Exopolysaccharide production by a genetically engineered Enterobacter cloacae strain for microbial enhanced oil recovery

Exploring the use of microbial enhanced oil recovery in Kazakhstan: a review

Microbial enhanced oil recovery (MEOR) is a promising method for improving oil recovery from challenging reservoirs such as those found in Kazakhstan. MEOR relies on the activities of microorganisms to modify the properties of the reservoir, such as reducing the oil viscosity, increasing the reservoir permeability, and generating by-products that mobilize the oil. Implementing MEOR in Kazakhstan could lead to significant economic benefits for the country by increasing oil production and royalties from fossil fuel exports. Oil production in Kazakhstan has seen fluctuations in recent years, with 2018 recording a production level of 1.814 million barrels per day. Among regions, Atyrau region contributed the most to oil production with 23.4 million tons of oil. Following Atyrau, the Mangystau region produced 8.2 million tons, and Aktobe produced 2.4 million tons. Overall, the use of MEOR in Kazakhstan's oil fields could offer a promising solution for enhanced oil recovery, while minimizing environmental impact and cost. While specific data on the current use of MEOR in field conditions in Kazakhstan might be limited, the fact that studies are underway suggests a growing interest in applying this technology in the country's oil fields. It is exciting to think about the potential benefits these studies could bring to Kazakhstan's oil industry once their findings are implemented in field operations. These studies have significant implications for Kazakhstan's oil production in the future.

Simultaneous production of biosurfactant and extracellular unspecific peroxygenases by Moesziomyces aphidis XM01 enables an efficient strategy for crude oil degradation

Crude oil is a hazardous pollutant that poses significant and lasting harm to human health and ecosystems. In this study, Moesziomyces aphidis XM01, a biosurfactant mannosylerythritol lipids (MELs)-producing yeast, was utilized for crude oil degradation. Unlike most microorganisms relying on cytochrome P450, XM01 employed two extracellular unspecific peroxygenases, MaUPO.1 and MaUPO.2, with preference for polycyclic aromatic hydrocarbons (PAHs) and n-alkanes respectively, thus facilitating efficient crude oil degradation. The MELs produced by XM01 exhibited a significant emulsification activity of 65.9% for crude oil and were consequently supplemented in an "exogenous MELs addition" strategy to boost crude oil degradation, resulting in an optimal degradation ratio of 72.3%. Furthermore, a new and simple "pre-MELs production" strategy was implemented, achieving a maximum degradation ratio of 95.9%. During this process, the synergistic up-regulation of MaUPO.1, MaUPO.1 and the key MELs synthesis genes contributed to the efficient degradation of crude oil. Additionally, the phylogenetic and geographic distribution analysis of MaUPO.1 and MaUPO.1 revealed their wide occurrence among fungi in Basidiomycota and Ascomycota, with high transcription levels across global ocean, highlighting their important role in biodegradation of crude oil. In conclusion, M. aphidis XM01 emerges as a novel yeast for efficient and eco-friendly crude oil degradation.

Modification of Welan gum with poly(2-oxazoline) to obtain thermoviscosifying polymer for enhanced oil recovery

Thermoviscosifying polymers refer to a category of smart materials that exhibit a responsive behavior to environmental stimuli, specifically demonstrating a natural rise in viscosity of solutions as the temperature increases. The temperature-dependent behavior exhibited by thermally viscous polymers renders them potentially advantageous in the context of Enhanced Oil Recovery (EOR). There exists a dearth of research pertaining to the application of thermoviscosifying polymer for better recovery in reservoirs characterized by high temperatures and high salt content. In order to tackle the mentioned concerns, this study examined the utilization of welan gum modified with poly(2-oxazoline) as thermally responsive chain segments to enhance viscosity. The objective was to evaluate the ability to enhance viscosity under thermal conditions and to assess their effectiveness in displacement of reservoir oil in high temperature and high salt environments. This study aimed to establish a theoretical framework for understanding the correlation between the molecular structure and performance of novel thermally viscous polymers. Additionally, it sought to offer practical insights into designing the molecular structure of thermally viscous polymers suitable for polymer flooding in high temperature and high salt environments. Furthermore, the study proposed the application of these new thermoviscosifying polymers for EOR.

