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Juanjuan

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ferric chloride dosing for odour control
May 31^st, 2012, 2:04am

Hi,

I need to calculate the theoretical dosing rate of Ferric Chloride (react with dissolved sulphide), here is my calculation, not sure if i am correct:

DS=6.25mg/l, sewer flow=150KL/d
FeCl3 at 42% w/w, density=1200kg/m3

1 mg of DS will require 1.13 mg of Fe, therefore, FeCl3 3.27 mg
1 mg DS in 0.16 L of sewer

dosing rate (mg/L)=3.27/0.16=20 mg/L

FeCl3 required per day = 6.25*150*1000*3.27/(0.42)=7299107.1 mg/d

FeCl3 dosage per day=7299107.1/(1200*1000000/1000)=6.08 L/d

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Eric Raj

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Re: ferric chloride dosing for odour control
Reply #1 - May 31^st, 2012, 10:10am

Your calculation just doesn't look right. I am getting that you need 16.9 mg/l dose of FeCl3 at 42% Fe in order to meet the need of 1.13mg/l per 1 mg/l of DS. This is based off of your 6.25 mg/l DS conc.

Coverting liters into MGD gives me .03963; plugging these values into a chemical feed formula then gives me this: lbs/day = (.03963)(16.9mg/l)(8.34lbs/gal) I get that you need to feed a little over 5.5 pounds of FECl3 each day.

~Eric

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Juanjuan

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Re: ferric chloride dosing for odour control
Reply #2 - May 31^st, 2012, 11:33pm

Hi Eric,

Thanks for the reply. I am just wondering how did you get 16.9 mg/L for 6.25 mg/L of DS.

I got 20 mg/L dose FeCl3 based on stochiometry relationship: 2Fe³⁺and 3HS^-, the ratio is 1.12 mg Fe³⁺ to 1 mg HS^-

Then it give me 1.12*6.25=7mg of Fe³⁺, therefore 7/0.34=20 mg of FeCl3 for 6.25 mg of DS in 1 L of sewer

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Victor

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Re: ferric chloride dosing for odour control
Reply #3 - Jun 1^st, 2012, 12:32am

You never dose chemicals on sewage based on theoretical calculations. You need to be doing jar testing. FeCl3 will react with other compounds in sewage such as P, solids (which acts like like a coagulant)......

2FeCl3 + 3H2S----->S + 2FeS + 6HCl

ppm FeCl3 to ppm H2S (in solution) 3.2:1.0 (theoretical stoichiometry)

13.75 ppm liquid FeCl3 (38%): 1 ppm P

4.49 ppm liquid FeCl3 (38%): 1 ppm PO4

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A4YB YaBB Newbies Offline I love Water and Wastewater.com Posts: 30 Company or Organization: awzi	Re: ferric chloride dosing for odour control Reply #4 - Jun 1^st, 2012, 1:40am Victor wrote on Jun 1^st, 2012, 12:32am: You never dose chemicals on sewage based on theoretical calculations. You need to be doing jar testing. Have to agree with this.
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Eric Raj God Member Offline As long as it flows, I'll treat it! Posts: 518 Gender: Company or Organization: City of Bedford	Re: ferric chloride dosing for odour control Reply #5 - Jun 1^st, 2012, 7:10am IF only 42% of the ferric is available, then you would need the 16.9mg/l. If 100% of the ferric is available then obviously you would not need as much. ~Eric
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Juanjuan YaBB Newbies Offline I love Water and Wastewater.com Posts: 3 Company or Organization: a	Re: ferric chloride dosing for odour control Reply #6 - Jun 6^th, 2012, 12:40am I understood that you can never dose based on the theoretical dose rate. Hi Eric, i think the ferric chloride solution contains 42% w/w FeCl3, it is content of Fe³⁺ is about 14.5%.
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