Hydrocarbons In Groundwater Research Articles

The enhanced degradation of trichloroethylene in the bioelectrochemical system integrated with iron‑carbon micro-electrolysis

Trichloroethylene (TCE) is one of the most abundant volatile chlorinated hydrocarbons in groundwater which threatens human health and the environment. Utilizing a bioelectrochemical system (BES) to treat TCE is a promising strategy; however, as the ionic strength of the groundwater is low and the extracellular electron transfer of BES is limited, BES degradation of TCE is impeded. In this research, iron and graphite were added to the cathode chamber to form a micro-electrolysis to enhance the degradation of TCE synergistically. The results showed that when the iron and carbon mixture dosage was 70 g/L with the mass ratio (Fe/C) of 1:2 and the initial TCE concentration of 100 mg/L, the degradation efficiency of BES reached 97.8 % at the cathodic potential of −0.3 V (vs.SHE). This was 1.31 times, 1.94 times, and 2.74 times that of Fe/C + open-circuit BES, Fe/C micro-electrolysis, and conventional BES without Fe/C, respectively, which implied that iron‑carbon mediated BES colligated the advantages of microbial degradation and micro-electrolysis, and iron‑carbon provided more electrons and accelerated electron transfer to improve the degradation of TCE significantly. Moreover, through the analysis of the microorganisms of Fe/C + BES, the highest abundances of microorganisms at phylum, class, and genus levels were Proteobacteria, Alphaproteobacteria, and Acetobacterium, respectively. By comparing Fe/C + BES with conventional BES, the addition of iron‑carbon enhanced the microbial diversity and species richness and improved the abundances of Pseudomonas and Geobacter at the genus level. In all, iron‑carbon micro-electrolysis can be integrated with BES to treat TCE and facilitate BES application in the volatile chlorinated hydrocarbon-contaminated sites.

Polydopamine-modified biochar supported polylactic acid and zero-valent iron affects the functional microbial community structure for 1,1,1-trichloroethane removal in simulated groundwater

In-situ enhanced bioreduction by functional materials is a cost-effective technology to remove chlorinated hydrocarbons in groundwater. Herein, a novel polydopamine (PDA)-modified biochar (BC)-based composite containing nanoscale zero-valent iron (nZVI) and poly-l-lactic acid (PLLA) (PB-PDA-Fe) was synthesized to enhance the removal of 1,1,1-trichloroethane (1,1,1-TCA) in simulated groundwater with actual site sediments. Its impact on functional microbial community structure in system was also investigated. The typical characterizations revealed uniform dispersion of PLA and nZVI particles on the BC surface, being smoother after PDA coating. The composite exhibited a significantly higher performance on 1,1,1-TCA removal (82.38%, initial concentration 100 mg/L) than Fe-PDA and PB-PDA treatments. The diversity and richness of the microbial community in the composite treatment consistently decreased during incubation due to a synergistic effect between PLLA-BC and nZVI. Desulfitobaterium, Pedobacter, Sphaerochaeta, Shewanella, and Clostridium were identified as enriched genera by the composite through DNA-stable isotope probing (DNA-SIP), playing a crucial role in the bioreductive dechlorination process. All the above results demonstrate that this novel composite selectively enhances the activity of microorganisms with extracellular respiration functions to efficiently dechlorinate 1,1,1-TCA. These findings could contribute to understanding the responsive microbial community by carbon-iron composites and expedite the application of in-situ enhanced bioreduction for effective remediation of chlorinated hydrocarbon-contaminated groundwater.

Biochar, microbes, and biochar-microbe synergistic treatment of chlorinated hydrocarbons in groundwater: a review.

