×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

ferric chloride, pacl, microbiological removal performance

ferric chloride, pacl, microbiological removal performance

ferric chloride, pacl, microbiological removal performance

(OP)


Can someone please advise comparison of efficiencies for removal of coliform and e-coli by ferric chloride and poly aluminium chloride for coagulation, flocculation, DAF and onto RGFs (and ph dependancies). We have a pre-treatment plant DAF plant with something like 75-80% turbidity removal at this early stage in its commissioning and optimisation. We dose ferric chloride as the coagulant but have found that we have majorly insufficient bacteria removal which are giving values above our clients trigger levels for water feeding disinfection systems.
The plant has a crypto risk and we have started to see some non-conforming cysts similar in size to oocysts coming through.
We have taken coliform and e-coli count samples and the removal is only around 80%. A similar plant we have built has a much higher removal of bactiria in the 99% etc percent range across the DAFs / RGFs. Although this plant is often assisted by ozone it operates well in bacteria removal with ozone off.
I have seen some preliminary notes that indicate PACL is much better at removing bacteria than ferric chloride and that at the lower pH towards 5-6 the removal is substantially higher for both(I am aware of the effieciencies and robustness of the two coagulants for NTU/solid loading, microbiological removal is where i am struggling). Concern is that ferric chloride is not a good bacteria removal coagulant at standard ph ranges.
Some current operating data:
pH = 7.8
Ferric Chloride Dose = 2.8mg/l
Raw Turbidity  = 4.5 NTU
DAF outlet = about 1.5 NTU
Raw Water coliform counts = about 870/100ml
Raw water e-coli counts = about 100/100ml
DAF outlet coliform counts = about 130/100ml
DAF outlet e-coli counts = about 20/100ml
RGF outlet coliform = about 80/100ml
RGF outlet e-coli = about 10/100ml
Platn is Reservoir fed, worsening water quality due to weather changes. Raw water count could get much worse up into the 1000s and concerned plant can't perform.

RE: ferric chloride, pacl, microbiological removal performance

I would not expect you to find the information that you request. There should not be major differences in treatment efficiences with different chemicals.

You probably should go back to jar testing to determine the optimum chemical feed dosage. Get some input from nearby water treatment operators if possible.

RE: ferric chloride, pacl, microbiological removal performance

(OP)

Bimr,
Thanks for the response
This source, although not definative, shows signs of a marked difference in microbiological removal outside of the normal solids loading removal.

http://books.google.co.uk/books?id=dQxFM_P7vUQC&pg=PA103&lpg=PA103&;dq=coagulation+%2B+coliform+%2B+pH&source=web&ots=cF5fvXRr7A&sig=qirZLzqFvCxCg6_9ci70Ncvh-sI&hl=en&sa=X&oi=book_result&resnum=4&;ct=result#PPA109,M1

RE: ferric chloride, pacl, microbiological removal performance

I have in the past operated a plant on ferric in the summer (cheaper) and then PACl in the winter when turbidities rise and temperature drops. When dosing aluminium we found we could reduce chlorine set points on super chlor as there appeared to be a better bacterial kill/removal through the upstream processes.

I have also used PACl on waste treatment where we have found it has a dual purpose of coagulation and a biocidal action in preventing filamentous organisms growing in activated sludge. This activity wasn't shown when dosing iron based coags, and we have used it time and time again.
The aluminium ion is significantly smaller than the Fe3+ ion and hence has a higher charge desnity making it both a better coag. It may this fact that also seems to make it a better bug killer.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources