08 Feb 2018

Membrane ageing − a hard life?

Just like the rest of us, membranes get old and don’t always perform as well as they used to. Unlike us, on the other hand, this doesn’t manifest itself in things like creaking joints, failing to remember other people’s names or having difficulty getting up from low-slung sofas. With membranes, it’s basically just about two things: permeability and integrity.

Permeability is the flux (in LMH, GFD or day-1) per unit pressure (in kPa, bar or psi). It reflects how irrecoverably fouled the membranes have become, irrecoverable fouling being that which is not removed by either mechanical or chemical cleaning. Integrity, in this context, does not refer to the probity and honesty of the membrane, or whether it’s ever invested in aggressive tax-avoidance schemes or been caught shoplifting. It instead relates to the extent to which the membrane has become physically damaged to the point at which the rejection of key contaminants is impaired.

In the case of MBRs, the key contaminants of concern which are directly rejected by the membrane are usually the micro-organisms, since things like the BOD, ammonia and nutrients are essentially dealt with by the system biochemistry. But, again like us, not all micro-organisms are the same. Some are bigger than others, some are a bit more needy, and some are just plain awkward.

Bacteria, like Escherichia coli or Enterococcus faecalis, are generally around 1−2 microns in size and are ‘free swimming’ in water. To remove them effectively, the membrane pores (or the pores in the fouling layer sitting on the membrane) have to be well below 0.5 microns in size. The same is also true of the slightly larger Cryptosporidium oocysts, which have been responsible for sporadic high-profile outbreaks deriving from faecal-contaminated drinking water in communities globally. Viruses and phages, on the other hand, are fractions of micron in size but are predominantly associated with the suspended solids. Since the solids in an MBR mixed liquor are anywhere between 20 and 500 microns in size, removal of any microbes associated with them would be expected to be pretty much absolute – so long as the membrane retains its selectivity (i.e. rejects the pollutants it’s supposed to).

When membranes become irrecoverably fouled it’s normally because colloidal and other material has become trapped in the pores, and/or the pores themselves have collapsed. In either case, this tends to increase the selectivity but reduce the permeability. On the other hand, selectivity decreases with a loss of membrane integrity (i.e. when the active membrane layer – often no more than a few microns thick – is breached in some way).

The lifespan of a membrane is of key concern in determining operating expenditure (OPEX). It is the key critical component of any large membrane-based installation. Extending the replacement frequency from five to ten years can reduce the overall OPEX by almost 20% for an immersed hollow fibre MBR (Judd, 2017), and more so for a flat sheet system.

So, what determines the membrane life? Logic dictates that chemical cleaning is likely to degrade the membrane to some extent. Practical measurements made on membranes of various ages suggest a noticeable loss in mechanical strength of flat sheet membranes (Ayala et al, 2010) and of micro-organism rejection by hollow fibre membrane (Branch et al, 2016) for membranes in use for 6−10 years. However, a study of actual membrane life based on change out of membranes across a large number of installations suggested a life of at least 8 years, with more recent membrane products tending to offer longer life (Côté et al, 2012). And, of course, ceramic membranes would be expected to last a lot longer than this.

So, MBR membranes are apparently reflecting human trends and are tending to live longer, it seems. This is probably because of improvements made in each generation of products. But it could also partly be because designers are getting better at designing the plants so they need less looking after and/or operators are getting better at looking after them so that less chemical cleaning is required. Whatever the reason, the extended life is serving to decrease this part of the OPEX. It may be a hard life, but at least it’s apparently a reasonably long one.


  • Ayala, D.F., Ferre, V., Judd, S.J. (2011). Membrane life estimation in full-scale immersed membrane bioreactors Journal of Membrane Science, 378 (1-2), 95-100.
  • Branch, A., G. James, T. Trinh, T. Minh Ta, G.L. Leslie, P. Le-Clech (2016). Membrane ageing and replacement – Impact on pathogen removal in full-scale MBR, AMTA Membrane Technology Conference and Exposition 2016, San Antonio, Texas, U.S.A, 1–5 February.
  • Côté, P., Z. Alam and J. Penny (2012). Hollow fiber membrane life in membrane bioreactors (MBR). Desalination 288, 145-151.
  • Judd, S. J. (2017). Membrane technology costs and me. Water Research, 122, 1-9.

Shift in log removal value (LRV)
09 May 2016

IFAT 2016

Come and see us at IFAT 2016 from 30th of May to 3rd of June 2016 in Munich, we will be in hall A3, at booth 338. We look forward to showing you the latest innovations and additions to our MicroClear range of products.

