English

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.

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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

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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.