Remediation Of Petroleum-contaminated Soil Research Articles

Microbial remediation of petroleum-contaminated soil focused on the mechanism and microbial response: a review.

The environmental pollution caused by petroleum hydrocarbons has received considerable attention in recent years. Microbial remediation has emerged as the preferred method for the degradation of petroleum hydrocarbons, which is experiencing rapid development driven by advancements in molecular biology. Herein, the capacity of different microorganisms used for crude oil bioremediation was reviewed. Moreover, factors influencing the effectiveness of microbial remediation were discussed. Microbial remediation methods, such as bioaugmentation, biostimulation, and bioventilation, are summarized in this review. Aerobic and anaerobic degradation mechanisms were reviewed to elucidate the metabolic pathways involved. The impacts of petroleum hydrocarbons on microorganisms and the environment were also revealed. A brief overview of synthetic biology and a unique perspective of technique combinations were presented to provide insight into research trends. The challenges and future outlook were also presented to stimulate contemplation of the mechanisms involved and the development of innovative techniques.

Enhancing petroleum-contaminated soil remediation using pulverized rice straw

Enhancing petroleum-contaminated soil remediation using pulverized rice straw

Updating risk remediation-endpoints for petroleum-contaminated soils? A case study in the Ecuadorian Amazon region

In Ecuador, the regulatory framework for the remediation of petroleum-contaminated soils is based on predefined concentration endpoints for a selected range of petroleum hydrocarbon compounds. However, such approach may lead to over or under-estimation of the environmental risk posed by contaminated soils. In this study, the end-point remediation criteria according to Ecuadorian Environmental legislation were evaluated using different approaches. The first one was based on Total Extractable Petroleum Hydrocarbons (TEPH) and the second one on Total Bioavailable Petroleum Hydrocarbons (TBPH). Both were compared with ecotoxicological determinations using EC50 -Microtox® bioassay at 5 and 15 min of exposure. The correlation (R2) between EC50 values vs TEPH was of 0.2 and 0.25 for 5 and 15 min, respectively. Meanwhile, R2 between EC50 and TBPH was of 0.9 and 0.65 for 5 and 15 min, respectively, demonstrating a stronger correlation. Our results suggest that a contaminated site where the concentration of the TEPH is higher than the relevant regulatory concentrations may be deemed to present an acceptable risk even though their concentrations exceed the target values in soils. The results also challenge the notion that hormesis is associated with TEPH, contrary to some literature. This study is the first in Ecuador to propose incorporating bioavailability into environmental regulations, highlighting the need for further research to establish realistic and achievable remediation goals based on toxicity studies involving various trophic levels.

UHPM dominance in driving the formation of petroleum-contaminated soil aggregate, the bacterial communities succession, and phytoremediation

This study focused on the effects of urea humate-based porous materials (UHPM) on soil aggregates, plant physiological characteristics, and microbial diversity to explore the effects of UHPM on the phytoremediation of petroleum-contaminated soil. The compositions of soil aggregates, ryegrass (Lolium perenne) biomass, plant petroleum enrichment capacity, and bacterial communities in soils with and without UHPM were investigated. The results showed that UHPM significantly increased soil aggregate content by 0.25 mm-5 mm, resulting in higher fertilizer holding capacity, erosion resistance capacity, and plant biomass and microbial number than the soil without UHPM mixed. In addition, UHPM decreased the absorption of petroleum by plants in the soil while increasing the abundance of degrading bacteria and petroleum-degrading-related genes in the soil, thereby promoting the removal of hard-to-degrade petroleum components. RDA showed that, compared with the unimproved soil, each soil indicator was positively correlated with a high abundance of degrading bacteria in the improved soil and was significant. UHPM can be regarded as a petroleum-contaminated soil remediation agent that combines slow nutrient release with soil improvement effects.

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.

