Review of technologies for oil and gas produced water treatment

Elucidate microbial characteristics in a full-scale treatment plant for offshore oil produced wastewater

Oil-produced wastewater treatment plants, especially those involving biological treatment processes, harbor rich and diverse microbes. However, knowledge of microbial ecology and microbial interactions determining the efficiency of plants for oil-produced wastewater is limited. Here, we performed 16S rDNA amplicon sequencing to elucidate the microbial composition and potential microbial functions in a full-scale well-worked offshore oil-produced wastewater treatment plant. Results showed that microbes that inhabited the plant were diverse and originated from oil and marine associated environments. The upstream physical and chemical treatments resulted in low microbial diversity. Organic pollutants were digested in the anaerobic baffled reactor (ABR) dominantly through fermentation combined with sulfur compounds respiration. Three aerobic parallel reactors (APRs) harbored different microbial groups that performed similar potential functions, such as hydrocarbon degradation, acidogenesis, photosynthetic assimilation, and nitrogen removal. Microbial characteristics were important to the performance of oil-produced wastewater treatment plants with biological processes.

Advances in the Synthesis and Application of Anti-Fouling Membranes Using Two-Dimensional Nanomaterials

This article provides a comprehensive review of the recent progress in the application of advanced two-dimensional nanomaterials (2DNMs) in membranes fabrication and application for water purification. The membranes fouling, its types, and anti-fouling mechanisms of different 2DNMs containing membrane systems are also discussed. The developments in membrane synthesis and modification using 2DNMs, especially graphene and graphene family materials, carbon nanotubes (CNTs), MXenes, and others are critically reviewed. Further, the application potential of next-generation 2DNMs-based membranes in water/wastewater treatment systems is surveyed. Finally, the current problems and future opportunities of applying 2DNMs for anti-fouling membranes are also debated.

Seven potential sources of arsenic pollution in Latin America and their environmental and health impacts

This review presents a holistic overview of the occurrence, mobilization, and pathways of arsenic (As) from predominantly geogenic sources into different near-surface environmental compartments, together with the respective reported or potential impacts on human health in Latin America. The main sources and pathways of As pollution in this region include: (i) volcanism and geothermalism: (a) volcanic rocks, fluids (e.g., gases) and ash, including large-scale transport of the latter through different mechanisms, (b) geothermal fluids and their exploitation; (ii) natural lixiviation and accelerated mobilization from (mostly sulfidic) metal ore deposits by mining and related activities; (iii) coal deposits and their exploitation; (iv) hydrocarbon reservoirs and co-produced water during exploitation; (v) solute and sediment transport through rivers to the sea; (vi) atmospheric As (dust and aerosol); and (vii) As exposure through geophagy and involuntary ingestion. The two most important and well-recognized sources and mechanisms for As release into the Latin American population's environments are: (i) volcanism and geothermalism, and (ii) strongly accelerated As release from geogenic sources by mining and related activities. Several new analyses from As-endemic areas of Latin America emphasize that As-related mortality and morbidity continue to rise even after decadal efforts towards lowering As exposure. Several public health regulatory institutions have classified As and its compounds as carcinogenic chemicals, as As uptake can affect several organ systems, viz. dermal, gastrointestinal, peptic, neurological, respiratory, reproductive, following exposure. Accordingly, ingesting large amounts of As can damage the stomach, kidneys, liver, heart, and nervous system; and, in severe cases, may cause death. Moreover, breathing air with high As levels can cause lung damage, shortness of breath, chest pain, and cough. Further, As compounds, being corrosive, can also cause skin lesions or damage eyes, and long-term exposure to As can lead to cancer development in several organs.

A critical review of state-of-the-art electrocoagulation technique applied to COD-rich industrial wastewaters

Electrocoagulation (EC) is one of the emerging technologies in groundwater and wastewater treatment as it combines the benefits of coagulation, sedimentation, flotation, and electrochemical oxidation processes. Extensive research efforts implementing EC technology have been executed over the last decade to treat chemical oxygen demand (COD)-rich industrial wastewaters with the aim to protect freshwater streams (e.g., rivers, lakes) from pollution. A comprehensive review of the available recent literature utilizing EC to treat wastewater with high COD levels is presented. In addition, recommendations are provided for future studies to improve the EC technology and broaden its range of application. This review paper introduces some technologies which are often adopted for industrial wastewater treatment. Then, the EC process is compared with those techniques as a treatment for COD-rich wastewater. The EC process is considered as the most privileged technology by different research groups owing to its ability to deal with abundant volumes of wastewater. After, the application of EC as a single and combined treatment for COD-rich wastewaters is thoroughly reviewed. Finally, this review attempts to highlight the potentials and limitations of EC. Related to the EC process in batch operation mode, the best operational conditions are found at 10 V and 60 min of voltage and reaction time, respectively. These last values guarantee high COD removal efficiencies of > 90%. This review also concludes that considerably large operation costs of the EC process appears to be the serious drawback and renders it as an unfeasible approach for handling of COD rich wastewaters. In the end, this review has attempted to highlights the potential and limitation of EC and suggests that vast notably research in the field of continuous flow EC system is essential to introduce this technology as a convincing wastewater technology.

