Relationship between Microbial Community Characteristics and Flooding Efficiency in Microbial Enhanced Oil Recovery

Microbial enhanced oil recovery (MEOR) is the research focus in the field of energy development as an environmentally friendly and low cost technology. MEOR can bes divided into indigenous microbial oil recovery and exogenous microbial oil recovery. The ultimate goal of indigenous microbial flooding is to enhance oil recovery via stimulation of specific indigenous microorganisms by injecting optimal nutrients. For studying the specific rule to activate the indigenous community during the long-term injection period, a series of indigenous displacement flooding experiments were carried out by using the long-core physical simulation test. The experimental results have shown that the movement of nutrients components (i.e., carbon/nitrogen/phosphorus) differed from the consumption of them. Moreover, there was a positive relationship between the nutrients concentration and bacteria concentration once observed in the produced fluid. And the trend of concentration of acetic acid was consistent with that of methanogens. When adding same activators, the impacts of selective activators to stimulate the indigenous microorganisms became worse along with the injection period, which led to less oil recovery efficiency.

Thinning air-water films stabilized by bacterial particles

The ability of particles to stabilize liquid films has broad applications in many fields,such as drug delivery,biofuel catalysis,and crude-oil separation.The mechanism of particles to stabilize emulsions has been widely studied.However,how particles affect the stability of suspension films is still unclear.Here,the dynamics of bacterial particles on free liquid films during evaporation is obtained by direct microscopic observation.We find that the initial concentration of the bacterial solution affects the evolution of the shapes and stabilities of liquid films.The liquid film with a low bacterial concentration exhibits a drainage and rupture process similar to pure water,and bacteria would be evacuated during the evaporation of liquid film.However,when the bacterial concentration is high,bacteria form a single-layer array in the center of the film and greatly enhance the stability of the liquid film.We demonstrate that these two distinct film evaporation dynamics are caused by the difference in the lateral capillary force of the particles at different positions on the liquid film,which is not affected by the active motility of particle.Together,our research reveals the critical role of bacteria concentration in stabilizing suspension liquid film.

Effect of humic acids and sunlight on the cytotoxicity of engineered zinc oxide and titanium dioxide nanoparticles to a river bacterial assemblage

The effect of a terrestrial humic acid （HA） and Suwannee River HA on the cytotoxicity of engineered zinc oxide nanoparticles （ZnONPs） and titanium dioxide nanoparticles （TiO2NPs） to natural aquatic bacterial assemblages was measured with spread plate counting. The effect of HA （10 and 40 ppm） on the cytotoxicity of ZnONPs and TiO2NPs was tested factorially in the presence and absence of natural sunlight （light irradiation （LI））. The experiment was of full factorial, completely randomized design and the results were analyzed using the General Linear Model in SAS analytical software. The method of least squares means was used to separate the means or combinations of means. We determined the mechanism of toxicity via measurements of oxidative stress and metal ions. The toxicity of ZnONPs and TiO2NPs to natural aquatic bacterial assemblages appears to be concentration dependent. Moreover, the cytotoxicity of ZnONPs and TiO2NPs appeared to be affected by HA concentration, the presence of sunlight irradiation, and the dynamic multiple interactions among these factors. With respect to light versus darkness in the control group, the data indicate that bacterial viability was inhibited more in the light exposure than in the darkness exposure. The same was true in the HA treatment groups. With respect to terrestrial versus Suwanee River HA for a given nanoparticle, in light versus darkness, bacterial viability was more inhibited in the light treatment groups containing the terrestrial HA than in those containing Suwanee River HA. Differences in the extent of reactive oxygen species formation, adsorption/binding of ZnONPs/TiO2NPs by HA, and the levels of free metal ions were speculated to account for the observed cytotoxicity. TEM images indicate the attachment and binding of the tested nanoparticles to natural bacterial assemblages. Besides the individual parameter, significant effects on bacterial viability count were also observed in the following combined treatments： HA-ZnONPs, HA-LI, ZnONPs-LI, and HA-ZnONPs-LI. The main effects of all independent variables, plus interaction effects in all cases were significant with TiO2NPs.