Nutrient optimization for indigenous microbial consortia of a Bhagyam oil field: MEOR studies

The microbial enhanced oil recovery (MEOR) method is an eco-friendly and economical alternative technology. The technology involves a variety of uncertainties, and its success depends on controlling microbial growth and metabolism. This study is one of a kind that showed successful tertiary recovery of crude oil through indigenous microbial consortia. In this study, a medium was optimized to allow ideal microbial growth under reservoir conditions through RSM. Once the nutrient recipe was optimized, the microbial metabolites were estimated through gas chromatography. The maximum amount of methane gas (0.468 mM) was produced in the TERIW174 sample. The sequencing data set showed the presence of Methanothermobacter sp. and Petrotoga sp. In addition, these established consortia were analyzed for their toxicity, and they appeared to be safe for the environment. Furthermore, a core flood study showed efficient recovery that was ~25 and 34% in TERIW70 and TERIW174 samples, respectively. Thus, both the isolated consortia appeared to be suitable for the field trials.

Research Advances of Microbial Enhanced Oil Recovery

Microbial enhanced oil recovery (MEOR), characterized with the virtues of low cost and environmental protection, reflects the prevalent belief in environmental protection, and is attracting the attention of more researchers. Nonetheless, with the prolonged slump in global oil prices, how to further reduce the cost of MEOR has become a key factor in its development. This paper described the recent development of MEOR technology in terms of mechanisms, mathematical models, and field application, meanwhile the novel technologies of MEOR such as genetically engineered microbial enhanced oil recovery (GEMEOR) and enzyme enhanced oil recovery (EEOR) were introduced. The paper proposed three possible methods to decrease the cost of MEOR: using inexpensive nutrients as substrates, applying a mixture of chemical and biological agents, and utilizing crude microbial products. Additionally, in order to reduce the uncertainty in the practical application of MEOR technology, it is essential to refine the reservoir screening criteria and establish a sound mathematical model of MEOR. Eventually, the paper proposes to combine genetic engineering technology and microbial hybrid culture technology to build a microbial consortium with excellent oil displacement efficiency and better environmental adaptability. This may be a vital part of the future research on MEOR technology, which will play a major role in improving its economic efficiency and practicality.

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Mechanisms of microbial enhanced oil recovery.

• The novel technology of microbial enhanced oil recovery.

• Field trails of microbial enhanced oil recovery.

Potential functions and applications of diverse microbial exopolysaccharides in marine environments

Exopolysaccharides (EPSs) from microorganisms are essential harmless natural biopolymers used in applications including medications, nutraceuticals and functional foods, cosmetics, and insecticides. Several microbes can synthesize and excrete EPSs with chemical properties and structures that make them suitable for several important applications. Microbes secrete EPSs outside their cell walls, as slime or as a "jelly" into the extracellular medium. These EPS-producing microbes are ubiquitous and can be isolated from aquatic and terrestrial environments, such as freshwater, marine water, wastewater, and soils. They have also been isolated from extreme niches like hot springs, cold waters, halophilic environments, and salt marshes. Recently, microbial EPSs have attracted interest for their applications such as environmental bio-flocculants because they are degradable and nontoxic. However, further efforts are required for the cost-effective and industrial-scale commercial production of microbial EPSs. This review focuses on the exopolysaccharides obtained from several extremophilic microorganisms, their synthesis, and manufacturing optimization for better cost and productivity. We also explored their role and applications in interactions between several organisms.