Predicting Spontaneous Emulsification in Saltwater Environments Using the HLD Model

Spontaneous emulsification of toluene with nonylphenol polyethoxylate (NPE) and sodium dodecylbenzenesulfonate (SDBS) surfactants in saltwater environments was studied. NaCl promoted the spontaneous emulsification of an otherwise non-spontaneous SDBS-toluene system. Dynamic light scattering and turbidity indicated that spontaneity increased with NaCl concentration. The mechanism of spontaneous emulsification was dependent on surfactant type; NPE emulsified via micelle swelling, and SDBS emulsified via nucleation and growth. Hydrophilic lipophilic difference (HLD) calculations were used to model spontaneous emulsification and spontaneity. As HLD approached zero, conditions became more favorable for spontaneous emulsification. Between HLD values of -2.4 and -2.05, samples transitioned from non-spontaneous to spontaneous. This study aids in predicting spontaneous emulsion formation in saltwater environments for applications in nanoemulsion formation and wastewater remediation.

Adsorptive batch and biological treatments of produced water: Recent progresses, challenges, and potentials

Produced water is responsible for the largest contribution in terms of waste stream volume associated with the production of oil and gas. Characterization of produced water is very crucial for the determination of its main components and constituents for optimal selection of the treatment method. This review aims to review and critically discuss various treatment options that can be considered cost-efficient and environmentally friendly for the removal of different pollutants from produced water. Great efforts and progresses were made in various treatment options, including batch adsorption processes, membrane filtration, advanced oxidation, biological systems, adsorption, coagulation, and combined processes. Chemical precipitation, membrane filtration, and adsorption have high removal efficiencies that can reach more than 90% for different produced water components. The most effective method among these methods is adsorption using different adsorbents media. In this review, date-pits activated carbons, microemulsions-modified date pits, and cellulose nanocrystals as low-cost adsorbents were thoroughly reviewed and discussed. Moreover, the potential of using biological treatments in the removal of various pollutants from produced water such as conventional activated sludge, sequential batch reactor, and fixed-film biological aerated filter reactors were systematically discussed. Generally, produced water can be utilized in various fields including habitat and wildlife, agricultural and irrigation sector, energy sector, fire control, industrial use also power regeneration. The degree of treatment will depend on the application that produced water is being reused in. For instance, to use produced water in oil and gas industries, water will require minimal treatment while for agricultural and drinking purposes high treatment level will be required. It can also be concluded that one specific technique cannot be recommended that will meet all requirements including environmental, reuse, and recycling for sustainable energy. This is because of various dominant factors including the type of field, platform type, chemical composition, geological location, and chemical composition of the production chemicals.

Fouling of polyelectrolyte multilayer based nanofiltration membranes during produced water treatment: The role of surfactant size and chemistry

Large volumes of water become contaminated with hydrocarbons, surfactants, salts and other chemical agents during Oil & Gas exploration activities, resulting in a complex wastewater stream known as produced water (PW). Nanofiltration (NF) membranes are a promising alternative for the treatment of PW to facilitate its re-use. Unfortunately, membrane fouling still represents a major obstacle. In the present work, we investigate the effect of surface chemistry on fouling of NF membranes based on polyelectrolyte multilayers (PEM), during the treatment of artificial produced water. To this end, oil-in-water (O/W) emulsions stabilized with four different surfactants (anionic, cationic, zwitterionic and non-ionic) were treated with PEM-based NF membranes having the same multilayer, but different top layer polymer chemistry: crosslinked poly(allylamine hydrochloride) (PAH, nearly uncharged), poly(sodium 4-styrene sulfonate) (PSS, strongly negative), poly(sulfobetaine methacrylate-co-acrylic acid) (PSBMA-co-AA, zwitterionic) and Nafion (negative and hydrophobic). First, we study the adsorption of the four surfactants for the four different surfaces on model interfaces. Second, we study fouling by artificial produced water stabilized by the same surfactants on PEM-based hollow fiber NF membranes characterized by the same multilayer of our model surfaces. Third, we study fouling of the same surfactants solution but without oil. Very high oil retention (>99%) was observed when filtering all the O/W emulsions, while the physicochemical interactions between the multilayer and the surfactants determined the extent of fouling as well as the surfactant retention. Unexpectedly, our results show that fouling of PEM-based NF membranes, during PW treatment, is mainly due to membrane active layer fouling caused by surfactant uptake inside of the PEM coating, rather than due to cake layer formation. Indeed, it is not the surface chemistry of the membrane that determines the extent of fouling, but the surfactant interaction with the bulk of the PEM. A denser multilayer, that would stop these molecules, would benefit PW treatment by decreasing fouling issues, as would the use of slightly more bulky surfactants that cannot penetrate the PEM.

