What do you think about stacked rapid sand filtration's use in the developing world?

So called rapid filtration is typical by air-bubble washing of the filtration bed. Without providing any information, with which process it was replaced, there is no possibility to answer the quiestion.

On the other hand, filtration is very useful - remember Milwaukee´s cryptosporidium outbreak (filtration step was jumped in one part of the drinking water plant) or check Rita Colwell´s work on cholera infection risk-minimizing by copepods´removing from the water by screening (or fitration).

But the filter washing???

In the tropics, slow filtration is also very useful.

Dear Nathan,

Stacked rapid sand filters have advantages over conventional filters in terms of back-washing requirement. In stacked rapid sand filters backwasing is also done by using hydaullic gradient of inlet BUT in conventional filters, backwashing is done by Air Water mixing. The air bubble washing leads to decompression of filter bed and effective filtration rate remains always high.

It would be interesting to see that how filtration rates changes over the couple of time. I think that in small utilities these filter could be very effective but in case of large plants, conventional filters have advantage.

Keep posting your results.

Regards

Pravin

I agree with Miroslav Macek Reply, we need more information for a reply.

But I have to add than sand filtration is not an absolute barrier against parasite; according to several publications and reports, only 1 to 2 log removals is achieve by sand filtration. Disinfection step (using UV) is required for this type of pathogen 

Here, University of Alicante, there is a invent to food and drinks desinfection using UV. This kind of desinfection is a good option to bacteriological disinfection.

Saludos!

A substantial amount of literature has been written about granular media filtration, particularly slow and rapid sand filtration. This literature should be reviewed since much experience has been documented, including clever ways of backwashing. But if any innovation is to make a meaningful impact, then the locals who will ultimately operate this process should be directly and intimately involved in the work from the beginning. Many beautiful projects on paper failed in the end due to neglect afterwards. Personally, I am a fan of slow sand filtration whenever space is not an issue as this process is very simple and inexpensive to operate. For a flashy river, sedimentation and a gravel roughing filter would be needed. See free publications from the WHO press by Huisman. 

For rapid sand filters performance standards may be based on low turbidity of 1NTU or less,filtrate should be free from color(with 3 or less on the cobalt scale). The filter runs should normally be not less than 24 hrs with a loss of head not exceeding 2 m. According to this criteria  it is an efficient filter, and also the wash water consumption should not exceed 2 per cent or the quantity filtered in between washing----hence it 's use is frequently increased in the  developing world. 

Rapid sand filters are generally advantageous over the slow sand filters since they require less land to put up and they work faster. However, there are some reservations regarding their usage especially because research has shown that they do not result into complete removal of pathogenic microbes like the Giardia cysts for example. So their usage may require additional treatment mechanisms such as disinfection by chlorine

Hi Nathan Howell

It can be a good alternative, but never forgetting the qualitative control of the water resources that will be filtered and their respective uses.

Regards!