What sort of level of smell can one expect from biogas or its effluent. I reckon that there should not be too much whilst in the digester, but does initial mixing, pumping to waste or burning as gas create any nasty odours. Can it be sited near to a house, are there any building regualations as to proximity.
Should one try to scrub out the H2S and if so how ?
Incidentally, like most of your other correspondents, thankyou for providing such an interesting site.
RJFW
Smell
Moderator:Bob
Your AD process can be managed so as to be quite odor-free. Of course that will depend on a lot of variables -- e.g. retention time, C/N ratio, temperature, loading rate, etc.
The small-scale system I have direct experience with is actually located inside the house (in the basement) in a negatively pressurized plenum connected to a vent on the roof (similar to any other plumbing roof vent). It is effectively odor-free. Yes, the digester itself is gas-tight of course, but the effluent overflows into an open drum (also located in the same negatively pressurized enclosure). But even if it was not located inside this enclosure, this effluent is aerated and has very little odor.
H2S can often be controlled to manageable levels without scrubbing. Lower pH, higher digestion temperature, increased retention time, high protein content of substrate and 'natural' sulfates in dilution water all contribute to elevated levels of H2S.
However, if you do need to scrub it, you can do so by passing it through a pipe packed with rust. Get some iron filings (e.g. from a local machine shop, preferably mild steel or cast iron), mix with some moist sawdust (about 25 lbs Fe/ cu ft of sawdust), & let it rust. Then pass the biogas through it. The reaction is:
FeO3 + 3H2S -> 3H2O + FeS3
Fe2O3 + 3H2S -> 2FeS + 3H2) + S
For larger operations (e.g. a farm), there are a number of suppliers of commercial scrubbers (e.g. as in this list).
[This message has been edited by Bob (edited 03-03-2003).]
The small-scale system I have direct experience with is actually located inside the house (in the basement) in a negatively pressurized plenum connected to a vent on the roof (similar to any other plumbing roof vent). It is effectively odor-free. Yes, the digester itself is gas-tight of course, but the effluent overflows into an open drum (also located in the same negatively pressurized enclosure). But even if it was not located inside this enclosure, this effluent is aerated and has very little odor.
H2S can often be controlled to manageable levels without scrubbing. Lower pH, higher digestion temperature, increased retention time, high protein content of substrate and 'natural' sulfates in dilution water all contribute to elevated levels of H2S.
However, if you do need to scrub it, you can do so by passing it through a pipe packed with rust. Get some iron filings (e.g. from a local machine shop, preferably mild steel or cast iron), mix with some moist sawdust (about 25 lbs Fe/ cu ft of sawdust), & let it rust. Then pass the biogas through it. The reaction is:
FeO3 + 3H2S -> 3H2O + FeS3
Fe2O3 + 3H2S -> 2FeS + 3H2) + S
For larger operations (e.g. a farm), there are a number of suppliers of commercial scrubbers (e.g. as in this list).
[This message has been edited by Bob (edited 03-03-2003).]