Potable water recovery from As, U, and F contaminated ground waters by direct contact membrane distillation process

In this study, the feasibility of the direct contact membrane distillation (DCMD) process to recover arsenic, uranium and fluoride contaminated saline ground waters was investigated. Two types of membranes (polypropylene, PP; and polytetrafluoroethylene, PTFE) were tested to compare the permeate production rates and contaminant removal efficiencies. Several experiments were conducted to study the effect of salts, arsenic, fluoride and uranium concentrations (synthetic brackish water with salts: 1000-10,000 ppm; arsenic and uranium: 10-400 ppb; fluoride: 1-30 ppm) on the desalination efficiency. The effect of process variables such as feed flow rate, feed temperature and pore size was studied. The experimental results proved that the DCMD process is able to achieve over 99% rejection of the salts, arsenic, fluoride and uranium contaminants and produced a high quality permeate suitable for many beneficial uses. The ability to utilize the low grade heat sources makes the DCMD process a viable option to recover potable water from a variety of impaired ground waters.     

Heat transfer characteristics of the ice slurry at melting process in a tube flow

The heat transfer characteristics were experimentally investigated for ice slurry made from 6.5% ethylene glycol–water solution flow in a 13.84 mm internal diameter, 1500 mm long horizontal copper tube. The ice slurry was heated by hot water circulated at the annulus gap of the test section. Experiments of the melting process were conducted with changing the ice slurry mass flux and the ice fraction from 800 to 3500 kg/m² s and 0–25%, respectively. During the experiment, it was found that the measured heat transfer rates increase with the mass flow rate and ice fraction; however, the effect of ice fraction appears not to be significant at high mass flow rate. At the region of low mass flow rates, a sharp increase in the heat transfer coefficient was observed when the ice fraction was more than 10%.     

Freeze separation of salt contaminated melt water and sand wash water at snow storage and sand recycling facilities

Freeze separation is used to concentrate dilute salt in snow melt water and sand recycling wash water into concentrated brine that will be supplemented with crystal salt to treat recycled road sand. This reuse decreases the salt released to the environment. Field observations from a case study of a snow storage site in Edmonton, Albert, Canada confirmed freeze separation naturally occurs in snow stockpiles. The first portions of the melt during March had salt concentrations often 10 times higher than the average concentration in the bulk snow. The natural separation of the salts can be further enhanced physically by collecting the first portion (high concentration) of the snow melt and subsequently spraying it into the cold winter air (spray freezing). A spray freezing field investigation was carried out using the sand recycling pond water. Up to 90% of the chloride and sodium was released from cores within the first 19% of the melt water.     

Mechanism for salt scaling of a cementitious surface

Freezing and thawing of concrete in the presence of deicer salts results in superficial damage known as salt scaling. Scaling damage consists of the removal of small flakes from the surface, leaving the body susceptible to water and ion ingress, thus posing a significant threat to the durability of the body. None of the proposed mechanisms for salt scaling account for all of the phenomenology observed during previous studies. We report a novel experimental method designed to measure the stress that arises when a solution is frozen on a cementitious plate. These experiments reveal a thermal expansion mismatch (or, bimaterial) mechanism that accounts for all of the observed salt scaling phenomenology. According to the bimaterial mechanism, scaling occurs when the stress in the freezing layer rises above the tensile strength of the brine-containing ice, resulting in cracking. A viscoelastic analysis of the stresses in the brine/ice layer shows that pure ice would not crack, but a layer containing >1% NaCl would. The damage from cracking of the ice is exacerbated by weakening of the cement paste by exposure to concentrated brine.     

Gravity-induced sea ice desalination under low temperature

The Bohai Rim is one of the water-scarce regions in China. But every winter, more than 1 billion m³ of sea ice formed in the sea, about 40% of which distributes within 10 km offshore and is expected to be exploited and utilized as source of freshwater. The salinity of the Bohai sea ice ranges from 4 to 11‰, under suitable ambient temperatures, gravity driven brine drainage and flushing from the melted water can convert sea ice into freshwater ice. To study the influence of ambient conditions on the process, we conducted two experiments on the coast of the Bohai Sea from January to March in 2011. The results showed that ambient temperature was a decisive and controlling factor in gravity-induced sea ice desalination, and that insulation could affect the duration, volume and salinity of the drainage. If the ambient temperature was controlled between − 4.0 and 3.0 °C, the drainage would have a low volume and high salinity. With a rise in the air temperature, the volume of the drainage increased and the salinity decreased. Sea ice desalination and freshwater production were negatively correlated: the higher the freshwater production, the lower the sea ice desalination and vice versa.     

