scholarly journals Force measurements between particles and the air-water interface: Implications for particle mobilization in unsaturated porous media

2009 ◽  
Vol 45 (6) ◽  
Author(s):  
Jianying Shang ◽  
Markus Flury ◽  
Youjun Deng
Keyword(s):  
Porous Media ◽  
Water Interface ◽  
Unsaturated Porous Media ◽  
Force Measurements ◽  
Air Water Interface

scholarly journals Adsorption of PFOA at the Air–Water Interface during Transport in Unsaturated Porous Media

2018 ◽  
Vol 52 (14) ◽  
pp. 7745-7753 ◽  
Author(s):  
Ying Lyu ◽  
Mark L. Brusseau ◽  
Wei Chen ◽  
Ni Yan ◽  
Xiaori Fu ◽  
...  
Keyword(s):  
Porous Media ◽  
Water Interface ◽  
Unsaturated Porous Media ◽  
Air Water Interface

Adhesion of Colloids and Bacteria to Porous Media: A Critical Review

2019 ◽  
Vol 7 (4) ◽  
pp. 417-460 ◽  
Author(s):  
Runwei Li ◽  
Changfu Wei ◽  
Hefa Cheng ◽  
Gang Chen
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Bacterial Adhesion ◽  
Fate And Transport ◽  
Theoretical Models ◽  
Water Interface ◽  
Subsurface Soil ◽  
Air Water Interface ◽  
Surface Physicochemical Properties ◽  
The Impact

Adhesion of colloids and bacteria to various surfaces is important for a variety of environmental phenomena including microbial biofouling and contamination prevention. Under saturated conditions, both colloids and bacteria have the opportunity to attach to porous medium surfaces. Under water unsaturated conditions or in the presence of the air-water interface, besides the porous medium surfaces, colloids and bacteria can also attach to the air-water interface, including the air-water-solid threephase interface. The magnitudes of adhesion of colloids and bacteria are correlated to the interactions of the colloids and bacteria with the surfaces, which are a function of their surface physicochemical properties. In this review, adhesion theories are revisited and adhesion of colloids and bacteria to porous media and the air-water interface is discussed. The interaction forces are quantified using various theoretical models including the DLVO models and used to interpret related adhesion. The impact of surfactants on colloid and bacterial adhesion is also discussed. The review also includes the implementation of the adhesion theory in interpreting colloid and bacterial fate and transport in the subsurface soil.

scholarly journals Assessing the Role of Pseudomonas aeruginosa Surface-Active Gene Expression in Hexadecane Biodegradation in Sand

2002 ◽  
Vol 68 (5) ◽  
pp. 2509-2518 ◽  
Author(s):  
P. A. Holden ◽  
M. G. LaMontagne ◽  
A. K. Bruce ◽  
W. G. Miller ◽  
S. E. Lindow
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Porous Media ◽  
Liquid Culture ◽  
Sand Culture ◽  
Water Interface ◽  
Unsaturated Porous Media ◽  
Wild Type ◽  
Active Compounds ◽  
Surface Active ◽  
Surface Active Compounds

ABSTRACT Low pollutant substrate bioavailability limits hydrocarbon biodegradation in soils. Bacterially produced surface-active compounds, such as rhamnolipid biosurfactant and the PA bioemulsifying protein produced by Pseudomonas aeruginosa, can improve bioavailability and biodegradation in liquid culture, but their production and roles in soils are unknown. In this study, we asked if the genes for surface-active compounds are expressed in unsaturated porous media contaminated with hexadecane. Furthermore, if expression does occur, is biodegradation enhanced? To detect expression of genes for surface-active compounds, we fused the gfp reporter gene either to the promoter region of pra, which encodes for the emulsifying PA protein, or to the promoter of the transcriptional activator rhlR. We assessed green fluorescent protein (GFP) production conferred by these gene fusions in P. aeruginosa PG201. GFP was produced in sand culture, indicating that the rhlR and pra genes are both transcribed in unsaturated porous media. Confocal laser scanning microscopy of liquid drops revealed that gfp expression was localized at the hexadecane-water interface. Wild-type PG201 and its mutants that are deficient in either PA protein, rhamnolipid synthesis, or both were studied to determine if the genetic potential to make surface-active compounds confers an advantage to P. aeruginosa biodegrading hexadecane in sand. Hexadecane depletion rates and carbon utilization efficiency in sand culture were the same for wild-type and mutant strains, i.e., whether PG201 was proficient or deficient in surfactant or emulsifier production. Environmental scanning electron microscopy revealed that colonization of sand grains was sparse, with cells in small monolayer clusters instead of multilayered biofilms. Our findings suggest that P. aeruginosa likely produces surface-active compounds in sand culture. However, the ability to produce surface-active compounds did not enhance biodegradation in sand culture because well-distributed cells and well-distributed hexadecane favored direct contact to hexadecane for most cells. In contrast, surface-active compounds enable bacteria in liquid culture to adhere to the hexadecane-water interface when they otherwise would not, and thus production of surface-active compounds is an advantage for hexadecane biodegradation in well-dispersed liquid systems.

