[Digestion] Floating manure

Fri Sep 14 12:54:02 EDT 2007

Biogas people,

I am now wondering if carbonates is cementing the foam and stuff 
together? If you take some hard stuff and add acid to it will it fizz? 
and break apart?

Thanks
Frank

Duncan Martin wrote:

> Frank, that's a very good question - but I think based on a slight 
> misunderstanding.
>
> I suspect the problem is not that the reaction stops but that the 
> non-digestible fraction becomes concentrated in the floating layer, so 
> is never discharged from the digester and accumulates..
>
> Any digestible material entrained with it probably digests quite well, 
> though perhaps a little slower than in the well mixed zone. However, I 
> am not aware that there have been any studies done on this.
>
> Essentially the same problem arises with solids that settle on the 
> bottom or crystallise on the walls. This is why it is so important to 
> have a mixing system that mixes the whole digester.  As the digesting 
> material is usually a non -Newtonian fluid, it can adopt a stable 
> mixing pattern in which the zone around the agitator is well mixed 
> while the remainder is stagnant. This can happen even when the 
> feedstock is a relatively thin liquid.
>
> There was a case over 30 years ago in Yorkshire, England, involving a 
> pharmaceutical effluent where the performance of the digester 
> gradually deteriorated, over a period of years.  When they opened it 
> up, they found it was almost full of crystalline deposits, so the 
> effective capacity of the digester was reduced to only a small 
> fraction of its nominal size. There was a void around each of the 
> three side-entry agitators, linked to each other and to the feed and 
> discharge pipes by "rat-holes"! And that's all - the rest was crystals!
>
> Such situations rarely arise at lab scale, which can lull you into a 
> false confidence. At large scale, unconfined sequential gas injection 
> is much more effective at avoiding such situations than gas injection 
> into a draft tube or agitator-based systems, because there is "no 
> hiding place" for deposits of any kind.
>
> The mechanism of flotation probaly isn't primarily large bubbles of 
> gas getting caught under lumps, as you describe it. It is more likely 
> to be the attachment of multiple microbubbles to small particles, 
> which then cohere to form a crust when concentrated near the surface. 
> This principle is widely applied in a number of industries, including 
> mineral processing and effluent treatment, to separate fine particles 
> from a dilute slurry.
>
> Best regards
>
> Duncan J Martin
>
> Chair
> Republic of Ireland Centre
> Chartered Institution of Wastes Management
>
> ================================
> CONTACT DETAILS
> Duncan J Martin, PhD, CEng, CSci, MIEI, MCIWM, MIChemE
> 24 Townsfield, Cloughjordan, N Tipperary, Ireland
> Mobile: +353 86 8377 906
> Home: +353 505 42087
> Email: duncanjmartin at eircom.net
> ================================
>
>
>
>
>
>
> ----- Original Message ----- From: "frank" <frank at compostlab.com>
> Cc: <digestion at listserv.repp.org>
> Sent: Thursday, September 13, 2007 5:02 PM
> Subject: Re: [Digestion] Floating manure
>
>
>> Biogas people
>> I assume the floating manure is methane getting caught under it and it
>> floats to the top? But why does this stop the reaction, production, of
>> methane? It should still be wet and under anaerobic conditions.
>>
>> Thanks
>> Frank
>>
>>
>>
>> Jaime Marti Herrero wrote:
>>
>>>> I haven't worked with cattle manure much. It seems to> float and 
>>>> form a heavy crust that interrupts gas flow.
>>>>
>>>>
>>>
>>> i rescue a mail i sent weeks ago about this subjet:
>>>
>>> Hi everybody.In the last moths im meeting people who is installing 
>>> tubular biodigesters and they are using 1:2 manure:water rate to 
>>> feed the biodigesters. From five years ago i started using 1:4 rate 
>>> (recomended by Lylian Rodriguez and Preston), but from two years ago 
>>> im using 1:3 because the in some places the are not that much water 
>>> for 1:4.the reason tu use 1:3 or 1:4 is to avoid the formation of 
>>> the foam that stop the production of biogas. But if really you can 
>>> work wiyh a lower rate (1:2) without problems with the foam, this 
>>> will be a great issue, because the volume required wil be lower and 
>>> the cost os materials and biodigester as well.So please, have you 
>>> got good expiriences with low rate manuere:water for long time with 
>>> out foam?thanks everybodywe keep in contactjaime> Date: Wed, 12 Sep 
>>> 2007 19:52:41 -0700> From: weiswar at yahoo.com> To: 
>>> Digestion at listserv.repp.org> Subject: [Digestion] Floating manure> > 
>>> > > > Do large digesters just add more water? > > My thinking w!
>>
>> as to weight it down with a steel screen.> Thoughts? > > > > 
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>>
>> -- 
>> Frank Shields
>> Soil Control Lab
>> 42 Hangar way
>> Watsonville, CA  95076
>> (831) 724-5422 tel
>> (831) 724-3188 fax
>> frank at compostlab.com
>> www.compostlab.com
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>

-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com