Dehalogenating bacteria are still deficient when targeted to deal with chlorinated hydrocarbons (CHCs) contamination: e.g., slow metabolic rates, limited substrate range, formation of toxic intermediates. To enhance its dechlorination capacity, biochar and its composites with appropriate surface activity and biocompatibility are selected for coupled dechlorination. Because of its special surface physical and chemical properties, it promotes biofilm formation by dehalogenating bacteria on its surface and improves the living environment for dehalogenating bacteria. Next, biochar and its composites provide active sites for the removal of CHCs through adsorption, activation and catalysis. These sites can be specific metal centers, functional groups or structural defects. Under microbial mediation, these sites can undergo activation and catalytic cycles, thereby increasing dechlorination efficiency. However, there is a lack of systematic understanding of the mechanisms of dechlorination in biogenic and abiogenic systems based on biochar. Therefore, this article comprehensively summarizes the recent research progress of biochar and its composites as a "Taiwan balm" for the degradation of CHCs in terms of adsorption, catalysis, improvement of microbial community structure and promotion of degradation and metabolism of CHCs. The removal efficiency, influencing factors and reaction mechanism of the degraded CHCs were also discussed. The following conclusions were drawn, in the pure biochar system, the CHCs are fixed to its surface by adsorption through chemical bonds on its surface; the biochar composite material relies on persistent free radicals and electron shuttle mechanisms to react with CHCs, disrupting their molecular structure and reducing them; biochar-coupled microorganisms reduce CHCs primarily by forming an "electron shuttle bridge" between biological and non-biological organisms. Finally, the experimental directions to be carried out in the future are suggested to explore the optimal solution to improve the treatment efficiency of CHCs in water.

Land-use interactions, Oil-Field infrastructure, and natural processes control hydrocarbon and arsenic concentrations in groundwater, Poso Creek Oil Field, California, USA

Like many hydrocarbon production areas in the U.S., the Poso Creek Oil Field in California includes and is adjacent to other land uses (agricultural and other developed lands) that affect the hydrology and geochemistry of the aquifer overlying and adjacent to oil development. We hypothesize that the distributions of hydrocarbons and arsenic in groundwater in such areas will be controlled by complex interactions between mixed land uses, oil-field infrastructure, and natural processes. In 2020–2021, samples of groundwater and surface water were collected and analyzed for a large suite of inorganic and organic chemicals and isotope and gas tracers to test this hypothesis. Those data are supplemented with ancillary data on historical geochemistry, hydrology, geology, and oil-field infrastructure. Hydrocarbons in groundwater (e.g., methane through pentane gases and benzene) are associated with natural processes (e.g., fault offsets or transition in sediment depositional environment) and oil-field infrastructure (e.g., fluid-migration pathways associated with uncemented annulus in oil wells or unlined pits). Arsenic concentrations >10 μg per liter (μg/L; maximum concentration 12.9 μg/L) are associated with natural processes in old, high-pH groundwater, and more recent recharge of water from natural and/or engineered recharge processes. Along the southwest margin of the oil field, pumping for drinking-water and irrigation supplies in combination with engineered groundwater recharge produce a depression in groundwater elevations where groundwater with elevated sulfate concentrations from agricultural areas and groundwater with hydrocarbons from the oil field mix to produce a zone of sulfate reduction that removes hydrocarbons and arsenic from groundwater but produces elevated sulfide (S2-) concentrations (maximum concentration 29 mg per liter, mg/L). In this study, multiple approaches were required to resolve the overlapping effects of land uses, oil-field infrastructure, and natural processes on the distributions of hydrocarbons and arsenic in groundwater. The combined use of geographic, historical, physical, chemical, isotopic, and other information to constrain processes could be a useful approach for studies in other hydrocarbon-production areas. This is particularly important where land uses affect aquifer hydrology to an extent that causes mixing of groundwaters with different chemical compositions.

A Critical Review of the Modelling Tools for the Reactive Transport of Organic Contaminants

The pollution of groundwater and soil by hydrocarbons is a significant and growing global problem. Efforts to mitigate and minimise pollution risks are often based on modelling. Modelling-based solutions for prediction and control play a critical role in preserving dwindling water resources and facilitating remediation. The objectives of this article are to: (i) to provide a concise overview of the mechanisms that influence the migration of hydrocarbons in groundwater and to improve the understanding of the processes that affect contamination levels, (ii) to compile the most commonly used models to simulate the migration and fate of hydrocarbons in the subsurface; and (iii) to evaluate these solutions in terms of their functionality, limitations, and requirements. The aim of this article is to enable potential users to make an informed decision regarding the modelling approaches (deterministic, stochastic, and hybrid) and to match their expectations with the characteristics of the models. The review of 11 1D screening models, 18 deterministic models, 7 stochastic tools, and machine learning experiments aimed at modelling hydrocarbon migration in the subsurface should provide a solid basis for understanding the capabilities of each method and their potential applications.

