What are the Causes of Rapid Sand Filter Clogging?

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Hello, I am working with municipal water treatment facility in Delhi, India.

We are facing a huge problem at our water filtration plant as sand filters are clogging/choking every 4-6 hours.

This problem is making our water filtration vulnerable and we need to backwash the filters multiple times per day. This is harming our water treatment efficiency.

Can anyone suggest a reason behind it and, if possible, a solution?

Please help. 

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31 Answers

  2. I have used AFM (Active Filtration Media) successfully for the last 15 years.  However, if the particle size in the water feeding the plant is too large or levels are too high then the filters will need backwashing more frequently.  A plant using AFM still has had the same backwash rate over the 15 years without any deterioration in water quality.  AFM doesn't become colonised by bacteria and the particles have a smoother surface making better filtration.  They like other filtration methods don't like algal strands, which can cause problems.

    Answered on by

  3. There could be possible biofilm formation which is causing mud-balling and wormhole channeling. These bacterial colonies can develop quite rapidly given the right temperature and food source.

    If you are looking for a more reliable filtration without clogging, I suggest switching your sand to an Activated Filter Media. Biofilm cannot grow on this type of media and performance is up to 80% better than sand. Thus, chlorine consumption is significantly reduced. 

    Please email me at andrew@waterandoilsolutions.com.au if you are interested in investigating further.

  4. Check your Coagulant dose rate seasonally to determine the optimum dose for each season because any change in raw water quality could results in flocs not flocculating and settling within the stipulated time.

    In this case you can use a flocculation aid or Bentonite Clay to make up for any of the decrease in the + or - charges otherwise called electrostatic forces of repulsion and vanderwaals forces of attraction.

    Another possibility is the raw water Alkalinity, if for any reason the dissolved alkalinity is low and you're dosing Hydrated Lime to raise the Alkalinity, there is need to check that because it can create a secondary precipitation that could be carried over to the filters as well.

  5. Dear Lokesh,

    Unfortunately, RG sand bed filters clog quite rapidly. Where is the upstream water coming from? Is it coming from, or even from sedimentation tanks, which are basically tanks without the mechanical rotating machinery which helps to coagulate the impurities. The clearwater from the sedimentation tank top spills over and enters the RG sand bed. Here, the micro-organisms in the water are trapped in between the sand particles and the final clear water is obtained which is chemically treated and sent to the distribution reservoir. This is how a RG filter bed works. It is normal for a  RG filter to clog in 8 hours or even faster. Therefore, the design is done in such a way that a number of filter beds are filled with water alternately i.e. when one lot is being back washed, another is working at full efficiency. That way you get continuous water. 
    When the Filter beds are built, the contractor has to guarantee a fixed output per day which is usually tested before the plant is taken over. Check with that figure. If there is a discrepancy, your upper water source i.e. the sedimentation process is not working as it should. If there is normal discrepancy taking into account efficiency loss of the system over the years, then you are getting the design flow. No use crying over it, in that case 

    You can occasionally change the top sand layers and loosen the sand at the bottom so that during backwash, compressed air is cleaning the passages between the sand particles thoroughly. It is also possible that your backwash pumps are too old and lack the head required to backwash properly? Perhaps you are just letting the impurities gather in the bed after each filtration cycle, rather than sieving them off the surface? Anyway, I've given you all the possibilities. All the best and happy 'Sherlocking'!!

    2 Comments

    2. I think what you're describing above is the Slow Sand Filter not the Rapid Gravity Filter. The slow sand filter is that filter that forms a dirt layer called Schumutdecker that traps and forms a colony of bacteria. Contrary to the slow sand filter, the RGF in a COAGULATION and FLOCCULATION water treatment process filters the carry over Flocs from the Clarifiers, just before Disinfection. The idea is to make sure the water passing out of the RGF has a turbidity less than 5.0 NTU/FTU and that is needed in order to achieve efficient disinfection. The consistent clogging/blockage of the RGF is as a result of those carry over flocs and that can be solved by checking the dosage rate of the Aluminum Sulphate or whatever coagulant they are using perhaps because of changes in the raw water quality seasonally certain changes needed to be done periodically. Another way is to look at the Alkalinity of the raw water if the alkalinity is low and pre-lime is used then secondary precipitation might result in that excess flocs carried over to the filters.

