Assessing benzene and toluene adsorption with peat depth: Implications on their fate and transport

Hydrogeochemical and isotopic evidences of the underlying produced water intrusion into shallow groundwater in an oil production area, Northwest China

The extensive use of fossil fuels (e.g., oil) poses a hidden danger to groundwater quality. However, inorganic pollution has received limited attention compared to organic pollution. In this study, the potential contaminant sources to shallow groundwater were investigated using hydrochemical (e.g., major and trace elements) and isotopic (δ2H and δ18O) methods at an oil field, northwest China, with emphasis on the identification of produced water (PW; oil production-related water) intrusion. The results showed that the groundwater samples can be chemically and isotopically classified into two groups: Group A (severely polluted) and B (slightly or non- polluted). The hydrochemical characteristics of Group A were similar to that of PW, with a comparable Na+/Cl- ratio and elevated levels of Na+, Ca2+, Cl-, Br-, Sr, Ba, Li, B and total volatile organic compounds (TVOCs; volatile and semi-volatile) concentration, but lower HCO3- and SO42- contents, and depleted δ2H and δ18O, which was not suitable for drinking. Groundwater salinity sources involve mineral dissolution (silicate, carbonate and evaporite), cation exchange and anaerobic microbial degradation, as well as deep PW intrusion (especially in Group A). The Cl mixing model showed that PW contributed 13.63-27.78 % to Group A, supported by the results of the isotope mixing model based on δ2H and δ18O (24.43-33.29 %). An overall pollution conceptual model involves three modes: fracturing, surface infiltration, and groundwater lateral runoff. This study validates the effectiveness of Na, Cl, Br, Sr, Ba, Li and B as favorable tracers for monitoring PW intrusion.

Sorption and desorption of naphthenic acids on reclamation materials: Mechanisms and selectivity of naphthenic acids from oil sands process water

This study investigated the application of materials peat-mineral mix (PT) and Pleistocene fluvial sands from different location (PF-1 and PF-2) obtained from surface mining of oil sands as sorbents of naphthenic acids (NAs) from oil sands process water (OSPW). To understand the sorption properties and mechanisms of NAs in the materials, sorption and desorption studies were performed using decanoic acid (DA) and 5-phenylvaleric acid (PVA). Additionally, the removal efficiency was evaluated using real OSPW to understand the effect of NA structure on sorption. Equilibrium of DA and PVA was reached at 2 days for PT, and 3 and 6 days for PF materials, respectively. Langmuir isotherm best fitted the equilibrium data. Maximum sorption capacities for DA and PVA were, respectively, 16.8 × 10³ and 10⁴ mg/kg for PT, 142.9 and 81.3 mg/kg for PF-1, and 600 and 476.2 mg/kg for PF-2. Hydrophobic interactions, hydrogen bonding, and π-π interaction were the main sorption mechanisms. Desorption of model compounds from post-sorption materials was not observed for 14 days. The removal of NAs from real OSPW ranged from 20 to 54%. PT is the most promising sorbent of NAs from OSPW because it partially removed NAs with a wide range of molecular weights and structures at very low dosage. Sorption of NAs was affected by the total organic carbon of the materials, emphasizing the hydrophobic interaction as an important sorption mechanism. The results suggest that some mobility of NAs is expected to take place if the reclamation materials come in contact with OSPW, which might occur in an oil sands reclamation landscape.

Response of environmental factors to attenuation of toluene in vadose zone

Contaminated groundwater migrates in reverse direction under capillary force in vadose zone, and the attenuation process of pollutant adsorption and microbial degradation changes the environment of vadose zone. In this study, the response of toluene to environmental factors during reverse migration and attenuation of toluene from aquifer to vadose zone was studied by column experiment and experimental data analysis. The changes of environmental factors, including potential of hydrogen (pH), dissolved oxygen (DO), and oxidation-reduction potential (ORP), and toluene concentration were monitored by soil column experiment under sterilized and non-sterilized conditions. The 16S rRNA molecular biological detection technology was used to quantitatively analyze the impact of microbial degradation on the environment. Finally, the correlation between environmental factors and concentration in the attenuation process of toluene in the vadose zone was quantitatively studied by Pearson Correlation Coefficient (PCC) and multivariate statistical equation. The results showed that pH was primarily affected by microbial degradation, and DO and ORP were primarily affected by both adsorption and microbial degradation. The attenuation of toluene was divided into two stages: adsorption dominated (0~26 d) and microbial degradation dominated (26~55 d). The degradation amounts of microorganisms at each position in the non-sterilized column from bottom to top were 9.37%, 55.34%, 68.64%, 75.70%, 66.03% and 42.50%. At the same time, the article proposes for the first time that there is an obvious functional relationship between environmental factors (DO, ORP, pH), time (t) and concentration (C_Toluene):C_Toluene=C₀+A100t+Bα+Cβ+D100γ, (α,β,γ are the pH, DO and ORP of capillary water, respectively; A, B, C and D are all undetermined coefficients), R² > 0.95. The results of this study may facilitate the use of simple and easy-to-obtain environmental factors to characterize the dynamic process of pollutant concentration changes.