Direct visualization of hollow fiber membrane fouling distribution

Submerged membrane bioreactor system is commonly used for water and wastewater treatment processes. This system is a more economical alternative to conventional activated sludge process due to small footprint and better effluent quality. Nevertheless, membrane fouling is a major issue that requires further studies. This paper covers the use of an optical microscope to observe membrane fouling. Bentonite was used as model particles to simulate activated sludge. In-situ observation of particle deposition along the surface of hollow fiber membranes during filtration was performed at various operating conditions. Results from this studies indicated that the flux distribution was affected by the permeate flux and cross flow velocity. Lower CFV and higher flux caused the flux to be more non-uniformly distributed due to more severe fouling. These findings provided useful information to further improve the membrane module design to achieve more evenly distributed permeate flux

Anti-scaling and water flux enhancing effect of alginate in membrane distillation

This study focused on the effect of sodium alginate on the performance of direct contact membrane distillation (DCMD). The feed solution contained various combinations of sodium chloride, sodium sulfate and calcium chloride along with bovine serum albumin, xanthan gum and sodium alginate. Unlike findings from the majority of prior studies that suggested the presence of alginate in feed solution caused the deterioration of membrane process performance, our results indicated that sodium alginate exhibited anti-scaling properties and water flux enhancing effect. However, this interesting phenomenon was exhibited by sodium alginate under particular conditions only. Experiments performed with other organic foulants such as xanthan gum did not display the same trend. It is believed that the presence of a hydrophilic layer (calcium alginate gel), which is much less thermal conductive as compared to the PTFE membrane, on the top of the membrane could reduce the amount of heat dissipated due to evaporative cooling or reduce conductive heat loss in the membrane, thus enhancing the thermal efficiency of the system.Economic Development Board (EDB)Submitted/Accepted versionFunding support from Singapore Economic Development Board to Singapore Membrane Technology Centre is gratefully acknowledged

Density and viscosity for a binary mixture of ethyl valerate and hexyl acetate with 1-pentanol and 1-hexanol at 293.15 K, 303.15 K, and 313.15 K

Density and viscosity for a binary mixture of ethyl valerate and hexyl acetate with 1-pentanol and 1-hexanol were measured in this experiment at three different temperatures (293.15, 303.15, and 313.15 K) and at atmospheric pressure. The measurements were carried out over the whole range of composition. Density values were used in the determination of the excess molar volume, V, and the viscosity deviations, Δη. The latter were fitted to the Redlich-Kister polynomial equation

Submerged hollow fibre membranes in bubbling systems

This study focuses on the optimisation of submerged hollow fibre membrane performance by analysing the role of air sparging on the reduction of membranefouling. In submerged hollow fibre membranes, rising bubbles have been shown to induce shear, liquid movement and fibre displacement. The interactionbetween fibre movement induced by bubbling and the microfiltration performance was assessed for various parameters (fibre tightness, fibre length, fibrediameter, air flowrate, nozzle size, and feed concentration). A model feed of yeast suspension and a series of isolated fibres were used. The fibre movementwas assessed by monitoring the displacement using video recording. Bubble population parameters were also measured. The results suggest that bubbleinducedfibre movement plays an important role in controlling membrane fouling. Investigations of the critical flux at various operating conditions alsosupported these conclusions.Since energy consumption for aeration is a major contributor to the cost in submerged membranes, the potential to minimise the aeration cost has been testedby implementing intermittent aeration and different nozzle sizes. It was found that an optimum condition associated with a low fouling rate could be reachedby combining various aeration intermittencies and nozzle sizes. An attempt to suppress fouling without aeration was made by incorporating vibrations into asubmerged hollow fibre membrane system. The effects of vibration frequency, type of yeast (washed and unwashed) on the filtration performance wereobserved. The impact of coagulant addition on filtration enhancement was also analysed. The performance of microfiltration was evaluated based on itscritical flux value. The findings in this preliminary study indicated potential fouling control by applying vibrations to submerged membranes.A semi-empirical model was developed to predict the filtration behaviour by taking into account the bubble-induced shear and fibre movement. Thepredicted critical flux values suggested that membrane fouling appears to be more prominent at low air flowrate, with tight fibres, and higher feedconcentrations. The model fits the experimental data with discrepancies from approximately 0.3% to 20%. The predicted filtration profiles at differentoperating modes demonstrate the importance of bubble-induced shear and fibre movement in the improvement of filtration performance

Recovery of lactic acid from traditional market wastes fermentation broth

This research was aimed to investigate the effect of temperature and water addition on lactic acid produced from fermentation using Lactobacillus plantarum. The effect of pH on lactic acid recovery from resin lRA-400 was also studied. The fresh organic wastes were collected from traditional market and then processed to be a media for fermentation. The vegetables wastes juice was sterilized, added nutrients and microorganisms. The mixtures were incubated at anaerobic condition at 30 and 40°C for 16 days. Following the fermentation process, the lactic acid in fermentation broth was recovered using resin at pH 2 and 5. The results showed that there was no significant difference in quantity of lactic acid recovered from resin at pH 2 and 5. Increasing temperature to 40oC increased the lactic acid produced. The highest concentration of lactic acid (0.6 g/lOO mL) was obtained from fermentation of pure vegetables juice at 40oC for 12 davs

