The chart accompanying today’s post shows the temperatures measured in the biomeiler at a height of 4’ above the ground. This height marks the boundary between the pre-existing biomeiler and the recent extension. The data were collected by a thermocouple buried in the pile at that height at the very center of the inner core, another placed halfway between the inner and outer walls of the outer core, and a third similarly placed between the inner and outer walls of the mantle. The air temperature was measured on a thermometer in the open air.
As January commenced, the temperatures in the inner and outer cores rapidly declined. Mid-month, the rates of decline lessened and there was an uptick in the last days of the month. The extension to the pile has been in operation, uninterrupted, for four months. So, I suspect that the composting action in the cores is simply following the natural trend and that the recent warmer weather has slowed the heat loss from the pile.
Commonly, compost in a conventional pile will follow a similar progression, having an initial period of high temperatures, followed by a significant decrease. When the pile is first assembled, the aerobic bacteria in the pile multiply rapidly and generate body heat which warms the pile. As time passes, the population exhausts the available oxygen and, as activity wanes, less heat is generated. If it were a conventional compost pile, turning the pile would be the customary solution. Reintroducing oxygen and redistributing the consumable materials allows the bacteria population to enjoy another cycle of growth and decline.
In my biomeiler, turning the material is neither practical nor advisable. The pile is covered by 18” of snow and the outdoor temperature is well below freezing. The amount of effort would be prohibitive and the exposure to such low temperatures would, in all likelihood, be so harmful to the bacteria population as to outweigh the advantage of redistribution and re-oxygenation.
It was with these considerations in mind that I built an aeration system into the biomeiler. Fresh air can be pumped into the bottom of the pile with an air compressor to displace the stale air inside and re-oxygenate the environment for the benefit of the aerobic bacteria population. My present plan is to continue to monitor the internal temperatures of the biomeiler and take action when the inner core drops below 100F. At that point, I will begin aeration in steps small enough as to minimize the danger of chilling the pile.
This type of research may seem dull to the non-enthusiast, but it is an absorbing mental occupation for those who choose it.
Today’s graph is very interesting. I don’t truly understand the “why” of everything – like why the middle core temperature is lower than the outer core – but I trust you have it well in hand.