Pesticides Removal (GAC)

[tipp79]

I'm currently designing a set of GAC contactors for pesticides (MCPA) removal at an existing water treatment works and was hoping someone could provide me with their thoughts on the following

The water authority currently installs GAC contactors as standalone units between primary and secondary (manganese removal) RGFs. Where in the treatment train is standard for pesticide removal GAC contactors to be installed? I would have thought it was downstream of both sets of filters as otherwise there would be a chance of manganese precipitating onto the GAC. However, the water authority seem comfortable with them being midstream and I've been advised that it's preferable to have them installed there so the secondary filters can act as a polishing step to filter out any GAC fines.

Would you advise ozone upstream of the GAC? Again I'd be worried about manganese precipitation.

Thanks in advance.

James

 

[bimr]

I agree with your position. Pre and post filtration of the water streams is recommended for GAC filtration. It will be difficult to ensure the removal of the managanese residuals from the GAC column.

I assume that you are using the GAC columns in series to maximize the efficiency of the GAC.

Following the GAC, a 1 to 3 micron post cartridge filter should be installed. This
filter will remove any residual colloidal material or carbon fines which may be sloughed off the GAC system.

 

[QualityTime]

Not sure what a RGF is but manganese is present in both soluable and solid form in the water. I assume there must be a treatment train to handle both these situations. A GAC contactor will not capture solid manganese unless the particles are big enough to be filtered. Also if you are adding chlorine to the water any free chloline will react with the manganese to give you black water