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Media blinding and bad cake formation

Hello! we are filtering a slurry containing fine calcium hydroxide and viscosity about 127 poise by using plate and frame filter press. we are facing the problem that the media blinds at negligible cake thickness and the filtrate remains hazy even at nearly zero flow. what should the actions that will remit this difficulty. is the filtration technique we are using is right if not then what technique will be right for this.

Ghulam Rasool
- Pakistan
2007

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2007

Hello, Ghulam. We don't know the source of this waste product, how it is generated, or what you may have done prior to filtering it, but . .

Has any polyelectrolyte been added? Is there any clarifier or settling tank, or are you just doing direct filtration? The first thing I would suggest is a jar test: take a beaker [beakers on eBay or Amazon] of mixed effluent (before filtration) and just let it sit, marking every 5 minutes how much of the top volume is clear. Try adding a little alum and repeat. Try adding a little ferric chloride [on eBay or Amazon] and repeat. Try the same after adding a few ppm of a few different polyelectrolytes. Come up with a laboratory understanding of how to treat and separate the waste before trying to fix it in the filter press.

Filter aid may solve your problem of blinding in the filter press and turbidity, but it may make for huge excessive volumes of waste products over the months and years. So try to understand the jar test before committing to filter aid. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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First of two simultaneous responses --

Ted offers good advice. I'll add: a diatomaceous earth precoat never hurts, makes for easy cake separation too.

Dave Wichern
Consultant - The Bronx, New York
2007

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Second of two simultaneous responses --

How are you operating your press? Most people feed them with a diaphragm pump. If this is the case with you, start the press cycle with a low pressure on the pump. As the cake forms the pump will slow down. you can then ease the pressure up a bit. It is easey to "Plug" the cloths if you start the press at too high a pressure.

Kurt Sammons
- Inman, South Carolina
2007