Combining low salinity water (LSW) with surfactants has an enormous potential for enhancing oil recovery processes. However, there is no consensus about the mechanisms involved, in addition to the fact that several studies have been conducted in model systems, while experiments with rocks and reservoir fluids are scarce. This study presents a core-flooding experiment of LSW injection, with and without surfactant, using the core and heavy oil samples obtained from a sandstone reservoir in southeastern Mexico. The effluents and the crude oil obtained at each stage were analyzed. The study was complemented by tomographic analysis. The results revealed that LSW injection and hybrid process with surfactants obtained an increase of 11.4 percentage points in recovery factor. Various phenomena were caused by LSW flooding, such as changes in wettability and pH, ion exchange, mineral dissolution, detachment of fines and modification of the hydrocarbon profile. In the surfactant flooding, the reduction of interfacial tension and alteration of wettability were the main mechanisms involved. The findings of this work also showed that the conditions believed to be necessary for enhanced oil recovery with LSW, such as the presence of kaolinite or high acid number oil, are not relevant.

Biosurfactant production at reactor level by Serratia marcescens SmSA was optimized and evaluated to enhance the heavy oil recovery on carbonate rocks. Temperature, agitation, and carbon/nitrogen (C/N) ratio were evaluated to optimize biosurfactant production by using a Taguchi (L9) design. The best conditions (C/N ratio: 6, 25 degrees C, and agitation: 100 rpm) were used to scale up the biosurfactant production with a 3-L bioreactor. The best aeration for biosurfactant production was 0.66 volume of air per volume of liquid per minute (vvm), producing the lowest surface tension (26 mN/m) in 14 h, with a biosurfactant yield of 14.26 g/L as a crude product and 2.85 g/L as a purified product, and a critical micelle concentration of 280 mg/L. The biosurfactant was characterized as a lipopeptide, and it was stable under extreme conditions: pH (2-12), salinity up to 200 g/L, and temperature up to 150 degrees C confirmed by thermogravimetric analysis. Enhanced oil recovery test was carried out with a carbonate core and heavy oil under reservoir conditions, obtaining an additional recovery of 8%, due to reduced interfacial tension and modified wettability of the rock. These findings highlight the potential application of S. marcescens SmSA biosurfactant in enhanced oil recovery.

Bioremediation of hydrocarbon contaminated soils requires releasing the oil from the porous matrix to render it bioavailable. This work aims at evaluating a biosurfactant produced by a Bacillus subtilis strain to improve the release and biodegradation of heavy crude oil contaminating limestone sand. The biosurfactant effect on biodegradation of crude oil was elucidated, using a Rhodococcus sp. strain. The CO2 production rate was used as indicator of biological activity that improved by 32.84%. Moreover, at least 67% of the >C20 fraction was degraded in the systems with biosurfactant, reducing aromatic and resin fractions (12.5% and 2%, respectively), whereas without biosurfactant only 37% of the > C20 fraction was removed compared with the null reduction in aromatics and resin. The decrease in surface and interfacial tension, as well as the modification to wettability caused by biosurfactant activity, were the main mechanisms promoting the release of heavy oil, thus making it bioavailable

A general 3D flow and transport model in porous media was derived applying an axiomatic continuum modeling approach, which was implemented using the finite element method to numerically simulate, analyze and interpret microbial enhanced oil recovery (MEOR) processes under laboratory conditions at core scale. From the methodological point of view the development stages (conceptual, mathematical, numerical and computational) of the model are shown. This model can be used as a research tool to investigate the effect on the flow behavior, and consequently the impact on the oil recovery, due to clogging/declogging phenomena by biomass production, and interfacial tension changes because of biosurfactant production. The model was validated and then applied to a case study. The experimental results were accurately predicted by the simulations. Due to its generality, the model can be easily extended and applied to other cases.

