Direct Contact Membrane Distillation Process Research Articles

Simulation of direct contact membrane distillation regeneration of liquid desiccant solutions used in air-conditioning

Membrane distillation (MD) has great potential for the treatment of hyper saline waters, including liquid desiccant solutions used in air-conditioning systems. Previous experimental investigations have demonstrated the technical feasibility of MD for regeneration of liquid desiccant solutions. In this study, a direct contact membrane distillation (DCMD) process of the LiCl liquid desiccant solution was simulated using MATLAB software. The simulation was first validated using data obtained from experimental tests. Then, it was used to elucidate the water temperatures, LiCl concentration, and water flux profiles along the membrane leaf inside the DCMD membrane module. Finally, with the help of the simulation, the effects of membrane properties and process operating conditions on the DCMD process performance were systematically examined. The results obtained from this simulation enrich the knowledge and hence facilitate the realization of MD for the liquid desiccant solution regeneration application.

Wetting-resistant photothermal nanocomposite membranes for direct solar membrane distillation

Efficient use of solar energy for desalination is one strategy to solve the world's water scarcity issues. In this work, a dual functional, omniphobic−photothermal nanocomposite membrane was developed to achieve wetting resistance and low energy consumption in desalination by direct solar membrane distillation (DSMD). The membrane was prepared by forming a hierarchical structure of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS17) modified carbon black (CB) nanoparticles (NPs) on a polyvinylidene fluoride (PVDF) membrane surface. The fluorinated CB NPs absorbed sun light to provide localized heating for DSMD, which increased membrane flux by 25% upon simulated solar irradiation at one sun unit. The utilization efficiency of solar energy in the DSMD process, 75.4%, is more than one order of magnitude higher than the energy efficiency of the conventional direct contact membrane distillation process. Furthermore, the re-entrant structure formed by the CB NPs together with the hydrophobic FAS17 coating led to low surface energy and hence omniphobicity, increasing the contact angle of the 80 vol% ethanol-in-water from 0 to 94.2°. As a result, the dual functional membrane exhibited much higher resistance to wetting by surfactants. Whereas the pristine PVDF membrane was wetted by 0.2 mM SDS, SDS had no effect on the dual function membrane over the whole SDS concentration range tested (0.1–0.4 mM). The photothermal activity, improved thermal efficiency, and strong wetting resistance make the dual functional omniphobic−photothermal membrane an excellent membrane material for the DSMD process.

Applying Membrane Distillation for the Recovery of Nitrate from Saline Water Using PVDF Membranes Modified as Superhydrophobic Membranes.

In this study, a flat sheet direct contact membrane distillation (DCMD) module was designed to eliminate nitrate from water. A polyvinylidene fluoride (PVDF) membrane was used in a DCMD process at an ambient pressure and at a temperature lower than the boiling point of water. The electrical conductivity of the feed containing nitrate increased, while the electrical conductivity of the permeate remained constant during the entire process. The results indicated that the nitrate ions failed to pass through the membrane and their concentration in the feed increased as pure water passed through the membrane. Consequently, the membrane was modified using TiO2 nanoparticles to make a hierarchical surface with multi-layer roughness on the micro/nanoscales. Furthermore, 1H,1H,2H,2H-Perfluorododecyltrichlorosilane (FTCS) was added to the modified surface to change its hydrophobic properties into superhydrophobic properties and to improve its performance. The results for both membranes were compared and reported on a pilot scale using MATLAB. In the experimental scale (a membrane surface area of 0.0014 m2, temperature of 77 °C, nitrate concentration of 0.9 g/Kg, and flow rate of 0.0032 Kg/s), the flux was 2.3 Kgm−2h−1. The simulation results of MATLAB using these data showed that for the removal of nitrate (with a concentration of 35 g/Kg) from the intake feed with a flow rate of 1 Kg/s and flux of 0.96 Kgm−2h−1, a membrane surface area of 0.5 m2 was needed.