Factors influencing arsenic and nitrate removal from drinking water in a continuous flow electrocoagulation (EC) process

An experimental study was conducted under continuous flow conditions to evaluate some of the factors influencing contaminant removal by electrocoagulation (EC). A bench-scale simulation of drinking water treatment was done by adding a filtration column after a rectangular EC reactor. Contaminant removal efficiency was determined for voltages ranging from 10 to 25 V and a comparative study was done with distilled water and tap water for two contaminants: nitrate and arsenic(V). Maximum removal efficiency was 84% for nitrate at 25 V and 75% for arsenic(V) at 20 V. No significant difference in contaminant removal was observed in tap water versus distilled water. Increase in initial As(V) concentration from 1 ppm to 2 ppm resulted in a 10% increase in removal efficiency. Turbidity in the EC reactor effluent was 52 NTU and had to be filtered to achieve acceptable levels of final turbidity (5 NTU) at steady-state. The flow regime in the continuous flow reactor was also evaluated in a tracer study to determine whether it is a plug flow reactor (PFR) or constantly stirred tank reactor (CSTR) and the results show that this reactor was close to an ideal CSTR, i.e., it was fairly well-mixed.     

The freeze-bond strength in first-year ice ridges. Small-scale field and laboratory experiments

The strength of freeze-bonds in-between blocks in first-year ridges has been investigated through field and laboratory tests. A series of small scale field tests with submerged ice blocks were carried out in Adventfjorden on Svalbard in March–April 2005. An opening was made in the landfast level ice and the ice was sawed into cubes with dimensions of 0.24 m. Some of the cubes were cut in two parts and then frozen together to simulate freeze bonds between the ice blocks. The other blocks were submerged without forming adfreeze bonds. In addition to that, laboratory tests with both laboratory made layered (fresh- and seawater) and sea ice were conducted in February–April 2006 at UNIS. The strength of the freeze bonds, the strength of the submerged ice blocks and their changes with time of submerging, confining pressure, block size and physical properties of ice were investigated. The average strength of freeze bonds was found to be 0.032 ± 0.018 MPa after 48 h of being submerged in the field. The corresponding values from the laboratory tests were 0.067 ± 0.052 MPa for the sea ice testing and 0.274 ± 0.142 MPa for the laboratory made layered freshwater ice up to 60 h of being submerged. The initial physical properties of ice, the confining pressure applied to the ice pieces before and during submerging together with the size of the ice blocks are the main parameters that affect the freeze bond strength.     

Dimensional and ice content changes of hardened concrete at different freezing and thawing temperatures

Samples of concrete at different water-to-cement ratios and air contents subjected to freeze/thaw cycles with the lowest temperature at about ?80 °C are investigated. By adopting a novel technique, a scanning calorimeter is used to obtain data from which the ice contents at different freeze temperatures can be calculated. The length change caused by temperature and ice content changes during test is measured by a separate experiment using the same types of freeze–thaw cycles as in the calorimetric tests. In this way it was possible to compare the amount of formed ice at different temperatures and the corresponding measured length changes. The development of cracks in the material structure was indicated by an ultra-sonic technique by measuring on the samples before and after the freeze–thaw tests. Further the air void structure was investigated using a microscopic technique in which air ‘bubble’ size distributions and the so-called spacing factor, indicating the mean distance between air bubbles, were measured. By analyzing the experimental result, it is concluded that damages occur in the temperature range of about ?10 °C to ?55 °C, when the air content is lower than about 4% of the total volume. For a totally water-saturated concrete, damages always occur independently of the use of entrained air or low water-to-cement ratios. It is, further, concluded that the length changes of these samples correspond to the calculated ice contents at different temperatures in a linear fashion.     