Oily sludge from gas processing facilities contains components that are major environmental pollutants. Biodegradation is an alternative treatment, but can be affected by other components of the sludge, such as sulphur compounds, so it is important to evaluate the effect of these on oil biodegradation in order to prevent negative impacts. This work studied the transformation of sulphur compounds in oily sludge biodegradation systems at the microcosm level. The predominant sulphur compounds in the original sludge were elemental sulphur and pyrite (9,776 and 28,705.4 mg kg−1, respectively). In the biodegradability assays, hydrocarbon concentrations decreased from 312,705.6 to 186, 760.3 mg kg−1 after 15 days of treatment. After this time, hydrocarbon degrading activity stopped, corresponding with a decrease in hydrocarbon degrading bacteria. These changes were related to a reduction in pH that inhibits biodegradation. During the assay, sulphur compounds were gradually oxidized and transformed. The concentration of sulphate increased from 5,096 to 64,868.3 mg kg−1 after 30 days in the assay, although controls were unchanged. Therefore, it is important to determine changes to the main compounds of the waste in order to assess their impact.

Background Several studies on oil recovery using a packed system have been reported; however, the majority use Berea (quartz). In Mexico, more than 37% of the proven reserves are found in reservoirs formed of carbonate and quartz rocks. In this study, the effects on microbial oil recovery of three types of porous media were evaluated: carbonate (Lm), quartz (Ot), and rock from a Mexican oil reservoir (Ch), formed of carbonate (45%) and quartz (38%). Results Oil recovery experiments using granulated porous media saturated with oil and two mixed cultures (AF1 and AF2) from a Mexican oil field, were assessed at 70 degrees C under anaerobic conditions. Microbial cultures were composed of thermophilic, fermentative microorganisms, including Thermoanaerobacter, Natronovirga and Geothermobacterium, among others. Biomass production (150240 mg L1), substrate consumption (0.1 mg L1 h1) and CO2 production (0.100.28 mmol L1) were measured. The systems presented significant differences in recovery (P= 0.000006), and carbonated systems presented the highest oil recovery; the best system combining the AF2 culture with porous medium from a Mexican reservoir (Ch) composed mainly of carbonate, achieving an oil recovery of 23.8%. Conclusion The efficiency of microbial enhanced oil recovery is dependent on the inoculum and the type of porous medium.

The biodegradation of oil sludge from Mexican sour gas and petrochemical facilities contaminated with a high content of hydrocarbons, 334.7 +/- 7.0 g kg(-1) dry matter (dm), was evaluated. Studies in microcosm systems were carried out in order to determine the capacity of the native microbiota in the sludge to reduce hydrocarbon levels under aerobic conditions. Different carbon/nitrogen/phosphorous (C/N/P) nutrient ratios were tested. The systems were incubated at 30 degrees C and shaken at 100 rpm. Hydrocarbon removals from 32 to 51% were achieved in the assays after 30 days of incubation. The best assay had C/N/P ratio of 100/1.74/0.5. The results of the Microtox (R) and Ames tests indicated that the original sludge was highly toxic and mutagenic, whereas the best assay gave a final product that did not show toxicity or mutagenicity. (C) 2011 Elsevier Ltd. All rights reserved.

