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High boron (B) levels in oil and gas produced waters prevent its beneficial reuse as irrigation water without proper treatment. Aluminum (Al) electrocoagulation (EC) is a promising technology for B removal, but further research and development is needed to optimize EC for use in removing B from produced waters. To this end, B removal by adsorption onto insoluble aluminum hydroxide solids, generated by EC in simulated brines (up to 50,000 mg/L NaCl) and real oilfield produced waters, was studied. B removal during EC was greater than when aluminum hydroxide solids formed by EC were subsequently exposed to B containing solutions. Working parameters affecting B removal during the EC process, including current, total dissolved solid (TDS), temperature, pH, scale-forming cations and organic matter, were investigated to explore ways to achieve higher B removal. Boron removal increased with increased current loading and time, and with the concomitant increased Al solids concentration. However, too high a current loading limited B removal because of a change in the structure of the aluminum hydroxide solids. Higher TDS decreased B removal slightly, but lower TDS concentrations limited the use of higher current loadings. Temperature increased during EC treatment, particularly at higher current loadings, and this inhibited B removal due to an accelerated aggregation of amorphous Al solids into larger, denser, and presumably more crystalline particles. The best B removal occurred at pH 8, corresponding to a slightly positive zeta potential for aluminum hydroxide and a small but significant fraction of negatively charged B species. Scale-forming cations such as Ba 2+ and Sr 2+ had no obvious effect on the EC process. The presence of high concentrations of Mg 2+ and Ca 2+ resulted in low bulk pH values during the EC process and greater formation of solid products, but B removal did not decrease during a pH-controlled (pH = 8) EC process with these divalent cations present. Two produced water samples collected from oilfields in Kansas, US were treated using EC for 1 h, resulting in up to ~70 % B removal from solution with a current loading of 6.67 A/L, and up to 78 % with 13.33 A/L., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Produced water is the wastewater formed when water is brought from subsurface reservoirs during oil or gas extraction. Currently, produced water is mainly treated using conventional trains that contain adsorbates, membrane filters, phase separators and cyclones. This paper reviewed the detailed characteristics of oilfield-produced water and the assessment of multiple technologies at primary, secondary, and tertiary treatments stages. The effectiveness of the treatment technology from the production of waste, energy requirements, usage of chemicals and the treatment effect of contaminants has been discussed. Then a qualitative assessment was presented in terms of energy requirements, robustness, flexibility, waste generation, modularity, and mobility, which has become critical to the development and application prospects of any technology., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Oilfield produced water (OPW) is one of the most important by-products, resulting from oil and gas exploration. The water contains a complex mixture of organic and inorganic compounds such as grease, dissolved salt, heavy metals as well as dissolved and dispersed oils, which can be toxic to the environment and public health. This article critically reviews the complex properties of OPW and various technologies for its treatment. They include the physico-chemical treatment process, biological treatment process, and physical treatment process. Their technological strengths and bottlenecks as well as strategies to mitigate their bottlenecks are elaborated. A particular focus is placed on membrane technologies. Finally, further research direction, challenges, and perspectives of treatment technologies for OPW are discussed. It is conclusively evident from 262 published studies (1965-2021) that no single treatment method is highly effective for OPW treatment as a stand-alone process however, conventional membrane-based