Hollow Fiber Membrane System Research Articles

Advanced electrochemical membrane technologies for near-complete resource recovery and zero-discharge of urine: Performance optimization and evaluation

The depletion of nutrient sources in fertilizers demands a paradigm shift in the treatment of nutrient-rich wastewater, such as urine, to enable efficient resource recovery and high-value conversion. This study presented an integrated bipolar membrane electrodialysis (BMED) and hollow fiber membrane (HFM) system for near-complete resource recovery and zero-discharge from urine treatment. Computational simulations and experimental validations demonstrated that a higher voltage (20 V) significantly enhanced energy utilization, while an optimal flow rate of 0.4 L/min effectively mitigated the negative effects of concentration polarization and electro-osmosis on system performance. Within 40 min, the process separated 90.13% of the salts in urine, with an energy consumption of only 8.45 kWh/kgbase. Utilizing a multi-chamber structure for selective separation, the system achieved recovery efficiencies of 89% for nitrogen, 96% for phosphorus, and 95% for potassium from fresh urine, converting them into high-value products such as 85 mM acid, 69.5 mM base, and liquid fertilizer. According to techno-economic analysis, the cost of treating urine using this system at the lab-scale was $6.29/kg of products (including acid, base, and (NH4)2SO4), which was significantly lower than the $20.44/kg cost for the precipitation method to produce struvite. Excluding fixed costs, a net profit of $18.24/m3 was achieved through the recovery of valuable products from urine using this system. The pilot-scale assessment showed that the net benefit amounts to $19.90/m3 of urine, demonstrating significant economic feasibility. This study presents an effective approach for the near-complete resource recovery and zero-discharge treatment of urine, offering a practical solution for sustainable nutrient recycling and wastewater management.

CFD modeling of braid-reinforced hollow fiber membranes for efficient water and bovine serum albumin (BSA) separation

This study presents a comprehensive investigation into the performance optimization of a braid-reinforced hollow fiber membrane (BHFM) system for protein separation from milk wastewater. Extensive CFD simulations were conducted to examine the effects of various effective parameters on system performance. The results reveal that at a feed protein concentration of 100 mg/l, the average water flux increases from 149.16 to 453.68 l/m2.h as the inlet feed pressure rises from 100 to 300 kPa. Similarly, for a feed protein concentration of 300 mg/l, the average flux rises from 98.69 to 299.84 l/m2.h. However, higher feed concentrations lead to increased fouling and lower water fluxes. Additionally, an increase in feed pressure results in a decrease in the protein rejection rate, particularly in the initial stages of separation. The study highlights that variations in membrane porosity and thickness significantly affect both protein rejection rate and water flux. Increasing membrane porosity from 0.2 to 0.8 leads to a decrease in protein rejection rate from 94.57 % to 78.47 % at an inlet pressure of 100 kPa, and from 93.33 % to 73.43 % at 300 kPa. Similarly, increasing membrane thickness from 0.1 to 1.0 mm decreases the time-averaged water flux from 105.76 to 8.64 l/m2.h at 100 kPa, and from 321.39 to 25.99 l/m2.h at 300 kPa. However, increasing membrane thickness also increases the protein rejection rate. The study's novelty lies in the quantitative results obtained through CFD simulations, providing valuable insights into BHFM system performance. Future research should focus on exploring innovative braid architectures and material selection to enhance the mechanical stability and durability of braid-reinforced structures under various operational conditions.