Heat input optimization for the ignition of self-sustained smoldering remediation of contaminated soils using concentrated solar power

In this paper, we explore the industrial-scale feasibility of using concentrated solar power (CSP) as the heat source in the smoldering remediation of petroleum-contaminated soil. Approximately 5 L soil samples were loaded in a narrow-channel reaction chamber and heated from the bottom with CSP to identify the required heat input to achieve ignition. Both petroleum and granular activated carbon (GAC) were used as combustible media. GAC was selected as a cleaner-burning alternative to petroleum and could emulate petroleum-contaminated soil at a mixture of 40 g GAC per kg pool sand on a 1.5 cm bed of GAC. This mixture of GAC showed robust ignition with a minimum power input of 240 W, which was slightly higher than the power input required to ignite industrially generated petroleum-contaminated soil. Preheat temperatures in excess of 300°C were achieved in most experiments, allowing for robust ignition of the smoldering remediation process. CSP was collected using parabolic reflectors 600 mm in diameter and was delivered to the reaction chamber with fiber optic bundles. Each solar concentrator delivered between 50 and 80 W to the reaction chamber, and four concentrators were required to reliably achieve the required power input.

Ball milling enhances pyrolytic remediation of petroleum-contaminated soil and reuse as adsorptive/catalytic materials for wastewater treatment

Petroleum-contaminated soil (PCS) requires an integrated treatment strategy for the simultaneous cleanup of pollutants and beneficial reuse of post-remediation soil. A combined process of ball milling and pyrolysis was used to treat PCS. The obtained carbonized soil (BRCS) was used to adsorb heavy metals and activate persulfate (PS) oxidation. The maximum adsorption capacity of BRCS for Pb2+ reaches 983.7 mg/g. When the BRCS and PS dosage is 3 g/L and 2 g/L, respectively, the removal rate of aniline (100 mg/L) is close to 100 %. Ball milling pretreatment significantly improves the heavy metal adsorption property and persulfate activation performance of the pyrolytic carbonized soil. According to sequential extraction, X-ray diffraction, Fourier transform ion cyclotron resonance, and X-ray photoelectron spectroscopy (XPS) analyses, ball milling pretreatment considerably increases the adsorption capacities of carbonized soil for heavy metals by enhancing carbonate binding and Fe/Mn oxide complexation/coprecipitation. Quenching experiments show that the nonradical path dominates the persulfate oxidation process. Electron paramagnetic resonance and linear sweep voltammetry analyses show that ball milling pretreatment produces more surface-bound semiquinone radical, which greatly activates persulfate oxidation by accelerating direct electron transfer. This study proposes an integrated resource utilization strategy for carbonized soil by stimulation of endogenous functional components in carbonized soil and beneficial reuse of hazardous environmental permanent free radicals.

Petroleum-contaminated soil bioremediation and microbial community succession induced by application of co-pyrolysis biochar amendment: An investigation of performances and mechanisms

This study aimed to remediate petroleum-contaminated soil using co-pyrolysis biochar derived from rice husk and cellulose. Rice husk and cellulose were mixed in various weight ratios (0:1, 1:0, 1:1, 1:3 and 3:1) and pyrolyzed under 500 °C. These biochar variants were labeled as R0C1, R1C0, R1C1, R1C3 and R3C1, respectively. Notably, the specific surface area and carbon content of the co- pyrolysis biochar increased, potentially promoting the growth and colonization of soil microorganisms. On the 60th day, the microbial control group achieved a 46.69% removal of pollutants, while the addition of R0C1, R1C0, R1C3, R1C1 and R3C1 resulted in removals of 70.56%, 67.01%, 67.62%, 68.74% and 67.30%, respectively. In contrast, the highest efficiency observed in the abiotic treatment group was only 24.12%. This suggested that the removal of petroleum pollutants was an outcome of the collaborative influence of co-pyrolysis biochar and soil microorganisms. Furthermore, the abundance of Proteobacteria, renowned for its petroleum degradation capability, obviously increased in the treatment group with the addition of co-pyrolysis biochar. This demonstrated that co-pyrolysis biochar could notably stimulate the growth of functionally associated microorganisms. This research confirmed the promising application of co-pyrolysis biochar in the remediation of petroleum-contaminated soil.

