Air gap membrane distillation: A detailed study of high saline solution

An experimental study is used to examine the effect of high concentration of several salts, i.e., NaCl, MgCl2, Na2CO3 and Na2SO4 on permeate flux and rejection factor by air gap membrane distillation (AGMD). A comparative study involving three different membrane pore sizes (0.2, 0.45 and 1.0 μm) were performed to investigate the influence of pore size on energy consumption, permeate flux and rejection factor. The permeate flux decline is higher than that predicted from the vapour pressure reduction. Furthermore, the energy consumption was monitored at different membrane pore size and was found to be increased when the concentration increased

Towards a Sustainable Water Supply: Humic Acid Removal Employing Coagulation and Tangential Cross Flow Microfiltration

Synthetic solutions assimilating irrigated groundwater containing varying concentrations of humic acid (10 -40 mg/L) and saline (10-35 g/L) and metal agents (5 mg/L) , were processed through a ceramic microfiltration membrane (Sterilox Ltd.,0.5 μm). This was done with enrichment schemes using polymeric coagulants (PDADMAC) applied to enhance the removal of the above-mentioned pollutants. The study was conducted with the scope of investigating the feasibility of sequential and hybrid coagulation and microfiltration as a method of choice for drinking water treatment. Membrane microfiltration is easily scalable into various arrangements, allowing versatility in operation and enrichment treatments, with a relatively lower cost which other treatment practices do not allow. The highest humic acid removal, 91.11 % was achieved with hybrid coagulation

Mercury, Arsenic and Lead Removal by Air Gap Membrane Distillation: Experimental Study

Synthetic industrial wastewater samples containing mercury (Hg), arsenic (As), and lead (Pb) ions in various concentrations were prepared and treated by air gap membrane distillation (AGMD), a promising method for heavy metals removal. Three different membrane pore sizes (0.2, 0.45, and 1 μm) which are commercially available (TF200, TF450, and TF1000) were tested to assess their effectiveness in combination with various heavy metal concentrations and operating parameters (flow rate 1–5 L/min, feed temperature 40–70 °C, and pH 2–11). The results indicated that a high removal efficiency of the heavy metals was achieved by AGMD. TF200 and TF450 showed excellent membrane removal efficiency, which was above 96% for heavy metal ions in a wide range of concentrations. In addition, there was no significant influence of the pH value on the metal removal efficiency. Energy consumption was monitored at different membrane pore sizes and was found to be almost independent of membrane pore size and metal type

Temperature and Velocity Measurements in Sub-cooled Boiling through a Vertical Rectangular Test Channel

Temperature and velocity measurements are performed in sub-cooled boiling experiments through a single-heated side rectangular test channel at various conditions. The temperature measurements involve the use of the Laser Induced Fluorescence (LIF) method with one heated single-phase (3.9 kw/m2 ) and two boiling conditions (30.9 and 36.6 kw/m2 ). Two flow rates are considered, for each heating level, and given by the Reynold’s number (Re) of 8121 and 20523. For the boiling cases, bubbles are allowed to slide along the heated surface and temperature fields are obtained along the bubbles sliding distance in the axial direction. Radial temperature profiles are mapped out to display the temperature distributions at various axial locations. The resultant temperature fields reveal insightful information about the temperature distribution in each condition. Boiling bubbles induce major changes to the temperature fields. In regions far from the heated wall, the temperature profiles are seen to fall within the range of the bulk fluid temperature values (21.6 ºC ± 1 ºC), as registered by the means of thermocouples. A large increase in temperature is observed near the heated wall (and at the sliding distance) to approximately 29.6 ºC ± 2 ºC. The reference temperature values obtained for this region by the infrared camera are seen to fluctuate between 30.9 and 31.9 ºC. A higher discrepancy is observed near the heated wall area due to weaker fluorescent signals can be captured in this region. The thermal boundary layers are shown to grow thicker with higher heating input and higher flow rates. The liquid velocity measurements are performed with the Particle Imaging Velocimetry (PIV) method. The liquid turbulence statistics are obtained for a heated single-phase (2.7 kw/m2 ) and two boiling conditions of varying heat flux (16.4 kw/m2 and 42.8 kw/m2 ). The same Reynold’s numbers used in temperature measurements are considered here as well (8121 and 20523). Velocity components, turbulence intensities, and Reynold’s stresses are obtained against the radial distance from the heated wall. The effect of the boiling bubbles on the flow structural behavior is clearly evident, as the liquid velocity values and turbulent intensities appear to increase near the bubble regions. This increase in liquid velocity is a function of the bubble sizes and flow rates. The sliding bubbles tend to grow in size and gain momentum as moving along the heater. The velocity boundary layer thickness is shown to grow with higher heat flux and bigger bubble’s size. This increase in the layer thickness is concomitant with the axial distance

