The appropriate coagulant to remove Zn & Fe from wastewater? 2

[ferrysianipar]

I'm trying to remove Zn & Fe from wastewater with chemical coagulation/precipitation method. From chemical compounds analysis there are 5 pollutants to be treated :

1. Iron (Fe) = 9.07 mg/lt to achieve value of 5 mg/lt
2. Zinc (Zn) = 5.87 mg/lt to achieve value of 5 mg/lt
3. BOD5 = 3,127 mg/lt to achieve value of 500 mg/lt
4. COD = 8,913 mg/lt to achieve value of 800 mg/lt
5. pH = 3.16 to achieve value range of 6 – 9

What is the appropriate coagulants to treat this wastewater. Or are there any better alternative treatment?

 

[bimr]

The traditional method to remove iron and zinc is the hydroxide precipitation process.

http://www.usace.army.mil/publications/eng-manuals/em1110-1-4012/chap3.pdf

If you desire to remove BOD and/or COD associated with organic pollutants, then you will have to use the activated sludge process.

http://www.earthplatform.com/activated/sludge/treatment

 

[ferrysianipar]

Thanks bimr
The reference for hydroxide precipitation is quite helpful.
If I can reduce the heavy metals (Fe&Zn), how is the effect on BOD and or COD value?

I think applying AS process is not suitable on this WW because the COD to BOD ratio is bigger than 1.0

 

[bimr]

Reducing the metals (Fe&Zn) will have only a slight affect on BOD and/ or COD.

I would not worry too much about the COD/BOD ratio, you still have lots of BOD that can be removed.

 

[ferrysianipar]

I still don't think that AS system is suitable for this WW.
Besides the large area requirement it's capital and operation cost are relatively high.
Do you have other idea to treat the BOD/COD?
How about absorption using activated carbon?

 

[bimr]

Activated carbon will be extremely expensive.

Maybe you can provide more information on the application. Is it a one time volume or a continuing stream? From what industrial process is this stream.

 

[ferrysianipar]

The WW is coming from paint stripping area in automotive industry. Goods (such as muffler, cylinder head of motorcycle) that have defect on it's paint must be repaired.

Those defect goods will have paint striping by dripping it in acid, "Halogenated Hydrocarbon solvent" and then sprayed with fresh water.

This sprayed water becoming waste water. Chemical composition analysis showed from 28 parameters tested, only 5 parameters (pH, Fe, Zn, BOD, COD) are becoming objectionable (pollutants) for environment.

The incoming WW flow is not stable because it depends on the quantity of defect goods. From their maximum water consumption about 5.0-7.0 m3/day, I'm planning to provide receiving tank with 3.0 m3 volume.

With this flow characteristic and the area constraint, continuous flow is not an option. I am planning to apply batch system using precipitation to reduce heavy metal contents. And now I still have to consider the BOD/COD.

 

[bimr]

Obviously the BOD/COD is related to the organic solvent in the paint stripper.

To remove the solvent, you should look into a batch distillation process.

To remove the metals, increase the pH of the solution to the point where the metals have minimum solubility and then pump the solution through a cartridge filter to filter the metals out.

The volume of waste fluid that you have is too small to have a continuous system, you will have to design a batch process.

Here is a reference site to give you some ideas:

http://www.p2pays.org/ref/13/12356.pdf

 

[mxmaciek]

The question is if your solvents are water soluble, or are creating the emulsion?
In case of poor water-solvent mixing and solubility, you can use the separators, similar to the oil separators.
If soluble... you can try oxidization with use of hypo. This will increase the metals removal as well.

 

[ferrysianipar]

@ bimr :
Thanks for the reference, I'm still trying to find similar literature for Halogenated solvent, cause your reference is for Non Halogenated.

 

[ferrysianipar]

@ maxmaciek :
That's a good idea, thanks!
There are two kinds of solvent they are using. One solvent is insoluble and I'm finding out how is the other one. If both are insoluble then I can propose them a separator.
Do you think a gravity separator is enough? Or should I use centrifuge type. This centrifuge type might extremely expensive.
And what do you mean by using hypo? Could you give me references?

 

[bimr]

You should visit the

http://www.p2pays.org

site for more information.

"Other than the filtration of stripper to prolong its use, recycling of spent stripper by means of distillation or other technology is seldom practiced. Most formulated strippers are a complex mixture of METH and acids that do not lend themselves to easy separation, recovery, and
reuse. Even if the METH was recoverable, it would still have to be formulated back into a viable product and all of the non-recoverable components disposed of as hazardous waste. The only way recycling of paint stripper would be readily viable would be if the facility was using pure METH for stripping. This practice is not common for immersion stripping but is common in the area of paint application equipment cleanup."

http://www.p2pays.org/ref/01/00666.pdf

As you can see, the mixutre is probably a combination of serveral chemicals that do not lead to easy separation. Hypochlorite will not work either since the metals are proably fully oxidized.

You should look into a distillation process to reduce the volume that will need to be disposed of offsite.

 

[moltenmetal]

ferrysianipar: no offence, but you're in well over your head. You're focusing on just COD, BOD and metals whereas you very likely need to reduce the concentration of some target organic micropollutants (probably methylene chloride but maybe others) by several orders of magnitude if your intention is to discharge this water after treatment rather than re-using it in your facility.

Chances are, there are process modifications possible to solve this problem better than simply treating it as an end of pipe water treatment problem.

If indeed it's an end-of-pipe solution that you need, you need a specialist to design the appropriate treatment system for you. There's no way you're going to get enough out of a forum like this, the

http://www and

a few textbooks to do this at all adequately. The likelihood that you accidentally create an operating cost nightmare or a treatment system that doesn't work properly is fairly high.