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?
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.
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.
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.
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.
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
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.
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.
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.
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...."
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.
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.
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.
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.
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.
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.
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.