[Digestion] Separating out the solids.

Ken Calvert renertech at xtra.co.nz
Mon Mar 10 18:01:09 CDT 2008 

Rex, Hi! Thanks for the reminder, sorry I didn't pick you first time round.
   Sorry also to say somethings gone wrong on my website www.coffee.20m.com 
and the four brochures on Farmers biogas plants won't load.
However I can describe.  My suggestion is to sink a small open topped tank 
in the ground beside your digester.  Our farmers use these to
load solid silage into their digesters by running out a few hundred litres 
of  digestate back down into them, adding a FEL bucket of silage and  mixing 
it into a slurry with a manure chopper pump before pumping it all back into 
the digester.  In this way thay can build up the solids to around 20%, and 
that is more like toothpaste squeezing out of a tube than anything else. 
New Chums start getting all upset that pumping into an open tank is putting 
oxygen into the digester  but its not that way at all.  The digestate comes 
out foaming gas, but it is pretty much all CO2. Its the CO2 that stays 
dissolved in the water in the bottom of the digester.  The CH4 is not nearly 
so soluble, and stays up in the headspace.   So, by having the tank low down 
there is a blanket of CO2  over the slop.  Just don't fall in the tank, even 
when it is empty.  I guess the OSH inspecters would go bananas if they 
realised what was happening.  Probably good to have an old vacuum cleaner 
around to flush it out with clean air after use.  Actually if you are 
pumping  liquid in you don't need an open top. Have a grill over it.
Anyway.  what I am suggesting is that you operate your membrane down in such 
a tank and then remove the solids and  pump back the liquid. Howzat!
Ken C.

----- Original Message ----- 
From: "Zietsman, Rex" <Rex at Process.co.za>
To: "Ken Calvert" <renertech at xtra.co.nz>
Cc: <finstein at envsci.rutgers.edu>
Sent: Monday, March 10, 2008 11:45 PM
Subject: RE: [Digestion] Digester for Algae waste


Part of what I want to do in this particular digester is to make is
multi-feed. I also have cow manure, cut grass, wetland plants and dam
plants that will be fed into this lot. This makes UASB a bit more
complicated. I am sorely tempted to install a membrane to keep the
solids in the reactor and only let the liquid out. That should increase
my SRT while having a low HRT, much like the UASB. As I want to compress
the biogas anyway, I could bring some of it back after the first stage
of compression and use that instead to agitate the membrane - they are
usually agitated with air which is not appropriate in an AD. I suppose I
could even use a small Roots type blower for the agitation.

What bothers me about this route is how do I get the solids out? They
need to come out eventually. Any ideas?

Kind regards
Rex

-----Original Message-----
From: Ken Calvert [mailto:renertech at xtra.co.nz]
Sent: 04 March 2008 11:36 PM
To: Zietsman, Rex
Subject: Re: [Digestion] Digester for Algae waste

Rex, as you will see from my website, I have had a bit of experience
with
digesting both coffee wastewater and
ensiled farmyard grass and wastes.  Using UASB, you wouldn't need to
worry
about the high water content.
We could process coffee waste waters in 24 hours, and consequently put
through high volumes.  I would think that your biggest   problem would
be to
kill the algae and disrupt cell contents  so that fermentation could
take
place.  Its the same with water hyacinth. You have to get down to
soluble
acetates before it goes into the digester to get a reasonably short
retention time.
I would be most interested to look at your design and comment.
Sincerely,  Ken Calvert.
www.coffee.20m.com


----- Original Message ----- 
From: "frank" <frank at compostlab.com>
To: "Zietsman, Rex" <Rex at Process.co.za>
Cc: <digestion at listserv.repp.org>
Sent: Wednesday, March 05, 2008 7:02 AM
Subject: Re: [Digestion] Digester for Algae waste


> Hi Rex and all,
>
> Perhaps Water Hyacinth is different than what you plan to do but it
sure
> grows fast. I battled a canoe to the center of a lake to collect a
> square meter of the stuff to calculate how much was there and try to
> find something to do with it. incase it helps......
> A square yard of material was ~58 lbs wet wt. Back at the lab it dried
> to nothing (93.9 % moisture) so you will have a lot of moisture to
> remove. Ash is 10.8 % on a dry basis so the organic matter is 89.2 %
dry
> weight. Nitrogen was 1.0 % dry wt.
> On a feed analysis (dry wt) the Crude protein is 6.8%
> Crude fat  0.4%
> Crude fiber 19%
>
> Should be a fun experiment to do.
>
> Frank
>
>
>
>
> Zietsman, Rex wrote:
>
>>Hi All,
>>
>>I am building a small algae raceway to see what kind of production I
can
>>get. I intend fermenting the algae and distilling off the ethanol
prior
>>adding the residue to an AD. The biogas will be used for heating the
>>still to get off the ethanol. The digestate will be added back to the
>>algae pond as nutrient. I also intend adding cow manure to the AD as
an
>>additional source of nutrients.
>>
>>I have my own design of this digester and would appreciate it if
anyone
>>on the list would be willing to give me feedback on the design. We are
>>about to start clearing the site to build the digester and I want a
last
>>review before committing.
>>
>>Kind regards
>>Rex
>>
>>_______________________________________________
>>Digestion mailing list
>>Digestion at listserv.repp.org
>>http://listserv.repp.org/mailman/listinfo/digestion_listserv.repp.org
>>Beginner's Guide to Biogas
>>http://www.adelaide.edu.au/biogas/
>>http://info.bioenergylists.org
>>
>>
>>
>>
>
> -- 
> 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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> Beginner's Guide to Biogas
> http://www.adelaide.edu.au/biogas/
> http://info.bioenergylists.org
>
>
>
>
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