Exopolysaccharide of Anoxybacillus pushchinoensis G11 has antitumor and antibiofilm activities

Exopolysaccharides (EPS/EPSs) possess several various applications in the food and pharmaceutical industries. This study was performed to investigate the biological (antibiofilm and antitumor), rheological (temperature, shear rate, and density) and chemical (solubility, carbohydrate and protein content, composition, molecular weight, functional group analysis, thermal analysis, X-ray diffraction pattern and scanning electron microscopy) properties of the EPS, which was purified from the locally isolated thermophilic bacterium Anoxybacillus pushchinoensis G11 (MN720646). EPS was found to have antibiofilm and antitumor [lung (A-549) and colon (Caco-2 and HT-29) cancer] activities. The viscosity of EPS showing Newtonian flow was temperature dependent. As chemical properties, the EPS was found to be a heteropolysaccharide containing arabinose (57%), fructose (26%), glucose (12%), and galactose (5%). EPS contained 93% carbohydrates and 1.08% protein. The molecular weight of EPS was determined as 75.5 kDa. The FTIR analysis confirmed the presence of sulfate ester (band at 1217 cm^-1), an indication of the antitumor effect. The EPS was semi-crystalline. It could maintain 36% of its weight at 800 °C and crystallization and melting temperatures were 221 and 255.6 °C. This is the first report on the EPS production potential and the biological activity of A. pushchinoensis.

Biopolymer production by Aureobasidium mangrovei SARA-138H and its potential for oil recovery enhancement

The world economy depends heavily on crude oil. With a conventional oil recovery process, only one-third of crude oil is extracted. Various technologies have been developed to maximize the recovery of oil resources from natural reservoirs. Polymer technology has been used in many oil fields around the world. The biopolymer pullulan, produced by some Aureobasidium species, has been used in many industrial applications, but no research has been conducted regarding its use in the microbial enhancement of oil recovery (MEOR). Here, we investigate the potential of pullulan produced by newly isolated species Aureobasidium mangrovei SARA-138H for enhancement of oil recovery. Our results indicate that under optimized conditions, that is, sucrose as the carbon source in the medium, a pH of 9, incubation at 25 °C, and 250 rpm agitation, the fungus was able to produce 10 g/L of pullulan. The maximum viscosity achieved under these conditions was 318 cP after 15 days of incubation. Pullulan solution (10 g/L) showed the ability to recover 36.7% of heavy crude oil after 34.2% of secondary oil recovery. However, diluted pullulan in brine at the ratio (1:1) resulted in the recovery of 20.23% of oil from the residual oil in the core after 22.6% of secondary oil recovery. A 20-day injectivity test revealed that pullulan passed smoothly through the core, causing no blockage. It was concluded that pullulan from A. mangrovei SARA-138H was able to increase oil recovery to a degree comparable to that achieved with many polymers used in oil fields around the world. KEY POINTS: • First report of biopolymer "pullulan" from A. mangrovie. • Optimum conditions for pullulan production were obtained. • Pullulan recovered 36.7% of heavy oil from residual oil in place, with good injectivity.

Production of 2,3-dihydroxyisovalerate by Enterobacter cloacae

2,3-Dihydroxyisovalerate is an intermediate of the valine synthesis pathway. However, neither natural microorganisms nor valine producing engineered strains have been reported yet to produce this chemical. Based on the 2,3-butanediol synthesis pathway, a biological route of 2,3-dihydroxyisovalerate production was developed using a budA and ilvD disrupted Klebsiella pneumoniae strain in our previous research. We hypothesised, that other 2,3-butanediol producing bacteria could be used for 2,3-dihydroxyisovalerate production. Here a budA disrupted Enterobacter cloacae was constructed, and this strain exhibited a high 2,3-dihydroxyisovalerate producing ability. Disruption of ilvD in E. cloacae ΔbudA further increased 2,3-dihydroxyisovalerate level. The disruption of budA, encoding an acetolactate decarboxylase, resulted in the acetolactate synthesized in the 2,3-butanediol synthesis pathway to flow into the valine synthesis pathway. The additional disruption of ilvD, encoding a dihydroxy acid dehydratase, prevented the 2,3-dihydroxyisovalerate to be further metabolized in the valine synthesis pathway. Thus, the disruption of both budA and ilvD in 2,3-butanediol producing strains might be an universal strategy for 2,3-dihydroxyisovalerate accumulation. After optimization of the medium components and culture parameters 31.2 g/L of 2,3-dihydroxyisovalerate was obtained with a productivity of 0.41 g/L h and a substrate conversion ratio of 0.56 mol/mol glucose in a fed-batch fermentation. This approach provides an economic way for 2,3-dihydroxyisovalerate production.