Phytoremediation: An Approach for Petrochemical Contaminated Soil of Assam

The presence of a component, impurity, or other unfavourable element that taints, corrupts, infects, renders unfit, or degrades a material, or natural environment is referred to as environmental contamination. Due to the potential negative effects caused by the chemical discharges, environmental issues have now become crucial factors to consider. Petrochemical wastes are one of the most serious environmental contaminants which comprise a large group of chemicals derived from petroleum and natural gases. The petrochemical pollutants, belonging to the groups such as greenhouse gases, volatile organic compounds, Particulate Matter (PM) with heavy metals, and polycyclic aromatic compounds, act as potential soil contaminants, causing disturbance and harm to the soil ecosystem. Phytoremediation is an emerging and eco-friendly way to mitigate petrochemical contamination of soil. It is an in situ technique to purify contaminated soil or water using plants (trees, shrubs, grasses and aquatic plants) and their associated microorganisms. This technique is favourable for tropical countries like India where there is immense growth of plants. Though plants like Mirabilis jalapa, Italian ryegrass, sorghum, maize, and alfalfa are used worldwide, in Assam also various plant species are used for remediation purposes in petrochemical-contaminated soil. Crotalaria pallida, Cyperus brevifolius, Cynodondactylon. Mimosa pudica etc. are some of the plant species that have been reported to possess the ability to degrade toxic chemicals into non-toxic or less-toxic products with the aid of microbial colonies in the soil. This review is an effort to through some light on the plants of Assam as well as worldwide along with their family in the remediation of petroleum-contaminated soil. Thus, it will be helpful to select appropriate plants for the purpose of phytoremediation.

Oxygen atmosphere enhances ball milling remediation of petroleum-contaminated soil and reuse as adsorptive/catalytic materials for wastewater treatment

Ball milling is an environmentally friendly technology for the remediation of petroleum-contaminated soil (PCS), but the cleanup of organic pollutants requires a long time, and the post-remediation soil needs an economically viable disposal/reuse strategy due to its vast volume. The present paper develops a ball milling process under oxygen atmosphere to enhance PCS remediation and reuse the obtained carbonized soil (BCS-O) as wastewater treatment materials. The total petroleum hydrocarbon removal rates by ball milling under vacuum, air, and oxygen atmospheres are 39.83%, 55.21%, and 93.84%, respectively. The Langmuir and pseudo second-order models satisfactorily describe the adsorption capacity and behavior of BCS-O for transition metals. The Cu2+, Ni2+, and Mn2+ adsorbed onto BCS-O were mainly bound to metal carbonates and metal oxides. Furthermore, BCS-O can effectively activate persulfate (PDS) oxidation to degrade aniline, while BCS-O loaded with transition metal (BCS-O-Me) shows better activation efficiency and reusability. BCS-O and BCS-O-Me activated PDS oxidation systems are dominated by 1O2 oxidation and electron transfer. The main active sites are oxygen-containing functional groups, vacancy defects, and graphitized carbon. The oxygen-containing functional groups and vacancy defects primarily activate PDS to generate 1O2 and attack aniline. Graphitized carbon promotes aniline degradation by accelerating electron transfer. The paper develops an innovative strategy to simultaneously realize efficient remediation of PCS and sequential reuse of the post-remediation soil.