Reactive Transport Modeling for Exploring the Potential of Water Quality Sensors to Estimate Hydrocarbon Levels in Groundwater

AbstractPetroleum products have contaminated groundwater with harmful organic compounds, such as benzene, toluene, ethylbenzene, and xylenes (BTEX). Collecting and analyzing polluted groundwater samples is expensive and undertaken infrequently. However, quick remedial action in case of unexpected events requires continuous monitoring. In‐situ water quality sensors (pH, EC, DO, ORP) may show correlations with the components of dissolved petroleum hydrocarbon (PHC) such as aromatics and non‐volatile mobile fractions. Correlations are prerequisite to ultimately develop real‐time prediction models. Since suitable field data sets are limited, we simulated the fate of hydrocarbons in groundwater under various realistic conditions using a reactive transport model as novel approach to explore when, where, and why correlations occur. A stationary oil source zone continuously dissolved at the top of a heterogeneous and shallow sandy aquifer over a two‐dimensional cross‐section. Our model considered transient conditions (fluctuating water table) and spatially uniform hydrogeochemical composition. We observed a strong correlation between PHCs and water quality sensors (rolling Spearman's correlation > |0.8|) at varying periods. These correlations are strongly affected by the location of observation wells, the aquifer's hydraulic conductivity, and the availability of calcite and oxide minerals, and other electron acceptors. DO and ORP are significant for the early detection of hydrocarbon contamination, whereas pH and EC are important features for the long‐term monitoring of hydrocarbons. Our findings lay the foundation for the subsequent development of a data analysis model to detect and estimate in real time PHC levels in groundwater using in‐situ water quality sensors.

Activation of persulfate by g-C3N4/nZVI@SBC for degradation of total petroleum hydrocarbon in groundwater

In this study, we synthesized a high removal efficiency catalyst using biochar-supported nanoscale zero-valent iron and g-C3N4, denoted as g-C3N4/nZVI@SBC, to activate persulfate (PS) for the degradation of total petroleum hydrocarbon (TPH) in groundwater. We characterized the morphology and physiochemical properties of g-C3N4/nZVI@SBC with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), BET surface area analysis, and X-ray photoelectron spectroscopy (XPS). To assess the performance of the g-C3N4/nZVI@SBC catalyst, we investigated various reaction parameters, such as the mass ratio of g-C3N4 to nZVI@SBC, PS concentration, initial pH, initial TPH concentration, and the presence of coexisting ions in the system. The results from batch experiments and repeated use trials indicate that g-C3N4/nZVI@SBC exhibited both excellent catalytic activation capability and impressive durability, making it a promising choice for TPH degradation. Specifically, when the PS concentration reached 1 mM, the catalyst dosage was 0.3 g/L, and the g-C3N4 to nZVI@SBC mass ratio was 2, we achieved a remarkable TPH removal efficiency of 93.8%. Through electron paramagnetic resonance (EPR) testing and quenching experiments, we identified sulfate radicals, hydroxyl radicals, and superoxide radicals as the primary active substance involved in the TPH degradation process. Moreover, the g-C3N4/nZVI@SBC composite proved highly effective for in-situ TPH removal from groundwater and displayed an 86% removal rate, making it a valuable candidate for applications in permeable reactive barriers (PRB) aimed at enhancing environmental remediation. In summary, by skillfully utilizing g-C3N4/nZVI@SBC, this study has made notable advancements in synthesis and characterization, presenting a feasible and innovative approach to addressing TPH pollution in groundwater.

