Homestead mailing list

[Rob <becida AT comcast.net>]

Return-Path: <bounce-homestead-227727 AT listserv.unc.edu>
From: "tvoivozhd" <tvoivozd AT infi.net>
To: "Homestead mailing list" <homestead AT listserv.unc.edu>
Subject: Re: Biodigesters for methane
Date: Sat, 12 Jan 2002 22:31:54 -0800
X-MSMail-Priority: Normal
X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4807.1700
Reply-To: "Homestead mailing list" <homestead AT listserv.unc.edu>


----- Original Message -----
From: "Logan VanLeigh" <loganv AT earthlink.net>
To: "Homestead mailing list" <homestead AT listserv.unc.edu>
Sent: Saturday, January 12, 2002 8:12 AM
Subject: Re: Biodigesters for methane


> Please note that research has shown that humanure alone is deficient in
> nitrogen for good methane production.  Check Journey to Forever's web
> site for _lots_ of details.
>
> Logan

tvoivozhd---no it isn't---like all manures it has an excess of nitrogen and
all are handled exactly the same way---in making compost, layered between
layers of carbonaceous materials, in a biodigester carbonaceous materials
are added in the same way to achieve anything from 20-1 to 30-1 C/N as an
adequate operating range.  Beyond that the reaction will either be
nitrogen-limited or carbon-limited, either will inhibit production of
methane.

In a biodigester it is desirable to have between 7 and 9 percent solids, so
the manure is watered down to produce a slurry with this percentage to give
anaerobic bactera a favorable medium in which to work.



The reaction is also temperature-limited, works best around 95 degrees F.

Different manures have different amounts of nitrogen and carbon---see the
lists below for comparison.



Biochemical Sources of Fuels
By John D. Keenan, Assistant Professor of Civil and Urban Engineering,
University of Pennsylvania, Philadelphia, Pa.

>From Considine, Douglas M. (Ed-in-Ch): Energy Technology Handbook
(McGraw-Hill, 1977)

Methane Fermentation
Methane and carbon dioxide are the primary gaseous end products of the
anaerobic digestion process which has been widely used for many years in the
stabilization of organic sewage solids. The quality of the digester
off-gases is dependent upon feed composition. Mixed feeds normally yield
approximately 65 percent methane and 35 percent carbon dioxide.
Approximately equal volumes arise from carbohydrates, and the methane yield
increases with proteins and lipids. In addition, the product gases contain
small volumes of hydrogen sulfide and nitrogen.

The generation of methane occurs as the last step of a series of biochemical
reactions. The reactions are divided into three groups, each mediated by
heterogeneous assemblages of microorganisms, primarily bacteria. A complex
feed, consisting of high-molecular-weight bipolymers, such as carbohydrates,
fats, and proteins, undergoes exocellular enzymatic hydrolysis as the first
step. The hydrolytic end products are the respective monomers (or other
low-molecular-weight residues), such as sugars, fatty acids, and amino
acids. These low-molecular-weight residues are taken up by the bacterial
cell before further metabolic digestion.

The second step is acid production in which the products of hydrolysis are
metabolized to various volatile organic fatty acids. The predominant fatty
acids are acetic and propionic acids. Other low-molecular-weight acids, such
as formic, butyric and valeric acid, have been observed. Additional end
products of the acid production step include lower alcohols and aldehydes,
ammonia, hydrogen sulfide, hydrogen, and carbon dioxide.

The products of the acid generation step are metabolized by the
methane-producing bacteria to yield carbon dioxide and methane, and, in
addition, methane arises from metabolic reactions involving hydrogen and
carbon dioxide. The current understanding of the biochemistry and kinetics
of the methane fermentation is summarized in Refs. 20 and 21.

