Methanol Removal in a Pressure Sand Filter

[gokhant]

Hello members,

Today i received a feed design for treating of sour stripper water which contains H2S and Methanol. The designer planned to remove the H2S (%99,5; 0.74ppm to 0.004ppm) by adding H2O2 in an oxidation tank. In the same oxidation tank, the desiner assumed that %60 of methonal will also be removed (from 20ppm to 7ppm).

Thereafter, serial connected Sand Filter and GAC Filters established for sieving the TSS, remaining oil, organic compounds and minimizing the dissolved organic prior to UF units.

In addition to this system, the designer has established a Pressure Swing Absorber producing %90 purity oxygen. This oxygen will be injected to the water before a static mixer and air saturating tank which are placed before the sand filter. Apart from that, in the same line nutrient(Ammonium Phospate Urea) will be dosed before the sand filter. As the designer said that the target of this system is to remove the methanol (%99,5; 6,4ppm to 0.032ppm) by creating biological activitiy in the sand filter. Apart from that, everything is same with the sand filter like it's conventional one.

So far everything is fine. But i have never heard such a system which removes the methanol in a sand filter. I know that the companies like veolia, degremont has special systems (biostyr, biofor) for such solutions. But sand filter is something unique for me.

Does anyone have such experience ? Does anyone have opion about this matter ?

Thank you all for your valueble comments.

Best Regards..

 

[ashtree]

gokhant
It might work but seems overly complex and will probably use a lot of energy and chemicals that may be unnecessary.
Biostyr and similar processes are somewhat like sand filters but usually have an artificial media that is both lighter and larger than sand to promote faster filtration rates, deep bed penetrations and lower backwash flowrate and volume. They are often relatively deeper beds than the 600-900mm often used for standard filters. The methanol is used as a food source for denitrification under anoxic conditions converting nitrates to nitrogen gas and dissolved oxygen.

A couple of issues I see.
1) You are actually adding ammonium phosphate to give the bugs something to nitrify so that you can then use the methanol to denitrify. This will be at some cost.
2) Nitrification requires an aerobic environment which typically means an amount of dissolved oxygen around 1-2mg/l. This will require energy to achieve this. A pressure swing absorber will obviously produce oxygen but seems like an expensive way to do this unless perhaps you are also generating ozone somewhere. If you connected a blower and an aeration diffuser to the current contact tank may well do the job cheaper than a pressure swing absorber.
3) Denitrification where the methanol is used as a food source is normally done under anaerobic conditions so provided the filter is deep enough that it can provide both nitrification in the top of the media under aerobic conditions and denitrification in the bottom under anoxic conditions it may work okay but control will be difficult and it will be very susceptible to flow rate changes and backwash conditions.
4) Its not clear where you are seeding your nitrifier and denitrifier bacteria from as you blast everything pretty well with peroxide up the front.

Like I said it might work okay but just seems like a complex and expensive way of doing things.
Regards
Ashtree

 

[ashtree]

gokhant,

Just another thing.
Nitrification and denitrification processes are very pH dependednt and like a reasonably consistent pH typically 6-9 but 6.5-8 is probably ideal.

I assume by the description of your process that you would be doing your initial oxidation at ph of 3-4 perhaps.

You might need to check what pH you will be running at and whether this will work for you.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[EmmanuelTop]

Not sure what are the final specs of the treated water but given the low initial concentrations of contaminants (H2S and Methanol), maybe a suitable adsorption process can be designed to meet your specifications. There are specialized adsorbents out there designed for removal of these contaminants.

Or perhaps you can get sour water stripper to remove H2S and then install adsorber to polish the stream with regards to Methanol content. See

http://msdssearch.dow.com/Published...seps/pdfs/noreg/177-01731.pdf&fromPage=GetDoc

It seems like the designer (and the vendors) want to sell you a lot of equipment. I think you can at least request some sort of technology evaluation report that will explain the technology/configuration selection process, and also get budgetary proposals from several licensors - just to give you feeling of what you need for water treatment.

Dejan IVANOVIC
Process Engineer, MSChE

 

[ashtree]

gohkant,

I agree with EmmanuelTopps comments.
I might strip the H2S separately then use the absorbent on the methanol but you would have to look at the costs and impacts of doing this.
He is right in that the concentrations are relatively low and all the process proposed would tend to suit a larger concentration.
After posting the other day I even looked at air stripping using a packed tower. Under the right conditions H2S can normally be stripped relatively easily. Methanol is much harder based on the Henry's law values but is possible. You would have to design the tower to strip the methanol but it might be worth looking at that as an option as well.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Sand filters are more common in the aquaculture industry and are in the form of a fluidized bed (FSB). It is a similar process to the biostyr, but probably a little more difficult to operate than the biostyr as it is more difficult to fluidize the sand.

You do not mention the capacity, but one would not think the proposed system is not economical. Pressure Swing Absorbers are also not very economical at low capacities.

FSBs are less expensive and more compact than the biostyr. On the down side, FSBs are relatively complex to design. FSB's must be operated within a fairly narrow water flow range, i.e., within 30% of its design flow, in order to maintain proper bed expansion. If water flow ceases, the static but biologically active bed may turn anaerobic, resulting in an upset.

Because of the operational issues with sand media, you would probably be better off with a different media.

http://www.jesc.ac.cn/jesc_en/ch/re..._no=20040308&year_id=2004&quarter_id=3&falg=1

http://www.sciencedirect.com/science/article/pii/S0144860905001184

One would think that this water may be recycled to a unit operation such as a desalter that does not require a high quality water.

 

[kybhosale]

For methanol removal one can use membrane-based vacuum stripping process. It may be cost effective for operation point of view and it will take small footprint.

Krunal Bhosale

http://waterengineer.co.in

All about Water and Wastewater Treatment