technologies are frequently used for the treatment of OPW with the ultrafiltration (UF) process being the most used for oil rejection form OPW and oily waste water. After membrane treatment, treated effluents of the OPW could be reused for irrigation, habitant and wildlife watering, microalgae production, and livestock watering. Overall, this implies that target pollutants in the OPW samples could be removed efficiently for subsequent use, despite its complex properties. In general, it is however important to note that feed quality, desired quality of effluent, cost-effectiveness, simplicity of process are key determinants in choosing the most suitable treatment process for OPW treatment., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In this study, the recent advances in standalone membrane technologies were investigated for produced water treatment and reclamation. The effect of operating parameters (i.e. temperature, flow rate, velocity, and pH) on membrane fouling were studied in detail. Results showed that microfiltration suffered severe fouling from suspended particles and flux deterioration reacheed 90 % in less than 1 h. Ultrafiltration showed enhanced removal of oil up to 95 % however, membrane hydrophilicity needs to be increased and the suspended particulates should be minimized to sustain operation. Nanofiltration was more prone to fouling with maximum oil removal 99 % and removal of 10 % to 20 % of dissolved solids. Reverse osmosis (RO) performance decreased rapidly against mild salts and oil concentrations in the range of 2000 ppm salts and 150 ppm crude oil and was therefore not suitable for standalone. Developed technologies such as membrane distillation (MD) and forward osmosis (FO) showed remarkable operation stability against high concentrations of oil and salts (1000 ppm crude oil and up to 150,000 ppm of salts). Hybridization of nanofiltration or RO with MD or FO processes showed promising results in pilot tests. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Graphitic carbon nitride (GCN) photocatalyst was incorporated in nanofibers. • Photocatalytic nanofibers were electrospun on alumina hollow fiber membranes. • Cross-flow microfiltration demonstrated purification of oilfield produced water. • Hydrophilic, highly-porous nanofiber coating exhibited excellent fouling resistance. • Photodegradation ability of GCN offered cleaning performance of robust membranes. Abstract Cost-effective purification technology of oilfield produced water (OPW) is becoming a global challenge for future petroleum exploration and production industry. Energy-efficient operation of membrane separation is potentially promising. However, severe fouling problem of oil droplets demands new robust and fouling-resistant membranes with high permeability and rejection efficiency. Here, we propose a photocatalytic nanofiber-coated inorganic hollow fiber membrane suitable for OPW treatment. The membrane was fabricated by coating polyacrylonitrile (PAN) nanofiber incorporated with graphitic carbon nitride (GCN) photocatalyst on an alumina (Al 2 O 3) hollow fiber membrane. While the highly porous coating made of smooth hydrophilic nanofibers facilitated water permeation, the coating effectively captured oil droplets in its opening, resulting in a better rejection efficiency of oil contaminants. Its sparse mesh morphology prevented oil contaminants to form dense fouling film on the membrane surface and maintained high permeate flux even after 180 min filtration. The best permeate flux of 640 L·m−2·h−1 and oil rejection percentage of 99% were recorded for 180 min crossflow filtration of OPW at 2 bar along with the highest pure water flux of 816 L·m−2·h−1. The photocatalytic activity of GCN enabled the coating to degrade the captured oil contaminants under UV irradiation, demonstrating permeate flux of 577 L·m−2·h−1 and oil rejection of 97% after three cycles of 180 min filtration. The excellent fouling resistance and cleaning performances of the membrane are considerably beneficial for a long-term repeated filtration operation. This work will motivate researchers to develop nanofiber-coated hollow fiber membranes for future membrane separation technology. [ABSTRACT FROM AUTHOR]

