Tubular Ultrafiltration Membrane Research Articles

Treatment of flue gas desulfurization wastewater by a coupled precipitation-ultrafiltration process

Flue gas desulfurization (FGD) wastewater is characterized by low pH, high content of hardness ions and COD. In this work, chemical precipitation and ultrafiltration (UF) membrane separation were corporately coupled to treat the FGD wastewater on a lab scale to remove the hardness as well as some organic compounds for further advanced treatment. Firstly, influential factors for precipitation to deal with the simulated wastewater, including reaction time, stirring speed, and dosage, were investigated by batch tests, while CaO and Na2CO3 were used as the first and second precipitants. The batch results showed that the removal rates of Mg2+ and Ca2+ could be both higher than 98% under the optimal reaction condition. Then a polyvinylidene fluoride tubular UF membrane was used to remove the precipitates without adding flocculants. Thirdly, the coupled process with the optimal operation parameters was adopted to treat real FGD wastewater. Almost all the hardness ions and most COD could be removed, while rapid permeability decline was observed in the UF process due to the high COD, which could be recovered by a simple cleaning. In summary, when the mass ratios of [CaO]/[Mg2+] and [Na2CO3]/[Ca2+] were 2.5 and 2.7, the flow velocity was around 5 m/s, the removal rates of the hardness ions can be above 98% and the membrane flux can be recovered by 98% with a backwash with pure water and an HCl solution of pH = 2. This work proved that the coupled process is a technically feasible technology for treating FGD wastewater to realize the ZLD.

Development of a biorefinery platform for urban waste valorisation into biogas and added-value products

This study focuses on the application of the circular economy approach, with generation of energy and production of added-value products from organic waste, while minimizing environmental impacts. Within this purpose, an urban biorefinery technology chain has been designed at pilot scale for the production of biogas and biopolymers (polyhydroxyalkanoates, PHA). The pilot system (100-400 L) comprised different units: a) biowaste acidogenic fermentation; b) solid/liquid separation unit (a coaxial centrifuge and a tubular ultrafiltration membrane); c) a Sequencing Batch Reactor (SBR) for the production of aerobic PHA-storing biomass; d) aerobic fed-batch PHA accumulation reactor and e) anaerobic co-digestion (ACoD). The thermal pre-treatment of the biowaste before mesophilic fermentation increased the carbon conversion into volatile fatty acids (VFA), being the final VFA/CODSOL (soluble COD) higher than 0.80. The VFA-rich stream was utilized in a high-rate SBR for the enrichment of PHA-accumulating biomass, at short solid retention time (SRT of 1 d), 12 h of cycle length and 4.0 gCOD/L d as organic loading rate (OLR). The aerobic biomass was characterized by a high accumulating capacity (with PHA content around 60% on cell dry weight). The global PHA yield of 0.1 kg PHA/kg VS (volatile solids) was estimated as the best scenario. The excess sludge and the solid-rich biorefinery overflows were utilized for biogas production in a dedicated anaerobic digestion section to sustain a closed loop approach and to prevent secondary wastes production.

Influence of Ceramic Membrane Surface Characteristics on the Flux Behavior of a Complex Fermentation Broth.

The valorization of agro-industrial residues using yeasts as biocatalysts requires efficient methods for biomass separation. Filtration with ceramic membranes is suitable for this task, however, the challenge of flux decline and the unavoidable cleaning must be taken into account. We investigated the filtration of fermentation broth and its components using tubular microfiltration and ultrafiltration membranes, and hollow-fiber ultrafiltration membranes, with cut-offs of 30 and 200 nm. The steady-state flux was limited by fouling under comparable wall shear stress conditions but increased when the wall shear stress was higher. Single-component filtration with two 30 nm tubular ultrafiltration membranes, whose average surface roughness ranged from 1.0 to 3.9 µm, showed that smoother surfaces experience less biomass fouling under more intense hydrodynamic conditions. Furthermore, we showed experimentally and by scanning electron microscopy in filtration with 30 nm tubular membranes that the thickness of the first separation layer is responsible for the degree of irreversible resistance caused by the deposition of organic material in the membrane pores. The thickness of this layer should therefore be minimized without compromising mechanical stability.

