pretreatment for surface water membrane filtration 1

[philippek]

My interest is in surface water treatment by membrane filtration (nanofiltration).
I am looking for an automatic backwashing prefilter that can remove particle between 10 an 2 microns in raw surface water.
A part from chemical treatment (coagulation/ flocculation …) do you know any other way to remove small particles (less than 10 microns) in surface water?
Thanks!

 

[cub3bead]

Nanofiltration like reverse osmosis requires proper pretreatment to prevent membrane fouling. The key is the water quality of the feed. You may be able to get by with multimedia filtration in some cases and in others wou may require either a conventional tratment system or a MF/UF pretreatment system.

Have you measured the SDI of the feed yet?

 

[philippek]

Yes, I measured the SDI that is very high, between 6 and 6,5 (SDI 15 min).
I tested multimedia filter, but not efficient enough.
I also tested integrated membrane systems (UF/NF). That's fine, but too expensive for small municipalities.
Conventional treatment system as pretreatment for membrane filtration is also expensive, but the chief problem is chemical wastes management, as small municipalities’ sewage treatment plants don't have enough capacity.
So I am looking for a less expensive pretreatment for a nanofiltration system.

 

[cub3bead]

When you tried the media filter did you pre-dose the water with polyaluminum chloride or something similar?

 

[philippek]

No chemical was pre-dosed, just physical separation with multimedia filter.

 

[whoislee]

Filtration without chemicals can be done. There are backwashable filters available in the market.

Chemicals improve the efficiency of filtration. You requirments of filtration down to 2 microns using backwashable membranes is possible.

If you need more info, contact me via email.

There are 2 sides of a coin
One is to give, one is to take
Give until it hurts with a smile

 

[philippek]

Are you talking about backwashable membranes? That is not what I am looking for. I have already tested backwashable ultrafiltration and microfiltration membranes. They do fine job, but too much expensive.
What I want is a backwashable prefilter.

 

[whoislee]

There is no other backwashable prefilters to meet the specs of 10 microns.

MMF removes 20 microns and larger with the aid of coagulants and flocculants. Without chemicals, the efficiency drops to more than 100 microns.

Filtering at such low specs definitely need some form of investment. But this investment can provide a consistent and fully automatic operation.

Think about long term cost.

There are 2 sides of a coin
One is to give, one is to take
Give until it hurts with a smile

 

[philippek]

Microfiltration, in surface water treatment, can efficiently remove particles much more lower than 20 microns without coagulant. Even some sand filters can remove 20 microns particles without coagulant. I tested one backwashable sand filter, and without coagulant, it can remove 75% of particles larger than 20 microns. I was looking for something thighter, but not membranes.
Anyway, thanks for your concern.