Study of the rectangular cross-flow flat-sheet membrane module for desalination by vacuum membrane distillation

This work presents a study of the heat and mass transfer performance of desalination in a laboratory-scale rectangular cross-flow flat-sheet membrane module by vacuum membrane distillation (VMD) experiments. Results show that the traditional Nusselt and Sherwood correlations, which are frequently employed in the membrane distillation literature, are not suitably used to estimate the heat and mass transfer coefficients in the VMD system for Reynolds numbers ranging from 150 to 1400. In this study, it was observed that approximately 30% of the experimental data fit well with semi-empirical correlations whose empirical constants are a=2.76×10−3, b=0.97 and c=3.7909. The heat transfer process is limited by the resistances in the feed boundary layer and the membrane. The heat transfer resistance in the membrane increases when that in the feed boundary layer decreases and vice versa. More than 50% of the heat transfer resistances occur in the liquid feed phase at feed flow rates below 1200 mL/min, whereas the remaining occur in the membrane itself. At feed flow rates that exceed 1200 mL/min, the heat transfer resistance in the membrane becomes dominant. The Knudsen-viscous resistance controls the mass transfer through the membrane while the mass transfer resistance in the liquid feed phase is absent

Ammonia removal from saline water by direct contact membrane distillation

Salts in wastewater can inhibit the biological treatment process when the microbes suffer from plasmolysis and become inactive. Membrane separation technology is an alternative method to remove dissolved ammonia from saline water, which is not affected by the presence of salt. In this study, flat porous membrane sheets made from polyvinylidene fluoride were fabricated by the phase inversion process and used to remove ammonia from saline water by direct contact membrane distillation (DCMD). Dimethylacetamide and sodium chloride were used as the solvent and a pore-forming additive, respectively. This study investigated the effect of adding varying sodium chloride concentrations, 0.00, 0.22 and 0.33 wt%, during membrane fabrication, on the resulting membrane porosity and pore size, as characterized by the gravimetric method and scanning electron microscopy, respectively. The additive increased the porosity of the membrane from 78% without additive to approximately 82 to 84%. The sodium chloride additive reduced the pore size of the porous membranes from 0.082 to 0.067 μm. The fabricated membranes were then applied in co-current DCMD for ammonia separation at 50oC. In the gas-liquid membrane separation, it was found that membranes that are highly porous were preferable because these membranes provide a low effective thermal conductivity, which results in a high flux. The greatest ammonia removal efficiency, approximately 20%, was achieved within two hours of operation when the membrane with a porosity of about 84% and a water-permeant system were used

An Overview of Recent Progress in Nanofiber Membranes for Oily Wastewater Treatment

Oil separation from water becomes a challenging issue in industries, especially when large volumes of stable oil/water emulsion are discharged. The present short review offers an overview of the recent developments in the nanofiber membranes used in oily wastewater treatment. This review notes that nanofiber membranes can efficiently separate the free-floating oil, dispersed oil and emulsified oil droplets. The highly interconnected pore structure nanofiber membrane and its modified wettability can enhance the permeation flux and reduce the fouling. The nanofiber membrane is an efficient separator for liquid–liquid with different densities, which can act as a rejector of either oil or water and a coalescer of oil droplets. The present paper focuses on nanofiber membranes’ production techniques, nanofiber membranes’ modification for flux and separation efficiency improvement, and the future direction of research, especially for practical developments

Point-of-use upflow sand filter for rural water treatment using natural local sand: Understanding and predicting pressure drop

A simple, small scale upflow sand filter was fabricated using a locally obtained sands at three different rivers in Sabah, Malaysia: Liwagu River (SL), Tamparuli River (ST), and Kaingaran River (SK). The grain size, porosity, bulk density, particle density and sphericity of the sands were characterized to associate with the corresponding pressure drop across the sand bed. The highest pressure drop per unit length for SK, PT, and SL are 15.85 kPa m-1 at 0.747 m s-1 vs, 10.18 kPa m-1 at 0.352 m s-1 vs, and 9.24 kPa m-1 at 0.747 m s-1 vs, respectively. The pressure drop per unit length at different filter bed depth were plotted, and compared against three theoretical models of Ergun, Kozeny-Carman, and Fair and Hatch. By analyzing the experimental-theoretical comparison using RMSE and Chi-Test, prediction of pressure drop in an upflow sand filter is able to be predicted using the Kozeny-Carman equation preceding filter bed fluidization and subsequently Fair and Hatch’s equation after bed is fluidized

The outlook of rural water supply in developing country: review on Sabah, Malaysia

