[Digestion] Removal of hydrogen sulphide from biogas

David david at h4c.org
Tue Sep 25 09:20:32 PDT 2012

Dear Isiaka,

On 9/24/2012 3:13 AM, multicareng at yahoo.com wrote:
> I am working on biogas application on farm and low / middle class 
> homes. [...]
> I am looking for simplest and easiest way(s) to eliminate hydrogen 
> sulphide from biogas and I think you can be of assistance.

In addition to the excellent advice and information you have already 
gotten, I would mention that there is a low-cost means of measuring 
the amount of H_2 S in the biogas detailed in a freely downloadable 
PDF from The Complete Biogas Handbook website, here 

Further, the following is from the same book:

        Henry (1961) claims that at mesophilic temperatures and pH
        5.0, 98% of all of the sulfides dissolved in the slurry show
        up as H_2 S, whereas at pH 7.2, this is reduced to 24% with an
        approximate 50% reduction for each 0.2 pH unit increase
        thereafter (e.g., 12% at 7.4, 6% at 7.6, 3% at 7.8, 1.5 % at
        8.0). Where scrubbing H_2 S is desirable but unrealistic for
        some reason, pH adjustment may be the answer--- but take care
        not to over-adjust. A further idea is the addition of the
        ferric ion of iron; Henry used ferric chloride at the rate of
        about 2 grams per liter. This tied up the sulfide ion and no
        H_2 S was produced in a digester with this high dosage of
        ferric chloride.

For a good recipe for creating a mixture that will assist scrubbing of 
H_2 S-- remembering the caveats mentioned by Alex-- I suggest looking 
at the booklet "Some Conditions Affecting the Usefulness of Iron Oxide 
for City Gas Preparation", by William. A. Dunkley (February, 1921). It 
can be downloaded from here 

My final thought is that we may ultimately find the best means of 
scrubbing H_2 S from biogas is by the use of sulfur-loving bacteria. 
However, to the best of my knowledge, no one has yet adapted this 
relatively high-tech process to low-tech-- i.e. village-- use. (One of 
the key hurdles to overcome, for example, is that these bacteria need 
just a hint of oxygen in order to metabolize the H_2 S into elemental 
S.) I would love to hear of anyone that has ideas or sources of 
information on this. Some steps in this direction are indicated (for 
example) by a thesis by Mary Elizabeth Fischer, "Biogas Purification: 
H2S Removal using Biofiltration," available here 

David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

"Make no search for water.   But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)

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