Clean Water Surface Research Articles

Mechanism of Photoinduced Bending and Twisting in Crystalline Microneedles and Microribbons Composed of 9-Methylanthracene

The solid-state photodimerization of 9-methylanthracene is used as a model system to investigate how crystal morphology and reaction dynamics affect photomechanical deformations of single microcrystals. By varying the crystallization conditions, two different crystal shapes, microneedles and microribbons, are grown on a clean water surface. The microribbons twist under irradiation, while the microneedles bend. In both shapes, the maximum deformation occurs at roughly the midpoint of the reaction, while further dimerization causes the crystals return to their original shapes. Powder X-ray diffraction patterns establish that the needles and ribbons have the same crystal orientation and that the photoreaction proceeds in a crystal-to-crystal manner. NMR spin-lattice relaxation measurements are consistent with the rapid formation of large (>100 nm) dimer crystal domains. Simultaneous measurement of the needle bending and monomer fluorescence signal allows us to correlate the bending with the reaction progress. The behavior is qualitatively reproduced by a model in which the motion is driven by strain between spatially distinct reactant and product domains, also called heterometry. We consider several different mechanisms that could give rise to these spatially distinct domains. The ability to control the photoinduced crystal deformation by manipulating crystal shape and solid-state reaction kinetics suggests that photoreactive molecular crystals may be useful for generating well-defined motions on small length scales.

The investigation of atmospheric deposition distribution of organochlorine pesticides (OCPs) in Turkey

Atmospheric deposition is a significant pollution source leading to contamination of remote and clean sites, surface waters and soils. Since persistent organic pollutants (POPs) stay in atmosphere without any degradation, they can be transported and deposited to clean surfaces. Organochlorine pesticides are an important group of POPs which have toxic and harmful effects to living organisms and environment. Therefore, atmospheric deposition levels and characteristics are of importance to determine the pollution quantity of water and soil surfaces in terms of POPs. This study reports the distribution quantities of atmospheric deposition including bulk, dry, wet and air–water exchange of particle and gas phase OCPs as a result of 1-year sampling campaign. Atmospheric deposition distribution showed that the main mechanism for OCPs deposition is wet processes with percentage of 69 of total deposition. OCP compounds' deposition varied according to atmospheric concentration and deposition mechanism. HCH compounds were dominant pesticide species for all deposition mechanisms. HCH deposition constituted the 65% of Σ10OCPs.

Short surface waves in the Canadian Arctic in 2007 and 2008

[1] We have collected time series data of short oceanic waves as a part of the International Polar Year (IPY) 2007–2008. Using a shipboard laser wave slope (LAWAS) system operating at 900 nm, we have obtained wave slopes measurements up to 60 rad m−1 wave number. We have compared our in situ wave slopes with collocated and concurrent high-resolution upwind Normalized Radar Cross Sections (NRCS) collected by QuikSCAT. The LAWAS measured wave slope spectra were consistent with local wind speeds and QuikSCAT measured NRCS. Our measured short wave mean slopes indicate their enhancement by long waves (0–1 rad m−1) at small values of long-wave slope. Concurrent with wave slope measurements, the strength of the reflected LAWAS light beam was analyzed in terms of the light attenuation coefficient at 900 nm. We have observed a correlation between surface elevation and light attenuation. The mechanism of wave modulated beam attenuation was found to be related to the instantaneous long wave skewness.

Bubble bouncing at a clean water surface

Experiments on the coalescence time of submillimeter bubbles colliding with a distilled water/air interface either being at rest (undisturbed) or vibrating vertically (with controlled amplitude and frequency) were carried out. It was found that the outcome of the bubble collision (coalescence or bounce) depends on impact velocity and size of the bubble, i.e. the parameters determining the bubble deformation degree. With the surface at rest, when the deformation of the bubble was sufficiently high, bubble bouncing was observed. It was caused by the fact that the radius of the intervening liquid film formed between the colliding bubble and water/air interface was large enough to prevent the liquid layer from reaching its thickness of rupture within the time of bubble-interface contact. Coalescence occurred in a consecutive collision if the bubble deformation was below a threshold value, as a result of dissipation of the kinetic energy associated with the bubble motion. The hypothesis about the crucial role of the bubble deformation and size of the liquid film formed in the bouncing mechanism was confirmed in a series of experiments where the bubble collided with a vibrating water/air interface. It was shown that when the kinetic energy was properly re-supplied from an external source (interface vibrations), the spectacular phenomenon of "immortal" bubbles, dancing indefinitely at the water/air interface, was achieved. It was shown that "immortal" bubble formation is a consequence of a similarly high degree of the bubble shape deformation and consequently a large enough radius of the liquid film formed.