Cellulose-based special wetting materials for oil/water separation: A review

Oil spill accidents and oily wastewater discharged by petrochemical industries have severely wasted water resources and damaged the environment. The use of special wetting materials to separate oil and water is efficient and environment-friendly. Cellulose is the most abundant renewable resource and has natural advantages in removing pollutants from oily wastewater. The application and modification of cellulose as special wetting materials have attracted considerable research attention. Therefore, we summarized cellulose-based superlipophilic/superhydrophobic and superhydrophilic/superoleophobic materials exhibiting special wetting properties for oil/water separation. The treatment mechanism, preparation technology, treatment effect, and representative projects of oil-bearing wastewater are discussed. Moreover, cellulose-based intelligent-responsive materials for application to oil/water separation and the removal of other pollutants from oily wastewater have also been summarized. The prospects and potential challenges of all the materials have been highlighted.

Graphene Oxide Membranes for High Salinity, Produced Water Separation by Pervaporation

Oil and gas industries produce a huge amount of wastewater known as produced water which contains diverse contaminants including salts, dissolved organics, dispersed oils, and solids making separation and purification challenging. The chemical and thermal stability of graphene oxide (GO) membranes make them promising for use in membrane pervaporation, which may provide a more economical route to purifying this water for disposal or re-use compared to other membrane-based separation techniques. In this study, we investigate the performance and stability of GO membranes cast onto polyethersulfone (PES) supports in the separation of simulated produced water containing high salinity brackish water (30 g/L NaCl) contaminated with phenol, cresol, naphthenic acid, and an oil-in-water emulsion. The GO/PES membranes achieve water flux as high as 47.8 L m-2 h-1 for NaCl solutions for membranes operated at 60 °C, while being able to reject 99.9% of the salt and upwards of 56% of the soluble organic components. The flux for membranes tested in pure water, salt, and simulated produced water was found to decrease over 72 h of testing but only to 50-60% of the initial flux in the worst-case scenario. This drop was concurrent with an increase in contact angle and C/O ratio indicating that the GO may become partially reduced during the separation process. Additionally, a closer look at the membrane crosslinker (Zn2+) was investigated and found to hydrolyze over time to Zn(OH)2 with much of it being washed away during the long-term pervaporation.

Fiber coalescence treatment of oily wastewater: A new theory and application

Oil pollution from produced water in the offshore petroleum industry is one of the most serious marine pollutants worldwide, and efficient separation technology is crucial for the control of oil pollutant emission. Medium coalescence is an efficient oil-water separation technology, but its theory is lacking and the development is slow. In this work, the microscopic mechanism of fiber coalescence was revealed, and found that the effective collision positions were the three-phase contact line and the exposed fiber surface. Further, a theoretical model for calculating the separation performance of a fiber bed was established. For a given inlet droplet size distribution and bed geometric parameters, the outlet droplet size distribution and the total separation efficiency of the fiber bed can be predicted. Then, an Ω-shaped woven method composed of oil-wet fibers and oil-phobic fibers was designed and the separation performance of the fiber beds prepared by the method and the influence law of various parameters were clarified through macroscopic experiment. Finally, the novel technology achieved its first engineering application on an offshore platform, with the average oil content of the outlet was less than 25 mg/L, which could reform the current treatment process of produced water.

Prediction of batch sorption of barium and strontium from saline water

Celestite and barite formation results in contamination of barium and strontium ions hinder oilfield water purification. Conversion of bio-waste sorbent products deals with a viable, sustainable and clean remediation approach for removing contaminants. Biochar sorbent produced from rice straw was used to remove barium and strontium ions of saline water from petroleum industries. The removal efficiency depends on biochar amount, pH, contact time, temperature, and Ba/Sr concentration ratio. The interactions and effects of these parameters with removal efficiency are multifaceted and nonlinear. We used an artificial neural network (ANN) model to explore the correlation between process variables and sorption responses. The ANN model is more accurate than that of existing kinetic and isotherm equations in assessing barium and strontium removal with adj. R² values of 0.994 and 0.991, respectively. We developed a standalone user interface to estimate the barium and strontium removal as a function of sorption process parameters. Sensitivity analysis and quantitative estimation were carried out to study individual process variables' impact on removal efficiency.

Fate of radium on the discharge of oil and gas produced water to the marine environment

Understanding the speciation and fate of radium during operational discharge from the offshore oil and gas industry into the marine environment is important in assessing its long term environmental impact. In the current work, ²²⁶Ra concentrations in marine sediments contaminated by produced water discharge from a site in the UK were analysed using gamma spectroscopy. Radium was present in field samples (0.1-0.3 Bq g^-1) within International Atomic Energy Agency activity thresholds and was found to be primarily associated with micron sized radiobarite particles (≤2 μm). Experimental studies of synthetic/field produced water and seawater mixing under laboratory conditions showed that a significant proportion of radium (up to 97%) co-precipitated with barite confirming the radiobarite fate pathway. The results showed that produced water discharge into the marine environment results in the formation of radiobarite particles which incorporate a significant portion of radium and can be deposited in marine sediments.

