Primary clarifier

[Lan123]

Is a primary clarifier ahead of the aeration tank a must for an extended aeration wastewater treatment plant? The screens are 6 mm bar screens. This is for municipal wastewater.

 

[bimr]

Primary clarifiers are rarely used for wastewater treatment plants sized for less than 10 mgd. In the past, primary clarifiers were widely used. Part of the reason that primary clarifiers are not widely used anymore is that aerobic digesters are now more common than anearobic digesters.

If you use screening in the front of the plant, it will help to minimize downstream problems with flotable solids.

 

[ch81pc]

Is there a grit trap before the ditch and if so what type? Found a plant last year with 6mm screens, pista type grit trap and dicth that had been passing fine grit since it was built. The ditch had gone from 10" deep to <2" in some places, and they wondered why it wasn;t meeting consent!

 

[Lan123]

Thanks folks for the feedbacks. Yes we do have an aerated grit chamber. We want to convert this to a vortex grit chamber.

bmir: why do we need a PST for an anearobic digester?

 

[bimr]

Primary and secondary biosolids have different compositions. Secondary biosolids generally consists of microorganisms. Because of the different compositions, it is more difficult to operate an digester (aerobic or anerobic) with combinded primary and secondary biosolids.

Anaerobic digesters are better suited for operating with primary biosolids than with secondary biosolids. Aerobic digestion of primary solids or a mixture of primary and waste-activated solids is not recommended.

Reference the NATIONAL MANUAL OF GOOD PRACTICE FOR BIOSOLIDS:

http://www.google.com/url?sa=t&source=web&cd=2&sqi=2&ved=0CB0QFjAB&url=http://

http://www.wef.org/WorkArea/linkit....o8WVBA&usg=AFQjCNFP94b4sJP0EGiOcFnaT6O-cG_zvg