Microbial exopolysaccharides: Synthesis pathways, types and their commercial applications

Polysaccharides are essential natural metabolites found in all life forms such as microorganisms, animals and plants with various biochemical structures and biological functions. Among all the life forms microbial exopolysaccharides are produced in shorter time duration as they responsible for the microbial cell adhesion and protection during unfavorable growth conditions. Microbial exopolysaccharides are composed of repeated sugar units of same or different types and form a complex by associating with proteins, lipids, metal ions, extracellular DNA (eDNA), organic and inorganic compounds to form a protective layer around the microbial colonies collectively known as biofilm. Specific functions of exopolysaccharides depend on structural composition and habitat of a host microorganism. There are various techniques to study the composition and structure of exopolysaccharides such as High Performance Anion Exchange Chromatography with Pulsed Amperometric Detection, Size Exclusion Chromatography coupled with multi-laser light scattering (SEC-MALLS),X-Ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) and Thermal Gravimetric Analysis (TGA), etc. In the current article, we reviewed microbial exopolysaccharides physiochemical properties, composition, analyzing techniques through which possible commercial applications in dairy products, cosmetics, research, agriculture and petroleum industry can be performed.

Potential applications of microbial enhanced oil recovery to heavy oil

Heavy oil accounts for around one-third of total global oil and gas resources. The progressive depletion of conventional energy reserves has led to an increased emphasis on the efficient exploitation of heavy oil and bitumen reserves in order to meet energy demand. Therefore, it is imperative to develop new technologies for heavy oil upgrading and recovery. Biologically-based technology that involves using microorganisms or their metabolites to mobilize heavy oil trapped in reservoir rocks can make a significant contribution to the recovery of heavy oils. Here, the results of laboratory experiments and field trials applying microbial enhanced oil recovery (MEOR) technologies are summarized. This review provides an overview of the basic concepts, mechanisms, advantages, problems, and trends in MEOR, and demonstrates the credibility of MEOR methods for applications in enhanced heavy oil recovery and the petroleum refining processes. This technology is cost-effective and environmentally-friendly. The feasibility of MEOR technologies for heavier oil has not yet been fully realized due to the perceived process complexity and a lack of sufficient laboratory research and field test data. However, novel developments such as enzyme-enhanced oil recovery continues to improve MEOR methods.HighlightsHeavy oil represents the largest known potentially-recoverable petroleum energy resource.Novel biotechnological processes are needed to recover or upgrade heavy oil.Microbial technologies have great potential for heavy oil recovery.Microorganisms can produce metabolic byproducts to mobilize oil trapped in reservoirs.More technological research is needed to develop microbial enhanced oil recovery.

Microbial enhanced oil recovery through deep profile control using a conditional bacterial cellulose-producing strain derived from Enterobacter sp. FY-07

Background

Heterogeneity of oil-bearing formations is one of major contributors to low oil recovery efficiency globally. Long-term water flooding will aggravate this heterogeneity by resulting in many large channels during the exploitation process. Thus, injected water quickly flows through these large channels rather than oil-bearing areas, which ultimately leads to low oil recovery. This problem can be solved by profile control using polymer plugging. However, non-deep profile control caused by premature plugging is the main challenge. Here, a conditional bacterial cellulose-producing strain, namely Enterobacter sp. FY-0701, was constructed for deep profile control to solve the problem of premature plugging. Its deep profile control and oil displacement capabilities were subsequently identified and assessed.