Desalination of a brick by application of an electric DC field

Salts in masonry can cause various problems as decay of the masonry itself, lost adhesion of plaster and hygroscopic moisture. Chlorides are among the most common building salts and the present paper is focused on removal of chlorides from a brick in an applied electric field as a step towards developing an electrochemical desalination method for brick masonry. Experiments were conducted in laboratory scale with one type of bricks that were contaminated with either NaCl or KCl through submersion in salt solutions prior to application of current. It was seen that NaCl was slower supplied to the brick during submersion and slower removed in the applied electric field than KCl. This indicates that the removal rate of chloride depends on the associated cation and this must be taken into account when desiding the duration of full scale actions. The electrochemical desalination was very efficient and 99% removal of chloride was obtained. The final concentration in the brick after treatment was less than 10 mg Cl/kg and this concentration is unproblematic. When low salt concentrations were reached during the electrochemical treatment, electroosmotic dewatering of the brick started, showing that electroosmotic dewatering occurs at low ionic concentrations.     

The influence of freeze–thaw cycles on the unconfined compressive strength of fiber-reinforced clay

Freeze–thaw cycling is a weathering process that frequently occurs in cold climates. In the freeze state, thermodynamic conditions at temperatures just below 0 °C result in the translocation of water and ice. Consequently, the engineering properties of soils such as permeability, water content, stress–strain behavior, failure strength, elastic modulus, cohesion, and friction angle may be changed. Former studies have been focused on changes in physical and mechanical properties of soil due to freeze–thaw cycles. In this paper, the effect of freeze–thaw cycles on the compressive strength of fiber-reinforced clay is investigated. For this purpose, kaolinite clay reinforced by steel and polypropylene fibers is compacted in a laboratory and exposed to a maximum of 10 closed-system freezing and thawing cycles. The unconfined compressive strength of reinforced and unreinforced specimens is then determined. The results of the study show that for the soil investigated, the increase in the number of freeze–thaw cycles results in the decrease of unconfined compressive strength of clay samples by 20–25%. Moreover, inclusion of fiber in clay samples increases the unconfined compressive strength of soil and decreases the frost heave. Furthermore, the results of the study indicate that fiber addition does not decrease the soil strength against freeze–thaw cycles. Moreover, the study shows that the addition of 3% polypropylene fibers results in the increase of unconfined compressive strength of the soil before and after applying freeze–thaw cycles by 60% to 160% and decrease of frost heave by 70%.     

Synthesis and characterization of Bi2MoO6/MIL-101(Fe) as a novel composite with enhanced photocatalytic performance: Effect of water matrix and reaction mechanism

The integration of Bi₂MoO₆ with MIL-101(Fe) as a novel structure enhanced photocatalytic activity for RhB degradation. Bi₂MoO₆/MIL-101(Fe) composites were synthesized via the solvothermal procedure and characterized by XRD, EDX, FE-SEM, TEM, FT-IR, BET, TGA, UV–vis DRS, and PL. The optimal molar ratio Bi₂MoO₆:MIL-101(Fe) equal to 1:1 showed better photocatalytic activity than Bi₂MoO₆ and MIL-101(Fe) and other heterostructure composites. The effect of pH (5–9), reaction time (60–120 min), catalyst concentration (0.1–0.5 g/L), and dye concentration (10–20 ppm) were investigated on the removal performance of RhB by using central composite face-centered (CCF). In the optimal process factors where the [Catalyst]:0.4 g/L, [RhB]:20 ppm, pH: 6.5, irradiation time: 120 min, the RhB and TOC removal efficiency were 85% and 84.2%, respectively. The holes and superoxide radicals played a major role in the degradation of RhB. The addition of salt (NaCl, Na₂SO₄, and NaHCO₃) at different concentrations (100, 200, 400, and 800 ppm) revealed that the salts have an inhibitory role in the photocatalytic performance. At low concentrations of 100 ppm, the salts had a negative effect on removal efficiency (k_{Pure water} = 0.0155 min^?1, k_NaCl = 0.0075 min^?1, k_Na2SO4 = 0.0132 min^?1, k_NaHCO3 = 0.006 min^?1). Increasing the salt concentration to 800 ppm caused improved efficiency for NaCl (k_NaCl = 0.0141 min^?1), while for Na₂SO₄ this trend was decreasing (k_Na2SO4 = 0.011 min^?1), and for NaHCO₃ sharply diminished (k_NaHCO3 = 0.0026 min^?1).     

Continuous ice slurry formation by using W/O emulsion with higher water content

A W/O (water-in-oil) emulsion was made from a water–lamp oil mixture with higher water content and a small amount of an additive of amino group-modified silicone oil, and the emulsion could be changed into an ice slurry by cooling with stirring. By using a new continuous ice formation system proposed by one of the authors of this paper, the ice slurry could be formed continuously and stably in an ice formation vessel made of stainless steel. From the experimental results, the conditions were clarified for realizing continuous ice formation for 10 h without ice adhesion to the cooling wall. Moreover, in order to propagate supercooling dissolution of the emulsion effectively and to decrease viscosity in the ice slurry, voltages were applied to the emulsion and ice slurry formed, respectively, and it was clarified that the voltage impression was effective for both.     

