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ABSTRACT: The transport of anionic drinking water contaminants (fluoride, chloride, nitrate and nitrite) through narrow pores ranging in effective radius from 2.5 to 6.5 Å was systematically evaluated using molecular dynamics simulations to elucidate the magnitude and origin of energetic barriers encountered in nanofiltration. Free energy profiles for ion transport through the pores show that energy barriers depend on pore size and ion properties and that there are three key regimes that affect transport. The first is where the ion can fit in the pore with its full inner hydration shell, the second is where the pore size is between the bare ion and hydrated radius, and the third is where the ion size approaches that of the pore. Energy barriers in the first regime are relatively small and due to rearrangement of the inner hydration shell and/or displacement of further hydration shells. Energy barriers in the second regime are due to partial dehydration and are larger than barriers seen in the first regime. In the third regime, the pore becomes too small for bare ions to fit regardless of hydration and thus energy barriers are very high. In the second regime where partial dehydration controls transport, the trend in the slopes of the change in energy barrier with pore size corresponds to the hydration strength of the anions.
Physical Chemistry Chemical Physics 07/2012; 14(33):11633-8. · 3.57 Impact Factor
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ABSTRACT: The transport of hydrated ions through narrow pores is important for a number of processes such as the desalination and filtration of water and the conductance of ions through biological channels. Here, molecular dynamics simulations are used to systematically examine the transport of anionic drinking water contaminants (fluoride, chloride, nitrate, and nitrite) through pores ranging in effective radius from 2.8 to 6.5 Å to elucidate the role of hydration in excluding these species during nanofiltration. Bulk hydration properties (hydrated size and coordination number) are determined for comparison with the situations inside the pores. Free energy profiles for ion transport through the pores show energy barriers depend on pore size, ion type, and membrane surface charge and that the selectivity sequence can change depending on the pore size. Ion coordination numbers along the trajectory showed that partial dehydration of the transported ion is the main contribution to the energy barriers. Ion transport is greatly hindered when the effective pore radius is smaller than the hydrated radius, as the ion has to lose some associated water molecules to enter the pore. Small energy barriers are still observed when pore sizes are larger than the hydrated radius due to re-orientation of the hydration shell or the loss of more distant water. These results demonstrate the importance of ion dehydration in transport through narrow pores, which increases the current level of mechanistic understanding of membrane-based desalination and transport in biological channels.
Small 03/2012; 8(11):1701-9. · 8.35 Impact Factor
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Desalination. 01/2010; 261(3):331-337.
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ABSTRACT: A wind-powered reverse osmosis membrane (wind-membrane) system without energy storage was tested using synthetic brackish water (2750 and 5500 mg/L NaCl) over a range of simulated wind speeds under both steady-state and fluctuating conditions. The parameters varied were: i) average wind speed from 3.7 (system start-up) to 8.7 m/s; ii) wind turbulence intensity from 0.0 (steady-state conditions) to 0.6 (extreme fluctuations); and iii) period of oscillation from 15 to 90 s. With a feed water of 2750 mg/L NaCl, the wind-membrane system produced good-quality permeate (<600 mg/L) over the full range of wind speeds and fluctuations. The system performance (in terms of permeate flux and NaCl concentration) at average wind speeds of 7.0 m/s or more was unaffected by fluctuations up to a turbulence intensity of 0.4 and was independent of the period of fluctuation within this operating range. With a feed water of 5500 mg/L NaCl an average wind speed of 7.0 m/s or more was required to produce adequate-quality permeate (<1000 mg/L) under fluctuating conditions. It is concluded that this wind-membrane system can be operated within a safe operating window with large power fluctuations, but further control strategies are required to deal with intermittent operation, especially with higher salinity feed waters.
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ABSTRACT: An interdisciplinary sustainable design project that combines membrane technology with renewable energy to provide water for remote communities and developing countries was offered to students for voluntary participation. Through continuous design stages and improvements on several prototypes, laboratory testing and several field trials in Australia, and interactions with industry partners and funding agencies, the project has offered very important experience to students and contributes significantly to graduate attributes that are difficult to gain during traditional coursework education. Such initiatives offer an exciting addition to the environmental engineering curriculum and can be adapted to various teaching frameworks and topic areas. In addition to acquiring technical skills, the students gained skills in the areas of team-work and interpersonal skills, project management, interdisciplinary skills, and confidence in interacting with non-engineers. A number of the students involved who have now graduated as well as peers were subsequently surveyed to evaluate student learning using critical incident questionnaires. One student felt that the involvement in the project was more important than the entire engineering degree. Students reported also a boost in confidence, motivation, inspiration, pride to be involved, high degree of engagement, especially during field trips. One drawback was negative team experiences, caused by students who thought they should have been selected as project managers. However, this was described by a student (now in the workforce) as a representation of later office politics and as a good opportunity to develop character strength. Poor communication, team building tools and lack of institutional support were additional issues needing addressing, as well as concerns from other academics that such activities could be to the detriment of other, more traditional, coursework-based learning activities. Significantly enhanced employment opportunities and extremely positive industry feedback were also noted. Industry emphasised the need for more project and time management skills.