The success of biotechnological processes for oil recovery depends on adequate understanding of the system components: microorganisms, oil and porous media. Nine oil samples were collected from a carbonate oil reservoir in Cordoba Platform, Veracruz, Mexico. Geochemical characterisation demonstrated heavy oils with: API gravity of 10.7 to 14.5 degrees, 3 to 5% sulphur, 36.58 to 54.06% aromatic hydrocarbons and -23.98 to -24.24 (parts per thousand) delta C-13 isotopic values in total oil. Additionally, the pristane/phytane ratio (Pr/Ph) <1 indicated an anoxic depositional environment. Results showed that native microbiota could have contributed to the biogeochemical transformation of the oil in the reservoir. Anaerobic, thermophilic, halotolerant and fermentative enrichment cultures were obtained from the nine oil samples (A1-A9). Metabolites such as CO2, CH4, ethanol, acetone, acetate and biosurfactants were detected. Mixed culture from the A7 sample showed the highest activity among all the mixed cultures screened, growing under 50 to 80 degrees C, 5 to 35 g NaCl and 0.8 to 14.2 MPa pressure. Its kinetic parameters were mu(max) = 0.321 h(-1) and Ks = 0.54 g L-1. These results were used to determine the conditions for oil recovery assays. A7 culture enhanced recovery of up to 12% of heavy oil (11.16 degrees API) in oil impregnated carbonate granular porous media. Analysis of the V3 region of the 16S rRNA gene of the A7 culture showed that the predominant taxon was Thermoanaerobacter. Phylogenetic approximations demonstrated that similitude percentage of 99.9% corresponded to Thermoanaerobacter ethanolicus, 99.6% to Thermoanaerobacter pseudethanolicus and 98.9% to Thermoanaerobacter brockii and Thermoanaerobacter finii. (C) 2011 Elsevier B.V. All rights reserved.

A considerable portion of oil reserves in Mexico corresponds to heavy oils. This feature makes it more difficult to recover the remaining oil in the reservoir after extraction with conventional techniques. Microbial enhanced oil recovery (MEOR) has been considered as a promising technique to further increase oil recovery, but its application has been developed mainly with light oils; therefore, more research is required for heavy oil. In this study, the recovery of Mexican heavy oil (11.1 degrees API and viscosity 32,906 mPa s) in a coreflood experiment was evaluated using the extremophile mixed culture A7, which was isolated from a Mexican oil field. Culture A7 includes fermentative, thermophilic, and anaerobic microorganisms. The experiments included waterflooding and MEOR stages, and were carried out under reservoir conditions (70 degrees C and 9.65 MPa). MEOR consisted of injections of nutrients and microorganisms followed by confinement periods. In the MEOR stages, the mixed culture A7 produced surface-active agents (surface tension reduction 27 mN m(-1)), solvents (ethanol, 1738 mg L-1), acids (693 mg L-1), and gases, and also degraded heavy hydrocarbon fractions in an extreme environment. The interactions of these metabolites with the oil, as well as the bioconversion of heavy oil fractions to lighter fractions (increased alkanes in the C-8-C-30 range), were the mechanisms responsible for the mobility and recovery of heavy oil from the porous media. Oil recovery by MEOR was 19.48% of the residual oil in the core after waterflooding. These results show that MEOR is a potential alternative to heavy oil recovery in Mexican oil fields. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.

The strain SmSA, identified as Serratia marcescens and known as a biosurfactant producer, was isolated from hydrocarbon contaminated soil from Veracruz, México. The interactions among the C/N, C/Mg and C/Fe ratios have not been examined for this microorganism. In this work was evaluated the effect of these nutrients at three levels using a mineral medium with glucose as the carbon source. A Box-Behnken experimental design was utilised to maximise biosurfactant production, which was assessed by oil spreading and surface tension tests. The treatment with C/N=5, C/Fe=26,000 and C/Mg=30 showed the best result since the surface tension was reduced to 30mNm−1. The multiple regression and response surface analyses indicated that the interaction between C/N and C/Mg had the utmost effect on the reduction of surface tension and biosurfactant production. The conditions of the best treatment were used to scale up biosurfactant production in a 3L bioreactor giving a yield of 4.1gL−1 of pure biosurfactant. It was found that the biosurfactant was mainly produced in the exponential phase and decreased the surface tension to 31mNm−1. The contact between the biosurfactant with heavy oil (15° API) increased its displacement from 9.3 to 18cm.

