Minimizing the Health Risks from Hydrocarbon Contaminated Soils by Using Electric Field-Based Treatment for Soil Remediation

New simplified design methods for engineering barriers around contaminated sites with Cauchy boundaries

Since the 1980s, low-permeability slurry trench cutoff walls have been widely constructed as barriers to retard the migration of contaminants. The thickness of the cutoff walls is a key determinant of the wall service life. Through a series of theoretical derivations, simplified methods for determining the flux limit and concentration limit were proposed to determine the thickness of cutoff walls for contaminated sites with constant pollutant flux. The relative errors of both the flux-based and concentration-based methods increase as the breakthrough criterion of the ratio between the specified limit concentration of the contaminant to the source concentration (C*) and the ratio of the limited value of contaminant flux to the constant source flux (F*) increases, with a given Peclet number PL. The maximum relative error reaches 4% and 6% when C* and F* are both 0.1, which covers most practical situations in cutoff wall design. Good agreements of wall thickness were obtained between the proposed simplified methods and analytical solutions via a clear example. The proposed method can efficiently simplify the design process of cutoff walls with high accuracy, providing a basis for containing contaminated sites.

Health Risk Assessment for the Residential Area Adjacent to a Former Chemical Plant

A health risk assessment was carried out for the residents of Łęgnowo-Wieś settlement adjacent to a former Zachem Chemical Plant, Bydgoszcz, Poland. Due to the unique Zachem site history and contamination profile, an innovative strategy for soil sampling and contaminant selection was applied. The novelty in the developed strategy consisted of selecting substances for the health risk assessment, taking into consideration the location and boundaries of the groundwater contamination plumes in relation to contamination sources. This allowed limiting the number of the analysed contaminants. The risk assessment focused on the surface soil of a residential area, which was divided into 20 sampling sectors and 6 backyards with wells from which water was used for watering edible plants. A total of 80 inorganic and organic substances were determined, including metals, phenol, aniline, BTEX, diphenyl sulphone, chloroaniline, epichlorohydrin, hydroxybiphenyl, nitrobenzene, octylphenols, toluenediamine, toluidine, 16 polycyclic aromatic hydrocarbons, tetrachloroethylene and trichloroethylene. For the health risk assessment, the United States Environmental Protection Agency’s deterministic method was applied. This applies conservative assumptions to obtain risk estimates protective for most of the potential receptors. Three exposure pathways were analysed: (1) incidental soil ingestion, (2) dermal contact with soil and (3) inhalation of fugitive soil particles and volatiles. In all sampling sectors and backyards, the total non-cancer risks (hazard index) were significantly lower than the acceptable level of 1. The acceptable cancer risk level for the single carcinogen of 1 × 10⁻⁵ was only insignificantly exceeded in the case of benzo(a)pyrene in three sectors and one backyard. The total cancer risks were lower than the acceptable level of 1 × 10⁻⁴ in all sampling sectors and all backyards. The findings show that the soil in the entire residential area is safe for the residents’ health and no remedial actions are required. However, since not all possible exposure pathways were analysed in this study, further research focused on assessing the health risk resulting from the consumption of locally grown food is strongly recommended.

High-Grade Chemicals and Biofuels Produced from Marginal Lands Using an Integrated Approach of Alcoholic Fermentation and Pyrolysis of Sweet Sorghum Biomass Residues

New global directions align agricultural land resources towards food production; therefore, marginal lands could provide opportunities for second-generation energy crops, assuming that in the difficult conditions of plant development, productivity can be maintained at relatively high levels. Sustainable bioenergy production on marginal lands represents an ambitious objective, offering high-quality biofuels without competing with the agri-food industry, since it allows successful feedstock production to be performed on unmanaged areas. However, marginal land feedstock production generally shows several agronomic, techno-economic, and methodological challenges, leading to decreases in the obtained quantities of biomass and profitability. Sweet Sorghum is a technical plant that has the needed qualities to produce large amounts of biofuels on marginal lands. It is a high biomass- and sugar-yielding crop, characterized by a high photosynthetic efficiency and low fertilizer requirement, is resistant to drought, and adapts well to different climate areas. Marginal lands and contaminated soils provide a favorable development environment for plants such as sweet sorghum; however, in-depth research studies on biomass productivity must be carried out, as well as advanced quality evaluation of the products, in order to develop combined technologies that use resources efficiently. The present study starts with a comparative evaluation of two sweet sorghum crops established on both marginal and regular lands, assessing plant development characteristics and juice production, and an evaluation of bioethanol generation potential. The vegetal wastes resulting from the processing were treated by pyrolysis, with the aim of maximizing the productivity of high-quality liquid biofuels and chemicals. The charcoal obtained in the thermal processes was considered as an amendment of the soil so that marginal land quality could be improved over time.