Results

The conditional bacterial cellulose-producing strain Enterobacter sp. FY-0701 was constructed by knocking out a copy of fructose-1, 6-bisphosphatase (FBP) encoding gene in Enterobacter sp. FY-07. Scanning electron microscope observation showed this strain produced bacterial cellulose using glucose rather than glycerol as the sole carbon source. Bacterial concentration and cellulose production at different locations in core experiments indicated that the plugging position of FY-0701 was deeper than that of FY-07. Moreover, enhanced oil recovery by FY-0701 was 12.09%, being 3.86% higher than that by FY-07 in the subsequent water flooding process.

Conclusions

To our knowledge, this is the first report of conditional biopolymer-producing strains used in microbial enhance oil recovery (MEOR). Our results demonstrated that the conditional bacterial cellulose-producing strain can in situ produce biopolymer far from injection wells and plugs large channels, which increased the sweep volume of injection water and enhance oil recovery. The construction of this strain provides an alternative strategy for using biopolymers in MEOR.

Use of Microorganisms in the Recovery of Oil From Recalcitrant Oil Reservoirs: Current State of Knowledge, Technological Advances and Future Perspectives

The depletion of oil resources, increasing global energy demand, the current low, yet unpredictable, price of oil, and increasing maturity of major oil fields has driven the need for the development of oil recovery technologies that are less costly and, where possible, environmentally compatible. Using current technologies, between 20 and 40% of the original oil in a reservoir can be extracted by conventional production operations (e.g., vertical drilling), with secondary recovery methods yielding a further 15-25%. Hence, up to 55% of the original oil can remain unrecovered in a reservoir. Enhanced oil recovery (EOR) is a tertiary recovery process that involves application of different thermal, chemical, and microbial processes to recover an additional 7-15% of the original oil in place (OOIP) at an economically feasible production rate from poor-performing and depleted oil wells. EOR can significantly impact oil production, as increase in the recovery rate of oil by even a small margin could bring significant revenues without developing unconventional resources. Microbial enhanced oil recovery (MEOR) is an attractive, alternative oil recovery approach, which is claimed to potentially recover up to 50% of residual oil. The in situ production of biological surface-active compounds (e.g., biosurfactants) during the MEOR process does not require vast energy inputs and are not affected by global crude oil prices. Compared to other EOR methods, MEOR can be an economically and more environmentally friendly alternative. In this review, the current state of knowledge of MEOR, with insights from discussions with the industry and other stakeholders, is presented and in addition to the future outlook for this technology.

Stimulation of indigenous microbes by optimizing the water cut in low permeability reservoirs for green and enhanced oil recovery

Low permeability oil reservoirs are a widespread petroleum reservoir type all over the world. Therefore, methods to recover these reservoirs efficiently are of importance to guarantee energy supply. Here we report our novel stimulation of indigenous microbes by optimizing the water cut in low permeability reservoirs for green and enhanced oil recovery. We aimed to investigate the characteristics of indigenous bacterial communities with changes in water cut in reservoirs by high-throughput sequencing technology, and reveal the mechanism and characteristics of the crude oil biotreatment under different crude oil-water ratio conditions and the optimum activation time of indigenous functional microbial groups in reservoirs. The indigenous microbial metabolism products were characterized by gas chromatography mass spectrometry. Results showed that Acinetobacter (47.1%) and Pseudomones (19.8%) were the main functional genus of crude oil degradation at the optimal activation time, and can reduce the viscosity of crude oil from 8.33 to 5.75 mPa·s. The dominant bacteria genus for oil recovery after activation of the production fluids was similar to those in the reservoirs with water cut of 60-80%. Furthermore seven mechanism pathways of enhancing oil recovery by the synergistic of functional microbial groups and their metabolites under different water cut conditions in low permeability reservoirs have been established.

