This is Tom Cleveland, Plants & Engineering Manager, Decatur Utilities in Decatur Alabama.  We own and operate a 68-MGD conventional surface water treatment plant which uses the Tennessee River as a source.  Our treatment processes are: coagulation, flocculation, sedimentation, filtration, and disinfection with chlorine gas.  The chemicals we use are: Sodium Permanganate (20%), pre-chlorine, poly-aluminum chloride (PACl), fluoride, post-lime, post-chlorine, and poly-orthophosphate.  On January 2, 2011 following a rain event which dropped ~5 inches of rain in 2 days, we had an elevated raw water turbidity of ~70-80 NTU.  We were feeding ~30-40 mg/L of PACl at the beginning and during the first few hours of the increased raw turbidity event.  We ended up "loosing" all of our 40 filters due to high filtered turbidities (~0.3 NTU) and high settled water turbidities (~16.0 NTU).  We eventually solved our problem by increasing our coagulant (PACl) dosage rate anywhere from 85 to 105 mg/L. 

Do you know of any water plant that has had to feed PACl at that high of a dosage rate?  Also, do you have as ideas as to what might create such a high coagulant demand with a raw water turbidity of only ~70 NTU?  Are there any resources or technical advice available to us as WEF members?  If so, please contact me via phone or e-mail.”

Thank you.

Tom Cleveland, p.E.

Plants & Engineering Manager

Decatur Utilities

(256) 301-4605Office

(256) 654-1630 Cell

(256) 552-1484 Fax

tcleveland@decaturutilities.com