[Digestion] Meso and Thermophilic Operating Temperature

[harrisfm at aapt.net.au]

G'day Bram et al,
I am Paul Harris, Hooroo is an Australian form of Goodbye (but you are
not the first to cal me Hooroo!).
Yield is how many litres/grams of methane you get per kg of waste and
rate is liters per kg per day. If you are specifying yield you really
need to give the conditions (batch/continuous, temperature, length of
test ) so different yield figures can be properly compared.
If you simply extend the Retention Time (keeping Temperature and
Loading Rate constant) Yield will go up because any kg of waste is in
the digester longer. Similarly if you keep everything except
Temperature constant and increase Temperature the Yield will go up
since the Rate is increased.
What you need to realise is that at higher temperatures the yield will
actually decrease if you cut back the Retention Time too much and that
the same yield (or even higher!) can be obtained at lower temperatures
when the Retention time is extended (and longer Retention time is
likely to give more robust operation, since any changes or
contamination will be a smaller percentage of the total volume).
Hope this helps,Happy digesting,
HOOROOPaul Harris

----- Original Message -----
From: "For Discussion of Anaerobic Digestion" 
To:"digestion at lists.bioenergylists.org" 
Cc:
Sent:Fri, 6 Jun 2014 10:25:52 +0000
Subject:Re: [Digestion] Meso and Thermophilic Operating Temperature

 Thank you for that HOOROO, a very valuble resource, the S curve is
indeed a very good fit. 

 However, it still leaves me with a question, or more of an area that
isn't quite clear yet. You speak of rate, I assume you mean conversion
rate. I've always believed and understood that conversion rate and
yield are two sides of the same coin. If temperature increases the
conversion rate, which is what the XL model does shows, doesn't it
also mean that you are able to retrieve more biogas per kg of
digestate. Which in my mind is an increase in yield. I am aware that
at a given temperature the only way to increase yield is with loading
rate and retention time. 

 I am however looking at the difference between the gas yield at
ambient operating temperatures (ca. 20 degrees) and at the mesophilic
range. What I've understood form quite a few research papers is that
the yield and coversion rate wil increase. 

 I think that possibly my understanding in the difference of Yield and
conversion rate my not be completly correct. 

 Regards. 

 Bram ter Heegde
 NAW: 258757
 Mob. Tel: 0653134337

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