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  • From: "Greg and April" <gregandapril@earthlink.net>
  • To: "Healthy soil and sustainable growing" <livingontheland@lists.ibiblio.org>
  • Subject: Re: [Livingontheland] Biogas etc./ was Fertilizer use by crop in Brazil
  • Date: Fri, 28 Apr 2006 17:56:55 -0600

The carbon came from the wood chips.

When I was saying chips, I wasn't talking about chunks, but, something more along 1/2-3/4 inch max. Shreds might have been a better term.

You can look up the data that New Alchemy used ( they have 69 references, but I'll just give a few ):

Compost:

Poincelot R. 1972
The Biochemistry and Methodogy of Composting.
Connecticut Agriculture Experiment Station
Bulletin 727 March 1972
New Haven Conn

Digested Manure:

Hog:
Taiganides, Eliseos P. 1963
Characteristics and Treatment of Wastes from a Confinement Hog Production Unit
PhD dissertation, Iowa State Univ.
Science and Technology, Agriculture Engineering.
Available from University Microfilm Inc.
An Arbor Mich #63-5200 ( 177 pg )

Cow:
Hart, Samuel 1960
Sludge Digestion Tests of Livestock Manures
Dept. Agr. Engr. Univ. of Calif. Davis
Offprint manuscript.

The amount of methane generated is based on several factors including waste material used ( even manure from different animal types can vary the amount ), the temperature, the time in the unit, and even the amount of dissolved solids in the slurry ( since it's the dissolved solids that actually do the job ).


Costs to build units vary, with such things as the materials used. Smaller units can be built from scrap 55 gal barrels that can be had for free, if you know where to look. They can be made from concrete if that is your style and your budget I built one out of a 3 gal pickle jar, when in high school, just to see if it would work, using dog manure ( from when the neighbors dog would go in our yard ) and it did.


Some rough figures.
(from Methane Digesters for Fuel Gas and Fertilizer )

Cattle manure
100% 1.4 cu Ft ( per lb of Volatile Solids) 65% CH4

Chicken manure
100% 5 cu Ft 59%

Chicken manure /
paper pulp
31%/69% 7.8 cu Ft 60%

Chicken manure /
grass clippings
50%/50% 5.9 cu Ft 68%

( from Hand Book on Bio Gas and It's Applications )
4 cattle ( as we can see above they are not the best source ) and a 5 cu m ( 177 cu Ft ) gas unit, and retain for 50 days you will be producing 1.55 cu m of gas @ 20*C ( 54.7 cu Ft @ 68* F ) every day.

How long it takes to repay initial investment is highly dependant on the amount invested, and what the gas is worth to the person using it.

The digester built by John Fry ( that I mentioned a month or so ago ) on his hog farm ( average 1000 hogs ), cost him about $10,000 to build, and produced 8000 cu ft of bio gas a day ( 4,680 BTU's a day ). His figures showed that this was worth $7.57 a day in Santa Barbara Cal. in 1973, or $16,578 in 6 years just for the gas alone, and not for any fertilizer value. So his return of investment, was less than 6 years.

Another way to look at it:

Average cost per Hog to build: $10
Average amount of Bio gas per hog: 8 cu ft a day
Average number of BTU's per hog: 4.68 each day
Amount of liquid fertalizer: Approximately 500 gal every 3-4 days ( 125 - 170 gal / day ) - for an average of 1000 hogs.

As mentioned above, even as few as 4 cattle can produce 54 cu ft of bio gas each day, and used effectively, that is enough to provide supplemental CO2 and keep a green house warm on chilly nights.

It all comes down to how people apply the resources that are available. Let manure do nothing over fall and winter, or use it to heat a greenhouse in winter that might otherwise go unheated. What is the value of growing cool crops in the middle of winter in the green house? That is something that people will have to figure out and decide for themselves. Is there value in fresh out of season crops? If so how much?

Every week I meet people that say " I didn't know that " or " I thought you couldn't ... "

Personaly, I think the problem with digesters is, people don't try because they thought they couldn't .... Until more people do try, we will never know for sure.