Sequencing batch airlift reactors (SBAR): a suitable technology for treatment and valorization of mineral oil wastewaters towards lipids production

Produced water (PW) and spent oil-based wastewaters are some of the largest mineral oil wastewaters produced. Due to the high toxicity of hydrocarbons, several countries set stringent discharge limits and its treatment is compulsory before discharge. In this work, biological treatment of mineral oil wastewaters coupled with the production of bacterial lipids is demonstrated in sequential batch airlift reactors (SBAR). Two SBAR (2 L working volume) were used for treatment of PW and lubricant-based wastewater (LW), inoculated with Alcanivorax borkumensis SK2 (SBAR_Ab+PW) and Rhodococcus opacus B4 (SBAR_R.o+LW), respectively. A total petroleum hydrocarbon removal (TPH) efficiency up to 96% and 80% were achieved for SBAR_Ab+PW and SBAR_R.o+LW, respectively. Intracellular lipids production in SBAR_Ab+PW increased when lower TPH/N ratios and higher feast stage duration were applied (up to 0.74 g g^-1 cell dry weight (CDW)), whereas in SBAR_R.o+LW higher lipids production was observed for higher TPH/N ratios (0.94 g g^-1 in CDW). Triacylglycerols (TAG) were the main intracellular lipid accumulated in both SBAR_Ab+PW and SBAR_R.o+LW operations, while wax ester (WE) production was only observed extracellularly in the SBAR_Ab+PW.

Kurstakin molecules facilitate diesel oil assimilation by Acinetobacter haemolyticus strain 2SA through overexpression of alkane hydroxylase genes

Biodegradation is a cost-effective process commonly used to eliminate many xenobiotic hydrocarbons such as diesel oils. However, their hydrophobic character reduces the biodegradation efficiency. In order to overcome this hurdle, kurstakins isolated from Bacillus thuringiensis strain 7SA were used as emulsifying agents. The influence of kurstakin molecules on diesel oil degradation by Acinetobacter haemolyticus strain 2SA was evaluated in the presence and absence of the aforementioned lipopeptide. The degradation rates and gene expressions of alkane hydroxylases were evaluated at days 4, 10, 14 and 21. Results showed that kurstakin molecules increased the hydrophobicity of 2SA. Moreover, diesel oil degradation activities were higher in the presence of kurstakin with 29%, 35%, 29% and 23% improvement at 4th, 10th, 14th and 21st day respectively. Statistical analysis indicated that the difference between the degradation rates in the presence and absence of kurstakin was significant with p = 0.03. The detection of three different hydroxylase genes namely alkB, almA and cyp153 in 2SA genome, might have allowed more efficient degradability of alkanes. According to the real-time PCR results, cyp153 was the most induced gene during diesel oil degradation in the presence and absence of kurstakin. Yet, the three genes demonstrated higher levels of expression in the presence of kurstakin when compared to its absence. This study showed that kurstakins enhance the diesel oil biodegradation rate by increasing the hydrophobicity of 2SA. In addition to their anti-fungal activities, kurstakins can be used as biosurfactant to increase biodegradation of diesel oil.

Conformance Control in Oil Reservoirs by Citric Acid-Coated Magnetite Nanoparticles

Reservoir conformance control methods may significantly improve enhanced oil recovery technologies through reduced water production and profile correction. Excessive water production in oil and gas reservoirs leads to severe problems. Water shutoff and conformance control are, therefore, financially and environmentally advantageous for the petroleum industry. In this paper, water shutoff performance of citric acid-coated magnetite (CACM) and hematite nanoparticles (NPs) as well as polyacrylamide polymer solution in a heterogeneous and homogeneous two-dimensional micromodel is compared. A facile one-step technique is used to synthesize the CACM NPs. The NPs, which are reusable, easily prepared, and environmentally friendly, are characterized using Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, dynamic light scattering, and X-ray diffraction. The results confirm uniform spherical Fe₃O₄ NPs of an average diameter of 40 nm, well coated with citric acid. CACM NPs provide a high pressure drop coupled with an acceptable resistance factor and residual resistance factor owing to NP arrangement into a solid-/gel-like structure in the presence of a magnetic field. A resistance factor and a residual resistance factor of 3.5 and 2.14, respectively, were achieved for heavy oil and the heterogeneous micromodel. This structure contributed to an appreciable plugging efficiency. CACM NPs respond to ∼1000 G of magnetic field intensity and display a constant resistance factor at intensities between 4500 and 6000 G. CACM NPs act as a gel, forming a solid-/gel-like structure, which moves toward the magnetic field and thereby shuts off the produced water and increases the oil fraction. The findings of this study suggest the ability to shut off water production using specially designed magnetic field-responsive smart fluids. The application would require innovative design of field equipment.