Anaerobic digestion of organic solids wastes has been investigated as an
alternative methane source. Various cost estimates have been made which
indicate production costs, including gas purification and compression, in
the range of $0.40 to $2.00 per million Btu. The major cost items, and
sources of variability in the estimates, are the digester capital costs,
waste sludge disposal cost, and the credit or debit associated with the
collection and preparation of the solid waste feed material. Multiple
staging and separate optimization of anaerobic digestion may provide reduced
capital costs through lower detention times and reduced operation and
maintenance costs by improved process stability.


http://www.cbc-canada.com/grow/nutrientorg.html  (Organic nutrient chart,
manures excluding human and pig)

http://res2.agr.ca/initiatives/manurenet/en/facts.html  (charts, including
human manure comparison to other animals---assuming the human weighs 83
kilograms)

http://www.inform.umd.edu/EdRes/Topic/AgrEnv/ndd/watermgt/GENERATING_METHANE
_GAS_FROM_MANURE.html  (more charts, data, small and large version of
biodigester, how much gas manure from one animal will produce per day.  Note
one error---near beginning says 950 degrees is a good temperature for
biodigester, that should obviously be 95 degrees F.

http://www.cseindia.org/html/dte/gobertimes/mar2000/gtimes_cov2.htm
The ever-increasing cost of the conventional sources of energy has led to a
search for alternative sources, that can provide cheaper power. Human
excreta is one such source. Anaerobic digestion of human excreta produces
biogas and also reduces pathogens in the excreta and yields manure that is
quite safe to handle. Production of biogas from human excreta has been tried
successfully at a number of places in India by Gandhians like Bindeshwar
Pathak of Sulabh International and Anna Hazare of Ralegansidhi in
Maharashtra.

Biogas can be used directly for cooking and lighting or indirectly through
production of electricity by running dual-fuel engine operated generators.

Difficult to accept? Well, even Anna had a tough time convincing his own
village. He first had the biogas plant built next to a temple and then ate
rotis cooked on it for a whole year to convince people that it was alright
to do so!

Biogas technology based on human excreta may not be economically viable on
its own as an alternative to other energy sources, but it may become so if
it is integrated with the excreta disposal system. This process should,
therefore, be evaluated keeping in view its contribution towards hygienic
excreta disposal, biogas production and fertiliser production.

Sulabh International has prepared a design on the basis of the research and
development on nightsoil based biogas plants. Since a nightsoil based Biogas
plant can operate economically only with a sizable quantity of nightsoil,
these plants are being provided only at the public toilets where a large
number of users come everyday. The Biogas produced entirely from human
excreta has a higher percentage of hydrogen sulphide than the Biogas
produced from cattle excreta. This is due to the presence of higher
percentage of crude proteins and fats (lipids) and a low C/N ratio in human
excreta.

Construction of sewage treatment plants is now being undertaken in cities
like Delhi and Hyderabad.

Assuming that the capacity of a plant is to process 25 million gallons per
day (MGD), it is estimated that about 3000 cubic metres of methane and
carbon dioxide will be formed everyday. But, even then, about 50 MGD of
sewage will remain untreated even after the commissioning of the plant.

In the plant, sewage first passes through screen chambers that filter out
big particles. In the next stage, sand and other minor particles are
removed. The sewage then enters the settling tanks where the sludge (slushy
sediment) settles at the bottom. The sludge is then pumped into 3 digesters
and kept here for about 20-28 days, where, due to an anaerobic process,
methane and carbon dioxide are formed. The gas thus formed is transferred to
'gas holders' while the sludge is passed on to drying beds where it
solidifies. This solid residue is high quality organic manure. The gas may
be supplied through pipelines or in cylinders like those used for LPG.




http://www3.gtz.de/gate/techinfo/biogas/toc.html  (comprehensive index of
biogas data)

http://www3.gtz.de/gate/techinfo/biogas/appldev/planning/substrate.html#HUME
X  Humanure works fine in millions of Chinese and Indian biodigesters, for
individual households, for villages and for cities.  Where the quantity is
insufficient, it merely requires supplement from other animal manures and/or
nitrogen-carbon compounds.)  Human manure should be handled with
common-sense precautions in the same manner as pig manure, to avoid spread
of disease.  Human manure has 5-7 percent N, 5-10 percent C.  A somewhat
less efficient digestive system of a pig results in manure containing 3.1 N,
14 C.  Cow manure contains 2.4 N, 19 C.  All of the above are modified
somewhat by variations in diet, and all are handled in exactly the same way,
adding carbonaceous material in a biodigester if you want methane, in a
compost pile if you want compost.  Every household and everything but a
factory farm has a hell of a lot more carbonaceous materials than materials
containing principally nitrogen.  See the list
http://www.weblife.org/huHumanure 5-7 5-10 manure/chapter3_7.html

