Oil Removal from Water (Filtration Unit Waste Stream) 4

[ChemEng87]

Hello everyone,

I am asked to design a process to remove "suspended solids" and "oil" from the waste stream of a filtration unit. I have been recommended to use a clarifier followed by a filter press to remove suspended solids. First I want to know if this is applicable for that purpose.

On the other hand, I have no idea how to remove oil for such a huge flowrate and oil content. It will be highly appreciated if anyone introduces me to any process or system to remove oil from water. If an equipment exists out there to do the job, it will be great to have the names of one or two of the manufacturers.

Below are the flow conditions:

- Flow= 72,500 BPD
- TSS= 200 ppm
- Oil Content= 300 ppm

Thank you in advance for your cooperation.

 

[bimr]

A clarifer is not applicable for this waste stream. You might consider the use of a DAF as pretreatment to a tubular ultrafilter.

You best option is probably the tubular ultrafilter to separate and remove the oil.

http://www.kochmembrane.com/Membrane-Products/Tubular/Ultrafiltration/Abcor-FEG-Series.aspx

I would try to recycle the waste oil that is recovered.

 

[ChemEng87]

bimr,

Thank you. May I know why a clarifier is not applicable in this case? I need to give some explanation as why I am not using a clarifier followed by a filter press.

Thank you again.

 

[moltenmetal]

Not all solids are created equal. Some suspended solids are easy to remove by any means- sand as an example. Some are very much more difficult, i.e. ferric hydroxide.

Easy solids can be removed by filtration directly, resulting in a highly dewatered cake.

Difficult solids must be removed by flocculation followed by clarification. A flocculant and/or polymer coagulant are typically used to pull down these colloidal-sized solids into a sludge which settles to the bottom of the clarifier, which may then be continuously removed and filtered.

Free product oil can be removed by a simple oil-water separator. Semi-emulsified oil may be removed by a hydrophobic coalescing filter or by dissolved air flotation. DAF can be done before filtration if you don't care about having solids in your recovered oil. Coalescing filtration must be done AFTER filtration to remove solids.

At 300 ppm total oil, some of the oil will be truly dissolved rather than emulsified or present as free product. Removing dissolved oil is difficult to say the least, and the method used depends greatly on where the water is going (i.e. reuse? Disposal to a treatment works? Disposal to a river or stream?) and on the nature of the oil or more properly on the toxic subcomponents of the oil mixture which are typically regulated to quite low concentrations for discharge.

 

[bimr]

A clarifier is not efficient at oil removal. Clarifiers are used for removal of large amounts of sediment.

Different equipment is used to remove oil, depending on the amount of oil and the type.

If you have large amounts of free oil, an API separator is used.

A parallel plate separator or a DAF can be used to remove oil. Air is used to help the oil float and be removed. If you equip the DAF with a bottom scraper, you can also separate out the suspended matter.

If the oil is emulsified, you probably need some type of chemical treatment (lowering pH) to break the emulsion.

Your people may be referring to some other type of equipment and using shorthand to describe the equipment. You will need more equipment than a clarifier and filter press. A clarifier is not efficient at oil removal. Clarifiers are used for removal of large amounts of sediment. A filter press is used to dewater solids.