       

  6. French

    Bonjour il n'y a aucune solution à envisager quand on utilise le principe de la filtration puisque par vocation un filtre retient et colmate vite si la masse solide est importante.

    Il colmatera d'autant plus vite encore quand il s'agit de matière organique genre matière fécale 

    Lyseconcept propose une solution globale, définitive, économique, biologique, pour tout traitement d'épuration des eaux usées 

    English

    Hello there is no solution to consider when using the principle of filtration since by vocation a filter retains and quickly clog if the solid mass is important.

    He defences to much faster when it comes to material organic kind fecal Lyseconcept offers a comprehensive, definitive, economic, biological, solution for any treatment of sewage treatment plant 

  8. This is a very common problem: I presume you have a conventional surface water treatment plant with coagulation/flocculation/sedimentation/rapid sand filtration. It is likely that the flocks are not proper settling before the rapid sand filters. You can check that based on the turbidity: the turbidity after sedimentation should be about 1 NTU and no flocks should be visible. If the turbidity is too high all these not settled flocks are going to the RSF while they are only there for polishing!!!. The reason that the flocks do not settle properly can be: 1) not optimal coagulant dosing 2) algae in the feed water(they rather float) you should try a high chlorine dose at the front of the plant. 3) not optimal fast mixing (should be >1000  4) not optimal slow mixing 5) more water production than the design capacity. 6) not optimal pH

  9. I suppose ​​this can be the ​​potential ​​reason of ​​Filter clogging.​​

    Actually, ​​because of ​​algae mass pH ​​of raw water (​​river water) ​​has increased ​​to a large (pH ​​About 8.2-8.4). ​​Coagulant PAC (​​Poly Aluminium ​​Chloride) does ​​not work ​​efficiently in ​​this pH range. ​​Nor high ​​Chlorination ​​was giving good ​​results. ​ ​

    So, we ​​Applied Alum as ​​Coagulant with ​​high dose. ​ ​

    However, ​​turbidity of ​​water is ​​between 20-26 ​​NTU Low. ​ ​

    Now, it is ​​working well ​​better than ​​before. ​ ​

    Thanks for ​​your comments ​​Sir

     

    Regards

  11. ​Lokesh- I ​concur with ​George.  ​First - check ​your source ​water and your ​pre-treatment ​processes. ​ Then - ​the filter ​material itself.​ One annoying ​problem we ​faced was the ​angular grain ​shape of the ​filter sand, ​ which had ​orders of ​magnitude lower ​k, than would ​have been ​expected based ​only on grain ​size.  ​Look at your ​filter material ​under a ​microscope - if ​it is ​moderately sub-​rounded to well-​rounded, then ​that is not the ​issue.  ​However, if it ​is sub-angular ​to angular, ​that may be an ​important part ​of the issue. ​

    1 Comment

  13. Hello, First of all you are supposed to give more details about the source of water and then It will be easy to find a solution. What is the source of water, The capacity of your plant per hour, percentage of sand in the water etc.     export@heray.com.tr

  14. new filter media : It is an antiseptic that does not generate biofilm.It avoids matting. Especially it has a high anti compaction technology  mc2

     

    1 Comment

  16. new filter media - classic filtering disadvantages disappears. 

    Disadvantages of the classical media :

    Limite lifespan

    High consumption of chemicals, water and energy

    Poot hygiene due to biofilm generation

    Groove creation that reduces the filtering quality

    Non environmentally friendly.Besides their high consumption by the end of their lifespan they become polluting waste

    Advantages of new filter media :

    Maximum lifespan

    Minimum consumption of chemicals, water and energy

    ideal filtering quality

    Pressure loss is practically negligible

    Maximum hygiene , it is a

  17. I would agree with Jeremy Biddle that these are likely to be the causes. I would also add from experience it is worth checking the following:

    1 the isolation valve is sealing during the backwash cycle. It is a relatively cheap fix to check and clean.

    2 Then check the backwash water rise rate with the air is sufficient to fully expand the bed for the average sand grain installed.

