[Digestion] Biogas yields for tropical energy crops

Tue Sep 11 22:35:32 EDT 2007

Lou, 

There are crops such as sugar beets and sugar cane
that people in countries all over the world are wiping
out whole forests to plant in order to generate
electricity. It makes no ecological sense to raise
crops to make biogas. Biogas should ONLY be made from
crop and animal or human waste. I am a strong opponent
of agricultural-scale digesters for this reason.

It takes only the most cursory experiment with a
couple of small digesters to know that small,
well-stirred digesters with mixed contents will always
out-perform single feedstock digesters by volume. This
mixing is not possible with larger---over 100
cu.m.---digesters. 

Warren Weisman
USA

--- Lou Dobb <congoagriculture at yahoo.com> wrote:

> Warren, thanks so much for these data. They're a
> great help.
> 
> Meanwhile, I found the following on sugarcane, and
> it puts us in front of an interesting question, I
> think:
> 
> =====================
> English Title: Sugar cane (Saccharum sp.) juice
> energetic potential as substrate in UASB reactor.
> Personal Authors: Colen, F., Pasqual, A.
> Author Affiliation: Aluno do Programa de
> PÃ³s-GraduaÃ§Ã£o em Agronomia, Energia na
> Agricultura, FCA/UNESP, Botucatu/SP, Brazil.
> Document Title: Energia na Agricultura, 2003 (Vol.
> 18) (No. 4) 58-71
> 
>
http://www.cababstractsplus.org/google/abstract.asp?AcNo=20053101335
> 
> Abstract:
> 
> The energetic potential of sugarcane juice was
> studied in an upflow anaerobic sludge blanket
> reactor (UASB) of 7.78 litres useful volume, working
> at a temperature of 35Â°CÂ±1Â°C. Before being added
> to the reactor, the juice was naturally fermented
> for 24 hours, with addition of sodium bicarbonate,
> urea and diacid potassium phosphate [potassium
> dihydrogen phosphate?] to correct the pH (between
> 6.00 and 6.60) and carbon/nitrogen and
> carbon/phosphorus relations respectively. In the
> reactor, 3 hydraulic retention times (HRTs) were
> used: 20 days, 18.78 days and 15.30 days. For the
> HRT of 20 days, the affluent chemical oxygen demand
> (COD) was 260 304 mg.litre-1 and the effluent COD
> was 16 991.40 mg.litre-1, an efficiency of 93.47%.
> The gas volume was 136.33 m3 of biogas.m-3 of juice,
> its average composition including 72.43% methane.
> For the HRT of 18.78 days, the affluent COD was 272
> 779 mg.litre-1 and the effluent COD was 8612
> mg.litre-1, an efficiency of 96.84%. The gas volume
>  was 147.42 m3 of biogas.m-3 of juice, its average
> composition including 72.91% methane. For the HRT of
> 15.30 days, the COD was reduced by 71.49%. The gas
> volume was 103.58 m3 of biogas.m-3 of juice, with an
> average methane content of 63.30%. When calculating
> the energetic potential, the figures from the HRT of
> 18.78 days were used, and the amount of energy
> produced was found to be 2767.82 MJ (661.21 Mcal)
> per tonne of processed sugar cane. This value was
> extrapolated using the average Brazilian cane
> productivity (69.50 tonnes per hectare) to give a
> figure of 192.36 GJ (45.95 Gcal) per hectare;
> compared to anhydrous ethanol production, biogas
> production gave an efficiency 35.33% higher than
> that of ethanol. When the energy from sugarcane
> bagasse, which is used as energy for ethanol
> distillation, was included in the calculations, the
> energy output increased to 4738.30 MJ.t-1 of
> processed sugar cane, compared with 2045.27 MJ.t-1
> of ethanol, not considering the bagasse input
>  in distillation, and the amount of energy obtained
> using biogas increased to 131.67% more than the
> figure for ethanol.
> 
> Publisher: Faculdade de CiÃªncias
> Agrono~circumflex~micas, Universidade Estadual
> Paulista (UNESP)
> ===============
> 
> Apparently, digesting an entire sugarcane crop
> yields far more energy than converting it into
> ethanol, even if you take into account that bagasse
> is used as a power source for the ethanol plant. I
> assume that the same is true for such species as
> sorghum and other high yielding tropical grass