Role of the Air–Water Interface in the Retention of TiO2Nanoparticles in Porous Media during Primary Drainage

2008 ◽  
Vol 42 (6) ◽  
pp. 1916-1921 ◽  
Author(s):  
Lixia Chen ◽  
David A. Sabatini ◽  
Tohren C. G. Kibbey
Keyword(s):  
Porous Media ◽  
Water Interface ◽  
Air Water Interface

Microplastic water repellency impacts water flow and microplastic transport in soils

2021 ◽  
Author(s):  
Andreas Cramer ◽  
Pascal Benard ◽  
Anders Kaestner ◽  
Mohsen Zare ◽  
Andrea Carminati
Keyword(s):  
Porous Media ◽  
Water Flow ◽  
Capillary Rise ◽  
Water Repellency ◽  
Water Infiltration ◽  
Water Interface ◽  
Deuterated Water ◽  
X Ray ◽  
Air Water Interface ◽  
The Impact

<p>Soils are considered the largest sink of microplastic particles (MP) in terrestrial ecosystems. However, there is little knowledge on the implications of MP contaminating soils. In particular, we do not know the extent of and conditions under which MP are transported through porous media and, if they are deposited, how they affect soil hydraulic properties and soil moisture dynamics. We hypothesize that: 1) hydrophobic MP enhance soil water repellency; 2) isolated MP are displaced and transported by the air-water interface; 3) clusters of MP impede water flow and are retained in air-filled pores.</p><p>We tested these hypotheses in mixtures of MP (µm range) and sands (mm range) in a series of experiments. The Sessile Drop Method (SDM) was applied to measure the average contact angle (CA) of the mixtures for MP and model porous media in the same size range, ranging from 0 - 100 % MP content. Based on the specific surface and shape factor of MP and soil particles, the results are extrapolated to different MP and soil particle sizes. Capillary rise experiments were performed to measure the impact of MP on water infiltration. The applied MP contents of 0.35 % and 1.05 % reflect an average CA of 60° and 90° from the SDM extrapolation. Capillary rise of water and ethanol were carried out to estimate the apparent CA. Additionally and with the same MP content, we simultaneously imaged in three-dimensions the movement of deuterated water and MP during repeated drying / wetting cycles using X-Ray and Neutron tomography (at the beamline ICON, PSI). The different neutron attenuation coefficients of deuterated water and MP allows for estimating their distribution in the sand packing.</p><p>Already at MP contents of 5 % the CA measured with the SDM exhibited a steep increase and reached 59° to 81°, depending on the grain size of MP. The capillary rise experiments showed that MP reduce capillary rise. The apparent CA (43° and 53°) were smaller compared to the average CA from the SDM (60° and 90°), but the added MP increased air entrapment during capillary rise leading to a reduced saturation of the pore space (18 % and 16.5 %). Accumulation of MP at the advancing air-water interface was visible. Neutron and X-ray imaging showed at high resolution that regions with major MP content are water repellent and, are bypassed by water flow, and remain in air-filled pores.</p><p>Extrapolation of these results to soils suggests that in microregions with high MP contents, water infiltration is hindered. The low water content in these microregions might limit MP degradation due to reductions in: hydrolysis, coating of MP by e.g. dissolved organic substances, and colonization by microorganisms.</p>

Sampling and analysis of the air-water interface with SEM and EDS of microlayers

1989 ◽  
Vol 47 ◽  
pp. 1004-1005
Author(s):  
Randall W. Smith ◽  
John Dash
Keyword(s):  
Heavy Metals ◽  
Surface Microlayer ◽  
Surface Films ◽  
Water Interface ◽  
Physical Processes ◽  
Infrared Spectroscopic Analysis ◽  
Eds Analysis ◽  
Air Water Interface ◽  
Significant Area ◽  
Bulk Chemical

The structure of the air-water interface forms a boundary layer that involves biological ,chemical geological and physical processes in its formation. Freshwater and sea surface microlayers form at the air-water interface and include a diverse assemblage of organic matter, detritus, microorganisms, plankton and heavy metals. The sampling of microlayers and the examination of components is presently a significant area of study because of the input of anthropogenic materials and their accumulation at the air-water interface. The neustonic organisms present in this environment may be sensitive to the toxic components of these inputs. Hardy reports that over 20 different methods have been developed for sampling of microlayers, primarily for bulk chemical analysis. We report here the examination of microlayer films for the documentation of structure and composition.Baier and Gucinski reported the use of Langmuir-Blogett films obtained on germanium prisms for infrared spectroscopic analysis (IR-ATR) of components. The sampling of microlayers has been done by collecting fi1ms on glass plates and teflon drums, We found that microlayers could be collected on 11 mm glass cover slips by pulling a Langmuir-Blogett film from a surface microlayer. Comparative collections were made on methylcel1ulose filter pads. The films could be air-dried or preserved in Lugol's Iodine Several slicks or surface films were sampled in September, 1987 in Chesapeake Bay, Maryland and in August, 1988 in Sequim Bay, Washington, For glass coverslips the films were air-dried, mounted on SEM pegs, ringed with colloidal silver, and sputter coated with Au-Pd, The Langmuir-Blogett film technique maintained the structure of the microlayer intact for examination, SEM observation and EDS analysis were then used to determine organisms and relative concentrations of heavy metals, using a Link AN 10000 EDS system with an ISI SS40 SEM unit. Typical heavy microlayer films are shown in Figure 3.

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