Recovery and purification of potato proteins from potato starch wastewater by hollow fiber separation membrane integrated process

Potato starch wastewater contains high-concentration potato proteins which have great potential in the fields of food and health care. Most researches on potato protein recovery by membrane separation technique are focused on flat sheet or tubular ultrafiltration (UF) and reverse osmosis (RO) membranes and lack the further protein purification and the in-depth discussions on the fouling behavior. In this laboratory-scale study, potato proteins were recovered and purified from the simulated potato starch wastewater by the self-made hollow fiber (HF) UF and nanofiltration (NF) separation membrane integrated process. 85.62% potato proteins with high molecular weight in the potato starch wastewater could be retained by UF membrane and 92.1% potato proteins with low molecular weight were rejected by NF membrane. The concentrated solution after UF and NF filtration was desalinated and purified by diluting the solution eight times and filtering the diluted solution with UF membrane. Both types of HF membranes, UF and NF, suffered the inevitable membrane fouling. After the traditional physical washing and chemical cleaning, water flux of UF and NF membranes can be effectively recovered. The corresponding recovery rates of UF and NF membranes can reach 93.5% and 84.7%, respectively. The hollow fiber UF-NF separation membrane integrated process was proved to be a promising technique of high-purity potato protein recovery from potato starch wastewater.

Ultrafiltration concentration of whey in a pilot plant

Experimental data on the retention coefficient and the output specific flow are obtained. The test solutions were goat and cow's milk whey after obtaining cheese. The description, general view and technological scheme of a pilot installation of a tubular type are given. The studies were carried out on semipermeable tubular type ultrafiltration membranes manufactured by AO "ZAVKOM". Based on the studies, graphical dependences of the retention coefficient on the specific output stream were constructed and analyzed. During the analysis, it was noted that with an increase in the output specific flow of the solvent, the retention coefficient decreases. The reason for this is the boundary layers of fat and protein formed in the near-membrane layers, which prevents the passage of protein molecules through the pores of the membrane. Also during the experiment, it was noted that goat milk serum has a more oily structure and requires prior separation. For the theoretical calculation of the retention coefficient and specific output stream, mathematical expressions are developed and numerical values of the values of empirical coefficients are obtained. The developed mathematical expressions describe the experimental data with good confidence. The obtained experimental and calculated data can be used with great reliability in the calculations of mass-transported flows of substances through semipermeable membranes, as well as in engineering methods for calculating and predicting the effectiveness of the use of membrane processes for the concentration of whey.

Fouling minimization at membranes having a 3D surface topology with microgels as soft model colloids

Cross-flow ultrafiltration of colloidal suspensions is mainly limited by the accumulation of retained particles adjacent to the membrane surface. The hydrodynamic conditions in the feed channel strongly affect the mass transfer rate of colloids from the membrane surface to the bulk and is therefore an important control measure. A common approach for enhancing mass transfer through hydrodynamics is to modify the geometry of the feed channel. In flat-sheet membrane configurations, feed spacers are typically installed, which function as turbulence promoters. In tubular and hollow-fiber membranes implementation of feed spacers is difficult, thus different strategies are sought for. Here we study the effect of a spiralling surface pattern (Helix) on the hydrodynamics and flux performance of tubular ultrafiltration membrane operated in cross-flow mode at inside-out configuration. We apply flow Magnetic Resonance Imaging (MRI) to visualize the flow-field inside the lumen and asses the length dependency of the permeate flux. We combine this information with classical filtration experiments at a wider range of operational parameters. Microgel suspensions were used as a model for soft colloidal systems. The transmembrane flux for the Helix as compared to the reference tubular membrane only increases when non-laminar flow developed inside the lumen channel. Yet the onset of transient non-laminar flow conditions starts at much lower Reynolds numbers of above 1700 for the Helix, while the regular tube shows a transition at high velocities and Re>3150. In consecutive filtration experiments, the Helix shows less flux decline as well. This improved fouling resistance is based on less flux decline at the end of the Helix membrane. Flow-MRI proves that the helical corrugations impose swirling flow patterns with contributions normal to the membrane surface opposing the deposition of microgels onto the membrane surface.

