Bethena (under table on the right) provided gas and effluent as expected throughout the warmer 8-10 months. The gas was used for cooking and CSA canning operations. The effluent was primarily spread on fallow fields [and a couple residential nanofarms]. The major changes to the system were preparations for placement of the second beast and insulating and strengthening the north wall of the greenhouse.
The north wall of the greenhouse – a thin layer of steel – was covered with a layer of ~ 1.5” X 18” steel-enclosed polyurethane panels to better insulate and support hydro- and/or aeroponic production growing spaces and apparatus.
The panels were also strong enough to provide walkways at the end of the trenches. Eight-inch concrete block was laid on its side along the second digester bed to provide a flat surface and 4, 5” square air channels for heating beneath the beast.
1. Birth and activation of Cloacina, digester No. 2
The nearly-twin second beast was finally sealed and began operation/life in the late spring. Leakage problems with endcaps and bulkhead fittings had been discovered and reliably repaired. Cloacina was started up with effluent from her older sister, Bathena, and quickly became nearly equally productive. [Scott Mann, of thepermaculturepodcasts.com provided two well-edited videos showing some of the process as well as a couple presentations. See the left-hand menu.]
The most relevant changes for Cloacina (#2) were;
- The inclusion of 3 plastic-net bags full of lava rock to provide some stable living space for the microbes; [I would now recommend the use of biochar instead of lava rock. Yes, it takes a while, but biochar does sink given time to soak up enough liquid]; and
- The bed for the beast consisted of concrete block, set on their side, so as to provide large tubes for much greater hot air flow from the top of the greenhouse to the bottom of the beast.
This second beast opens great possibilities for a wide variety of comparison studies which will hopefully be taken up in the future. The following photo shows the operating first digester on the left and air-pressure-testing of the second beast on the right.
Spring and Fall succulent growth was possible on the table, but the unventilated greenhouse got so hot that the best mid-summer use was found to be wood drying for biochar production.
High Summer biochar wood drying with both beasts in production. But what to do with all the gas?
2. Tank adaptation for compressed biogas storage and gas line supply
The red tank was adapted for pressurization by two, in-series, Puxin pumps. This was fabricated to provide adequate pressure to ¼ mile gas lines to residences and the Farm’s CSA kitchen. The gas line has recently been approved by local fire officials… but not yet installed. So adaptation is still in progress.
3. Potting soil sterilization
High biogas production from the two digesters lead to development of alternative means for gas utilization. The growing regimens at Dickinson College Farm require large amounts of sterilized potting soil. A functional prototype soil sterilization unit was fabricated and is in operation. Biogas-generated steam flows through copper pipes near the bottom of a box holding the soil being sterilized.
4. Small electric generator adaptation for biogas use
Most large-scale digester systems have been primarily justified by their financial potential for electricity production… while “externalizing”/ignoring the benefits of nutrient conservation and the great potentials for regenerative effluent use.
Nevertheless, electricity generation remains a quite viable option for biogas use for smaller systems when it can be utilized locally. Trial-and-error adaptation for biogas’ relatively low fuel content is necessary, but is becoming easier with more adaptation units appearing on “markets”.
5. Adaptation of wood splitter to operate on biogas
With increased interest in biochar production and increased biogas production, it became obvious that adaptation of the gas-powered log-splitter to run on biogas was most appropriate. Again, dedicated adaptors are becoming more available, but it still takes some trial-and-error to make full use of the equipment given raw biogas’ energy content.
6. Increased biochar production and beginning integration with digester effluent
Biochar production provides a wonderfully regenerative means for dealing with woody, ligneous residues – which are indigestible. The biochar process produces a nearly pure carbon, extremely porous substrate which easily bonds with plant nutrients. These nutrients are held in plant available form via weak bonds on biochar’s internal surfaces. These weak bonds are easily overcome by plant roots in need. Incorporation of biochar into the soil greatly increases cation and anion-exchange and enhances water-holding capacities.
But distributing “raw” biochar can result in a brief period when the biochar may excessively be collecting nutrients. Not to worry, the biochar will keep them available for ages.
Digester effluent provides a nearly full spectrum of plant nutrients. I suggest that soaking/infusing “raw” biochar in digester effluent before soil distribution provides a great preliminary nutrient “charge” to the biochar.
An initial study of some of the potential interactions was carried out. This involved temperature measurement of 1 cubic meter compost piles with varying amounts of compost, biochar, and effluent.
Wood for biochar, a couple containers of new biochar ready for crushing and digester effluent infusion, along with several piles of compost-biochar-effluent mixture trials. (Results still pending)
The new much larger biochar production vessel. Filled with a ladder and still emptied by turning it on its side and top.
Please note: The Dickinson College Farm is a production operation first responsible for providing much food for the college’s cafeterias, a CSA, educational and intern possibilities, etc. The DCF has been an early innovator with integrating many sustainable technological and regenerative farming practices – including biodiesel, standing and mobile photovoltaics, solar water heating, greenhouse utilization – and more recently, biogas integration with greenhouses and biochar production and use. The innumerable research opportunities seem significantly limited by the possibilities for interested students and other farm participants to be able to find adequate reaearch support from college faculty.
— Biogas Bob Hamburg, 11/19 —