    3 Finally check there is no sand in the under floor obstructing the water and air flow. 

    1 Comment

  19. Hello Lokesh,

    If this is a new problem, pl review what changes happened during this time.  It could be related to pre-treatment process like high turbidity, insufficient coagulant dose, poor flocculation and settling. Or filtration issues: did you put new sand media (size?), are all the filtration units working, are both air and water backwash rates sufficient?

    I worked with Dr. Amirtharajah who was the international expert on filtration. In 1980s I lived in New Delhi and familiar with treatment plants there.  Hope we can help you.

    Thanks,

     

    1 Comment

  21. French English

    Bonjour La réponse est dans votre question.

    On fait croire qu'un système de filtration c'est un traitement. Bien entendu que c'est faux. la vocation d'un filtre c'est de retenir. Par ce fait sa performance épuratoire s'amenuise au fur et à mesure qu'il est en fonction.

    Plus la performance épuratoire du filtre est élevée, plus vite il colmate.

    En colmatant il retient de fines particules de matière ou de matériaux. S'il s'agit de matière organique, le colmatage va faire entrer la zone en putréfaction et polluer l'eau de passage.

    Tout le contraire de l'objectif à atteindre confronté par votre compte rendu.

    Une donnée qui vient aussi annuler la perforamnce épuratoire d'un système, c'est le besoin, la demande de plus en plus importante qui ne permet pas à un dispositif d'être performant.

    Dans votre exposé on se demande à quel moment le filtre n'a plus aucune utilité?

    Dans mon concept d'épuration Biologique des eaux usées je donne un temps de transit de 12 jours à 15 jours de traitement.

    Ensuite le liquide en sortie débarrassé dans la majorité de la masse flottante, il peut alors être purifié.

    A un certain stade l'épuration ne suffit pas il faut passe par la phase de purification qui est une autre pratique que la technicité humaine ne peut pas aujourd'hui  reproduire.

     

    Hello, the answer is in your question.

    We do believe that a filtration system is a treatment. Of course it's fake. the purpose of a filter is to retain. Therefore its purification performance thins as and as it is in operation.

    The purification performance of the filter, the faster it clogged.

    In closing he retains fine particles of material or materials. If it's organic, clogging go enter the area in rot and pollute the water passage.

    The opposite of the goal faced by your report.

    Data which has also just cancel the purification perforamnce of a system, it is the need, demand more important which does not allow a device to be successful.

    In your presentation you wonder when the filter has no use?

    In my concept of biological treatment of wastewater I give a transit time of 12 days to 15 days of treatment.

    Then the liquid output RID in the majority of floating mass, it can then be purified.

    At a certain stage the treatment is not enough there are going through the phase of purification which is another practice that the human technicality today cannot reproduce.

     

    2 Comments

    2. Lokesh- I concur with George.  First - check your source water and your pre-treatment processes.  Then - the filter material itself. One annoying problem we faced was the angular grain shape of the filter sand,  which had orders of magnitude lower k, than would have been expected based only on grain size.  Look at your filter material under a microscope - if it is moderately sub-rounded to well-rounded, then that is not the issue.  However, if it is sub-angular to angular, that may be an important part of the issue.

  22. Dear Lokesh, 

    I have faced the same problem several years ago and it was due to the fact that suspended solids were escaping from the settling tank, along with clear water, as a result of not frequent operation of the filter press.

    So the reasons for your problem could be :

    1. High concentration of suspended solids, much higher than the initial filter design.

    2. Suspended solids escaping from your settling tank, if you've got any.

    3. Poor SAND QUALITY. If the sand is not QARTZ type- special sand for sand filters-  but it's normal building sand then the susdpended solids stick with the sand particles. This blocks the water routes and as a result you get high pressure drop and frequent backwash.

    Please note that if No3 is your problem then when you backwash the filter only a small part of the suspended solids are rejected so only a small part of the filter works. The rest 

    is blocked.   

    N.B. You must remember that the filtration speed should never exceed the value of 15 m/h. To calculate that you need to divide your flowrate by the cross-sectional area of the filter. 

