Valorisation of soil contaminated by petroleum hydrocarbons and toxic metals in geopolymer mortar formation

Solid-oil separation of coal tar residue to reduce polycyclic aromatic hydrocarbons via microwave-assisted extraction

Coal tar residue (CTR) is acknowledged as hazardous industrial waste with high contents of carbon and toxic polycyclic aromatic hydrocarbons (PAHs). Microwave-assisted extraction for separating tar and residue in CTR was investigated to reduce the content of PAHs. The key operating factors such as solvent type, solvent addition amount, radiation temperature, and radiation time in the extraction process were evaluated. Results showed that extreme extraction performance in the solvent with cyclic structure was attained, and an enhancement in extraction efficiency was achieved in elevated solvent addition amount, radiation temperature, or radiation time in a certain range. The optimized conditions were determined as benzene was chosen as extractant, solvent-solid ratio of 5:1 mL/g, radiation temperature of 75 °C, and radiation time of 10 min. Relative extraction efficiency of CTR and reduction efficiency of 16 priority control PAHs were 28.70% and 92.82%, respectively. According to the characterizations of extracted residue (MCTR) and tar (MCT) under optimum experimental conditions, it is possible to convert them into value-added products (carbon materials, solid fuels, or chemicals). Solid-oil separation via microwave-assisted extraction is a safe and high-valued utilization approach for CTR.

Metagenomics-metabolomics analysis of microbial function and metabolism in petroleum-contaminated soil

Contamination of soil by petroleum is becoming increasingly serious in the world today. However, the research on gene functional characteristics, metabolites and distribution of microbial genomes in oil-contaminated soil is limited. Considering that, metagenomic and metabonomic were used to detect microbes and metabolites in oil-contaminated soil, and the changes of functional pathways were analyzed. We found that oil pollution significantly changed the composition of soil microorganisms and metabolites, and promoted the relative abundance of Pseudoxanthomonas, Pseudomonas, Mycobacterium, Immundisolibacter, etc. The degradation of toluene, xylene, polycyclic aromatic hydrocarbon and fluorobenzoate increased in Xenobiotics biodegradation and metabolism. Key monooxygenases and dioxygenase systems were regulated to promote ring opening and degradation of aromatic hydrocarbons. Metabolite contents of polycyclic aromatic hydrocarbons (PAHs) such as 9-fluoronone and gentisic acid increased significantly. The soil microbiome degraded petroleum pollutants into small molecular substances and promoted the bioremediation of petroleum-contaminated soil. Besides, we discovered the complete degradation pathway of petroleum-contaminated soil microorganisms to generate gentisic acid from the hydroxylation of naphthalene in PAHs by salicylic acid. This study offers important insights into bioremediation of oil-contaminated soil from the aspect of molecular regulation mechanism and provides a theoretical basis for the screening of new oil degrading bacteria.

Cost reduction strategies in the remediation of petroleum hydrocarbon contaminated soil

Petroleum hydrocarbon spill on land pollutes soil and reduces its ecosystem. Hydrocarbon transport in the soil is aided by several biological, physical, and chemical processes. However, pore characteristics play a major role in the distribution within the soil matrix. Restoring land use after spills necessitates remediation using cost-effective technologies. Several remediation technologies have been demonstrated at different scales, and research is ongoing to improve their performances towards the reduction of treatment costs. The process of removing the contaminants in the soil is through one or a combination of containment, separation, and degradation methods under the influence of biological, physical, chemical, and electrically-dominated processes. Generally, performance improvement is achieved through the introduction of products/materials and/or energy. Nevertheless, the technologies can be categorized based on effectiveness period as short, medium, and long term. The treatment cost of short, medium, and long-term technologies are usually in the range of $39 - 331/t (/tonne), $22 - 131/t, and $8 - 131/t, respectively. However, the total cost depends on other factors such as site location, capital cost, and permitting. This review compiles cost-saving strategies reported for different techniques used in remediating petroleum hydrocarbon polluted soil. We discuss the principles of contaminant removal, performance enhancing methods, and the cost-effectiveness analysis of selected technologies.