A casting based process to fabricate 3D alginate scaffolds and to investigate the influence of heat transfer on pore architecture during fabrication

The fabrication of 3-dimensional (3D) tissue scaffolds is a competitive approach to engineered tissues. An ideal tissue scaffold must be highly porous, biocompatible, biodegradable, easily processed and cost-effective, and have adequate mechanical properties. A casting based process has been developed in this study to fabricate 3D alginate tissue scaffolds. The alginate/calcium gluconate hydrogel was quenched in a glass mold and freeze dried to form a highly porous tissue scaffold whose tiny pores retain the shape of the ice crystals during quenching. Knowing that the water in the alginate hydrogel would form ice crystals if frozen and that different cooling conditions may dramatically influence the pore architecture, the speed and direction of the heat transfer in freeze drying hydrogel were examined with regard to pore size and orientation. The pore architecture at the different locations of the fabricated scaffolds was characterized using scanning electron microscopy. The fabricated scaffolds consist of pores that are highly interconnected, with a diameter about 200 µm (average diameter of a capillary) to permit blood vessel penetration. It also has been found that the pore size, orientation, and uniformity are significantly affected by the condition of heat transfer during freeze drying. Tailoring the pore architecture of the scaffolds is feasible by controlling heat transfer. This study provides an insight on pore architecture formation and control by altered process parameters.     

Removal of aluminum from metallurgical grade silicon using electron beam melting

Small amounts of metallurgical grade silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the aluminum (Al) evaporation behavior during the electron beam melting (EBM) process. Impurity was significantly decreased in the early periods of melting at 9, 15, and 21 kW. These changes slowed down with the extension of the melting time. Moreover, the removal reaction of Al by evaporation from molten silicon during the EBM process occurred in accordance with the first order kinetics. The calculated mass transfer coefficients of Al at 1941, 1964, and 2051 K increased with the increase of melting temperature. The removal rate of Al was controlled by the transportation of Al from the bulk of silicon metal to the molten/vacuum interface within the range of the experimental temperature.     

Removal of aluminum from metallurgical grade silicon using electron beam melting

Small amounts of metallurgical grade silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the aluminum (Al) evaporation behavior during the electron beam melting (EBM) process. Impurity was significantly decreased in the early periods of melting at 9, 15, and 21 kW. These changes slowed down with the extension of the melting time. Moreover, the removal reaction of Al by evaporation from molten silicon during the EBM process occurred in accordance with the first order kinetics. The calculated mass transfer coefficients of Al at 1941, 1964, and 2051 K increased with the increase of melting temperature. The removal rate of Al was controlled by the transportation of Al from the bulk of silicon metal to the molten/vacuum interface within the range of the experimental temperature.     

Ballast water treatment technologies: hydrocyclonic a viable option

Many governments, international maritime environmental entities and public health organizations have recognized the environmental, economic and health threats caused by the translocation and release of ballast water. A wide variety of ballast water treatment systems are available at both commercial and under evaluation levels. The available ballast water treatment technologies are reviewed. This work reviews the various types of technologies used in treating ballast water and special attention is given to hydrocyclonic system. Small scale pilot plant hydrocyclone was investigated to identify the behaviour of solid particle separation under the effect of alum addition during the separation. The addition of alum gave a clear improvement on the particle separation but still the use of such a chemical is questionable due to the environmental impact and quantity and time to get effective separation. For particle size greater than 0.8 mm, the removal efficiency ranges from 70 to 86% without alum and from 73 to 90% with alum. The improvement in the removal efficiency is estimated around an average of 4% only. Whereas, for particle size less than 0.3 mm, the removal efficiency ranges from 16.5 to 57% without alum and from 27 to 75% with alum. The addition of alum gave around an average of 15% improvement in the removal efficiency. This concludes that the addition of alum has greater impact on the removal efficiency for particle sizes less than 0.3 mm and less impact on greater particle sizes.     

