GRAVITY THICKENER OPERATION

Gravity thickeneers can be a useful and easy to operate piece of equiment.  However, there are many who do not operate it properly.  This includes the engineers who wrotde the chapter on gravity thickening in the soon to be published EPA solids handling manual.  If you do not operat it properly, you will have poor performance and a smelly putrid mess.

Here is what is important:

Gravity thicvkening depends upon compressive settling. that is, you allow a sludge blanet to form so the the weight of the blanket above presses water out of the sludge on the bottom.  The sludge collectors have vertical bars, or pickets on theem to stir the blanket a bit and release watger and gas from the blanket.  If the blanket gets septic, you will have lots of gas and scum poor performance and a big stink.

How to optimize thickener operation

• Pump lots of thin fresh sludge.  Your primary clarifier should ave a ZERO blanket.  Yes, it should.  This keeps the sludge fresh and promotes fast settling in the thickener.  I taught this co9ncept to PSG at the old New Bedford MA plant and the assistant supt. said that they imrpooved primary clarifier removals by 30%.
• Your surrface overgflow rate should be 400-800 gpd/sf  sometimes you can go higher
• Use plenty of dilution water to keep the overflow rate up where it belongs.  dilution water should be secondary or final effluent
• If you arer thickening primary sludge your solids loading rate can be up to 15 Lbs/day/sf
• If you are thickening WAS it should be no more than 8 Lbs/day/sf and a rate of 4 Lbs/day/sf is better.  Even lower can be better.
• Draw sludge out on a regular basis.  Put the underflow pump on a timer.  If you have fancy monitoring equipment, you can have the underflow pump shit off when the density meter says the sludge is thin.
• Check your blanket and maintain what works best.
• If you thicken cosettled primary and WAS, treat it as WAS for the purpose of solids loading

That waswn't so difficult, was it?