Evaluation of direct contact membrane distillation coupled with fractionation and ozonation for the treatment of textile effluent

Direct contact membrane distillation (DCMD) coupled with fractionation or ozonation as a pretreatment method was investigated for the treatment of combined textile effluent. The stand-alone DCMD process has difficulty in directly treating the effluent due to the wetting issue, in particular at higher feed temperatures. Fractionation was conducted to 21 L combined effluent for 24 h. After the pretreatment, total organic carbon (TOC) and conductivity decreased by 47 % and 28 %, respectively, but an additional 5% concentrate was also generated. A long-term DCMD experiment was conducted to treat the fractionated effluent for 50 h and a high water recovery of 98 % was achieved. The optimum recovery of 95 % was identified to maintain stable performance of membrane. Ozonation was used to treat 550 mL combined eluent in batch mode. The TOC removal increased with time and reached the plateau after 1 min. The TOC was reduced by 38 %, while the colour of the combined effluent became lighter after 1 min treatment. As the temperature increased, longer ozonation time was required to inhibit the membrane wetting. For the feed inlet temperatures of 50 °C and 70 °C, the ozonation times of 40 s and 60 s were able to suppress the membrane wetting in the short-term tests. For the fractionated effluent, near zero discharge (water recovery of 98 %) could be achieved without serious wetting issue. To avoid membrane fouling issues, 95 % water recovery is recommended. For the 40 s ozonation pretreated effluent, DCMD could only achieve 38 % of the feed recovery before occurrence of wetting.

Antiscaling 3D printed feed spacers via facile nanoparticle coating for membrane distillation

Surface modification of feed spacers rather than membranes may hold more merit as an antiscaling strategy in membrane distillation (MD), as it avoids compromising the functionality of MD membrane. In this work, an antiscaling polyamide 3D printed spacer was developed for MD. The surface of the printed spacer was coated with fluorinated silica (FS) nanoparticles synthesized via a sol-gel process. The sol-gel approach used to synthesize the FS nanoparticles is considered a convenient and easy approach for engineering the spacer's surface structure and roughness. The performance of the FS coated printed surface was evaluated against other coating materials of different chemical properties. The coated surfaces were characterized using water contact angle measurements, ATR-FTIR, Raman, FESEM-EDX, atomic force and 3D microscopes. The 3D printed surface's microscale roughness and hydrophobicity increased, while its surface-free energy decreased with FS nanoparticles coating. The antiscaling performance of uncoated and FS coated spacers was then assessed in a direct contact MD process, using a scale-inducing aqueous solution of calcium sulfate as its feed. The scalant (Ca2+) attachment on the FS coated spacer was 0.24 mg cm−2, 74% lower than on the uncoated 3D spacer (0.95 mg cm−2). Also, by using the antiscaling FS coated spacer, scaling on the membrane surface dropped by 60%. The predominant factors that helped minimize scaling with FS coating were microscale roughness-induced hydrophobicity and reduced surface-free energy that weakened the scalant 's interaction with the spacer surface.

Efecto de antiincrustantes y variables de operación en la eficiencia de desalinización por destilación por membranas por contacto directo (DMCD)

The effect of hydrodynamic conditions (feed and permeate flow rates) and the action of six different types of antiscalants on desalination of seawater from the Gulf of Mexico by direct contact membrane distillation (DCMD) was studied. The effect of feed temperature during the DCMD process was also evaluated on performance of two microfiltration membranes (0.5 µm) having different thickness (300 and 250 µm). Results showed more than 100 % increments on water vapor flux by raising feed temperature from 50 to 70 oC and feed flow rates up to 7 L·min-1. No significant effect on process performance was determined by raising permeate flow rates in the range tested. Choosing the type and concentration of antiscalants is critical during seawater desalination by DCMD. Performance of this process increased by up to 49.2 % during desalination of real seawater by adding the KMRO S-516 antiscalant designed to disperse iron, silica and calcium carbonate salts. During DCMD no important water vapor flux decay and no increase on conductivity of the distillate was observed by antiscalants’ dosage. In addition, scanning electron microscopy (SEM) from the membrane surface after DCMD desalination of seawater treated with the KMRO S-516 antiscalant confirmed the absence of scaling.

Spent caustic wastewater treatment using direct contact membrane distillation with electroblown styrene-acrylonitrile membrane

Spent caustic is classified as a highly polluted and high-risk hazardous wastewater, which severely threatens the environment. In this work, a novel approach was proposed to treat the neutralized spent caustic wastewater using an electroblown nanofibrous styrene-acrylonitrile (SAN) membrane for direct contact membrane distillation (DCMD). The obtained results revealed that the permeate flux of the SAN membrane was lower compared to the commercial polytetrafluoroethylene (PTFE) membrane owing to the thicker structure. The higher surface hydrophobicity of the SAN membrane limited the intrusion of the feed water into the membrane pores. Therefore, extremely pure permeate water was produced. Stable permeate flux (12.03 kg/m2 h) and rejection factor (99.98%) were achieved for the hot-pressed SAN membrane during 96 h continuous DCMD test. Water contact angle of ˃ 90° was remained for both PTFE and SAN membranes, showing that DCMD performance was considerable even after 96 h operation. Besides, the chemical oxygen demand and sulfide removal factor for the fabricated membrane were 99.2 and 99.99%, respectively. Overall, the neutralization followed by the DCMD process can be considered as a proper alternative for treating the spent caustic wastewater.

