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Owing to the soaring urge to meet the demand for oil and gas on different frontiers, its exploration all over the world is of paramount importance. Exploration and production of oil calls for handling a huge volume of associated water, produced along with it, referred to as Oilfield Produced Water (OFPW). OFPW is considered a potential threat to the environment due to the presence of toxic constituents such as dissolved and dispersed oil compounds, dissolved formation minerals, production chemical compounds, production solids (formation, corrosion, scale, bacteria, waxes, and asphaltenes), dissolved gases. This review is intended to provide information on OFPW, its constituents, impact, and treatment technologies of OFPW from various oilfields across the world. It presents a meticulous analysis of the scope of reusing OFPW instead of freshwater for various processes such as well drilling and completion, re-injection to the reservoir for pressure maintenance, and water flooding process for secondary recovery of crude oil. The reuse of OFPW can reduce the demand for fresh water and turn the wastewater into useable water resources after proper treatment. The paper provides rigorous information on the importance of developing an eco-friendly treatment process for the proper reuse and management of OFPW.

In this study, we synthesized a novel electrode for electrocatalytic adsorption by fabricating ACF‐TiO2 via the sol‐gel method and binding it with IrO2‐TaO2. The electrode's effectiveness in treating oilfield produced water (OPW) was evaluated using batch techniques. Comprehensive characterization, including scanning electron microscopy (SEM), energy‐dispersive spectrometry (EDS), Brunauer‐Emmett‐Teller (BET) analysis, and Fourier‐transform infrared (FTIR) spectroscopy, confirmed uniform TiO2 loading onto the ACF surface, preserving structural integrity. BET analysis indicated increased mesopore volume and enhanced organic adsorption capacity without compromising microporous structure. Additionally, FTIR analysis revealed the emergence of functional groups conducive to adsorption and catalytic reactions. Freundlich isotherms and pseudo‐first‐order kinetics best fit the adsorption data. Remarkably, even after five cycles, the electrode maintained high removal efficiencies for chemical oxygen demand (COD) and oil content at 91.35 % and 91.12 %, respectively. We further investigated the complex phenomena of material adsorption, electrochemical oxidation, and desorption during electrocatalytic adsorption, highlighting the importance of solid‐phase adsorption and liquid‐phase electrocatalytic oxidative decomposition in OPW treatment. Comparison with similar electrodes and DSA electrodes demonstrated the superior performance and practicality of the IrO2‐TaO2‐ACF(TiO2) electrode. Its cost‐effectiveness and regeneration method further enhance its applicability in real‐world scenarios, emphasizing its potential in water treatment. [ABSTRACT FROM AUTHOR]

The selection of an apt technology for the treatment of Oilfield Produced Water (OFPW) depends mainly on the quality of OFPW and methods of pre-and post-treatment processes. The most challenging part of the OFPW treatment process is the removal of Suspended Solid (SS), Oil & Grease (O&G) and dissolved organics. SS and O&G pose an acute problem to the membrane filtration system by fouling the membrane surface which increases operation & maintenance costs and decreases the life of the membrane. Fouling of the membrane surface is mainly attributed to the presence of low molecular weight aromatic compounds and naphthenic acids in the suspended and dissolved organic compounds. Thus, the removal of these suspended and dissolved organic compounds before membrane filtration proffers a challenge to the researchers. In this research, bioremediation process has been applied to remove the organic compounds and the performance and fouling behaviour of hollow fibre Microfiltration (MF), Ultrafiltration (UF) and Nanofiltration (NF) membranes after the bioremediation process has been analyzed in detail. The level of toxicity was determined by comparing the pollutants with the safe discharge limit for disposal into the environment set by Central Pollution Control Board (CPCB), India. The research presents its novelty by using a hydrocarbon-degrading bacteria, Pseudomonas aeruginosa for the Reduction of Organic Loads (ROL) from OFPW of Moran oil field of Upper Assam as a pre-treatment to membrane filtration. The Total Sum Corrected Area (TSCA) method through chromatographic analyses was used for this. The organic loads removal from OFPW by the TSCA method was found to be 67–100%, 100% and 100% after 7, 14 and 21 days of bioremediation respectively. The major parameters in feed OFPW of Moran oil field were found to be pH (7.5–9.3), Total Dissolved Solid (TDS) (1.79–4.75) ppt, O&G (1.78–2.8) ppt, Salinity (2.94–6.98) ppt, Chloride (Cl−) (1.6–3.86) ppt, Bicarbonate (HCO3−) (2.89–4.03) ppt. It was observed that the ranges of pollutants removal by NF was highest such as TDS (26–86%), salinity (81–86%), turbidity (78–94%), hardness (67–75%), O&G (96–99%), Cl− (80–89%) and HCO3− (95–97%).