Ceramic-supported thin film composite membrane for organic solvent nanofiltration

The commercial success of membrane-based separation processes related to water treatment has helped launch an emergent field of membrane-based organic solvent nanofiltration (OSN). Polyamide, a mainstay selective layer material found in reverse osmosis (RO) thin film composite (TFC) membranes, has demonstrated excellent performance in OSN. RO membranes, however, are built on solvent-intolerant support layers, thus necessitating the use of other types of supporting materials that can operate in solvents without dissolution or swelling. In this work, we demonstrated the formation of a polyamide selective barrier layer in-situ onto a ceramic ultrafiltration (UF) membrane and evaluated the TFC membrane for use in OSN. We selected ceramic tubular UF membranes provided by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) as substrates for this work. Some of our best performing membranes demonstrated a pure methanol permeance of 22.9 Lm−2 h−1 bar−1 and dye rejection for methyl orange (327.3 g/mol), acid fuchsin (585.5 g/mol), chlorophyllin (724.2 g/mol) and brilliant blue FCF (792.9 g/mol) of 42.8%, 92.9%, 99.4%, and 94.1%, respectively. This work represents the first time that polyamide selective has been directly formed onto a tubular ceramic membrane and tested for OSN.

Continuous enzymatic hydrolysis of lignocellulosic biomass in a membrane‐reactor system

AbstractBACKGROUNDConverting abundant lignocellulosic biomass to sugars as fungible precursors to fuels and chemicals has the potential to diversify the supply chain for those products, but further process improvements are needed to achieve economic viability. In the current work, process intensification of the key enzymatic hydrolysis unit operation is demonstrated by means of a membrane reactor system that was operated continuously.RESULTSLignocellulosic biomass (pretreated corn stover) and buffered enzyme solution were fed to a continuously stirred‐tank reactor, and clarified sugar solution was withdrawn via a commercial tubular ultrafiltration membrane. The membrane permeance decline and membrane cleaning efficacy were studied and did not vary significantly when increasing fraction insoluble solids (FIS) from 2.5% to 5%. Continuous enzymatic hydrolysis was successfully operated for more than 80 h. A model for the reactor system was able to predict dynamic behavior that was in reasonable agreement with experimental results.CONCLUSIONThe modeled technical performance of anticipated commercial batch and continuous enzymatic hydrolysis processes were compared and showed that continuous operation would provide at least twice the volumetric productivity for the conditions studied. Further improvements are anticipated by better membrane selection and by increasing FIS. © 2017 Society of Chemical Industry

Mass transfer coefficient of tubular ultrafiltration membranes under high‐flux conditions

The effect of suction flow on the mass transfer coefficient of tubular ultrafiltration membranes, in particular that under a high‐flux condition, was studied. We pointed out that is proportional to under turbulent conditions, and that the proportional constant, b, exceeds 0.023 when the effect of suction flow is not negligible. We conducted the velocity variation method using ultrafiltration membranes with MWCOs of 20k and 100k and dextrans having molecular weights of 40,000 and 70,000 at the conditions, where exceeded . We demonstrated that the effect of suction flow includes not only flux but also the diffusion coefficient of solute, and that the ratio of the flux to the diffusion coefficient, expressed as , is an important index. Finally, we concluded that , when is smaller than , giving the Deissler equation itself, and that , when exceeds . © 2017 American Institute of Chemical Engineers AIChE J, 64: 1778–1782, 2018

Fouling membrane in an anaerobic membrane bioreactor treating municipal wastewater

