"Blogging the world's first basement biodigesters" by T.H. Culhane


Domestic food wastes have been the focus of many environmental remediation efforts, from municipal attempts to encourage source separation and collection to “Do it Yourself” (DIY) and commercial attempts to treat organic residuals on-site through aerobic composting. We claim that the problems associated with the prodigious production of inedible and underconsumed food products at the household level have not been solved satisfactorally by any previous approaches because of the entropic losses to the system. The energetics associated with household waste management are unfavorable in the case of municipal solutions because of the hidden costs associated with separation, binning, handling, transport and disposal, while the “backyard solution” suffers from a net loss in value caused by nitrogen depletion of substrate through aerobic catabolism and restrictions on the amount and type of waste matter composted.

A further barrier has been the temperature limitations imposed by temperate climatic regions. In this paper the authors detail an experiment they have been conducting in a household in the Hudson Valley in New York that shows promise in sidestepping both of these problems.Through the use of America's first “basement bio-digesters” built by the authors and students from Mercy College the organic garbage from a family of 4 (two adults and two small children) are being transformed into a surplus of clean cooking fuel and nitrogen-rich liquid fertilizer that the family uses on a daily basis to meet their domestic food preparation needs and the fertilizer needs of their vertical aeroponic 'tower gardens' which are used indoors to grow healthy salad greens and vegetables for the family.The system has continued its high production rate through the coldest winter months and eliminated the waste management issue of the household.

The paper details the qualitative, construction, engineering, and social aspects of this novel approach to an ancient technology, and suggests further steps and studies to improve the systems for more widespread deployment



In his magnum opus “The Entropy Law and the Economic Process”(Georgescu-Roegen, 1971) Nicholas Georgescu-Roegen pointed out that the second law of thermodynamics governs our economic realities. From an entropic perspective, current waste management practices are as wasteful as the processes that created the waste they are trying to deal with because they use more energy in reducing the waste stream than there is energy within the waste stream.“digesting 1 tonne of food waste can generate about 300 kWh of energy” according to http://www.biogas-info.co.uk/faqs.html, transporting food wastes consumes about 0.58 million BTUs (http://epa.gov/epawaste/conserve/tools/warm/pdfs/Energy_Impacts.pdf) or 169 kWh. This figure might suggest a positive energy balance and is used to rightly justify investment in food waste recycling, but it discounts the hidden energetic costs associated with labor and machinery -- feeding and paying for people and equipment to move and sort and process the food wastes ex-situ. With over half of the energy gain consumed by transportation fuel costs alone, the savings are dependent on low cost labor to create a long-term positive return and this proves to be unsustainable. ) Handling food wastes, in particular, has led to more problems than it has solved, particularly considering that food wastes are a secondary source of solar energy, captured through photosynthesis and that this energy, unlike the food that is eaten, is literally thrown away.

Marx and Engels (1844) spoke in their Economic and Philosophical Manuscripts about this concept when referring to the crisis capital would face as energy in the form of food was transported from the English countryside to London at great expense, consumed, and then thrown or flushed into the Thames to be buried at sea in a one-way “cradle to grave” scenario that historian John Bellamy Foster (2000) called “The Metabolic Rift”(Foster, 2000). (Foster has since linked the Marxian metabolic rift with other ecological rifts and with the Entropy Law in "Classical Marxism and the Second Law of Thermodynamics: Marx/Engels, the Heat Death of the Universe Theory, and the Origins of Ecological Economics (Bellamy Foster et al., 2008))

The problems associated with obtaining sufficient energy from organic wastes to justify their transport and recycling becomes particularly acute in the north temperate zones of our Earth where biological processes that could recover the energy contained within the chemical bonds is severely curtailed by seasonal cold temperatures. Balasubramaniyam et al. (2008)

1.1 The home basement biodigester

In late 2009 and early 2010 Dr. T.H. Culhane, a National Geographic Emerging Explorer, received the first National Geographic/Blackstone Ranch Foundation Innovation Challenge grant along with Dr. Katey Walter Anthony of U Fairbanks, to conduct experiments on small scale biodigesters in cold climateCulhane et al. (2011) (Walter Anthony et al., 2014). In December we built 6 Solar CITIES style IBC digesters, 3 to a room, in a separated 40 foot container that we insulated with 2 inch pink foam boards and heated with electricity so that one room stayed at about 15 C and the other at 25 C. We compared treatments of psycrophilic microbes, mesophilic microbes and a mix of both psychrophiles and mesophiles at these two temperature regimes and found, as expected, that 25 C ambient temperatures created substantially more gas than 15C even when using psychrophiles. Surprisingly, the mix of psychrophiles and mesophiles produced more than either type alone . These preliminary results led to our current practice of using both psychrophile contianing lake or pond mud along with mesophile containing animal manures when we start digesters. However, the energetics of keeping the container warm enough to support useful gas production became self-defeating, and the number of kWh of energy produced by the tanks was not enough to justify the amount invested in keeping the container warm.

Since gas production is non-linear with a sharp slope, and we observed that at 30 C substantially more energy was produced than at 25 C, some discussion at the local town hall in Cordova Alaska when we gave a presentation on our work revolved around the idea of building the digesters indoors, in a basement. But while the local fire marshall had approved the keeping of biodigesting IBC tanks in a container at the school detached from the school building itself (Interestingly the container was located across the street from the fire marshall's home and was directly observable by him) there was little enthusiasm for an indoor trial.

Culhane continued to experiment with his own porch-deck biogas tanks (also IBCs), placing one in a small polycarbonate greenhouse, both heated by used bath and showerwater, and demonstrated useful gas productio throughout several German winters.

Temperature monitoring was conducted inside the digester in the green- house, conducted and analyzed by Katey Walter Anthony, using four data loggers. One was placed at the bottom of the tank, one at the top of the tank,one inside the greenhouse in a shaded area and one outside the greenhouse in a shaded area. The results arehown in the figure below, reproduced from the Walter-Anthony Report:


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The data reveal that a greenhouse is marginally helpful in reducing the frequency of freezing events (temperatures in the greenhouse only dropped to 0 C a few times in early January, while ambient temperature went to zero or below from January through as late as April and again in November through January. This was indeed helpful. Also, the bottom of the digester, heated by pulses of war bath water, stayed above freezing all year.

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On the other hand, for optimizing gas production, a greenhouse certainly isn't a denitive solution. Culhane has also called into question traditional greenhouse design and recommends several innovations.