Determining stemness and exosome production from nutrient-dependent cells: Influence of the molecular weight cut-off in hollow fiber membrane systems

This study aimed to optimize parameters for cultivating adipose-derived stem cells (ADSCs) in hollow fiber membrane systems. Enhanced ADSC cultivation was achieved in this study by utilizing a higher cell seeding rate (10 mL/min) and fibronectin coating (8 μg/cm²) on the membrane. A pulsatile flow perfusion (30 min on / 3 h off) for 24 h, followed by continuous flow perfusion at a lower rate (<20 mL/min), was employed. Notably, a two-day medium change maintained CD73 expression (79.26 %) compared to scenarios without changes (1.92 %) over eight days. Using a membrane cut-off of 20 kDa and <0.1 μm, a 1.4- and 2.8-fold increase in proliferated cells was observed; however, CD73 expression decreased by 10.07 and 33.63 %, respectively. The membrane with a pore size of <0.1 μm exhibited 1.4-fold higher exosome particle numbers. In conclusion, nutrient supplementation emerged as crucial for optimal ADSC cultivation in hollow fiber systems.

Algal-Based Hollow Fiber Membrane Bioreactors for Efficient Wastewater Treatment: A Comprehensive Review

The treatment of living organisms is a critical aspect of various environmental and industrial applications, ranging from wastewater treatment to aquaculture. In recent years, algal-based hollow fiber membrane bioreactors (AHFMBRs) have emerged as a promising technology for the sustainable and efficient treatment of living organisms. This review provides a comprehensive examination of AHFMBRs, exploring their integration with algae and hollow fiber membrane systems for diverse applications. It also examines the applications of AHFMBRs in various areas, such as nutrient removal, wastewater treatment, bioremediation, and removal of pharmaceuticals and personal care products. The paper discusses the advantages and challenges associated with AHFMBRs, highlights their performance assessment and optimization strategies, and investigates their environmental impacts and sustainability considerations. The study emphasizes the potential of AHFMBRs in achieving enhanced nutrient removal, bioremediation, and pharmaceutical removal while also addressing important considerations such as energy consumption, resource efficiency, and ecological implications. Additionally, it identifies key challenges and offers insights into future research directions. Through a systematic analysis of relevant studies, this review aims to contribute to the understanding and advancement of algal-based hollow fiber membrane bioreactors as a viable solution for the treatment of living organisms.

Preparation of a novel polymer microspheres and application in solid phase extraction combined with hollow fiber membrane system for capturing lactic acid from simulated fermentation broth

To separate the fermentation products in real time and improve the fermentation yield, a novel poly-4-vinylpyridine-vinylbenzeneboronic acid polymer microspheres (p4VP-VPBA) with bifunctional groups was prepared by suspension polymerization. The spherical p4VP-VPBA was 5–20 μm and thermally stable below 355.4 °C. The elemental contents of N and O were 1.36% and 5.72%, respectively, and the content of boronic acid was 0.1357 mmol/g. Its adsorption performance to lactic acid was satisfactory. Under pH 4 and 20 °C, the maximum static adsorption of p4VP-VPBA was up to 185.31 mg/g in 3 h. Its selectivity on lactic acid to glucose was 70.05 at pH 2, 7.71 at pH 4, and only 0.81 at pH 10, which indicated a good selectivity to lactic acid at low pH fitting to fermentation process. Furthermore, a p4VP-VPBA-combined with hollow fiber membrane (HFM) separation system was proposed and the removal rate of 5 mg/mL lactic acid was maintained at about 90% after 5 consecutive cycles. These data showed a huge potential for future real-time capturing lactic acid from fermentation, which also was a reference for other fermentation inhibited by product concentration.

Computational Fluid Dynamics Analysis of a Hollow Fiber Membrane Module for Binary Gas Mixture

The membrane gas separation process has gained significant attention using the computational fluid dynamics (CFD) technique. This study considered the CFD method to find gas concentration profiles in a hollow fiber membrane (HFM) module to separate the binary gas mixture. The membrane was considered with a fiber thickness where each component’s mass fluxes could be obtained based on the local partial pressures, solubility, diffusion, and the membrane’s selectivity. COMSOL Multiphysics was used to solve the numerical solution at corresponding operating conditions and results were compared to experimental data. The two different mixtures, CO2/CH4 and N2/O2, were investigated to obtain concentration gradient and mass flux profiles of CO2 and O2 species in an axial direction. This study allows assessing the feed pressure’s impact on the HFM system’s overall performance. These results demonstrate that the increment in feed pressures decreased the membrane system’s separation performance. The impact of hollow fiber length indicates that increasing the active fiber length has a higher effective mass transfer region but dilutes the permeate-side purities of O2 (46% to 28%) and CO2 (93% to 73%). The results show that increasing inlet pressure and a higher concentration gradient resulted in higher flux through the membrane.