An anaerobic membrane reactor (AnMBR) treating municipal wastewater was evaluated. The experiments were performed using a pilot-scale up-flow anaerobic sludge blanket reactor with a submerged tubular ultrafiltration membrane at a hydraulic retention time of 8 hours. The system worked at an intermittent filtration mode (4 min on/1 min off) with and without nitrogen gas bubbling during the relaxation time (IF4NP and IF4P, respectively). The chemical oxygen demand (COD) removal achieved by the AnMBR was 68.6% and 87.9% for IF4P and IF4NP. Nitrogen bubbling also improved the filtration performance, as the elapsed time to reach 40 kPa for IF4NP and IF4P were 443 and 108 hours, respectively. Results show that intermittent filtration combined with nitrogen bubbling during the period of relaxation was an effective operation strategy in order to minimize membrane fouling and to increase COD removal.

Ultrafiltration of non-axenic microalgae cultures: Energetic requirements and filtration performance

Microalgae represent a promising source of biomass for the production of bioproducts and biofuels. However, microalgae cultures are usually diluted. Harvesting processes need then to achieve high levels of volumetric reduction, which is normally energetically demanding. Membrane processes have been recently proposed as an alternative for microalgae concentration. During this research, membrane concentration of non-axenic cultures of saline microalga Nannochloropsis gaditana and freshwater Chlorella sorokiniana was evaluated by a series of batch filtration tests, using tubular ultrafiltration membranes. Theoretical energy demands were determined, based on filtration performance during lab-scale filtration tests. Surface response methodology was also used to determine the effect of cross-flow velocity and biomass concentration over critical flux. Results indicate that exposure of the microalgae culture to cross-flow conditions for long periods may affect suspension properties, decreasing particle size, affecting permeate flux. This would result in high-energy demands when high concentration factors are required, starting from diluted cultures. Moreover, presence of bacteria, resulting from non-sterile conditions, may also determine filtration performance. However, membrane filtration may be an interesting alternative as a post-concentration step for processes normally providing low concentration factors, such as flotation and settling. Short term experiments show that critical fluxes of 50–70L/m2/h can be achieved, depending on the microalgae, at cross flow velocities in the range of 1.5–2m/s, when working at 40–50g/L of VS. Further research would be needed to evaluate if this fluxes can be sustained for long periods.

Application of tubular membranes for surface water treatment: effect of membrane properties and operation modes

AbstractFiltration characteristics in surface water treatment using tubular microfiltration and ultrafiltration membranes made of polypropylene or ceramic were investigated. A series of filtration experiments were performed to examine the flux behaviors and fouling propensity. When the initial flux was set to be same, the fouling rates were similar regardless of the membrane materials and pore size, suggesting that the hydrodynamic effect was dominant compared with physicochemical interactions between foulants and membranes. Based on theoretical analysis of critical flux, the major foulants were identified to be colloidal particles which size ranges from 0.01 to 0.1 μm. To control the membrane fouling, three methods were compared including (1) periodic backwashing; (2) intermittent operation (periodic pump stop); and (3) the mixed operation of dead end and cross-flow modes. Considering the anti-fouling effect and energy consumption, the mixed operation of dead end and cross-flow modes was better than othe...

Treatment of Anaerobically Digested Cattle Manure Wastewater by Tubular Ultrafiltration Membrane

A resurgent interest in anaerobic treatment of organic wastes intrigues the subsequent wastewater purification and nutrient recovery. This study investigated the feasibility of tubular ultrafiltration to treat anaerobically digested wastewater (AnDW) in the pilot-scale. Due to the gel-layer filtration mechanism, which primarily governed the AnDW wastewater passing through the membrane module, the change of operating pressure in the experimental conditions showed a minor effect on the permeate flux, while the cross-flow tangential velocity showed a significant effect on the permeate flux. A permeate flux on average of 22 l m−2 h−1 was obtained when the feed superficial-velocity was up to 2 m s−1. The permeate flux decreased with increasing suspended solid concentration, implying a potential advantage of preliminary solid-liquid separation such as mechanical centrifugation. Irrespective of the arranged order of the sequential cleaning, the fouled membrane can be successfully cleaned using specific cleaning agents, which included a weak acid, a detergent, and an oxidant, respectively. A commercial detergent, namely KLD II, exhibited the greatest contribution to the flux recovery during the sequential cleaning.

