Membrane autopsy helps to provide solutions to operational problems

doi:10.1016/j.desal.2004.06.133

Desalination

Volume 167, 15 August 2004, Pages 239-245

https://doi.org/10.1016/j.desal.2004.06.133 Get rights and content

Abstract

Within the lifetime of most membranes some fouling will adversely affect membrane performance and cleaning will be necessary. The cleaning will depend on the type of deposit such as organic fouling, inorganic scaling or colloidal deposition. However strong the circumstantial evidence as to the identity of the foulant, the only reliable method of determining the true identity of the foulant with confidence, is by membrane autopsy. Different deposits affect the performance of the plant in different ways. Deposits such as organic fouling cause reduced output and increased differential pressure along the membranes and often require higher operating pressure to maintain output. Inorganic deposits can be a cause of irreversibly increase in salt passage. All forms of membrane fouling cause a significant increase in plant downtime and maintenance costs. Following an extensive study of membrane fouling during the autopsy procedure, we can usually recommend a protocol for the most suitable cleaning procedure. Cleaning procedures can be supported by proposals for antiscalant treatments to avoid the formation of deposits and in some cases retard membrane fouling. It is common to find deterioration in the salt rejection layer leading to a significant increase in salt passage. In some cases this is associated with an increase in product flow and may be caused by oxidation of the membrane, deposition of inorganic salts, abrasion or even the tearing of the membrane leaves themselves. If the cause of the fouling can be identified, recurrence of the problem can often be prevented, although in some cases, salt rejection performance maybe irrecoverable. This paper considers the results of some autopsies from plants with different problems and presents a general opinion of current operating practice. Photographic evidence is included showing some of the different forms of scale and fouling. Conclusions are given based on the general experiences of the staff carrying out these autopsies.

References (2)

F. del Vigo et al.
Autopsia de membranas: solucion al problema
E.G Darton et al.
A statistical review of 150 membrane autopsies