Separation and purification of oilfield produced water (OPW) is a major environmental challenge due to the co-production of the OPW during petroleum exploration and production operations. Effective capture of oil contaminant and its in-situ photodegradation is one of the promising methods to purify the OPW. Based on the photocatalytic capability of graphitic carbon nitride (GCN) which was recently rediscovered, photodegradation capability of GCN for OPW was investigated in this study. GCN was synthesized by calcination of urea and further exfoliated into nanosheets. The GCNs were incorporated into polyacrylonitrile nanofibers using electrospinning, which gave a liquid-permeable self-supporting photocatalytic nanofiber mat that can be handled by hand. The photocatalytic nanofiber demonstrated 85.4% degradation of OPW under visible light irradiation, and improved the degradation to 96.6% under UV light. Effective photodegradation of the photocatalytic nanofiber for OPW originates from synergetic effects of oil adsorption by PAN nanofibers and oil photodegradation by GCNs. This study provides an insight for industrial application on purification of OPW through photocatalytic degradation under solar irradiation. [ABSTRACT FROM AUTHOR]

The application of the ceramic membrane separation processes are suitable for the generation of a treated effluent with high quality, enabling the reuse of the effluent and consequently reducing the emission of contaminants into the sea, the chemical consumption and the need to capture and treat seawater. Besides these advantages, membrane systems represent a reduction in weight and footprint, which are very limited on oil platforms. In this study, a technical analysis of an industrial unit to treat produced water was integrated with the seawater treatment system and carried out using data obtained from pilot scale tests, conducted with an industrial zirconia oxide ceramic membranes module, and from actual conventional systems operating data. Considering the integrated configuration, the additional investment cost was estimated at MUS$ 7.3 and it was possible to estimate that the extra cost would be recovered in about seven years, considering a unit capable of generating 1500 m 3 h −1 of treated effluent. This scenario represents a favorable condition for the application of ceramic membranes for oilfield produced water treatment on industrial units and its potential used on offshore oil production platforms. [ABSTRACT FROM AUTHOR]

[Display omitted] • A polymer reaction method was proposed to prepare acrylate-modified cationic flocculants. • Microfluidic technology has been applied to study the aggregation process of flocculants on oil droplets. • The flocculant had promising application for oilfield produced water. Introducing a lipophilic group into a cationic polymer flocculant can effectively improve the flocculation performance for treating oilfield-produced water. Copolymerization of acrylate and cationic monomers is the most commonly used method; however, the acrylate content in the copolymer is limited by its solubility in water. In this study, a polymer reaction method was proposed to introduce a suitable acrylate into a cationic polymer to improve flocculation performance. Acrylate was introduced into the copolymer (PDD) of methacryloyloxyethyltrimethylammonium chloride (DMC) and diallylamine (DAA) via the reaction between acrylate and the secondary amine in PDD. The effects of the acrylate type, amount of acrylate introduced, and reaction conditions on the flocculation performance of the product were investigated. The experimental results showed that the hydroxy-terminated acrylate-modified PDD exhibited considerably better performance than PDD, especially the hydroxyethyl acrylate (HEA)-modified PDD (PDD-HEA). When the dosage was 20 mg/L, the oil removal of PDD-HEA was 95.8 %, which was 1.5 times higher than that of PDD. The introduction of HEA can improve the ability of PDD to aggregate oil droplets, but it causes curling of the PDD molecular chain and weakens its bridging and flocculation ability. Therefore, a higher amount of HEA introduced does not necessarily lead to a better performance of the PDD-HEA. The most suitable modification degree of the structural units in PDD was 3.3 %. This study provides new insights into the synthesis and properties of hydrophobically modified cationic polymer flocculants and is helpful for the development of flocculants for oilfield-produced water treatment. [ABSTRACT FROM AUTHOR]

Oilfield produced water (OPW) contains not only a complex mixture of organic and inorganic compounds, but also a significant amount of suspend solids and oil and grease (O&G), that need to be almost completely removed prior to reinjection (reuse) in oilfield reservoirs. For the separation of both contaminants from OPW, membrane technology has been described as a potential solution. Therefore, for this study, a multichannel ultrafiltration ceramic membrane (ZrO 2 ) was used in experiments. The effect of operational conditions on membrane filtration efficiency and the membrane cleaning strategy were investigated using real OPW. The permeate obtained with the membranes was free of suspended solids and presented an O&G content under 5 mg L −1 . Based on the results obtained, it is possible to highlight the ceramic membrane separation process as a promising technology for treating OPW in offshore units, being capable to generate a permeate stream suitable for reinjection in restrictive oilfield reservoirs. [ABSTRACT FROM AUTHOR]

Abstract: Oil and gas field wastewater or produced water is a significant waste stream in the oil and gas industries. In this study, the performance of a membrane sequencing batch reactor (MSBR) and membrane sequencing batch reactor/reverse osmosis (MSBR/RO) process treating produced wastewater were investigated and compared. The MSBR was operated in different hydraulic residence time (HRT) of 8, 20 and 44h. Operation results showed that for a HRT of 20h, the combined process effluent chemical oxygen demand (COD), total organic carbon (TOC) and oil and grease (O&G) removal efficiencies were 90.9%, 92% and 91.5%, respectively. The MSBR effluent concentration levels met the required standard for oil well re-injection. The RO treatment reduced the salt and organic contents to acceptable levels for irrigation and different industrial re-use. Foulant biopsy demonstrated that the fouling on the membrane surface was mainly due to inorganic (salts) and organic (microorganisms and their products, hydrocarbon constituents) matters. [Copyright &y& Elsevier]

