[Digestion] What Happens to Chlorine in digestion?

[David Fulford]

Tom,

Interesting question.

I suspect that it remains in the slurry. A good anaerobic digester is 
well-buffered, which means that it contains carbonate ions that can absorb 
carbon dioxide to become bicarbonate, which means the pH is kept at around 
neutral. If you have carbonate ions, there must also be metal ions, such as 
sodium, potassium and calcium. If there is free chlorine, or chlorine bound 
fairly loosely to organic compounds, it will react with the metal ions 
fairly quickly to form chlorides.

As far as engines are concerned, sulphur is more of a problem, as it 
emerges as hydrogen sulfide. If the biogas is used in an engine, this burns 
to make sulphur dioxide and does corrode the exhaust pipes. Any free 
chlorine in the gas will also form acid in the exhaust.

Most biogas engines are either dual-fuel (i.e. diesel) or are based on a 
diesel engine, but with a spark plug, so they are usually strong enough to 
cope with a bit of corrosion. Where gasoline engines have been used with 
biogas, they have had a fairly short life. Several years ago a group in the 
Philippines (Maya Farms) had a set of second-hand Japanese engines to 
generate power, but they could get them cheaply and did not worry about the 
short lifetime.

Cheers,

David Fulford

At 10:07 14/08/2006 -0700, Tom Miles wrote:
>All,
>
>What happens to chlorine during digestion? Many manures can contain up to 1%
>chlorine (dry basis). What reactions occur and what happens to the chlorine
>during digestion? Does it stay with the effluent or does it carry off with
>the gas? If it goes with the gas what is done to protect engines in most
>applications?
>
>Thanks
>
>Tom Miles
>
>
>
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