Chemical interferences when using high gradient magnetic separation for phosphate removal: consequences for lake restoration

A promising method for lake restoration is the treatment of lake inlets through the specific adsorption of phosphate (P) on strongly magnetizable particles (Fe) and their subsequent removal using in-flow high gradient magnetic separation (HGMS) techniques. In this work, we report an extensive investigation on the chemical interferences affecting P removal efficiencies in natural waters from 20 Mediterranean ponds and reservoirs. A set of three treatments were considered based on different Fe particles/P concentration ratios. High P removal efficiencies (>80%) were found in freshwater lakes (conductivities < 600 μS cm⁻¹). However, a significant reduction in P removal was observed for extremely high mineralized waters. Correlation analysis showed that major cations (Mg²⁺, Na⁺ and K⁺) and anions (SO₄²⁻ and Cl⁻) played an essential role in P removal efficiency. Comparison between different treatments have shown that when increasing P and Fe concentrations at the same rate or when increasing Fe concentrations for a fixed P concentration, there exist systematic reductions in the slope of the regression lines relating P removal efficiency and the concentration of different chemical variables. These results evidence a general reduction in the chemical competition between P and other ions for adsorption sites on Fe particles. Additional analyses also revealed a reduction in water color, dissolved organic carbon (DOC) and reactive silicate (Si) concentrations with the addition of Fe microparticles.     

Effective removal and fixation of Cr(VI) from aqueous solution with Friedel's salt

Friedel's salt (3CaO·Al₂O₃·CaCl₂·10H₂O or Ca₄Al₂(OH)₁₂Cl₂(H₂O)₄) is a calcium aluminate hydrate formed by hydrating cement or concrete in seawater at a low cost. In the current study, we carefully examined the adsorption behaviors of Friedel's salt for Cr(VI) from aqueous solution at different concentrations and various initial pHs. The adsorption kinetic data are well fitted with the pseudo-first-order Lageren equation at the initial Cr(VI) concentration from 0.10 to 8.00 mM. Both the experimental and modeled data indicate that Friedel's salt can adsorb a large amount of Cr(VI) (up to 1.4 mmol Cr(VI)/g) very quickly (t_1/2 = 2–3 min) with a very high efficiency (>99% Cr(VI) removal at [Cr] < 4.00 mM with 4.00 g/L of adsorbent) in the pH range of 4–10. In particular, the competitive adsorption tests show that the Cr(VI) removal efficiency is only slightly affected by the co-existence of Cl⁻ and HCO₃⁻. The Cr(VI)-fixation stability tests show that only less than 0.2% adsorbed Cr(VI) is leaching out in water at pH 4–10 for 24 h because the adsorption/exchange of Cr(VI) with Friedel's salt leads to the formation of a new stable phase (3CaO·Al₂O₃·CaCrO₄·10H₂O). This research thus suggests that Friedel's salt is a potential cost-effective adsorbent for Cr(VI) removal in wastewater treatment.     

Investigation on influence of dimensions of ice containing ozone micro-bubbles on characteristics of ozone concentration

Addition of sterilization and deodorization capabilities to ice is effective for a cold storage of food. Therefore, authors clarified the characteristics of ozone micro-bubbles (MBs) concentration fixed in the ice and ozone gas concentration released due to melting. In this paper, ice with different dimensions are prepared by cutting and crushing the formed ice containing ozone MBs, after which influences of dimensions of cut and crushed ice on the above characteristics are examined. Furthermore, using ice slurry is more effective to cool fresh food; therefore, a pseudo ice slurry formed by mixing crushed ice containing MBs with pure water is investigated. Cut ice and original uncut ice mixed with pure water, respectively, are also investigated as a reference. And validities of above ice mixed with pure water, respectively, are shown by measuring ozone concentration in water. Finally, oxidation characteristics due to ozone gas released into fish oil are also clarified.     

Arsenate removal by zero valent iron: Batch and column tests

This study investigates the efficiency of zero valent iron (ZVI) to remove arsenate from water. Batch experiments were carried out to study the removal kinetics of arsenate under different pH values and in the presence of low and high concentrations of various anions (chloride, carbonate, nitrate, phosphate, sulphate and borate), manganese and dissolved organic matter. Borate and organic matter, particularly at higher concentrations, inhibited the removal of arsenic. Column tests were carried out to investigate the removal of arsenate from tap water under dynamic conditions. The concentrations of arsenic and iron as well as the pH and Eh were measured in treated water. Efficient removal of arsenate was observed resulting at concentrations below the limit of 10 μg/L in treated waters.