Microbial Mineralization of Montmorillonite in Low-Permeability Oil Reservoirs for Microbial Enhanced Oil Recovery

Microbial mineralization (corrosion, decomposition, and weathering) has been investigated for its role in the extraction and recovery of metals from ores. Here we report our application of biomineralization for the microbial enhanced oil recovery in low-permeability oil reservoirs. It aimed to reveal the etching mechanism of the four Fe(III)-reducing microbial strains under anaerobic growth conditions on Ca-montmorillonite. The mineralogical characterization of Ca-montmorillonite was performed by Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive spectrometry. Results showed that the microbial strains could efficiently reduce Fe(III) at an optimal rate of 71%, alter the crystal lattice structure of the lamella to promote interlayer cation exchange, and efficiently inhibit Ca-montmorillonite swelling at a rate of 48.9%.IMPORTANCE Microbial mineralization is ubiquitous in the natural environment. Microbes in low-permeability reservoirs are able to facilitate alteration of the structure and phase of the Fe-poor minerals by reducing Fe(III) and inhibiting clay swelling, which is still poorly studied. This study aimed to reveal the interaction mechanism between Fe(III)-reducing bacterial strains and Ca-montmorillonite under anaerobic conditions and to investigate the extent and rates of Fe(III) reduction and phase changes with their activities. Application of Fe(III)-reducing bacteria will provide a new way to inhibit clay swelling, to elevate reservoir permeability, and to reduce pore throat resistance after water flooding for enhanced oil recovery in low-permeability reservoirs.

Influence of pH on dynamics of microbial enhanced oil recovery processes using biosurfactant producing Pseudomonas putida: Mathematical modelling and numerical simulation

In present work, the influence of reservoir pH conditions on dynamics of microbial enhanced oil recovery (MEOR) processes using Pseudomonas putida was analysed numerically from the developed mathematical model for MEOR processes. Further, a new strategy to improve the MEOR performance has also been proposed. It is concluded from present study that by reversing the reservoir pH from highly acidic to low alkaline condition (pH 5-8), flow and mobility of displaced oil, displacement efficiency, and original oil in place (OOIP) recovered gets significantly enhanced, resulting from improved interfacial tension (IFT) reduction by biosurfactants. At pH 8, maximum of 26.1% of OOIP was recovered with higher displacement efficiency. The present study introduces a new strategy to increase the recovery efficiency of MEOR technique by characterizing the biosurfactants for IFT_min/IFT_max values for different pH conditions and subsequently, reversing the reservoir pH conditions at which the IFT_min/IFT_max value is minimum.

Rhamnolipids Produced by Indigenous Acinetobacter junii from Petroleum Reservoir and its Potential in Enhanced Oil Recovery

Biosurfactant producers are crucial for incremental oil production in microbial enhanced oil recovery (MEOR) processes. The isolation of biosurfactant-producing bacteria from oil reservoirs is important because they are considered suitable for the extreme conditions of the reservoir. In this work, a novel biosurfactant-producing strain Acinetobacter junii BD was isolated from a reservoir to reduce surface tension and emulsify crude oil. The biosurfactants produced by the strain were purified and then identified via electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The biosurfactants generated by the strain were concluded to be rhamnolipids, the dominant rhamnolipids were C26H48O9, C28H52O9, and C32H58O13. The optimal carbon source and nitrogen source for biomass and biosurfactant production were NaNO3 and soybean oil. The results showed that the content of acid components increased with the progress of crude oil biodegradation. A glass micromodel test demonstrated that the strain significantly increased oil recovery through interfacial tension reduction, wettability alteration and the mobility of microorganisms. In summary, the findings of this study indicate that the newly developed BD strain and its metabolites have great potential in MEOR.