Remediation of Petroleum-contaminated Soil by Highly Efficient Oil-degrading Bacteria and Analysis of Its Enhancement Mechanism

A 120-day in situ remediation of oil-contaminated soil was carried out by using highly efficient oil-degrading bacteria. The effects of bio-enhanced remediation and changes in soil physicochemical properties and enzyme activities were investigated. Combined with metagenomic sequencing and bioinformatics analysis, the strengthening mechanism was revealed. The results showed that compared with the blank control group (Ctrl), the degradation rate of total petroleum hydrocarbons in the bioremediation group (Exp-BT) was significantly increased, reaching 81.23%. During enhanced bioremediation by highly efficient oil-degrading bacteria, the pH of the soil was stable, the oxidation capacity of the system was improved, and the electrical conductivity was in the range suitable for agricultural activities. Lipase and dehydrogenase maintained high activity during repair. In addition, the analysis of the initial contaminated soil (B0), the highly efficient oil-degrading bacteria obtained from domestication (GZ), and the soil samples after bioremediation (BT) in the obtained samples showed that, at the phylum level, the total proportion of Proteobacteria and Actinobacteria increased by 17.1%. At the genus level, the abundance of Nocardioides, Achromobacter, Gordonia, and Rhodococcus increased significantly. The species and function contribution analysis of COG and KEGG proved that the above bacterial genera had important contributions to the degradation of petroleum hydrocarbons. A high abundance of petroleum hydrocarbon-related metabolic enzymes and five petroleum hydrocarbon-related degradation genes was found in the soil after remediation:alkM, tamA, rubB, ladA, and alkB. The analysis showed that the introduction of the exogenous petroleum hydrocarbon-degrading bacteria group enhanced the metabolic activity of microorganism-related enzymes and the expression of corresponding functional genes.

Enhanced degradation of petroleum in saline soil by nitrogen stimulation and halophilic emulsifying bacteria Bacillus sp. Z-13

Remediation of petroleum-contaminated soil is a widely concerned challenge. As an ecofriendly method, the performance improvement of indigenous microbial degradation is facing the bottleneck. In this study, a strain with high efficiency of petroleum degradation was isolated from the petroleum-contaminated soil and identified and named as Bacillus sp. Z-13. The strain showed the ability to produce lipopeptide surfactant which could improve 66% more petroleum hydrocarbons eluted. Strain Z-13 and its biosurfactant exhibited broad environmental adaptability to salinity (0–8%), pH (6−9) and temperature (15–45 °C). With the addition of strain Z-13 and the stimulation of NH4Cl, up to 59% of the petroleum in the contaminated soil was removed at the carbon to nitrogen ratio of 10. Microbial community analysis showed that petroleum-degrading bacteria, represented by Bacillus, became the dominant species at genus level and played an important role in the remediation. Additionally, ammonium stimulation facilitated both pathways of ammonium assimilation and nitrification in native microorganisms to achieve efficient degradation of petroleum hydrocarbons. This study could provide a promising approach for stable, environmental-friendly and efficient remediation of petroleum-contaminated soil.

Experimental study on remediation of petroleum-contaminated soil by combination of freeze-thaw and electro-osmosis

Electro-osmosis has been well recognized as a technique for the remediation of petroleum-contaminated soil, however seasonally freezing and thawing adds the complexity of petroleum mobility in cold regions. To investigate the influence of freeze-thaw on the electroosmotic removal of petroleum and explore the enhancement of freeze-thaw on the electroosmotic remediation efficiency in remediating the petroleum-contaminated soils, a set of laboratory tests were performed in three types of treatment modes, freeze-thaw (FT), electro-osmosis (EO) and freeze-thaw combined electro-osmosis (FE). The petroleum redistributions as well as the moisture content changes after the treatments were evaluated and compared. The petroleum removal rates of the three treatments were analyzed, and the underlying mechanisms were elaborated. The results indicated that the overall efficiency of the treatment mode regarding petroleum removal from soil followed the order of FE > EO > FT, corresponding to 54%, 36% and 21% in maximum, respectively. A considerable amount of water solution with surfactant was driven into contaminated soil during FT process, but the petroleum mobilization primarily occurred inside of the specimen. A higher remediation efficiency was yield in EO mode, but the induced dehydration and cracks leaded to the dramatical depression in the efficiency in further process. It is proposed that the petroleum removal is closely related to the flow of water solution with surfactant that is favorable to the solubility and mobilization of the petroleum in soil. Thus, the water migration induced by freeze-thaw cycles substantially improved the efficiency of the electroosmotic remediation in FE mode that gave the best performance for the remediation of the petroleum-contaminated soil.