Application of Hollow Fiber Membrane for the Separation of Carbon Dioxide from Atmospheric Air and Assessment of Its Distribution Pattern in a Greenhouse

Research on carbon management is fueled by the growing concern over rising carbon dioxide (CO2) levels in the atmospheric air and its possible impacts on the climate. In this study, we proposed a method of CO2 separation from atmospheric air. This study aimed to investigate the effects of CO2 enrichment on the air temperature inside a greenhouse using a hollow fiber (HF) membrane system. The experiment was conducted over a period of 30 days in two experimental conditions: 15 days without CO2 enrichment (WCS) and 15 days with CO2 enrichment (CS). Results showed that the mean CO2 concentration and air temperature were highest inside the greenhouse during the CS period, with values of 1120 ppm and 37.42 °C, respectively. Regression analysis revealed a positive correlation between CO2 concentration and temperature during the CS period (R2 = 0.628). The HF membrane system was found to be effective in increasing both the CO2 concentration and air temperature inside the greenhouse. However, the system also has limitations, including the cost, maintenance, and suitability for all types of crops. Further experiments are needed to address these limitations and determine the optimal CO2 concentration for different kinds of crops growing in greenhouses.

Modeling, simulation, and techno-economic optimization of argon separation processes

High-purity argon is conventionally recovered from air by cryogenic distillation, which is a mature, efficient but high-cost technology. In recent years, membrane gas separation technology is starting to emerge illustrating the potential to achieve lower production costs compared to distillation, without compromising the final product quality. In this work, a flowsheet of a conventional cryogenic distillation system for the separation of an oxygen-argon mixture was built and simulated in the gPROMS™ modeling environment. Then, a detailed mathematic modeling framework of a hollow fiber membrane system for the same separation was developed. The predictive power of the model is in a good agreement with theoretically expected results for a wide range of operating conditions. The results indicate that commercially available polymeric membranes are not capable of achieving a high-purity argon product while innovative materials, such as carbon membranes, turn out to be more efficient. Finally, the performance of the membrane process was compared with the cryogenic distillation process using an optimization-based techno-economic analysis. The comparison revealed that the distillation process has a lower operational cost compared to a membrane process for a final product purity of 99.9 mol%.

Flux modulation: A novel approach for ultrafiltration fouling control

Control of membrane fouling is critical for the long term production of water in a membrane system. Backwashing with or without relaxation is the most common method to control fouling in-situ with ultrafiltration (UF) hollow fiber membrane systems. The inclusion of relaxation is intended to assist with decompression of the membrane cake layers and assist with backwashing. However, it also results in a loss of membrane productivity. This study aimed to investigate the effect of flux modulation with single and dual mode cycles, as well as relaxation, on the performance of an UF membrane with respect to fouling control. Results demonstrated that modulating the flux in place of relaxation results in a substantial improvement in control of membrane fouling while still maintaining membrane productivity. By modulating the flux at different levels compared to a control of flux of 36 LMH, the fouling index values decreased by over 80% while specific water production only dropped 8% (2489 vs 2702 L/m2). Incorporating a relaxation step had minimal impact (<8%) on the performance of a given flux cycle with regards to fouling control. Therefore, high membrane performance can be achieved without the need for a relaxation step, as long as an appropriate flux modulation cycle is selected. This research demonstrates the potential for significant fouling control on an UF membrane by alternating the stress on the membrane surface through flux modulation.