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ABSTRACT: The objective of this study was to evaluate the effects of fluctuating energy and pH on retention of dissolved contaminants from real Australian groundwaters using a solar (photovoltaic) powered ultrafiltration–nanofiltration/reverse osmosis (UF–NF/RO) system. Four NF/RO membranes (BW30, ESPA4, NF90, and TFC-S) were used. Energy fluctuations affected pressure and flow. Solar irradiance levels impacted retention of fluoride, magnesium, nitrate, potassium, and sodium where convection/diffusion dominated retention. Retention of calcium, strontium, and uranium was very high and independent of solar irradiance, which was attributed to a combination of size and charge exclusion and for some solutes sorption and precipitation. Groundwater characteristics affected retention and the solutes were categorized into two groups according to retention as a function of pH: (1) pH-independent retention (arsenic, calcium, chloride, nitrate, potassium, selenium, sodium, strontium, and sulfate) and (2) pH-dependent retention (copper, magnesium, manganese, molybdenum, nickel, uranium, vanadium, and zinc). The retention of Group 1 solutes was typically high and attributed to steric effects. Group 2 solutes had dominant, insoluble species under certain conditions which led to deposition on the membrane surface (and thus varying apparent retention). The renewable energy membrane system removed a large number of groundwater solutes reliably over a range of real energy and pH conditions.Graphical abstractView high quality image (175K)Research highlights▶ Energy affected retention of F, NO3− and TDS (convection/diffusion mechanisms). ▶ Retention of Sr, Ca and U high and energy-independent (size and charge mechanisms). ▶ pH affected retention of Cu, Mg, Mn, Mb, Ni, U, V and Zn leading to precipitation. ▶ Retention of As, NO3−, Se, Sr and SO42− did not change between pH 3 and 11.
Journal of Membrane Science 369:188-195. · 3.85 Impact Factor
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ABSTRACT: This paper reports on the design and successful field testing of a photovoltaic (PV)-powered desalination system. The system described here is intended for use in remote areas of the Australian outback, where fresh water is extremely limited and it is often necessary to drink high salinity bore water. A hybrid membrane configuration is implemented, whereby an ultrafiltration (UF) module is used for removing particulates, bacteria and viruses, while a reverse osmosis (RO) or nanofiltration (NF) membrane retains the salts. The concepts of water and energy recovery are implemented in the design. Field trials, performed in White Cliffs (New South Wales), demonstrated that clean drinking water was able to be produced from a variety of feed waters, including high salinity (3500 mg/l) bore water and high turbidity (200 NTU) dam water. The specific energy consumption ranged from 2 to 8 kW h/m3 of disinfected and desalinated drinking water, depending on the salinity of the feed water and the system operating conditions. The optimum operating pressure when filtering bore water was determined to be in the range 6–7 bar.
Renewable Energy.
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ABSTRACT: In some areas limited water resources combined with the fast growing population are leading to a crucial situation because of the increase in water demand. Besides, an estimated one billion people are living both without access to clean drinking water or electricity. Therefore, a stand alone photovoltaic-power based hybrid membrane desalination prototype has been designed to meet this challenge. Several parameters were examined in order to optimise the system performance, including i) feed water salt concentration, ii) operating pressure, iii) system recovery, iv) specific energy consumption (SEC) and v) salt retention. With a SEC varying from 2.2 to 7.7 kWh.m−3, the installation designed for remote villages is able to produce up to 1.2 m3.d−1
Desalination.
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ABSTRACT: Water in many areas of Australia is scarce and of poor quality. In some areas high levels of treatment are required either due to contamination of waters or due to high salinity. Nanofiltration (NF) and low-pressure reverse osmosis membranes are well-recognized technologies to treat waters of qualities ranging from low salinity surface water to high salinity seawater. In remote communities the operation of such facilities may be limited by the availability of electricity. Solar, or photovoltaic, energy is the ideal source of renewable energy in Australia to overcome this problem. This paper considers the various options for a small system, designed to deliver a permeate flow of 400–1000 l/d from brackish wells. The most suitable membrane for salt retention and very high organics retention was selected and the pump energy requirements calculated. A submerged ultrafiltration (UF) membrane is used as an alternative to the traditional sand and/or prefilter cartridges. The removal of natural organics is important where disinfection of the water is required, as chlorination of waters containing natural organics may produce potentially carcinogenic by-products.
Desalination.
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ABSTRACT: The results of a field trial desalinating brackish bore water in an Australian remote national park site are reported in this paper. Two membranes, operated with varying operation pressures, were tested with regards to flux, recovery, retention, power and specific energy consumption. The aim of such a performance evaluation is the determination of a safe operating window when the system is driven with solar energy and hence a variable power source. Submerged ultrafiltration was effective in reducing high feedwater turbidity of up to 370 NTU. For the system, designed for a production of about 1000 L/d for remote communities, the specific energy consumption (SEC) was below 5 W.h/L when operated at a pressure above 7 bar. Retention of multivalent ions was stable at > 98% while the retention of monovalent ions varied between 88 and 95% depending on system pressure with a maximum between 7 and 10 bar.
Desalination.