Levels, distribution, origins, and human health risk evaluation of polycyclic aromatic hydrocarbons in groundwater around a petroleum depot wastewater discharge point

This study is an attempt to assess the influence of the oil storage depot discharges on proximate water sources in Ibadan, southwest Nigeria. Fifteen priority polycyclic aromatic hydrocarbons (PAHs) were examined in a total of 15 water samples (10 groundwater +4 surface water samples) utilizing gas chromatography–mass spectrometry, after extraction of the waters with dichloromethane and clean-up of the extracts. Results revealed that values of overall PAHs in groundwater (GW) and surface water (SW) varied from 0.01 to 3.45 mg/L (mean = 0.42 mg/L) and 0.01 to 0.09 mg/L (mean = 0.05 mg/L), correspondingly. The highest value of ∑15 PAHs (3.45 mg/L) was observed at 24 m to the discharge point. The ring wise distribution pattern of the PAHs in collected water samples follows the order: 2–3 rings >5–6 rings >4 – ring PAHs and low molecular weight (LMW) PAHs accounted for 90.73% relative to HMW (9.27%) in groundwater samples. The diagnostic ratios suggested that the PAHs pollution in water were likely from incomplete combustion of fossil fuels, vehicle emissions and released petroleum effluents from nearby depot. The concentration of carcinogenic PAHs in GW and SW ranged from 1×10−2to 9×10−2 mg/L and 1×10−2to 7×10−2 mg/L, correspondingly, which highlights possible human health risks. The values of hazard index (HI) for the studied samples via the oral ingestion and dermal exposure pathways are less than unity, suggesting no adverse non-carcinogenic health effects. The calculated incremental lifetime cancer risk (ILCR) for adults and children are in the 10−2–10−3 range, implying noteworthy possible carcinogenic health effects to human beings, with children being the most susceptible. Correspondingly, dibenzo [a, h] anthracence (DahA) and Benzo [a] pyrene (BaP) were established to be of greater carcinogenic threats in the waters taken from the study location. The study advocates complete discontinuance of discharge release into the neighboring environment.

Degrading characteristics of oil‐degrading bacteria and its study of petroleum hydrocarbon metabolites

AbstractExploring the community characteristics of petroleum degrading bacteria and revealing the types of petroleum metabolites produced by degrading bacteria play an important role in solving the problem of oil pollution. In this study, the bacterial suspension was extracted from the sludge of the sewage treatment plant, and the efficient dominant bacteria were enriched and cultured by microbial screening. The optimal environmental conditions and kinetic behavior of microbial degradation of petroleum hydrocarbons in groundwater were discussed, and the metabolites of microbial degradation of petroleum hydrocarbons were analyzed. The results showed that the optimum degradation conditions of the strain were as follows: bacterial suspension inoculum: 2%, pH: 7, temperature: 30°C, initial concentration of contaminated water sample: 500 mg/L. Under these conditions, the microbial petroleum hydrocarbon degradation efficiency was 84.7% and followed the first‐order kinetics; qualitative and quantitative statistical analysis of the metabolites of the microbial degradation of petroleum hydrocarbons by gas chromatography‐time‐of‐flight mass spectrometry was performed. A total of 10 significantly upregulated products and 12 significantly downregulated products were screened, which were significantly different from the metabolites of the control group. Further microbial community analysis showed that Pseudomonas was dominant in the bacterial suspension, more than 99.5%, which was significantly different from the sludge sample, providing data support for the degradation of petroleum hydrocarbons by Pseudomonas. This study has provided a scientific basis for in situ remediation of petroleum pollution in groundwater.