Full Scale Sanitary Landfill Leachate Treatment by MBR: Flat Sheet vs. Hollow Fiber Membrane

The aim of this study was to find a cost-efficient leachate treatment system by comparing two MBR systems, flat sheet and hollow fiber. Data collected through continuous monitoring and laboratory analysis over the last two years has been evaluated in terms of treatment performance and economic analysis. MBR systems were found to be as effective and economical in terms of color, SS removal, and total treatment efficiency. It has been observed that the flat sheet membranes were clogged up in six weeks, while the hollow fiber membranes took 12–16 weeks to clog. Moreover, the hollow fiber module was less clogged and needed shorter washing times, resulting in lower amounts of chemical consumption. Hollow fiber membrane systems, compared to flat sheet membrane systems, have higher operational availability and lower maintenance costs. For the first time, the advantage of using submerged hollow fiber for the treatment of high-strength landfill leachate has been clearly demonstrated.

Effect of fuel type on the performance of an aircraft fuel tank oxygen-consuming inerting system

The properties of aviation fuel have a great influence on the performance of oxygen-consuming inerting systems. Based on the establishment of the catalytic inerting process, the flow relationship of each gas component flowing through the catalytic reactor was derived. The mathematical model of the gas concentration in the gas phase of the fuel tank was established based on the mass conservation equation, and the fuel tank model was verified by performing experiments. The results showed that the fuel type exerts a considerably higher influence on the performance of the oxygen-consuming inerting system compared to the corresponding influence on the hollow fiber membrane system, and the relative magnitude of the inerting rates of the four fuel types is RP5 > RP3 > RP6 > JP8. In addition, a higher catalytic efficiency or fuel load rate corresponds to a higher rate of decrease of the oxygen concentration in the gas phase, and the inerting time is inversely proportional to the suction flow rate of the fan. When different fuels are used, the amount of cooling gas and water released from the inerting system are different. Therefore, the influence of fuel type on the system performance should be extensively considered in the future.

Experimental investigation of heat and moisture transfer performance of CaCl2/H2O-SiO2 nanofluid in a gas–liquid microporous hollow fiber membrane contactor

In this study, aqueous solution of CaCl2/SiO2 nanoparticles has been used as a desiccant in a gas–liquid hollow fiber membrane (HFM) air dehumidifier contactor system. The heat and mass (H/M) transfer properties HFM energy exchanger with CaCl2/H2O-SiO2 as desiccant solution studied experimentally for first time. Effects of different parameters on H/M transfer characteristics of system, including the nanoparticle concentration, liquid flow rate and liquid temperature were examined experimentally. The experiments arranged for desiccant temperatures of 20 °C and 26 °C, desiccant solutions of 0, 1%wt and 2%wt concentration and flow rates of 1.1, 1.25, 1.4 and 1.7 ml/s. The results indicated that the influence of particles on moisture removal rate is the greatest for the conditions of highest solution temperature and the highest particle. By introducing nanofluid solution as liquid desiccant in system the enhancing effect of reducing desiccant temperature on moisture removal lessens and declined to zero by increasing the solution flow rate with a high descending rate. For 2%wt nanoparticle concentration by 53% increase of absorbent flow rate, the value of temperature effectiveness reduced by 30%. This justifies adiabatic application of hollow fiber membrane systems with nanofluid desiccant.

Process Simulation of Syngas Purification by Gas Permeation Application

Nowadays, syngas production from renewable energy sources particularly by methanation process has taken great interest. The aim of the process is energy saving by converting surplus produced energy into a truthful chemical product. Methanation reactor outlet stream contains a gas mixture which is not feasible to be used directly in distributing grids, where a higher purity of methane is necessary to obtain the highest power density. To reach the different grades of methane (for heat, electricity and vehicle fuels applications), various purification levels should be provided for syngas. For use as a fuel, elimination of carbon dioxide and water is needed, because water affects negatively on the mechanical components within the vehicles’ engine equipment. Moreover, CO2 removal should be carried out to enhance heat quality of methane and cause less pollution in the atmosphere. In the current study, the performance of a combination of flash separator and hollow fiber membranes for syngas purification was studied. For this purpose, a flash separator model was implemented to condense water from the wet feed. Then for the elimination of CO2 from methane, a hollow fiber membrane system was considered. Therefore, a unit operation user model in FORTRAN was developed to incorporate into Aspen Plus® V8.6. Different designs and arrangements of membrane modules were compared, and the best result was to purify methane up to 98 %vol. obtained using a two-stage gas permeation system with recycle streams. The model scheme can be beneficial in the design and performance analysis of a complex methanation plant system prior to practical realization.

