Rapid assessment of the impact of microwave heating coupled with UV-C radiation on the degradation of PAHs from contaminated soil using FTIR and multivariate analysis

Recent trends in polycyclic aromatic hydrocarbons pollution distribution and counteracting bio-remediation strategies

Polycyclic aromatic hydrocarbons (PAHs) are distributed worldwide due to long-term anthropogenic pollution sources. PAHs are recalcitrant and highly persistent in the environment due to their inherent properties, such as heterocyclic aromatic ring structures, thermostability, and hydrophobicity. They are highly toxic, carcinogenic, immunotoxic, teratogenic, and mutagenic to various life systems. This review focuses on the unique data of PAH sources, exposure routes, detection techniques, and harmful effects on the environment and human health. This review provides a comprehensive and systematic compilation of eco-friendly biological treatment solutions for PAH remediation, such as microbial remediation approaches utilizing microbial cultures. In situ and Ex situ bioremediation of PAH methods, including composting land farming, biopiles, bioreactors bioaugmentation, and phytoremediation processes, are discussed in detail, as is a summary of the factors affecting and limiting PAH bioremediation. This review provides an overview of emerging technologies that use multi-process combinatorial treatment approaches and answers to generating value-added by-products during PAH remediation.

Isolation, identification, and screening of biosurfactant-producing and hydrocarbon-degrading bacteria from oil and gas industrial waste

Qatar is one of the biggest oil and gas producers in the world, coupled with it is challenging environmental conditions (high average temperature: >40 °C, low annual rainfall: 46.71 mm, and high annual evaporation rate: 2200 mm) harbors diverse microbial communities that are novel and robust, with the potential to biodegrade hydrocarbons. In this study, we collected hydrocarbon contaminated sludge, wastewater and soil samples from oil and gas industries in Qatar. Twenty-six bacterial strains were isolated in the laboratory from these samples using high saline conditions and crude oil as the sole carbon source. A total of 15 different bacterial genera were identified in our study that have not been widely reported in the literature or studied for their usage in the biodegradation of hydrocarbons. Interestingly, some of the bacteria that were identified belonged to the same genus however, demonstrated variable growth rates and biosurfactant production. This indicates the possibility of niche specialization and specific evolution to acquire competitive traits for better survival. The most potent strain EXS14, identified as Marinobacter sp., showed the highest growth rate in the oil-containing medium as well as the highest biosurfactant production. When this strain was further tested for biodegradation of hydrocarbons, the results showed that it was able to degrade 90 to 100% of low and medium molecular weight hydrocarbons and 60 to 80% of high molecular weight (C35 to C50) hydrocarbons. This study offers many promising leads for future studies of microbial species and their application for the treatment of hydrocarbon contaminated wastewater and soil in the region and in other areas with similar environmental conditions.

Effects of polycyclic aromatic hydrocarbons fluoranthene on the soil aggregate stability and the possible underlying mechanism

Soil contamination by polycyclic aromatic hydrocarbons (PAHs) is an increasing problem in many countries, impacting the ecological environment's sustainable development. This study investigated the effects of fluoranthene (Fla) on soil aggregate stability. A possible mechanism for the interaction of Fla with soil aggregates was proposed by characterizing the aggregate structure. The results showed that Fla significantly improved the aggregate stability in the concentration range of 0-30.0 mg/kg. The content of macro-aggregates reached the maximum value at 10 mg/kg of Fla, which increased by 24.25% compared with the control group, while the content of large-aggregates decreased by 12.11%. Meanwhile, the mean weight diameter (MWD) and geometric mean diameter (GMD) increased by 56.63% and 37.66%, respectively. However, the macro-aggregates zeta potential value and specific surface area (SSA) decreased by 12.68% and 13.61%, respectively. The cracks of macro-aggregates were also significantly reduced. In addition, Fla-based free radicals were detected on the macro-aggregates. The absorption peak of the C-O group significantly increased, indicating that Fla may be covalently bound to the aggregates by aromatic ether bonds, which is a possible mechanism for the interaction between Fla and aggregates. This study provides theoretical support for revealing the effects of PAHs on soil.

Insights into removal efficiency and mechanism of microwave remediation of soils contaminated with polyaromatic hydrocarbons of low molecular weight assisted by bluecoke-based conditioner

Microwave remediation of polyaromatic hydrocarbons-contaminated soils has garnered extensive attention owing to its cost effectiveness, time saving, homogeneous heating, and low energy consumption. The prepared bluecoke-based conditioner (KHCO₃@BC) was used in this study to enhance microwave remediation and improve the naphthalene (NA) removal efficiency and soil properties. We investigated the optimal conditions, including the heating time, microwave power, bluecoke-based conditioner, initial concentration of NA, and moisture content of the soils. We evaluated the removal efficiency of NA and compared the remediation products after the addition of bluecoke, KHCO₃, and KHCO₃@BC conditioners. The results showed that the removal efficiency of NA reached 96.46% under the following optimized conditions: heating time of 20 min, microwave power of 700 W, 2 g of KHCO₃@BC conditioner, initial NA concentration of 1 wt%, and soil moisture content of 4 wt%. The KHCO₃@BC conditioner improved the contents of total K and fast-acting K during microwave remediation, and the mechanical components of the remediation soils were also optimized significantly. We proposed a feasible mechanism and evaluated the main reasons for the removal of NA from the soils based on the mechanical components of remediation soil and the remediation products, namely, gas stripping, boiling vaporization of NA, and breakage of soil grains by thermal stress.