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Improving cold season biogas digester efficiency for global energy solutions by Katey Walter Anthony and T.H. Culhane, Report Description:
PROJECT SUMMARY
Energy is a high cost, imported commodity to most communities. Biogas digester
systems, which take organic material into an air-tight tank, where microbes break down the
material under anaerobic conditions and release methane-rich biogas, may offer an alternative
energy solution. Biogas can be burned as a fuel for cooking, heating, generating electricity and
powering lights; and the liquid effluent can be used as organic compost. While small-scale
biogas digesters are being used by thousands of households in India, Egypt, Costa Rica, and
other warm-climate countries, seasonal limitation to biogas production is experienced in colder
climates due to the shut-down of mesophilic (warm loving) microbial communities in winter.
This project set out to improve the efficiency of biogas digesters under cold climate regimes by
inoculating digesters with active-methane-producing psychrophiles (cold-tolerant microbes)
readily available in Alaskan thermokarst (thawing permafrost) lake mud and the natural mud in
ecosystems of other regions characterized by seasonally cold temperatures. Psychrophilic
methanogens, despite a temperature optimum of 25°C, still actively produce methane year-round
at temperatures as low as 0°C in Alaska, unlike conventional microbes.
5
The objectives of this project were to:
● Improve the efficiency of existing small-scale methane biogas digesters, including by
using cold-adapted microbes to increase cold-season biogas production
● Produce a renewable and alternative fuel
● Reduce the release of harmful greenhouse gasses
● Implement dwelling-size and community-scale applications to evaluate their acceptance
and sustainability for widespread application in the United States, Germany, Egypt, and
other locations
● Test the technology to help fight deforestation in Africa by using biogas to replace
firewood
This project was carried out in three phases. Phase I and II were accomplished through
collaboration with a Denali Emerging Energy Technology Grant obtained by PI K. Walter
Anthony; results were previously reported to the Denali Commission Alaska. In Phase I, we used
an experimental approach to compare biogas production rates from psychrophilic (lake mud) vs.
mesophilic (manure) microbial consortia in six small, 1000-L household scale digesters under
two relatively cold temperature regimes (150C and 250C) in Cordova, Alaska. Phase II research
focused on the utilization (the capture, compression, analysis and usage) of biogas produced
during the project and assessment of this technology for widespread application in cold-climate
boreal and arctic communities. Phase III involved implementing knowledge gained from
experiments in Alaska in other regions of the world where utilization of cold-adapted microbes
could improve biogas efficiency during cold seasons.
In Phase I, we found that digesters containing psychrophiles were more robust to
temperature and pH fluctuations. Among our experimental digesters, tanks containing
psychrophile-rich lake mud produced more biogas (275 ± 82 L gas d-1
deviation) than tanks inoculated with only mesophile-rich manure (173 ± 82 L gas d-1
digester temperature appeared to be the overarching control over biogas production among all
tanks. Extrapolating the linear relationship between biogas production and mean digester
temperature observed among our study tanks [Production (L gas d-1
432] to the temperatures typically used for biogas production in warmer climates (35-400C), it is
possible that our digesters would have produced 770-940 L gas d-1
for warm climate digesters. Without knowing the temperature response from the microbial
communities in our specific digesters, it is not possible to extrapolate these results with a high
level of certainty; however, we can conclude that psychrophile-rich lake mud is a viable source
of microbial inoculums for producing biogas at cold temperatures, albeit at only 28-56% of rates
typical of warmer temperature regimes. Other benefits of the psychrophile-rich lake mud
digesters included reduction of foul odor and a source of nutrient-rich, liquid organic fertilizer
for growing plants.
Combining the observed biogas production rates with the long-term mean methane
concentration of biogas collected from the digesters (~67% CH4 by volume), biogas had an
equivalent BTU rating of 3,950-6,270 BTU per digester per day (mean) and 12,750 BTU per
digester per day (maximum).