Non-ideal modelling of polymeric hollow-fibre membrane systems: Pre-combustion CO2 capture case study

Some membrane gas separation applications operate at high temperature and pressure. However, the majority of membrane gas separation models employ simplifying assumptions which are not realistic under these conditions. In this study, a rigorous model is developed for polymeric hollow-fibre membrane modules incorporating non-isothermal separation (the Joule-Thomson effect), real gas behavior and concentration polarization. The model also accounts for temperature-dependent permeability, friction-based pressure loss on both feed and permeate sides and variable physical and transport properties. The rigorous model is applied for pre-combustion CO2 capture, i.e. CO2/H2 separation, and compared with a simplistic model for various polymeric membranes through changing temperature-independent activation energy of permeation and pre-exponential factor. Two types of H2- and CO2-selective membranes are then chosen for further analysis. As feed conditions change, the deviation between the rigorous and simplistic models ranges approximately from 2 to 12% for stage-cut and 2–20% for the permeate composition. The difference is mostly because of real gas behavior at low stage-cuts, while the Joule-Thomson effect adds to this behavior at high stage-cuts (≥40%) resulting in the greater deviation. The influence of concentration polarization, however, is found negligible even at high stage-cuts.

Enhanced CO2 bio-utilization with a liquid–liquid membrane contactor in a bench-scale microalgae raceway pond

Microalgae are able to absorb CO2 generated from sources such as flue gas to produce biomass with high lipid content. In this research, an immersed liquid–liquid membrane contactor was investigated to deliver CO2 captured by a chemical solvent to the microalgae culture via semipermeable membranes. Experiments showed that the CO2 mass transfer could be facilitated by using a thinner membrane support layer, or avoiding a support altogether, as the support was liquid filled which reduced the mass transfer coefficient. In order to better condition the culture media, the solvent flow was controlled by pH feedback. This scenario showed comparable biomass productivity (0.10 g L−1 d−1) to the conventional direct bubbling method, but with a lower energy cost and higher CO2 utilization efficiency. Further, a pond liner was formed from flat sheet membranes as a more effective alternative to a hollow fiber arrangement. The optimized system achieved a CO2 utilization efficiency of up to 90% compared to 47% with the uncontrolled hollow fiber membrane system and 11% for air sparging, thereby reducing the CO2 released to the atmosphere.

Modelling tool to assess membrane regeneration by periodical hydraulic cleaning and fouling control in pressurized membrane process for surface water treatment

In this study, a mathematical model was developed to assess fouling as well as membrane regeneration in a pressurized, hollow-fiber membrane system for the treatment of highly turbid surface water using periodical cleaning by backwashing and forward flushing. The model was validated using experimental data of trans-membrane pressure obtained when filtering separately, a SiO2 solution, a mixed SiO2/sodium alginate (SA) solution, a mixed SiO2/bovin serum albumin (BSA) solution and a mixed SiO2/humic acid (HA). Experimental and theoretical studies highlighted the synergistic fouling effect between SiO2 simulating the colloidal particles and the different elements (HA, SA and BSA) simulating the natural organic matter. Protein fouling was mitigated when mixed with SiO2. While the highest fouling rate was obtained for mixed SiO2/SA solution, the majority of this fouling was removed by periodic cleaning. Moreover, mixed SiO2/HA solution showed also high fouling which was mainly irreversible.