Numerical modelling of biophysicochemical effects on multispecies reactive transport in porous media involving Pseudomonas putida for potential microbial enhanced oil recovery application

pH and resident time of injected slug plays a critical role in characterizing the reservoir for potential microbial enhanced oil recovery (MEOR) application. To investigate MEOR processes, a multispecies (microbes-nutrients) reactive transport model in porous media was developed by coupling kinetic and transport model. The present work differs from earlier works by explicitly determining parametric values required for kinetic model by experimental investigations using Pseudomonas putida at different pH conditions and subsequently performing sensitivity analysis of pH, resident time and water saturation on concentrations of microbes, nutrients and biosurfactant within reservoir. The results suggest that nutrient utilization and biosurfactant production are found to be maximum at pH 8 and 7.5 respectively. It is also found that the sucrose and biosurfactant concentrations are highly sensitive to pH rather than reservoir microbial concentration, while at larger resident time and water saturation, the microbial and nutrient concentrations were lesser due to enhanced dispersion.

A novel bioemulsifier from Geobacillus stearothermophilus A-2 and its potential application in microbial enhanced oil recovery

A novel glycoprotein emulsifier from the thermophilic, facultative anaerobic strain A-2 showing excellent, stable emulsifying properties and its potential application in MEOR.

Applications of biosurfactants in the petroleum industry and the remediation of oil spills

Petroleum hydrocarbons are important energy resources. However, petroleum is also a major pollutant of the environment. Contamination by oil and oil products has caused serious harm, and increasing attention has been paid to the development and implementation of innovative technologies for the removal of these contaminants. Biosurfactants have been extensively used in the remediation of water and soil, as well as in the main stages of the oil production chain, such as extraction, transportation, and storage. This diversity of applications is mainly due to advantages such as biodegradability, low toxicity and better functionality under extreme conditions in comparison to synthetic counterparts. Moreover, biosurfactants can be obtained with the use of agro-industrial waste as substrate, which helps reduce overall production costs. The present review describes the potential applications of biosurfactants in the oil industry and the remediation of environmental pollution caused by oil spills.

Construction and evaluation of an exopolysaccharide-producing engineered bacterial strain by protoplast fusion for microbial enhanced oil recovery

Enterobacter cloacae strain JD, which produces water-insoluble biopolymers at optimal temperature of 30°C, and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at high temperatures by protoplast fusion. The obtained fusant strain ZR3 produced exopolysaccharides at up to 45°C with optimal growth temperature at 35°C. The fusant produced exopolysaccharides of approximately 7.5 g/L or more at pH between 7.0 and 9.0. The feasibility of the enhancement of crude oil recovery with the fusant was tested in a sand-packed column at 40°C. The results demonstrated that bioaugmentation of the fusant was promising approach for MEOR. Mass growth of the fusant was confirmed in fermentor tests.

Optimization of fermentation conditions and properties of an exopolysaccharide from Klebsiella sp. H-207 and application in adsorption of hexavalent chromium

The novel exopolysaccharide HZ-7 is produced by Klebsiella sp. H-207, and its fermentation conditions were optimized by response surface methodology (RSM). In this study, the optimized medium consisted of sucrose 31.93 g/L, KNO₃ 2.17 g/L and K₂HPO₄ 5.47 g/L; while the optimized culture conditions consisted of seed age 13 h, with an inoculum size of 10.6% and incubation temperature of 28.9°C. A maximum HZ-7 yield of about 15.05 g/L was achieved under the optimized conditions using RSM and single-factor experiments. Next the exopolysaccharide HZ-7 was partially purified and characterized. The resulting product showed good properties, such as high concentration of uronic acid (41.67%), low average molecular weight (about 1.94×10⁵ Da) and porous surface structure, were very advantageous to biosorption. Therefore HZ-7 was applied to absorb hexavalent chromium (Cr(VI)). The maximum adsorption efficiency (99.2%) which was obtained at an initial pH of 1.0 along with an initial Cr(VI) concentration of 20 mg/L, was not affected by ordinary metal ions and temperature. These data suggest Klebsiella sp. H-207 exopolysaccharide will be promising potential for industrial application.