In this study, a flat sheet ceramic membrane experimental device was constructed, and the thermodynamics of membrane fouling interface was studied for oilfield produced water. The flux of ceramic membrane in three kinds of model solutions were measured with time, as well as the surface tension, contact Angle and Zeta potential of solid. The thermodynamic mechanism of membrane fouling interface combined with XDLVO theory were explored for three kinds of model solutions. The thermodynamic study of the interface of ceramic plate membrane shows that the total interaction energy between membrane and oil droplets decreases with the increase of the distance between two interfaces at initial stage of membrane fouling, and finally transforms from the mutual attraction to the mutual repulsion. The total interaction energy between reservoir and oil droplet is shown as mutual attraction, and the total interaction energy decreases with the increase of the distance between reservoir and oil droplet interface. The zeta potential of crude oil was affected by salinity to some extent. The electrostatic shielding effect of the salt ions leads to a decrease in the ζ-potential of the three solutions. They are in the order: model solution A > model solution B > model solution C. This leads to a decrease in the electrostatic interaction (EL). And since the oil layer has the same composition as the oil droplets, the EL interactions in the three solutions can behave as mutual repulsion. [ABSTRACT FROM AUTHOR]

Oilfield Produced Water (OPW) has been identified as a viable solution to mitigate water scarcity in California's Central Valley. However, consumer perception on the use of OPW outside of the oil and gas industry remains unknown and poses a hurdle for large-scale adoption. This paper, based on 134 randomly selected residents of Kern County (California's largest oil-producing county and top agricultural region), examined attitudes towards OPW reuse. In the survey, more than half (52.3%) of participants said that they have heard about oilfield-produced water and other reclaimed waters. Findings also suggest that participants mostly preferred rain and stormwater, and interestingly scored OPW higher than industrial and black waters for irrigation purposes. Around 67% of the participants supported the use of oilfield-produced water for irrigating crops. Younger people (18–29 years) expressed greater concern about using OPW compared to the older residents. Given the drought conditions in Central Valley, policymakers might need to focus on a circular economy and mandate the use of OPW in Central Valley considering that this region's economy lies at the nexus of the O&G and agriculture industries. [ABSTRACT FROM AUTHOR]

Biofilm formation can help to mitigate the stress placed on organisms during biological treatment of high-salinity wastewaters, such as "produced water" resulting from oil and gas extraction. This study investigated the implementation of two different biofilm-based biological reactors, activated carbon as an adsorptive biofilm surface (Bio-GAC) and aerobic granular sludge (AGS), and a conventional activated sludge (CAS) reactor for the treatment of synthetic produced water (PW) under hypersaline conditions (85,000 mg/L NaCl). A mixture of benzyl alcohol, o-cresol, and phenol were used as a carbon source with concentrations of 100, 100, and 250 mg/L, respectively. The performance of Bio-GAC was higher than AGS, with overall removal efficiencies for aromatic compounds of 100% and 93%. The presence of catechol in all three reactors during the reaction cycle confirmed that biodegradation was occurring. The performance of CAS was significantly lower in terms of removal efficiency for aromatic compounds (73%) and resilience to high salinity. Scanning electron microscopy showed that biofilm-based biosystems establish stronger biofilm texture. Microbial community analysis showed that carbon source and biosystem type played a crucial role in selecting for microbiome structure. These findings show that biofilm reactors can be used to successfully biodegrade toxic organic contaminants in a high-salinity environment, and that the hybrid Bio-GAC process is particularly promising for treating PW. [ABSTRACT FROM AUTHOR]

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.

The corrosion behavior of Q235B carbon steel is investigated in water, LB medium, and oilfield produced water adding Pseudomonas fluorescens FSYZ01. After immersion at 30 °C for 13 days, the weight loss of carbon steel with this strain decreased by 32.23%, 54.07%, and 78.34%, respectively. X-ray diffraction (XRD) results show that P. fluorescens FSYZ01 inhibited conversion of iron oxides by hindering oxygen from approaching metal surface. Fourier transform infrared (FT-IR) and X-ray photoelectron spectrometer (XPS) results show that specific functional groups and bonds reacted with Fe(II/III) to form a dense and stable chelate-oxide protective layer, thereby inhibiting corrosion. Pyrolysis gas chromatography-mass spectrometer (Py-GCMS) results demonstrate the bacteria degraded C12 to C20 alkanes in oil. The inhibitory mechanism of crude oil-degrading bacteria P. fluorescens FSYZ01 on the carbon steel corrosion was proposed, so as to slow corrosion of oilfield produced water system pipeline and prolong its service life, helping to comprehend the microbial corrosion in the actual environment. [ABSTRACT FROM AUTHOR]

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]

In this study, a novel COF TABT @COF TATp modified magnetic MXene composite (CoFe 2 O 4 @Ti 3 C 2 @COF TABT @COF TATp) was synthesized by Schiff base reaction and irre-versible enol-keto tautomerization, and employed to establish a sensitive monitoring method for six thiophene compounds in oilfield produced water samples based on magnetic solid-phase extraction (MSPE) prior to gas chromatography coupled with a triple quadruple mass spectrometer (GC-MS/MS). The designed magnetic materials exhibited unexpected enrichment ability to target thiophene compounds and achieved good extraction efficiencies ranging from 83 % to 98 %. The developed MSPE/GC-MS/MS method exhibited good linearity in the range of 0.001–100 μg L−1, and obtained lower limits of detection ranging from 0.39 to 1.9 ng L−1. The spiked recoveries of thiophene compounds obtained in three oilfield produced water samples were over the range of 96.26 %−99.54 % with relative standard deviations (RSDs) less than 3.7 %. Notably, benzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene were detected in three oilfield-produced water samples. Furthermore, the material still kept favorable stability after six recycling experiments. The adsorption kinetics, adsorption isotherms as well as adsorption thermodynamics of thiophene compounds were investigated in detail to provide insight into the mechanisms. Overall, the present work contributed a promising strategy for designing and synthesizing new functionalized materials for the enrichment and detection of typical pollutants in the environment. [Display omitted] • CoFe 2 O 4 @Ti 3 C 2 @COF TABT @COF TATp was synthesized via Schiff base reaction and irreversible enol-keto tautomerization. • MSPE-GC-MS/MS was established for sensitive detection of thiophene compounds. • The constructed method provided wide linearity and low detection limits. • DBT, 4-MDBT, and 4,6-DMDBT were successfully detected in oilfield produced water. • The adsorption of thiophene compounds was hybrid and affected by temperature. [ABSTRACT FROM AUTHOR]