Field test of thermally activated persulfate for remediation of PFASs co-contaminated with chlorinated aliphatic hydrocarbons in groundwater

The co-occurrence of per- and polyfluoroalkyl substances (PFASs) and chlorinated aliphatic hydrocarbons (CAHs) in groundwater has drawn increased attention in recent years. No studies have been conducted concerning the oxidative degradation of PFASs and/or CAHs by in situ thermally activated persulfate (TAP) in groundwater, primarily due to the difficulty in cost-effectively achieving the desired temperature in the field. In this study, the effects and mechanisms of PFASs degradation by in situ TAP at a site with PFASs and CAHs co-contaminants were investigated. The target temperature of 40.0–70.0 °C was achieved in groundwater, and persulfate was effectively distributed in the demonstration area – the combination of which ensured the degradation of PFASs and CAHs co-contaminants by in situ TAP. It was demonstrated that the reductions of perfluoroalkyl carboxylic acids (PFCAs) concentration in all monitoring wells were in the range of 43.7 %–66.0 % by in situ TAP compared to those maximum rebound values in groundwater, whereas no effective perfluoroalkane sulfonic acids (PFSAs) degradation was observed. The conversion of perfluoroalkyl acids (PFAAs) precursors was one of the main factors leading to the increase in PFCAs concentrations in groundwater during in situ TAP. CAHs were effectively degraded in most monitoring wells, and furthermore, no inhibitory effects of CAHs and Cl− on the degradation of PFASs were observed due to the presence of sufficient persulfate. Additionally, there were significant increases in SO42− concentrations and reductions of pH values in groundwater due to in situ TAP, warranting their long-term monitoring in groundwater. The integrated field and laboratory investigations demonstrated that the reductions in PFCAs and CAHs concentrations can be achieved by the oxidative degradation of in situ TAP.

Seasonal distribution, source apportionment and risk assessment of polycyclic aromatic hydrocarbons in groundwaters in Owo, Southwestern Nigeria

Abstract The study focused on evaluating the seasonal distribution, source apportionment, and probabilistic risk assessment of polycyclic aromatic hydrocarbons (PAHs) in groundwater. Groundwater samples were obtained from Owo, southwestern Nigeria and subjected to liquid–liquid extraction and quantified using gas chromatography–mass spectrometry. Total PAH concentrations varied from about 180 to 23,600 ng/L during the dry season. The wet season, on the other hand, exhibited a wider range, from about 1,550 to 150,000 ng/L. Seasonal variations were also found in PAH types and concentrations, with relatively higher concentrations recorded during the wet season. Diagnostic ratios and positive matrix factorization indicated that coal/biomass combustion and traffic-related vehicular emissions were the prevalent sources of PAHs in groundwater. Health risk assessment indicated potential carcinogenic risks (incremental lifetime cancer risk (ILCR) > 1E − 04), while ecological assessment suggested medium (RQNC < 800 and RQMPC ≥ 1) and high ecological risks (RQNC ≥ 800 and RQMPC ≥ 1). The study reflected the need for effective mitigation strategies.

Evaluating the potential of wax impregnated reactive components for long-term acenaphthene removal

The catalytic oxidation of acenaphthene (ANA) was investigated using a controlled-release persulfate candle (PSC) and Fe(II) candle (Fe(II)C) to provide long-lasting oxidation conditions during groundwater remediation. To the best of our knowledge, this study is the first attempt to compare the pseudo-first-order rate constant (kobs) and % removal of ANA oxidation using PSC/Fe(II)C, PS solution (PSaq)/Fe(II) solution (Fe(II)aq), PSC/Fe(II)aq, and PSaq/Fe(II)C systems. The kobs and % removal of ANA in the PSC/Fe(II)C system exceeded those in the other systems. The optimal degradation conditions used were 0.1 mM ANA; 3.08 mM equilibrium concentration of PS (Ce,PS) released from PSC (controlled-release rate constant, kcr = 7.731 day−1); 5.673 mM equilibrium concentration of Fe(II) (Ce,Fe(II)) released from Fe(II)C (kcr = 3.796 day−1); unadjusted pH (~7.0); and 25 °C. Radical scavenger studies and electron spin resonance (ESR) spectra showed that sulfate (SO4•−) and hydroxyl (•OH) radicals were involved in the ANA oxidation, but •OH was the dominant radical species in the PSC/Fe(II)C system. Cl−, SO42−, and HCO3− acted as radical scavengers. The introduction of hydroxylamine (HA) into the PSC/Fe(II)C system resulted in a notable enhancement of ANA removal efficiency, increasing it from 51.8 % to 82.6 % within 10 min. Additionally, the PSC/Fe(II)C + HA system exhibited a higher Fe(II) consumption efficiency of 96.6 %, surpassing that of the PSC/Fe(II)aq + HA system, which registered an efficiency of 88.6 %. Intermediate byproducts after 24 h of reaction were detected as non-toxic byproducts by liquid chromatography-mass spectrometry (LC-MS). The PSC/Fe(II)C system would be beneficial for the remediation of polycyclic aromatic hydrocarbons in groundwater due to the continuous supply of Fe(II) and PS for a long time.