A dual-layer, nanofibrous styrene-acrylonitrile membrane with hydrophobic/hydrophilic composite structure for treating the hot dyeing effluent by direct contact membrane distillation

A robust, nanofibrous membrane with dual-layer composite structure and remarkable features has been developed in this work. The new membrane is based on the affordable styrene-acrylonitrile (SAN) polymer and a commercial hydrophilic nonwoven for the support layer. This can help to step forward the industrialization of the direct contact membrane distillation (DCMD) process for treating the hot dyeing effluent in the textile industry. The modified electrospinning with a gas-jet surrounding the Taylor cone was used for fabricating the membrane samples. Using the gas-assisted electrospinning, a nanofibrous nonwoven structure embedded with micro-cups and micro-spheres can be achieved in a one-step, gas-assisted electrospinning. The hydrophilic substrate was used for enhancing the permeate flux of the resultant composite membrane. The fabricated membrane showed remarkable features in comparison with a commercial polytetrafluoroethylene (PTFE) membrane, including high surface hydrophobicity (≥148°), higher porosity (≥81%), and smaller tortuosity factor (1.71). The unique properties of the membrane with the best performance provided a promising permeate flux (28.31 kg.m−2.h−1) and contaminant rejection (RCOD: 98.15%) compared to the commercial membrane (flux: 18.50 kg.m−2.h−1 and RCOD: 97.10%), without considerable pore wetting. However, the new membrane possessed lower liquid entry pressure (LEP) owing to its higher porosity, larger maximum pore size (0.76 μm), and thinner structure (150 μm). Results indicated that the decline in the permeate flux was mainly caused by the cake layer formation on the surface of the membrane rather than the partial pore wetting during the long-term operation for 48 h. Therefore, the newly developed nanofibrous SAN membrane with hydrophobic/hydrophilic composite structure is a promising, robust candidate for DCMD application in the textile wastewater treatment.

Superhydrophobic (polyvinylidene fluoride-co-hexafluoropropylene)/ (polystyrene) composite membrane via a novel hybrid electrospin-electrospray process

A novel hybrid electrospin-electrospray process was introduced to manipulate the membrane hierarchical structure towards enhanced surface superhydrophobicity and structural integrity. In this study, the two-nozzle mode was used to simultaneously electrospin PH (polyvinylidene fluoride-co-hexafluoropropylene) fibers and electrospray PS (polystyrene) beads to prepare a PH-PS composite membrane, during which fibers and beads alternatingly deposited and entangled together on the collector. Upon using the optimized PS solvent and PS content, the optimal PH-PS membrane exhibited superhydrophobicity (water contact angle of 157.6°) and good structural integrity, benefiting from the combination of the tough PH network and the interspersed porous irregular PS beads, as well as their homogeneous blending and good adhesion during this advantageous hybrid electrospin-electrospray process. In addition to superhydrophobicity, the PH-PS composite membrane was also endowed with a uniform pore distribution and high porosity, leading to a greatly enhanced liquid entry pressure of water (LEPw). Once applied in the direct contact membrane distillation (DCMD) process, it showed high desalination robustness and excellent anti-wetting performance with stable flux and high salt rejection under harsh feed conditions, providing great potential in practical desalination applications.

Integrated green membrane distillation-microalgae bioremediation for arsenic removal from Pengorak River Kuantan, Malaysia

This study introduces an integrated system of direct contact membrane distillation (DCMD) and microalgae bioremediation for green removal of arsenic from the polluted river water. An inexpensive hydrophobic kaolin hollow fiber membrane (h-KHFM) was fabricated and used in the DCMD process for arsenic treatment on the polluted river water. The membrane demonstrates an excellent arsenic rejection of 100 % and a stable flux of 23.3 kg/m2h throughout the prolonged operation of 70 h. The performance of this membrane was compared with those of NF and RO; the results indicate superior performance of h-KHFM over the latter two processes in terms of permeate flux, arsenic rejection, as well as the performance flexibility and consistency at various pH conditions. The arsenic-rich retentate of the DCMD process is then bioremediated using Botryococcus sp. with an initial cell concentration of 1 × 106 cells/mL at the outdoor conditions. The findings show that Botryococcus sp. successfully grow in the retentate with a common microalgae growth pattern during the 20 days test period, which indicates the potential and feasibility of this integrated system for the arsenic retentate management. This study is pioneer and could provide an insight for the development of wastewater treatment technologies with zero waste discharge.

