Dynamical Modelling and Simulation of Waste water Filtration Process by Submerged Membrane Bioreactors

A mathematical model was developed for the filtration process and the influence of aeration on Submerged Membrane Bioreactors. The dynamics of sludge attachment to and detachment from the membrane, in relation to the filtration and a strong intermittent aeration, were included in the model. The influence on the membrane fouling of intermittent aeration injected on the membrane surface, and its synchronization with intermittent filtration, were studied numerically and experimentally. For the evaluation of filtration cake development, the assumption of the presence of two cake layers (one dynamic and the other stable) was considered. The model development and simulation focused on the description of existing relationships among important system variables like mixed liquor suspended solids concentration, aeration, temperature of the sludge suspension, transmembrane pressure, and the fouling increase during the filtration process. The model obtained offers the possibility of improving the design configuration and operation strategies of Submerged Membrane Bioreactors in wastewater treatment, and it allows the of aeration-filtration cycles to be optimized

Effect of membrane character and solution chemistry on microfiltration performance

To help understand and predict the role of natural organic matter (NOM) in the fouling of low-pressure membranes, experiments were carried out with an apparatus that incorporates automatic backwashing and long filtration runs. Three hollow fibre membranes of varying character were included in the study, and the filtration of two different surface waters was compared. The hydrophilic membrane had greater flux recovery after backwashing than the hydrophobic membranes, but the efficiency of backwashing decreased at extended filtration times. NOM concentration of these waters (7.9 and 9.1 mg/L) had little effect on the flux of the membranes at extended filtration times, as backwashing of the membrane restored the flux to similar values regardless of the NOM concentration. The solution pH also had little effect at extended filtration times. The backwashing efficiency of the hydrophilic membrane was dramatically different for the two waters, and the presence of colloid NOM alone could not explain these differences. It is proposed that colloidal NOM forms a filter cake on the surface of the membranes and that small molecular weight organics that have an adsorption peak at 220 nm but not 254 nm were responsible for “gluing” the colloids to the membrane surface. Alum coagulation improved membrane performance in all instances, and this was suggested to be because coagulation reduced the concentration of “glue” that holds the organic colloids to the membrane surface

Modelling of submerged membrane bioreactor: Conceptual study about link between activated slugde biokinetics, aeration and fouling process

A mathematical model was developed to simulate filtration process and aeration influence on Submerged Membrane Bioreactor (SMBR) in aerobic conditions. The biological kinetics and the dynamic effect of the sludge attachment and detachment from the membrane, in relation to the filtration and a strong intermittent aeration, were included in the model. The model was established considering soluble microbial products (SMP) formation-degradation. The fouling components responsible of pore clogging, sludge cake growth, and temporal sludge film coverage were considered during calculation of the total membrane fouling resistance. The influence of SMP, trans-membrane pressure, and mixed liquor suspended solids on specific filtration resistance of the sludge cake was also included. With this model, the membrane fouling under different SMBR operational conditions can be simulated. The influence of a larger number of very important process variables on fouling development can be well quantified. The model was developed for evaluating the influence on fouling control of an intermittent aeration of bubbles synchronized or not with the filtration cycles, taking into account the effects of shear intensity on sludge cake removal

Slow colloidal aggregation and membrane fouling

We observed that the concept of critical flux, although established on physical bases, does not describe all typical fouling situations found in membrane filtration. We especially focus on the slow flux decline that is observed in many industrial membrane applications, and that has found several types of explanations that we briefly discuss. In order to get a better understanding of this situation, we have considered the orders of magnitude of the slow aggregation kinetics that are expected to happen within a boundary layer, on an ultrafiltration or microfiltration membrane in operation. The results help to understand that whereas the critical flux is limiting cross-flow filtration of stable colloids, it should be combined to kinetics aspects of slow aggregation in cases of colloids of intermediate stability (metastable). We discuss some consequences on the design and operation of processes using membrane filtration

Flow and filtration imaging of single use sterile membrane filters

Sterile filters incorporating endotoxin adsorption function emerged recently to pretreat dialysate liquids fed to a hemodialysis filtration process. Their application significantly enhances the survival rate during dialysis treatment as they function as sterile filters as well as an endotoxin adsorber. Little is known about the fluid flow distribution in such single use membrane modules. We report a detailed analysis of the local 3D flow field distribution in such membrane modules using magnetic resonance flow imaging. Next to pure water filtration representing the application case of endotoxin adsorption from an already pure liquid, we also used the module as a filtration device rejecting for instance colloidal silica. Such experiments performed in-situ allow the quantification of cake layer development and its concomitant redistribution of the flow field. Particularly novel is the quantification of the time evolution of local permeate flux distribution. These detailed insights of this study encourage the use of flow-MRI when designing and applying new membrane module configurations

Why on earth do we need experiments to choose the right membrane?

Ultrafiltration (UF) is a relatively inexpensive, versatile, expedient, simple, non destructive, and reagent free technique for fractionating biological solutions in order to purify and concentrate high added value compounds. However its practical use appears to be somewhere limited. To account for this fact, it is often referred to various problems of membrane fouling, investment costs....But the first problem encounters is the choice of the right membrane! In order to prepare different fractions of fructo oligosaccharides from agave juice, 9 different membranes with molecular weigh cut off (MWCO) between 5 and 10 kDa were selected and tested in dead-end filtration cell. The results were then expressed in terms of flux and retention rates. First it is important to note that membranes prepared from the same polymer (polyethersulfone (PES)) with the same MWCO lead to very different performances which cannot be explained by membrane structure. The membrane which showed the more porous structure by SEM observation presented the lowest flux. Its poor performances are related to a high fouling index which cannot be estimated without any experiment. However, thanks to an appropriate experimental procedure, it was possible to selected with only few experiment the best membrane allowing the total retention of fructo oligosaccharides with degree of polymerization (DP) higher than 40. Furthermore the results obtained in dead-end filtration cell were confirmed in a tangential filtration device. (Texte intégral