Effective anaerobic treatment of produced water from petroleum production using an anaerobic digestion inoculum from a brewery wastewater treatment facility

Produced water is a major waste problem in oil production yet it also represents a potential water source if treated properly, especially in arid regions. In this study, we investigate the anaerobic treatability of an oil-produced water with extremely high chemical oxygen demand (COD) and total dissolved organic carbon (TOC) from Wyoming's Greater Green River Basin using anaerobic microcosms inoculated with a microbial consortium derived from a brewery wastewater treatment facility. The results demonstrate that for this water and an appropriate microbial inoculation, high-COD/TOC can be effectively removed with concomitant energy recovery as a form of methane. 93% and 89% of the COD and TOC were removed with a final high methane yield of 33.9 mmol/g carbon (848 μmol/g carbon/day). Chemical analyses showed that the ethylacetate-extractable compounds were much more amenable to biodegradation than the CH₂Cl₂ extractable compounds. Furthermore, compounds that were added during drilling and completion remained in the water and contributed significantly to the COD and anaerobic degradability. This study demonstrates that produced waters are amenable to anaerobic biological treatment and also that thorough chemical analyses are necessary to fully understand the potential for treatment.

Chemical characterization of non-volatile dissolved organic matter from oilfield-produced brines in the Nanyishan area of the western Qaidam Basin, China

Oil and gas (O&G) produced water (PW) is the largest waste stream generated in oil and gas industries. A comprehensive understanding of the compositions and features of dissolved organic matter (DOM) in O&G PWs from different geologic formation, ages, and origins is crucial for controlling their adverse effects and developing efficient technologies for treatment and reuse. In this study, four non-volatile DOM samples were isolated from oilfield-produced brines in the Nanyishan area of the Qaidam Basin and characterized by a multi-analytical approach. Results indicated that the compositions of the studied DOM samples were dominated by aliphatics, which may originate from shale-derived oil hydrocarbons as well as plants, algae, and bacteria from lacustrine deposits. Smaller amounts of cyclic aliphatic compounds were also identified in the DOM samples. Samples contained relatively low concentrations of carbohydrates that probably related to microbes in the oilfield brines. Concentrations of polycyclic aromatic hydrocarbons and aromatics were also low, likely due to limited influence from petroleum oil and/or organic chemicals added to the oilfield brines. The contents of nitrogen- and sulfur-containing heterocyclic compounds were all very low and could have been partly influenced by inorganic compositions of the brines. Moreover, the abundance of unsubstituted aliphatics and halogen-containing compounds may be potential indicators of the age and/or the type of oil/gas wells. Results from this study can further our knowledge of the structures and compositions of oilfield PW DOM samples originating from continental sources.

Potentiality of Azolla pinnata R. Br. for Phytoremediation of Polluted Freshwater with Crude Petroleum Oil

The pollution of freshwater resources with crude petroleum oil is a major environmental issue in oil-producing countries. As a result, the remediation of polluted aquatic ecosystems using eco-friendly and cost-effective technology is receiving increased global attention. In this study, the ability of Azolla pinnata R. Br. to remediate petroleum-polluted freshwater was assessed. The remediation potentiality was determined by evaluating the total petroleum hydrocarbon degradation percentage (TPH%) and changes in the molecular type composition of saturated and aromatic hydrocarbon fractions. TPH% was estimated gravimetrically, and changes in the molecular type composition of saturated and aromatic fractions were measured using gas chromatography and high-performance liquid chromatography, respectively. The results reveal that A. pinnata has the potential to phytoremediate freshwater polluted with low levels (up to 0.5 g/L) of petroleum hydrocarbons (PHs). After seven days of phytoremediation, the degradation rate of total PHs was 92% in the planted treatment compared with 38% in the unplanted positive control. The highest breakdown of PHs for the normal paraffinic saturated hydrocarbon fraction occurred in the presence of A. pinnata combined with Anabena azollaea (A-A), which showed a moderate degradation capacity toward total aromatic hydrocarbons (TAHs) and total polycyclic aromatic hydrocarbons (PAHs). The results indicate that A. pinnata effectively removed C18, a saturated PH, and acenaphthene (Ace), an aromatic PH. Therefore, this study suggests that A. pinnata is a useful tool for the remediation of freshwaters contaminated with low pollution levels of crude oil.