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In this study, a fouled reverse osmosis (RO) membrane from a full-scale ultrapure water (UPW) facility was autopsied and investigated to propose the fouling mechanism and mitigation strategies. Although the influent was introduced to the coagulation and ultrafiltration as the pre-treatment processes, thick fouling layers were found over the entire RO surface. The foulant was mainly composed of aluminum silicates due to the elevated Al concentration (up to 100 μg/L) originated from the coagulation process utilizing polyaluminum chloride, and high recovery (up to than 90%) of RO process. Lab-scale fouling tests also confirmed that the elevated Al concentration in the RO influent contributed to significant flux decline due to a bridging effect with negatively charged organic matter and the formation of aluminum silicates. The application of polydiallyldimethylammonium chloride as an alternative coagulant successfully mitigated the organic and silicate fouling. Therefore, control of the residual aluminum ions originated from the coagulation process is critical to mitigate both organic and inorganic fouling on RO membrane surfaces during the production of UPW.
Recent advances in novel membranes for improved anti-wettability in membrane distillation: A mini review
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Fouling in reverse osmosis membranes: monitoring, characterization, mitigation strategies and future directions
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Water scarcity has been a global challenge for many countries over the past decades, and as a result, reverse osmosis (RO) has emerged as a promising and cost-effective tool for water desalination and wastewater remediation. Currently, RO accounts for >65% of the worldwide desalination capacity; however, membrane fouling is a major issue in RO processes. Fouling reduces the membrane's lifespan and permeability, while also increases the operating pressure and chemical cleaning frequency. Overall, fouling reduces the quality and quantity of desalinated water, and thus hinders the sustainable application of RO membranes by disturbing its efficacy and economic aspects. Fouling arises from various physicochemical interactions between water pollutants and membrane materials leading to foulants' accumulation onto the membrane surfaces and/or inside the membrane pores. The current review illustrates the main types of particulates, organic, inorganic and biological foulants, along with the major factors affecting its formation and development. Moreover, the currently used monitoring methods, characterization techniques and the potential mitigation strategies of membrane fouling are reviewed. Further, the still-faced challenges and the future research on RO membrane fouling are addressed.
Membrane distillation for wastewater treatment: Current trends, challenges and prospects of dense membrane distillation
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Citation Excerpt :
In MD, the concentration polarization may aggravate the heterogeneous crystallization as the concentration of the non-volatile material on the membrane surface is higher than that in the bulk solution. The most common inorganic fouling in MD is CaCO3, CaSO4, calcium phosphate, and silicate [85]. However, the compounds can be varied, depending on the composition of the treated water.
Membrane distillation (MD) has excellent potential for wastewater treatment, and studies on this subject have increased recently. The unique features of MD to pass only volatile component through the pores has led to the exploration of hybrid MD, particularly membrane distillation bioreactor (MDBR) and osmotic membrane bioreactor-membrane distillation (OMBR-MD). Fouling and wetting are recognised as drawbacks in particular applications despite the excellent performance. The application of classical porous MD is highlighted as the main concern that leads to poor separation performances. This review highlights the possibility of applying dense membrane to push forward MD applications for wastewater treatment. The development of self-standing and composite dense MD and their performances in applications of wastewater treatment are summarized and discussed. The operational parameters affecting MD performance in the treatment of various types of feed are presented to analyze the robustness and the critical shortcomings of dense MD for wastewater treatment. Challenges, such as the trade-off between mechanical integrity and permeate flux, lack of studies using real wastewater for long-term operation, stability of the dense membrane against rigorous operation conditions, complicated fabrication methods, and the use of harsh chemicals during the fabrication of dense MD membranes are elaborated for further improvement in the development of dense MD membranes for wastewater treatment.
Integration of Forward Osmosis Membrane Bioreactor (FO-MBR) and Membrane Distillation (MD) units for water reclamation and regeneration of draw solutions
2021, Journal of Water Process Engineering
Citation Excerpt :
Various techniques have been used for fouling analysis in FO. In one study, fouling analysis for forward osmosis has been performed using membrane autopsy, and involved dissection of the membrane to check deposited foulants and surface properties [36]. Atomic force microscopy (AFM) has also been used for interfacial force measurements between foulants, and between foulants and membrane [37].
In the current lab scale study, the two treatment technologies of FO (Forward osmosis) and DCMD (Direct contact membrane distillation) were used in combination to create a continuous treatment system for water reclamation using, inorganic NaCl, surfactant (Tetraethyl ammonium bromide, TEAB) and polyelectrolyte (Polydiallyldimethylammonium chloride, PDAC) as FO draw solutes with both DI water (FO-MD), and monoculture municipal synthetic wastewater with Bacillus subtillis inoculum as feed (FOMBR-MD).
Each of the units was optimized separately at bench scale, and then combined to form a Forward Osmosis Membrane Bioreactor – Membrane Distillation (FOMBR-MD) hybrid for water reclamation from wastewater. In this hybrid system, the diluted draw solution was fed to the MD unit for reconcentration. The MD unit was tested at various operating temperatures; for FO-MD, a temperature difference of 15 °C was chosen, with a feed temperature of 35 °C and a permeate temperature of 20 °C. For the FOMBR, the temperature difference was increased to 25 °C. When the cross flow velocity was kept constant, the MD flux increased significantly with increasing temperature. Low grade waste heat from industry can potentially be utilised for the FO-MD process. The increase in flux was higher for NaCl and TEAB (60–80 %) when compared to PDAC (20–50 %), as the temperature difference increased to 35 °C. A greater feed flow velocity increased the turbulence in the flow channel, and increased the MD flux. Up to a 60 % increase in flux was observed when the feed velocity was increased from 0.12 to 0.17 m/s, while the increase in flux was not as high when the flow was increased from 0.17 to 0.21 m/s and thus 0.17 m/s was chosen as the cross- flow velocity for MD. Higher feed concentrations tended to reduce vapour pressures and hence decreased the MD water fluxes.
The flux for FO-MBR and MD were well balanced for lower molecular weight draw solutes, but lower FO fluxes were observed for higher molecular weight draw solutes (TEAB, PDAC). This greater imbalance reflected their lower diffusivities and greater tendencies toward concentration polarization. Reverse solute transport (RST) values leading to salinity or toxicity were not reflected by the observations, and therefore it was feasible to run an FOMBR-MD Hybrid for extended times. However, a greater decline in flux versus time was observed for NaCl than for TEAB. PDAC showed the lowest but most stable flux, and a lesser fouling tendency compared to that of TEAB. Overall, The FO-MD hybrid enabled pure water production and a non-volatile component rejection of nearly 99 %, with an RST of <0.1 GMH for the draw solutions back to the FO feed and a much lower solute transport from the MD feed to the permeate. NaCl and other low molecular weight solutes are recommended when high fluxes and system stability are priorities and where high reverse solute transport (RST), leading to salinity or solute toxicity in the MBR feed tank, is not an issue. Higher molecular weight solutes, such as TEAB or PDAC, are recommended when high flux is less critical and when the sensitivity of the microbial consortium to RST and solute toxicity is a concern. In all cases, some degree of process control is recommended in order to bring the systems more quickly to a stable operating state; periodic membrane cleaning is deemed necessary to maintain this state.

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^*: Presented at the EuroMed 2004 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and Office National de l'Eau Potable, Marrakech, Morocco, 30 May–2 June 2004.

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Membrane autopsy helps to provide solutions to operational problems*

Abstract

Autopsia de membranas: solucion al problema

A statistical review of 150 membrane autopsies