Response of Microbial Community Stability to Chemical Oxidation Remediation Process in a Petroleum Hydrocarbon Contaminated Groundwater Site

The stability of the microbial community is a vital indicator of microbial ecosystems. However, the mechanism of microbial community stability during in situ chemical oxidation in petroleum-hydrocarbon-polluted groundwater is unclear. This study analyzed the biomass, diversity, co-occurrence network feature and negative cohesion of microbial community at different stages to identify the changes in microbial community stability under chemical oxidation. In addition, microbial module compositions and crucial functions were analyzed to further explore the reason for the change in community stability at the module level. Multiple regression analysis was conducted to explore the microbial module explanatory degree to microbial community stability changes. The results indicated that the microbial community stability was destroyed by chemical oxidation. The carbon source effect was the main reason in the early oxidation stage, while the oxidation stress effect was the main reason in the late oxidation stage. Most microbial modules were transformed from K-strategists to r-strategists, and modular keystones were transformed to stress-tolerant species in the oxidation stage. This study suggested that microbial clusters were essential indicators of the microbial community in petroleum hydrocarbon groundwater during the chemical oxidation period.

Adsorption of total petroleum hydrocarbon in groundwater by KOH-activated biochar loaded double surfactant-modified nZVI

Introduction: Crude oil and petroleum hydrocarbon contamination is commonly found in the soil and groundwater during the various processes of mining, processing, and utilization due to issues such as inefficient environmental management, random wastewater discharge, and storage tank leakage.To address this issue, we will use corn stalk biochar (SBC) and surfactants to improve the stability and chemical reactivity of nZVI, thereby enhancing its ability to remove pollutants, and explore the adsorption effect and mechanism of composite materials for petroleum hydrocarbons.Methods: Modified corn stalk biochar (SBC) was synthesized through high-temperature carbonization and KOH activation. Subsequently, the iron/carbon composite PN-nZVI@SBC (PNMSBC) was prepared by loading nano zero-valent iron modified with dual surfactants, and it was adopted to adsorb total petroleum hydrocarbons(TPH) in groundwater. The physical and chemical properties, surface patterns, and elemental mapping of PNMSBC particles were analyzed using SEM, EDS, TEM,XRD, BET, and FTIR spectroscopy. Kinetics and isotherm tests were performed to evaluate the adsorption properties of the composites. TPH adsorption was dependent on ionic strength, initial TPH concentration, as well as pH. The adsorption mechanism combining XPS and EPR spectroscopy was explored.Results: The characterization results by SEM and TEM showed that the particle size of nZVI particles modified by surfactants became smaller, and the dispersibility was enhanced. The characterization results by XRD and FTIR confirmed the successful preparation of the composites. The BET results showed that MSBC and PNMSBC were mesoporous structures. The characterization results indicated that Polyvinylpyrrolidone (PVP) and Sodium oleate (NaOA) inhibited the oxidation of nZVI while effectively improving its reactivity. The result of the experiments on adsorption showed that the removal of TPH by PNMSBC followed Freundlich isotherm and pseudo-second-order kinetic models, thus suggesting that the main adsorption processes comprise chemisorption and multilayer heterogeneous adsorption. The adsorption capacity of PNMSBC was increased by the abundance of macro and microporous structures. To be specific, a maximum Langmuir adsorption capacity (qm) was achieved as 75.26 g/g. The result of batch experiments indicated that PNMSBC continuously removed considerable TPH under a wide pH range from 2 to 6. The adsorption mechanism of PNMSBC includes surface adsorption, oxidation, complexation, and electrostatic interaction.Discussion: In brief, PNMSBC has a promising application for the adsorption of TPH in groundwater remediation.