The Effect of Operating Parameters on Ultrafiltration and Reverse Osmosis of Palm Oil Mill Effluent for Reclamation and Reuse of Water

An attempt was made to reclaim and recover palm oil mill effluent (POME) for water reuse using tubular ultrafiltration (UF) and reverse osmosis (RO) membranes. The reclaimed water was compared with the final discharged water of the local mill. The raw POME was first subjected to a physical pre-treatment process to remove the content of organic matter and suspended solids. The pre-treatment process was coupled with membrane technology (UF and RO) to reclaim the clean water from POME. From the combined techniques of UF (5 bar) and RO (30 bar) the results showed that the turbidity and BOD5 were reduced by 99% and 98.9%, respectively. Compared to the final discharged POME, this suggested method gives a significant difference in BOD5 and turbidity. The final permeate of RO was found to comply with the standards for water reuse. Therefore, the combined UF and RO method is a viable alternative and has a great potential for use in the palm oil industry.

Anaerobic membrane bioreactors for treating waste activated sludge: Short term membrane fouling characterization and control tests

There is limited information on the impact of sludge characteristics, membrane type and operation parameters on membrane fouling under anaerobic conditions. This paper examined filtration characteristics of anaerobic sludges with solids concentration between 6 and 33 g/L and the interaction with negatively and neutral charged membranes at various fluxes within the subcritical region. The study employed a short term filtration protocol using a bench-scale tubular ultra-filtration membrane operated at a cross-flow velocity of 1 m/s and under constant pressure. The results showed that the effects of anaerobic sludge concentration and membrane surface charge on membrane fouling were a function of the operating flux. Their impact on fouling was found to be minimal at the lower fluxes (8 LMH) however detrimental at higher fluxes (30 LMH). Further study on impact of anaerobic sludge composition on membrane fouling indicated that the decline in membrane performance at the higher subcritical fluxes was associated mainly with the colloidal fraction when the suspended solids concentrations were less than 20 g/L whereas at higher concentrations both the solids and colloidal fractions contributed to development of the fouling layer. Integration of a relaxation cycle and addition of cationic polymer were found to be effective in controlling anaerobic membrane fouling.

Effects of Organic Solvent Treated on the Performance and Structure of Polysulfone Tubular Ultrafiltration Membrane

The paper studied the effect of different kinds of organic solvents treated polysulfone tubular ultrafiltration membrane on its performances and structure. The results show that the surface of membrane treaded with n-hexane are smoother and less hydrophily, the content of carbon element increased at the same time. On the other hand, the water flux of membrane treated with alkane decrease, but the rejections to MgSO4 and egg protein increase. While the surface of membrane treated with ethanol are rougher and more hydrophily, the contents of carbon and oxygen increase too. The water flux of membrane treated with alcohols increase obviously, but the rejection to egg protein decrease slightly.

Non-feasibility of magnetic adsorbents for fouling control in anaerobic membrane bioreactors

A magnetic adsorbent with an approximate diameter of 1μm was manufactured and used for fouling control in an anaerobic membrane bioreactor, equipped with a side flow inside-out tubular ultra-filtration membrane, operated under slug flow conditions. Without the addition of the magnetic adsorbent, a short-term experiment showed that the applied slug flow conditions enabled membrane operation at a flux exceeding 20L/m2h with a low trans-membrane pressure (TMP) increasing rate. Then, the magnetic adsorbent (1g/L) and subsequently more magnetic adsorbent was added that increased the concentration of the adsorbent from 1g/L in the reactor to 5g/L. However, the introduction of the magnetic adsorbent resulted in an increased TMP, even at the low concentration applied (1g/L). The TMP increasing rate increased with the applied adsorbent concentration. Strikingly, addition of the adsorbent had no effect on sludge viscosity, although filterability deteriorated significantly. Removal of adsorbent from the sludge using an external magnetic field was unfortunately accompanied by significant biomass loss. Hence, under the applied conditions, the proposed methodology is not considered viable for fouling control.