Haloalkaliphilic sulfur-oxidizing mixed cultures for the treatment of alkaline–saline effluents containing sulfide were characterized and evaluated. The mixed cultures (IMP-PB, IMP-XO and IMP-TL) were obtained from Mexican alkaline soils collected in Puebla (PB), Xochimilco (XO) and Tlahuac (TL), respectively. The Ribosomal Intergenic Spacer Analysis (RISA) revealed bacteria related to Thioalkalibacterium and Thioalkalivibrio in IMP-XO and IMP-PB mixed cultures. Halomonas strains were detected in IMP-XO and IMP-TL. In addition, an uncultured Bacteroides bacterium was present in IMP-TL. Mixed cultures were evaluated at different pH and NaCl concentrations at 30°C. IMP-PB and IMP-TL expressed thiosulfate-oxidizing activity in the 7.5–10.5 pH range, whereas IMP-XO presented its maximal activity with 19.0 mg O2 g protein −1  min−1, at pH 10.6; it was not affected by NaCl concentrations up to 1.7 M. In continuous culture, IMP-XO showed a growth rate of 15 day−1, productivity of 433.4 mgprotein l−1 day−1 and haloalkaliphilic sulfur-oxidizing activity was also detected up to 170 mM by means of N-methyl-diethanolamine (MDEA). Saline–alkaline soil samples are potential sources of haloalkaliphilic sulfur-oxidizing bacteria and the mixed cultures could be applied in the treatment of inorganic sulfur compounds in petroleum industry effluents under alkaline–saline conditions.

Microcosm assays and Taguchi experimental design was used to assess the biodegradation of an oil sludge produced by a gas processing unit. The study showed that the biodegradation of the sludge sample is feasible despite the high level of pollutants and complexity involved in the sludge. The physicochemical and microbiological characterization of the sludge revealed a high concentration of hydrocarbons (334,766+/-7001 mg kg(-1) dry matter, d.m.) containing a variety of compounds between 6 and 73 carbon atoms in their structure, whereas the concentration of Fe was 60,000 mg kg(-1) d.m. and 26,800 mg kg(-1) d.m. of sulfide. A Taguchi L(9) experimental design comprising 4 variables and 3 levels moisture, nitrogen source, surfactant concentration and oxidant agent was performed, proving that moisture and nitrogen source are the major variables that affect CO(2) production and total petroleum hydrocarbons (TPH) degradation. The best experimental treatment yielded a TPH removal of 56,092 mg kg(-1) d.m. The treatment was carried out under the following conditions: 70% moisture, no oxidant agent, 0.5% of surfactant and NH(4)Cl as nitrogen source.

This chapter describes biotreatment of water pollutants from the petroleum industry. Water has been considered as one of the main raw materials of the petroleum industry, and its treatment and reuse with advanced treatment technology is being developed. Biological processes are a cost-effective technology for the removal of organic, sulfur and nitrogen compounds from wastewaters. Anaerobic processes are one of the most viable alternatives for the treatment of complex effluents such as those produced in the petroleum industry. The chapter presents some of the recent developments in biological wastewater treatment technology with application to the petroleum industry and discusses anaerobic biodegradation of aromatic compounds such as phenol, alkylphenols, and terephthalate. The chapter also discusses the biotransformation of S- and N-bearing inorganic compounds and methyl-tert-butyl ether (MTBE) biodegradation. MTBE is a high recalcitrant compound and a potential water contaminant that only in few cases can be treated with technology originally developed for biological wastewater treatment.

In the refinery industry, the washing processes of middle-distillates using caustic solutions generate phenol- and sulfide-containing waste streams. The spent caustic liquors generated contain phenols at concentrations higher than 60 g dm(-3) (638.3 mmol dm(-3)). For sulfur compounds, the average sulfide concentration was 48 g dm(-3) (1500 mmol dm(-3)) in these streams. The goal of this study was to evaluate the specific impact of phenol and sulfide concentrations towards the phenol-biodegradation activity of a phenol-acclimated anaerobic granular sludge. An inhibition model was used to calculate the phenol and sulfide inhibitory concentrations that completely stopped the phenol-biodegradation activity (IC100). A maximum phenol-biodegradation activity of 83 mumol g(-1) VSS h(-1) was assessed and the IC100 values were 21.8 mmol dm(-3) and 13.4 mmol dm(-3) for phenol and sulfide respectively. The limitation of the phenol biodegradation flow by phenol inhibition seemed to be related to the more important sensitivity of phenol-degrading bacteria. The up-flow anaerobic sludge bed reactor operating in a non-phenol-dependent inhibition condition did not present any sensitivity to sulfide concentrations below 9.6 mmol dm(-3). At this residual concentration, the pH and bisulfide ions' concentration might be responsible for the general collapsing of the reactor activity. (C) 2004 Society of Chemical Industry.