Improving the performance of trays solar still by using sand beds and reflectors

In order to maintain access to freshwater resources in water-stressed regions, it is important to improve the performance of solar-powered desalination systems with lower cost units like solar stills (SS). However, the SS produces low productivity especially through the rainy or cloudy days due to the indirect diffused beams. Therefore, the main aim of this study is to increase the yield from brackish/seawater via a solar still operating with renewable energy sources. The water depth was lowered, and thermal storage materials with different sand beds trays solar still (TSS) are used to augment the amount of yield from a SS. The effects of sandy bed height, and sand type (black and yellow) on the performance of TSS were investigated. Also, the effect of internal reflectors on the sand TSS performance was investigated. Experimental results revealed that the sandy layer (storage beds) improves the TSS production. The maximum increase in accumulated production of sandy TSS with internal reflectors was reached at sand beds height of 1 cm and black sand. In this case, the freshwater was heightened by 105 % over CSS

Ceramic Microfiltration Membranes in Wastewater Treatment: Filtration Behavior, Fouling and Prevention

Nowadays, integrated microfiltration (MF) membrane systems treatment is becoming widely popular due to its feasibility, process reliability, commercial availability, modularity, relative insensitivity in case of wastewater of various industrial sources as well as raw water treatment and lower operating costs. The well thought out, designed and implemented use of membranes can decrease capital cost, reduce chemical usage, and require little maintenance. Due to their resistance to extreme operating conditions and cleaning protocols, ceramic MF membranes are gradually becoming more employed in the drinking water and wastewater treatment industries when compared with organic and polymeric membranes. Regardless of their many advantages, during continuous operation these membranes are susceptible to a fouling process that can be detrimental for successful and continuous plant operations. Chemical and microbial agents including suspended particles, organic matter particulates, microorganisms and heavy metals mainly contribute to fouling, a complex multifactorial phenomenon. Several strategies, such as chemical cleaning protocols, turbulence promoters and backwashing with air or liquids are currently used in the industry, mainly focusing around early prevention and treatment, so that the separation efficiency of MF membranes will not decrease over time. Other strategies include combining coagulation with either inorganic or organic coagulants, with membrane treatment which can potentially enhance pollutants retention and reduce membrane fouling

Effect of lithium chloride additive on forward osmosis membranes performance

The research efforts on the development of ideal forward osmosis membranes with high water flux and low reverse salt flux have been devoted in the recent years. In this study, thin film composite polyamide forward osmosis membranes were prepared. The porous polysulfone (PSU), polyphenylsulfone (PPSU), and polyethersulfone (PESU) substrates used in this study were prepared by the phase inversion process, and the active rejection layer was prepared by interfacial polymerization. All the membranes showed highly asymmetric porous structures with a top dense upper layers and finger-like porous substrates with macro voids in the bottom layer. The addition of 3% lithium chloride (LiCl) to the membrane substrates resulted in an increase in both the water flux and reverse salt flux. PSU and PESU showed the highest water flux when the active layer faced the feed solution (AL-FS), while the largest water flux was obtained when the active layer faced the draw solution (AL-DS). For all the membranes, the water flux under the AL-DS orientation was higher than that under the AL-FS orientation