In order to further investigate photocatalytic materials for the degradation of typical benzene series (benzene, toluene and xylene) in oilfield produced water, Cu2+/ZnO/TiO2 nanocomposites were synthesized by sol-gel method. It was characterized and analyzed using XRD, SEM, FT-IR, UV–vis and TGA. The results show that a certain percentage of doping increase the activity of the photocatalyst and that pH, temperature, initial concentration and catalyst dosage all affected the specific pollutant degradation. After 7 h of photocatalytic treatment, the residual concentrations of pollutants were all in compliance with the required emission standard.

In order to predict the corrosion trendency of X100 pipeline steel in flowing oilfield produced water, the effect of flow rate on the corrosion behavior of X100 pipeline steel was studied under general dynamic condition and simulated real working condition at the flow rate of 0.2, 0.4, and 0.6 m·s−1. Potentiodynamic polarization curves and electrochemical impedance spectroscopy were used to study the corrosion behavior of X100 steel. Energy dispersive spectroscopy, X-ray diffraction and scanning electron microscopy were used to analyze corrosion product composition and micromorphology. The experimental results show that the corrosion is more serious under simulated real working conditions than that under the general dynamic conditions. In any case the corrosion current density increases with the increase of the flow rate, and the total impedance value decreases. The corrosion products include Fe3O4, Fe2O3, and FeOOH. The mass transfer and electrochemistry were simulated by flow coupled in COMSOL software. The multiphysical field coupling simulation results are closer to the engineering practice than the single flow field simulation, and similar results from the experiments were obtained. Both experimental and simulation results reveal that the higher flow rate is, the more serious corrosion appear and the more corrosion products accumulate. By combining experimental and COMSOL simulation data, the corrosion process model of X100 steel was proposed. [ABSTRACT FROM AUTHOR]

Reuse of oilfield‐produced water (OPW) for crop irrigation has the potential to make a critical difference in the water budgets of highly productive but drought‐stressed agricultural watersheds. This is the first peer‐reviewed study to evaluate how trace metals in OPW used to irrigate California crops may affect human health. We modeled and quantified risks associated with consuming foods irrigated with OPW using available concentration data. The probabilistic risk assessment simulated OPW metal concentrations, crop uptake, human exposures, and potential noncancer and carcinogenic health effects. Overall, our findings indicate that there is a low risk of ingesting toxic amounts of metals from the consumption of tree nuts, citrus, grapes, and root vegetables irrigated with low‐saline OPW. Results show increased arsenic cancer risk (at 10−6) for adult vegetarians, assuming higher consumption of multiple foods irrigated with OPW that contain high arsenic concentrations. All other cancer risks are below levels of concern and all noncancer hazards are far below levels of concern. Arsenic risk concerns could be mitigated by practices such as blending high‐arsenic OPW. Future risk assessment research should model the risks of organic compounds in OPW, as our study focused on inorganic compounds. Nevertheless, our findings indicate that low‐saline OPW may provide a safe and sustainable alternative irrigation water source if water quality is adequately monitored and blended as needed prior to irrigation. [ABSTRACT FROM AUTHOR]

• B. velezensis demonstrated effective inhibition of X65 steel corrosion. • Biomineralized film prepared by B. velezensis exhibited corrosion resistance. • This paper offered a more environmental solution to corrosion inhibition. The issue of material failure attributed to microbiologically influenced corrosion (MIC) is escalating in seriousness. Microorganisms not only facilitate corrosion but certain beneficial microorganisms also impede its occurrence. This study explored the impact of marine B. velezensis on the corrosion behavior of X65 steel in simulated offshore oilfield produced water. B. velezensis exhibited rapid growth in the initial stages, and the organic acid metabolites were found to promote corrosion. Subsequently, there was an increase in cross-linked "networked" biofilms products, a significant rise in the prismatic shape of corrosion products, and a tendency for continuous development in the middle and late stages. The organic/inorganic mineralized film layer formed on the surface remained consistently complete. Metabolic products of amino acid corrosion inhibitors were also observed to be adsorbed into the film. B. velezensis altered the kinetics of the X65 steel cathodic reaction, resulting in a deceleration of the electrochemical reaction rate. The mineralization induced by B. velezensis effectively slowed down the corrosion rate of X65 steel. [ABSTRACT FROM AUTHOR]