     

    2 Comments

    2. Greg Moss a few seconds ago

      Lokesh- I concur with George.  First - check your source water and your pre-treatment processes.  Then - the filter material itself. One annoying problem we faced was the angular grain shape of the filter sand,  which had orders of magnitude lower k, than would have been expected based only on grain size.  Look at your filter material under a microscope - if it is moderately sub-rounded to well-rounded, then that is not the issue.  However, if it is sub-angular to angular, that may be an important part of the issue.

       REPLY (0)  LIKE (0) 

  23. Greetings from Oz: What is the constituency of the backwash - is it primarily organic or inorganic - installation of baleen with/without flocculation as a pre-filter will dramatically reduce your backwash concerns. Please visit www.baleen.com for background information. I am happy to advise further at yuri@baleen.com

    1 Comment

  24. Could you potentially have filter clogging algae in your raw water?

    1 Comment

    1. I suppose this can be the potential reason of Filter clogging.

      Actually, because of algae mass pH of raw water (river water) has increased to a large (pH About 8.2-8.4). Coagulant PAC (Poly Aluminium Chloride) does not work efficiently in this pH range. Nor high Chlorination was giving good results.

      So, we Applied Alum as Coagulant with high dose.

      However, turbidity of water is between 20-26 NTU Low.

      Now, it is working well better than before.

      Thanks for your comments Sir

       

      Regards

  25. Many things could results in Rapid gravity filter blockage but most all mud balls formation leading to decline in the efficiency of the filter. With such a problem, you will not only backwash several times a day but often it will over flow and if the plant is located in temperate region might lead to mud balls formation further deteriorating the filter. What causes this phenomenon is mostly the efficacy of the coagulation and flocculation process. First you need to make sure you find the optimum dose of your coagulant also within that you have to make sure the flocculation is taking place within the available settlement time. Often times we tend to forget there are two forces acting on the flocs; Vander walls forces of attraction and Electrostatic repulsive forces and until these two are in equilibrium the charges will repel thereby resulting in suspended flocs that will later be carried forward to the filter and that carried over flocs is the genesis of your filter blockages, mud balls formation, backwash and a resultant turbidity greater than 5.0 NTU.

     

    1 Comment

    1. I suppose ​this can be the ​potential ​reason of ​Filter clogging.​

      Actually, ​because of ​algae mass pH ​of raw water (​river water) ​has increased ​to a large (pH ​About 8.2-8.4). ​Coagulant PAC (​Poly Aluminium ​Chloride) does ​not work ​efficiently in ​this pH range. ​Nor high ​Chlorination ​was giving good ​results. ​

      So, we ​Applied Alum as ​Coagulant with ​high dose. ​

      However, ​turbidity of ​water is ​between 20-26 ​NTU Low. ​

      Now, it is ​working well ​better than ​before. ​

      Thanks for ​your comments ​Sir

       

      Regards

  26. Rapid head loss increase may be caused by several factors:

    1. Poor raw water quality, high coagulant dosages, i.e. high sludge production/high solids load to the filter

    2. Too high filtration rate combined with too high solids load (too high solids load). The higher the filtration rate, the shorter the filter runs...

    3. Too high polymer doses (if used), may cause depositions in the upper part of the filter bed only

    4. Poorly designed filters - with poor distribution of filter deposits over the filter depth (dual media filtration performs much better than single medium sand filters)

    5. Inadequate pre treatment - if used (e.g. poor flocculation: too large, and too strong (polymer aided)  flocs for the filter pores); poor sedimentation), etc

    "There is no such thing as a good filter - it depends on the water too be filtered...."

    1 Comment

  28. Dear Lokesh,

     

    Would you mind telling us a little more about your process. Are your filters installed after a clarification systrem, or they are fed by raw water?

    If possible do add a raw water analysis and a brief description of the whole plant process.

