Chemical Phosphorus Removal 1

[sadochemeng]

Hi,
We are designing a phosphorus removal system for a wwtp. and we r gonna use feeric chloride as a chemical, we are gonna buy it at 35% concentration and dilute it down to 1-5% adn pump about 50-250 ft before primary clarifiers after them and stuff, but in a book it says this is unnecessary and may be undesirable due to the occurence of hydrolysis at dilute concentrations of ferric chloride. Do you know anything about this? Coz at 35% ferric chloride solution is really viscous and so hard to pump. if anybody used a similar system or knows anything about this, it would be great to hear.
thanks all.

 

[FiltrationEngineer]

I think you just use a chemical metering pump that can pump very viscous fluids. If you flows are outside the range of a metering pump, just use a pump designed for the fluid you're pumping.

There really isn't any reason to dilute the ferric, you just have to buy bigger equipment and put in bigger chemical dosing piping.

By the way, why did you choose ferric over alum? I'm just interested...

 

[bimr]

I think that you have not received the proper advice.

"Ferric chloride’s rapid hydrolysis in water aids in making it an ideal flocculating and precipitating agent for water treatment."

DOSING: Ferric Chloride should be fed straight. No dilution or preparation is required. A diaphragm metering pump of non-corrosive material is suitable.

http://www.orcawatertech.com/product/Prod101.pdf

 

[sadochemeng]

coz ferric chloride is more efficient than alum or lime or any other...

 

[sadochemeng]

bimr,

I guess I found my reply, yea pre-hydrolization of ferric chloride defects phosphorus removal but increases BOD COD removal... since in our case we wanna remove phosphorus we dont want that, and it happens really really low concentrations, under 5-10 percent...or even less in this case hydroxy groups reacts with your ferric and decrease the free ion numbers for phosphorus but if u have enough, it doesnt effect...this is something like more at molecular level...

 

[redbridge]

I have designed phosphorus removal for wwtp. Initially I was going to use ferric chloride but we had a chemical supply company come in and do some pilot test and it ended up being more economical to use an alum based polymer.

 

[ch81pc]

Within the last year I have had 9 ferric chloride dosing units set up on the WWTP I look after. We dose 45% FeCl3 using a diaphragm pump. Speed is controlled on crude sewage flow and stroke controlled on a preset "crude sewage strength" profile programmed into the PLC, to account for diurnal variations in sewage strength and hence save chemical.

We do not dilute the FeCl3 before dosing upstream of our PST's (distance from pump to point of delivery upto 30 meters). We have found in a few applications that our flash mixing needs to be more engergetic than first thought to acheive flocculation and should be as close as possible to the point of delivery.

 

[sadochemeng]

Hi ch81pc,

Thanks for all replies. I have one more question if you dont mind...where do you mix your ferric in the system? do you connect your line to your mix liqour line or do you send directly to a tank or something? and if you mix it in the pipe line what kind of equipment do you use? I mean we are thinking here we should mix it in a pipline rapidly and then in the tanks a slow mix so we will have better system but we couldnt find any equipment to make this rapid mixing in the pipeline coz quills or all other stuff is sticking out in the pipeline and if some rags and stuff comes with the sludge, after a while pipeline will be cloged because these stuff will get stuck on the mixer in the line. So if anybody did some application close to this what kind of quipment did you use or how is your system working?it would be great to know. Did you have any corrosion problems in the pipeline after mixing?did you do anythging about it?
thanks again...

 

[ch81pc]

Hi sadochemeng

We dose directly down stream of preliminary treatement. So either direct into the flow to primary settlement (at a flume, cascade or drop pipe anywhere with a good strong vortex, or lots of turbulance) or for activated sludge without primary tanks I drop it in with the crude sewage.

We had problem on one site where we were dosing onto a weir with a 1' drop. We thought that the turbulance would be enough to mix the ferric in but we ended up with inefficient mixing, we got ionised species in the water, rather than the solids that made the primary sludge impossible to settle. As a quick fix (until the civils boys could do it properly) we simply dropped in some concrete blocks to creat additional turbulance anto waht used to be laminar flow.