• PMM as a promising substratum to meet Canadian oil sands' zero waste goal and SDGs. • Both low and high strengths produced waters were efficiently reclaimed. • Chemisorption, supported by AD, along limited physical adsorption were key findings. • High conductivity, presence of Geobacter and Methanosaeta indicate DIET during AD. • The 'microbial dark matter' (∼50%) warrants further investigations for microbial activities. Nature-based solutions are encouraged for treating oilfield produced water from oil and gas extraction, a crucial undertaking that aligns with the Canadian oil sands industry's ambitious goal of zero waste, and the globally recognized Sustainable Development Goals (SDGs) pertaining to water conservation and ecosystem preservation. This study explored the use of peat-mineral mix (PMM), a leftover of inevitable oil sands mining, for treating low and high-strength wastewaters during biofiltration, which contained large molecular weight (44.3 kDa), which include alcohols, aliphatics, aromatics, and ketones, and can impart high toxicity to both fauna and flora (MicroTox: 99 %). The breakthrough curve indicated an effective initial adsorption phase driven by advection within the column dynamics. For complete organics removal and mechanistic insights, the wastewater was re-circulated in a continuous mode for up to 42 days. Here, we found that chemical oxygen demand was reduced from ∼85,000 mg/L to ∼965 mg/L). Kinetics investigations along with physicochemical characterization of PMM and wastewater suggested that chemisorption and anaerobic digestion contributed to the overall removal of contaminants. Chemisorption, led by hydrogen bonding and hydrophobic interactions, was the dominant mechanism, with a limited contribution from physical adsorption (surface area: 2.85 m2/g). The microbial community within the PMM bed was rich/diverse (Shannon > 6.0; Chao1 > 600), with ∼ 50 % unclassified phylotypes representing 'microbial dark matter'. High electric conductivity (332.1 μS cm−1) of PMM and the presence of Geobacter , syntrophs, and Methanosaeta suggest that direct interspecies electron transfer was likely occurring during anaerobic digestion. Both low and high-strength wastewaters showed effective removal of dissolved organics (e.g., naphthenic acids, acid extractable fraction, oil and grease content), nutrients, and potentially toxic metals. The successful use of PMM in treating oilfield produced water offers promising avenues for embracing nature-based remediation solutions at oil refining sites. [Display omitted] [ABSTRACT FROM AUTHOR]

A molecularly imprinted polymer (MIP) sensor was successfully constructed on glassy carbon electrode for the determination of 1‐naphthol (1‐Nph). The sensor was constructed by electropolymerization on bare GCE in the presence of the target molecule. The recognition of 1‐Nph was conducted indirectly using [Fe(CN)6]3−/4− as redox probe. The MIP sensor presented wide linear working range and limit of detection of 1.5×10−9 mol L−1. The MIP sensor was applied for the determination of 1‐Nph in oilfield produced water. The results obtained showed good selectivity and sensitivity of the proposed sensor in terms of 1‐Nph quantification. [ABSTRACT FROM AUTHOR]

Determining a representative microbial signature from any given location is dependent on robust sample collection and handling. Different sampling locations and hence sample properties can vary widely; for example, soil would be collected and handled differently compared to liquid samples. In the event that sample material has a low concentration of biomass, large quantities need to be collected for microbial community analysis. This is certainly the case when investigating the microbiology of oilfield systems, wherein produced water (PW) is one of the most common sources for microbial sampling. As the detrimental effects of microbial metabolism within these industrial milieus are becoming increasingly well-established, the characterization of microbial community composition using molecular biological analyses is becoming more commonplace for accurate monitoring. As this field continues to develop, the importance for standardized operating protocols cannot be understated, so that industry can make the most informed operational decisions possible. Accurately identifying oilfield microbial communities is paramount, as improper preservation and storage following sample collection is known to lead to erroneous microbial identifications. Preserving oilfield PW can be challenging, as many locations are remote, requiring lengthy periods of time before samples can be processed and analyzed. While previous studies have characterized the effects of various preservatives on concentrated, filtered, or purified microbial samples, to the best of our knowledge, no such study has been undertaken on low biomass liquid samples. To this end, we investigated the effectiveness of nine different preservation conditions on PW collected from the same sampling location within a heavy-oil producing field, and monitored how the microbial community changed over the period of a month. Our results reveal that the choice of preservative drastically affects microbial community, and should be selected with careful consideration before sampling occurs.

This study focused on resolving the query "which is the most beneficial clay system for the petroleum industry, intercalated or exfoliated"? Dimethyl sulfoxide (DMSO) and ethylenediaminetetraacetate ions (EDTA2-) were used as well-known agents in the tailoring of intercalated- and exfoliated-organoclays, respectively. Both systems were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, dynamic light scattering, N2-physisorption, transmission electron microscopy, and atomic force microscopy techniques, and examined in treating oilfield produced water. EDTA-clay exhibited long-term ordered, uniformly negatively charged, and high swellable tactoids of hexagon shapes with enhanced pore structure. The lamellar structure of DMSO-clay was highly degenerated and roughened conducting uneven highly charged particles of poor surface features. EDTA-clay was preferentially managed in the petroleum industry as a perfectly safe and efficient agent for (i) long-lasting removal of scale-forming cations (Fe3+, Mg2+, Ca2+, and Sr2+) from oilfield produced water with high adsorption rates yielding performances ≥85% within excellent six repeating regeneration/reuse runs, (ii) corrosion protection of steel pipelines, and (iii) killing of sulfate-reducing bacteria (near 100%). Increased demand for exploration of multidiscipline materials for the petroleum industry will revitalize clay intercalation systems to a magnificent renaissance. [ABSTRACT FROM AUTHOR]

To improve the separation efficiency of oil field-produced water, a novel oil-water separation apparatus is developed. The high-efficiency cyclone separation apparatus could meet the continued increase of oil field-produced water and comply with the improvements in emission standards. Effectivity of the self-designed apparatus in oil removal was determined in laboratory and field tests. The effects of inlet flow, oil concentration and aeration amount were determined through laboratory tests. The particle size distribution of the influent and effluent oil-produced water was presented also. Results show that under optimal process conditions, i.e., the inlet flow rate is 2.0 m3/h, imported oil concentration is 1189 mg/L, and aeration rate is 0.6 L/min, effective separation can reach 93.1%. The oil removal rate is generally above 90% and the range of influent concentration is 900-1200 mg/L in the field test. Compared to the traditional oilfield produced water treatment device, the self-designed apparatus can combine both air flotation separation and cyclonic separation. The joint effect of the two kinds of separation, can promote the collision adsorption probability of micro bubbles and oil droplets, and effectively improve the separation efficient. [ABSTRACT FROM AUTHOR]