Enhanced oriented oxidation of all alkanes through redistributing hydroxy radical by inactivating oxygen-containing functional groups in soil organic matter

To explore the effect of oxygen-containing functional groups in SOM on the oriented oxidation of all n-alkanes (OX-A) (C10 - C30), different proportions of NaOH (NaOH: protein I = 1:1 and 2:1) were used to pretreat two soils (S1 and S2). Then the crude oil (S1: 18,173 mg/kg; S2: 9853 mg/kg) was added to carry six groups of Fenton oxidation treatments. The results showed that when the content of C-O, O-H of phenol or alcohol, and O-H of carboxyl in the soil decreased, the two soils realized oriented oxidation of all n-alkanes under the low intensity of hydroxyl radical (•OH) (1.02 a.u.). The oriented oxidation of all n-alkanes group was as high as 4477.00 mg/kg (S1) and 2685.00 mg/kg (S2), respectively, which was 0.53–2.33 times of the other groups. In addition, after 1:1 regulation, the ability of •OH to capture oxygen-containing functional groups in SOM decreased, then the relative reactivity coefficient k of •OH to total petroleum hydrocarbons (TPH) increased to 2.01 and 1.81 (k > 1), which was 1.02–1.47 and 0.93–1.32 higher than the other five groups. The competition of SOM for oxidants was decreased by improving the reactivity of •OH with TPH. Thus, more •OH (S1: 48%, S2: 46%) transferred to efficiently oxidize TPH (S1: 310.60 mg/mmol, S2: 220.20 mg/mmol). In general, this study reduced the ineffective consumption of oxidants after developing inactivation, thereby the utilization efficiency of H2O2 was improved and the stability of petroleum-contaminated soil remediation was enhanced.

Synergistic effects of rice husk biochar and aerobic composting for heavy oil-contaminated soil remediation and microbial community succession evaluation

Soil petroleum pollution is an urgent problem in modern society, which seriously threatens the ecological balance and environmental safety. Aerobic composting technology is considered economically acceptable and technologically feasible for the soil remediation. In this study, the combined experiment of aerobic composting with the addition of biochar materials was conducted for the remediation of heavy oil-contaminated soil, and treatments with 0, 5, 10 and 15 wt% biochar dosages were labeled as CK, C5, C10 and C15, respectively. Conventional parameters (temperature, pH, NH4+-N and NO3--N) and enzyme activities (urease, cellulase, dehydrogenase and polyphenol oxidase) during the composting process were systematically investigated. Remediation performance and functional microbial community abundance were also characterized. According to experimental consequences, removal efficiencies of CK, C5, C10 and C15 were 48.0%, 68.1%, 72.0% and 73.9%, respectively. The comparison with abiotic treatments corroborated that biostimulation rather than adsorption effect was the main removal mechanism during the biochar-assisted composting process. Noteworthy, the biochar addition regulated the succession process of microbial community and increased the abundance of microorganisms related to petroleum degradation at the genus level. This work demonstrated that aerobic composting with biochar amendment would be a fascinating technology for petroleum-contaminated soil remediation.

