Presence Of Membrane Fouling Research Articles

Understanding of Adsorption and Desorption Mechanisms of Anthocyanins and Proanthocyanidins on Heterogeneous and Homogeneous Cation-Exchange Membranes.

The presence of membrane fouling is the main drawback in membrane processes, and it is related to the premature use and high cost for the replacement of membranes. Polyphenols in cranberry juice are associated with ion-exchange membrane fouling, and it results in a loss of these beneficial compounds in the juice when treated by membrane processes such as electrodialysis. In the present work, four heterogeneous or pseudohomogeneous cation-exchange membranes (CSE-fg, MK-40, CEM Type-II, and CJMC-5), different in terms of the polymer matrix (aromatic, aliphatic), exchange capacity, size, and location of meso and macropores, were studied to understand the impact of the membrane structure and physico-chemical properties on adsorption and desorption of phenolic compounds (anthocyanins and proanthocyanidins) from cranberry juice. It appeared from these results that MK-40, CEM Type-II, and CSE-fg were more prone to fouling due to their high ion-exchange capacity, their thickness, and the presence of meso and macropores in their structure. Indeed, electrostatic interactions occurred between fixed groups of membranes and polyphenolic ions. Desorption of the entire membrane and cryogenic grinding with pH adjusted to 10 allowed a better recovery of anthocyanins and proanthocyanidins (PACs), respectively, since hydroxide ions competed with polyphenols and membrane that induced desorption of polyphenols. In the future, this new knowledge will become the basis for a more sensible choice of membranes and for the development of protocols for extending their life cycle.

Air-gap membrane distillation for the separation of bioethanol from algal-based fermentation broth

More than 80% of the energy consumed in the world comes from fossil fuels alone. However, fermentative production of bioethanol has recently gained a considerable interest as an alternative and renewable fuel. Among the different biomasses, the use of macro-algae hydrolysate as the fermentation substrate has been shown to be interesting. However, after fermentation, ethanol has to be separated from the complex broth containing numerous compounds such as microorganisms, fermentation co-products, non-fermentable organic matter, salts, etc. In this study, Air-Gap Membrane Distillation (AGMD) was evaluated to extract ethanol from these complex mixtures. Experiments were conducted using synthetic mixtures and real algal-based fermentation broths. AGMD was able to obtain an ethanol-enriched permeate while other compounds were retained by the membrane. Furthermore, by adjusting the operating parameters, it was possible to maximize the process productivity and selectivity at the same time. Finally, working with the real biofluids revealed that AGMD operation was robust toward membrane wetting, even in presence of membrane fouling. AGMD was thus demonstrated to be a suitable technique for bioethanol extraction from algal-based fermentation broths.

Practical limit of energy production from seawater by full-scale pressure retarded osmosis

Pressure retarded osmosis (PRO) produces energy using the salinity gradient between two solutions (draw solution (DS) and feed solution (FS)). Net energy production (NEP) of PRO was analyzed using a module-scale model developed in this work. The NEP analysis determines net energy from PRO by the difference between energy production by turbine and energy consumption by DS, FS, and booster pumps. Especially, the effects of system capacity and membrane fouling on NEP are investigated using a module-scale modeling approach for the first time. The maximum net specific energy (NSE) per PRO system capacity (sum of DS and FS flow rates) is close to 0.1 kWh/m3 without pretreatments. The maximum NSE decreases at smaller system capacities, and it becomes around 0.03 kWh/m3 from a PRO system with 520 m3/d as capacity. NSE from seawater decreases in the presence of membrane fouling, but it remains positive under the severe fouling condition where water flux decreases by 32% if the system capacity is large enough to have efficient pumps and turbines.

Combined Estimation and Optimal Control of Batch Membrane Processes

In this paper, we deal with the model-based time-optimal operation of a batch diafiltration process in the presence of membrane fouling. Membrane fouling poses one of the major problems in the field of membrane processes. We model the fouling behavior and estimate its parameters using various methods. Least-squares, least-squares with a moving horizon, recursive least-squares methods and the extended Kalman filter are applied and discussed for the estimation of the fouling behavior on-line during the process run. Model-based optimal non-linear control coupled with parameter estimation is applied in a simulation case study to show the benefits of the proposed approach.