Determining a representative microbial signature from any given location is dependent on robust sample collection and handling. Different sampling locations and hence sample properties can vary widely; for example, soil would be collected and handled differently compared to liquid samples. In the event that sample material has a low concentration of biomass, large quantities need to be collected for microbial community analysis. This is certainly the case when investigating the microbiology of oilfield systems, wherein produced water (PW) is one of the most common sources for microbial sampling. As the detrimental effects of microbial metabolism within these industrial milieus are becoming increasingly well-established, the characterization of microbial community composition using molecular biological analyses is becoming more commonplace for accurate monitoring. As this field continues to develop, the importance for standardized operating protocols cannot be understated, so that industry can make the most informed operational decisions possible. Accurately identifying oilfield microbial communities is paramount, as improper preservation and storage following sample collection is known to lead to erroneous microbial identifications. Preserving oilfield PW can be challenging, as many locations are remote, requiring lengthy periods of time before samples can be processed and analyzed. While previous studies have characterized the effects of various preservatives on concentrated, filtered, or purified microbial samples, to the best of our knowledge, no such study has been undertaken on low biomass liquid samples. To this end, we investigated the effectiveness of nine different preservation conditions on PW collected from the same sampling location within a heavy-oil producing field, and monitored how the microbial community changed over the period of a month. Our results reveal that the choice of preservative drastically affects microbial community, and should be selected with careful consideration before sampling occurs. [ABSTRACT FROM AUTHOR]

The presence of carbon dioxide (CO2) in oilfield produced water, which could be natural or intentionally injected component in oil and gas production, is extremely corrosive to pipelines and tubings. Oilfield produced water is mainly brine solution comprising organic acids, purely condensed water as well as aggressive ions like SO42−, Cl− and dissolved acid gases (like CO2). CO2 induced corrosion in this media is more detrimental than corrosion induced by HCl. This study critically unveiled the CO2 corrosion behavior of steel in oilfield produced water. The subjects covered include the chemistry of CO2 in water, supercritical CO2 condition, computational fluid dynamics (CFD) and corrosion control. Corrosion resistant alloy has been proved to exhibit remarkable corrosion resistance due to formation of strong protective film that can prevent localized corrosion. Moreover, the use of viable surface-active compounds, which are constituents of crude oil is a promising strategy for pipeline steel corrosion mitigation. [ABSTRACT FROM AUTHOR]

This review discusses bioreactor-based methods for industrial hydrocarbon-containing wastewater treatment using different (e.g., stirred-tank, membrane, packed-bed and fluidized-bed) constructions. Aerobic, anaerobic and hybrid bioreactors are becoming increasingly popular in the field of oily wastewater treatment, while high concentrations of petroleum hydrocarbons usually require physico-chemical pre-treatments. Most efficient bioreactor techniques employ immobilized cultures of hydrocarbon-oxidizing microorganisms, either defined consortia or mixed natural populations. Some advantages of fluidized-bed bioreactors over other types of reactors are shown, such as large biofilm–liquid interfacial area, high immobilized biomass concentration and improved mass transfer characteristics. Several limitations, including low nutrient content and the presence of heavy metals or toxicants, as well as fouling and contamination with nuisance microorganisms, can be overcome using effective inocula and advanced bioreactor designs. The examples of laboratory studies and few successful pilot/full-scale applications are given relating to the biotreatment of oilfield wastewater, fuel-contaminated water and refinery effluents. [ABSTRACT FROM AUTHOR]

Fluorescence spectroscopy is a powerful tool to determine polycyclic aromatic hydrocarbons (PAHs) owing to the strong endogenous fluorescence of these compounds. However, the presence of unknown interferences and overlapped spectra hinders the accurate determination of PAHs in oilfield produced water. Moreover, surfactants frequently coexist in oilfield produced water and will seriously affect the fluorescence signals of PAHs. Herein, a new methodology applying third-order calibration to process four-way (4D) fluorescence data was proposed to solve these problems and achieve accurate determination of pyrene, fluorene, phenanthrene, and fluoranthene as an example in oilfield produced water. The methodology is based on excitation-emission matrix fluorescence modulated by different concentrations of sodium dodecyl benzene sulfonate (SDBS) in the analyzed samples. The 4D fluorescence data were processed by third-order calibration methods including four-way parallel factor analysis (4-PARAFAC) and alternating weighted residue constraint quadrilinear decomposition (AWRCQLD), and the results were compared with those of second-order calibration methods. It was proved that third-order calibration was capable of accurately identifying and quantifying PAHs together with SDBS in oilfield produced water, which has better quantitative results and figures of merit compared to second-order calibration. This study provided a new approach to generating 4D fluorescence data and opened up an avenue for the accurate determination of PAHs in complex oilfield produced water with surfactants. [Display omitted] • 4D excitation-emission matrix fluorescence data modulated by SDBS was first constructed. • Chemometric multi-way calibration algorithms were used to process the 4D fluorescence data. • The proposed strategy could determine PAHs in oilfield produced water with surfactants. • Third-order calibration has more robust performances than second-order calibration. • SDBS could be successfully predicted as an added bonus in third-order calibration. [ABSTRACT FROM AUTHOR]

In recent years, the corrosion problem of equipment and pipeline caused by oilfield produced water is becoming increasingly serious. In this work, corrosion inhibitor of triazine, synthesized from formaldehyde and ethanolamine, was evaluated using weight-loss techniques. The triazine was found to inhibit the corrosion of mild steel in simulated oilfield produced water. The adsorption of inhibitor was studied, which was consistent with the assumption of Langmuir adsorption model. Thermodynamic parameters of corrosion inhibition process were further calculated and analyzed, which indicated that adsorption of triazine inhibitor was exothermic, spontaneous and physical process.