This experimental paper deals with the development of a hybrid biological reactor for the treatment of a synthetic oilfield produced water under an increase in total dissolved solids (TDS) concentration. To comply with strengthening regulations concerning produced water discharge and peculiar produced water compositions, a moving bed biofilm reactor (MBBR) consisting in a combination of free activated sludge and moving biofilm supports was compared to a fixed bed hybrid biological reactor (FBHBR) consisting in a combination of free activated sludge and a fixed biofilm support. After a 216 days experimental period, the MBBR and the FBHBR were efficient to treat a synthetic produced water with chemical oxygen demand (COD) removal rate above 90% under an increase in TDS concentrations from 1.5 to 20 g·L−1. Ecotoxicity measurements on freshwater and marine microorganisms revealed an absence of toxicity on treated waters. A decrease in bacterial diversity indices with respect to the inoculum was observed in both bioreactors. This suggests that the increase in TDS concentrations caused the predominance of a low number of bacterial species. [ABSTRACT FROM AUTHOR]

Kuwait is a desert country with scarce water resources and increasing population, which means that more water sources should be tapped, not only for irrigation but also to provide for the citizens of the country. Oilfield waters are produced at increasing levels in Kuwait, being a foremost oil producer in the gulf region. It contains lots of contaminants that, if left untreated, will pollute the surrounding areas when disposed of improperly. This paper examines the possibility of treating oilfield water to be used as an additional resource for irrigation and for improving its treatment prior to proper disposal. The water treatment concept being introduced was performed through several treatment stages including biological treatment combined with nitrification and denitrification (sedimentation), chemical treatment (flocculation and coagulation), reverse osmosis, and disinfection using ultraviolet process as the final treatment process. This was accomplished through the combination of conventional and membrane technology process. After the treatment, the water samples were tested and compared with the parameters set by the Kuwait Environment Public Authority (KEPA) for irrigation, as well as disposal. The results indicated that the treatment methods are efficient in treating oilfield water as the treated samples showed significant reduction in original concentration, such as to name a few, total suspended solids, total dissolved solids, ammonia, total Kjeldahl nitrogen, sulfide, turbidity, phosphate and biological oxygen demand with a reduction percentage of 94.23%, 95.86%, 76.47%, 80.39%, 94.59%, 98.0%, 54.54%, 80.19%, respectively. Grease, oil and chemical oxygen demand level can be lowered from the treated water by further treatment. Oilfield water can, therefore, be utilized for irrigation and eventual allowable discharge to sewage network conventional wastewater treatment methods combined with membrane technology. [ABSTRACT FROM AUTHOR]

In this study, an organophosphonate scale inhibitor, ethylenediamine tetra(methylenephosphonic acid) sodium salt (EDTMPA-Na) draw solution, was adopted for alleviating the membrane fouling in the forward osmosis (FO) application of produced water treatment. Compared with the typical NaCl draw solution, the employment of EDTMPA-Na draw solution can alleviate the membrane fouling effectively and therefore achieve a higher water recovery rate (60.6%) after a continuous 48-h test. And the mechanism of membrane fouling control with EDTMPA-Na draw solution has been systemically explored by varying the feed or draw solution compositions. The results turn out that the leakage of EDTMPA-Na draw solute to the feed solution can alleviate the formation of gypsum scales on the membrane surface effectively, ascribed to its excellent scale inhibition ability and the unique diffusion route of the draw solute (resulting in a relative higher concentration of EDTMPA-Na near the membrane surface) in FO process. And the alleviation of membrane scaling can further mitigate the accumulation of organic foulant on the FO membrane. This study may provide an efficient strategy for alleviating the membrane fouling in the FO application of produced water treatment. Image 1 • EDTMPA-Na draw solution can alleviate membrane fouling effctively in FO process. • 60.6% freshwater can be recovered from simulated oilfield produced water. • High J W and low J S are achieved with scale inhibitor of EDTMPA-Na draw solution. • Scaling control derives from its intrinsic property and unique diffusion route. • Alleviation of membrane scaling further mitigates the organic fouling. [ABSTRACT FROM AUTHOR]