Applications of functional nanoparticle–stabilized surfactant foam in petroleum-contaminated soil remediation

Surfactant foam (SF) can be used to remediate petroleum-contaminated soil because of its easy transfer to inhomogeneous and low-permeability formations. Nanoparticles (NPs) not only stabilize SF under extreme conditions but also impart various functions, aiding the removal of petroleum contaminants. This review discusses the stabilization mechanisms of nanoparticle-stabilized SF (NP-SF) as well as the effects of NP size, chargeability, wettability, and NP-to-surfactant ratio on foam stability. SF stabilized by inert SiO2 NPs is most commonly used to remediate soil contaminated with crude oil and diesel. Low dose of SF stabilized by nano zero-valent iron is cost-effective for treating soil contaminated with chlorinated organics and heavy metal ions. The efficiency and recyclability of Al2O3/Fe3O4 NPs in the remediation of diesel and crude oil contamination could be enhanced by applying a magnetic field. This review provides a theoretical basis and practical guidelines for developing functional NP-SF to improve the remediation of petroleum-contaminated soils. Future research should focus on the structural design of photocatalytic NPs and the application of catalytic NP-SF in soil remediation.

Efficient catalytic degradation of alkanes in soil by a novel heterogeneous Fenton catalyst of functionalized magnetic biochar.

In this study, sodium dodecyl sulfate (SDS) functionalized magnetic biochar (SDS-Fe@BC) was successfully prepared. Compared to other traditional heterogeneous Fenton catalysts, more total petroleum hydrocarbons (TPH) (3499.40mgkg-1) was adsorbed from soil to the surface of SDS-Fe@BC through hydrophobic interaction between alkyls in alkanes and SDS-Fe@BC, which formed an efficient interface oxidation system. In SDS-Fe@BC-mediated heterogeneous Fenton system, 10,191.41mgkg-1 (88.10%) TPH was degraded in the presence of 400mM H2O2, which was 1.38-5.67 folds than that of H2O2 alone, Fe2+, zero valent iron (ZVI), Fe3O4, pristine biochar (BC), and Fe@BC. Moreover, all individual alkanes were efficiently degraded (>75%), and the higher the initial amount of individual alkane, the more the degradative amount in the SDS-Fe@BC/H2O2 system. Additionally, TPH degradation was highly related to the mass ratio of SDS/Fe@BC, H2O2 concentration, SDS-Fe@BC dosage, and initial pH in the SDS-Fe@BC/H2O2 system, and the optimal values were 1:5, 400mM, 50mgg-1, and pH 7, respectively. Radical quenching experiments revealed that hydroxyl radicals (•OH) generated on the surface of SDS-Fe@BC was the dominated reactive oxidative species (ROS) responsible for alkanes degradation. After five cycles, SDS-Fe@BC still remained a high catalytic activity for alkanes degradation (73.21%), showing its excellent reusability. This study proved that the SDS-Fe@BC can be used as a potential heterogeneous Fenton catalyst for petroleum-contaminated soil remediation.

Temporal effect of phytoremediation on the bacterial community in petroleum-contaminated soil

Phytoremediation is a promising bio-technology where plants associated with microbes are employed to remediate sites co-contaminated with petroleum. With the in-depth study of plant restoration, it is necessary to explore the dynamic changes of microbial communities in petroleum-contaminated soil. This study investigated the effects of Ryegrass on bacterial community and diversity in petroleum contaminated soil. High-throughput sequencing technology was used to compare the bacterial communities in 14 groups samples at different repair stages. It was concluded that different responses were observed to promote or inhibit microbial reproduction. The most significant bacterial family were Comamonadaceae, Nocardiaceae, Blastocatellaceae, and Cytophagacea. Comamonadaceae showed the highest level of remediation in non-petroleum-contaminated soils at 90 days. However, Blastocatellaceae and Cytophagaceae exhibited high microbial contents in petroleum-contaminated soil at 0 and 40 days, respectively. In all samples, plants improved the remediation of petroleum-contaminated soil and the highest abundance of microbial communities were found after 90 days. These data indicate that not only rhizosphere secretions but also petroleum, will promote microbial growth. Moreover, the repair time has a vital effect on microbial community changes. This study supports the foundation to control soil pollution and highlight the periodic dynamic of microbial community diversity and structure.

Study on the Enhanced Remediation of Petroleum-Contaminated Soil by Biochar/g-C3N4 Composites.