Negligible water surface charge determined using Kelvin probe and total reflection X-ray fluorescence techniques

The water surface charge has been extensively debated in recent decades. Electrophoretic mobilities of air bubbles in water and disjoining pressures between the surfaces of aqueous films suggest that the surface of water exhibits a significant negative charge. This is commonly attributed to a strong adsorption of hydroxide ions at the interface, though spectroscopic measurements and simulation studies suggest surface depletion of hydroxide ions. Alternatively, the negative surface charge could arise from surface contamination with trace charged surfactants. We have probed the variation in the surface charge of water with pH by measuring surface potentials using the Kelvin probe technique. Independently, the abundance in the interfacial layer of "reporter ions" (Rb(+) and Br(-)), which must be affected by a charged surface, has been monitored using the total reflection X-ray fluorescence (TRXF) technique. Special care was taken to prove the high sensitivity of this technique as well as to avoid surface contaminants. The magnitude of the surface charge was found to be below 1 e per 500 nm(2) (TRXF). No evidence of variations in the surface potential between pH 2-3 and pH 9-12 was detected within the accuracies of the methods (5 mV for Kelvin probe and 2 mV for TRXF). Hence, our findings suggest that the clean water surface exhibits negligible charge in a wide pH range.

Sherwood–Rayleigh parameterization for evaporation in the presence of surfactant monolayers

Presented here is an experimental investigation of the effects of several surfactant monolayers on evaporation driven by natural convection in the air above a water surface. Experiments were performed in a controlled laboratory setting with tanks of heated water for the following cases: (1) a clean water surface, and for surfaces covered with monolayers of (2) oleyl alcohol, (3) stearic acid, and (4) stearyl alcohol. Evaporation rates were measured using a laser‐based method, and the Sherwood and Rayleigh numbers, Sh and Ra, were computed from the data. Power law scalings of the form Sh = B·Ram were developed for each case which yielded, essentially, m = 1/3 for all four surface conditions. The oleyl alcohol and stearic acid conditions give essentially the same value for B as for the clean surface case. For stearyl alcohol, B is smaller than for all other surface conditions; this result is attributed to the ability of the stearyl alcohol monolayer to inhibit evaporation by blocking the passage of water molecules through the monolayer: the barrier effect. The surface temperature is measured in this work enabling a separation of the effect of surfactants on evaporation due to a reduction in surface temperature from their effect on evaporation due to a true barrier effect. This has not been accomplished heretofore. © 2012 American Institute of Chemical Engineers AIChE J, 59: 303–315, 2013

Alkalinity production as an indicator of failure in steel slag leach beds treating acid mine drainage

Acid mine drainage is a serious environmental problem throughout mining regions of the US and around the world. In Appalachia, reuse of steel slag from steel production as a source of alkalinity for treatment of acid mine drainage has become a common practice. In these systems, dubbed steel slag leach beds, relatively clean surface water is percolated through a bed of steel slag to add large amounts of alkalinity to the water before mixing it with acidic, metalliferous mine water. These beds do not operate consistently and their failure mechanisms are poorly understood. Using the experience of Raccoon Creek watershed in southern Ohio, the alkalinity distribution of the discharge of six steel slag leach beds is compared. Two of these beds are still functional, one has been abandoned and three are operating poorly. The difference in alkalinity distribution between these beds suggests that a carbonate-dominated alkalinity system is an indicator of a poorly performing steel slag leach bed, while a more even distribution between hydroxide, carbonate and bicarbonate may point to more ideal operating conditions. In eight laboratory column experiments, this evidence was then expanded upon by testing different mixed media substrates (differing mixes of steel slag, wood chips and river gravel) to see which provided the most ideal alkalinity distributions. The columns that had steel slag mixed either with wood chips or wood chips and river gravel outperformed the column with slag only in terms of alkalinity distribution, perhaps due to microbial processes or increased hydraulic conductivity without significant added calcium or carbon that could drive calcium carbonate precipitation within the beds and causing them to fail.