     

    Kind Regards,

     

    S. Cotic

     

    1 Comment

    1. I suppose ​​this can be the ​​potential ​​reason of ​​Filter clogging.​​

      Actually, ​​because of ​​algae mass pH ​​of raw water (​​river water) ​​has increased ​​to a large (pH ​​About 8.2-8.4). ​​Coagulant PAC (​​Poly Aluminium ​​Chloride) does ​​not work ​​efficiently in ​​this pH range. ​​Nor high ​​Chlorination ​​was giving good ​​results. ​ ​

      So, we ​​Applied Alum as ​​Coagulant with ​​high dose. ​ ​

      However, ​​turbidity of ​​water is ​​between 20-26 ​​NTU Low. ​ ​

      Now, it is ​​working well ​​better than ​​before. ​ ​

      Thanks for ​​your comments ​​Sir

       

      Regards

  30. Has the inlet SS concentration changed?

    You must open the filter and take a look about the sand. Microbiological developments can foul the sand. In this case you must make a strong backwash with hipoclorite to remove the biofilm.

    In some cases the sand acts like a nucleation agent and a mineral scale could be seen.

    1 Comment

    1. I suppose ​​this can be the ​​potential ​​reason of ​​Filter clogging.​​

      Actually, ​​because of ​​algae mass pH ​​of raw water (​​river water) ​​has increased ​​to a large (pH ​​About 8.2-8.4). ​​Coagulant PAC (​​Poly Aluminium ​​Chloride) does ​​not work ​​efficiently in ​​this pH range. ​​Nor high ​​Chlorination ​​was giving good ​​results. ​ ​

      So, we ​​Applied Alum as ​​Coagulant with ​​high dose. ​ ​

      However, ​​turbidity of ​​water is ​​between 20-26 ​​NTU Low. ​ ​

      Now, it is ​​working well ​​better than ​​before. ​ ​

      Thanks for ​​your comments ​​Sir

       

      Regards

  31. Dear Lokesh, sorry to hearing that. Are You using chemicals prior to SF? If it is so, have You made any Jar test to assess the right amount to be metered?
    Maybe some post-coagulation in the SF due to excess of chemical?
    Maybe poor backwash? Is it air+water, right? Let's tune up the cycles and see.

    2 Comments

    1. I suppose ​​this can be the ​​potential ​​reason of ​​Filter clogging.​​

      Actually, ​​because of ​​algae mass pH ​​of raw water (​​river water) ​​has increased ​​to a large (pH ​​About 8.2-8.4). ​​Coagulant PAC (​​Poly Aluminium ​​Chloride) does ​​not work ​​efficiently in ​​this pH range. ​​Nor high ​​Chlorination ​​was giving good ​​results. ​ ​

      So, we ​​Applied Alum as ​​Coagulant with ​​high dose. ​ ​

      However, ​​turbidity of ​​water is ​​between 20-26 ​​NTU Low. ​ ​

      Now, it is ​​working well ​​better than ​​before. ​ ​

      Thanks for ​​your comments ​​Sir

       

      Regards

    2. There is a lot of relevant advice above. One point I would like to add about the coagulant and/or flocculant dosing is to check the mixing energy and how well the reagent stream is mixed in to the entire inflowing water body. I have seen a single small diameter pipe dropping reagent at one point into a water stream that is 1meter or more wide.  That will not work effectively. It is better to add the coagulant/flocculant to the water stream using a perforated spreader bar for distribution across the entire flow width and it is important that there is a hydraulic jump, drop, baffles or some other form of hydraulic or mechanical mixing at that point to make sure the reagent is mixed throughout the water body.

      Treatment works in India are normally well enough designed hydraulically, if they follow the CPHEEOO manual. If you have enough kinetic and/or potential energy at the dosing point you can create turbulent mixing energy by adding baffles. If not a mechanical mixer may be required.

      1 Comment reply

      1. I suppose ​​this can be the ​​potential ​​reason of ​​Filter clogging.​​

        Actually, ​​because of ​​algae mass pH ​​of raw water (​​river water) ​​has increased ​​to a large (pH ​​About 8.2-8.4). ​​Coagulant PAC (​​Poly Aluminium ​​Chloride) does ​​not work ​​efficiently in ​​this pH range. ​​Nor high ​​Chlorination ​​was giving good ​​results. ​ ​

        So, we ​​Applied Alum as ​​Coagulant with ​​high dose. ​ ​

        However, ​​turbidity of ​​water is ​​between 20-26 ​​NTU Low. ​ ​

        Now, it is ​​working well ​​better than ​​before. ​ ​

        Thanks for ​​your comments ​​Sir

         

        Regards