal gas aphrons for in situ and targeting remediation of phenanthrene-contaminated sediment-aquifer

The hydrophobic polycyclic aromatic hydrocarbons (PAHs) are apt to adhere tightly to the sediments in aquifer and thus pose great threats to the aquatic environment of groundwater and surface water as well as human health. The present study constructed functionalized microbubbles, named colloidal ozone aphrons (COAs), by dissolving ozone-contained air into the nonionic surfactant (Tween-20) solution at the pressure of 300 kPa for the in situ remediation of phenanthrene (PHE)-contaminated sediments. The COA system aimed at improving the PHE elimination in terms of (i) enhancing the migration and transportation ability of the bubble system in the contaminated aquifer matrix, (ii) accurately desorbing the target hydrophobic contaminants from sediments, and (iii) reinforcing the in situ oxidation degradation immediately after or simultaneously when the PAHs are desorbed into the aqueous phase. Experimental results demonstrated that the COAs exhibited similar characteristics as the classical colloidal gas aphrons (CGAs), including the high stability (half-life time > 200 s), typical morphology and average bubble size (114-162 μm); higher air hold-up of COAs was achieved (i. e. > 20%) compared with the air-microbubbles (1-2%) obtained under the same generation conditions. Although the encapsulated ozone could oxidize the surfactant-layers, the properties and behaviors of COAs were not greatly affected. The surfactant multi-layers endowed the COAs with strong hydrophobic attraction with PHE, great migration capacity and enlarged oxidation area in the sediment matrix. Approximately 96.9% of PHE was removed from the sediments and 84.9% of the overall PHE was oxidized at the high ozone concentration of 0.6 mg/L when the initial PHE concentration was 240.0 μg/kg. The COA-involved remediation technology provided the insight of combining the processes of washing and oxidizing through adopting the particularly conceived microbubbles. The in situ and selective removal of hydrophobic organic contaminants from sediments in aquifer was well achieved in this study.

Influence of immobilization on phenanthrene degradation by Bacillus sp. P1 in the presence of Cd(II)

Suspended microbes gradually lost advantages in practical applications of PAHs and heavy metals bioremediation. Therefore this study investigated the effect of immobilization on phenanthrene degradation by Bacillus sp. P1 in the presence of different Cd(II) concentrations. Condensed Bacillus sp. P1 was immobilized with polyvinyl alcohol and sodium alginate and PVA-SA-cell cryogel beads were prepared. The results indicated that the use of gel beads increased the number of adsorption sites thus accelerating phenanthrene degradation. In addition, changes in detoxification indices, including superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH), were determined to elucidate the immobilization mechanisms related to cells protection from Cd(II) when degrading phenanthrene. By protecting the gel membrane, oxidative damage was minimized, while SOD activity increased from 55.72 to 81.33 U/mgprot as Cd(II) increased from 0 to 200 mg/L but later dropped to 44.29 U/mgprot as Cd(II) increased to 300 mg/L for the non-immobilized system. On the other hand, the SOD activity kept increasing from 52.23 to 473.35 U/mgprot for the immobilized system exposed to Cd(II) concentration between 0 and 300 mg/L. For CAT and GSH, immobilization only slowed down the depletion process without any change on the variation trends. The changes in surface properties and physiological responses of microbes caused the differences of immobilization effect on phenanthrene biodegradation in the presence of Cd(II), which is a novel finding.

Remediation of aged diesel contaminated soil by alkaline activated persulfate

The present work studies the efficiency of alkaline activated persulfate (PS) to remediate an aged diesel fuel contaminated soil from a train maintenance facility. The Total Petroleum Hydrocarbon (TPH) concentration in soil was approximately 5000mgkg^-1 with a ratio of aliphatic:aromatic compounds of 70:30. Aromatic compounds were mainly naphtalenes and phenanthrenes. The experiments were performed in batch mode where different initial concentrations of persulfate (105mM, 210mM and 420mM) and activator:persulfate ratios (2 and 4) were evaluated, with NaOH used as activator. Runs were carried out during 56days. Complete TPH conversion was obtained with the highest concentration of PS and activator, whereas in the other runs the elimination of fuel ranged between 60 and 77%. Besides, the abatement of napthalenes and phenantrenes was faster than aliphatic reduction (i. e. after 4days of treatment, the conversions of the aromatic compounds were around 0.8 meanwhile the aliphatic abatements were 0.55) and no aromatic oxidation intermediates from naphtalenes or phenantrenes were detected. These results show that this technology is effective for the remediation of aged diesel in soil with alkaline pH.