<html><head><title>Re: [Digestion] Biogas production</title>
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<span style=" font-family:'Verdana'; font-size: 9pt;">Hello Kyle,<br>
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The reason for your low gas production is that you are running it at 19˚C. The rule of thumb is that gas production reduces by half for every 10˚C reduction from 35˚C, between 16 and 35˚C. The process can roughly be modelled by the Arrhrenius equation (see my book) which relates chemical activity to temperature. <br>
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When I worked in Nepal, many years ago, a Swiss project had a biogas plant fed by dung from several pigs. The pigs became infected, so they were all fed with antibiotics, and the plant stopped working. However, low concentrations of antibiotics will be digested as biomass. Usually if antibiotics are used to treat cattle, the levels will be designed to be lower than that required to kill the microbes in the gut, otherwise the cattle will not be able to digest food. If a cow gets a bad enough infection to require high levels of antibiotics, it is normally isolated from the herd, so its dung can be kept separate. <br>
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<span style=" font-size: 8pt; color: #31652c;"><i>-- <br>
Best regards,<br>
David<br>
</i></span></span><a style=" font-family:'verdana';" href="mailto:davidf@kingdombio.com">mailto:davidf@kingdombio.com</a><br>
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<span style=" font-family:'verdana'; color: #31652c;"><i>Wednesday, November 14, 2012, 1:06:33 AM, you wrote:<br>
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<td width=865><span style=" font-family:'verdana'; font-size: 9pt;">Good day Kyle,<br>
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We have been running digesters using cow dung as feed stock for the last ten years. On an average, we are getting 1 m3 of biogas from 15 to 20 kgs of cow dung. The cows are grazing outside no concentrates were given. If we add cow urine to the dung the biogas increase at least by 25%. The urine quantity is roughly 30% of the feedstock. The dilution of cow dung and water is 1:1.<br>
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Our digesters are built for 45 days HRT and now we are reducing the HRT to 30 days.<br>
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Most of the intensive care cow farms are using antibiotics but I do not think the digesters are stopping or under performing. Of course, if the dose of antibiotics is quite high, perhaps it may effect the production.<br>
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Krishna.<br>
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On Tue, Nov 13, 2012 at 1:14 PM, Takamoto <</span><a style=" font-family:'verdana'; font-size: 9pt;" href="mailto:kyle@takamotobiogas.com">kyle@takamotobiogas.com</a><span style=" font-family:'verdana'; font-size: 9pt;">> wrote:<br>
Dear Biogas List,<br>
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I have been testing a plastic (LLDPE) floating drum digester with cow dung and found that the biogas production was lower than expected (pH 7, 19˚C) at around 0.5 cubic meters of biogas per day at 67% methane. The reactor volume is 3.2 cubic meters. I discovered that our dung supplier had recently used the antibiotic Tetracycline for a few of his cows so there is a chance of contamination, though at this point, I feel like the antibiotic concentration would be very low and should not affect gas production. Does anyone have experience with the effect of antibiotics? Also, what gas production should I expect from a 3.2 cubic meter reactor that I add 40 kg of cow dung to per day (plus 40 kg of water)? If I assume 15% TS and 80% of TS are VS then the Organic Loading Rate is around 1.5 kg -VS/m3/day and our specific methane yield is 0.07 m3 CH4/kg-VS and our digester efficiency is 0.1 m3 CH4/m3 reactor/day. Does this sound reasonable?<br>
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I have also been reviewing research articles on gas production from cow dung but the results vary widely and sometimes I am not sure if the reported results are accurate. Also, research papers often use CSTR (continuously stirred tank reactors?) at 37˚C which makes comparing their results to my results rather difficult. We are getting a new load of non-contaminated cow dung today to see if that makes a difference. I'll let you know.<br>
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I am sure this topic has been discussed before, so I am sorry if I have repeated the topic. I am newish to the forum so I haven't seen anything on this yet.<br>
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Thanks for your advice,<br>
<br>
<span style=" font-size: 14pt;">Kyle<br>
Managing Director<br>
Schutter Energy Ltd.<br>
</span></span><a style=" font-family:'verdana'; font-size: 14pt;" href="http://www.takamotobiogas.com">www.takamotobiogas.com</a><br>
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<span style=" font-family:'verdana'; font-size: 9pt;">for more information about digestion, see<br>
Beginner's Guide to Biogas<br>
</span><a style=" font-family:'verdana'; font-size: 9pt;" href="http://www.adelaide.edu.au/biogas/">http://www.adelaide.edu.au/biogas/</a><br>
<span style=" font-family:'verdana'; font-size: 9pt;">and the Biogas Wiki </span><a style=" font-family:'verdana'; font-size: 9pt;" href="http://biogas.wikispaces.com/">http://biogas.wikispaces.com/</a><br>
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<span style=" font-family:'verdana'; font-size: 9pt;">-- <br>
<span style=" font-family:'comic sans ms'; color: #000066;">Regards.<br>
<br>
Murali Krishna<br>
Chairman<br>
Hyderabad, Andhra Pradesh, India.<br>
Ph:+91-40-24339999, 24333333,243355555, 24333555<br>
</span></span><a style=" color: #000066; font-family:'comic sans ms'; font-size: 9pt;" href="http://www.villagevisionindia.com">www.villagevisionindia.com</a><br>
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<span style=" font-family:'Verdana'; font-size: 9pt;"> ********************************************************************<br>
Dr David Fulford CEnv MEI, 15, Brandon Ave, Woodley, Reading RG5 4PU<br>
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