G'day All,
In the discussion below I see the term TS (Total Solids) used, and it is important to remember that flour and sugar TS will be almost 100% VS (Volatile Solids) and equate to very high COD per kg. It is VS/COD that is available as substrate for anaerobic digestion, so when comparing other substrates we really need a VS figure (or VS as % of TS) as a measure of digestibility - manure VS is about 10% of TS so there will be huge differences. I also noticed in an earlier post the comment about methanogens being present in our digestive tract (I agree that they are), but why? I think it has been suggested they balance the H+ and H2 system so our digestive system can operate (so they may be "good" bugs) but it may also be that we provide an environment for their survival so they compete for nutrients. I know CSIRO have done work on reducing methane emissions from cattle so I will try to follow that up and I will also ask a gastroenterology colleague here as well, but comments are welcome. Happy digesting, HOOROO Mr. Paul Harris, Room S116b, Waite Main Building Faculty of Sciences, The University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph : +61 8 8303 7880 Fax : +61 8 8303 4386 <mailto:[email protected]> mailto:[email protected] <http://www.adelaide.edu.au/directory/paul.harris> http://www.adelaide.edu.au/directory/paul.harris CRICOS Provider Number 00123M This email message is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient please notify the sender by reply email and immediately delete this email. Use, disclosure or reproduction of this email by anyone other than the intended recipient(s) is strictly prohibited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. From: [email protected] [mailto:[email protected]] On Behalf Of Alexander Eaton Sent: Friday, 8 October 2010 3:30 AM To: For Discussion of Anaerobic Digestion Subject: Re: [Digestion] Attachment to previous Article - More scientific based research and questions Thanks All for the background documents. These are extremely useful. Best, A On Thu, Oct 7, 2010 at 7:56 AM, David Fulford <[email protected]> wrote: Hello Alex and Listers, The best independent papers on the ARTI system are by EAWAG (www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_swm / <http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publicati ons_swm/index_EN#owm> ) who have also looked at the digestion of food residues from markets in Kerala, South India. While food residues have an average TS of 50% or less, Dr Karve bases his results on starch residues (e.g. flour dropped on the floor from milling). Suich residues have a TS of almost 100%. This means that we need to consider his gas production results as per kg total solids, rather than per kg of wet material. As the assessor from Ashden Awards who visited ARTI in 2006 (see www.ashdenawards.org/winners/arti06), I had to evaluate Dr Karve's statements.and his technology. The biogas plant uses simple cylindrical drums, so there is nothing special about the design. The major difference is the use of food residues rather than dung as the feed material. Since an animal has used as much of the input energy in the food as it can before it evacuates the rest, the gas production from undigested food is likely to be much higher than that from dung. Processed food (flour, sugar and cooked food) is likely to have a higher gas output than raw food, as much more of the material is accessible to the microbes. There are several other biogas projects in India using food residues as feed material, that started at about the same time as the ARTI one. I have visited the first Biotech Ltd project in Kerala (www.ashdenawards.org/winners/biotech) about which the EAWAG report was written and another in Mumbai called the Nisargruna system developed by BARC (see www.green-ensys.org/site/Biogas_Plant.html), which uses a two-stage digestor design. Looking at the basic thermodynamics of the process, it seems quite feasible to generate 1 kWh of electrical energy from 1 kg of starch, as Dr Karve suggests, although it does suggest a very high efficiency for the conversion of starch to biogas. However, in practice, a 1 cu.m ARTI biogas plant is too small to run an ic engine, as small ic engines are not very efficient. Regards, David Fulford
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