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.

The corrosion performances of X100 steels in the oilfield produced water with different temperature (30°C, 40°C, 60°C) under the simulated working conditions were studied by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) test. Energy dispersive spectroscopy (EDS) was used to measure the element composition of the sample after corrosion. The phase and chemical compositions of the specimens were analyzed by X-ray diffraction (XRD) and Raman spectrometry. The electrochemical results showed that the corrosion resistance of the specimen exposed for 24 hours increased with the increase of the testing temperature, indicating the better protective effect due to the corrosion product film formed under high temperature despite the impact of turbulence. The corrosion products consist of Fe3O4, Fe2O3, α-FeOOH, and γ-FeOOH. The corrosion mechanism model of X100 steel was established and the corrosion behavior was analyzed under simulated working conditions. [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]

This study investigated the microbial community in a full scale anaerobic baffled reactor and sequencing batch reactor system for oil-produced water treatment in summer and winter. The community structures of fungi and bacteria were analyzed through polymerase chain reaction–denaturing gradient gel electrophoresis and Illumina high-throughput sequencing, respectively. Chemical oxygen demand effluent concentration achieved lower than 50 mg/L level after the system in both summer and winter, however, chemical oxygen demand removal rates after anaerobic baffled reactor treatment system were significant higher in summer than that in winter, which conformed to the microbial community diversity. Saccharomycotina, Fusarium, and Aspergillus were detected in both anaerobic baffled reactor and sequencing batch reactor during summer and winter. The fungal communities in anaerobic baffled reactor and sequencing batch reactor were shaped by seasons and treatment units, while there was no correlation between abundance of fungi and chemical oxygen demand removal rates. Compared to summer, the total amount of the dominant hydrocarbon degrading bacteria decreased by 10.2% in anaerobic baffled reactor, resulting in only around 23% of chemical oxygen demand was removed in winter. Although microbial community significantly varied in the three parallel sulfide reducing bacteria, the performance of these bioreactors had no significant difference between summer and winter.

In general, the oil industry has been searching for ways to alleviate the abundant disposal of oilfield produced water, which contains dissolved hard-removal and highly toxic organic compounds. Advanced oxidative processes (AOPs) have revealed to be effective in the degradation of organic compounds, because they generate hydroxyl radicals with high oxidizing potential which are capable of degrading these compounds. The present study has demonstrated the degradation efficiency of effluents containing organic compounds although the photo-Fenton process using a tubular photochemical reactor under different energy sources. This reactor allowed the use and evaluation of two ultraviolet irradiation sources, the sun and black light lamps, besides other relevant variables to the process, such as reagents concentration and the irradiated area, using a model effluent containing phenol. A sample of oilfield produced water was photochemically degraded through the optimum experimental conditions found for the phenol degradation. Solar irradiation was more efficient than lamplight, and it corresponds an important factor for the reduction of operating costs of this process. The solar reaction system applied to the oilfield produced water showed a removal of organic components up to 76%. [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]

This review discusses bioreactor-based methods for industrial hydrocarbon-containing wastewater treatment using different (e.g., stirred-tank, membrane, packed-bed and fluidized-bed) constructions. Aerobic, anaerobic and hybrid bioreactors are becoming increasingly popular in the field of oily wastewater treatment, while high concentrations of petroleum hydrocarbons usually require physico-chemical pre-treatments. Most efficient bioreactor techniques employ immobilized cultures of hydrocarbon-oxidizing microorganisms, either defined consortia or mixed natural populations. Some advantages of fluidized-bed bioreactors over other types of reactors are shown, such as large biofilm−liquid interfacial area, high immobilized biomass concentration and improved mass transfer characteristics. Several limitations, including low nutrient content and the presence of heavy metals or toxicants, as well as fouling and contamination with nuisance microorganisms, can be overcome using effective inocula and advanced bioreactor designs. The examples of laboratory studies and few successful pilot/full-scale applications are given relating to the biotreatment of oilfield wastewater, fuel-contaminated water and refinery effluents.

