Extending the range of biogas digesters using Extremophiles

Lest one believe that psychrophils only have potential for winter biogas production it is worth noting that this summer in Essen, Germany, in mid-July, the average daytime temperature was highs of 16 degrees C ( 60.8 F) and lows of 13 degrees C (55 F) with a couple of days peaking at 24 degrees C (75 F). 15 Celsius is generally considered sweater-wearing weather and professional biogas producers have had to add heat to the systems (resulting in profit losses) to keep them productive. Our own mesophilic biogas system on our porch, which prefers temperatures of 37 degrees C (body temperature, 98.6 F) , has given us very poor performance this summer with the temperatures being at the bottom of the mesophiles range. We have supplemented by putting in heating coils connected to our solar hot water system at additional expense. But Katey's bacteria are at their best at this new European summer temperature range. We can expect that temperature swings will become the norm as climate change continues, threatening conventional systems that use warm-loving bacteria with unexpected shut downs and performance drops. But it isn't only the northern countries that can benefit from this; we believe our psychrophilic digesters can immediately address biodiversity and social challenges in tropical and subtropical areas.

Working with National Geographic Explorers in Residence Dereck and Beverly Joubert and fellow National Geographic Emerging Explorer and Ethnobotanist Grace Gobbo we intend to build identical systems our testing phase in Botswana and Rwanda at the Joubert's networks of eco-safari lodges and in villages at the edge of critical habitats and in Tanzania at or near The Jane Goodall Institute at the Gombe Reserve so as to determine whether or not biogas can be an effective solution to that part of the deforestation problem caused by the collection of cooking and water heating fuel.

Although these African sites are considered tropical locations, NG Explorers confirm published reports that, for example, at Gombe temperatures in July can be as low as 11 degrees C, with an average minimum of 19 degrees. Most importantly, many of the remaining forested and vegetated areas that serve as the last strongholds of great apes and other endangered megafauna are areas pushed up into the mountainous parts of the country where the altitude can create almost alpine temperature regimes.

In the Usambara mountains of Tanzania, for example, the average temperature at 900 meters is a mere 19 degrees. Even at 300 meters the mean temperature is only 24 degrees C (see W.D Newmark, Conserving biodiversity in East African forests,Springer, 2002) . While this is far too cool for the normal methanogenic bacteria found in biodigesters, Katey has shown that her psychrophiles, while happy at 0 degrees, perform best at 25 degrees C, a temperature at which mesophiles generally shut down production. This suggests that the use of these Arctic extremophiles is ideal for African deployment of biodigesters in the very environments whose biodiversity is most under threat.

The goal is to discourage any regress to the use of wood fuel in these critical forest edge habitats as well as in the lowlands during colder times. Grace shared with us that the the chimpanzee populations are very threatened because of habitat destruction but ironically even the scientific research stations and park protection facilities use fossil fuels, wood and charcoal for cooking and heating and have a hard time disposing of their waste, thus providing an example to visitors that only exacerbates the very problem they are struggling to solve. Meanwhile the Jouberts have documented a surplus of "rotting yams and other poverty class produce" in most of these areas that could completely eliminate the need for collecting firewood. A viable year-round biogas system (coupled with solar energy systems) could mitigate and even solve many habitat destruction root causes, particularly as the high profile of the Joubert's safari eco-lodges and the Goodall Institute act as catalysts for regional and international change.

What the Walter-Anthonys and the Fruetel-Culhanes have decided to do is to start using psychrophiles and mesophiles together in the same digester, much in the same way the Chinese (and now development agencies) have done "stereo-breeding" of different species of fish in the different temperature zones of aquaculture tanks to improve productivity. The cold loving bacteria will occupy the colder bottom strata, while the mesophiles will occupy the upper, warmer parts of the tanks thermocline. It might even be possible to populate the top region of the digester with thermophiles and have "a bacteria for all seasons". Theoretically, if the tank is designed correctly, the psychorophiles will dominate in the winter and the mesophiles (and possibly some thermophiles?) in the summer, but both will hang on during the periods when the temperatures are not optimal for them by occupying the parts of the tank most suitable to their metabolism. And together they will keep the system producing gas all year round. In this way, it is surmised, the winter energy costs for keeping a biogas digestor at the appropriate temperature can be reduced, hopefully to the point where it makes sense to depend on biogas and obviate the need for fossil fuels. (It would also obviate the need for external garbage disposal, since all the other household wastes would remain clean and easily recyclable, and it would eliminate most need for composting, which tends to shut down in the winter time; the biogas digestors would produce liquid fertilizer all year). The key is finding the right combination of bacterial species that can work together across different temperature regimes.