Isolation and characterization of a halophilic Modicisalibacter sp. strain Wilcox from produced water

We report the isolation a halophilic bacterium that degrades both aromatic and aliphatic hydrocarbons as the sole sources of carbon at high salinity from produced water. Phylogenetic analysis of 16S rRNA-gene sequences shows the isolate is a close relative of Modicisalibacter tunisiensis isolated from an oil-field water in Tunisia. We designate our isolate as Modicisalibacter sp. strain Wilcox. Genome analysis of strain Wilcox revealed the presence of a repertoire of genes involved in the metabolism of aliphatic and aromatic hydrocarbons. Laboratory culture studies corroborated the predicted hydrocarbon degradation potential. The strain degraded benzene, toluene, ethylbenzene, and xylenes at salinities ranging from 0.016 to 4.0 M NaCl, with optimal degradation at 1 M NaCl. Also, the strain degraded phenol, benzoate, biphenyl and phenylacetate as the sole sources of carbon at 2.5 M NaCl. Among aliphatic compounds, the strain degraded n-decane and n-hexadecane as the sole sources of carbon at 2.5 M NaCl. Genome analysis also predicted the presence of many heavy metal resistance genes including genes for metal efflux pumps, transport proteins, and enzymatic detoxification. Overall, due to its ability to degrade many hydrocarbons and withstand high salt and heavy metals, strain Wilcox may prove useful for remediation of produced waters.

Occurrence and biodegradation of hydrocarbons at high salinities

Hypersaline environments are found around the world, above and below ground, and many are exposed to hydrocarbons on a continuous or a frequent basis. Some surface hypersaline environments are exposed to hydrocarbons because they have active petroleum seeps while others are exposed because of oil exploration and production, or nearby human activities. Many oil reservoirs overlie highly saline connate water, and some national oil reserves are stored in salt caverns. Surface hypersaline ecosystems contain consortia of halophilic and halotolerant microorganisms that decompose organic compounds including hydrocarbons, and subterranean ones are likely to contain the same. However, the rates and extents of hydrocarbon biodegradation are poorly understood in such ecosystems. Here we describe hypersaline environments potentially or likely to become contaminated with hydrocarbons, including perennial and transient environments above and below ground, and discuss what is known about the microbes degrading hydrocarbons and the extent of their activities. We also discuss what limits the microbial hydrocarbon degradation in hypersaline environments and whether there are opportunities for inhibiting (oil storage) or stimulating (oil spills) such biodegradation as the situation requires.

Boehmite nanopowder recovered from aluminum cans waste as a potential adsorbent for the treatment of oilfield produced water

In the present study, high surface area boehmite nanopowder was recovered from aluminum cans waste. The sodium aluminate solution was first prepared by dissolving aluminum cans in NaOH solution and then, H2O2 solution was added to precipitate boehmite. The prepared boehmite was characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and N2 adsorption–desorption techniques. The thermal stability of the boehmite sample was investigated using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. The feasibility of using the prepared boehmite powder as a new low-cost adsorbent for the treatment of oilfield produced water was investigated. For comparison, commercial activated carbon was used for the treatment of the produced water under the same conditions. The efficiency of both of boehmite and activated carbon in the treatment of produced water was determined by monitoring the values of a number of pollution indicators [i.e. turbidity, sulfides, sulfates, total organic carbon (TOC), total petroleum hydrocarbon (TPH), and chemical oxygen demand (COD)] before and after the treatment. The boehmite powder showed very good efficiency in the treatment of the produced water, which is very close to that of commercial activated carbon under the same conditions. The effect of adsorbent dose, treatment time, and pH of the media on the adsorption efficiency of both of boehmite and activated carbon was examined at room temperature using chemical oxygen demand as a pollution indicator. The maximum capacity for COD reduction was 69.6% for boehmite and 83.5% for activated carbon at 40 g/l adsorbent dosage, pH7, and 24-h contact time.

Graphic abstract

Fouling mitigation in produced water treatment by conjugation of advanced oxidation process and microfiltration

This work explored the use of ozonation and photoperoxidation before the microfiltration process to reduce fouling. Produced water was synthesized with salt, viscosifier, and surfactant. The additives influence on membrane fouling was evaluated. Photoperoxidation process led to an overall better performance than ozonation in terms of oil removal and fouling reduction. The maximum oil removal efficiency was 86%, obtained for emulsions with salt after 2 h of treatment (COD: H₂O₂ ratio 1:1, UV dose of 965 J/m²). The inclusion of chemical additives impaired the oxidative power of hydroxyl radicals leading to a moderate oil removal; however, they were still able to reduce membrane fouling, mainly in oil/water emulsions with viscosifier. Higher salt concentration promoted fouling resistance and also benefited the permeate quality. Cross-flow microfiltration process integrated with photoperoxidation was able to improve the permeate flux from 84 to 182 L/m².h after 3 h of exposure to UV radiation, resulting in a permeate with less than 10 mg/L of oil content. Graphical abstract.