In this study, novel coagulant poly(silicate aluminum)/Fe3O4 nanoparticles (PFeNPs) were prepared via magnetic iron oxide nanoparticles (FeNPs) modified by poly(silicate aluminum) (PSA). The physiochemical properties of the PFeNPs were investigated with Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and ζ-potential metric analysis. The effect of the aging time on the Al distribution of the PFeNPs was analyzed by the Al-Ferron timed complex colorimetric method. Oilfield-produced water was used for the assessment of the coagulation performances. The fractal dimensions, formation, breakage, and regrowth of the flocs were studied in turn. The experimental results show that the PFeNPs exhibited a porous layer of a net structure, and the PSA grafted onto the PFeNPs via Si--O--Fe enhanced the positive charge of the FeNPs. Meanwhile, the coagulation performance of the PFeNPs on total organic carbon, the turbidity, and the calcium removal were beyond 98%. In addition, the moisture content of the flocs derived from the PFeNPs was 68.7% (it is normally >98%). We found that the compactness of the flocs derived from the PFeNPs was far greater than those of PSA. This will provide new sight into the preparation of magnetic singlephase inorganic polymer coagulants. VC [ABSTRACT FROM AUTHOR]

Microbiologically influenced corrosion (MIC) is the primary mechanism causing failures of upstream oil pipelines. This work investigated the biofilm formation and MIC of an X70 pipeline steel in oilfield produced water containing sulfate reducing bacteria at various flow velocities. Results demonstrate that the fluid flow affects the biofilm formation, and thus MIC of the steel under biofilm. At low flow velocities such as 0.2 m/s, a layer of biofilm forms on the steel surface, and the steel suffers from MIC, especially pitting corrosion. With the increase of flow velocity to 1.0 m/s, the biofilm is not able to form. Thus, the steel MIC reduces with the increasing flow velocity of the fluid. Moreover, the corrosion products and biofilm are overlapped at the low flow velocity. At the high flow velocity, the surface layer formed on the steel is mainly corrosion products. Corrosion pits can be formed on the steel at the low flow velocity due to microbial attack. [ABSTRACT FROM AUTHOR]

Produced water (PW) is the largest waste stream in the oil production process: it contains light polar and aliphatic hydrocarbons, production process compounds, dissolved gases, anions and cations. Disposal of PW is subjected to strict legislations. Oil producing countries are focused on finding effective and economic methods for its treatment. Some physical and chemical methods have been used for treatment of PW and biological treatments have been proven to efficiently remove dissolved hydrocarbon compounds. Coupling of anaerobic biological treatment with electrochemical technology in microbial fuel cells (MFCs) can in principle lead to the production of clean water and electric energy. The suitability of MFCs for improving the treatment of PW was investigated in the present work. For the first time, the simple design of single chamber MFCs fed with real PW (PW-MFCs) was studied, in different configurations: (i) with and without membrane; (ii) with and without Pt cathodic catalyst. The results demonstrate the effectiveness of the membraneless configuration without chemical catalyst at the cathode. Even though the electrical output of PW-MFCs was very low (3 mW m −2 ), it is currently the best reported performance. Furthermore, almost complete hydrocarbon degradation was achieved for each fed-cycle (96.6 ± 1.94%). The Coulombic efficiency was limited by the difficulty to obtain strict anaerobic condition at the anode, since the biocathode of PW-MFCs remained more permeable to oxygen than in acetate-fed MFCs. The DNA sequencing of operating anodic biofilm detected electroactive Desulfobulbaceae mixed to aerobic biodegraders ( Burkholderiales ) likely through cycling sulfur compounds, which enriched from the PW initial pool in the hypersaline environment. Above all, the results pointed to the practical possibility of using a MFC to enhance and monitor the PW biodegradation process. In fact, the MFC electrical output indicated the occurrence of anaerobic degradation, while the electrochemical parameters of cathode (Tafel slope) resulted correlated to aerobic degradation, suggesting the possibility to design an on-line sensor of the biotechnological industrial treatments of PW. [ABSTRACT FROM AUTHOR]

A visible-light driven superhydrophobic composite of MIL-101(Cr)/Fe 3 O 4 -SiO 2 was synthesized via hydrothermal method. Various physicochemical techniques were employed for the characterization of the nanoparticles such as XRD, FTIR, FESEM, TEM, EDS, BET, UV–Visible DRS, PL, and pH pzc. The adsorption and photocatalytic performance of the synthesized nanoparticles were evaluated by synthetic and real oilfield produced water (OPW) treatment. The optimal loading amount of Fe 3 O 4 -SiO 2 was determined by analysis tests and investigation of photocatalytic activity. The results showed that the superhydrophobic composite with 35% weight percent of Fe 3 O 4 -SiO 2 exhibited the maximum removal efficiency. Effect of operational parameters such as pH, reaction time, and initial concentration of pollutants on the removal efficiency were evaluated. The chemical oxygen demand (COD) removal efficiency of synthetic oilfield produced water (SOPW) achieved 95.17% and 96.6% under visible and UV light irradiation by MIL-101(Cr)/Fe 3 O 4 -SiO 2 (35%), at the optimum conditions of pH 4, photocatalyst dosage 0.5 g/L, COD initial concentration 600 mg/L, and illumination time 150 min. Moreover, the gas chromatography-mass spectroscopy (GC–MS) analysis results showed 97.7% and 99.2% removal efficiency of total petroleum hydrocarbons (TPH) for real and synthetic OPW, respectively. The results of kinetic and isotherm study showed that the kinetic data followed the pseudo-second-order and equilibrium adsorption was described by the Freundlich model. The high specific surface area, narrow bandgap energy as well as the charge carrier separation based on the Z -scheme heterostructure caused the improvement of binary composite photocatalyst features. The results demonstrated that the MIL-101(Cr)/Fe 3 O 4 -SiO 2 superhydrophobic composite are promising photocatalyst in the degradation of oilfield produced water pollutants. Synergistic effect of adsorption and photocatalytic degradation of OPW help to enhance the removal performance. [Display omitted] • Synthesis and characterization of MIL-101(Cr)/Fe 3 O 4 -SiO 2 using hydrothermal method. • Modifying the wettability properties of nanoparticles by octadecylamine. • Investigating the adsorption and photocatalytic degradation of oilfield produced water pollutants under UV and visible light irradiation. • The adsorption kinetic and isotherm study, as well as the kinetic of photocatalytic degradation.. • The presence of Fe 3 O 4 -SiO 2 in the composite increases the magnetic property, decreases the band gap and improves the photocatalytic performance. [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]