In Phase II of the project, we designed and implemented a new gas collection system
suitable for small-scale applications. The system, based on a telescoping holding tank principle,
is simple and easy to assemble in areas where elaborate mechanized storage and gas delivery
systems are not available. The gas was collected from the primary digesters using the telescoping
, mean ± standard
); however,
) = 34.35*Temperature (0C )-
, a rate similar to that reported
6
storage system and delivered for use in a variety of applications to demonstrate biogas utility as a
source of combustion fuel. The most notable demonstration projects included the use of biogas
as a cooking fuel with a cast iron single-burner stove, powering of a 4-cycle lawn mower engine,
production of electricity using a converted gas-powered generator and use of digester effluent as
liquid fertilizer in a student greenhouse project.
A Benefit-Cost Analysis and Sensitivity Analysis to assess the economic feasibility of the
project showed that small scale biogas digesters are not cost-effective at the current prices of
displaced fuels and electricity in Alaska. While replication of the small, household-scale biogas
digester technology is unlikely in Alaska due to the heat and energy requirements of maintaining
digesters above freezing in winter, the time required for building and maintenance, and the
relatively low energy yield; this technology could be economically viable in regions with
different economies.
In Phase III we implemented knowledge gained in Phases I and II to help improve small-
scale biogas digester efficiency in various other regions of the world where seasonally cold
temperatures challenge biogas production. This phase of the project involved strong
collaboration among the project participants and collaborators in the United States and other
countries (see Collaborators). This phase provided the opportunity for collaboration among
various National Geographic, Blackstone Ranch, and other national and international partners to
establish a foundation for climate friendly household and community-scale energy independence.
We observed in Phase III that the benefits of biogas technology are global. The collection and
utilization of methane, one of the strongest greenhouse gases, prevents its release into the
atmosphere. Waste streams often present a liability to communities by filling landfills and posing
environmental hazards; however, biogas technology offers other uses for waste streams. The
overall impacts of biogas technology include protection of the environment and the potential for
reduced energy costs, even when implemented at small scales in some regions.
Improving cold season biogas digester efficiency for global energy solutions by Katey Walter Anthony and T.H. Culhane, Report Description:
PROJECT SUMMARY
Energy is a high cost, imported commodity to most communities. Biogas digester
systems, which take organic material into an air-tight tank, where microbes break down the
material under anaerobic conditions and release methane-rich biogas, may offer an alternative
energy solution. Biogas can be burned as a fuel for cooking, heating, generating electricity and
powering lights; and the liquid effluent can be used as organic compost. While small-scale
biogas digesters are being used by thousands of households in India, Egypt, Costa Rica, and
other warm-climate countries, seasonal limitation to biogas production is experienced in colder
climates due to the shut-down of mesophilic (warm loving) microbial communities in winter.
This project set out to improve the efficiency of biogas digesters under cold climate regimes by
inoculating digesters with active-methane-producing psychrophiles (cold-tolerant microbes)
readily available in Alaskan thermokarst (thawing permafrost) lake mud and the natural mud in
ecosystems of other regions characterized by seasonally cold temperatures. Psychrophilic
methanogens, despite a temperature optimum of 25°C, still actively produce methane year-round
at temperatures as low as 0°C in Alaska, unlike conventional microbes.
5
The objectives of this project were to:
● Improve the efficiency of existing small-scale methane biogas digesters, including by
using cold-adapted microbes to increase cold-season biogas production
● Produce a renewable and alternative fuel
● Reduce the release of harmful greenhouse gasses
● Implement dwelling-size and community-scale applications to evaluate their acceptance
and sustainability for widespread application in the United States, Germany, Egypt, and
other locations
● Test the technology to help fight deforestation in Africa by using biogas to replace
firewood
This project was carried out in three phases. Phase I and II were accomplished through
collaboration with a Denali Emerging Energy Technology Grant obtained by PI K. Walter
Anthony; results were previously reported to the Denali Commission Alaska. In Phase I, we used
an experimental approach to compare biogas production rates from psychrophilic (lake mud) vs.
mesophilic (manure) microbial consortia in six small, 1000-L household scale digesters under
two relatively cold temperature regimes (150C and 250C) in Cordova, Alaska. Phase II research
focused on the utilization (the capture, compression, analysis and usage) of biogas produced
during the project and assessment of this technology for widespread application in cold-climate
boreal and arctic communities. Phase III involved implementing knowledge gained from
experiments in Alaska in other regions of the world where utilization of cold-adapted microbes
could improve biogas efficiency during cold seasons.