Energy Efficient Ultrahigh Flux Separation of Oily Pollutants from Water with Superhydrophilic Nanoscale Metal-Organic Framework Architectures

The rising demand for clean water for a growing and increasingly urban global population is one of the most urgent issues of our time. Here, we introduce the synthesis of a unique nanoscale architecture of pillar-like Co-CAT-1 metal-organic framework (MOF) crystallites on gold-coated woven stainless steel meshes with large, 50 μm apertures. These nanostructured mesh surfaces feature superhydrophilic and underwater superoleophobic wetting properties, allowing for gravity-driven, highly efficient oil-water separation featuring water fluxes of up to nearly one million L m-2  h-1 . Water physisorption experiments reveal the hydrophilic nature of Co-CAT-1 with a total water vapor uptake at room temperature of 470 cm3  g-1 . Semiempirical molecular orbital calculations shed light on water affinity of the inner and outer pore surfaces. The MOF-based membranes enable high separation efficiencies for a number of liquids tested, including the notorious water pollutant, crude oil, affording chemical oxygen demand (COD) concentrations below 25 mg L-1 of the effluent. Our results demonstrate the great impact of suitable nanoscale surface architectures as a means of encoding on-surface extreme wetting properties, yielding energy-efficient water-selective large-aperture membranes.

The Separation of Emulsified Water/Oil Mixtures through Adsorption on Plasma-Treated Polyethylene Powder

This paper addresses the preparation and characterization of efficient adsorbents for tertiary treatment (oil content below 100 ppm) of oil/water emulsions. Powdered low-density polyethylene (LDPE) was modified by radio-frequency plasma discharge and then used as a medium for the treatment of emulsified diesel oil/water mixtures in the concentration range from 75 ppm to 200 ppm. Plasma treatment significantly increased the wettability of the LDPE powder, which resulted in enhanced sorption capability of the oil component from emulsions in comparison to untreated powder. Emulsions formed from distilled water and commercial diesel oil (DO) with concentrations below 200 ppm were used as a model of oily polluted water. The emulsions were prepared using ultrasonication without surfactant. The droplet size was directly proportional to sonication time and ranged from 135 nm to 185 nm. A sonication time of 20 min was found to be sufficient to prepare stable emulsions with an average droplet size of approximately 150 nm. The sorption tests were realized in a batch system. The effect of contact time and initial oil concentrations were studied under standard atmospheric conditions at a stirring speed of 340 rpm with an adsorbent particle size of 500 microns. The efficiency of the plasma-treated LDPE powder in oil removal was found to be dependent on the initial oil concentration. It decreased from 96.7% to 79.5% as the initial oil concentration increased from 75 ppm to 200 ppm. The amount of adsorbed oil increased with increasing contact time. The fastest adsorption was observed during the first 30 min of treatment. The adsorption kinetics for emulsified oils onto sorbent followed a pseudo-second-order kinetic model.

Degradation of benzo[a]pyrene by halophilic bacterial strain Staphylococcus haemoliticus strain 10SBZ1A

The exploitation of petroleum oil generates a considerable amount of “produced water or petroleum waste effluent (PWE)” that is contaminated with polycyclic aromatic hydrocarbons (PAHs), including Benzo[a]pyrene (BaP). PWE is characterised by its high salinity, which can be as high as 30% NaCl, thus the exploitation of biodegradation to remove PAHs necessitates the use of active halophilic microbes. The strain 10SBZ1A was isolated from oil contaminated soils, by enrichment experiment in medium containing 10% NaCl (w/v). Homology analyses of 16S rRNA sequences identified 10SBZ1A as a Staphylococcus haemoliticus species, based on 99.99% homology (NCBI, accession number GI: MN388897). The strain could grow in the presence of 4–200 μmol l^-1 of BaP as the sole source of carbon, with a doubling time of 17–42 h. This strain optimum conditions for growth were 37 ^oC, 10% NaCl (w/v) and pH 7, and under these conditions, it degraded BaP at a rate of 0.8 μmol l^-1 per day. The strain 10SBZ1A actively degraded PAHs of lower molecular weights than that of BaP, including pyrene, phenanthrene, anthracene. This strain was also capable of removing 80% of BaP in the context of soil spiked with BaP (10 μmol l^-1 in 100 g of soil) within 30 days. Finally, a metabolic pathway of BaP was proposed, based on the identified metabolites using liquid chromatography-high resolution tandem mass spectrometry. To the best of our knowledge, this is the first report of a halophilic BaP degrading bacterial strain at salinity > 5% NaCl.

Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

The wetting and evaporation behavior of droplets of aqueous solutions of mixtures of poly(diallyldimethylammonium chloride) solution, PDADMAC, with two different anionic surfactants, sodium laureth sulfate, SLES, and sodium N-lauroyl N-methyl taurate, SLMT, were studied in terms of the changes of the contact angle θ and contact length L of sessile droplets of the mixtures on silicon wafers at a temperature of 25 °C and different relative humidities in the range of 30–90%. The advancing contact angle θa was found to depend on the surfactant concentration, independent of the relative humidity, with the mixtures containing SLES presenting improved wetting behaviors. Furthermore, a constant droplet contact angle was not observed during evaporation due to pinning of the droplet at the coffee-ring that was formed. The kinetics for the first evaporation stage of the mixture were independent of the relative humidity, with the evaporation behavior being well described in terms of the universal law for evaporation.