Enhanced removal of cis-1,2-dichloroethene and vinyl chloride in groundwater using ball-milled sulfur- and biochar-modified zero-valent iron: From the laboratory to the field

Sulfidated zero-valent iron (ZVI) and biochar-supported ZVI have received increasing attention for their potential to dechlorinate trichloroethylene. However, minimal data are available regarding the combined effect of sulfur and biochar ZVI on trichloroethylene byproducts. The primary aim of the current study is to determine whether sulfur- and biochar-modified ZVI (ZVI-BC-S) enhances the removal of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) from groundwater. Results show that biochar and sulfur facilitated the milling of ZVI-BC-S into micro- and nanoscale particles and increased FeS formation. Moreover, the rates of cDCE and VC removal by ZVI-S increased by 30.1% and 30.2%, respectively, compared to those obtained with ZVI, owing to enhanced dechlorination via β-elimination by sulfur. Meanwhile, treatment with ZVI-BC-S harnessed the benefits of biochar and sulfur to enhance the cDCE and VC removal rates by 62.0% and 67.7%, respectively. Mechanistically, biochar enhanced the corrosion of ZVI-S to increase FeS production and enhance the electron transfer, β-elimination, and hydrogenolysis involved in cDCE and VC dechlorination. The effectiveness of ZVI-BC-S was confirmed in a field demonstration, during which cDCE and VC concentrations significantly decreased within 10 days following injection. The findings of this study can help inform the rational design of ZVI for in-situ remediation of chlorinated hydrocarbons in groundwater.

ASSESSMENT OF THE IMPACT OF GROUNDWATER TABLE FLUCTUATIONS ON THE TRANSFORMATION OF SUBSURFACE CONTAMINATION WITH PETROLEUM PRODUCTS

This paper describes the actual problem of groundwater contamination with petroleum products and its transformation under the influence of climatic factors. The global experience of studying the influence of groundwater table fluctuations on the transformation of petroleum contamination, in particular, the processes of redistribution of mobile petroleum products, dissolution, evaporation, and biodegradation of hydrocarbon compounds, as well as the difference between the actual thickness of a mobile petroleum product layer in porous media and the apparent thickness of a mobile petroleum product layer in a monitoring well was analyzed, which is important to plan remedial actions. The impact of groundwater table fluctuations on transformation of the petroleum contamination source within the warehouse of fuels and lubricants of the Boryspil airport was studied. As a result of groundwater table fluctuations, kerosene was “smeared” in the vadose zone, which led to an increase in the soil contamination area. During the observation period, a mobile kerosene layer almost disappeared when a groundwater table rose and restored when a groundwater table decreased, while the vadose zone was additionally contaminated since a new capillary zone was formed during each rise ofa groundwater table and kerosene. The long-term amplitude of groundwater table fluctuations was 2.4 m, and apetroleum contamination zone was also within these limits. During the observation period, the largest area of groundwater contamination with dissolved petroleum products was observed at the lowest groundwater table elevations in 2016. The highest concentration of dissolved hydrocarbons in groundwater (75.98 mg/dm3) wasfound within amobile kerosene lens. Beyond the mobile kerosene lens, spreading of groundwater contamination with dissolved hydrocarbons is limited. The analysis of the monitoring data of the petroleum contamination source within the warehouse of fuels and lubricants of the Boryspil airport indicates that at present subsurface contamination with petroleum products is localized, and its further spreading is not expected. It is recommended to continue in the future monitoring of the natural attenuation of subsurface contamination.

Estimation of Polycyclic Aromatic Hydrocarbons in Groundwater from Campania Plain: Spatial Distribution, Source Attribution and Health Cancer Risk Evaluation.