Olive mill waste water (OMWW) treatment by diafiltration

The present work studied the feasibility of diafiltration for processing olive mill waste water (OMWW). An experimental apparatus, consisted of a tubular membrane accommodation module, a controlled temperature raw material stock tank and a positive displacement pump, was developed to investigate the effects of transmembrane pressure, temperature, membrane type and OMWW dilution on diafiltraion flux. Three tubular Ultrafiltration membranes were used, with Molecular Weight Cut Off (MWCO) 8,000, 25,000 and 100,000 Da, respectively. The performance of each one of the three membranes, in terms of UF permeation flux, was studied by using four OMWW:water dilutions (1:2, 1:3, 1:5 and 1:10), at three temperature settings (30, 40 and 60°C). For each one of the 12 respective combination of temperature and dilution setting, six flux measurements at transmembrane pressure values adjusted within the range of 1–6 bars were taken. The experimental results showed that the overall OMWW diafiltration flux, especially in the case of the membranes withMWCO(Daltons) 25,000 and 100,000, was of high magnitude. This fact creates optimism for the commercial follow-up of the process itself by its use as the main component of a promising hybridic scheme for total handling the OMWW pollution problem in an environmentally friendly and sustainable way, according to the EU adopted environmental principle of zero discharge.

Outside skin tubular ultrafiltration membranes for separation of proteins and polysaccharides and removal of turbidity from seawater

In this study, ultrafiltration (UF) membranes were prepared in outside skin tubular configuration using polysulfone and sulfonated polysulfone polymers in order to study the effect of chemical nature of membrane surface on separation performance as well as surface fouling. Separation of polysaccharide and protein with its fouling tendency, removal efficiency of turbidity from seawater with flux recovery after fouling were evaluated. Tubular configuration was chosen, as the membrane surface is most exposed for cleaning after fouling than any other configurations. Bovine serum albumin (BSA) and sodium salt of alginic acid were used as model protein and polysaccharide, respectively, to probe the rejection behavior of these tubular membranes. Sulfonated polymeric membranes were compared with pure polymer membranes for resistance to fouling by the model protein and polysaccharide solutions. Pure water fl ux recovery on water flushing for polysaccharide fouled membrane was comparatively more (6–8%) than protein...

Grafting of alginates on UF/NF ceramic membranes for wastewater treatment

The mechanism of heavy metal ion removal in processes involving multi-layered tubular ultrafiltration and nanofiltration (UF/NF) membranes was investigated by conducting retention experiments in both flow-through and cross-flow modes. The prospect of the regeneration of the membranes through an acidic process was also examined and discussed. The UF/NF membranes were functionalised with alginates to develop hybrid inorganic/organic materials for continuous, single pass, wastewater treatment applications. The challenge laid in the induction of additional metal adsorption and improved regeneration capacity. This was accomplished by stabilizing alginates either into the pores or on the top-separating layer of the membrane. The preservation of efficient water fluxes at moderate trans-membrane pressures introduced an additional parameter that was pursued in parallel to the membrane modification process. The deposition and stabilization of alginates was carried out via physical (filtration/cross-linking) and chemical (grafting) procedures. The materials developed by means of the filtration process exhibited a 25–60% enhancement of their Cd 2+ binding capacity, depending on the amount of the filtered alginate solution. The grafting process led to the development of alginate layers with adequate stability under acidic regeneration conditions and metal retention enhancement of 25–180%, depending on the silane involved as grafting agent and the solvent of silanisation.