> crops.
> 
> Now why don't we see big biogas plants all over the
> developing world? Why ethanol when biogas would be
> so much more efficient? Are capital and O&M costs
> for anaerobic digesters so much higher than for
> ethanol plants? I don't think so. Is it because
> biogas cannot be transported as easily? 
> 
> Why isn't anyone digesting tropical grass species on
> a large scale to ship the biomethane out as an
> alternative to natural gas? CNG ships are already
> here, so this should be possible.
> 
> Why isn't anyone in the (tropical) developing world
> building dedicated biogas plants and energy
> plantations to fuel the poor's CNG-fleet? This must
> become a possibility, certainly in remote regions. 
> 
> I'm confused and very optimistic at the same time. 
> 
> Deducing a bit: 4750MJ per ton of sugarcane at 80
> ton/ha comes down to a spectacular 10,000 cubic
> meters of methane per hectare (worth US$ 2300 at
> current NG prices).
> 
> Common, with that much energy you can power all CNG
> cars/tricycles in a typical small village in the
> developing world for an entire year.
> 
> Am I missing something?
> 
> Yours, Lou
> 
> 
> [PS: sorry for sending this mail twice to you alone,
> Warren; forgot to check "reply to all"].
> 
> 
> 
> Warren Weisman <weiswar at yahoo.com> wrote: 
> I think there's so little and so much conflicting
> data
> is that digestion is not an exact science. A small,
> well-maintained digester can out-perform a big,
> fancy
> one. The second most important aspect of digestion,
> after an airtight environment, is the proper carbon
> to
> nitrogen ratio, which I did not see referred to in
> the
> article. 
> 
> Here's the volumes from "A Chinese Biogas Manual",
> which I consider the best source of information on
> digestion and biogas, since its empirical data
> gathered from making MILLIONS of digesters...
> 
> volumes are per tonne of material:
> 
> General Stable Manure 260-280 cu.m. gas  50-60% CH4
> Pig Manure 561 cu.m. gas  
> Horse Manure 200-300 cu.m. gas
> Rice husks  615 cu.m. gas
> Fresh grass   630 cu.m. gas   70% CH4
> Flax stalks or hemp   359 cu.m. gas  59% CH4
> Straw       342 cu.m. gas 59% CH4
> Leaves from trees   210-294 cu.m. gas   58% CH4
> Potato plant leaves & vine, etc.  260-280 cu.m.
> Sunflower leaves & stalks  300 cu.m. 58% CH4
> Sludge   640 cu.m.     50% CH4
> Waste water from wine or spirits making 300-600
> cu.m.
> 58% CH4
> 
> --- Lou Dobb  wrote:
> 
> > Hi all, I'm new to this mailing list. Thanks for
> the
> > very interesting resources and discussions. 
> > 
> > I have been trying to find some data on biogas
> > yields for tropical energy crops (such as
> sugarcane,
> > sweet sorghum, cassava, sweet potato, grass
> species,
> > tropical sugar beet, etc...). But I can't find
> much.
> > 
> > In my search I only found data on crops grown in
> > temperate and even cold climates (Finland). 
> > 
> > E.g. Annimari Lehtomï¿½ki: "Biogas production from
> > energy crops and crop residues", Jyvï¿½skylï¿½
> Studies
> > in Biological and Environmental Sciences 163, PhD
> > Dissertation, Faculty of Mathematics and Sciences,
> > University of Jyvï¿½skylï¿½, 2006.
> > 
> >
> http://dissertations.jyu.fi/studbiol/9513925595.pdf
> > 
> > Could anyone help me compile a list of yields for
> > tropical crops?
> > 
> > We could use the list for a wiki, as a basic
> > reference.
> > 
> > 
> > How come there are so little data on this? I don't
> > understand.
> > 
> > Best regards,
> > Lou
> > 
> >        
> > ---------------------------------
> > Boardwalk for $500? In 2007? Ha! 
> > Play Monopoly Here and Now (it's updated for
> today's
> > economy) at Yahoo! Games.
> > _______________________________________________
> > Digestion mailing list
> > Digestion at listserv.repp.org
> >
> 
=== message truncated ===

____________________________________________________________________________________
Moody friends. Drama queens. Your life? Nope! - their life, your story. Play Sims Stories at Yahoo! Games.
http://sims.yahoo.com/  