This paper reviews the challenges in the water supply provision, water source availability and quality and the distribution approaches in rural Sabah. The main challenges to provide potable water in Sabah is the variance in terrain and geographical distance between populated regions. Review reveals that other than the river water, average annual precipitation of 3000 millimetres (mm) could be harvested for domestic and agricultural purposes. Numbers of aquifer uncovered in the eastern and western region of Sabah with underlying sandstone and Quaternary Alluvium have significant potential for groundwater reservoirs. Aquifer along the coastal areas and islands around Sabah also gives sufficient potable water supplies. Minimal pollutant content was found in all water sources and acceptable under the National Water Standard of Malaysia, except for contaminants coming from septic tanks and agricultural activities. A decentralized water system is more beneficial for Sabah’s rural areas. Smaller scaled plants are flexible to collect from any water sources and treat at the point of use. Expenditure is significantly decreased by a shorter distribution network and lower installation and maintenance cost. Nonetheless, the treatment utilized may be limited to a simpler process as semiskilled or un-skilled personnel will be required to operate and maintain the system

Coalescence of Oil Droplets using Sponge-like Structure of Polyvinylidene Fluoride Membranes

This work reports the effect of the membrane pore size distribution on the oil droplets size distribution in permeate using the polyvinylidene fluoride (PVDF) membranes. The spongelike structures of the PVDF membranes were fabricated via the phase inversion technique using 30% v/v ethanol aqueous solution as coagulation medium. Water and polyethylene glycol (PEG1000) were used as the pore forming additives in the dope solutions. Microfiltration was employed to coalesce the oil droplets at the transmembrane pressure of 2.5 bar. Simulated alkaline-surfactant-polymer (ASP) produced water was tested as the feed solution. Results revealed that the PVDF membranes with sponge-like structure were formed. The additives in the dope solutions have induced the membranes to become thicker due to more porous, spongy and resilient structure. The membrane pore sizes increased with the presence of the additives in the dope solutions especially when larger molecular weight of the additive, i.e., PEG1000 was used. The mode of the oil droplets radius increased from 61.2 nm in the feed solution to 95.1, 356.2 and 1335 nm in the permeates by the corresponding membranes without additive, with water and PEG1000 as the additives. The membranes with larger pore sizes as well as more open structure were able to trap and coalesce more oil droplets which produced larger size of the oil droplets in the permeates

Membrane processes for microalgae in carbonation and wastewater treatment

The objective of this work is to present the integration of membrane processes in the field of bioenergy resource and wastewater treatment using microalgae. There are two main processes involved: carbonation and separation, which were conducted and reported as a separated work within this chapter. The chapter begins with the introduction of membrane processes, followed by carbonation of microalgae and separation of biomass from the wastewater effluent. The experimental work on the carbonation aims to evaluate the effectiveness of hydrophobic hollow fibre membrane in transporting CO2 into microalgae culture and microalgae accumulation within the membrane. The experimental work on the separation process of microalgae biomass from the wastewater effluent on the other hand, aims to evaluate Ultrafiltration (UF) membrane capability in removing BOD and COD as well as its ability to retain microalgae biomass which were used by the turbidity reading of the membrane permeate. The application of hydrophobic membrane in the carbonation process has increased the carbonation efficiency up to 83% in comparison with the carbonation without membrane and only a small amount of mirage was accumulated within the membrane. The experimental result also shows that, the carbonised microalgae can be further used for wastewater treatment. Based on the result of separation process of microalgae biomass of wastewater effluent, the UF membrane utilization shows high separation efficiency in turbidity to lower than 5 Fau, and was able to facilitate in nutrient removal for less time required compared to the biological treatment without application of the membrane

Use of melt blown polypropylene nanofiber templates to obtain homogenous pore channels in glycidyl methacrylate/ethyl dimethacrylate-based monoliths

An important characteristic of a monolith is its porous structure. However, it is difficult to obtain a homogenous porous structure in a monolith due to dead-end and uneven distributions of pores, but nanofibers can act as templates to induce a porous structure. Hence, the aim of this research was to study melt-blown polypropylene nanofibers produced under process conditions designed by response surface methodology (RSM), i.e., air pressures between 0.30 and 0.50 MPa, motor speeds between 30 and 50 Hz, and die-to-collector distances between 20 and 50 cm. The air pressure was found to be an important factor in determining the diameters of the fibers from the RSM analysis, and we found the diameters to be between 3.58 and 11.00 × 103 nm. Macropore monoliths were fabricated successfully with conditions of 0.45 MPa, 40 Hz, and 60.23 cm. Thus, it was concluded that polypropylene nanofibers can be used as a template to produce a monolith

Water desalination by air-gap membrane distillation using meltblown polypropylene nanofiber membrane

This paper presents a study of air gap membrane distillation (AGMD) using meltblown polypropylene (PP) nanofiber membrane to produce fresh water via desalination process. PP nanofiber membranes with the effective area 0.17 m2 are tested with NaCl solutions (0.5 – 4.0 wt.%) and seawater as the feed solutions (9400 – 64800 µS/cm) in a tubular membrane module. Results show that the flux decreases with increasing the membrane thickness from 547 to 784 µm. The flux increases with the feed flow rate and temperature difference across the membrane. The feed concentration affects the flux insignificantly. The AGMD system can reject the salts at least 96%. Water vapor permeation rate is relatively higher than solute permeation rate resulting in the conductivity value of permeate decreases when the corresponding flux increases. The AGMD system produces the fresh water (200 – 1520 µS/cm) that is suitable for drinking, fisheries or irrigation