The aim of this study was to evaluate the concentrations of polycyclic aromatic hydrocarbons (PAHs) in 1168 groundwater samples of the Campania Plain (Southern Italy), taken using a municipal environmental pressure index (MIEP), and to analyze the distribution of these compounds to determine source PAHs using ratios of isomers diagnostic. Lastly, this study also aimed to estimate the potential health cancer risk in groundwaters. The data indicated that the highest concentration of PAHs was found in groundwater from Caserta Province and the contents of BghiP, Phe, and Nap were detected in the samples. The spatial distribution of these pollutants was evaluated using the Jenks method; moreover, the data indicated that incremental lifetime cancer risk ILCRingestion ranged from 7.31 × 10-20 to 4.96 × 10-19, while ILCRdermal ranged from 4.32 × 10-11 to 2.93 × 10-10. These research findings may provide information about the Campania Plain's groundwater quality and aid in the development of preventative measures to lessen PAH contamination in groundwater.

Analysis on Contamination Characteristics, Pollution Source Identification and Ecological Risk Assessment of Polycyclic Aromatic Hydrocarbons of Groundwater in a Large Coking Plant Site of Province

Polycyclic aromatic hydrocarbons (PAHs), as a highly toxic persistent organic pollutant, are commonly found in soil and water environments. In recent years, the pollution of PAHs in groundwater has attracted wide attention from scientists. To study the pollution characteristics and sources of polycyclic aromatic hydrocarbon in groundwater of the coking site, 16 PAHs priorly controlled by the US EPA were analyzed and discussed. In this study, we identified the contamination characteristics of PAHs in groundwater, analyzed the pollution sources of PAHs, and evaluated the ecological risk of PAHs in the coking site by combining statistical techniques, the positive matrix factorization (PMF) model, and risk quotient (RQ) methods. The results indicated that the total detection rate of PAHs in groundwater of the coking plant was 46.7%. The concentrations of PAHs in groundwater of the coking plant ranged from below the detection limit to 444.9 μg·L-1, with the average value of 1.88 μg·L-1. The concentration of PAHs in the groundwater of different production workshops was significantly different. The most polluted workshop was in the tar-refining area, and the concentration of 16 PAHs was 444.9 μg·L-1. Based on the PMF model, we identified the two primary contamination sources of PAHs in groundwater of the coking plant:① oil combustion and ② coal and biomass combustion and oil leakage. The contribution ratios of the two sources to PAHs of groundwater were 38.6% and 61.4%, respectively. The results of the ecological risk assessment indicated that Σ16PAHs in groundwater of the coking plant had high ecological risk, and the ecological risk of single PAHs in 53.4% of the groundwater sampling site was at a high ecological risk level. In conclusion, it is urgent to carry out the treatment and restoration of the groundwater environment in the coking plant site.

Solubilization and remediation of polycyclic aromatic hydrocarbons in groundwater by cationic surfactants coupled nanobubbles: Synergistic mechanism and application

Polycyclic aromatic hydrocarbons pose a severe threat to groundwater and the soil environment. Improving the efficiency of the surfactant-enhanced remediation (SER) technique is a research hotspot. Nanobubbles (NBs) were introduced to enhance the solubilization effect of cationic surfactant dodecyltrimethylammonium bromide (DTAB) on phenanthrene (PHE). The interaction between NBs and DTAB was favorable in reducing the critical micelle concentration of DTAB. The equilibrium solubilization of DTAB to PHE was upgraded by up to 30.4% with the synergy of NBs. The effect of DTAB concentration on the stability of NBs was an essential reason for the different upgrade rates. The kinetic study showed that the process of equilibrium solubilization was accelerated, while NBs were “consumed”. Based on the classic DLVO framework, OH– and inorganic ions in groundwater can participate in the formation of micelles and change the double electric layer thickness of bubbles, which are the key factors affecting the stability of NBs. The results revealed the colloidal interface characteristics and the particle behavior of micelles with NBs, providing new insight into the combined application of micelles or vesicles with NBs.

Polycyclic aromatic hydrocarbons in groundwater of oil-rich regions of upper Brahmaputra Valley, India: linkages of colloidal transport

Polycyclic aromatic hydrocarbons in groundwater of oil-rich regions of upper Brahmaputra Valley, India: linkages of colloidal transport