I think that washing membranes using hot waters or steams may be more profitable than using chemicals which deteriorate the membrane texture at the long term. Applying an electric field during washing process would enhance the efficiency and reduce the required cleaning time.

Research will confirm it through laboratory tests and microscopic analyses of membranes.

Best wishes,

Dear Djamel Ghernaout thanks for you answer.

Dear Muhammad Saad Khan

There are many ways to reduce membrane fouling,some of these are related to the membrane ,which including improved the membrane properties against fouling ( such as contact angle ,membrane roughness, pore size and pore size distribution). The other are related to the system (modified the system design and improvement the system operating condition such as operating pressure ,which must be lower than the membrane liquid entry pressure"LEP" ).

Regards

Dear Khalid Turki Rashid thanks for you answer.

Basically there are 2 kind of fouling which is possible on membrane surface. Bio/ organic fouling & in-organic fouling. Bio fouling could be removed by high pH cleaning (NaOH, EDTA, SLS)- ph 11 to 12.5 and Inorganic fouling could be handled with low Ph Cleaning (Citric acid, HCl; pH 2.5 to 4.0). If we perform the cleaning at controled temp. ( 35 to 40 deg C), it would be very effective. Chemical solution prepartion & filtering the chemical soultion through cartridge filter before allowing to membarne is very important. Probing to be done before perforimg the CIP to identify the most critical element/ affected one.

Dear Dinesh Ramalingam thanks for your informative answer.

Several approaches are currently adopted for membrane fouling removal and control strategies. While several technologies are commercialized, alternative control strategies are published in peer review scientific journals. From physical and chemical cleaning, biological control, quorum quenching, air scouring, and potentially membrane surface modification, all of the aforementioned approaches were proven to be highly successful.

In my opinion, the objective would be to extend as much as possible the occurrence of membrane biofouling using a multidisciplinary approach, hence focusing on the optimization of the reactor's operating conditions and the pre-treatment of the feed solution. There wouldn't be a single solution for fouling removal that applies to all fouling scenarios; therefore each situation should be treated depending on the membrane type, treatment system (MBR, RO, NF, MF, MD, etc ...) and the composition of the fouling layer (microorganisms, EPS products, organic and inorganic fouling, etc ...).

Dear Gerald Matar thanks for your informative answer.

Hello Muhammad;

As the rest of the collegues have said, dealing with membrane fouling is not straightforward as we need to considered the nature of foulants, the type of filtration (MF, UF, NF or RO), and the membrane characteristics. However there are a number of practical recommendations that can be followed to remove fouling. The objective here is to recover as much as possible the original permeate flux of the membrane. My filtration experience is with micro and ultrafiltration of biologicals: mainly for protein and biomass separations. Based on the technical and scientific literature I use the following method when performing an intense membrane cleaning procedure (drastic fouling):

1. Initial RO water rinse to remove the bulk of suspended particles until both the permeate and the retentate turn clear.

2. Alkaline flush. 0.2% NaOH. 30 min, 50 °C (temperature depends on the membrane used in all cases). Here it is also recommended to use sufractants 0.025% Na-DSS (though I hadn´t tried this). - removal of inorganic colloids, silica, biofilms and organic (see attached technical sheet for DOW RO membranes)

3. RO water rinse

4. Acid flush. 0.2% HCl, 20-30 min, 50 °C - removal of inorganic salts.

5. RO water rinse

6. Enzymatic treatment. I use commercial enzymatic detergent. 4 g/L, 20-30 min, 40 °C. In the literature it is recommended soaking up to 4 h - hydolisys of proteinaceous and carbohydrate materials.

7. RO water rinse

8. Sodium hypochlorite NaOCl (100-200 ppm) if compatible with membrane materials - 30 min or soaking overnight.

8. Final RO water rinse.

In some technical literature a backwash step is recommended for extreme fouling at low permeate flow rate, which also includes the use of cleaning solutions as the above (See attached table of cleaning process, in DOW´s UF product manual). It is also good to check the flux in every water rinse step to follow on the performance of the membrane. It is also recommended a two-stage flush for the different cleaning procedures: starting with a low feed/retentate flow rate followed by a high retentate flow.

Hope this helps. Regards,

Rogelio.

Dear Rogelio Valadez-Blanco thanks for your detailed informative answer.

Dear Mohammed Saad Khan. Without chemical washing, membrane operation is not possible. Wash solutions are selected for specific pollution. For the past 6 years I have been development washing agents. And I can definitely say that it is not possible to recommend universal compositions. The selection of reagents depends on the source water and the type of membrane apparatus.

Regards, Nick Nechitailo

Dear Nick Nechitaylo thanks for you answer.

Dear Muhammad Saad Khan,

There are two approaches to minimise fouling. First one is try and avoid membrane fouling using primary and secondary treatments (which include coagulation, flocculation, biological treatment, microfiltration etc) and then use ultra/nanofiltration and/or reverse osmosis. Second approach will be to modify the membrane surface so that it will become fouling resistant.

But as you said the membranes are already fouled and need to be treated, In this case they should be either cleaned by 1) Physical cleaning 2) Chemical cleaning 3)Ultrasound assisted cleaning 4) Hybrid approach : One or more (above said methods) treatments combined. e.g. Sonochemical treatment

The method for the treatment should be chosen wisely as polymeric and ceramic membranes have different physical and chemical properties and some cleaning treatments may harm the membranes and in turn may change membrane morphology and damage the membrane permanently.

Dear Nitin Thombre thanks for your informative answer.

Dear Muhammad Mubashir Please enlighten your thoughts on memebrane fouling and how to overcome it? Thanks

I would like to thank all of you who dedicate part of your free time to my question. Your answers stimulate my thinking on the subject. I am also glad to get information from people from various countries of the world.

Dear Saad,

We are working on the biological chattering feasibilities of membrane fouling.

In brief, including all feasibility studies, the membrane biofouling is still the main hardliner in the area of membrane technology. We are working on Quorum quenching (QQ) technology for biofouling delay in the Membrane bioreactors (MBR). The idea is, the degradation of the communication system (quorum sensing) signal molecules of microbes in the activated sludge by indigenous bacteria entrapped in different types of media.

Many thanks.

Dear Syed Salman Ali Shah appreciates your addition regarding biofouling and indeed biofouling still is the “Achilles heel” of the membrane bioreactors.

Dear Muhammad Saad Khan ,

Several approaches can be taken to minimize membrane fouling:

- Optimize pH and ionic strength of the feed solution to minimize the adsorption or deposition of the feed materials;

- Select an appropriate pre-filtration procedure or other means to remove large molecules, since the presence of larger molecules or particles could cause a steric hindrance to the passage of smaller molecules through the membrane;

- Select a membrane with an optimum pore size to result in good separation performance as well as optimized permeate flux;

- Optimize the operating conditions. This includes increasing transmembrane pressure to maximize flux without introducing more fouling potential;

- Increase the cross-flow velocity, which generally results in an improvement in permeate flux.

Best wishes!

For me, the answer is finally economic because when processes and pretreatments are added, the process becomes more expensive globally to the point that it can make it unfeasible.

Dear Aldo Saavedra agrees with your viewpoint since the industrial application of the process generally based on economical feasibilities.