Remediation of soil contaminated with PAHs and γ-HCH using Fenton oxidation activated by carboxymethyl cellulose-modified iron oxide-biochar

Green mechanochemical activation of solid persulfate to remove PAHs in soil: Performance and mechanism

Due to the high biotoxicity and persistence of polycyclic aromatic hydrocarbons (PAHs), the remediation of PAHs-contaminated soil becomes an intractable problem. Persulfate-based advanced oxidation processes are widely used to degrade PAHs in aquatic environment. However, they are not convenient for used in soil due to the heterogeneity and complexity of soil matrix. In this study, a green and convenient ball milling process is introduced to activate persulfate for the remediation of PAHs-contaminated soil. About 82.5% PAHs were removed with 10% wt. Na2S2O8 (PS) addition and ball-milling for 2 h under 500 r/min. The degradation of PAHs is attributed to the attack of radicals (SO4·- and·OH) generated from the activation of PS by mechanochemistry. Moreover, stable Si-O bonds were disrupted during ball-milling process, and formed free electron on the surface of soil particles. This facilitates the electron transfer from oxidants to contaminants. The particle size, surface element composition, functional group, and thermogravimetric analysis confirmed the slight disturbance of ball-milling-assisted PS process on the physical and chemical properties of soil. Therefore, ball-milling assisted PS approach would be a promising technology for the remediation of PAHs-contaminated soil.

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

A novel remediation strategy of mixed calcium peroxide and degrading bacteria for polycyclic aromatic hydrocarbon contaminated water

Polycyclic aromatic hydrocarbons (PAHs) are a class of toxic organic pollutants commonly detected in the aqueous phase. Traditional biodegradation is inefficient and advanced oxidation technologies are expensive. In the current study, a novel strategy was developed using calcium peroxide (CP) and PAH-degrading bacteria (PDB) to effectively augment PAH degradation by 28.62-59.22%. The PDB consisted of the genera Acinetobacter, Stenotrophomonas, and Comamonas. Applying the response surface model (RSM), the most appropriate parameters were identified, and the predictive degradation rates of phenanthrene (Phe), pyrene (Pyr), and ΣPAHs were 98%, 76%, and 84%, respectively. The constructed mixed system could reduce 90% of Phe and more than 60% of ΣPAHs and will perform better at pH 5-7 and lower salinity. Because PAHs tend to bind to dissolved organic matter (DOM) with larger molecular weights, humic acid (HA) had a larger negative effect on the PAH-degradation efficiency of the CP-PDB mixed system than fulvic acid (FA). The proposed PAH-degradation pathways in the mixed system were based on the detection of intermediates at different times. The investigation constructed and optimized a novel environmental PAH-degradation strategy. The synergistic application of PDB and oxidation was extended for organic contaminant degradation in aqueous environments.

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.

Tropical soil remediation from pyrene: Release the power of natural iron content in soil for the efficient oxidant's activation

Natural soil minerals often contain numerous impurities, resulting in comparatively lower catalytic activity. Tropical soils are viewed as poor from soil organic matter, cations, and anions, which are considered the main impurities in the soil that are restricted to utilizing natural minerals as a catalyst. In this regard, the dissolved iron and hematite crystals that presented naturally in tropical soil were evaluated to activate oxidants and degrade pyrene. The optimum results obtained in this study were 73 %, and the rate constant was 0.0553 h-1 under experimental conditions [pyrene] = 300 mg/50 g, pH = 7, T = 55 °C, airflow = 260 mL/min, [Persulfate (PS)] = 1.0 g/L, and humic acid (HA) ( % w/w) = 0.5 %. The soil characterization analysis after the remediation process showed an increase in moieties and cracks of the soil aggregate, and a decline in the iron and aluminium contents. The scavengers test revealed that both SO4•- and O2•- were responsible for the pyrene degradation, while HO• had a minor role in the degradation process. In addition, the monitoring of by-products, degradation pathways, and toxicity assessment were also investigated. This system is considered an efficient, green method, and could provide a step forward to develop low-cost soil remediation for full-scale implementation.