Preparation of diblock copolymer films for the localization of C60 and multiwalled carbon nanotubes on aqueous substrate

Dropping polystyrene-block-poly(ethylene oxide) (PS-b-PEO) solution on a still and clean water surface caused the formation of homogeneous films of diblock copolymer at the organic vapor/water interface. The morphologies of the PS-b-PEO were studied to control and modulate the arrangement of ordered structures by applying different solvents at different annealing times. After 24 h of annealing under toluene vapor, a lamellar morphology was produced, whereas a cylindrical morphology was produced under chloroform vapor. This simple method was used to obtain more than one type of ordered microdomain structure using the same symmetric diblock copolymer. Interestingly, the microdomain size reached 120 nm, much larger than that obtained by bulk or solution self-assembly. The microphase-separated PS-b-PEO copolymer was utilized as a novel template for the selective self-assembly of the polymer-functionalized C60 and the carbon nanotubes (CNTs) by combining aqueous substrate with solvent annealing. The PS-grafted C60 enhanced the PS-b-PEO to form a lamellar microstructure. The PS-grafted C60 accommodated in the PS phase expanded the scale of PS domains. The PEO-covered CNTs were prepared to form a PEO-covered CNT/water solution for application to a complex substrate with diblock copolymer templates. This methodology enables accommodation of a selective assembly of the CNTs onto the PEO phase. This assembly strategy is a versatile approach and may open a new route for the controlled assembly of anisotropic nanostructured materials with desirable patterns on soft substrate.

Safe access to safe water in low income countries: Water fetching in current times

A substantial portion of the world’s population does not have ready access to safe water. Moreover, obtaining water may involve great expense of time and energy for those who have no water sources in or near home. From an historical perspective, with the invention of piped water, fetching water has only recently become largely irrelevant in many locales. In addition, in most instances, wells and clean surface water were so close by that fetching was not considered a problem. However, population growth, weather fluctuations and social upheavals have made the daily chore of carrying water highly problematic and a public health problem of great magnitude for many, especially women, in the poor regions and classes of the world. In this paper, we consider gender differences in water carrying and summarize data about water access and carrying from 44 countries that participated in the Multiple Indicator Cluster Survey (MICS) program. Women and children are the most common water carriers, and they spend considerable time (many trips take more than an hour) supplying water to their households. Time is but one measure of the cost of fetching water; caloric expenditures, particularly during droughts, and other measures that affect health and quality of life must be considered. The full costs of fetching water must be considered when measuring progress toward two Millennium Development Goals – increasing access to safe drinking water and seeking an end to poverty.

Spectroscopic Study of Heavy Metals at Different Depths in Southeastern Soil of Nile Delta, Egypt

ABSTRACT The present work has been conducted to study the level of pollutants in six sectors at southeastern soil of Nile delta of Egypt. The level of major, minor and trace metals were surveyed by conventional atomic emission spectroscopy. Flame atomic absorption spectroscopy was used to study Cd, Cu, Ni, and Pb in both soil and irrigating water at different depths up to 100 cm. Results indicate that heavy metals were found with higher concentrations in soil that is irrigated with untreated wastewater. Some samples from locations irrigated with clean surface water also showed higher metal concentrations because of uncontrolled use of fertilizers. The level of metals in surface samples down to 100 cm depth, indicate the possible mobilization of heavy metals that subsequently transported to groundwater and/or the drainage water in these areas. The possible pollution of groundwater and/or drainage water leads to further contamination of soil in other areas through infiltration and diffusion causing wide deterioration of Nile delta agricultural land.

Distribution of trace elements in the water column of middle Baikal

Presented are the results from investigating Baikal’s water samples collected in June 2009 for two profiles in Middle Baikal. Mean concentrations of 34 elements were obtained by the ICP-MS method using high-resolution instrument ELEMENT-2, and Zn, Cu, Fe, Al, Pb and Mn content levels were quantified. The Mo, U and Sr concentrations in Baikal’s water characterize the geochemical background in the lake’s region. According to the occurrence scale, the contents of the other elements approach the mean values for the world’s fresh surface waters or are substantially below the worldwide values for clean surface waters.