Application of rotational vibration in a submerged hollow fibre membrane system for bioseparation of high concentration yeast suspensions

A novel submerged rotational vibration membrane system was investigated using high concentration yeast suspensions to demonstrate the capability of this system for the separation of high concentration biomass. The critical flux and shear rate for this system can be correlated by the expression, Jcritical=1.2γ̅0.55, for the filtration of 200 g/L yeast suspension. Good fouling control performance as indicated by low and stable TMP at approximately 13 kPa as well as high protein transmission of 84% was maintained over 26 h of filtration using 200 g/L yeast suspension at a constant permeate flux of 15 L/m2 h before a rapid TMP rise was observed mainly due to the increase of feed concentration. It was determined that there is a limiting concentration, defined here as the critical concentration point, below which low and stable TMP operation can be maintained and above which rapid TMP rise was observed. Fractionation analysis of the foulant layer at the end of long term filtration experiments showed that majority of fouling was loose and reversible, which can be easily recovered by simple rinsing. The implementation of intermittent shear enhancement and periodical relaxation were found to be effective in fouling limitation, which extended the critical concentration point. However, applying periodical backwash using the permeate is not advantageous as the permeate contains protein and carbohydrate which can cause internal fouling of the pores.

Preparation and characterization of thin film composite membrane for the removal of water vapor from the flue gas at bench scale

Water inadequacy is increasing day by day and researchers are developing several technology to fulfill the pure water demand. Currently membrane technology is coming in big way to save and recovered the water. Herewith we introduce the thin-film composite (TFC) hollow fiber membranes to recover water vapor from flue gas in industrial power plants and it has become a promising technology. TFC membranes were prepared by interfacial polymerization between the aqueous monomer of 3,5-diaminobenzoic acid (DABA) in various concentrations and the organic monomer of trimesoyl chloride (TMC) on inner surface of a polysulfone (PSf) hollow fiber substrate. The selective polyamide layers of TFC membranes were comprehensively characterized by attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurement (WCA). The effect of aqueous monomer concentration on water vapor permeance and selectivity was investigated at lab-scale. As a result, a maximal selectivity of 313, along with 2873 GPU permeance, was obtained using an aqueous monomer concentration of 0.5 wt%; these synthetic conditions were applied for the preparation of bench-scale TFC membranes module. Subsequently, bench-scale experiments using real flue gas were carried out using different operating variables. Consequently, maximal water flux and water vapor removal efficiency (recovery ratio) of 2.3 kg/m2h and 27.7% were obtained. It is possible that the TFC hollow fiber membrane system will be a sustainable approach for water recycling and conservation.

Special Issue on Wastewater Treatment and Reuse Technologies

Wastewater treatment allows for the safe disposal of municipal and industrial wastewater to protect public health and the ecosystem[...]

Influence of selective permeation of backwashing solution on the cleaning effectiveness in hollow fiber system

The effectiveness of backwashing is strongly affected by selective permeation of backwashing solution along the fiber length in dead-end hollow fiber membrane system. This critical issue was systematically investigated with laser bijection sensing (LBS) technology to detect the position reached by the cleaning agent inside the fiber lumen. The limited effective backwashing distance revealed by LBS could be attributed to the outflow flux of backwashing solution in axial direction, which dissipates the driving force (pressure) of the cleaning solution further to the longer distance along the hollow fibers. An instantaneous pressure jump of backwashing solution was measured in the first pressure sensor when the pump was opened on. The principle of pressure jumps in the fiber lumen and affecting factors were speculated with novel mathematical models. Pressure variation as well as modeling prediction showed that the pressure decrease inside fiber lumen was the fundamental reason for the ineffective backwashing for long membrane fibers. Inspired by the instantaneous pressure jump in backwashing process, an intermittent backwashing mode was employed and the experimental setup was also upgraded to provide a more accurate monitoring of the cleaning solution of long membrane fibers. The results showed that the intermittent backwashing mode outperformed the continuous backwashing mode by reaching a longer fiber length in a short washing period.