Biofilter for odour control

[Chris73]

Hi Eng's,

I am designing a sludge treatment facility as an upgrade of a WWTP. I figure the sludge dewatering building needs ventilation and I want to lead the exhaust air through a biofilter unit. In order to keep the moisture of the bed material appropriate, I think a mist nozzle (or so) injecting into the air inlet duct would be prudent. Anybody any idea which mist/spray nozzle qualifies for that and how I could make a raw estimate how much water will be distributed over the filter by using such a mister - just to get an idea how often and how long the mister would have to be operated to increase the material moisture to a certain degree. Is there a raw formula which comprises duct lenght from injection point, temp, air flow, filter area and volume etc...
Thanks folks!

 

[grimma]

Hi Chris 73,

Depending on the material you use in the bed of the biofilter, you will also have to add water on the top of it (spray nozzles are fine too).
Humidifying air/media is always hard to calibrate because there's no easy way to estimate the needs... What we do is we set the electrovalve to open for X minutes (usually more than 30) Y times a day, and we take a look at how much water flows down the biofilter, knowing that too much or not enough are both bad.

If someone knows a simple way to estimate what you asked, I'd like to know it too!

Delphine
d.ranslant@europe-environnement.com

http://www.esil.univ-mrs.fr/~dranslan

 

[Chris73]

grimma,

thanks for replying! Don't you think just one mist/spray nozzle installed in the inlet duct would be sufficient? Do you usually cover your filter bed? I think a side-open cover would help to keep a more constant climate underneath. Let us see if somebody comes up with a good way to estimate the efficiency of a mist/spray nozzle!

 

[quark]

Chris!

You can do it if you have some practical data. As it is difficult to predict what is the moisture taking capacity of air (as it is very dynamic w.r.t DBT, WBT, bed packing etc) you have to have some data before you.

Take the dry bulb and wet bulb temperatures of air before and after bed. By plotting these points on a psychrometric chart you can other data like total enthalpy and specific humidity. You can now calculate it by two ways.

To the right of the chart you can find grains of moisture per lb of dry air. You take this value for both the conditions and the difference gives you the amount of water content per lb of air. Multiply it with the air quantity.(Note: 1 cu.m air weighs 1.2kgs) This will give you the amount of water which you have to top up.

The other way is to check the moisture content from enthalpy difference. (latent heat of vaporisation of water is 550 kcal/kg)

Here are two suggestions for you.
1. There are charcoal filters (charcaolspread on filter paper) which remove odour from air in a ductwork. (caution: I didn't give a try so far)
2. If you post your question in HVAC section of this forum somebody else may help.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[Chris73]

Thanks quark!
I think I wont get around some test measures during commissioning period. What kind of thermometer would you use for measuring wet bulb temperature? Hope I won't need an expensive device!
Kind regard!

 

[AggieCE]

Chris73,

If you haven't looked into it already, you might want to check into Biocube, Inc. odor control systems. They manufacture a modular, low maintenance biofiltration system that I recently looked at. It looked pretty interesting and addresses the areas that have traditionally caused problems for "in ground biofilter" designs (per their lit.), including adequate control over air flow distribution, media compaction, operational temperature, and moisture content. Their system is pretty slick. They also manufacture compact skid-mounted systems for lift stations and inserts for manholes. Check them out at

http://www.biocube.com

or call them at (716) 924-2220. I spoke with Rick Williams and he was very helpful. They are located in upstate NY.

Mike D.

p.s.: Thanks for replying to my question regarding sewage viscosity. I'm glad I could reciprocate.

 

[AggieCE]

One more thing...I just went to the biocube website and it didn't have all of the info on it that the brochure has. If you'd like me to fax a copy of the brochure to you, email me at michael.demotte@kimley-horn.com

 

[quark]

Chris!

Put a cotton wick around the bulb and wet it. Put the thermometer in the air stream and you have your wet bulb thermometer.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[stanier]

I have been involved in the installation of a number of biofilters on WWTP sludge facilities. I was not the designer however. Some of the critical issues were:

1) Make sure the bed is covered to prevent rain water problems

2) Biofilter was good for removal of H2S but had difficulty with ammonia. So if you sludge plant has lime stabilisation there could be a problem and you may need another solution.

3)The formation of the actual biofilter media appeared to be a bit of a black art rather than a science

4) There are a number of manufacturers of biofilters that fit into a container sized module. If you need more you just stack the containers together and manifold them.

 

[grimma]

Stanier and Chris 73,

When treating effluents with ammonia and H2S, we use a scrubber for ammonia, then a biofilter for H2S.
We also cover most of our biofilters, be it in rainy regions or sunny ones, to prevent water problems in either way.

And yep, black art here - you always have measurment solutions, but predicting how an organic media will evolve is difficult.

Please Chris, let us know about your measurments.

Grimma

 

[Chris73]

Thank you all for your helpful tips! I will let you know how it works out!

Chris73