Human excrements
In most cultures, handling human excrement is loaded with taboos. Thus, if
night soil is to be used in a biogas system, the toilets in question should
drain directly into the system so that the night soil is fermented without
pretreatment. The amount of water accompanying the night soil should be
minimized by ensuring that no water taps or other external sources drain
into the toilet bowls, and cleaning/flushing should be limited to rinsing
out with about 0.5 - 1 liter water from a bowl. Western-style flush tanks
should not be used in connection with small-

http://shell.world-net.co.nz/~sphil/HomeMethane.html  (states human manure
same as cow manure---not probable but the difference is more quantity than
quality.  Site also discusses biodigester temperatures, making and using a
simple 55 gallon drum digester for batch process---have to modify it a lot
for continuous output.  Also vegetation can be used with some
caution---primarily not to create tough floating scum that impedes flow of
methane)  Some interesting statistics on one pound of cow manure producing
enough gas for cooking a meal for four people, the gasoline energy
equivalent in one year, etc.

http://cluster.energyguide.com/esu/textpage.asp?bid=nyserda&page=40
Methane can also be produced through "biodigestion" of manure or human
waste. Most often seen in less developed nations, these small-scale methane
production systems often turn manure into methane that can be burned as
cooking fuel or used to generate electricity for lighting in rural villages.


http://www.artrans.com/rmsg/fuel/methane.htm   (source of eight paragraphs
below, and a seller of more methane books)

The Potential of Thermophilic Anaerobic Fermentation for Biological Methane
Production and Odor Control Using Swine Manure as a Substrate The potential
for biological methane production from swine manure, under thermophilic
(50°C) conditions, and the impact of the process on odor parameters was
investigated in the laboratory. A methanogenic culture was systematically
enriched from a variety of environments including swine manure, primary
treatment lagoon sediment and rumen fluid. The culture was successful in
producing a biogas yield of approximately 300 l/kg VS fed. The methane
fraction of biogas produced exceeded 60% and biogas yields were consistently
stable.

Methanol General info from the Alternative Fuels Data Center

AgSTAR This site houses information regarding one of EPA's joint voluntary
programs. AgSTAR is designed to assist farmers and anyone else with large
volumes of animal waste to explore anaerobic digestion as a low-cost way of
reducing disposal costs, eliminating environmental liabilities while
poroducing heat and power for their operation. EPA has other methane
outreach programs that can be accessed from this page. Take a look.

PRACTICALLY GREEN An environmental consultant firm in Magherafelt, Northern
Ireland (the County of Londonderry) that specializes in "research,
consultancy and engineering to convert organic wastes into biogas ,
electricity and hot water (Co-generation of Heat and Power CHP), compost and
liquid fertiliser." The headquarters of the firm is situated in a building
designed to have minimal energy requirements after construction, and which
used as much recycled materials, in the process, as possible. Practically
Green specializes in anaerobic digesters for "sour gas" - gas that has a
higher hydrogen sulphate content.

"Methane Digesters" Huge and highly informative article on building, running
& maintaining a methane digester for biogas production. See also, below, the
downloadable file which, I assume, includes this article and the appropriate
illustrations and designs.

"The Methane Digester" Downloadable file. I assume this has plans &
illustrations as well as instructional text. See above for text only
article.

Whipple - Methane Production From Dave Paxton's BioGas Series

http://www.webconx.com/2000/biofuel/methane.htm   (early work by Ram Bux
Singh established biodigestor parameters---modify the fuel if need be to
maintain 30-1 carbon, nitrogen ratio to keep the reaction going.

The C:N ratio for optimal biological activity is about 25:1, with higher
values being nitrogen limited and lower values being carbon limited.

PERCENTAGE OF SOLIDS

The anaerobic decay of organic matter proceeds best if the raw material
consists of about 7 to 9 percent solids. Fresh cow manure can be brought
down to approximately this consistency by diluting it with an equal amount
of water.

http://www.energyideas.org/energy_solutions/res_details.cfm?resourceID=1868&;
keyword=biomass  (lo-o-o-ng list of bioenergy links)

Cow dung slurry is composed of 1.8-2.4% nitrogen (N), 1.0-1.2/a phosphorus
(P2O5), 0.6-0.8% potassium (K2O) and from 50-75% organic humus.



Gobar gas may be improved by filtering it through limewater (to remove
carbon dioxide), iron filings (to absorb corrosive hydrogen sulphide) and
calcium chloride (to extract water vapor