The Effect of Inclination Angle and Reynolds Number on the Performance of a Direct Contact Membrane Distillation (DCMD) Process

In this numerical study, a direct contact membrane distillation (DCMD) system has been modeled considering various angles for the membrane unit and the Reynolds number range of 500 to 2000. A two-dimensional model developed based on the Navier–Stokes, energy, and species transport equations were used. The governing equations were solved using the finite volume method (FVM). The results showed that with an increase in the Reynolds number of up to 1500, the heat transfer coefficient for all membrane angles increases, except for the inclination angle of 60°. Also, an increase in the membrane angle up to 90° causes the exit influence to diminish and the heat transfer to be augmented. Such findings revealed that the membrane inclination angle of 90° (referred to as the vertical membrane) with Reynolds number 2000 could potentially have the lowest temperature difference. Likewise, within the Reynolds numbers of 1000 and 2000, by changing the inclination angle of the membrane, temperature difference remains constant, however, for Reynolds numbers up to 500, the temperature difference reduces intensively.

Highly Saline Water Desalination Using Direct Contact Membrane Distillation (DCMD): Experimental and Simulation Study

The path for water molecules transported across a membrane in real porous membranes has been considered to be a constant factor in the membrane distillation (MD) process (i.e., constant tortuosity); as such, its effect on membrane performance at various operating conditions has been ignored by researchers. Therefore, a simultaneous heat and mass transfer model throughout the direct contact membrane distillation (DCMD) module was developed in this study by taking into account the hypothetical path across the membrane as a variable factor within the operating conditions because it exhibits the changes to the mass transfer resistance across the membrane under the DCMD run. The DCMD process was described by the developed model using a system of nonlinear equations and solved numerically by MATLAB software. The performance of the poly-tetra-fluoroethylene (PTFE) membrane was examined to treat 200 g/L NaCl saline at various operating conditions. The simulation results in the present work showed that the hypothetical proposed path across the membrane has a variable value and was affected by changing the feed temperature and feed concentration. The results estimated by the developed model showed an excellent conformity with the experimental results. The salt rejection remained high (greater than 99.9%) in all cases. The temperature polarization coefficient for the DCMD ranged between 0.88 and 0.967, and the gain output ratio (GOR) was 0.893. The maximum thermal efficiency of the system was 84.5%.

Styrene-acrylonitrile (SAN) nanofibrous membranes with unique properties for desalination by direct contact membrane distillation (DCMD) process

In this work, novel, nanofibrous styrene-acrylonitrile (SAN) membranes were fabricated via the electroblowing technique. The dope solution (22.5 wt% SAN polymer in N,N-dimethylformamide) was electroblown at three times (30, 45 and 60 min) with the rate of 270 μL.min-1. Nanofibers with the average diameter of 168.2 ± 4.8 nm were fabricated. The self-sustained membranes were treated via the hot-press technique. The electroblown nanofibrous membranes (ENMs) were then characterized for their morphology and properties. Results showed that with increasing the spinning time, the membrane properties including mechanical durability, liquid entry pressure (LEP) and hydrophobicity enhanced. However, using hot-press treatment led to slight decrease in the surface contact angle. ENMs were then tested by different feeds (0, 35 and 70 g.L-1) and real seawater. A commercial PTFE membrane (0.22 μm) was used as the control for comparing the desalination results. The ENMs were used in the direct contact membrane distillation process (ΔT = 60 °C) using different feed flowrates (0.32, 0.48 and 0.64 L.min-1). Results indicated that the thinner membrane provided higher permeate flux (84.4 kg.m-2.h-1), while the thicker membrane performed more stable, even for seawater desalination (40.7 kg.m-2.h-1). In all conducted tests, the salt rejection of >99% was achieved.