Designing a next generation solar crystallizer for real seawater brine treatment with zero liquid discharge

Proper disposal of industrial brine has been a critical environmental challenge. Zero liquid discharge (ZLD) brine treatment holds great promise to the brine disposal, but its application is limited by the intensive energy consumption of its crystallization process. Here we propose a new strategy that employs an advanced solar crystallizer coupled with a salt crystallization inhibitor to eliminate highly concentrated waste brine. The rationally designed solar crystallizer exhibited a high water evaporation rate of 2.42 kg m⁻² h⁻¹ under one sun illumination when treating real concentrated seawater reverse osmosis (SWRO) brine (21.6 wt%). The solar crystallizer array showed an even higher water evaporation rate of 48.0 kg m⁻² per day in the outdoor field test, suggesting a great potential for practical application. The solar crystallizer design and the salt crystallization inhibition strategy proposed and confirmed in this work provide a low-cost and sustainable solution for industrial brine disposal with ZLD.

Proper disposal of industrial brine remains a critical environmental challenge. Here, the authors devise a solar crystallizer and propose a salt crystallization inhibition strategy, which together provide a low-cost and sustainable solution for industrial brine disposal with zero liquid discharge.

Treatment of wastewater containing oil and grease by biological method- a review

One of the complex environmental problems that triggers at present is oily wastewater contamination arising out of the activities related to engineering vehicular (automobile) workshop or garage, kitchens in houses and restaurants, gas stations, metal finishing house, petrochemical industry, edible oil production unit etc. Oily wastewater discharge is a major issue of environmental pollution in the present decade as some of its constituents are hazardous in nature. Hence, appropriate treatment technology for oily wastewater needs to be addressed. Biological treatment (BT) technique would be the best option in this regard, because it has multiple advantages over various other techniques as available today. BT degrades effectively the harmful constituents of oily wastewater into innocuous products that are environment friendly and it is considered to be the economical method. The resulting effluent of pretreatment followed by biological treatment of oily wastewater can be reused after conforming discharge limits. Again, numerous research works in these days have optimized the function and result of existing laboratory and pilot scale treatment technologies. This review paper describes a comprehensive understanding of the origin and characteristics, existing techniques in laboratory and pilot scale, screening of different methods, justification for advocating biological methods for treatment of oily wastewater.

Hydrodynamic and Performance Evaluation of a Porous Ceramic Membrane Module Used on the Water-Oil Separation Process: An Investigation by CFD

Wastewater from the oil industry can be considered a dangerous contaminant for the environment and needs to be treated before disposal or re-use. Currently, membrane separation is one of the most used technologies for the treatment of produced water. Therefore, the present work aims to study the process of separating oily water in a module equipped with a ceramic membrane, based on the Eulerian–Eulerian approach and the Shear-Stress Transport (SST k-ω) turbulence model, using the Ansys Fluent^® 15.0. The hydrodynamic behavior of the water/oil mixture in the filtration module was evaluated under different conditions of the mass flow rate of the fluid mixture and oil concentration at the entrance, the diameter of the oil particles, and membrane permeability and porosity. It was found that an increase in the feed mass flow rate from 0.5 to 1.5 kg/s significantly influenced transmembrane pressure, that varied from 33.00 to 221.32 kPa. Besides, it was observed that the particle diameter and porosity of the membranes did not influence the performance of the filtration module; it was also verified that increasing the permeability of the membranes, from 3 × 10⁻¹⁵ to 3 × 10⁻¹³ m², caused transmembrane pressure reduction of 22.77%. The greater the average oil concentration at the permeate (from 0.021 to 0.037 kg/m³) and concentrate (from 1.00 to 1.154 kg/m³) outlets, the higher the average flow rate of oil at the permeate outlets. These results showed that the filter separator has good potential for water/oil separation.

Shock effects of monovalent cationic salts on seawater cultivated granular sludge

Saline wastewater is commonly encountered in various industries, posing challenges to biological treatments. The application of seawater as a seed source provides a media of diverse halophilic organisms for rapid startup. However, effects of transitioning from a mixed salt source to monovalent salt solutions prevalent in industry remains unexplored. Hence, seed sludge was cultivated using seawater and later granulated under a mixed-salt synthetic medium comprising a mixture of NaCl, KCl and Na₂SO₄ at a combined concentration of 0.8 M (0.27 M each). The stable, acclimated granules were then tested against single salt media of 0.8 M NaCl, KCl, or Na₂SO₄. Shift to single salt media resulted in granule disaggregation, poor settling, sludge washout and development of fluffy or slimy flocs. Changes in exopolysaccharides composition after the single salt shift was the predominant reason for the large changes in sludge morphology. The impacts of KCl and Na₂SO₄ were more significant than the shift to NaCl. The resulting impacts also had a major influence on the treatment performance. A complex mechanism involving monovalent cation stimulation of proteins; ionic strength impacts on exopolysaccharides and morphology; solution density influence on sludge density and settling; and tonicity impacts on cell viability and treatment is described.