Self-organized dendritic patterns in the polymer Langmuir–Blodgett film

We report the formation of a self-organized dendritic pattern of nanometer thickness in polymer Langmuir–Blodgett (LB) films. Poly(N-dodecylacrylamide) (pDDA)/chloroform solution was spread on a water surface to form a stable polymer monolayer. A pDDA monolayer was deposited onto a hydrophilic silicon substrate by upward deposition from a water subphase, and a second layer was then deposited by downward deposition. The substrate with the two layers was withdrawn from a clean water surface at a high speed to form the dendritic pattern, which was imaged by atomic force microscopy. The height of the pattern, 3.5nm, corresponds to the height of a bilayer pDDA LB film, suggesting that the pattern forms when the deposited outermost layer overturns by meniscus oscillation. A similar dendritic structure of narrower width and lower height was fabricated on a hydrophobic silicon substrate.

The effect of a surfactant monolayer on oxygen transfer across an air/water interface during mixed convection

A set of laboratory experiments are presented that reveal the effect of a surfactant monolayer on the transport of oxygen across an air/water interface during mixed convection conditions. The experiments were conducted in a wind/water tunnel where forced convection was imposed via the air flow, and natural convection by heating the water bulk above the air temperature, resulting in mixed convection conditions. The data acquired during these experiments were used to develop a parameterization between the Sherwood number for oxygen transport Sh and the Reynolds Re and Rayleigh Ra numbers. This parameterization was obtained for the case of a clean water surface and for a water surface covered with a surfactant monolayer. The data reveal that, at a given Ra and Re, the presence of a surfactant monolayer reduces Sh by approximately one order of magnitude. The elasticity of the air/water interface which results from the presence of a surfactant is used to explain these results. The data also show that Sh was not sensitive to Re. For both the clean and surfactant cases, Sh increases with Ra.

Differences in metal sequestration between zebra mussels from clean and polluted field locations

Organisms are able to detoxify accumulated metals by, e.g. binding them to metallothionein (MT) and/or sequestering them in metal-rich granules (MRG). The different factors involved in determining the capacity or efficiency with which metals are detoxified are not yet known. In this work we studied how the sub-cellular distribution pattern of cadmium, copper and zinc in whole tissue of zebra mussels from clean and polluted surface waters is influenced by the total accumulated metal concentration and by its physiological condition. Additionally we measured the metallothionein concentration in the mussel tissue. Metal concentration increased gradually in the metal-sensitive and detoxified sub-cellular fractions with increasing whole tissue concentrations. However, metal concentrations in the sensitive fractions did not increase to the same extent as metal concentrations in whole tissues. In more polluted mussels the contribution of MRG and MT became more important. Nevertheless, metal detoxification was not sufficient to prevent metal binding to heat-sensitive low molecular weight proteins (HDP fraction). Finally we found an indication that metal detoxification was influenced by the condition of the zebra mussels. MT content could be explained for up to 83% by variations in Zn concentration and physiological condition of the mussels.

Nano- and Microstructure of Air/Oil/Water Interfaces

We report the creation of air/oil/water interfaces with variable-thickness oil films using polyisobutylene-based (PIB) surfactants cospread with long-chain paraffinic alkanes on clean water surfaces. The resultant stable oil layers are readily measurable with simple surface techniques, exhibit physical densities the same as expected for bulk oils, and are up to approximately 100 A thick above the water surface as determined using X-ray reflectometry. This provides a ready system for studying the competition of surfactants at the oil/water interface. Results from the competition of a nonionic polyamide surfactant or an anionic sodium dodecyl sulfate with the PIB surfactant are reported. However, this smooth oil layer does not account for the total volume of spread oil nor is the increase in thickness proportional to the film compression. Brewster angle microscopy (BAM) reveals surfactant and oil structures on the scale of 1 to 10 microm at the interface. At low surface pressure (pi < 24 mN m(-1)) large, approximately 10 microm inhomogeneities are observed. Beyond a phase transition observed at pi approximately = 24 mN m(-1), a structure with a spongy appearance and a microscale texture develops. These structures have implications for understanding the microstructure at the oil/water interface in emulsions.

Statistics of the surface temperature field of an air/water interface under air flow

Experimental results are presented that reveal the relationship between the root mean square of the surface temperature field of an air/water interface (σ) and the heat flux (q′′) emanating from that interface, over a range of wind speeds. Experiments were conducted for wind speeds ranging from 1.0 to 4.0 m/s to determine if and how the σ versus q′′ relationship was affected by wind speed. Consistent surfactant coverage conditions were maintained for wind speeds ranging from 1.0 to 2.6 m/s, and these are the focus of the results presented herein. For wind speeds above 2.6 m/s the surfactant was consistently pushed downstream, resulting in an inhomogeneous surface condition for the air/water interface. For wind speeds less than 2.6 m/s the relationship between σ and q′′ is approximately linear and is weakly dependent on wind speed. The surface temperature field was obtained by infrared (IR) imaging. Sample IR images are presented in addition to the σ versus q′′ data. IR images are presented for surfaces covered with insoluble surfactants (liquid phase and solid phase), a soluble surfactant, and a clean water surface.