Chemical and petrochemical industries are important sources of aromatic pollutants. Petrochemical processes like caustic washing of middle distillates produce the spent caustic liquors highly concentrated in phenol and alkyl phenols. The anaerobic technology is considered a feasible strategy for petrochemical wastewater pre-treatment although high concentrations of phenol could limit its efficiency. The goal of this work was to determine the toxicity of both selected alkyl phenols and a synthetic "spent-caustic phenols mixture" on the acetoclastic Specific Methanogenic Activity (SMA) of unadapted and phenol-adapted granular sludge. Alkyl phenols were responsible for 50% (IC50) and 100% (IC100) inhibition of the SMA at concentrations ranging from 1.6 to 5.0 mM and from 4.1 to 27.5 mM, respectively, for un-adapted granular sludge. In the case of phenol-adapted granular sludge, the inhibitory concentrations ranged from 1.7 to 14.9 mM and from 4.0 to 83.0 for IC50 and IC100, respectively, highlighting the impact of sludge acclimation. The inhibition produced by 2-ethylphenol was more acute compared to phenol and was not reduced by the phenol acclimation process. The IC50 and IC100 values obtained for the synthetic "spent-caustic phenols mixture" were 9.5 mM and 88.4 mM, respectively. The inhibitory concentrations of phenol compounds were closely correlated with compound apolarity (log P), indicating that the lipophilic character of the tested compounds was responsible for their methanogenic toxicity. An inhibition model is confirmed to estimate the IC50 and IC100.

The anaerobic biodegradability of mixtures of phenolic compounds was studied under continuous and batch systems. Continuous experiments were carried out in up-flow anaerobic sludge bed (UASB) reactors degrading a mixture of phenol and p-cresol as the main carbon and energy sources. The total chemical oxygen demand (COD) removal above 90% was achieved even at organic loading rates as high as 7 kg COD/m(3)/day. Batch experiments were conducted with mixtures of phenolic compounds (phenol, p-cresol, and o-cresol) to determine the specific biodegradation rates using unadapted and adapted anaerobic granular sludge. Phenol and p-cresol were mineralized by adapted sludge with rates several orders of magnitude higher than unadapted sludge. Additionally, an UASB reactor was operated with the mixture phenol, p-cresol, and o-cresol. After 54 days of operation, 80% of o-cresol (supplied at 132 mg/L) was eliminated. The phenol biodegradation was not affected by the presence of o-cresol. These results demonstrate that major phenolic components in petrochemical effluents can be biodegraded simultaneously during anaerobic treatment.

A mixed culture aerobically metabolized phenol, cresol isomers (o-,m-,p-), 2-ethylphenol and xylenol isomers (2,5-DMP and 3,4-DMP) as the sole carbon and energy source. This culture had a high tolerance towards phenol with values of maximum degradation rate (V\max) of 47 μM phenol mg−1 protein h−1 and inhibition substrate constant (Ki) of 10 mM. These kinetic parameters were considerably diminished and the toxicity increased with the alkylphenols. For example with 2,5-xylenol, V\max and Ki values of 0.8 μM 2,5-xylenol mg−1 protein h−1 and 1.3 mM, respectively, were obtained. The cresols were 5-fold more toxic than phenol, whereas 2-ethylphenol and 3,4-xylenol were 11-fold more toxic, and 2,5-xylenol was 34-fold more toxic than phenol.