To avoid disappointment, book a slot ahead of time and discover the flexible, modular approach of our  MicroClear® MBR systems.

Please contact:

06 Aug 2015

newterra introduces new MX-modules for MBR Technology

newterra GmbH is behind the latest developments in modular, scalable water treatment.

The company recently introduced two innovative, new ultrafiltration (UF) modules – the MicroClear® MX640 (640 m²) and MX800 (800 m²). Both offer tremendous flexibility in capacity – allowing them to be fully operational when only partially populated with MicroClear® membrane cassettes. More cassettes can be added to the modules to facilitate plant expansion or optimization of the process design.

The robust, open stainless steel frame construction increases packing density, and improves access to the individual UF cassettes for simplified maintenance. Additionally, the self-supporting MicroClear® module structures can be easily transported by forklift – eliminating the time-consuming process of lifting modules by crane.

The first MX640 modules are installed at a labour camp in the Middle East, where the newest generation of MicroClear’s modular treatment technology is being used in a wastewater application.

09 Apr 2015

WETEX 2015 in Dubai

Visit us in Dubai at WETEX 2015 from 21th - 23th April 2015. We will be in the Hall 7 on stand BW37. We would be pleased to acquaint you with the latest innovations in our product range and our latest references and projects in Middle East.

We recommend that you book an appointment in advance - come and see the new MicroClear®, you are most welcome.

07 Apr 2015

Bubble Point for Pore Size Measurements

The pore size in filters, membranes, and fabrics can be determined at Cambridge Polymer Group by a variety of methods, including optical and scanning electron microscopy, mercury porosimetry, and particle size exclusion. A commonly used method is ASTM F316 "Pore size characteristics of membrane filters by bubble point and mean flow pore test." This standard describes two test methods to obtain pore size in filtration media by making use of gas transmission through the filtration media. In both methods, the filtration media (in the form of a sheet) is cut into a disc, which is then placed in a filter holder. One side of the filter holder is connected to a gas line with a pressure regulator. The other side is vented to the atmosphere. In Method A, a fluid of known surface tension is placed on top of the filtration media on the vented side. The gas pressure on the other side of the filtration media is slowly increased, and the experimenter looks for the lowest pressure where gas bubbles begin to rise from the filter, indicating that the gas pressure has overcome the interfacial tension of the liquid in the pores. The maximum pore size can be calculated from this pressure and the surface tension of the fluid. In Method B, the same apparatus is used, but with the addition of a gas flow meter. In this variation, the gas pressure is also slowly increased, and the flow rates of gas through both a wet filter (using the fluid of known surface tension) and a dry filter are recorded.  The percentage of filter flow rate can then be determined as a function of pressure, which in turn is related to the pore size.

14 Nov 2014

MicroClear Website Wins Südwestfalen Award

Victory in the b2b Corporate Communications Category

MicroClear's website has won the Südwestfalen Award in the b2b corporate communications category. The internet presence for the leader in membrane-bioreactor water treatment was up against a total of 65 other websites. The jury of experts were impressed with's responsive design, its integration of social media, and the emotion conveyed by its images. The site's integrated information portal also contributed to its success.

Outstanding design, technology and layout

Björn Otto, Sales and Marketing Manager at the water treatment specialists newterra GmbH, was delighted with the award for the MicroClear site: “It's nice to know that even the experts are impressed with our internet presence. It seems that we found the right partner to develop the site”. The Welke Consulting Group, a Siegen-based agency for brand management and integrated communications, were responsible for designing, developing and programming the site, and also entered it for the competition.

The Südwestfalen Award is a joint initiative from the chambers of industry and commerce of Hagen, Arnsberg, Hellweg-Sauerland and Siegen. At a ceremony in Siegen's Lÿz art centre, Hermann-Josef Droege, deputy managing director of Siegen's chamber of industry and commerce, presented the award.

26 Mar 2014

IFAT 2014

Come and see us at IFAT 2014 from 5th to 9th May 2014 in Munich, we will be in hall A3, at booth 518. We look forward to showing you the latest innovations and additions to our range of products.

To avoid disappointment, book a slot ahead of time and discover the new face of MicroClear®:

Please contact:

12 Mar 2014

MicroClear<sup>®</sup> Pilot Plant

Universal test platform for membrane bioreactor applications

Read more

17 Feb 2014

WETEX 2014

Visit us in Dubai at WETEX 2014 from 14th - 16th April 2014. We will be in the German Pavilion on stand D-51. We would be pleased to acquaint you with the latest innovations in our product range. We recommend that you book an appointment in advance - come and see the new MicroClear®, you are most welcome.