Numerical analysis of the transport and restoration schemes of aqueous oil in soils

On the basis of field investigations and tests, the authors developed a coupling model of water and solute movement to quantitatively analyse the effects of climate condition, irrigation mode, chemical reactions and restoration schemes on aqueous oil (effective oil) distribution using the finite difference method. It is concluded from this study that the effect of strong adsorptive forces between aqueous oil and the soil matrix is the distribution of aqueous oil in the plough layer rather than its migration to groundwater. In addition, restoration schemes involving clean-wastewater mixing irrigation and crop-type adjustment may greatly reduce the aqueous oil concentrations, but clean surface water or groundwater irrigation must be used for complete restoration of the contaminated soils.

Infrared imaging of the surface temperature field of water during film spreading

Deposition of a spontaneously-spreading film on a clean water surface creates a front which propagates radially outward from the point of deposition. This rapidly spreading film was used as a tool to quickly change the boundary condition of a water surface from one which is shear-free, to a boundary condition which supports shear. Infrared images of a water surface experiencing evaporative convection were recorded as this film spread. These images were converted to surface temperature fields. The amount of turbulent structure present in these fields changes dramatically across the front. Ahead of the front, significant variations at large and small spatial scales are evident, while behind the front the small scale structures are eliminated. The time scale at which this damping occurs is short and has not been reported on heretofore. In addition to being relevant to free surface turbulence, these results demonstrate the utility of infrared imaging in the study of spreading films.

Relationship between air‐sea gas transfer and short wind waves

Laboratory studies have been conducted in two circular wind wave flumes to investigate the relationship between air‐sea transfer velocities of weakly soluble, nonreactive gases and wind‐generated surface waves over clean water surfaces and in the presence of surface films. Detailed surface wave measurements have been made using a scanning laser slope gauge. In the circular tanks, longer gravity waves (wavenumber below 12 rad/m) are hardly affected by surfactant, while shorter waves (above 100 rad/m) are significantly reduced. With higher surfactant concentrations, waves above 200–300 rad/m may be completely eliminated. Because of the absence of narrow‐banded fetch‐limited gravity waves, the wave fields in the circular tanks are significantly different from those in linear wind wave flumes. At a given wind friction velocity, the transfer velocity may decrease by as much as 60% because of surface films. Regardless of the surfactant concentrations, the transfer velocity shows a reasonable correlation with the total mean square slope and with the mean square slope of shorter wind waves (wavenumber above 200 rad/m). However, it shows a poor correlation with the mean square slope of longer wind waves (wavenumber below 50 rad/m). These observations suggest that short wind waves play an important role in air‐sea gas exchange.

Determination of arsenic in ambient water at sub-part-per-trillion levels by hydride generation Pd coated platform collection and GFAAS detection

A method for trace determination of total arsenic in ambient waters is described. Arsenic is separated on-line from a large volume water sample by hydride generation and purging, pre-collected on a Pd coated pyrolytic platform cuvette using a simple and inexpensive system, and finally detected by GFAAS. Instrument parameters, hydride generation, transportation, and collection were optimized. The analytical behavior for major species including As 3+, As 5+, monomethyl As (MMA), and dimethyl As (DMA) were investigated individually. Problems arising from use of the system were discussed and eliminated. The necessity of sample digestion and an efficient digestion method were studied. Sample digestion for water with low organic content such as tap water and clean ground water and some clean surface water can be omitted. The method detection limit (MDL) is 0.3 ng l −1 for a 25 ml water sample. Recoveries close to 100% with R.S.D.<5% can be easily achieved. Typical aqueous samples including tap, ground, lake, river, rain, sewage effluent, and saline water from different origins in the US, China, and Canada were collected and analyzed using ultra clean sampling and analysis techniques. The background levels of As in most water analyzed were established for the first time, and found to be far above the EPA's health effect criteria, 18 ng l −1.