This work developed an environmentally-friendly soil remediation method based on BC and g-C3N4, and demonstrated the technical feasibility of remediating petroleum-contaminated soil with biochar/graphite carbon nitride (BC/g-C3N4). The synthesis of BC/g-C3N4 composites was used for the removal of TPH in soil via adsorption and photocatalysis. BC, g-C3N4, and BC/g-C3N4 have been characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface area analyzer (BET), FT-IR, and X-ray diffraction (XRD). BC/g-C3N4 facilitates the degradation due to reducing recombination and better electron-hole pair separation. BC, g-C3N4, and BC/g-C3N4 were tested for their adsorption and photocatalytic degradation capacities. Excellent and promising results are brought out by an apparent synergism between adsorption and photocatalysis. The optimum doping ratio of 1:3 between BC and g-C3N4 was determined by single-factor experiments. The removal rate of total petroleum hydrocarbons (TPH) by BC/g-C3N4 reached 54.5% by adding BC/g-C3N4 at a dosing rate of 0.08 g/g in a neutral soil with 10% moisture content, which was 2.12 and 1.95 times of BC and g-C3N4, respectively. The removal process of TPH by BC/g-C3N4 conformed to the pseudo-second-order kinetic model. In addition, the removal rates of different petroleum components in soil were analyzed in terms of gas chromatography–mass spectrometry (GC-MS), and the removal rates of nC13-nC35 were above 90% with the contaminated soil treated by BC/g-C3N4. The radical scavenger experiments indicated that superoxide radical played the major role in the photocatalytic degradation of TPH. This work definitely demonstrates that the BC/g-C3N4 composites have great potential for application in the remediation of organic pollutant contaminated soil.

Effect of plant waste addition as exogenous nutrients on microbial remediation of petroleum-contaminated soil

PurposeThis study investigates the feasibility of bio-enhanced microbial remediation of petroleum-contaminated soil, and analyzes the effect of different plant wastes as exogenous stimulants on microbial remediation of petroleum-contaminated soil and the effect on soil microbial community structure, in order to guide the remediation of soil in long-term petroleum-contaminated areas with nutrient-poor soils.MethodsThe study was conducted in a representative oil extraction area in the Loess Hills, a typical ecologically fragile area in China. Through indoor simulated addition tests, combined with the determination of soil chemical and microbiological properties, the degradation efficiency of petroleum pollutants and the response characteristics of soil microbial community structure to the addition of different plant wastes in the area were comprehensively analyzed to obtain the optimal exogenous additive and explore the strengthening mechanism of plant wastes on microbial remediation of petroleum-contaminated soil.ResultsCompared with the naturally decaying petroleum-contaminated soil, the addition of plant waste increased the degradation rate of petroleum pollutants, that is, it strengthened the degradation power of indigenous degrading bacteria on petroleum pollutants, among which the highest degradation rate of petroleum pollutants was achieved when the exogenous additive was soybean straw; compared with the naturally decaying petroleum-contaminated soil, the addition of soybean straw and dead and fallen leaves of lemon mallow made the microbial species in the contaminated soil significantly reduced and the main dominant flora changed, but the flora capable of degrading petroleum pollutants increased significantly; the addition of exogenous nutrients had significant effects on soil microbial diversity and community structure.ConclusionsSoybean straw can be added to the contaminated soil as the optimal exogenous organic nutrient system, which improves the physicochemical properties of the soil and gives a good living environment for indigenous microorganisms with the function of degrading petroleum pollutants, thus activating the indigenous degrading bacteria in the petroleum-contaminated soil and accelerating their growth and proliferation and new city metabolic activities, laying a foundation for further obtaining efficient, environmentally friendly and low-cost microbial enhanced remediation technology solutions. The foundation for further acquisition of efficient, environmentally friendly, and low-cost microbial-enhanced remediation technology solutions. It is important for improving soil remediation in areas with long-term oil contamination and nutrient-poor soils.