Code states that you need to exhaust the air.  Use an ERV to reduce the heating and cooling costs.

Why would you reintroduce contaminated air to a bathroom?
Seems counterintuitive.

Ok Chowder, do you like the smell of farts or something?  Or has conserving energy gone too far this time?

mecheng
You are so funny!!
 

Actually it has some sort of energy recovery thing. We currently designing ventilation system for 42 nos dressing rooms with individual toilets including common toilets.  

Whoever suggested this for energy conservation should be ignored in future.

Some well meaning ideas just don't smell right.  An ERV is the right solution for more than just bathroom odors.  Helps with any other offgassing or just stale air in a tight building envelope.  My dream house will include an ERV along with the HEPA filter and integrated humidifier/dehumidifier.  I intend to be effortlessly comfortable and healthy in my old age.

- how much the exhaust cfm is?
- how many fan do you have?
- did fans work 24/7 or just when someone use the bathroom?
- does the HVAC supply fan is "On" all the times or in Auto mode?

 

The odors (and moisture from showers etc) in some bathrooms should go straight outside.  Some amount of building Fresh air exchange generally is required too, although perhaps there is some fresh air makeup in the system now.  
If energy saving is the driver An air-air heat exchanger is likely to be the reasonable and economical way to reclaim some heating/cooling energy

A activated carbon filter will scrub the air and remove all odors.
Good luck

If the "bathroom" portion of the OP's question is a shower room and there is a lot of high humidity present, and... the OP is located in a warm climate where lots of air conditioning is involved, you might find that there is more energy saved by simply exhausting the moist air than removing the moisture from the air via the A/C evaporator handling the latent heat of the water vapor in the air.

Do the calcs.  They are eye-opening.

I spent most of my life resenting anyone in my household exhausting air that I had paid cold hard cash to heat or cool.  Then I got involved in a project at work with a Hx that takes humidity out of air at various operating conditions and when I saw the duty required to do the condensing (as opposed to the sensible air cooling), I am now the one that insists that the vent fan is run when anyone showers.

rmw

Activated charcoal filters as estidmated stated should do the trick for organic compounds but these filters will need periodic replacement or rejuvanation the latter of which may not be advisable as these fitters would be too small.  In my estimation, there is no substitute to fresh air unless you are in China.

Activated charcoal filters are anything BUT small. Thae one I have is three foot tall and weighs at least a hundred pounds. Good for 2 years and then I heard you can re-activate the charcoal somehow and re- use it but I will just replace it.
I don't think that they are practical at all but the man asked and I answered. That's his decision to make. Just offering options that work and carbon filters WORK!!!

I got two over my kitchen stove and they are about 12" by 16" and 1-1/2" thick  

I think air extracted from the toilets shouldn't be supplied back to the bathroom. All you have to do is just to exhaust the air, use an ERV.
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plumbing