The removal process of Hg(II) and MeHg(II) from aqueous solution by surface modified agrowaste biomass (AWB) was studied. The surface modifications were carried out by methods of mercerization, oxidative delignification, acid treatment, and biological treatment using laccase. The modifications promoted disruption of AWB structural surfaces and thus changed their physical and chemical properties as well as Hg(II) and MeHg(II) adsorption performances. The adsorption efficiency of Hg(II) was higher than MeHg(II) for all AWB adsorbents. The adsorption capacity of Hg(II) and MeHg(II) for AWB-Pure was 0.97 and 0.17 mmol/g, respectively. The highest adsorption capacity of Hg(II) and MeHg(II) was respectively observed for the AWB-Laccase (0.98 ± 0.04 mmol/g) and AWB-NaOCl/NaOH (0.40 ± 0.07 mmol/g). The adsorption selectivity of modified AWB adsorbents towards Hg(II) and MeHg(II) studied using oilfield produced water and natural gas condensate samples was found to be lower as compared to AWB-Pure, but higher selectivity was observed for other metals. The renewability studies show that the pure and modified AWB adsorbents had similar adsorption performance characteristics. The high Hg(II) adsorption efficiency (η > 90 %) was observed up to the third adsorption cycle, while for the MeHg(II), it decreased after each adsorption–desorption cycle. [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]

One of the key challenges for reuse of produced water as boiler feedwater in oilfield is scaling, which detrimentally affects the thermal efficiency and security of boiler. To explore the influence of silica-rich, softened feedwater (240 mg/L, calculated with SiO 2 ) on the scale, three kinds of softening degrees named primary softening (PS), general softening (GS), and advanced softening (AS) were implemented in a 5-month pilot-scale test. The average total hardness in each of the PS, GS, and AS water was 802 μg/L, 282 μg/L, and 31 μg/L, respectively. Morphology and composition of scale were determined by a scanning electron microscope–energy dispersive spectrometer (SEM–EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Calcium scaling (CaSiO 3 , CaCO 3 ) was the main crystalline phases in the PS scales, whereas the AS scales were mainly composed of iron oxide. However, with the softening enhanced, types of organic functional groups and species of inorganic compound in scales were decreased. Simultaneously, the dissolution rates were increased due to the corrosion of tubes. It is concluded that the characteristics of scales were mainly determined by concentrations of Ca and Fe ions in silica-rich feedwater. These findings can offer an important reference for reuse of oilfield produced water without desilication. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a pH sensor for monitoring hydrogen ion activity in situ in oilfield-produced water under subsurface conditions. An iridium oxide film was prepared, and the performance of the iridium oxide film was evaluated in produced water using a series of high salinities, temperatures, and pressures. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were employed to assess the morphology and oxidation state of the iridium oxide film. A series of open-circuit potential (OCP) measurements were performed to access the sensitivity and stability of the iridium oxide film electrode in produced water. Research results indicated that the pH sensor exhibits a very high sensitivity in the environment with varied interference ions, including Na, Mg, Ca, Cl, and SO, and the existence of sodium chloride in produced water made a slight positive shift of potential. The iridium oxide film-based pH sensor exhibited a near-Nernstian response at −57.9 mV/pH in produced water. An increase in temperature from 24 to 80 °C decreased the pH potential. Compared with the theoretical Nernst equation, the iridium oxide sensor showed fair Nernstian behavior at high temperatures. The iridium oxide pH sensor was accurately investigated under high pressure; the sensor seems independent of pressure, and the slope is the same at different potentials under a wide range of pressures. [ABSTRACT FROM AUTHOR]

Oilfield produced water (OPW) with crude oil is a huge threat to the natural environment. For the treatment of OPW, degradation of crude oil in OPW by microorganisms and OPW activation by microbial metabolites for oil recovery improvement after reinjection may be an effective and sustainable approach. In this study, the degradation of crude oil in OPW by immobilized isolated bacteria was designed and the enhancement of oil recovery by reinjecting treated OPW was examined. Aldehyde fiber was found to show the optimum immobilization effect for three isolated oil-degrading-bacteria (Pseudomonas sp. ZJI-1, Acinetobacter sp. YMJ-1, and Gordonia sp. G1). The crude oil degradation rate of the immobilized bacteria reached 82.6% within 7 days. The contents of some bioactive molecules helpful for oil recovery, including rhamnolipid and acetic acid, increased continuously in the designed system. Core flooding tests demonstrated that oil recovery increased by 8.61% after the treated-OPW reinjection. In summary, the immobilized bacteria could effectively remove crude oil from OPW, increase the contents of rhamnolipid and acetic acid, and in particular, improve the oil production efficiency after reinjection. [Display omitted] • Aldehyde fiber was found to be the best immobilized carrier for three isolated bacteria. • A OPW treatment device was designed and the immobilized bacteria performed high removal efficiency of crude oil in it. • The contents of rhamnolipid and acetic acid in the system increased continuously. • Gordonia, Pseudomonas and Achromobacter became the predominant genera in the degrading system. • The core flooding test showed that the oil recovery rate increased significantly after OPW reinjection. [ABSTRACT FROM AUTHOR]