Omniphobic PVDF nanofibrous membrane for superior anti-wetting performance in direct contact membrane distillation

Membrane wetting caused by low surface tension pollutants in feed solution has been a major challenge for membrane distillation (MD), and omniphobic membranes have been proposed as a promising solution to address this challenge due to their strong repellence towards liquids with a broad range of surface tensions. In this study, we report a nanoparticle-free strategy to fabricate omniphobic polyvinylidene fluoride (PVDF) nanofibrous membranes for robust MD desalination. A solvent-thermal induced roughening method was used to create multiscale hierarchical nanofin structures on electrospun PVDF nanofibers, followed by a polydopamine-anchored surface fluorination treatment to reduce the surface energy of the nanofibrous membrane. We show that the as-prepared membrane exhibited super repellence (>150°) to diverse liquids with surface tension ranging from 73 to 30 mN m−1. Moreover, the omniphobic membrane maintained stable salt rejection and water flux in direct contact MD processes in the presence of sodium dodecyl sulfate surfactant (up to 0.4 mM) or mineral oil (up to 480 mg L−1), demonstrating its promising potential in practical water reclamation from MD applications.

A novel dual-layer, gas-assisted electrospun, nanofibrous SAN4-HIPS membrane for industrial textile wastewater treatment by direct contact membrane distillation (DCMD)

In this work, a dual-layer nanfibrous SAN4-HIPS membrane has been fabricated via the gas-assisted electrospinning, and employed for industrial textile wastewater treatment by direct contact membrane distillation (DCMD). The obtained results showed that the new membrane is robust and able to remove the contaminants, remarkably, with almost 99.28 %, 97.93 %, and 100 % reductions for COD, BOD and color, respectively. However, a flux decline of up to 42.58 % was observed after 48 h DCMD process. Concerning the rejection results, it can be concluded that the flux decline is mainly caused by the membrane fouling rather than the partial pore wetting as the membrane remained hydrophobic after the 48-h experiment. The surface contact angle reduced from 143.2° to 121.5°. Foulants accumulation on the membrane surface can increase the mass transfer resistance of vapor molecules. This can considerably reduce the productivity. The obtained results were also compared with the literature on the other MD processes, as well as the conventional pressure-driven membrane processes. Further studies on enhancing the membrane surface properties are required to control and reduce the fouling tendency caused by the contaminants in the industrial textile wastewater. This is of crucial for the long-term DCMD performance.

Inorgainc fouling and it fouling reduction in direct contact membrane distillation process

Inorgainc fouling and it fouling reduction in direct contact membrane distillation process

Engineering hierarchically structured superhydrophobic PTFE/POSS nanofibrous membranes for membrane distillation

Membrane distillation (MD) is an attractive thermally-driven membrane process for desalination, brine and wastewater treatment. One of the main obstacles impeding MD application is the absence of effective MD membranes with sufficient water permeability and long-term stability. Attributed to the outstanding hydrophobicity, excellent thermal and chemical resistance, the most ideal polymer to develop MD membrane is polytetrafluoroethylene (PTFE). However, the fabrication of PTFE membranes is challenging due to its poor processability. This work describes a novel strategy to develop superhydrophobic and highly porous PTFE membranes via electrospinning. The hydrophobic nanoparticles 8 vinyl-grafted polyhedral oligosilicone (vinyl-POSS) were firstly incorporated into PTFE nanofibers to promote the crystallization of PTFE nanofiber, enhance nanofiber roughness, and improve membrane mechanical robustness and porosity. The effects of vinyl-POSS concentration, temperature and salt concentration of feed solutions on MD performance of PTFE/POSS nanofibrous membranes were investigated systemically in this study. The optimized PTFE/POSS nanofibrous membrane #POSS-2 has a three-dimensional (3D) superhydrophobic property with a water contact angle of 151 ± 4°. It exhibited a competitive water flux of 40 ± 2 Lm−2 h−1 in the direct contact membrane distillation (DCMD) process when the feed and permeate temperatures were 60 and 20 °C, respectively. Moreover, #POSS-2 possessed an excellent long-term stability in a 200-h continuous DCMD operation.

