Hydrocarbon transformation pathways and soil organic carbon stability in the biostimulation of oil-contaminated soil: Implications of 13C natural abundance

Low dose phosphorus supplementation is conducive to remediation of heavily petroleum-contaminated soil-From the perspective of hydrocarbon removal and ecotoxicity risk control

Biostimulation by supplementing of nitrogen and phosphorus nutrients is a common strategy for remediation of petroleum-polluted soils. However, the dosage influence of exogenous nitrogen or phosphorus on petroleum hydrocarbon removal and soil ecotoxicity and microbial function remain unclear. In this study, we compared the efficiencies of hydrocarbon degradation and ecotoxicity control by experiment conducted over addition of inorganic nitrogen or phosphorus at C/N ratio of 100/10, C/N/P ratio of 100/10/1, and C/P ratio of 100/1 in a heavily petroleum-contaminated loessal soil with 12,320 mg/kg of total petroleum hydrocarbon (TPH) content. A 90-day incubation study revealed that low-dose of phosphorus addition with the C/P ratio of 100/1 promoted hydrocarbon degradation and reduced soil ecotoxicity. Microbial community composition analysis suggested that phosphorus addition enriched hydrocarbon degrader Gordonia and Mycolicibacterium genus. The key enzymes EC 5.3.3.8, EC 6.2.1.20 and EC 6.4.1.1 which referred to degradation of long-chain hydrocarbons, unsaturated fatty acids and pyruvate metabolism were abundance by phosphorus supplementation. While nitrogen addition at C/N ratio of 100/10 or C/N/P ratio of 100/10/1 inhibited hydrocarbon degradation and exacerbated soil ecotoxicity due to promoting denitrification and coupling reactions with hydrocarbons. Our results suggested that low-dose phosphorus addition served as a favorable strategy to promote crude oil remediation and ecotoxicity risk control in heavily petroleum-contaminated soil. Hence, the application of suitable doses of exogenous biostimulants is an efficient approach to restore the ecological functions of organically contaminated soils.

Effects of biochar immobilization of Serratia sp. F4 OR414381 on bioremediation of petroleum contamination and bacterial community composition in loess soil

Petroleum hydrocarbons pose a significant threat to human health and the environment. Biochar has increasingly been utilized for soil remediation. This study investigated the potential of biochar immobilization using Serratia sp. F4 OR414381 for the remediation of petroleum-contaminated soil through a pot experiment conducted over 90 days. The treatments in this study, denoted as IMs (maize straw biochar-immobilized Serratia sp. F4), degraded 82.5% of the total petroleum hydrocarbons (TPH), 59.23% of the aromatic, and 90.1% of the saturated hydrocarbon fractions in the loess soils. During remediation, the soil pH values decreased from 8.76 to 7.33, and the oxidation-reduction potential (ORP) increased from 156 to 229 mV. The treatment-maintained soil nutrients of the IMs were 138.94 mg/kg of NO3- -N and 92.47 mg/kg of available phosphorus (AP), as well as 11.29% of moisture content. The activities of soil dehydrogenase (SDHA) and catalase (CAT) respectively increased by 14% and 15 times compared to the CK treatment. Three key petroleum hydrocarbon degradation genes, including CYP450, AJ025, and xylX were upregulated following IMs treatment. Microbial community analysis revealed that a substantial microbial population of 1.01E+ 09 cells/g soil and oil-degrading bacteria such as Salinimicrobium, Saccharibacteria_genera_incertae_sedis, and Brevundimonas were the dominant genera in IMs treatment. This suggests that the biochar immobilized on Serratia sp. F4 OR414381 improves soil physicochemical properties and enhances interactions among microbial populations, presenting a promising and environmentally friendly approach for the stable and efficient remediation of petroleum-contaminated loess soil.