Many people still think that cars can only run on something that comes out of the fuel pump at the gas station, and don't think that they can make it them selves, because that is what they are used to thinking ( not to mention brainwashing ).


Greg H.



----- Original Message ----- From: "TradingPostPaul" <tradingpost@riseup.net>
To: <livingontheland@lists.ibiblio.org>
Sent: Friday, April 28, 2006 13:21
Subject: [Livingontheland] Biogas etc./ was Fertilizer use by crop in Brazil



There is always some nitrogen loss, and the longer it waits before composting the more loss. Regardless of what a TV program claimed, frankly I doubt that any method can turn wood chips into actual finished compost in two months - unless they're shredded into finer particles first. Another thought: if much of the carbon compounds are removed in a biogas unit, how much of the carbon is left for the compost? We do want those carbon compounds in the soil too, don't we? I don't believe the New Alchemy people said what kind of "garden compost" they were comparing with the digested sludge. Without knowing the source and condition of the compost, the comparison isn't useful. And a dry sludge end product should certainly have a higher percentage of nutrients per ton than fresh manure, due to moisture loss. Pit composted manure would likely show the same nutrient increase per ton after drying.

One figure I haven't seen is how much usable methane can be produced from how many livestock, horses, cattle, etc. And how long it would take for a given biogas digester to repay it's initial cost, figuring in the labor involved. I suspect the low return is the reason we've never seen the numbers on payback. Manure digesters have been experimental for a long time, and from what I've seen they're always subsidized one way or another, much like ethanol. I'd like to see something showing it's practical for the small farmer in terms of investment and ongoing labor required.

paul, tradingpost@riseup.net
---------------
The outstanding scientific discovery of the twentieth century is not television, or radio, but rather the complexity of the land organism. Only those who know the most about it can appreciate how little we know about it.
- Aldo Leopold in Round River, 1933
*********** REPLY SEPARATOR ***********

On 4/28/2006 at 12:26 PM Greg and April wrote:

How do you figure that? How do you think that nitrogen is removed?

The nitrogen compounds stay with the liquid as ammonia mixes with the
water.

In fact IIRC, water will absorb gaseous ammonia, that is the concept
behind
the old "Icy Ball " and other ammonia / water absorption refrigerator
systems. Water in the first chamber absorbs gaseous ammonia, lowering
the
vapor pressure, then with the lower vapor pressure allows more liquid
ammonia to evaporate thus cooling the second chamber.

Most of the ammonia formed in a biogas unit, absorbs into the water/slurry
in the unit.


About 3 yrs ago, I saw a program on TV, about a bio gas unit, that
recovered
methane from manure, and the resulting liquid was still so rich in
nutrients
that they would shred aspen and mix the resulting chips with the liquid
and
compost it. A mound of aspen chips 30ft high would reduce to finished
compost in about 2 months. If the liquid was not rich in Nitrogen,
about
all that would happen is that it would fungus ( take a very long time to
break down ), not compost.


It is true, that if you leave manure out, exposed to the weather, it will
lose nitrogen through liquid evaporation and/or through leaching ( as seen
if a bale of hay is left out in the open ), but, in the case of a biogas
unit, the nutrient rich liquid is retained, and used elseware, after much
of
the carbon is removed, in the form of CO, CO2, CH4, you might lose a small
amount of nitrogen, but, that part that you may lose is but a fraction of
the total.


The New Alchemy Institute ( Methane Digesters for Fuel Gas and Fertilizer
)
calculates that garden compost has from 1.4 - 3.5 % ( dry weight )
nitrogen,
while digested cow manure sludge has from 2.7 - 4.9 % ( dry weight )
nitrogen and that jumps to 6.1 - 9.1% with digested hog manure.

The fact that digested sludge has higher amounts of nutrients than compost
( even compost made under cover so nutrients are not baked out by the sun
and leached out by the rain, is backed up by The National Institute of
Industrial Research ( India ).


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