Remediation of soils and sediments polluted with polycyclic aromatic hydrocarbons: To immobilize, mobilize, or degrade?

Polycyclic aromatic hydrocarbons (PAHs) are generated due to incomplete burning of organic substances. Use of fossil fuels is the primary anthropogenic cause of PAHs emission in natural settings. Although several PAH compounds exist in the natural environmental setting, only 16 of these compounds are considered priority pollutants. PAHs imposes several health impacts on humans and other living organisms due to their carcinogenic, mutagenic, or teratogenic properties. The specific characteristics of PAHs, such as their high hydrophobicity and low water solubility, influence their active adsorption onto soils and sediments, affecting their bioavailability and subsequent degradation. Therefore, this review first discusses various sources of PAHs, including source identification techniques, bioavailability, and interactions of PAHs with soils and sediments. Then this review addresses the remediation technologies adopted so far of PAHs in soils and sediments using immobilization techniques (capping, stabilization, dredging, and excavation), mobilization techniques (thermal desorption, washing, electrokinetics, and surfactant assisted), and biological degradation techniques. The pros and cons of each technology are discussed. A detailed systematic compilation of eco-friendly approaches used to degrade PAHs, such as phytoremediation, microbial remediation, and emerging hybrid or integrated technologies are reviewed along with case studies and provided prospects for future research.

Assessment of European and hybrid aspen clones efficiency based on height growth and removal percentage of petroleum hydrocarbons-a field trial

Soils polluted by organic or inorganic pollutants are an emerging global environmental issue due to their toxic effects. A phytoremediation experiment was conducted to evaluate the extraction potential of three European aspen clones (R2, R3, and R4) and seven hybrid aspen clones (14, 27, 34, 134, 172, 191, and 291) grown in soils polluted with hydrocarbons (includes polycyclic aromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH)). Height growth, plant survival rates, and .hydrocarbon removal efficiencies were investigated over a 4-year period at a site in Somerharju, Luumaki Finland, to assess the remediation potential of the clones. Hydrocarbon content in the soil was determined by gas chromatography and mass spectrometry. The results revealed that hybrid aspen clones 14 and 34 and European aspen clone R3 achieved greater height growth (171, 171, and 114 cm, respectively) than the other clones in the study. Further, the greatest removals of PAH (90% at depth 10-50 cm) and (86% at depth 5-10 cm) were observed in plot G15 planted with clone R2. Furthermore, the greatest TPH removal rate at 5-10 cm depth (C₂₂-C₄₀, 97%; C₁₀-C₄₀, 96%; and C₁₀-C₂₁, 90%) was observed in plot 117 with clone 134. However, other clones demonstrated an ability to grow in soils with elevated levels of TPH and PAH, which indicates their tolerance to hydrocarbons and their potential capacity for phytoremediation of hydrocarbon-polluted soils. Our study suggests that European aspen and hybrid aspen clones could be used for the remediation of soils polluted with PAH and TPH.

Pilot-scale electro-bioremediation of heavily PAH-contaminated soil from an abandoned coking plant site

This study presents a systematic pilot-scale study on removal of PAHs from the abandoned site of Shenyang former Coking Plant in China (total PAH concentration of 5635.60 mg kg^-1 in soil). Three treatments, including the control treatment (without inoculation and electric field), bioremediation (with inoculation), and the electro-bioremediation (with inoculation and electric field), were conducted with a treatment time of 182 days to assess their PAH-removal efficiency. All the treatments were conducted from May to October under natural conditions. Results show that electro-bioremediation enhanced the removal of total PAHs, especially high-ring (>3 rings) PAHs. At 182 days, the degradation extents of total and 4-6-ring PAHs reached 69.1% and 65.9%, respectively, under electro-bioremediation (29.3% and 44.4% higher, respectively, than those under bioremediation alone). After electro-bioremediation, the total toxicity equivalent concentrations of total PAHs and 4-, 5- and 6-ring PAHs reduced 49.0%, 63.7%, 48.2% and 30.1%, respectively. These results indicate that electro-bioremediation not only effectively removed the PAHs but also reduced the health risks of soil in an abandoned coking plant site. In addition, electro-bioremediation with polarity reversal could maintain uniform soil pH, the degradation extent of PAHs and soil microorganism numbers at all sites. The environmental conditions, such as temperature and rainfall, had little influence on the process of electro-bioremediation. These findings suggest that electro-bioremediation may be applied for field-scale remediation of heavily PAH-contaminated soil in abandoned coking plant sites.