Regulating the biodegradation of petroleum hydrocarbons with different carbon chain structures by composting systems

Composting can decrease petroleum hydrocarbons in petroleum contaminated soils, however the microbial degradation mechanisms and regulating method for biodegradation of petroleum hydrocarbons with different carbon chain structures in the composting system have not yet been investigated. This study analyzed variations of total petroleum hydrocarbon concentrations with C ≤ 16 and C > 16, Random Forest model was applied to identify the key microorganisms for degrading the petroleum hydrocarbon components with specific structure in biomass-amended composting. Regulating method for biodegradation of petroleum hydrocarbons with different carbon chain structures was proposed by constructing the influence paths of "environmental factors-key microorganisms- total petroleum hydrocarbons". The results showed that composting improved the degradation rate of C ≤ 16 fraction and C > 16 fraction of petroleum hydrocarbons by 67.88 % and 61.87 %, respectively. Analysis of the microbial results showed that the degrading bacteria of the C ≤ 16 fraction had degradation advantages in the heating phase of the compost, while the C > 16 fraction degraded better in the cooling phase. Moreover, microorganisms that specifically degraded C > 16 fractions were significantly associated with total nitrogen and nitrate nitrogen. The biodegradation of C ≤ 16 fraction was regulated by organic matter, moisture content, and temperature. The composting system modified by biogas slurry was effective in removing of petroleum hydrocarbons with different carbon chain structures in soil by regulating the metabolic potential of the 46 key microorganisms. This study given their expected importance to achieve the purpose of treating waste with waste and contributing to soil utilization as well as pollution remediation.

The application of biosurfactant-producing bacteria immobilized in PVA/SA/bentonite bio-composite for hydrocarbon-contaminated soil bioremediation

Oil spills that contaminate the environment can harm the surrounding ecosystem. The oil contains petroleum hydrocarbon which is toxic to the environment hence it needs to be removed. The use of bacteria as remediation media was modified by immobilizing into a matrix hence the bacteria can survive in harsh conditions. In this research, the ability of biosurfactant-producing bacteria (Pseudomonas aeruginosa, Bacillus subtilis, and Ralstonia pickettii) immobilized in the PVA/SA/bentonite matrix was tested in remediation on oil-contaminated soil. The immobilized beads filled with bacteria were added to the original soil sample, as well as washed soil. The beads were characterized by using FTIR and SEM. Based on FTIR analysis, the PVA/SA/bentonite@bacteria beads had similar functional groups compared to each other. SEM analysis showed that the beads had non-smooth structure, while the bacteria were spread outside and agglomerated. Furthermore, GC-MS analysis results showed that immobilized B. subtilis and R. pickettii completely degraded tetratriacontane and heneicosane, respectively. Meanwhile, after soil washing pre-treatment, immobilized bacteria could completely degrade octadecane (P. aeruginosa and R. pickettii) and tetratriacontane (P. aeruginosa and B. subtilis). Based on those results, immobilized bacteria could degrade oil compounds. The degradation result was influenced by the enzymes produced, the ability of the bacteria, the suitability of the test media, and the matrix used. Therefore, this study can be a reference for further soil remediation using eco-friendly methods.

Exploration of potential driving mechanisms of Comamonas testosteroni in polycyclic aromatic hydrocarbons degradation and remodelled bacterial community during co-composting

Polycyclic aromatic hydrocarbons (PAHs) are a cluster of highly hazardous organic pollutants that are widespread in ecosystems and threaten human health. Composting has been shown to be an effective strategy for PAHs degredation. Here, we used Comamonas testosteroni as an inoculant in composting and investigated the potential mechanisms of PAHs degradation by co-occurrence network and structural equation modelling analysis. The results showed that more than 60% of PAHs were removed and the bacterial community responded to the negative effects of PAHs by upgrading the network. Inoculation with C. testosteroni altered bacterial community succession, intensified bacterial response to PAHs, improved metabolic activity, and promoted the degradation of PAHs during co-composting. The increased in the positive cohesion index of the community suggested that agents increased the cooperative behaviour between bacteria and led to changes in keystones of the bacterial network. However, the topological values of C. testosteroni in the network were not elevated, which confirmed that C. testosteroni altered communities by affecting other bacterial growth rather than its own colonisation. This study strengthens our comprehension of the potential mechanisms for the degradation of PAHs in inoculated composting.

Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting

This study examined the effects of biochar, biogas residue, and their combined amendments on CO₂ and CH₄ emission, enzyme activity, and related functional genes during rice straw composting. Results showed that the biogas residue increased CO₂ and CH₄ emissions by 13.07 % and 74.65 %, while biochar had more obvious inhibition. Biogas residue addition enhanced functional gene abundance more than biochar. Biogas residue raised the methanogens mcrA gene by 2.5 times. Biochar improved the Acetyl-CoA synthase and β-glucosidase activities related to carbon fixation and decreased coenzyme activities related to methanogens. Biochar and biogas residue combined amendments enhanced the acsB gene abundance for CO₂ assimilation process and decreased methyl-coenzyme M reductase α subunit activity. Pearson correlation analysis indicated that organic matter was the significant variable affecting CO₂ and CH₄ emissions (P < 0.01). These results indicated biochar played significant roles in carbon loss and greenhouse emissions caused by biogas residue incorporation during composting.

Geotechnical properties of oil-polluted soil: a review

Soil polluted by oil and its derivatives is a critical environmental issue worldwide that jeopardizes ecological systems and causes geotechnical problems. This review paper focuses on the previous studies concerning the impacts of oil pollution on soil geotechnical properties. To this end, related academic literature on this topic was investigated and discussed. The findings of this study demonstrated that the addition of oil pollution in coarse-grained soils significantly reduces particle surface roughness. On the other hand, in fine-grained soils, it results in flocculation and secondary aggregation of clay particles, less aggregated and loose packing in the soil matrix, the formation of isometric pores, the formation of fissure-like pores, and an increase in mesoporosity. In general, it was found that the geotechnical properties of oil-polluted soils are mostly determined by the physicochemical and/or physical interactions between the soil and contaminant. Additionally, previous research has demonstrated that oil pollutants alter the geotechnical properties of cohesive and non-cohesive soils significantly, including the Atterberg limits, particle-size distribution, compaction behavior, unconfined compressive strength, friction angle, cohesion, hydraulic conductivity, and consolidation characteristics. However, no general pattern could be established for the majority of them. Besides, it was found that the degree of geotechnical property alteration of oil-polluted soil is strongly influenced by the soil type and features, as well as the quantity, type, and chemical composition of oil pollutants.

Fingerprint analysis reveals sources of petroleum hydrocarbons in soils of different geographical oilfields of China and its ecological assessment

The distribution and characteristics of petroleum in three different geographic oilfields in China: Shengli Oilfield (SL), Nanyang Oilfield (NY), and Yanchang Oilfield (YC) were investigated. The average concentration of the total petroleum hydrocarbons (TPHs) conformed to be in the following law: SL Oilfield > NY Oilfield > YC Oilfield. Fingerprint analysis on the petroleum contamination level and source was conducted by the geochemical indices of n-alkanes and PAHs, such as low to high molecular weight (LMW/HMW) hydrocarbons, n-alkanes/pristine or phytane (C17/ Pr, C18/Ph), and ratio of anthracene/ (anthracene + phenanthrene) [Ant/(Ant + Phe)]. Soils adjacent to working well oils indicated new petroleum input with higher ratio of low to high molecular weight (LMW/HMW) hydrocarbons. The oil contamination occurred in the grassland soils might result of rainfall runoff. Petroleum source, petroleum combustion source, and biomass combustion were dominant PAHs origination of soils collected from oil exploitation area, petrochemical-related sites, farmland and grassland, respectively. The suggestive petroleum control strategies were proposed in each oilfield soils. Ecological potential risk of PAHs was assessed according to the toxic equivalent quantity (TEQ) of seven carcinogenic PAHs. The results showed that high, medium, and low ecological risk presented in petro-related area, grassland soils, and farmland soils, respectively. High ecological risk was persistent in abandoned oil well areas over abandoned time of 15 years, and basically stable after 5 years. This study can provide a critical insight to ecological risk management and source control of the petroleum contamination.