In Phase I, we found that digesters containing psychrophiles were more robust to
temperature and pH fluctuations. Among our experimental digesters, tanks containing
psychrophile-rich lake mud produced more biogas (275 ± 82 L gas d-1
deviation) than tanks inoculated with only mesophile-rich manure (173 ± 82 L gas d-1
digester temperature appeared to be the overarching control over biogas production among all
tanks. Extrapolating the linear relationship between biogas production and mean digester
temperature observed among our study tanks [Production (L gas d-1
432] to the temperatures typically used for biogas production in warmer climates (35-400C), it is
possible that our digesters would have produced 770-940 L gas d-1
for warm climate digesters. Without knowing the temperature response from the microbial
communities in our specific digesters, it is not possible to extrapolate these results with a high
level of certainty; however, we can conclude that psychrophile-rich lake mud is a viable source
of microbial inoculums for producing biogas at cold temperatures, albeit at only 28-56% of rates
typical of warmer temperature regimes. Other benefits of the psychrophile-rich lake mud
digesters included reduction of foul odor and a source of nutrient-rich, liquid organic fertilizer
for growing plants.
Combining the observed biogas production rates with the long-term mean methane
concentration of biogas collected from the digesters (~67% CH4 by volume), biogas had an
equivalent BTU rating of 3,950-6,270 BTU per digester per day (mean) and 12,750 BTU per
digester per day (maximum).
In Phase II of the project, we designed and implemented a new gas collection system
suitable for small-scale applications. The system, based on a telescoping holding tank principle,
is simple and easy to assemble in areas where elaborate mechanized storage and gas delivery
systems are not available. The gas was collected from the primary digesters using the telescoping
, mean ± standard
); however,
) = 34.35*Temperature (0C )-
, a rate similar to that reported
6
storage system and delivered for use in a variety of applications to demonstrate biogas utility as a
source of combustion fuel. The most notable demonstration projects included the use of biogas
as a cooking fuel with a cast iron single-burner stove, powering of a 4-cycle lawn mower engine,
production of electricity using a converted gas-powered generator and use of digester effluent as
liquid fertilizer in a student greenhouse project.
A Benefit-Cost Analysis and Sensitivity Analysis to assess the economic feasibility of the
project showed that small scale biogas digesters are not cost-effective at the current prices of
displaced fuels and electricity in Alaska. While replication of the small, household-scale biogas
digester technology is unlikely in Alaska due to the heat and energy requirements of maintaining
digesters above freezing in winter, the time required for building and maintenance, and the
relatively low energy yield; this technology could be economically viable in regions with
different economies.
In Phase III we implemented knowledge gained in Phases I and II to help improve small-
scale biogas digester efficiency in various other regions of the world where seasonally cold
temperatures challenge biogas production. This phase of the project involved strong
collaboration among the project participants and collaborators in the United States and other
countries (see Collaborators). This phase provided the opportunity for collaboration among
various National Geographic, Blackstone Ranch, and other national and international partners to
establish a foundation for climate friendly household and community-scale energy independence.
We observed in Phase III that the benefits of biogas technology are global. The collection and
utilization of methane, one of the strongest greenhouse gases, prevents its release into the
atmosphere. Waste streams often present a liability to communities by filling landfills and posing
environmental hazards; however, biogas technology offers other uses for waste streams. The
overall impacts of biogas technology include protection of the environment and the potential for
reduced energy costs, even when implemented at small scales in some regions.
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