Review on carbon-based adsorbents from organic feedstocks for removal of organic contaminants from oil and gas industry process water: Production, adsorption performance and research gaps.

Large amounts of process water with considerable concentrations of recalcitrant organic contaminants, such as polycyclic aromatic hydrocarbon (PAHs), phenolic compounds (PCs), and benzene, toluene, ethylbenzene, and xylene (BTEX), are generated by several segments of oil and gas industries. These segments include refineries, hydraulic fracturing (HF), and produced waters from the extraction of shale gas (SGPW), coalbed methane (CBMPW) and oil sands (OSPW). In fact, the concentration of PCs and PAHs in process water from refinery can reach 855 and 742 mg L-1, respectively. SGPW can contain BTEX at concentrations as high as 778 mg L-1. Adsorption can effectively target those organic compounds for the remediation of the process water by applying carbon-based adsorbents generated from organic feedstocks. Such organic feedstocks usually come from organic waste materials that would otherwise be conventionally disposed of. The objective of this review paper is to cover the scientific progress in the studies of carbon-based adsorbents from organic feedstocks that were successfully applied for the removal of organic contaminants PAHs, PCs, and BTEX. The contributions of this review paper include the important aspects of (i) production and characterization of carbon-based adsorbents to enhance the efficiency of organic contaminant adsorption, (ii) adsorption properties and mechanisms associated with the engineered adsorbent and expected for certain pollutants, and (iii) research gaps in the field, which could be a guidance for future studies. In terms of production and characterization of materials, standalone pyrolysis or hybrid procedures (pyrolysis associated with chemical activation methods) are the most applied techniques, yielding high surface area and other surface properties that are crucial to the adsorption of organic contaminants. The adsorption of organic compounds on carbonaceous materials performed well at wide range of pH and temperatures and this is desirable considering the pH of process waters. The mechanisms are frequently pore filling, hydrogen bonding, π-π, hydrophobic and electrostatic interactions, and same precursor material can present more than one adsorption mechanism, which can be beneficial to target more than one organic contaminant. Research gaps include the evaluation of engineered adsorbents in terms of competitive adsorption, application of adsorbents in oil and gas industry process water, adsorbent regeneration and reuse studies, and pilot or full-scale applications.

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.

Pristine and engineered biochar for the removal of contaminants co-existing in several types of industrial wastewaters: A critical review.

Biochar has been widely studied as an adsorbent for the removal of contaminants from wastewater due to its unique characteristics, such as having a large surface area, well-distributed pores and high abundance of surface functional groups. Critical review of the literature was performed to understand the state of research in utilizing biochars for industrial wastewater remediation with emphasis on pollutants that co-exist in wastewater from several industrial activities, such as textile, pharmaceutical and mining industries. Such pollutants include organic (such as synthetic dyes, phenolic compounds) and inorganic contaminants (such as cadmium, lead). Multiple correspondence analyses suggest that through batch equilibrium, columns or constructed wetlands, researchers have used mechanistic modelling of isotherms, kinetics, and thermodynamics to evaluate contaminant removal in either synthetic or real industrial wastewaters. The removal of organic and inorganic contaminants in wastewater by biochar follows several mechanisms: precipitation, surface complexation, ion exchange, cation-π interaction, and electrostatic attraction. Biochar production and modifications promote good adsorption capacity for those pollutants because biochar properties stemming from production were linked to specific adsorption mechanisms, such as hydrophobic and electrostatic interactions. For instance, adsorption capacity of malachite green ranged from 30.2 to 4066.9 mg g-1 depending on feedstock type, pyrolysis temperature, and chemical modifications. Pyrolyzing biomass at above 500 °C might improve biochar quality to target co-existing pollutants. Treating biochars with acids can also improve pollutant removal, except that the contribution of precipitation is reduced for potentially toxic elements. Studies on artificial intelligence and machine learning are still in their infancy in wastewater remediation with biochars. Meanwhile, a framework for integrating artificial intelligence and machine learning into biochar wastewater remediation systems is proposed. The reutilization and disposal of spent biochar and the contaminant release from spent biochar are important areas that need to be further studied.