Dear Lokesh, am curious to know whereabout you are located. Is it rainy season now and are you collecting water from a river, then probably we are facing surface wash. Do you monitor the quality of raw water (suspended solids)? can you share?

best regards

Johannes

Dear colleague,

The clogging of your sand filter shows that the quality of the inlet water has changed. What we need to keep in mind is: why the quality of the inlet water has changed? As Dr. Fresner said, the first thing that comes to our mind is: if your filter is clogged by increasing of suspended solids in the inlet water. It may also be due to living cells that the possibility of biofilm formation in the sand filter and algal-bacterial cells may be responsible for this event by increasing the temperature of the air.

Kind Regards.

Dear Lokesh,

Do you face this problem each year in the same period?

If yes, the most likely reason for your frequent backwashing needs is the higher solids loads in the feed water.

If no, and your problems are becoming more pronounced, you should look at the efficiency of the backwash strategy: are you washing with water only or also with air, how long, combined or separate?    

Best regards, Hans 

Short intervals between filter backwash indicate too much particles in the filtered water. If this occur periodically it is typically caused by algal blooms in the river or reservoir as mentioned above.

Likely solutions are to apply pretreatment for the filter such as coagulation-flocculation. Another option is to apply a continuous backwashing filter.

With out much details we will all be guessing - It does though not have to be Increased TSS causing trouble, what I have seen now several placed in the world giving this kind of phenomena was a change in the nature of incoming solids due to seasonal changes taking place in the river see or reservoir. Instead of mineral like and easy to filter Influent you start to get an organic influent - most probably even with algae as also Henrik mentioned. They tend to cause what is called surface filtration, were the upper 10 - 20 cm of your filtration media will clog. This problem can partially be improved by better Coagulation/Flocculation settling up front, but unfortunately it is seldom very efficient in reducing the algae sufficiently and the better solution in the long run, is to change from mono media filtration to Double layer filtration. Here an upper layer with larger particle size will allow the algae to penetrate deeper into the filter bed - increasing the running time. The lower layer will act as police layer having the same finer particle size and the original media assuring that the right effluent turbidity will be achieved. This means though often changes in Backwash water pumps and Blowers also.

One help for plant running were nothing else can be done right away is to introduce so called mini-backwashes, were after drain down to just above the media, an air alone period of maybe 5 minutes to break up the clogged media zone, is followed up by just 1 water volume exchange. This can help to recover more than 1/2 of the available head loss utilising 1/4 to  1/3 of the water amount

Thanks Henrik Rasmus Andersen Sir and Kim Helleshoj Soerensen Sir for your valuable comments. Now, we have controlled the situation to a great extent by using Alum as a coagulant with high dose. But, one more question strikes my mind that I have also observed increase in pH value of raw water (river water) during this season (dry season/winter).

What can be the reason for increased pH of water during this season.

Please guide/ suggest further.

regards

It is likely that there is a connection with pH. Among other factors higher pH in the river can be caused by high algae growth. Another factor could be that the river water in the dry season come from ground water or a large lake which has more dissolved minerals. Compared to this the flow of water in the rainy season would to larger and more of the water would come from directly from rain and surface runoff that contains less dissolved minerals and thus have lower pH.

Thanks Friend Henrik Rasmus for your valuable comments.

Regards

Lokesh Kumar