Enhanced omniphobicity of mullite hollow fiber membrane with organosilane-functionalized TiO2 micro-flowers and nanorods layer deposition for desalination using direct contact membrane distillation

In this study, a novel omniphobic mullite hollow fiber membrane (HFM) was successfully fabricated to reduce the fouling and wetting propensity of direct contact membrane distillation (DCMD). The surface of the mullite hollow fiber membrane was functionalized with flower-like (FL) and rod-like (RL) TiO2 rough layer. Then, surface fluorination was carried out using 1H,1H,2H,2H-perfluorodecyltriethoxysilane (97%) (C8). The modified mullite hollow fiber membrane, which was initially hydrophilic in nature, exhibited high liquid repellency towards water and low surface tension liquids such as ethylene glycol (47.3 mN/m) and olive oil (32 mN/m). The order of the membranes in terms of wetting resistance for low surface tension liquids is as follows: C8-FL/TiO2-HFM > C8-RL/TiO2-HFM > C8-HFM. The omniphobic membrane that was fabricated with TiO2 micro-flowers (C8-FL/TiO2-HFM) was the only membrane that exhibited superomniphobic properties towards ethylene glycol (~150°) and was nearly superomniphobic towards olive oil (~140°). In addition, the formation of air layers was observed on submerged C8-FL/TiO2-HFM and C8-RL/TiO2- HFM, which was proven to significantly reduce organic fouling even after 500 min of DCMD with an aqueous NaCl (3.5%) feed solution containing humic acid (10 mg/L). At the macroscopic level, no significant fouling was observed for the C8-FL/TiO2-HFM. This could be attributed to the hierarchical structure induced by TiO2 micro-flowers, which played a critical role in achieving excellent anti-fouling properties. This has also translated into the high flux stability of the C8-FL/TiO2-HFM. Rise in permeate conductivity was observed for the C8-HFM but not for C8-FL/TiO2-HFM and C8-RL/TiO2- HFM. These results suggest that the fabricated omniphobic mullite hollow fiber membrane with flower-like structure is promising for a robust DCMD process, even for the desalination of real seawater that contains organic contaminants.

Membrane distillation of a silver leaching solution: Role of the coexisting aluminum ions on silica scaling

Silver, with excellent physicochemical properties, has been widely used in modern industry. Silver recovery from end-of-life product is economically significant for sustainability. However, silver leaching solution (SLS) containing diverse heavy metal ions as well as dissolved silica is a challenging waste stream for treatment and silver recovery. In this work we explored treatment of a real SLS via direct contact membrane distillation (DCMD). Results showed that silica scaling in DCMD process was closely related to the coexisting aluminum ions (Al3+) in SLS. The amount of Al(OH)3 formed was dependent on the initial pH of SLS and was effective to reduce concentration of the total dissolved silica in SLS, which was the key factor that influenced particle size distribution of SLS and degree of silica scaling. The highest silica removal rate of 83.7% was achieved at pH of 11. Moreover, it was found that the Al(OH)3 with positive charge accelerated mono-silicic acids aggregation, leading to prompt silica polymerization. This hypothesis was underpinned by evidence that amorphous yet compact aggregates formed on membrane surface and trimer silicates formed in the concentrated SLS with initial pH of 11. As a result, the most severe silica scaling occurred during DCMD treatment of SLS, resulting in the lowest initial permeate flux and water recovery. Our results shed light on prevention and management of silica scaling in treatment of waste stream.

Permeate Flux and Rejection Behavior in Submerged Direct Contact Membrane Distillation Process Treating a Low-Strength Synthetic Wastewater

The effects of operational conditions such as permeate recirculation velocity, mixing intensity, and trans-membrane temperature on the performances of hydrophobic polyethylene (PE) hollow-fiber membrane were investigated by operating the submerged direct contact membrane distillation (SDCMD) process treating a synthetic low-strength wastewater. Permeate flux of the membrane increased with increasing a permeate recirculation velocity through the fiber lumen. However, the effectiveness was less pronounced as the velocity was higher than 0.5 m/s. Increasing rotational speed to 600 rpm, which can lead to mixing intensity from a bulk wastewater toward hollow-fiber membrane, enhanced permeate flux. Feed temperature played a more significant role in enhancing permeate flux rather than a permeate temperature under constant trans-membrane temperature. The SDCMD process treating a synthetic low-strength wastewater achieved an excellent rejection efficiency which is higher than 97.8% for both chemical oxygen demand (CODCr) and total phosphorus (T-P) due to the hydrophobic property of membrane material which can allow water vapor through membrane. However, the rejection efficiency of the ammonia nitrogen (NH3-N) was relatively low at about 87.5% because ammonia gas could be volatized easily through membrane pores in SDCMD operation. In a long-term operation of the SDCMD process, the permeate flux decreased significantly due to progressive formation of inorganic scaling on membrane.