Recovery of lactic acid from traditional market wastes fermentation broth

This research was aimed to investigate the effect of temperature and water addition on lactic acid produced from fermentation using Lactobacillus plantarum. The effect of pH on lactic acid recovery from resin lRA-400 was also studied. The fresh organic wastes were collected from traditional market and then processed to be a media for fermentation. The vegetables wastes juice was sterilized, added nutrients and microorganisms. The mixtures were incubated at anaerobic condition at 30 and 40°C for 16 days. Following the fermentation process, the lactic acid in fermentation broth was recovered using resin at pH 2 and 5. The results showed that there was no significant difference in quantity of lactic acid recovered from resin at pH 2 and 5. Increasing temperature to 40oC increased the lactic acid produced. The highest concentration of lactic acid (0.6 g/lOO mL) was obtained from fermentation of pure vegetables juice at 40oC for 12 davs

Analysis of Membrane Distillation Crystallization System for High Salinity Brine Treatment with Zero Discharge Using Aspen Flowsheet Simulation

An environmentally friendly membrane distillation crystallization (MDC) system is proposed to treat high salinity reverse osmosis (RO) brine with zero discharge. The raw brine from RO desalination plants is concentrated in direct contact MD to produce pure water, and the concentrate is then crystallized to produce solid salts without secondary disposal. A comprehensive analysis on the MDC system has been performed by Aspen flowsheet simulation with a user customized MD model, which was verified by our previous experiments. Simulation results reveal that the total energy consumption is negligibly changed by integration of a crystallization unit into the system, as over 97.8% of the energy was consumed by the heater of the MD subsystem. Higher inlet temperatures of both the feed and permeate streams in the MD module can improve the thermal efficiency. The introduction of a heat recovery unit in the MDC system, to recover the heat in the permeate for feed preheating, can increase the gain output ratio (GOR) by 28%. Moreover, it is shown that in a hollow fiber MD module, the permeate yield is a linear function of the length-to-radius ratio of the membrane module, and a longer MD module can reduce the specific energy consumption. A relatively high feed flow rate is preferred to avoid the potential problem of crystal blockage in the MD module

Preparation of high performance nanofiltration (NF) membranes incorporated with aquaporin Z

Aquaporin (AQP) based biomimetic membrane has attracted increasing attention in recent years because of its potential application for water purification and seawater desalination, attributed to the exceptionally high permeability and selectivity of AQPs. Despite its superior performance, AQP based membrane faces several challenges associated with the design and preparation of such membranes for practical application. In this current study, a novel and simple method was introduced to prepare an aquaporin Z (AqpZ) based biomimetic nanofiltration (NF) membrane with a relatively large membrane area of 28.26 cm2. The proteoliposome, incorporated with AqpZ, was fully encapsulated into the selective layer through crosslinking of a polyelectrolyte with the membrane substrate made by poly(amide–imde) (PAI). The water flux of the AqpZ based membrane was around 50% higher than the mutant one. At optimal preparation conditions, the AqpZ based membrane could offer a water flux of 36.6 L m−2 h−1 with a MgCl2 rejection of 95% at 0.1 MPa. Results from this study showed that AqpZ could maintain its activity even under harsh environmental conditions of thermal treatment at 343 K for 2 h. These results and findings may provide useful insights on developing next generation of biomimetic membranes.NRF (Natl Research Foundation, S’pore)EDB (Economic Devt. Board, S’pore)Accepted versio

Understanding the interaction between biomacromolecules and their influence on forward osmosis process

Abstract This paper presents studies on the interactions and effects of biomacromolecules compounds on forward osmosis (FO) membrane performance. Individual components and a combination of various organic substances such as bovine serum albumin (BSA), dextran, sodium alginate and xanthan gum were used as model feeds and tested for their influences on FO performance with the active layer of the FO hollow fiber membrane facing the feed solution (AL-FS). The interactions between foulants were examined by using fluorescence spectroscopy, rotational rheometry and laser doppler micro-electrophoresis techniques. For a system containing combined organic foulants, it was found that viscosity was not the dominant factor governing FO membrane fouling as the decrease in viscosity did not always result in less fouling. The effect of divalent cations on the FO fouling behavior was also studied by adding CaCl2. The presence of calcium ions has exacerbated the flux decline, this occurred particularly for any combined organic foulants containing alginate, due to intermolecular bridging among alginate molecules. It is interesting to note that combined BSA+alginate caused moderate flux decline, while BSA and alginate alone did not cause any observable water flux loss. The (BSA+alginate) fouling became more severe with the presence of calcium ions

Generalized criterion for the onset of particle deposition in crossflow microfiltration via DOTM : modeling and experimental validation

The concept of a critical permeation flux for the onset of particle deposition in crossflow microfiltration (CFMF) is well-established. However, the critical flux is known to be a function of process parameters such as the particle size, bulk concentration and crossflow velocity. In the present study, the critical modified Peclet number (Pecrit) is explored instead as a generalized criterion for the onset of particle deposition that incorporates the effects of these process parameters as well as the axial position along the membrane. A proper determination of Pecrit requires an accurate prediction of the concentration polarization boundary layer thickness δc and shear-induced diffusion coefficient Ds. The classical Lévêque model is adapted to allow for the effect of the permeation flux on the velocity profile. Moreover, the assumptions of a constant concentration at the membrane surface cw and constant Ds that have been made in prior studies are relaxed in an improved numerical solution to the convective diffusion equation that is used to predict δc and Ds. The critical permeation flux is determined from particle deposition data taken for 6 and 10 μm latex spheres via Direct Observation Through the Membrane (DOTM) characterization. A constant value of Pecrit=4.00±0.08 is found to characterize the effects of particle diameter, bulk concentration and crossflow velocity as well as axial position on the onset of particle deposition.Accepted versio