An Investigation of Psychrophiles for Generating Heating Gas in Arctic Environments - An Emerging Energy Technology Grant Project
This research and application project investigated the use of psychrophiles (cold loving microbes) for the purpose of improving efficiency in biogas digesters for generation of cooking and heating gas for Alaskan households.
Small-scale biogas digesters are commonly used throughout regions with tropical and subtropical climates: Southeast Asia, Central and South America, the Middle East, and Africa. Digesters are used to generate biogas, which is a mixture of methane, carbon dioxide, and other trace gases. Biogas can be used as a fuel for a number of different applications including cooking, heating, and running an electric generator. Typically, the methanogens responsible for biogas production are limited in application to warm environments. This project investigated the development of biogas digesters in cold climates using recently discovered psychrophilic (cold loving) methanogens.
The goal of this project was to test the viability of small-scale biogas digesters in rural Alaska using psychrophilic methanogens, with the intent of displacing standard energy sources and reducing organic waste. The psychrophiles were collected from lakes in local areas. Since these methanogens evolved in arctic and subarctic climates, it was postulated that they could be used to generate biogas in cold regions similarly to how mesophilic methanogens produce biogas in warm regions. The project was divided into two phases:
- Construction of six 1000-L biogas digesters containing different methanogen cultures in two different temperature regimes.
- Monitoring of physical and chemical characteristics of the digester environments.
- Production and measurement of biogas.
- Demonstration and application of biogas and digester effluent.
- Economic evaluation based on installation/maintenance costs and biogas production.
Project activities began with a small pilot study in November 2009. Phase I began with construction of biogas digesters in January 2010. The digesters were monitored beyond the conclusion of Phase I in March 2011. Phase II began immediately after Phase I was completed and ended in September 2011.
This project successfully investigated and compared methane production by mesophiles and psychrophiles in cool and tepid conditions in Alaska and demonstrated potential applications of residential-scale biogas production. Although it was shown that residential-scale biogas digesters for cold climates are not economically viable at this time and that significant barriers prevent annual outdoor siting of system components, psychrophilic methanogenesis could be relevant for other types and/or scales of systems and applications in Alaska.
Phase I verified that methanogens produce more biogas in warmer environments. Psychrophiles can produce methane at lower temperatures than mesophiles, but they do not necessarily produce more methane in mutually hospitable temperatures. Further research is required to verify comparative methate production in environments with identical temperatures. The methane content of the biogas produced was slightly higher than the methane content of the biogas from average digesters, meaning the energy content was slightly higher as well. This higher percentage of methane is not enough to offset the low production in cool or tepid climates. A single digester at approximately 25°C produces 4–6 MJ each day. This amount is comparable to about 110 g of diesel (0.04 gal), or 110 g of propane (2 cu ft). Typical digesters in warm climates produce approximately 21 MJ per day, which is equivalent to 0.58 L (0.15 gal) of diesel.
During Phase II, the project team demonstrated realistic applications of biogas as a fuel in Alaska. Biogas was used to run a cooking stove and an electric generator that had been converted to use gas. Potential applications extend beyond those demonstrated in Phase II. In addition to its use for cooking meals and running a generator, biogas can be used as heating fuel. A digester could alleviate waste disposal. Rather than putting food waste in the garbage, it can be used to feed a digester. The effluent still must be dealt with, but Phase II experiments showed that effluent can be used as liquid fertilizer.
Residential psychrophilic biogas digestors are technically feasible in cold climates, but homeowners must consider carefully siting, economics, and system maintenance concerns. In addition, more work is needed in the design and development of a residential-scale cold-climate biogas digestor system before the technology can be deployed more widely.
Further research is needed to investigate psychrophilic biogas digestors applied at larger scales, such as commercial or industrial scale. The presence of significant fish waste in many coastal Alaska communities and fish processing operations, for example, may offer opportunities for the application of this technology.
Photo 1: The Cordova High School Science Club. Courtesy of Casey Pape, ACEP.
Photo 2: Biogas digestor testing chamber interior. Courtesy of Casey Pape, ACEP.
Photo 3: Biogas digestor testing chamber exterior. Courtesy of Casey Pape, ACEP.