Time-optimal control of diafiltration processes in the presence of membrane fouling

Abstract This paper deals with time-optimal operation of batch diafiltration processes in the presence of membrane fouling. Fouling causes a decrease in the effective membrane area and, hence, an increase in processing time. In this work we study a time-optimal operation with several fouling models available in literature. Pontryagin's minimum principle is applied to characterize the structure of the optimal operation which voids any further on-line optimization. Due to the specific structure of the problem, it is possible, in several problem setups, to derive and verify an explicit analytic solution. Obtained results are applied in case studies where we provide a comparison between traditional operation and the proposed time-optimal operation. In cases, where the optimal operation cannot be identified analytically, we analyze the performance of sub-optimal control derived from neighboring analytical solution and compare it to optimal operation found via numerical optimization techniques.

Time-Optimal Control and Parameter Estimation of Diafiltration Processes in the Presence of Membrane Fouling

This paper deals with the time-optimal operation and parameter estimation problem of a general diafiltration process in the presence of fouling. Fouling stands for one of the dominant problems in the membrane separation processes. The dynamic behavior of the fouled membrane is described by a general fouling model taken from literature. An Extended Kalman filter is proposed for the recursive estimation of unknown parameters in the fouling model. A model-based optimal nonlinear controller, whose control law is obtained explicitly via Pontryagin’s minimum principle, is coupled with the parameter estimation and subsequently applied in a simulation case study to show benefits of the proposed approach.

Time-optimal Diafiltration in the Presence of Membrane Fouling

This paper is a preliminary study that deals with time-optimal control of a batch membrane diafiltration processes where fouling of the equipped membrane is pronounced. We account for the membrane fouling by its dynamic model where the pore blocking mechanism applies. It is assumed that due to the deposit of foulants, the radius of membrane pores decreases and the part of membrane surface becomes unavailable for the filtration. We apply Pontryagin's minimum principle to solve the time-optimal control problem in an analytical fashion. It is found that the analytical approach enables to fix the control structure into sequence of arcs. It is further shown that once the sequence of control arcs is fixed, the optimal solution is determined by identification of switching times between the control arcs using a simple numerical technique. The method is demonstrated by its application to some of the most commonly used models of diafiltration processes.

Taguchi Method in the Evaluation of Vacuum Membrane Distillation in Water Desalination

Taguchi method has been applied to evaluate the effects of operational parameters on the efficiency of vacuum membrane distillation (VMD) in the desalination of water. It was observed that permeate increases with an increase in feed temperature and vacuum pressure. However, feed salt concentration adversely affected the amount of the collected permeate due to the reduction of vapour pressure as a result of the presence of the solute in water. Flow rate, however, could only increase the permeate if it was increased from 37.5 to 50 ml/s. Any further increase in flow rate to 100 ml/s, negatively lowered the permeate due to the limited feed/membrane contact time. We observed that at very high salt concentration (300 g/l) the permeate reduces accordingly, highlighting the fact that VMD should be used with care due to the presence of membrane fouling and/or other simultaneous flux-lowering effects present at concentrated feeds.

Long-term investigation of fouling of cation and anion exchange membranes in microbial desalination cells

The fouling of ion exchange membranes in microbial desalination cells (MDCs) was investigated through an eight-month operation. Multiple MDCs were set up by using cation (CEM), anion (AEM), and/or proton (Nafion) membranes. The MDCs exhibited relatively constant reduction of conductivity of artificial seawater during the testing period (46.3±6.3% in the CEM-MDC and 78.7±0.8% in the Nafion-MDC in an operating cycle). However, the current generation decreased from 99 to 56A/m3 in the CEM-MDC after 250days, and from 97 to 46A/m3 in the Nafion-MDC after 130days, indicating the presence of membrane fouling. Theoretically the MDCs removed 6.7–12.1kgTDS/m3/d with a high charge transfer efficiency of 230–440%, suggesting that electric current was not the only factor to drive desalination; water dilution played an important role in conductivity reduction as well. It was observed that the AEM contained significant biofouling, resulting from wastewater and microbial growth on organic compounds migrating across the membrane, while the CEM had substantial inorganic scaling, mainly consisting of calcium and magnesium. The membrane resistance of the CEM increased more significantly than that of the AEM, indicating that CEM needs more maintenance during MDC operation.