[Digestion] 5000 dairy cow AD system

Mon Jan 9 09:43:29 CST 2012

I concur on Paul's preference for smaller systems.  I have seen a handful
of proposals based on trucking waste from a number of small to medium farms
where they have tried to show energy balance (all the trucks are methane
powered, etc.), but the numbers never add up.  Specifically, de-watering
this waste requires relatively well developed systems at each site, and
likely still leaves you with a serious amount of waste water treatment for
each site to achieve healthy discharge levels (in Mexico it is the water,
not the solids that is the treatment challenge).  The management system is
also more complex and requires a high level of coordination.  The
alternative de-centralized option will likely have similar initial capital
costs, but you can make a better case for farmer investment as they will
reap the benefits.  You then have much smaller long-term operating costs,
and all that energy for trucking can go to good use (or maybe still
trucking some effluent fertilizer to local fields).  As Paul mentioned, the
option to eventually pipe gas a larger distance for centralized use is an
option that may make sense (but I have not seen it outside of the European
context or large landfill gas context yet).

Cheers

A

On Sun, Jan 8, 2012 at 10:51 PM, Paul Harris <paul.harris at adelaide.edu.au>wrote:

>  G’day Rex,****
>
> ** **
>
> Apparently a lot of the biogas comes from the fines/solutes in the liquid
> – I noticed that with piggery effluent the raw effluent was almost
> impermeable to water (it would hold puddles for quite a while) but after
> treatment the solids were pretty free draining (water disappeared in
> minutes).****
>
> ** **
>
> I will also raise my usual point in favour of distributed systems – why
> not put smaller (cheaper!) digesters at each farm and if necessary pipe the
> biogas to a central generator (depending on distance)? You will be spending
> a lot of energy on trucking waste in and then you have to truck the
> digestate out from the central facility again. The total capital cost may
> be higher, with more units to maintain, but you can start with one or two
> and spread the finances out a bit as well as helping local employment (I
> guess people will be working on digesters instead of driving trucks!).****
>
> ** **
>
> Happy digesting,****
>
> HOOROO****
>
> -- ****
>
> Mr. Paul Harris, Room 202, Charles Hawker 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:paul.harris at adelaide.edu.au <paul.harris at adelaide.edu.au>****
>
> http://www.adelaide.edu.au/directory/paul.harris****
>
> ** **
>
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> *From:* digestion-bounces at lists.bioenergylists.org [mailto:
> digestion-bounces at lists.bioenergylists.org] *On Behalf Of *REX
> *Sent:* Sunday, 8 January 2012 5:26 PM
> *To:* digestion at lists.bioenergylists.org
> *Subject:* [Digestion] 5000 dairy cow AD system****
>
> ** **
>
> Hi All,****
>
>  ****
>
> I have been approached to put together a proposal for a centralised AD
> using the manure from 5000 dairy cows. The intention is to pre-concentrate
> the dairy manure slurry and to truck the solids to a central processing
> unit. As silage and grass is extensively used as feed, we would be able to
> co-digest this with the manure to increase the gas output. Furthermore, it
> is intended to use the exhaust gas and the AD liquor to grow macro algae or
> a plant such as hyacinth (an indigenous variety that is not likely to
> become an invader should it get out) which can be shredded and added back
> to digestion. We aim to use the gas for power generation and to use the
> heat to keep the digester(s) warm.****
>
>  ****
>
> Questions:****
>
> 1. By leaving the water behind, do we lose most/all/some of the FFA? What
> impact would it have on gas production?****
>
> 2. Can anyone recommend a supplier of technology for this size of plant?**
> **
>
> 3. 5000 cows is an arbitrary amount at this stage - 10 farms of 500 cows
> each. Is there a better/more economical size?****
>
>  ****
>
> Kind regards****
>
> Rex Zietsman****
>
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>
>
>

-- 
Alexander Eaton
Sistema Biobolsa
IRRI-Mexico
RedBioLAC

Mex cel: (55) 11522786
US cel: 970 275 4505

alex at irrimexico.org
alex at sistemabiobolsa.com

sistemabiobolsa.com
www.irrimexico.org
www.redbiolac.org
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