Fouling mechanisms in constant flux crossflow ultrafiltration

Four fouling models due to Hermia (complete pore blocking, intermediate pore blocking, cake filtration and standard pore blocking), have long been used to describe membrane filtration and fouling in constant transmembrane pressure (ΔP) operation of membranes. A few studies apply these models to constant flux dead-end filtration systems. However, these models have not been reported for constant flux crossflow filtration, despite the frequent use of this mode of membrane operation in practical applications. We report derivation of these models for constant flux crossflow filtration. Of the four models, complete pore blocking and standard pore blocking were deemed inapplicable due to contradicting assumptions and relevance, respectively. Constant flux crossflow fouling experiments of dilute latex bead suspensions and soybean oil emulsions were conducted on commercial poly (ether sulfone) flat sheet ultrafiltration membranes to explore the models’ abilities to describe such data. A model combining intermediate pore blocking and cake filtration appeared to give the best agreement with the experimental data. Below the threshold flux, both the intermediate pore blocking model and the combined model fit the data well. As permeate flux approached and passed the threshold flux, the combined model was required for accurate fits. Based on this observation, a physical interpretation of the threshold flux is proposed: the threshold flux is the flux below which cake buildup is negligible and above which cake filtration becomes the dominant fouling mechanism

Characterization of amorphous silica and crystalline silica from rice husk ash on water filtration application

The presence of water pollution which consists of heavy metals, fecal and others has produced a major problem. These can lead the water to the toxicity and the impurity of water will be disrupted. Therefore, it would not be safe to drinks and could be threatening to live health. In addition, the current market now is dealing with high-cost production to develop ceramic membranes and has been using expensive material to make the filtration system works. In order to challenge the issue, the preparation of ceramic water filtration at low-cost production and using an effectively silica from natural waste rice husk was evaluated. Rice husk was fired at 700ºC and 1000ºC respectively and produced rice husk ash which mutated to amorphous and crystalline silica. Five samples were fabricated after been mixed with the compositions of rice husk ash, kaolin clay, and wheat flour, used at 40:40:20 ratios by weight respectively. The fabrications of the ceramic membrane were conducted by using dry pressing. The samples then were dried in the oven at 60ᵒC for 1 hour followed by sintering at 1000ᵒC respectively. These samples (OO, C1, C2, N1, and N2) were tagged based on unwashed and washed material with the chemical. The properties of silica which are the microstructure and pore size, from rice husk ash were obtained by using Scanning Electron Microscopy (SEM), X-Ray Fluorescence (XRF) and x-ray diffractometer (XRD). Effect of silica content in ceramic filtration membrane was investigated and characterized in term of porosity, density, water absorption, membrane hardness, pore size, flow rate, the turbidity of water (before and after filtration) and pH value. From the result, sample C2 was the best option to support the objective by 98.60% silica content, 64.82% of porosity, 1.1433 mg/cm3 of density, 40.59% of water absorption, 171.0 Hv of hardness, 0.177 l/hr of flowrate and pH of 7.62 of water after filtration. In general, the quality of the ceramic filter membrane is reliant on the raw material, while the flow rate and water clarity are dependent on the pore size of the filter membrane

Interpretation of Particle Fouling in Submerged Membrane Filtration by Blocking Models

The particle fouling in a submerged membrane filtration system is analyzed by use of membrane blocking models. Two kinds of ceramic membranes made of ZrO2-TiO2, K-04 and K-06, are used in experiments. Their mean pore sizes on the outer surfaces are 8 and 5 m, respectively. The values of blocking index under various filtration pressures are calculated and discussed. At the initial period of a filtration, the membrane internal blocking is dominant, and the blocking index decreases quickly. The index then suddenly drops to zero at a critical condition and keeps invariably thereafter. The boundary between membrane blocking and particle bridging conditions can be grasped by this blocking index analysis. Membrane blocking occurs only under higher filtration flux or less particle accumulation, while a filter cake may be formed to the contrary conditions. To compare the filtration performances of used membranes, membrane K-04 results in more severe membrane blocking at the initial period of filtration because of more large nominal pores. However, more particles can be continuously held up in the large pores of membrane K-06 due to a little wider pore size distribution and its higher internal porosity. This study provides a useful method to understand the variation of each filtration resistance source during filtration. An increase in filtration pressure leads both resistances due to membrane blocking and cake formation to be increased, as a result, causes to a decrease in the filtration flux. The agreement between calculated filtration resistances and experimental data demonstrates the reliability of the proposed method.補正完畢國際EITW

Adsorption of MS2 bacteriophage on ultrafiltration membrane laboratory equipments

Virus adsorption has been quantified (i) on different materials including various containers made of glass, plastic or stainless steel and hollow fiber membranes made of polyethersulfone, polysulfone, PVDF or cellulose acetate (with two configurations: in/out and out/in and various molecular weight cut-offs); and (ii) on the filtration equipment. The selected virus is MS2 bacteriophage used as a model to estimate viral survival in water or to quantify virus elimination by membrane filtration. A series of experiments have been conducted with suspensions of MS2 at different concentrations prepared in a sterilized saline solution (8 g/L of KCl) or in sterilized distilled water. This study has shown that the most appropriate material to be used as a filtration test tank is Pyrex glass. We show that an addition of a virus solution 15 min after the beginning of the experiment allows keeping the virus concentration at a high level in the system (including tank, tubing,and pump). No adsorption was observed on membrane materials tested during soaking